Instructor Experiment Guide

TM

Hy-Expert Instructor Fuel Cell System

Experiments Guide Including Components Description

Heliocentris Energiesysteme GmbH

TM

Experiments guide and components description for the Hy-Expert

Instructor Fuel Cell System

5th Edition, September 2005 Copyright © 2005 Heliocentris Energiesysteme GmbH All rights reserved. These manual and individual parts thereof are protected by copyright. All exploitation, duplication or photocopying is prohibited except in cases permitted by law. Components of the hy-Expert™ Instructor Fuel Cell System are protected by patent applications and/or registered designs.

Head office:

North American customers contact:

Heliocentris Energiesysteme GmbH Rudower Chaussee 29 12489 Berlin Germany

Heliocentris Energy Systems Inc. 3250 East Mall Vancouver, BC Canada V6T 1W5

Tel. (+49 30) 63 92 63 26 Fax (+49 30) 63 92 63 29

Tel. 604 827 5066 Fax 604 827 5069

[email protected] www.heliocentris.com

[email protected] www.heliocentris.com

General notes

General notes

Heliocentris Energiesysteme GmbH provides this documentation to facilitate the safe and correct use of the hy-ExpertTM Instructor fuel cell system. All statements, technical information and recommendations in this documentation and accompanying documents are believed reliable, but the accuracy and completeness thereof are not guaranteed or warranted. They are not intended to be, nor should they be understood to be, representations or warranties concerning the products described. The following Components Description is a brief version of the hy-ExpertTM Instructor Operation Guide. It is intended to assist while operation under the supervision of trained personnel and does not replace the Operation Guide. Before operating this fuel cell system, please make sure to read and understand the information of the hyExpertTM Instructor Operation Guide. If you have questions, please contact Heliocentris Energiesysteme GmbH or your supplier. The hy-ExpertTM Instructor fuel cell system has been sold subject to the limited warranties set forth in the warranty statement. Further, Heliocentris reserves the right to make changes in the specifications of the products described in this manual at any time without notice and without obligation to notify any person of such changes.

© Heliocentris – Energizing education

Table of contents

Table of contents A: Operating References A.1

Warnings and safety references

A.2

Product overview

A.3

Fuel Cell Module FC50

A.4

Electronic Load Module EL200

A.5

Voltage Converter Module VC100

A.6

Traffic Light Module TL10

A.7

Control software

A.8

Hydrogen supply option I: Connection set for compressed hydrogen cylinders

A.9

Hydrogen supply option II: Metal hydride storage with refilling kit

A.10

Hydrogen supply option III: Hydrogen generator with metal hydride storage

B: Technical basics and didactics B.1

Learning objectives

B.2

Teaching references and methodology

B.3

Recommended web sites

B.4

References for further reading

© Heliocentris – Energizing education

Table of contents

C: Teacher guides for the experiments C.1

The basic functions of the fuel cell system

C.2

The characteristic curve of a fuel cell

C.3

Parameters influencing the characteristic curve

C.4

Determination of the hydrogen current curve

C.5

Efficiency of the fuel cell stack

C.6

Set-up of a fuel cell power supply

C.7

Efficiency of a fuel cell power supply

C.8

Fuel cell application I: Remote traffic light

C.9

Fuel cell application II: Fuel cell car

D: Student experiments D.1

The basic functions of the fuel cell system

D.2

The characteristic curve of a fuel cell

D.3

Parameters influencing the characteristic curve

D.4

Determination of the hydrogen current curve

D.5

Efficiency of the fuel cell stack

D.6

Set-up of a fuel cell power supply

D.7

Efficiency of a fuel cell power supply

D.8

Fuel cell application I: Remote traffic light

D.9

Fuel cell application II: Fuel cell car

© Heliocentris – Energizing education

A.1

Warnings and Safety References

1

A.1 Warnings and Safety References

1

Symbols used in this guide

The following symbols are used in the Experiments Guide to indicate warnings and specific dangers:

Warning

Indicates a potentially dangerous situation. Serious injuries can occur if this reference is ignored.

Warning

Indicates danger of explosion.

Warning

Indicates danger from rotary parts.

Warning

Indicates danger of short-circuits or electrical shock.

Prohibition

No open fire!

Prohibition

Smoking prohibited!

Prohibition

Do not attempt to extinguish with water!

Reference

Draws attention to application tips and other useful information. This is not a reference to dangerous situations.

Indicates highly flammable material.

© Heliocentris – Energizing education

2

2

Warnings and Safety References

A.1

General Warnings and Safety Instructions

The hy-ExpertTM Instructor fuel cell system has been developed and manufactured according to recognized technical regulations and is tested for function and safety before delivery. The hy-ExpertTM Instructor fuel cell system is a laboratory instrument designed for operation by trained personnel in education and research. The hy-ExpertTM Instructor is not a "consumer-oriented" product, whose appropriate operation is generally known and which is protected against operation errors or inappropriate use. Improper operation or abuse can lead to dangers to the health of the operator, the fuel cell system itself and other property items. The Fuel cell system produces low voltage electricity by converting hydrogen electrochemically. The hydrogen is stored in pressurized cylinders, a metal hydride tank, or generated by a special hydrogen generator. The operating and maintenance conditions laid down in these Components Descriptions must be observed. If the hy-ExpertTM Instructor fuel cell system is passed on to a third party, the Operating Instructions must also be passed on.

3

Restricted use

The hy-ExpertTM Instructor fuel cell system and its components may only be used for experimentation, demonstration or research purposes. All other uses are not intended and therefore prohibited. For safety reasons, unauthorized modifications or changes to the system or its components are prohibited. The parts and components of the system may not be disassembled. In particular, all gas components, such as the gas fittings or the mounting bolts of the fuel cell stack must not be loosened, since this can cause hydrogen leakage.

4

Sources of danger Source of danger

Possible consequences

Precautions

Use of hydrogen

Fire and danger of explosion

Avoid open fire and smoking in the vicinity.

Avoid electrostatic charges. Wrong polarity when making electrical connections

Danger of short-circuits

Make sure to have the correct polarity when making the electrical connections.

Rotating parts of the cooling fans

Danger from rotating parts

Do not put your fingers or other items into the fan housing.

© Heliocentris – Energizing education

A.1

5

Warnings and Safety References

3

Authorized operators

Anyone setting-up, operating or maintaining the hy-ExpertTM Instructor fuel cell system must be aware of applicable local industrial health and safety regulations. Measures must be taken to prevent unauthorized persons installing, operating or maintaining the system. In education, the hy-ExpertTM Instructor fuel cell system may only be used by students under the supervision of teaching staff. As the teacher you must ensure proper handling of the system. You have an obligation to draw attention to potential dangers. Installation, start-up, shut-down—and if necessary, maintenance—of the hydrogen supply as well as filling the metal hydride storage device may be done only through the teaching staff.

6

Workplace

The hy-ExpertTM Instructor fuel cell system is intended for installation and operation in a suitable laboratory area. In particular, the room must be equipped with an effective airevacuation system that prevents the formation of explosive hydrogen-air mixtures in the event of any uncontrolled escape of hydrogen. Measures must also be taken to avoid electrostatic discharge. Local safety regulations that apply at the installation site must be observed. This applies in particular to the use and storage of hydrogen compressed gas cylinders that are not part of the supplied system. The fuel cell system must be installed on a stable, horizontal and solid base; it must stand firm. The catalysts and membranes of the fuel cell are sensitive to dust and reactive chemicals, e.g. H2S and other sulfur compounds, carbon monoxide, ammonia, chlorine compounds, solvents, etc. The system must therefore not be set up, operated or stored in rooms where there is a risk of exposure to these substances. The permissible working temperature is between +5 °C and +35 °C.

© Heliocentris – Energizing education

4

Warnings and Safety References

7

A.1

Safety information about using hydrogen

•

Hydrogen is a highly flammable gas.

•

Users must take care to ensure that hydrogen is not allowed to collect in an enclosed or unventilated area, which would cause a flammability hazard

•

Avoid heat in the area surrounding the fuel cell system and hydrogen source.

•

Smoking and open flames are forbidden.

•

Measures must be taken to avoid electrostatic charge.

In addition to its fire danger, hydrogen if allowed to collect in an enclosed or unventilated area can displace oxygen, thereby creating a risk of asphyxiation. The operator must ensure the following safety precautions are met: • Adequate ventilation of the laboratory area • Proper installation of the hydrogen equipment • Regular examination of the hydrogen piping and connections for leaks.

8

Safety precautions in an emergency

Significant hydrogen escape: •

Do not operate electrical devices, light switches, etc. as an explosive gas mixture could be present in the area.

•

Immediately shut off the hydrogen source.

•

Provide adequate ventilation to clear the affected area.

Fire or explosion: •

Immediately shut off the hydrogen source.

•

Report the fire and follow the fire response procedures for your laboratory.

•

Leave escaping hydrogen to "burn down". The flame of burning hydrogen is not visible!

•

Use a class D fire extinguisher or dry sand to extinguish burning metal hydride powder. Do not use water or CO2 extinguishers. If smoldering metal hydride powder cannot ignite adjacent materials, it may be best to leave the hydride burning.

Other emergencies not involving hydrogen escape: Immediately switch off the FC50, remove its hydrogen connecting tube and if necessary close the valve of the compressed hydrogen cylinder or the metal hydride storage canister.

© Heliocentris – Energizing education

1

Product Overview

A.2

A.2 Product overview 1

Basic package

The Basic system package includes essential components of the hy-ExpertTM Instructor fuel cell system. These are the minimum components needed to perform experiments 1 through 5 (basic experiments). Hydrogen is supplied using one of the three listed options. Pressurized hydrogen cylinders needed for options I and II must be obtained from the local technical gas supplier. Air

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Component

Item No.

Fuel Cell Module FC50 (including power supply, control software, documentation)

610

Electronic Load module EL200

620

Choice of Hydrogen Supply Options: I Connection set for compressed gas cylinders II Metal hydride storage with refilling kit III Hydrogen generator with metal hydride storage

630 642 652

© Heliocentris – Energizing education

A.2

2

Product Overview

2

Off-grid package

In addition to essential components of the hy-ExpertTM Instructor fuel cell system, the Off-grid system package includes the additional devices which are necessary to build a gridindependent fuel cell power supply. With this package the application-orientated experiments 6 through 9 can also be performed. Hydrogen is supplied using one of the three listed options. Pressurized hydrogen cylinders needed for options I and II must be obtained from the local technical gas supplier. Air +

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Module EL200

Component

Item No.

Fuel Cell Module FC50 (including power supply, control software, documentation)

610

Electronic Load Module EL200

620

Voltage Converter Module VC100

621

Traffic Light Module TL10

622

Choice of Hydrogen Supply Options: I Connection set for compressed gas cylinders II Metal hydride storage with refilling kit III Hydrogen generator with metal hydride storage

630 642 652

© Heliocentris – Energizing education

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Fuel Cell Module FC50

A.3

A.3 Fuel Cell Module FC50 1

Use

The FC50 Fuel Cell Module is the central component of the hy-ExpertTM Instructor fuel cell system. It must only be used with one of the hydrogen supply options sold by Heliocentris.

2

Overview and parts list 12

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Quick coupler connection for hydrogen supply

2 3 4 5 6 7 8 9 10 11 12 13

Start button Control connection to hydrogen supply valve RS232 connector to computer Main switch RS485 system data bus connector 12V DC power input Fuel cell stack power output Purge valve with hose connection Fan power control Fuel cell stack Cooling and air supply fans Hydrogen flow meter

© Heliocentris – Energizing education

A.3

3

Fuel Cell Module FC50

2

Basic functions

The fuel cell stack is designed for hydrogen-air operation. Hydrogen is supplied through a gas-tight quick-coupler (1); air is blown into the cells at atmospheric pressure by the fans (12) attached to the cell stack (11). The fans provide air both for the electro-chemical cell reaction and for cooling. In the fuel cell stack, 10 single cells are connected in series. The current is tapped via current collectors at the two end plates. The fans (12) are controlled either by the user or the internal control. If the fan control knob (10) is in the position "AUTO", the fan speed is set automatically according to the stack power output, so that adequate cooling is ensured at all times. In positions other than “AUTO”, the user has direct control of the fan speed. Detailed operating conditions are given in the experiment guides. The purging valve (9) automatically opens at intervals to purge the system. This is necessary to clear inert gases and water vapor from the fuel cell stack (11). The integrated microprocessor controls the fuel cell and monitors system status. It also communicates with modules EL200 and VC100, and your computer, if attached.

4

Hydrogen source

For operating the FC 50 the purity of supplied hydrogen gas must be at least 4.0 (99.99 % pure). The permissible hydrogen input pressure is 0.4…0.8 bar gauge. Using hydrogen of purity 5.0 (99.999 % pure) will increase the life of the fuel cell stack.

© Heliocentris – Energizing education

3

Fuel Cell Module FC50

5

Operation directions

5.1

Start-up

A.3

Observe the safety instructions during installation and start-up. Provide adequate ventilation and keep away from sources of ignition. 5.2

Manual operation, powered by external AC power supply:

• Place the FC50 panel into the upper right area of the support frame. • Plug the connection cable of the 12V DC regulated power supply into the “12V=” jack (7) of the FC50 and plug the power supply into an AC power outlet. • Using the supplied test leads, connect a suitable load to the stack power output (8). Observe correct polarity. If you are using the Electronic Load Module EL200 as a load: (See chapter A.4 for details) o

Place the EL200 panel into the lower right area of the support frame.

o

Using the supplied power cord, connect the EL200 to an AC power outlet, and turn on the power switch (located behind the front plate, right side).

o

Using the short test leads, connect the stack power output (8) of the FC50 to the load input of the EL200. Observe correct polarity.

o

Ensure that the multi-turn load potentiometer is set to zero (fully counterclockwise).

o

Turn the switch on the EL200 front plate to "ON".

• Attach your chosen hydrogen supply with the quick-coupler to the hydrogen input (1) of the FC50. Connect the cable of your hydrogen supply’s solenoid valve to connector "H2supply" (3). For the correct start-up of your hydrogen supply refer to the appropriate installation and operating instructions found in chapters A.8 to A.10 of this Guide. • Set the fan power knob (10) to “AUTO”. • Turn the main switch (5) to “ON”. • Press the “Start” button (2). • The system now performs a self-check for about 10 seconds. If no error occurs, the FC50 begins operating. If an error occurs the error message is displayed in the display “H2 flow”. In this case please refer to section 8 of this chapter “Error messages and causes”.

© Heliocentris – Energizing education

A.3

5.3

Fuel Cell Module FC50

4

Manual operation, self-powered by the VC100 module:

• Place the FC50 panel into the upper right area of the support frame, and the VC100 in the lower center area. • Using the supplied test leads, connect the FC50 stack power output (8) to the voltage input of the VC100. Observe correct polarity. • Using the provided 3-pin cable, connect the output marked "Parasitic load" of the VC100 to the "12V =" jack (7) of the FC50. • Connect a load (e.g. EL200 or TL10) to the output marked "available power" of the VC100. Observe correct polarity. (In addition to the VC100, you can connect additional loads directly to the FC50 stack power output.) Use only the supplied test leads for connecting loads. If you are using the Electronic Load Module EL200 as a load: (See chapter A.4 for details) o

Place the EL200 panel into the lower right area of the support frame.

o

Using the supplied power cord, connect the EL200 to an AC power outlet, and turn on the power switch (located behind the front plate, right side).

o

Using the short test leads, connect the stack power output (8) of the FC50 to the load input of the EL200. Observe correct polarity.

o

Ensure that the multi-turn load potentiometer is set to zero (fully counterclockwise).

o

Turn the switch on the EL200 front plate to "ON".

• Attach your chosen hydrogen supply with the quick-coupler to the hydrogen input (1) of the FC50. Connect the cable of your hydrogen supply’s solenoid valve to connector "H2supply" (3). For the correct start-up of your hydrogen supply refer to the appropriate installation and operating instructions found in chapters A.8 to A.10 of this guide. • Set the fan power knob (10) to “AUTO”. • Turn the main switch (5) to “ON”. • Press the “Start” button (2). • Initially powered by the starting battery of the VC100, the FC50 system now performs a self-check for about 10 seconds. If no error occurs, the FC50 begins operating. The VC100, now receiving voltage from the fuel cell stack, continues to power the FC50 with regulated 12V DC. If an error message is displayed, please refer to section 8 of this chapter “Error messages and causes”.

© Heliocentris – Energizing education

5

5.4

Fuel Cell Module FC50

A.3

Computer-assisted operation:

Computer-assisted operation is available regardless of how the FC50 is powered. In computer-assisted operation, you can adjust the EL200 load current and FC50 fan power only through the computer. The computer monitors and logs all system parameters of the FC50 and also, through the RS485 data connections, the EL200 and VC100. Before you run the FC50 software, ensure the following conditions exist: • The long 9-pin cable connects "RS232" (4) on the FC50 with a COM port on the computer. • The short 9-pin cables connect "RS485" (6) on the FC50 with the EL200 and if necessary connect the EL200 and VC100. • The provided experiment software has been correctly installed on the computer. • The FC50 is not yet started. Then run the software and select one of the experiment programs. The program will ask you to start the FC50 by pressing the start button (2). When you do, the FC50 begins to run in a computer-assisted mode. See chapter A.7 “Control software” for details of the FC50 experiment software.

6

Shutting down

When you are through using the system, proceed as follows to shut down and turn off: • Turn off any attached load. • If using the EL200: Turn the potentiometer fully anti-clockwise, move the switch to the "OFF" position and turn off the power switch located on the side of the module. See chapter A.4 for details. • Turn the fan control knob (10) to "AUTO" and turn the main switch (5) to "OFF". • Shut down the hydrogen supply following the detailed descriptions found in chapters A.8 to A.10 in this Guide. Compressed gas cylinder: Shut off cylinder main valve. Metal hydride storage canister: Close shut-off valve of the storage canister.

• Disconnect the quick-coupler at the FC50 hydrogen inlet (1).

© Heliocentris – Energizing education

A.3

7

Fuel Cell Module FC50

6

Factors affecting operation

The performance of a fuel cell system and the voltages of individual cells of the stack are affected by various factors. The most important are: •

Current

•

Temperature

•

Air supply

•

Prior operating conditions, especially the wetness of the membrane.

Because of the complexity of the system, no universal rules for its management can be given. In the Experiments Guide detailed investigations are described, in which parameters can be varied, to demonstrate the relations and dependences of those parameters. Usually optimal operating parameters are achieved only after a series of tests. We recommend using the experiment guide as the basis of your work, observing the guidelines contained there. Before attempting your own experiments with the fuel cell system, become familiar with the system parameters as described in the Experiments Guide. Also, in order to avoid damage to the fuel cells and to achieve good electrical efficiency: •

Control the fan power so that the stack temperature does not exceed 45 °C. If the temperature exceeds 50 °C, the system automatically shuts down.

•

The longer the fuel cell stack is in continuous operation, the more powerful the stack becomes. After long periods without use, the membranes can dry out and the stack may need a longer time to reach its full power.

8

Error messages and causes

The microprocessor control of the FC50 is responsible for the management of the fuel cell system, for the monitoring of limit values and for the safety shut down of the system. In case of an operation error, the system will go into an error state, in which it: •

Puts the system into a safe condition, switching off the hydrogen supply and disconnecting the power output from the stack;

•

Displays an error code for 30 seconds in the top-left window—labeled "H2 flow";

•

After 30 seconds turns off the system completely.

While the system is in the error state, or after turning off, you can restart it by pressing the start button. If the reason for the error still exists, the system again displays the error code. The following table lists individual errors and appropriate responses.

© Heliocentris – Energizing education

7

Fuel Cell Module FC50

Error code

Description

State: reason

Er 01

Hydrogen is missing

Starting: after three seconds of purging the cell, the voltage of the last cell of the stack is still below 0.6 V

Er 02

Starting: < 7.5 V Voltage of the fuel cell stack too Operation: <4V low • Excessive load

A.3

Response • See if hydrogen supply is empty, or improperly connected.

• Reduce load on the fuel cell system • Set fan power knob to "AUTO”

• Fan power set too low Er 03

> 45 °C Temperature of Starting: the fuel cell stack Operation: > 50 °C too high • Fan power set too low

• Ensure cooling fans are working • Set fan power higher or to "AUTO” • Ensure the ambient temperature is within range

Er 04

• Ensure no short-circuit is present Load current too Current > 10.5 A high • Reduce the load • In self-powered mode, activating the purge valve briefly increases the load

Er 05

Leaking in the system

Er 06

Er 07

Starting: Hydrogen flow > 60 ml/min with no current Operation: Hydrogen flow > 40 ml/min over expected value

• Return FC50 to the manufacturer for examination.

No voltage supply to FC50

In self-powered mode:

• Ensure stack power output is connected to the input of VC100

Communication with computer interrupted

Computer-assisted operation:

• Fuel cell stack power output not connected to VC100 input

EL200 problem

• Ensure RS232 cable attached

• RS232-cable not connected

• Start control software

• Control program not running

• Ensure your computer meets requirements

• Computer too slow to respond Er 08

If this error occurs several times, the system has a hydrogen leak.

Temperature in Electronic Load too high Voltage at the input of Electronic Load > 20 V

Er 10

Cooling fan control

Starting: Cooling fan power not set to "AUTO"

Er 11

In self-powered mode: No internal power in VC100 • Starting battery dead or improperly installed

• Turn off the EL200 • Ensure cooling fans at the rear of the EL200 are working • Set fan power knob to "AUTO” • Ensure cells are properly installed in the VC100. • Renew cells if necessary.

© Heliocentris – Energizing education

A.3

9

Fuel Cell Module FC50

8

Improper modes of operation The fuel cells must be sufficiently supplied with hydrogen at all times. Starving the stack of hydrogen while current is being drawn can lead to the destruction of the membranes or catalysts. Never connect the fuel cell to an external power source (e.g. laboratory power supply or solar module). A current flow forced from outside can immediately destroy the fuel cell.

10

Technical data Fuel cell stack Rated power output

40 W

Maximum power output

Approx. 50 W

Open circuit voltage

Approx. 9 V

Current at rated power

8A

Voltage at rated power

5V

Maximum Current

10 A Approx. 580 NmL/min

Hydrogen consumption during rated output Hydrogen nominal pressure

0.6 ± 0.1 bar gauge

Max. permissible hydrogen pressure

0.4…0.8 bar gauge Operation: 50 °C Starting: 45 °C

Max. permissible cell temperature

Module FC50 Supply voltage

12V DC

Power consumption

no-load operation: 5.2 W at 10A load current: 6.4 W

Hydrogen connection

Swagelok® quick-coupler type QM2-S

Ambient operating temperature Dimensions

+5 …+35 °C 400 x 297 x 200 mm (WxHxD)

Weight

3.5 kg

Noise emissions

< 70 dB(A)

Transport and storage conditions

Protect against reactive chemicals and frost

© Heliocentris – Energizing education

1

Electronic Load Module EL200

A.4

A.4 Electronic Load Module EL200

1

Use

The EL200 Electronic Load Module is used as a variable load in the hy-ExpertTM Instructor system. It is designed to work optimally with the FC50 fuel cell stack. It is intended to be used only for educational and research purposes.

2

Overview and parts list 5

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RS485 system data bus connectors Status indicator Switch to connect/disconnect load Load adjustment Connection to load (on the right side) Socket for power cord and main on/off switch

© Heliocentris – Energizing education

A.4

3

Electronic Load Module EL200

2

Basic function

When connected to a voltage source this electronic load functions as an electronically regulated resistance converting electrical energy into heat in a controlled way. The EL200 works in the so-called constant current mode compensating for voltage fluctuations in the load circuit and adjusting the resistance to maintain a constant current. A 10-turn potentiometer on the front panel allows the load current to be precisely set.

4

Operation directions

4.1

Start-up

• Place the EL200 panel into the lower right area of the support frame. Ensure sufficient air circulation at the rear of the module, so heat produced in the device can be dissipated. In particular, do not block the vent openings. • Attach the power cord to the AC power socket (6) at the right rear of the module and plug it into an AC power outlet. • Set the load control (4) to zero (anti-clockwise) and the front panel switch (3) to “OFF”. This will prevent an uncontrolled load current flowing when the module is turned on. • Turn on the power switch (6) at the right rear of the module. • Using two of the supplied 4mm test leads, connect the load input (5) to either the FC50 power output or the VC100 power output. 4.2

Manual operation

• Set the front panel load switch (3) to "ON". • Use the potentiometer (4) to adjust the current flowing into the electronic load. The load current is shown in the “current” display of the FC50. The actual power drawn by the electronic load (load current times the clamp voltage) is shown in the “power” display of the EL200. • Changing the position of load switch (3) will make abrupt changes in the load. However, before you make large load changes in this way, make sure that the fuel cell has been in operation for a while. Sudden large changes in loading can damage cells that are not thoroughly wet.

© Heliocentris – Energizing education

3

4.3

Electronic Load Module EL200

A.4

Computer-assisted operation

Connection/disconnection of the load and a current setting can be externally controlled through the RS485 interface (1). Power values from the EL200 are also available through this interface. Thus the EL200 can be operated with the FC50 in computer-assisted mode. In order to control the EL200 through your computer, proceed as follows: • Using the supplied data cable, connect the RS485 socket (1) on the EL200 with the RS485 plug on the FC50. • Start computer-assisted operation of the FC50, as described in section 3.6. • Set the front panel load switch (3) to "ON". 4.4

Shutting down

• Set the load control potentiometer (4) to zero (anti-clockwise). • Set the front panel load switch (3) to "OFF". • Turn off the power switch (6) at the right rear of the module • If appropriate, remove all cables from the equipment.

5

Possible malfunctions

Overloading the EL200 leads to excess temperatures and a temporary safety shutdown. When the temperature has returned to normal, operation is automatically restored. If the excess voltage protection activates, disconnect the load from the voltage source to restore operation. All other malfunctions and irregularities can only be repaired by the manufacturer. In such cases please notify your dealer, who will advise you about further measures to be taken.

6

Improper modes of operation The Electronic Load EL200 must not be connected to sources of alternating current. It must not be connected to sources of direct current that exceed 20 V. Always operate the EL200 with the supplied test leads, in order to keep the contact resistances to a minimum and prevent heating of the supply terminals.

© Heliocentris – Energizing education

A.4

7

Electronic Load Module EL200

4

Technical data Maximum continuous load

200 W (cooling by fans)

Load voltage

1.2…20 V DC

Load current

0…10 A

Control

Manual by 10-turn potentiometer, externally by RS485 data bus

Stability (with ∆V load ± 20%) Overload protection

≤ 0.1% of I max + 3 mA Power limiter, cut-off at excess temperatures, automatic power restore

Protection against reverse polarity Overvoltage protection

Diode and fuse Disconnection at VLoad, max + 10%

Insulation voltage

1,5 kVeff load input to cabinet 2,5 kVeff mains to load input

AC power supply

115/230 V AC, 50…60 Hz

Ambient operating temperature

+5 … +35 °C < 70 dB(A)

Noise emission Dimensions

400 x 297 x 135 mm

Weight

5.4 kg

Transportation and storage conditions

Protect against humidity

© Heliocentris – Energizing education

1

Voltage Converter Module VC100

A.5

A.5 Voltage Converter Module VC100

1

Use

The VC100 Voltage Converter Module supplies regulated power for the FC50 module control and fans, so that you can operate the hy-ExpertTM Instructor fuel cell system as a “gridindependent” power supply. It can also provide power for other devices that need 12V DC. It is intended to be used only for educational and research purposes.

2

Overview and parts list

+

1

5

,1

9

2 9

287

3DUDVLWLF/RDG

$YDLODEOH3RZHU

W (LJHQEHGDUI

W 1XW]OHLVWXQJ

+

3

1 2 3 4 5

4

RS485 system data bus connectors Start-up battery holders 12V DC power output for FC50 control system and fans 12V DC power output Unregulated power input (2…10 V DC)

© Heliocentris – Energizing education

A.5

3

Voltage Converter Module VC100

2

Basic functions

The VC100 acts as a DC-to-DC converter or a kind of "step-up transformer". It converts an input voltage within the range of 2…10 V DC into a regulated 12 V DC output. To avoid thermal overload caused by exceeding the output power level, the converter has integrated current regulation to limit the input current. When the voltage converter is connected so it supplies the FC50 with control and fan power, (modeling a grid-independent system), an internal battery allows the VC100 to provide power to the system during the 10-second starting sequence until the fuel cell itself can generate power.

4

Operation directions

• Place the VC100 panel into the lower middle area of the support frame. Ensure sufficient air circulation at the rear of the module, so heat produced in the device can be dissipated. In particular, do not block the vent openings. • Place the 8 supplied alkaline cells into the battery holders. Observe the polarity as indicated in the battery holders. Press the battery holders into the VC100 front panel until they positively engage. • Use the 4mm test leads to connect the VC100 power input (5) with the FC50 stack power output. • If you want to operate the system in self-powered (“grid-independent”) mode, use the provided cable to connect the output (3) of the VC100 (3pin socket) with the FC50 connector labeled "12V =". • Use the provided test leads to attach suitable loads such as the traffic light module TL10 and/or the electronic load EL200 to the VC100 output. Pay attention to the voltage and power consumption of the attached loads. • For computer-assisted operation, use the 9-pin data cable to connect the VC100 and the FC50 via its RS485 bus. If the EL200 is already connected to the FC50 data port, you can connect the VC100 to the EL200.

5

Technical data Input voltage

2…10 V DC

Output voltage

12 V DC

Max. input current

10 A

Max. input power

100 W (with Vin = 10 V)

Power output

max.40 W (with Vin = 5 V)

Starting battery

8 x 1.5 V cells in series, type AA

Operating ambient temperature Noise emission

+ 5…+ 35 °C < 70 dB(A)

Dimensions, weight

200 x 297 x 95 mm, 1.0 kg

Transportation and storage conditions

Protect against humidity

© Heliocentris – Energizing education

1

Traffic Light Module TL10

A.6

A.6 Traffic Light Module TL10

1

Use

The TL10 Traffic Light Module is a 12 V sample load for the hy-ExpertTM Instructor fuel cell system.

2

Overview

1

21r (,1

2 $872

+

3

1 2 3

LED arrays Mode switch 12V DC power input

The operation mode switch (2) has three positions. In the middle position the TL10 is switched off. In the position “AUTO” the TL10 cycles as a traffic light. In position “ON” all three LED arrays are lit.

3

Technical data Input voltage

12 V DC

Capacity

approx. 8 W (position "ON")

Ambient operating temperature Dimensions / weight

+5…+ 35 °C 100 x 297 x 140 mm / 0.6 kg

© Heliocentris – Energizing education

1

Control software

A.7

A.7 Control software The FC50 system including integrated microprocessor can be operated manually through its fan power and load knobs. You can alternatively run a program to operate it in a computerassisted mode, in which the physical knobs don’t work. It is necessary run a program before starting the FC50. (See section 5.4 of chapter A.3.)

1

Running an FC50 Program

To run a program and operate the system in computer-assisted mode, you must connect the FC50 module to your computer through the RS232 interface. Start a program as follows: • The FC50 ON/OFF switch can be ON, but the system must not be operating—that is, the physical panel displays must not be illuminated. • On the Windows Start menu, select Programs > FC50 Software > FC50 Software 1.2E. The following selection menu appears:

• In the item Serial Port select the port you are using to connect the computer to the FC50 fuel cell module. • Click to expand the “Experiments” categories if needed, then select a program in one of the three program groups: o

User Interface: This application displays an image of the physical FC50 fuel cell panel on your computer’s monitor. It also controls the FC50 and the EL200 modules and displays actual data from the system. The most important parameters are displayed in a time-dependent graph.

o

Experiments: Using the programs listed in this group, you can perform experiments and collect data. The collected data are not analyzed, but only stored in a file where they can be used in other programs or printed out for analysis. For additional information, refer to the Experiments Guide.

o

Automated Experiments: These programs are similar to some in the Experiments group, but they run and collect data automatically. Data points are plotted and saved for further examination.

• Click START. Descriptions typical of programs in the three categories are given below.

© Heliocentris – Energizing education

A.7

2

Control software

2

Control window (left side)

A common control window appears at the left side of the screen in all the FC50 programs. It contains buttons to start and exit, system messages, names of the log file and data storage file, and program sequence controls. The actual appearance of the control window may vary in different programs. The Messages text box contains requests and notes about the operation of the system. If an error occurs in the system, for 30 seconds the Error Messages text box displays an error code and a short description. See section 8 “Error messages and causes” of chapter A.3. In addition an error message appears on the screen. You can click the displayed OK button after the Instructor is turned off (automatically after 30 seconds or by turning the main switch off). Then correct the cause of the error, restart the FC50 and continue with the experiment. The previously measured values are not lost. The FC50 software can store measured data in two ways simultaneously: as an array of selected values particular to the experiment being performed, and as a continual stream of logged values. The item Experiment Data specifies the name of a text file containing the array of selected values. If the file already exists, new values are appended to the existing file. The item Log File specifies the name of a text file containing a stream of measured values. Click Start Logging to store values every 100 ms. This function is particularly helpful when analyzing abrupt changes in the load. Log files can become very large, and should not be allowed to grow over long periods. It is better to save several smaller files. The item Starting Temperature specifies a stack temperature that must be reached before some experiments can begin to make and save measurements. Clicking the Start Measuring button begins the experiment. If the stack temperature is less than the specified minimum, the warm-up panel is displayed. Clicking the EXIT button terminates the current program and returns to the selection menu. Measurements already taken are retained.

© Heliocentris – Energizing education

3

3

Control software

A.7

Warm-up panel

When you click Start Measuring in the control window, and the stack temperature is lower than the starting temperature you specified for that experiment, the warm-up panel appears. Use these controls to apply increased load to the system, raising the stack temperature. Setting a lower-than-normal fan power will raise the temperature more quickly. However you should watch carefully the system values shown in the background, particularly the stack voltage. In some experiments a similar panel appears when it is necessary to lower the system temperature. You can lower the temperature by increasing the fan speed.

4

User Interface program

If you selected the User Interface program, you will see on your computer screen a graphic representation of the physical system modules. In the Messages box, you will be asked to “press START on FC50”. At that time, ensure the FC50 main switch is ON, but the system is not operating. Then press the green START button on the (physical) front panel. The FC50 and EL200 can then be controlled only through the computer; the physical knobs have no effect. The User Interface program lets you change the load and fan power, and display and log data. The Panel Display window shows the system layout and its most important parameters. Use the virtual Load Current and Fan Power knobs to change those values.

© Heliocentris – Energizing education

A.7

Control software

4

In addition to the Panel Display window, a Data Display window is available. As before, you can use the virtual Load Current and Fan Power knobs to change those values. The Data Display shows in a graph the changing values of •

Stack voltage

•

Stack current

•

Stack temperature

•

Fan Power

•

Hydrogen flow.

Click and drag at any point on the graph to change the time segment or value range displayed.

To terminate the program, click the EXIT button at any time. The main selection menu is displayed.

© Heliocentris – Energizing education

5

5

Control software

A.7

Experiment programs

If you selected one of the Experiment programs (see section 1), you will see instructions in the Messages box, beginning with “Press Start on FC50”. Ensure the FC50 main switch is ON, but the system is not operating. Then press the green START button on the (physical) front panel. In Experiment Data enter the name of a text file to contain the array of measured values. In Starting Temperature enter the stack temperature that must be reached before you will begin to save measurements. Click the Start Measuring button to begin the experiment. If the stack temperature is less than the specified minimum, the warm-up panel is displayed. A typical experiment, C.3.1 – Effect of Air Supply is shown below:

You should follow closely the detailed instructions for individual experiments as given in the Experiments Guide. Specific instructions for measuring values may appear in the Messages text box. In this example, when you click Take Pre-Set Values, the values you previously set with the virtual knobs Load Current and Fan Power are applied. The timing Clock begins to count. Click Store Measurement when you want to capture the current measurements. They are stored in the file as specified in Experiment Data, and displayed in the adjacent table. With the additional button Delete Last Row you can erase the last set of data in your data table. The data will be deleted in the screen table but not in the file named in Experiment Data. Some experiments offer a Curve 2 button to save a second set of measurements. When the experiment is complete, click EXIT to terminate the program and go back to the main selection menu. The values stored in the specified file can be analyzed.

© Heliocentris – Energizing education

A.7

6

Control software

6

Automated Experiment programs

If you selected one of the Automated Experiment programs, you will see instructions in the Messages box, beginning with “Press Start on FC50”. Ensure the FC50 main switch is ON, but the system is not operating. Then press the green START button on the (physical) front panel. In Experiment Data enter the name of a text file to contain the array of measured values. In Starting Temperature enter the stack temperature that must be reached before you will begin to save measurements. Click the Start Measuring button to begin the experiment. If the stack temperature is less than the specified minimum, the warm-up panel is displayed. After the warm-up phase, the program automatically sets operating points, takes and displays measurements. After the curve has been plotted, the Start Measuring button changes to Restart Measuring. Clicking this button will repeat the measurements and plot another curve. A typical automated experiment, C.2A – Characteristic Curve is shown below:

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7

Control software

A.7

At any time you can click EXIT to terminate the program and go back to the main selection menu. The values stored in the specified file can be analyzed. If an error occurs during an automated experiment the software stops the experiment. The measurement can be restarted by clicking Restart Measuring.

7

Troubleshooting

Port naming On some computers the list of interface ports in the “Serial Port” drop-down box may appear different. Instead of “COM1”, the port appears as “ASRL1::INSTR". On these computers, make your selection as follows: To use this port …

…Select this item in “Serial Port”

COM1

ASRL1::INSTR

COM2

ASRL2::INSTR

LPT1

ASRL10::INSTR

© Heliocentris – Energizing education

Hydrogen Supply Option I: Connection set for compressed gas cylinders

1

A.8

A.8 Hydrogen Supply I: Connection set for compressed gas cylinders 1

Use

The connection set for compressed gas cylinders lets you connect standard cylinders of compressed hydrogen gas to the hy-ExpertTM Instructor fuel cell system, supplying the FC50 with hydrogen at a constant operating pressure of approx. 0.6 bar gauge. Its use is only to supply the hy-ExpertTM Instructor fuel cell system with hydrogen for educational or research purposes.

2

Overview and parts list 9

3

2

4

10 1 6

5 7

8

1

Two-stage regulator with pressure gauges for cylinder and delivery pressure

2 Inlet connection fitting for compressed hydrogen cylinder 3 Solenoid valve, normally closed 4 Control cable for solenoid valve 5 Hydrogen line 1/4" for supply to the FC50 6 Quick-coupler for connection to the FC50, closed when disconnected 7 Union nut for connecting hydrogen line to the solenoid valve (3) 8 Unattached coupling plug, to mate with quick-coupler (6) 9 Spare gaskets, for connection (2) to compressed hydrogen cylinder 10 Relief valve (1 bar) Not shown: Support for user-supplied hydrogen cylinder

© Heliocentris – Energizing education

Hydrogen Supply Option I: Connection set for compressed gas cylinders

A.8

3

2

Basic Function

The regulator (1) reduces the pressure of the hydrogen stored in the cylinder (max. 200 bar pressure) to a constant pressure of approx. 0.6 bar gauge necessary for the FC50. It is equipped with inlet and outlet pressure gauges and has a relief valve (10) on the outlet side, which opens at a gauge pressure of approx. 1 bar so that the attached components cannot be damaged by excessive pressure. The solenoid valve (3) is normally closed and opens only if the cable (4) is attached to the FC50 and energized. The connecting tube (5) with quick-coupler (6) delivers hydrogen to the FC50.

4

Special safety considerations for handling compressed hydrogen cylinders

You must be aware of and follow local safety regulations for handling compressed gas cylinders and hydrogen. In a full compressed hydrogen cylinder, the pressure is approximately 200 bar. Compressed hydrogen cylinders may not be stored in closed areas without appropriate installations. For indoor storage, special gas cylinder cabinets with a permanent explosionproof exhaust are required. If this is not possible, cylinders must be stored outdoors. When using the cylinders in a laboratory area, the following precautions are recommended: •

Provide good ventilation of the area.

•

Smoking and open flame are forbidden.

•

Avoid sources of heat near the compressed hydrogen cylinder and hydrogen piping.

•

Take measures to prevent electrostatic charges.

•

Use the supplied cylinder support or appropriate equipment provided by your hydrogen supplier to prevent the cylinder from falling over.

•

The cylinders must not be left unsupervised in the area.

•

If no hydrogen is being used, always close the main valve on the cylinder.

In case of fire: •

Immediately report the fire and follow the fire response procedures for your laboratory.

•

Evacuate and secure the area and building

•

Leave escaping hydrogen gas to "burn down".

Note: Hydrogen flames are not visible!

© Heliocentris – Energizing education

Hydrogen Supply Option I: Connection set for compressed gas cylinders

3

5

Operation directions

5.1

Installation

A.8

• Place the compressed hydrogen cylinder on the floor beside the experimental set-up, and use the supplied cylinder support or appropriate equipment provided by your hydrogen supplier to prevent the cylinder from falling over. • Before attaching the regulator, in order to clear out impurities, carefully open the main valve of the hydrogen cylinder for one second. The cylinder is at high pressure. Do not direct escaping gas toward personnel.

• Remove protective cap from the inlet connection (2). • Screw the regulator onto the gas cylinder, and hand-tighten (left-hand threads). • On the initial setup: Screw union nut (7) of the hydrogen connecting line (5) onto the output of the solenoid valve (3) finger-tight only. Then further tighten 1/8 turn with a 9/16" wrench. • Slowly open the main valve of the compressed hydrogen cylinder. Do not attempt to adjust the output pressure, as the regulator is preset to the correct 0.6 bar output pressure, and is not adjustable. 5.2

Pausing and shutting down

When you are not using hydrogen, even during rest breaks, you should close the main valve of the compressed hydrogen cylinder. To shut down operation, proceed as follows: • Close the main valve of the compressed hydrogen cylinder. • Relieve pressure in the regulator so that the pressure gauge reads zero. To do this, disconnect the quick-coupler (6) from the FC50 and instead connect it to the unattached coupling plug (8) allowing residual gas in the regulator to leak out. • Remove the regulator from the hydrogen cylinder. Pressure in the regulator must be relieved before unscrewing it, else the gasket at the cylinder connection can be destroyed.

© Heliocentris – Energizing education

Hydrogen Supply Option I: Connection set for compressed gas cylinders

A.8

6

Technical data Regulator

2 stage, Hydrogen gas

Input connector

cylinder connection, appropriate for national standard

Max. permissible input pressure Outlet pressure

200 bar gauge 0.6 ± 0.1 bar gauge (depending on flow), preset

Relief valve opening pressure Power to operate solenoid valve Hydrogen connecting tube

1.5 bar gauge 2 W (at 12 V DC) PFA, outside diameter 1/4" Swagelok® type QM2-B

Quick-coupler Ambient temperature operating range

+ 5 … +35 °C

Dimensions, without connecting cable

190 x 115 x 110 mm (LxWxH)

Weight

1.6 kg

© Heliocentris – Energizing education

4

Hydrogen Supply Option II: Metal hydride storage, with refilling kit

1

A.9

A.9 Hydrogen Supply II: Metal hydride storage, with refilling kit

1

Use

The HS150 Hydrogen Storage Module supplies the hy-ExpertTM Instructor fuel cell system with hydrogen from a metal hydride storage canister. Using the supplied refilling kit, this panel-mounted canister can be refilled from a standard compressed hydrogen cylinder. Its use is only to supply the hy-ExpertTM Instructor fuel cell system with hydrogen for educational or research purposes.

2

Overview and parts list

9 1 8 2

7

3

6

5 4

1

Single-stage regulator with pressure gauges

2

Relief valve (1 bar)

3

Connecting tube 1/4" with coupler for connecting to metal hydride storage canister

4

Shut off valve for metal hydride storage canister

5

Metal hydride storage canister with shut off valve and quick-coupler

6

Mounting plate with screw-down clamps for storage canister

7

Hydrogen line 1/8" with quick-coupler for supply to the FC50

8

Solenoid valve, normally closed

9

Control cable for solenoid valve

© Heliocentris – Energizing education

Hydrogen Supply Option II: Metal hydride storage, with refilling kit

A.9

3

2

Basic function

The storage canister (5) is filled with a special metal hydride alloy. It has a shut-off valve (4) and a gas outlet with quick-coupler. The pressure in the storage canister is indicated on the gauge of the regulator (1). The regulator reduces the storage pressure to a set operating pressure of approximately 0.6 bar gauge. It has a relief valve (9), which opens if the outlet pressure exceeds 1.4 bar, so that the attached components cannot be damaged by excessive pressure. The solenoid valve (8) is normally closed and opens only if the cable (9) is attached at the operating FC50. The connecting line with quick-coupler (7) delivers hydrogen to the fuel cell of the FC50. Using regulator (10) the metal hydride storage can be re-filled from commercial compressed hydrogen cylinders. Metal hydride storage is based on the chemical reaction of hydrogen with certain metal alloys which are able to chemically bind hydrogen in a reversible reaction. The absorption of hydrogen is an exothermic process; the hydrogen delivery is an endothermic process. Both procedures are influenced by the thermodynamic properties of the chemical reactions between hydrogen and the respective metal alloys. The hydrogen pressure in the storage canister mainly depends on the temperature of the metal alloy.

4

Special safety considerations for metal hydride storage canisters

The storage canister is equipped with a temperature and pressure-sensitive relief valve. This valve provides pressure release of the canister in case of unexpected extreme operation or storage conditions e.g. open fire. The release conditions of the valve are specified in section 7 “Technical Data”. The storage canister must be installed and stored in a position such that no danger results from a possible opening of the relief valve. Do not block the relief valve. The connections of the storage system must be regularly examined for tightness. The storage canister must be checked regularly for damage, deformation, etc. If irregularities are found, immediately stop using the storage system and inform Heliocentris. In case of leakage or canister damage, hydrogen may be released. Due to the nature of metal hydrides, only a small portion of the stored hydrogen will be released spontaneously. The canister temperature will decrease and further hydrogen release will occur at a fairly low rate. Therefore it is recommended to put the leaking canister in a well ventilated place (if possible outside of the building) until the canister is completely empty. During this time the canister should be on a fire-proof base away from any sources of ignition. The area should be marked in a suitable way. Only the manufacturer can repair a damaged storage canister.

© Heliocentris – Energizing education

Hydrogen Supply Option II: Metal hydride storage, with refilling kit

3

Possible consequences

Source of danger Storage canister contains Hydrogen

Danger of fire and ignition when opening the canister

A.9

Preventive measures • Do not open the canister. Do not remove the valve • Store the canister in a wellventilated place • Keep away from sources of ignition • Take precautions against electrostatic charge • No open fire • No smoking

Storage canister contains pyrophoric / self heating metal powder

Danger of fire when opening the canister

Canister is under pressure. Pressure rises with increasing temperature.

Unauthorized excess pressure

• Do not open the canister. Do not remove the valve • In case of fire use class D powder extinguisher; do not use carbon dioxide extinguisher or water

• Do not expose to sunlight; protect the canister from temperatures above 50°C • Do not heat a filled storage canister without releasing hydrogen at the same time • The maximum working pressure of the canister must not be exceeded at any time (see technical data)

5

In case of fire

Immediately inform the fire department Hydrogen burning:

Note: Hydrogen flames are not visible!

•

Evacuate and secure the area and building

•

Leave escaping hydrogen gas to "burn down".

Metal hydride powder burning: •

Evacuate and secure the area and building

•

Suffocate fires with class D fire extinguisher or dry sand

•

Do not use water or CO2 extinguishers

•

If smoldering metal hydride powder cannot ignite adjacent materials, it may be best to leave the hydride burning.

© Heliocentris – Energizing education

Hydrogen Supply Option II: Metal hydride storage, with refilling kit

A.9

4

Operation directions 5.1

Installation of the metal hydride storage canister on its panel

• Loosen the knurled nuts of the storage canister mounting (6) a few turns. • From the right side, slide the filled metal hydride storage canister into the mounting and align it. • Connect the tube (3) to the quick-coupler of the storage canister (5). • Align the canister and evenly tighten the knurled nuts of the storage mounting plate (6) finger-tight only. • Connect the hydrogen connecting tube (7) to the quick-coupler and the control cable for the solenoid valve to the FC50. When the two sides of the quick-coupler are connected and under pressure do not rotate them! 5.2

Using hydrogen from the metal hydride storage canister

After successful installation and having made all connections the shut-off valve (4) of the storage canister needs to be opened. When the FC50 fuel cell system has been started as described in 4.5 and the system is in operation, hydrogen flows from the storage canister (5) through the regulator (1) and the solenoid valve (8) into the fuel cell system. The fuel cell system must be operated with a pressure of 0.6 ± 0.1 bar gauge. The setting of the regulator on the mounting panel is fixed and must not be changed. While the storage canister is delivering hydrogen (discharging), the canister temperature decreases and the pressure in the canister decreases correspondingly. To keep the hydrogen pressure constant, the storage canister needs to absorb heat from the environment. Normal air circulation is generally enough. Take care that while operating the fuel cell, the storage canister pressure does not decrease below 1 bar gauge. If it does, reduce the load on the fuel cell until the storage canister again warms to room temperature and shows higher pressure. If the pressure within the storage canister falls below 1.0 bar gauge while the canister is at room temperature, the storage canister needs to be refilled. You should keep some pressure in the storage canister at all times. If the canister has little or no pressure at a particular temperature, and the canister becomes further cooled, a negative pressure can develop, sucking air into the canister through the open valve. 5.3

Pausing and shutting down When you are not using hydrogen, and the FC50 is switched off, you should close the shut-off valve (4) of the metal hydride storage canister. Otherwise over time pressure may rise at the regulator so that the relief valve can open and empty the canister.

© Heliocentris – Energizing education

Hydrogen Supply Option II: Metal hydride storage, with refilling kit

5

6

Technical data Storage Canister Intended gas specification

Dry Hydrogen, purity 5.0 or higher

Storage capacity:

Max. 225 standard liters approx. 150 standard liters

• if charging @ 10 bar gauge Gas connection

Quick-coupler Parker, type Q4CY

Discharge operation: Approx. 8 bar gauge @ 20°C (initially higher)

• Discharging pressure

+50 °C

• Max. canister temperature Charge operation:

10 bar gauge @ +20 °C 17 bar gauge

• recommended charging pressure • Max. charging pressure

+15 ... +30 °C

• Allowed canister temperature Max. storage temperature

+50 °C

Opening conditions of relief valve

P ≈ 82 bar / T ≈ +88 °C 64 mm x 305 mm

Dimensions (∅ x length) Weight

2.2 kg Module HS150

Regulator

Single stage, Hydrogen gas

Max. allowed input pressure Delivery pressure

19 bar gauge @ +20 °C 0.7 ± 0.1 bar gauge (flow depending), preset

Relief valve opening pressure

1.5 bar gauge

Connection to storage canister

Parker quick-coupler, type Q4VY

Hydrogen connecting tube Connection to fuel cell system Power consumption single solenoid valve Recommended operating temp. Dimensions (w x h x d)

PFA, outside diameter 1/8" Swagelok® quick-coupler, Type QM2-B 2 W @ 12 V DC + 5 … +35 °C 400 mm x 297 mm x 95 mm

Weight (without storage canister)

1.95 kg

© Heliocentris – Energizing education

A.9

Hydrogen Supply Option III: Hydrogen generator with metal hydride storage

1

A.10

A.10 Hydrogen Supply Option III: Hydrogen generator with metal hydride storage

1

Use

A hydrogen generator together with HS150 Hydrogen Storage Module supplies the hyExpertTM Instructor fuel cell system with hydrogen. The panel-mounted metal hydride storage canister stores gaseous hydrogen produced in the generator. Hydrogen is supplied to the fuel cell system at the required operating conditions (see technical data). Its use is only to supply the hy-ExpertTM Instructor fuel cell system with hydrogen for educational or research purposes.

2

Special safety considerations for the hydrogen generator

The hydrogen generator produces only the amount of hydrogen which will later be used in the fuel cell system. Thus the quantity of combustible gas is kept to a minimum. To lessen the risk of a hydrogen leakage, it is however necessary to regularly check the tightness of all hydrogen pipes and connections. In addition to hydrogen, the hydrogen generator also produces oxygen. The oxygen is released with the equipment cooling air into the environment. The hydrogen generator may only by used in an environment that has sufficient air circulation, so that the released oxygen can dissipate. The power switch and connection cord are at the back of the equipment. They must be freely accessible at all times during operation.

3

Overview, scope of supply and operation

Please refer to the separate operating instructions provided with the hydrogen generator and HS150 Hydrogen Storage Module.

© Heliocentris – Energizing education

1

Learning Objectives

General learning objectives The Experiments Guide teaches the basic operation of fuel cell systems, including: • • • • •

Starting up a fuel cell system Behavior of fuel cell systems in theory and practice Evaluating the characteristics Analyzing and designing components of a fuel cell system Handling hydrogen safely

Specific learning objectives Experiments in the guide support the following learning objectives.

C.1 The basic functions of the fuel cell system •

Working with technical manuals

•

Structure and safe handling of electrical devices and the hydrogen supply

•

Learning the individual components of the fuel cell system

•

Starting in the various operating modes

•

Working with the control software

•

Recognizing and eliminating errors

•

Setting operating points and reading measured values

•

Shutting down the fuel cell system

C.2 The characteristic curve of a fuel cell •

Recording measured values

•

Drawing and evaluating the voltage-current-curve and the power-current-curve

•

Comparing with the theoretical behavior of fuel cells

•

Interrelation between the different physical values of a fuel cell

•

Designing a fuel cell

© Heliocentris – Energizing education

B.1

2

Learning Objectives

C.3 Parameters influencing the characteristic curve •

Investigating the effects of reduced air supply on the V-I curve

•

Applying Faraday’s laws

•

Investigating the effects of increased internal resistance on the V-I curve

•

Developing an equivalent circuit diagram

•

Investigating the effects of the fuel cell temperature on the V-I curve

•

Exploring possible optimization, based on prior observations

C.4 Determination of the hydrogen current curve •

Determining the hydrogen-current relation

•

Developing the relationship between hydrogen flow rate and increased current

•

Applying Faraday’s laws

•

Calculating hydrogen consumption related to current and number of cells

C.5 Efficiency of the fuel cell stack •

Determining the stack efficiency by power balance

•

Comparing stack efficiency and stack power

•

Effect of stack efficiency in practical applications

•

Determining the stack efficiency by current and voltage efficiency

•

Determining and analyzing the efficiency losses

•

Thermodynamic view of the different reference voltages

C.6 Set-up of a fuel cell power supply •

Setting up and starting a grid-independent power supply

•

Using the traffic light module "TL10" acting as a typical consumer

•

Determining power consumption, stack power and available power

•

Analyzing the parasitic load

•

Determining losses and optimization possibilities

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B.1

3

Learning Objectives

B.1

C.7 Efficiency of a fuel cell power supply •

Determining and comparing overall efficiency, system efficiency and stack efficiency

•

Determining the optimum operating range for the fuel cell

•

Influence of the parasitic load on the overall efficiency

C.8 Fuel cell application I: Remote traffic light •

Using the traffic light module to determine the fuel requirement of a system

•

Evaluating the data using a spreadsheet program

•

Sizing and designing a hydrogen storage system

•

Comparing different hydrogen storage systems with batteries

C.9 Fuel cell application II: Fuel cell car •

Evaluating the use of fuel cells in motor vehicles

•

Using load profiles

•

Evaluating the data using a spreadsheet program

•

Determining the efficiencies of different operating ranges

•

Linking load profiles to practical applications

•

Comparing a fuel cell with a combustion engine

•

Using Carnot and Gibbs efficiency

•

Calculating volumetric and gravimetric power densities

•

Comparing different hydrogen storage systems with gasoline

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1

Teaching references and methodology

B.2

Hydrogen fuel cells will play a significant role in future power supplies. The areas of application will include stationary power such as for households, mobile power for transportation, and power supplies for portable electronic devices. Becoming acquainted with fuel cell technology and exploring its various areas of application are indispensable for training in the fields of electric power supplies, electric propulsion technology, electronics, environmental technology, and electrochemistry. Using this experiment guide, students can acquire basic and extended knowledge about fuel cell technology. The guide also examines various areas of practical application, and suggests further inquiry. The included technical manuals contain both operating instructions and detailed information about the operating parameters, providing an opportunity for problemoriented student tasks. The experiments are arranged below to offer suggestions for practical courses. Such courses could offer learning at a particular level or in a particular field of activity. Depending on the desired learning objective, some experiments can be done using only a part of the given procedure.

Getting to know the system components: •

C.1

The basic functions of the fuel cell system

Basic knowledge about the design and function of fuel cells: •

C.2

The characteristic curve of a fuel cell

•

C.4

Determination of the hydrogen current curve

•

C.5

Efficiency of the fuel cell stack (up to and including section 4)

Basic knowledge about the structure of a fuel cell system: (only for package "Instructor Off-Grid") •

C.6

Set-up of a fuel cell power supply

Extended knowledge about the behavior of fuel cells: •

C.3

Parameters influencing the characteristic curve

•

C.5

Efficiency of the fuel cell stack

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2

Teaching references and methodology

B.2

Extended knowledge and applications of fuel cell systems: (only for " Instructor Off-Grid " package) •

C.7

Efficiency of a fuel cell power supply

•

C.8

Fuel cell application I: Remote traffic light

•

C.9

Fuel cell application II: Fuel cell car

Electrotechnical emphasis: •

C.2

The characteristic curve of a fuel cell

•

C.3

Parameters influencing the characteristic curve (up to and including section 4)

•

C.5

Efficiency of the fuel cell stack

•

C.6

Set-up of a fuel cell power supply

•

C.7

Efficiency of a fuel cell power supply

•

C.8

Fuel cell application I: Remote traffic light

Thermodynamic emphasis: •

C.2

The characteristic curve of a fuel cell

•

C.3

Parameters influencing the characteristic curve

•

C.4

Determination of the hydrogen current curve

•

C.5

Efficiency of the fuel cell stack

•

C.9

Fuel cell application II: Fuel cell car

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1

Recommended web sites

B.3

Large development potentials still exist in fuel cell technology as well as hydrogen production and storage. Because of the rapid rate of change in these areas, in order to remain wellinformed it is recommended that you use the Internet as an ongoing source of information. The following web sites are recommended sources about fuel cells and hydrogen, conveniently arranged. These same links are available in HTML format on the included CD.

Design and function of fuel cells: • • •

U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy www.eere.energy.gov/RE/hydrogen_fuel_cells.html Ballard Power Systems www.ballard.com/be_informed/fuel_cell_technology/how_the_technology_works Japan Hydrogen & Fuel Cell Demonstration Project www.jhfc.jp/e/fc/fc_struct.html

•

BEWAG: Fuel Cell Innovation Park www.innovation-brennstoffzelle.de/e/index.html

•

Initiative Brennstoffzelle www.initiative-brennstoffzelle.de/en/live/start/8.html

Generation, storage and use of hydrogen: •

U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy www.eere.energy.gov/RE/hydrogen_production.html www.eere.energy.gov/RE/hydrogen_transport.html

•

Shell Hydrogen www.shell.com/home/Framework?siteId=hydrogen-en

•

The European Thematic Network on Hydrogen www.hynet.info/hydrogen_e/index00.html

•

BEWAG: Fuel Cell Innovation Park www.innovation-brennstoffzelle.de/e/index.html

•

Federal Environmental Agency of Germany www.umweltbundesamt.de/uba-info-daten-e/daten-e/brennstoffzelle.htm

Experiments in fuel cell technology: • •

U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy www.eere.energy.gov/education American Hydrogen Association www.clean-air.org

© Heliocentris – Energizing education

2

Recommended web sites

Fuel cell and hydrogen associations: •

European Hydrogen and Fuel Cells Technology Platform www.hfpeurope.org

•

European Hydrogen Association www.h2euro.org The European Thematic Network on Hydrogen www.hynet.info Canadian Hydrogen Association www.h2.ca National Hydrogen Association NHA www.hydrogenus.com American Hydrogen Association www.clean-air.org China Association for Hydrogen Energy www.chinahydrogen.org/ Engineering Advancement Association of Japan www.enaa.or.jp/EN/index.html The National Hydrogen Association of Australia www.hydrogen.org.au

• • • • • • •

Information about fuel cell vehicles: •

H2 Cars http://www.h2cars.de

•

California Fuel Cell Partnership www.fuelcellpartnership.org Japan Hydrogen & Fuel Cell Demonstration Project www.jhfc.jp/e/index.html

•

Glossary about fuel cells and hydrogen: • •

Fuel Cell Industry Report www.sanewsletters.com/fcir/glossary1.asp hyWeb http://www.hyweb.de

Fuel cell and hydrogen news: •

The Hydrogen & Fuel Cell Letter www.hfcletter.com/

•

Fuel Cell Industry Report www.fcellreport.com

•

Fuel Cell Magazine www.fuelcell-magazine.com/fc_newsletter_current.htm

© Heliocentris – Energizing education

B.3

1

References for Further Reading

James Larminie, Andrew Dicks Fuel Cell Systems Explained John Wiley & Sons ISBN: 047084857X Gregor Hoogers (Editor) Fuel Cell Technology Handbook  CRC Press ISBN: 0849308771 Tom Koppel Powering the Future: The Ballard Fuel Cell and the Race to Change the World John Wiley & Sons ISBN: 0471644218 Rebecca L. Busby Hydrogen And Fuel Cells: A Comprehensive Guide Pennwell Books ISBN: 1593700431 Jeremy Rifkin The Hydrogen Economy Tarcher ISBN: 1585422541 John S. Rigden Hydrogen: The Essential Element Harvard University Press ISBN: 0674012526 Ulrich Stimming, L. G. S. De Haart, J. Meusinger Fuel Cell Systems: Pemfc for Mobile and Sofc for Stationary Application Wiley-VCH Verlag GmbH ISBN: 3527297952 R.H. Thring Fuel Cells for Automotive Applications ASME Press ISBN: 0791802124 Richard E. Sonntag, Claus Borgnakke, Gordon J. Van Wylen Fundamentals of Thermodynamics Wiley ISBN: 0471152323

© Heliocentris – Energizing education

B.4

Solutions 1

The basic functions of the fuel cell system

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

Voltage converter VC100 (optional)

621

Traffic light TL10 (optional)

622

Hydrogen supply (alternates)

I II III

Arrange the devices as in the following diagram:

Fuel cell Cell FC50 Hydrogen supply

Traffic light Light TL10 (optional)

Voltage Converter Spannungswandler VC100 (optional)

Electronic Load Elektronische Last EL200

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C.1

Solutions 2

The basic functions of the fuel cell system

C.1

Task: Learn about the FC50 Fuel Cell System and its components by stepping through their operation. Notice how the system reports operation errors and learn how to correct them.

Execution: Note: This procedure shows you the operating modes of the individual components and later helps you to easily recognize and correct errors. You should follow the sequence step by step as indicated here. If you notice a mistake or omission in the procedure steps, you should nevertheless do the steps as indicated in order to learn the behavior of the system in the event of an error. To solve the following problems and answer the questions it will be necessary to refer to the Component Descriptions of the devices used. 1

Installation and start-up of FC50, EL200 and hydrogen supply: When setting up and starting the equipment, follow the instructions provided in Part A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Place the modules into the mounting frame arranged as shown in the above illustration. Use the AC power cord to connect the EL200 Electronic Load to the source of AC power. (Connection is on the right side behind the front panel.) Ensure the toggle switch on the EL200 front panel is OFF. Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.2

On the FC50, set the main (toggle) switch to ON and press the START button. Which problem occurs and how can it be corrected? Problem:

The FC50 shows no reaction and does not start.

Solution:

Attach the AC power pack to the 12V= DC Input socket, to supply power to its control board.

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Solutions 3

1.3

The basic functions of the fuel cell system

C.1

After you have corrected the problem, press the START button again. Which problem now occurs and how can it be corrected? Use the error list in A.3 Fuel Cell Module FC50 to explain. Problem:

The FC50 reacts, but immediately displays error Er01 in the ‘H2 flow' window.

Solution:

On the “Error messages” list (see A.3 Fuel Cell Module FC50) the error description is: 'hydrogen is missing'. To correct this problem, put the hydrogen supply you are using into operation, following the appropriate instructions in section A.8 – A.10. Pay particular attention to the correct assembly of the quick-coupler at the FC50 and to connecting the 9-pin plug of the relief valve with the FC50 port 'H2 SUPPLY'.

1.4

Press the START button again. For approx.10 seconds a system test is performed. If this is successful, the displays are illuminated. The FC50 is now ready for use.

1.5

Turn the main power switch located behind the EL200 front panel on. The ‘Power’ display is illuminated. Turn the 10-turn potentiometer, in order to apply a load current. What does this show? Problem:

Both on the ’CURRENT’ display on the FC50 and ’Power’ on the EL200 indicates no load current and no power.

Solution:

The AC voltage supply of the EL200 is switched on; however the load is not applied. The toggle switch on the front panel must be switched to ’ON’. As an indication, the green operating-LED is lit when the EL200 is active.

1.6

The load current previously set on the potentiometer is drawn from the Fuel cell and can be read on the appropriate display. The power Pload absorbed by the electronic load is shown in the EL200 display window.

1.7

Cooling fans supply air necessary for the operation of the fuel cell. The speed of the fans can be adjusted to suit the load current automatically or manually. Use the knob beside the display ' Fan Power ', to set a fan power between 5 % and 100 %. Try setting different operating points on the EL200 and try to set an appropriate fan power. Watch how the system reacts when you change these settings.

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Solutions 4

1.8

The basic functions of the fuel cell system

C.1

Now apply a load current of 9 A and reduce the fan power slowly to 5 %. Watch the stack voltage display. What did you observe? Use the “Error messages” list (see A.3 Fuel Cell Module FC50) in order to explain why the FC50 shut off.

1.9

Problem:

After reducing the fan power, the voltage falls. The FC50 switches off automatically and announces Er02.

Solution:

In the “Error messages” list see the error description: “Voltage of the fuel cell stack too low.” The FC50 has a protection circuit which automatically switches the system off when the voltage falls below 4 V thereby protecting the fuel cell from damage.

Note:

See a detailed explanation of the problem in experiment C.3 "Parameters influencing the characteristic curve".

Switch the FC50 off. Ensure that the potentiometer of the EL200 is set to zero and the toggle switch on the front panel is OFF.

1.10 If you are not making further measurements with the system, proceed to shut down and switch off the system as follows:

2

•

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

Installation and start-up of COMPUTER-SUPPORTED Operations To operate the FC50 in the COMPUTER-SUPPORTED mode, it is necessary to have a computer with RS232 interface on which you have installed the provided software. Refer to operation of the software in the section A.7 "Control Software".

2.1

Connect the port ’ RS232 ’ of the FC50 to the appropriate interface on your computer using the provided long 9-pin data cable. Start the program ’FC50 software’ on your computer selecting the menu option ’user Interface’ and click the ’START’ button. Follow the instructions in the reporting window of the control software.

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Solutions 5

2.2

The basic functions of the fuel cell system

C.1

When you are requested from the software, switch on the FC50 and start it. Which problem occurs and how can it be corrected? Problem:

Both FC50 and the software announce Er10 (Cooling fan control)

Solution:

Before starting the FC50 the fan control must be set to ’ AUTO’. Follow the instructions in the error message: Switch the FC50 off, correct the error by placing the fan power on ’ AUTO ’ and start the FC50 again. Afterwards you can acknowledge the error message with the "Ok" Button and continue working.

2.3

The measured values of the FC50 are now shown on both the module and on your computer. But you can adjust the fan power only through the software.

2.4

Also, setting the load current is only possible through the software. Set a value of Iload = 2 A Why doesn’t the EL200 react? Problem:

The EL200 does not react to computer-set values.

Solution:

Communication between EL200 and FC50 is made through the RS485 bus. Therefore it is necessary to connect the two components with the provided short 9pin cable. Also you must ensure that both the toggle switch on the front panel of the EL200 and the switch in the software are in the 'ON’ position.

2.5

In the ’user Interface’ of the FC50 software click the label ’data display’. Observe the behavior of the different fuel cell parameters when you change the load current.

2.6

When you are through with the system, proceed to shut down and switch off the system as follows: •

Terminate the FC50 software. The FC50 sees the interruption of communication and displays an error.

•

Turn the potentiometer of the EL200 to zero, set the toggle switch to OFF and switch off the main switch behind the front panel.

•

Turn the knob for the fan power to AUTO and turn the FC50 main switch OFF.

•

Put the hydrogen supply out of operation correctly.

•

Remove the hydrogen inlet to the FC50 by disconnecting the quick-coupler.

© Heliocentris - Energizing education

Solutions 6

3

The basic functions of the fuel cell system

C.1

Installation and start-up of VC100 and TL10 (optional) This part can only be performed if the voltage converter VC100 and the traffic light TL10 is available. It does not matter if the FC50 is operating in COMPUTERSUPPORTED mode or in manual mode. Follow the safety instructions provided in section A: Component Descriptions for the individual components.

3.1

In the following the fuel cell system is self-powered. Switch the FC50 off and remove the AC power pack. Instead connect the 12 V DC input of the FC50 to the “Parasitic Load” output of the VC100 using the provided 3-pin cable. From the “Available Power” output of the VC100, the traffic light TL10 or other loads can be supplied. Use the provided short 9-pin RS485 data cable to connect the VC100 to the unused interface port of the EL200, to provide communication in the COMPUTERSUPPORTED mode. Start the FC50. Which error occurs?

3.2

Problem:

The FC50 starts, but after the system test announces: Er06 (No voltage supply to FC50).

Solution:

The voltage input of the VC100 must be attached at the output of the FC50. During the system test the FC50 is supplied by the batteries inside the VC100. Afterwards the supply is switched to the voltage converter, which is supplied by the fuel cell. If this connection between output of the FC50 and input of the VC100 is missing, the FC50 loses power and switches off.

Note:

See a detailed explanation of the problem in experiment C.6 "Structure of a network-independent current supply".

Restart the FC50 and wait for the system test to complete. In the VC100 display ‘parasitic load' see the power consumed by the FC50. In the display 'available power' see the power consumed by the attached load. Briefly try out the traffic light TL10 and observe the ‘available power’ display: At switch position ON all lamps shine; at position AUTO, a normal traffic light sequence occurs. In the middle position the device is off.

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Solutions 7

3.3

The basic functions of the fuel cell system

C.1

The electronic load EL200 can be operated in parallel with the traffic light. Gradually increase the load current of the fuel cell using the EL200 potentiometer. Try to reach the maximum EL200 load current. Explain why the FC50 switches off. What has to be considered when restarting?

3.4

4

Problem:

The FC50 automatically turns off and announces Er04 (Load current too high).

Solution:

The load current reached a value of 10.5 A. In order to protect the fuel cell, the system switches off at this value. To restart, set the potentiometer of the EL200 to zero.

Note:

See a detailed explanation of the problem in experiment C.6 "Structure of a network-independent current supply".

When you are through with the system, proceed to shut down and switch off the system as follows: •

Turn the potentiometer of the EL200 to zero, set the toggle switch to OFF and switch off the main switch behind the front panel.

•

Turn the knob for the fan power to AUTO and turn the FC50 main switch OFF.

•

Put the hydrogen supply out of operation correctly.

•

Remove the hydrogen inlet to the FC50 by disconnecting the quick-coupler.

Summary Considering the problems and the associated error messages again, look at the error list in section A.3 Fuel Cell Module FC50. Explain why it is useful to divide the errors into two groups: start-up errors and operating errors. Give at least one example of each group. Start-up errors are recognized by the FC50 during the system test. This group includes errors in the structure, the previous condition or in the start-up sequence. For example the error message Er01 (Hydrogen is missing) appears. The cause of the error is an incorrect installation of the hydrogen supply or an empty hydrogen storage device. To remedy the error activate the hydrogen supply, referring to the appropriate section in Component Descriptions or refill your hydrogen storage. In operating errors, parameters reach certain limit values during operation. For example the error message Er03 (Temperature of the fuel cell stack too high) appears. The reason for this error is a stack temperature exceeding 50 °C. The FC50 will not restart until the stack temperature falls below 45 °C. To remedy the error, increase the fan power to cool the fuel cell stack.

© Heliocentris - Energizing education

Solutions 1

The characteristic curve of a fuel cell

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

I II III

Hydrogen supply (alternates)

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Electronic Load EL200

© Heliocentris - Energizing education

C.2

Solutions 2

The characteristic curve of a fuel cell

C.2

Task: In this experiment we determine the voltage-current characteristic of a fuel cell and plot a power-current diagram. This provides a basic knowledge of the behavior of a fuel cell. The results can be used to size and design fuel cell stacks.

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Connect the AC power pack cable to the 12V= DC power input on the FC50 Fuel Cell. Connect the other end of the AC power pack to a source of AC power. On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.2

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.3

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.4

If you want to use the provided software program to help perform the experiment, make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Solutions 3

2

The characteristic curve of a fuel cell

C.2

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: If you want to use the provided software program to assist with the experiment, start the FC50 software on your PC and select experiment C.2. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on

and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

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Solutions 4

The characteristic curve of a fuel cell

C.2

3

Data acquisition

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Using the potentiometer of the EL200, increase the load current until the Current display on the FC50 shows approximately 5 amperes. To further cause stack temperature to rise, turn the fan control knob on the FC50 so the Fan Power display indicates 10%. After the temperature reaches 40 °C, ensure the load potentiometer is turned back to zero and set fan control knob to AUTO.

3.2

Using the EL200 potentiometer, set in turn each load current listed in the following table. After waiting at least 15 seconds at each point, record the measured values of stack current Istack and stack voltage Vstack in the table. When measuring the first point (no-load operation) turn the toggle switch on the EL200 to OFF to ensure that there is no load on the fuel cell. Nominal current

Measured values

Calculated

Istack (A)

Istack (A)

Vstack (V)

Pstack (W)

0.0

0.00

8.99

0.00

0.2

0.20

8.30

1.66

0.5

0.52

7.92

4.12

1.0

1.00

7.62

7.62

1.5

1.52

7.39

11.23

2.0

2.00

7.17

14.34

3.0

3.01

6.78

20.41

5.0

5.01

6.12

30.66

7.0

7.00

5.71

39.97

10.0

10.00

5.12

51.20

Because of experimental technique and prior condition of the fuel cell, students’ measured values may differ from the example values given here.

3.3

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

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Solutions 5

The characteristic curve of a fuel cell

C.2

4

Data interpretation

4.1

Draw the fuel cell voltage-current relation Vstack = f (Istack) and describe the characteristic curve. Voltage-Current Characteristic 10

Stack Voltage Vstack (V)

9 8 7 6 5 4 3 2 1 0 0

1

2

3

4

5

6

7

8

9

10

Current Istack (A) The characteristic curve of the fuel cell shows an exponential relation between 0 A and 2 A. As the current rises further the relationship between current and voltage becomes linear.

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Solutions 6

4.2

The characteristic curve of a fuel cell

C.2

How do you explain the characteristic curve? This experiment shows that at small (near zero) load currents the voltage falls exponentially with rising current. Here catalytic procedures at the electrodes determine the voltage curve. This exponential process is characteristic of all electro-chemical processes, for example batteries. At middle to large currents the Ohmic internal resistance of the fuel cell determines the characteristic. The voltage depends on the load current in a linear relationship, according to Ohm’s law. Note:

Also draw the fuel cell power-current relation Pstack = f (Istack). Use the calculated electrical power from table 3.2. Then considering the characteristic curve, make a statement about the maximum power of the fuel cell. Power-Current Characteristic 60 50 40 Power Pstack (W)

4.3

To get the entire characteristic curve of the fuel cell including the diffusion part please perform experiment C.3 “Parameters Influencing the Characteristic Curve”.

30 20 10 0 0

1

2

3

4

5

6

7

8

9

10

Current Istack (A) At a current of 10 A the fuel cell produces approximately 50 W. If we extrapolate the characteristic for larger currents, we see that the maximum power of the fuel cell lies outside the examined range. The flattening suggests a maximum of 60 W to 65 W. However with the given equipment, this point cannot be determined experimentally.

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Solutions 7

4.4

The characteristic curve of a fuel cell

C.2

For the power of fuel cell stacks two parameters are significant: the number of cells and the current density (in A/cm2). From the results of your measurement of the stack at a load current of 10 A, determine the voltage and the current density of an individual cell. Note: The active surface of these cells (surface of the electrodes) is 25 cm2. Assuming these values are transferable to larger fuel cells, use your results to specify two fuel cell stacks: •

a 1 kW el rated stack with a working voltage Vstack = 24 V

•

a 5 kW el rated stack with a working voltage Vstack = 42 V

For both stacks give the following values: cell current, number of cells and active cell surface. The experimental fuel cell stack has a voltage of 5 V. As there are 10 cells in the stack, each 2 cell has a voltage of 0.5 V. The current density per cell is 0.4 A/cm at a current of 10 A. With these parameters the two stacks can be specified. Fuel cell stack 1: Pel = 1 kW; Vstack = 24 V To get a nominal voltage of 24 V you will need a stack of 48 cells. The cell current must be 41.67 A to reach a stack power of 1 kW. Using the same current density, an active cell surface 2 of 104 cm is needed. Fuel cell stack 2: Pel = 5 kW; Vstack = 42 V For this stack the following parameters result: 119 A cell current, 84 single cells and 300 cm cell surface.

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2

Solutions 8

4.5

The characteristic curve of a fuel cell

C.2

The power density of a fuel cell (in W/L) is an important characteristic for the capacity of a fuel cell, for example for use in a motor vehicle. Calculate this value for the experimental fuel cell (without fan and end plates) for a power of 50 W. Then compare this value with fuel cells that are used today in automobile prototypes. Here values of 1 to 2 kW/L are being reached. How might the power density of the experimental fuel cell stack be optimized? State some ideas. The power density of the stack can be determined as follows: The volume of the stack, L x H x 3 W without fan and end plates, is Vstack = 6 cm × 7 cm × 8 cm = 336 cm . At 50 W the stack has a power density of 149 W/L. Other state-of-the-art stacks therefore have a power density 10 times higher. The power density of the stack could be improved by the following measures: •

Higher current densities of the electrodes by improved catalysts or optimized reaction guidance, thereby increasing the current density. A doubling of the current density would produce a doubling of the power density.

•

Thinner bipolar plates: The cell thickness of industrial fuel cells can easily be only one third of the thickness of the experimental fuel cell. Thus the power density would be three times greater.

•

Reduction of the inactive cell surface: The entire cell surface of the used fuel cells amounts 2

2

to 7 cm × 8 cm = 56 cm , whereas the active surface is only 5 cm × 5 cm = 25 cm . This corresponds to an inactive cell surface of 55 %. A reduction of the inactive surface with constant external dimensions has a larger cell current and an increase in the power density. •

Further optimization is possible by reducing the volume of the stack end plates.

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Solutions 1

Parameters influencing the characteristic curve

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

I II III

Hydrogen supply (alternates)

External voltmeter

-

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Electronic Load EL200

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C.3

Solutions 2

Parameters influencing the characteristic curve

C.3

Task: In this experiment we investigate the effects of reduced air supply, increased internal resistance, and fuel cell temperature on the characteristic curve of the fuel cell.

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Connect the AC power pack cable to the 12V= DC power input on the FC50 Fuel Cell. Connect the other end of the AC power pack to a source of AC power. On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.2

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.3

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.4

If you want to use the provided software program to help perform the experiment, make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Solutions 3

2

Parameters influencing the characteristic curve

C.3

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: If you want to use the provided software program to assist with the parts of the experiment described in section 3 and 5 (automated support for section 4 is not possible), start the FC50 software on your PC and select experiment C.3. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

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Solutions 4

Parameters influencing the characteristic curve

C.3

3

Effect of the air supply on the characteristic curve of a fuel cell

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Using the potentiometer of the EL200, increase the load current until the Current display on the FC50 shows approximately 5 amperes. To further cause stack temperature to rise, turn the fan control knob on the FC50 so the Fan Power display indicates 10%. After the temperature reaches 40 °C, ensure the load potentiometer is turned back to zero and set fan control knob to AUTO.

3.2

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 15 s at each current setting before copying the measured values of stack current Istack and stack voltage Vstack to the measured value table. For the first series of measurements place the fan setting at AUTO. For the second series, adjust the control so that Fan Power is 6%. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Note: The last measured values of the second series of measurements should be taken quickly, because inadequate cooling will cause the fuel cell temperature to rise. If necessary, you can cool the stack by temporarily removing the load and increasing fan power. If the temperature does rise above 50 °C, for safety the FC50 automatically switches off and will not restart until the temperature falls below 45 °C.

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Solutions 5

Parameters influencing the characteristic curve

Nominal current 1

Measured values, Fan at AUTO

Nominal current 2

C.3

Measured values, Fan at 6%

Istack (A)

Istack (A)

Vstack (V)

Istack (A)

Istack (A)

Vstack (V)

0.0

0.0

9.1

0.0

0.0

9.1

0.2

0.2

8.4

0.2

0.2

8.4

0.5

0.5

8.0

0.5

0.5

8.0

1.0

1.0

7.7

1.0

1.0

7.6

1.5

1.5

7.5

1.5

1.5

7.3

2.0

2.0

7.3

2.0

2.0

7.1

3.0

3.0

6.9

3.0

3.0

6.7

5.0

5.0

6.3

5.0

5.0

6.0

7.0

7.0

5.9

7.0

7.0

5.4

10.0

10.0

5.3

7.4

7.4

5.1

7.6

7.6

4.8

7.8

7.8

4.4

8.0

-

-

8.2

-

-

Because of experimental technique and prior condition of the fuel cell, students’ measured values may differ from the example values given here.

3.3

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

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Solutions 6

3.4

Parameters influencing the characteristic curve

C.3

Use the measured values to draw on the following diagram the voltage-current characteristic Vstack = f( Istack) of the fuel cell for both fan settings. Briefly describe the shape of the resulting characteristic curve. Effect of air supply 10 Fan at AUTO Fan at 6%

8 7 6 5

Range II

3 2 1

Range III

4 Range I

Stack voltage Vstack (V)

9

0 0

1

2

3

4

5

6

7

8

9

10

Stack current Istack (A)

With automatic fan control the characteristic curve of the fuel cell shows an exponential shape at currents between 0 A and 2 A. As the current increases the relationship between current and voltage becomes linear. With reduced air supply (fan power 6%) the shape of the characteristic curve corresponds to the “auto” shape up to approximately 3 A. In the following linear range the voltage drops more. Beyond a stack current of approximately 7 A the cell voltage clearly breaks down. As Vstack falls below 4V a control device automatically switches off the FC50 for the protection of the fuel cell.

3.5

How do you explain the divergence of the reduced-air characteristic curve? On the diagram mark the individual ranges of the reduced-air characteristic. The fundamental function of the fuel cell consists of gaining electrical energy from the exothermic reaction of hydrogen and oxygen. If one of these reactants is insufficient, the reaction is partly or completely restrained, and the stack power falls. Because the load current is being kept constant, it is the stack voltage that falls. At reduced air supply, the oxygen concentration at the cathode drops depending upon load. Up to a stack current of 2 A still no effects are seen. Here in Range I the characteristic has the typical exponential shape, which is due to the catalytic process at the electrodes.

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Solutions 7

Parameters influencing the characteristic curve

C.3

The deviation within the linear range (Range II) of the characteristic is due to the different conditioning of the membrane during the measurements. Because of the fuel cell temperature rising during the measurement with reduced air, the membrane dries up. This results in a lower ionic conductivity and thus increased voltage drop. The influence of the air supply on the characteristic of the fuel cell becomes particularly clear with currents over 7 A (Range III). Due to the high load current, more oxygen is needed at the membrane than can pass through the gas diffusion layer (GDL). The low oxygen concentration in the cathode air reduces the density gradient, that’s why the effect of limited diffusion is already apparent at this load.

3.6

Transfer from 3.2 the measured values for the stack current Istack to the following table and calculate the associated stack power Pstack. Then use the calculated values to draw on the following diagram the characteristic Pstack = f( Istack) of the fuel cell with the two air supplies and briefly describe the shape of the characteristic curve. Fan at ’AUTO’

Fan at ’6%’

Measured value Calculated Measured value Calculated Istack (A)

Pstack (W)

Istack (A)

Pstack (W)

0.0

0.0

0.0

0.0

0.2

1.8

0.2

1.8

0.5

4.3

0.5

4.2

1.0

7.7

1.0

7.6

1.5

11.4

1.5

11.1

2.0

14.5

2.0

14.1

3.0

20.8

3.0

20.2

5.0

31.6

5.0

30.3

7.0

41.2

7.0

37.7

10.0

52.7

7.4

38.0

7.6

36.4

7.8

34.1

-

-

-

-

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Solutions 8

Parameters influencing the characteristic curve

C.3

Effect of air supply on the power curve 60

Stack power Pstack (W)

Fan at AUTO Fan at 6%

50 40 30 20 10 0 0

1

2

3

4

5

6

7

8

9

10

Stack current Istack (A) Both curves are parallel up to a stack current of 3 A. With rising stack current the stack power increases approximately in the same relationship. This results in a nearly linear shape of the characteristic curve. The performance curve of the fuel cell with automatic fan control (AUTO) continues to rise over the entire measuring range. At large currents, a gradual flattening is seen. The characteristic of the fuel cell with reduced air supply only rises up to a stack current of 7.4 A where it reaches a maximum stack power of 38 W. With further increase of stack current the stack power drops sharply.

3.7

What do you observe about the operation of fuel cells from the shape of the performance curve at reduced air supply? To obtain maximum power from the fuel cell with reduced air supply, you must select the appropriate stack current. At too-high current, the stack power drops off sharply.

3.8

Calculate the oxygen flow rate needed at an individual cell and the rate of water formation in order to produce an electric current of 10 A. Use a formula derived from Faraday’s laws for the determination of the substance change. Then determine the theoretically needed volumetric air flow for the entire stack on the assumption that the usable oxygen portion in air is 20 %. Consider the number of cells of the stack. Note: Perform the calculation at standard conditions (0 °C, 1.01325 bar). The molecular standard volume is Vm = 22.4 L/mol; the Faraday constant F = 9.648 × 104 C/mol.

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Solutions 9

Parameters influencing the characteristic curve

C.3

Faraday’s First Law:

m = ECE ⋅ I ⋅ t From the Second Law, the electrochemical equivalent ECE can be written as: M ECE = . z⋅F Equating the two expressions of ECE we have:

m M = . I ⋅t z⋅F Rearranging for the number of moles n:

n=

m I ⋅t = . M z⋅F

The rate of substance change is:

I . z ⋅F For each oxygen molecule four electrons are transferred in the conversion, as seen in the half cell cathode reaction: + O2 + 4 H + 4 e- Å 2 H2O . n& =

4

With I = 10 A and F = 9.648 × 10 C/mol the rate of substance change can be calculated: 10 mol n& O2 = = 2.591 × 10 −5 . 4 s 4 × 9.648 × 10 Using the molecular volume Vm = 22.4 L/mol the oxygen flow rate per cell at standard conditions follows: ml V&O2 = 2.591 ⋅10 − 5 ⋅ (22.4 ) ⋅ (1000 ) ⋅ (60 ) = 34.82 . min As we have a 10-cell stack and air is only 20 % oxygen, the required rate of air flow is: ml  1  V&air = (34.82 ) ⋅ (10 ) ⋅  .  = 1741 min  0.20 

(

3.9

)

The fuel cell stack actually operates with excess air mean and why is it necessary?

= 10. What does “excess air”

Note: Also consider the temperature behavior of the fuel cell at reduced fan power. The excess air gives the relationship between the supplied and the theoretically determined volumetric air flow. = 10 means that the fuel cell is supplied with 10 times as much air as is necessary for the electro-chemical reaction. The theoretically computed volumetric air flow is not enough in practice, because by the chemical reaction the oxygen concentration in air is reduced. Below a certain oxygen concentration sufficient oxygen no longer reaches the membrane, and the reaction is restrained. It is always necessary to provide excess air to ensure sufficient oxygen concentration. Because the available fuel cell stack is air-cooled, the air flow must be calculated on the basis of the heat to be dissipated. The air flow needed for stack cooling is clearly greater than the air flow needed for the electro-chemical reaction.

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Solutions 10

Parameters influencing the characteristic curve

C.3

4

Effect of internal resistance on the characteristic curve of a fuel cell

4.1

In this part of the experiment software support is not possible, because an external voltage measurement is necessary. Connect a suitable voltmeter to measure the terminal voltage Vterminal at the output of the FC50.

4.2

The recommended operating temperature is the same as in the previous part, 40 °C. If the fuel cell has cooled, heat it again as described in 3.1.

4.3

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 15 s at each current setting before copying the measured values of stack current Istack, stack voltage Vstack and terminal voltage Vterminal to the measured value table. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Nominal

Measured values

Istack (A)

Istack (A)

Vstack (V)

Vterminal (V)

0.0

0.00

8.90

8.95

0.2

0.21

8.19

8.25

0.5

0.49

7.94

7.99

1.0

1.00

7.65

7.67

1.5

1.51

7.42

7.42

2.0

2.02

7.22

7.20

3.0

3.00

6.88

6.81

5.0

5.02

6.38

6.23

7.0

6.99

5.89

5.67

10.0

9.95

5.21

4.89

Because of experimental technique and prior condition of the fuel cell, students’ measured values may differ from the example values given here.

4.4

If you are not making further measurements with the system, proceed to shut down and switch off the system as described in 3.3.

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Solutions 11

4.5

Parameters influencing the characteristic curve

C.3

Draw the two voltage-current characteristics Vstack = f(Istack) and Vterminal = f(Istack) and describe the shapes of both characteristic curve.

Effect of internal resistance 10 Stack voltage

9

Terminal voltage

Voltage (V)

8 7 6 5 4 3 2 1 0 0

1

2

3

4 5 6 7 Stack current Istack (A)

8

9

10

Both curves follow the characteristic appearance of a fuel cell V-I curve. Up to approximately 3 A no differences in the characteristic curve are seen. In the following linear range terminal voltage drops in comparison to the stack voltage. The voltage difference increases evenly with increasing stack current.

4.6

Describe the diverging shape of the characteristic curve with the FC50 fuel cell structure and suggest causes for it. The difference between stack and terminal voltage is caused by internal resistances, which arise between stack and connecting terminals. The higher these resistances are the more strongly voltage drops with rising load. For example losses arise in the lines and the current measurement.

4.7

Consider the FC50 as a real power supply and describe the make-up of internal resistance Rint. Divide it into two partial resistances and draw an appropriate schematic diagram. The Ohmic resistances between the fuel cell and the terminals are in series to the internal resistance of the fuel cell stack. If you consider the FC50 as real power supply, these resistances can be summarized as the internal resistance Rint: Rint = Rstack + Raddl

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Solutions 12

Parameters influencing the characteristic curve

C.3

Fuel Cell FC50 Vstack Istack Rstack V0

Raddl

Vterminal 4.8

Determine with the help of the curves in 4.5 the size of the resistances in the diagram of 4.7. Calculate the power losses due to these resistances at a stack current of 10 A. From the gradient of the characteristic curves within their linear range the resistance values can be determined: ∆Vstack 2V Rstack = = = 0.23 Ω ∆Istack 8.8 A

Rint =

∆Vterminal 2.5V = = 0.26 Ω ∆Istack 9.6 A

R addl = R int − R stack = 0.03 Ω The energy dissipation caused by internal resistance is:

Pint = Rint ⋅ (I stack )2 = 26 W .

4.9

To which physical causes can the Ohmic resistance be attributed within the fuel cell stacks? What optimization possibilities exist? The Ohmic resistance of the fuel cell is the result of the resistance of the electron conduction (bipolar plates) and the resistance of the ionic conduction (electrolyte). Also the contact resistances at the material transitions play a crucial role. Optimization possibilities exist in different places: •

Reduction of material thickness so that electrons have less distance to travel;

•

Decrease of the material resistance of the bipolar plates;

•

Improvement of the ionic conductivity electrolytes;

•

Plane surfaces and high assembly pressures to decrease the contact resistances.

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Solutions 13

Parameters influencing the characteristic curve

C.3

5

Effect of the temperature on the characteristic curve of a fuel cell

5.1

In this part of the experiment two series of measurements are taken at different fuel cell temperatures. The recommended temperatures at the beginning of each series are approximately 28 °C and 44 °C. During the experiment temperatures will unavoidably drift. In order to keep the deviations small, currents and voltages should be measured and recorded as quickly as possible.

5.2

If you want to use the provided software program to assist with this part of the experiment, you must now switch off the FC50 and start the FC50 software on your PC. Select the appropriate experiment and wait until the program requests you to press the FC50 START button.

5.3

It is recommended to take first the series of measurements at the lower temperature. If the temperature is already too high, you can use the fan to lower it. Cool the fuel cell as quickly as possible to avoid drying the membranes. After reaching the desired operating temperature, reset the fan control to AUTO. To reach the fuel cell temperature of the second series of measurements load the fuel cell for a few minutes with a current of approximately 7 A. Using the potentiometer of the EL200, increase the load current until the Current display on the FC50 shows approximately 7 amperes. To further cause stack temperature to rise, turn the fan control knob on the FC50 so the Fan Power display indicates 12%. After the temperature reaches 44 °C, ensure the load potentiometer is turned back to zero and set fan control knob to AUTO.

5.4

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 15 s at each current setting before copying the measured values of stack current Istack and stack voltage Vstack to the measured value table. Begin the first series of measurements at a stack temperature of approx. 28 °C, the second series of measurements at approx. 44 °C. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Note: The last measured values of the first series of measurements should be taken quickly, because high current will cause the fuel cell temperature to rise. If necessary, you can cool the stack by temporarily removing the load and increasing fan power.

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Solutions 14

Parameters influencing the characteristic curve

Nominal

C.3

Measured values Tstack = 28 °C

Tstack = 44 °C

Istack (A)

Istack (A)

Vstack (V)

Istack (A)

Vstack (V)

0.00

0.00

9.20

0.00

9.20

0.20

0.19

8.57

0.19

8.65

0.50

0.49

8.11

0.50

8.24

1.00

1.01

7.72

1.01

7.93

1.50

1.49

7.48

1.49

7.73

2.00

2.00

7.25

1.99

7.56

3.00

3.01

6.89

3.01

7.21

5.00

5.02

6.37

5.02

6.62

7.00

7.03

5.92

6.99

6.27

10.00

9.99

5.37

9.99

5.60

Because of experimental technique and prior condition of the fuel cell, students’ measured values may differ from the example values given here.

5.5

If you are not making further measurements with the system, proceed to shut down and switch off the system as described in 3.3.

5.6

Draw the voltage-current characteristic curve for each operating temperature and describe the shape of the curve.

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Solutions 15

Parameters influencing the characteristic curve

C.3

Effect of stack temperature 10 28°C

9

44°C

Stack voltage Vstack (V)

8 7 6 5 4 3 2 1 0 0

1

2

3 4 5 6 Stack current Istack (A)

7

8

9

10

The typical voltage-current characteristic curve of a fuel cell is recognizable for both temperatures. But the characteristic of the high temperature measurement flattens more strongly already within the range of the catalysis influence. Within the linear range (Ohmic resistance) the characteristics are approximately parallel, but a gradual convergence occurs at Istack greater than 7 A.

5.7

Explain the described characteristic curves considering the electrochemical reaction occurring here and the electrical conductivity. The chemical reaction occurring in the fuel cell is subject to a catalytic process. Catalytic processes are always accelerated by high temperatures, whereby also the total reaction can occur faster. In the case of the fuel cell it means more electrons are available, resulting in a higher stack current. Similarly you get a higher stack voltage at the same current. This effect can also be seen if you regard to the function which describes the characteristic -1/T within this range. The function has the form e , where T represents the process temperature. From the minus sign in the exponent it is evident that with rising T the entire term grows, thus with rising temperature the voltage increases. The convergence of both characteristics at large load can be explained by the ionic conduction of the membrane and the electron conduction of the bipolar plates. With rising fuel cell temperature the reaction water can evaporate more easily, whereby the membrane dries up more and more. Because the protons can be conducted only through wet membranes, the ionic conductivity decreases. That is, less charge carrier can be transported by the membrane, and the Ohmic resistance increases. Another reason for the convergence is the increasing resistance of the bipolar plates with rising temperature.

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Solutions 16

Parameters influencing the characteristic curve

C.3

This effect can be seen only at large loads, because the voltage drop due to resistance increases proportional to the current.

5.8

Draw conclusions about the optimum operating temperature. At too-low temperatures the catalytic process is restrained; at too-high temperatures the resistance increases, particularly from drying of the membranes. However the optimum temperature depends on further factors, e.g. on the air flow and on the load current. Therefore the intended application of the fuel cell also affects its optimum temperature.

5.9

By which measure can the optimal operating temperature be increased? Draw on your conclusions in 5.7 and consider whether the effect is applicable in every case. At too-high temperatures drying of the membrane has a negative effect on the operation of the fuel cell. Humidifying the air which supplies oxygen and cooling can prevent this. The humidification of air would need to be done by an upstream air moisturizer, requiring additional energy. Therefore this measure is only useful for high-power stacks.

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Solutions 1

Determination of the hydrogen current curve

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

Hydrogen supply (alternates)

I II III

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Electronic Load EL200

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C.4

Solutions 2

Determination of the hydrogen current curve

C.4

Task: In this experiment we determine the relationship between the hydrogen flow rate and electrical current, and how this is expressed in Faraday’s first law.

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Connect the AC power pack cable to the 12V= DC power input on the FC50 Fuel Cell. Connect the other end of the AC power pack to a source of AC power. On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.2

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.3

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.4

If you want to use the provided software program to help perform the experiment, make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Solutions 3

2

Determination of the hydrogen current curve

C.4

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: If you want to use the provided software program to assist with the experiment, start the FC50 software on your PC and select experiment C.4. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

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Solutions 4

Determination of the hydrogen current curve

C.4

3

Determination of the hydrogen-current relation

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Using the potentiometer of the EL200, increase the load current until the Current display on the FC50 shows approximately 5 amperes. To further cause stack temperature to rise, turn the fan control knob on the FC50 so the Fan Power display indicates 10%. After the temperature reaches 40 °C, ensure the load potentiometer is turned back to zero and set fan control knob to AUTO. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system.

3.2

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 60 s at each current setting before copying the measured values of stack current Istack and hydrogen flow rate V&H 2 to the measured value table. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Note: For reaching even hydrogen concentration at all membranes it is necessary to purge the hydrogen channels of the fuel cell. This takes place automatically and for a brief time visibly increases the hydrogen flow rate. If a purging occurs during the measurement, you should restart the 60 s waiting period for that operating point. The previously measured values are still valid.

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Solutions 5

Determination of the hydrogen current curve

Nominal

C.4

Measured values

Istack (A)

Istack (A)

V&H 2 (ml/min)

0.0

0.00

10

1.0

1.00

80

2.0

1.99

145

3.0

3.01

215

4.0

4.02

285

5.0

5.01

350

6.0

6.01

420

7.0

7.00

490

8.0

8.00

560

9.0

8.99

629

10.0

10.01

700

Because of experimental technique and prior condition of the fuel cell, students’ measured values may differ from the example values given here.

3.3

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

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Solutions 6

3.4

Determination of the hydrogen current curve

C.4

Plot the measured hydrogen consumption as a function of current in a diagram: ) V&H 2 = f (I VWDFN

Hydrogen - current curve Rate of hydrogen flow VolH2 (ml/min)

800 700 600 500 400 300 200 100 0 0

3.5

1

2

3 4 5 6 Stack current Istack (A)

7

8

9

10

Describe and explain the characteristic curve, using the First Faraday Law. Then explain the observed behavior in no-load operation (I = 0 A). VWDFN

From Faraday’s First Law, the rate of hydrogen flow is directly proportional to the current: ~I V& H2

That is, with rising current the hydrogen requirement of the fuel cell increases in the same proportion. The linear process of the measured curve shows this relation. We observe however that a small hydrogen flow occurs even in the no-load operation. Since no electric current is produced in the fuel cell, no hydrogen is converted in the chemical reaction. The hydrogen must escape in other ways. Because of the pressure difference between the hydrogen and oxygen sides, hydrogen molecules are pressed through the membrane. In addition microscopic leakages occur because of the way the cells are interconnected and through the screw connections in the gas supply. The resulting hydrogen flow is called leakage rate.

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Solutions 7

3.6

Determination of the hydrogen current curve

C.4

When specifying fuel cell systems it is important to know the current-dependent hydrogen flow rate of a stack. This indicates how much hydrogen the stack needs to supply a given current. Determine this value from the diagram in 3.4 neglecting the leakage rate. Then with the help of Faraday’s laws calculate the theoretical value and compare it to the observed value. Note: The displayed values of hydrogen flow rate have been converted to the equivalent ml/min at standard conditions (0 °C, 1.01325 bar). Calculate the theoretical value of the hydrogen flow rate at standard conditions. The molecular standard volume is Vm = 22.4 L/mol; the Faraday constant F = 9.648 × 104 C/mol. The current-dependent hydrogen flow in the stack corresponds to the upward slope of the characteristic curve.

ml 500 ∆V&H 2 min = 69.4 ml . = 7.2 A A ⋅ min ∆I To calculate the theoretical value use the First Faraday Law: m = ECE ⋅ I ⋅ t From the Second Law, the electrochemical equivalent ECE can be written as: M ECE = . z ⋅F With the amount of material n: m n= M the material flow n& becomes: I n& = . z⋅F Using the molecular standard volume Vm the required flow rate can be determined. Rearranging for the flow rate per unit current yields the following equation. The currentdependent flow rate is: V&H 2 a ⋅ Vm = . I z ⋅F With the number of cells per stack a = 10 and the number of electrons for each converted molecule z = 2 (from the cathode reaction) for theoretical value can be calculated: L   10×  22.4 V&H 2 L ml mol   = = 1.16×10-3 = 69.65 . C  I As A min  2×  9.648×104 mol   The theoretically calculated and the experimentally determined value agree very closely. Small deviations can arise from measurement inaccuracies.

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Solutions 8

3.7

Determination of the hydrogen current curve

C.4

The current-dependent hydrogen flow rate determined in 3.6 is valid only for this stack. Express the hydrogen flow rate as a function of the number of cells a of a fuel cell stack and develop a general formula for the required hydrogen volume of a stack related to current, number of cells and time. Use this formula to calculate how much hydrogen is needed to draw 30 A from a 25cell stack for 8 hours. What is the required hydrogen flow rate? From the rearranged formula in 3.6:

VH 2 V ml = m ≈7 . I ⋅a ⋅t z ⋅F A cell min That is, 7 ml hydrogen are required to draw one ampere from a cell for one minute. Therefore for a current of 30 A from 25 cells for 8 hours the hydrogen volume required: ml VH 2 = 7 × 30 A × 25 cells × 8 h = 2.52 m3 . A cell min The computation for the hydrogen flow rate can be deduced from the same formula: V ml L × 30 A × 25 cells = 5.25 . V&H 2 = H 2 = 7 A cell min min t

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Solutions 1

Efficiency of the fuel cell stack

C.5

Required devices: Description Hydrogen supply (alternates)

I II III

Item 630 642 652

Fuel cell FC50

610

Electronic load EL200

620

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Electronic Load EL200

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Solutions 2

Efficiency of the fuel cell stack

C.5

Task: In this experiment we determine the efficiency of the fuel cell stack. By analyzing the power efficiency characteristic you will gain important knowledge about sizing a fuel cell. Two additional methods are used to measure efficiency in different ways: •

Stack efficiency as determined from voltage and current efficiency;

•

Efficiency calculation using the free reaction enthalpy, lower heat value (LHV) or higher heat value (HHV).

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Connect the AC power pack cable to the 12V= DC power input on the FC50 Fuel Cell. Connect the other end of the AC power pack to a source of AC power. On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.2

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.3

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.4

If you want to use the provided software program to help perform the experiment, make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Solutions 3

2

Efficiency of the fuel cell stack

C.5

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: If you want to use the provided software program to assist with the experiment, start the FC50 software on your PC and select experiment C.5. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

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Solutions 4

Efficiency of the fuel cell stack

C.5

3

Data acquisition

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Using the potentiometer of the EL200, increase the load current until the Current display on the FC50 shows approximately 5 amperes. To further cause stack temperature to rise, turn the fan control knob on the FC50 so the Fan Power display indicates 10%. After the temperature reaches 40 °C, ensure the load potentiometer is turned back to zero and set fan control knob to AUTO.

3.2

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 60 s at each current setting before copying the measured values of stack current Istack, stack voltage Vstack and hydrogen flow V&H 2 to the measured value table. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Note: For reaching even hydrogen concentration at all membranes it is necessary to purge the hydrogen channels of the fuel cell. This takes place automatically and for a brief time visibly increases the hydrogen flow rate. If a purging occurs during the measurement, you should restart the 60 s waiting period for that operating point. The previously measured values are still valid.

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Solutions 5

Efficiency of the fuel cell stack

Nominal

C.5

Measured values

Istack (A)

Istack (A)

Vstack (V)

V&H 2  (ml/min)

0.0

0.00

9.05

14

0.2

0.20

8.31

25

0.5

0.52

7.94

45

1.0

1.00

7.51

79

1.5

1.51

7.21

110

2.0

1.99

6.96

145

3.0

3.01

6.51

215

5.0

5.01

6.02

350

7.0

7.00

5.63

490

10.0

10.00

5.12

698

Because of experimental technique and prior condition of the fuel cell, students’ measured values may differ from the example values given here.

3.3

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

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Solutions 6

Efficiency of the fuel cell stack

4

Determination of the stack efficiency of the fuel cell

4.1

Determine the stack efficiency stack of this fuel cell by power balance (the ratio of delivered power to the power used).

C.5

Perform an example calculation for a selected measuring point (other than the no-load operation point) and then calculate all values for the table. Also note the delivered stack power Pstack in the table. Note: The displayed values of hydrogen flow rate have been converted to the equivalent ml/min at standard conditions (0 °C, 1.01325 bar). The heat value of hydrogen at standard conditions is LHV = 10.8 MJ/m3. Example calculation at the second measurement point (Istack = 0.2 A):

ηstack =

ηstack =

Pout Vstack ⋅ Istack = Pin LHV ⋅ V&H 2

8.31 V × 0.2 A = 0.37 MJ ml 10.8 3 × 25 min m

Measured value Istack (A)

Calculation stack

Pstack (W)

0.00

0.00

0.00

0.20

0.37

1.66

0.52

0.51

4.13

1.00

0.53

7.51

1.51

0.55

10.89

1.99

0.53

13.85

3.01

0.51

19.60

5.01

0.48

30.16

7.00

0.45

39.41

10.00

0.41

51.20

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Solutions 7

4.2

Efficiency of the fuel cell stack

C.5

Transfer the calculated data from the table into the following diagram and draw the graphs of the functions stack = f(Istack) and Pstack = f(Istack) Briefly describe the shape of both characteristics.

60

1,0

50

0,8

40

0,6

30

0,4

20

0,2

10 stack eta_E PPstack 0 9 10

Efficiency

1,2

0,0 0

1

2

3

4 5 6 7 Stack current Istack (A)

8

Power Pstack (W)

Efficiency-Power comparison

The power Pstack delivered by the stack rises over the entire range while the stack efficiency stack is greatest at low currents.

4.3

What important principles for the optimum design of fuel cells can be learned from these characteristic curves of power and efficiency? Consider for each principle a possible area of application, and an example of use. The optimum efficiency of a fuel cell occurs in the low-load range. However the optimum delivered power occurs in the high or maximum current range. Therefore depending on the application you have to choose whether the fuel cell will operate with maximum efficiency or with maximum power. With optimum efficiency the supplied fuel is optimally converted into electricity, however the fuel cell has a higher maximum power than may be used. Consequently larger weight and volume result, and greater cost. Such efficiency concerns are meaningful only for stationary applications, for which weight and size are not relevant and which operate for a long time with constant load, e.g. energy production in a power station. However if a fuel cell works in the power optimum, a clear reduction in weight, volume and purchase price can be achieved despite poorer fuel utilization. This mode of operation is particularly interesting for mobile applications, since the fuel cell must itself be transported, e.g. for applications in the automobile industry.

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Solutions 8

Efficiency of the fuel cell stack

C.5

5

Determination of the stack efficiency from current and voltage efficiency

5.1

Determine the voltage efficiency V of the fuel cell from the measured values of 3.2. Perform the calculation with the reversible thermodynamic voltage related to the lower heat value (LHV) of hydrogen. Also determine the current efficiency I and then calculate the stack efficiency stack from both. Perform an example calculation for a selected measuring point (other than the no-load operation point) and then calculate all values for the table. Note: The values of the hydrogen flow rate are converted to standard conditions (0 °C, 1.01325 bar). The reversible thermodynamic voltage related to the lower heat value LHV of hydrogen is Vrev LHV = 1.254 V, the Faraday constant F = 9.648 x 104 C/mol and the molecular standard volume Vm = 22.4 L/mol. Example calculation at the second measuring point (Istack = 0.2 A): The voltage efficiency is the relationship of cell voltage to the reference voltage:

ηV =

Vstack . a ⋅ Vrev LHV

With the number of cells in the stack a = 10 it follows: 8.31 V ηV = = 0.66 . 10 × 1.254 V The current efficiency is equal to the relationship of stack current to theoretically possible current: I ηI = stack . I th The theoretically possible current computes as follows: V& ⋅ F ⋅ z I th = . a ⋅ Vm With the number of electrons per molecule conversion in the reaction z = 2 and the number of cells in the stack a = 10 the current efficiency is calculated: l 0.2 A × 10 × 22.4 mol ηI = = 0.56 . ml C 25 × 9.648 × 104 ×2 min mol As the stack efficiency is the product of voltage and current efficiency: stack  V‡ I for the selected measuring point it is therefore: stack = 0.66 × 0.56 = 0.37.

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Solutions 9

Efficiency of the fuel cell stack

Measured value

Computation

Istack (A)

V

I

stack

0.00

0.72

0.00

0.00

0.20

0.66

0.56

0.37

0.52

0.63

0.81

0.51

1.00

0.60

0.88

0.53

1.51

0.57

0.96

0.55

1.99

0.56

0.96

0.53

3.01

0.52

0.98

0.51

5.01

0.48

1.00

0.48

7.00

0.45

1.00

0.45

10.00

0.41

1.00

0.41

Transfer the calculated data from the table into the following diagram and draw the graphs of the functions V f(Istack), I = f(Istack) and stack = f(Istack) Briefly describe the characteristic curves and the mutual influence of the graphs on one another. Note: Consider and compare the characteristic processes particularly for small and large currents.

Efficiencies of the fuel cell 1,2 1,0 Efficiency

5.2

C.5

0,8 0,6 0,4 I eta_I

0,2

V eta_U stack eta_E

0,0 0

1

2

3

4 5 6 7 Stack current Istack (A)

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8

9

10

Solutions 10

Efficiency of the fuel cell stack

C.5

The current efficiency rises steeply from the zero point, quickly approaching the limit value of 1. The voltage efficiency has a constantly falling trend, which however flattens with increasing current. Since the stack efficiency is the product of the two other graphs, it behaves for small currents similar to the current efficiency, since the lower limit value of zero is the determining factor. For large currents the stack efficiency is determined by the voltage efficiency. As a result of the initially rising then falling process, the stack efficiency has a maximum point where the fuel cell optimally converts the supplied fuel into electricity.

5.3

What determines the current efficiency and which losses decrease it? Why is the efficiency for large currents nearly 1? The current efficiency measures fuel utilization. It indicates how much of the consumed hydrogen is electro-chemically converted. Losses which affect the current efficiency do not occur in the chemical (main) reaction, but rather in chemical side reactions and leakages (membrane, screw connections). These losses decrease with rising current and their affect on the amount of hydrogen used electro-chemically are negligible. Thus at large currents the efficiency is nearly 1.

5.4

Now consider the voltage efficiency more exactly. What does it affect and which losses decrease it? Why isn’t it 1 also in the no-load operation? The voltage efficiency is a measure of the efficiency of the electro-chemical (main) process. It specifies the quality of conversion from internal energy of the participating molecules into electricity. Losses that affect the voltage efficiency are: •

Catalysis losses at the cathode;

•

Losses due to limited diffusion of gases to the electrodes;

•

Losses due to hydrogen passage through the membrane (decrease of the electro-chemical potential between anode and cathode);

•

Ohmic losses of the electrolyte, the bipolar plates and at the material interfaces (gas diffusion layer).

In the no-load operation the losses are caused by hydrogen passage through the membrane to the cathode. The hydrogen leads to a mixing potential at the cathode and thus to the lowering of the electro-chemical potential between the electrodes. Therefore the theoretical reference voltage cannot be achieved, and efficiency losses result at no-load operation.

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Solutions 11

Efficiency of the fuel cell stack

6

Thermodynamic view of the reference voltage

6.1

For the determination of the voltage efficiency a reference voltage is necessary.

C.5

What different ways are there to calculate this reference voltage and how might they be used? If you consider the process of the electro-chemical transformation from hydrogen and oxygen to water, you can calculate the reversible thermodynamic voltage (also reversible terminal voltage or theoretical equilibrium voltage) with the help of the free reaction enthalpy. From it a reference 0 voltage of Vrev =1.23 V results. However if you compare the fuel cell with internal combustion engines, you can use the energy liberated by the combustion for the calculation of the reversible thermodynamic voltage. Depending upon the structure of the comparison system the lower heat value LHV (Vrev LHV = 1.254 V) or the higher heat value HHV (Vrev HHV = 1.482 V) of hydrogen is used.

6.2

Briefly describe the theoretical determination of the reference voltages sought in 6.1. Use the thermodynamic terms "formation enthalpy", "reaction enthalpy", "reaction entropy" and "free reaction enthalpy". The determination of the reversible thermodynamic voltages related to the heat of combustion R Vrev LHV and Vrev HHV is based on the understanding that the entire reaction enthalpy H of the formation reaction from water (related to the first law of thermodynamics) is available as usable energy. The reaction enthalpy is calculated thereby as the difference of the formation enthalpies H if of the reaction products (water) and the formation enthalpies H if of the basic materials (hydrogen, oxygen). Whether the lower heat value LHV or the higher heat value HHV is used in this calculation depends on the state of aggregation of the water after the reaction: If the water is present after the reaction as a vapor, it still contains the energy of condensation. Since this energy in the "exhaust gas" is released from the system and is not used, the Lower Heat Value must be used for the calculation. If the product water is present as liquid however, the energy of condensation is available to the system. So the usable energy is greater. In this case the higher heat value must be used in calculations. By the second law of thermodynamics the reaction enthalpy can never be completely converted R into usable energy. Reducing the reaction enthalpy by the reaction entropy S, one receives R the technically usable energy, the free reaction enthalpy (Gibbs energy) G. Reaction entropy rev means that entropy which is transported by the heat of reaction Qm .

6.3

Calculate the voltage efficiencies based on the reference voltages in 6.1. Use them with selected measured values from 3.2. Discuss the results and interpret the meaning. Which calculation is most meaningful, in order to determine the electrical efficiency of the fuel cell compared with a conventional power station? Note: If you don’t know the reference voltages mentioned in 6.1, you can use the values V1 = 1.23 V, V2 = 1.254 V and V3 = 1.482 V.

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Solutions 12

Efficiency of the fuel cell stack

C.5

Calculation of the voltage efficiency using the reversible thermodynamic voltage related to the 0 free reaction enthalpy Vrev :

ηV =

Vstack 0 a ⋅ Vrev

.

0 With the number of cells of the stack a = 10 and Vrev = 1.23 V the voltage efficiency is:

8.31 V = 0.68 . 10 × 1.23 V Using the reversible thermodynamic voltage related to the lower heat value Vrev LHV the voltage efficiency is: Vstack 8.31 V ηV = = = 0.66 . a ⋅ Vrev LHV 10 × 1.254 V

ηV =

Selecting the higher heat value as basis for the reversible thermodynamic voltage the voltage efficiency is: Vstack 8.31 V ηV = = = 0.56 . a ⋅ Vrev HHV 10 × 1.482 V Depending upon the reference voltage, different voltage efficiencies result. Since the reference voltage is in the denominator, the efficiency is inversely proportional to the reference voltage. It is therefore important to refer the measured voltage to the correct reference voltage. The selected reference voltage should always be indicated, as otherwise substantial errors can develop when using the voltage efficiency. When considering a fuel cell used in a co-generation plant, the efficiency must be calculated with one of the heat values. Whether the lower heat value or the higher heat value should be used depends on the processing in the co-generation plant: if the condensation heat of the water contained in the exhaust gas is utilized, use the higher heat value; otherwise use the lower heat value.

6.4

In step 5.4 the different losses which affect the voltage efficiency should be listed. Even neglecting all losses which directly affect the characteristic, the voltage efficiency does not become 1.0. Which additional deviation from the theoretical occurs in this system? Note: Consider which thermal boundary conditions affect the formation enthalpy of the materials. The formation enthalpy of a material is always given with the assumption that the reaction product has the same temperature as the input material. Because of the increased temperature of the membrane compared to the environment, the reaction product of the fuel cell (water) is delivered at a higher temperature than the reactants (oxygen and hydrogen). One part of the energy is thus transferred to the environment in the form of heat in the water and thus cannot be converted into electricity. These losses are not considered in the reference voltage and thus reduce the voltage efficiency.

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Solutions 1

Set-up of a fuel cell power supply

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

Voltage converter VC100

621

Traffic light TL10

622

Hydrogen supply (alternates)

I II III

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Traffic Light TL10

Voltage Converter VC100

Electronic Load EL200

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C.6

Solutions 2

Set-up of a fuel cell power supply

C.6

Task: In this experiment a grid-independent power supply is assembled and examined. We examine the parasitic load and the available power of the entire system as a function of the stack current.

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Power to operate the FC50 Fuel Cell module will be provided by the VC100 Voltage Converter. Use the provided 3-pin cable to connect the Parasitic Load output on the VC100 Voltage Converter to the 12V= DC power input on the FC50 Fuel Cell.

1.2

On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.3

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.4

Use two test leads to additionally connect the FC50 with the input of the VC100, paying attention to the polarity.

1.5

Use two medium test leads to connect Available Power on the VC100 with the TL10 traffic light, paying attention to the polarity. Place the toggle switch on the front panel of the TL10 in its middle position.

1.6

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.7

If you want to use the provided software program to help perform the experiment, make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Solutions 3

2

Set-up of a fuel cell power supply

C.6

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: If you want to use the provided software program to assist with the experiment, start the FC50 software on your PC and select experiment C.6. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

2.5

Voltage converter VC100: The module starts automatically. When voltage is applied at the VC100 input, a constant 12 V appears at the Available Power output. During start-up, when no voltage is applied at its input, the internal battery temporarily provides 12 V at the Parasitic Load output.

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Solutions 4

Set-up of a fuel cell power supply

C.6

3

Grid-independent fuel cell system for traffic light supply

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Using the potentiometer of the EL200, increase the load current until the Current display on the FC50 shows approximately 5 amperes. To further cause stack temperature to rise, turn the fan control knob on the FC50 so the Fan Power display indicates 10%. After the temperature reaches 40 °C, ensure the load potentiometer is turned back to zero and set fan control knob to AUTO.

3.2

For this part of the test leave the TL10 traffic light switch in its middle position, so it consumes no power. Then record the displayed FC50 and VC100 values in the following table.

Size

Measured value

Parasitic load Pself

5.20 W

Stack voltage Vstack

7.6 V

Stack current Istack

1.03 A

Because of experimental technique and prior condition of the fuel cell, students’ measured values may differ from the example values given here.

3.3

Although no power is taken from the Available Power output of the VC100, the fuel cell is producing a current (see Current display on the FC50). Where is this power being used? Mention at least two consumers. Since the fuel cell system is operating as grid-independent, power is needed to operate the auxiliary devices of the fuel cell. Thus the fuel cell, in addition to its Available Power output, must always supply a basic load. The basic load is divided among different consumers. These include the control board, solenoid valve, fans, displays and lights and various losses (including voltage converter, cables, etc.)

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Solutions 5

3.4

Set-up of a fuel cell power supply

C.6

Compare the parasitic load PSelf indicated by the VC100 with the stack power Pstack = Vstack · Istack, which is being generated by the fuel cell. Explain the difference of these values. What is the actual power consumed by the entire system? The fuel cell stack has to supply the system with a power of Pstack = 7.6V × 1.03A = 7.8W. But the VC100 indicates PSelf = 5.2 W only. A cause for this difference is the position of the measuring instrument in the circuit. The VC100 measures only the power used by the FC50.. Since however between the stack and the internal requirement measurement of the VC100 consumers and/or losses already occur, the two powers differ. Before the internal requirement measurement, losses already occur during the voltage conversion, during the current measurement in the FC50 and in the cables. The control board of the VC100 and its displays are further consumers. Since these losses and consumers are also part of the fuel cell system, the actual internal requirement of the system is equal to the stack power determined above.

3.5

In the following part the internal requirement Pself of the FC50, and the available power Pusable of the traffic light are measured during the different traffic light phases. Switch the toggle switch on the front panel of the TL10 to AUTO (lower position). Record the displayed values of the VC100 in the following table of measured values. Note: Because of the short duration of traffic light phases, it may be necessary to repeat some of the measurements. Measured values Traffic light phase Pself (W)

Pusable (W)

Green

5.25

0.90

Yellow

5.39

4.00

Red

5.26

3.00

Red-yellow

5.40

7.10

Because of experimental technique and prior condition of the fuel cell, students’ measured values may differ from the example values given here.

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Solutions 6

3.6

3.7

Set-up of a fuel cell power supply

C.6

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

Compare the internal requirement Pself with the available power Pusable for each phase of the light and describe the differences between phases. The available power Pusable varies depending upon traffic light phase. That is, for each traffic light color the traffic light module presents a different load. The internal requirement changes little, indicating that the FC50 has a number of consumers which are load-independent. If we compare the powers of the individual traffic light phases, we see that the ratio of available power to internal requirement varies widely. For example, in the "green" phase the internal power consumption is nearly six times as high as the power to the light. In the "red-yellow" phase however the internal consumption is smaller than the power to the light.

3.8

At which measuring point does the fuel cell system work most efficiently and what conclusions can you draw from this? Justify your statements and refer if necessary to questions already answered. The fuel cell system works at the traffic light phase "red-yellow" most efficiently, since the used power in relation to the internal requirement is highest here. In 3.3 we determined that a basic system load is always present, independent of the available power. Therefore it is impractical to load a fuel cell system lightly (at low power) particularly if this load is less than the basic system load.

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Solutions 7

Set-up of a fuel cell power supply

C.6

4

Determination of the parasitic load characteristic of a fuel cell system

4.1

For the determination of the parasitic load characteristic, the traffic light module is not needed. Set the toggle switch on the front panel of the TL10 to its middle position (OFF) and remove the test leads between the VC100 and TL10.

4.2

If you want to use the provided software program to assist with this part of the experiment, you must now switch off the FC50 and start the FC50 software on your PC. Select the appropriate experiment and wait until the program requests you to press the FC50 START button.

4.3

The recommended operating temperature is the same as in the previous part, 40 °C. If the fuel cell has cooled, heat it again as described in 3.1.

4.4

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 15 s at each current setting before copying the measured values of stack current Istack stack voltage Vstack, internal requirement Pself and power of the electronic load Pload into the measured value table. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Note: Although you are adjusting the load current of the EL200, make sure that the preset values and displayed values you record are actually the FC50 stack current Istack. Also be aware of the automatic safety disconnect at stack currents > 10.5 A. Nominal

Measured values

calculated

Istack (A)

Istack (A)

Vstack (V)

Pself (W)

Pload (W)

Pstack (W)

min

0.99

7.75

5.20

0.00

7.67

2

2.06

7.22

5.32

6.60

14.87

3

3.01

6.85

5.34

12.40

20.62

4

3.96

6.51

5.40

17.10

25.78

5

5.04

6.14

5.51

21.50

30.95

6

6.07

5.95

5.60

25.80

36.12

7

7.05

5.72

5.73

28.90

40.33

8

7.98

5.53

5.91

31.90

44.13

9

8.95

5.34

6.11

33.90

47.79

10

10.00

5.18

6.39

36.40

51.80

Because of experimental technique and prior condition of the fuel cell, students’ measured values may differ from the example values given here.

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Solutions 8

Set-up of a fuel cell power supply

C.6

4.5

If you are not making further measurements with the system, proceed to shut down and switch off the system as described in 3.3.

4.6

Transfer the function Pself = f(Istack) onto the diagram. Transfer in addition the appropriate measured values from the table in 4.4 to the following diagram and describe briefly the behavior of the characteristic.

Internal power requirement of the fuel cell system 8

Power Pself (W)

7

6

5

4 0

1

2

3

4

5

6

7

8

9

10

Stack current Istack (A) The characteristic of the internal requirement of the fuel cell system as a function of stack current smaller than 1 A is not defined. It rises continuously over the considered range, having an upward gradient with increasing current.

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Solutions 9

4.7

Set-up of a fuel cell power supply

C.6

The internal requirement of the fuel cell system can be attributed to different peripheral devices (see 3.3). These internal consumers can be divided into two groups. Identify and describe this division on the basis the characteristic curve as described in 4.6 and identify at least one consumer in each group. The internal requirement of the fuel cell can be divided into a fixed and a variable portion. The fixed portion corresponds to the basic load, thus the part of the internal requirement which must be always supplied. When no available power is delivered, this portion, is measurable. In this fuel cell system the fixed portion of the internal requirement is 5.2 W which includes the control board, solenoid valve and displays. The cooling fans are responsible for the variable portion of the internal requirement. The greater the stack current, the more air is needed for the electro-chemical reaction and for the cooling of the stack. Because the air is provided by the cooling fans, the power to the fans increases with increasing load current.

Compute the stack powers Pstack in the table in 4.4. Transfer onto the diagram values from the table in 4.4 showing the difference between usable power and the calculated power produced at the stack. Draw the characteristics Pstack = f(Istack) and Pload = f(Istack). Note: The available power corresponds to the EL200 load Pload.

Stack power – Usable power comparison 60 50 Power P (W)

4.8

40 30 20 10

Usable power Stack power

0 0

1

2

3

4 5 6 7 Stack current Istack (A)

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8

9

10

Solutions 10

4.9

Set-up of a fuel cell power supply

C.6

Describe and explain the process of the characteristics in diagram 4.8. Consider the two characteristics with the internal requirement characteristic in diagram 4.6 and explain the observed deviations. Both characteristics in diagram 4.8 have a positive upward gradient, i.e. with increasing stack current the power also increases. The difference between the characteristics corresponds to the power used within the system. Since power is always used, to operate the peripheral devices the stack power curve always lies above the available power curve. The difference corresponds to the power consumption of the fuel cell system determined in 4.6. Since the internal requirement with rising current increases, the curves in 4.8 diverge. If one computes the difference between stack power and available power, this deviates from the measured internal requirement. The reasons are already described in 3.4: losses and consumers between the stack current/voltage measurement and the internal requirement measurement. In addition even greater losses occur during voltage conversion in the VC100.

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Solutions 11

Set-up of a fuel cell power supply

C.6

5

Determination of the losses of the potential transformer

5.1

In this part of the experiment the losses which arise during the DC voltage transformation in the VC100 are determined. The EL200 must be attached to the Available Power output of the VC100. Switch the FC50 and EL200 off before you change these connections. Make sure that the potentiometer of the EL200 is set to zero.

5.2

The recommended operating temperature is the same as in the previous part, 40 °C. If the fuel cell has cooled, heat it again as described in 3.1.

5.3

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 15 s at each current setting before copying the measured values of stack current Istack, and power of the electronic load Pload to the measured value table. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Carefully increase the stack current Istack greater than 8 A and note the behavior of the system. Note: Although you are adjusting the load current of the EL200, make sure that the preset values and displayed values you record are actually the FC50 stack current Istack. Also be aware of the automatic safety disconnect at stack currents > 10.5 A. Nominal

Measured values

Istack (A)

Istack (A)

Pload (W)

min

1.00

0.00

2

2.04

5.30

3

2.99

9.70

4

4.06

14.10

5

5.05

17.90

6

6.01

21.10

7

7.04

23.90

8

7.93

25.10

9

-

-

10

-

-

Because of experimental technique and prior condition of the fuel cell, students’ measured values may differ from the example values given here.

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Solutions 12

Set-up of a fuel cell power supply

C.6

5.4

If you are not making further measurements with the system, proceed to shut down and switch off the system as described in 3.6.

5.5

Transfer the measured values from the table in 5.3 to draw a characteristic curve for the available power of the fuel cell system with voltage converter. Also transfer the characteristic curve for available power without transducer losses from the diagram in 4.8. Note: The usable power corresponds to the EL200 load power.

Converter Losses 60 Usable power without converter

Power P (W)

50

Usable power with converter

40 30 20 10 0 0

5.6

1

2

3

4 5 6 7 Stack current Istack (A)

8

9

10

Describe and explain the process of the characteristic curves. Describe the differences between the curves, and refer to the diagram in 4.8. The available power with-converter curve lies below without-converter. The difference between curves corresponds to the losses which occur during the voltage conversion. Increasing conversion losses can be seen in the divergence of the curves with increasing currents. These converter losses are added to those which are apparent in diagram 4.8.

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Solutions 13

5.7

Set-up of a fuel cell power supply

C.6

What is the function of a voltage converter in a fuel cell system; is it possible to operate without it? The voltage converter produces from the load-sensitive (not constant) voltage of the fuel cell a constant output voltage. In this system Vout = 12 V. This voltage is necessary for the self-supply of the FC50, and for the supply of external devices. Without voltage conversion an external supply voltage is necessary for the operation of the fuel cell system, since the control and other peripheral devices can operate only with a constant voltage. Additionally the applications of a fuel cell system would be limited, since for many electrical devices a constant output voltage is needed.

5.8

Summarize your conclusions from this experiment. How can one increase the available power of a fuel cell system during continuous stack power? Suggest at least two optimization possibilities. The stack power can be divided into the available power and the internal requirement of the system. To optimize the available power the internal requirement must be minimized. There are optimization possibilities with all peripheral devices and losses. In particular: •

Control

•

Fan Power

•

LED displays (would not exist in industrial applications)

•

Transducer losses

•

Line losses

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Solutions 1

Efficiency of a fuel cell power supply

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

Voltage converter VC100

621

Hydrogen supply (alternates)

I II III

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Voltage Converter VC100

Electronic Load EL200

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C.7

Solutions 2

Efficiency of a fuel cell power supply

C.7

Task: The goal of this experiment is to determine the efficiency of a grid-independent fuel cell system. The terms system efficiency and stack efficiency are explained and measured for the experimental system. In addition the effect of parasitic load on the system efficiency is examined.

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Power to operate the FC50 Fuel Cell module will be provided by the VC100 Voltage Converter. Use the provided 3-pin cable to connect the Parasitic Load output on the VC100 Voltage Converter to the 12V= DC power input on the FC50 Fuel Cell.

1.2

On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.3

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.4

Use two test leads to additionally connect the FC50 with the input of the VC100, paying attention to the polarity.

1.5

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.6

If you want to use the provided software program to help perform the experiment, make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Solutions 3

2

Efficiency of a fuel cell power supply

C.7

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: If you want to use the provided software program to assist with the experiment, start the FC50 software on your PC and select experiment C.7. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

2.5

Voltage converter VC100: The module starts automatically. When voltage is applied at its input, a constant 12 V appears at the Available Power output. If no voltage is applied at its input, the internal battery provides 12 V at the Parasitic Load output.

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Solutions 4

Efficiency of a fuel cell power supply

C.7

3

Data acquisition

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Using the potentiometer of the EL200, increase the load current until the Current display on the FC50 shows approximately 5 amperes. To further cause stack temperature to rise, turn the fan control knob on the FC50 so the Fan Power display indicates 10%. After the temperature reaches 40 °C, ensure the load potentiometer is turned back to zero and set fan control knob to AUTO.

3.2

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 60 s at each current setting before copying the measured values of stack current Istack, stack voltage Vstack and hydrogen flow rate V&H 2  to the measured value table. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Note: For reaching even hydrogen concentration at all membranes it is necessary to purge the hydrogen channels of the fuel cell. This takes place automatically and for a brief time visibly increases the hydrogen flow rate. If a purging occurs during the measurement, you should restart the 60 s waiting period for that operating point. The previously measured values are still valid. Note: Although you are adjusting the load current of the EL200, make sure that the preset values and displayed values you record are actually the FC50 stack current Istack. Also be aware of the automatic safety shut-down at stack currents > 10.5 A.

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Solutions 5

Efficiency of a fuel cell power supply

Nominal

C.7

Measured values

Istack (A)

Istack (A)

Vstack (V)

V&H 2 (ml/min)

Pload (W)

min

1.06

7.64

85

0.00

1.2

1.20

7.48

94

0.60

1.5

1.52

7.20

115

2.60

2.0

2.03

6.82

148

5.40

2.5

2.51

6.72

182

8.20

3.0

3.00

6.51

215

10.70

4.0

4.02

6.15

283

15.40

6.0

5.97

5.82

417

24.20

8.0

7.95

5.53

557

31.60

10.0

9.97

5.16

697

36.90

Because of experimental technique and prior condition of the fuel cell, students’ measured values may differ from the example values given here.

3.3

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

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Solutions 6

Efficiency of a fuel cell power supply

C.7

4

Calculation of the overall efficiency

4.1

Using the measured values in 3.2 determine the ratio of delivered power to consumed power (the overall efficiency) total of this fuel cell system. Perform an example calculation for a selected measuring point (other than the no-load operation point) and then calculate all values for the table. Also transfer the delivered electrical power of the EL200 Pload into the table. Note: The measured values of the hydrogen flow rate are converted to standard conditions (0 °C, 1.01325 bar). The lower heating value of hydrogen at standard conditions is LHV = 10.8 MJ/m3. Example calculation for the second measuring point (Istack = 1.2 A): The overall efficiency is the ratio of delivered power (from the entire system) to absorbed power (from the hydrogen):

ηtotal =

ηtotal =

Pout,total Pin

=

Pload LHV ⋅ V&

H2

0.6 W = 0.04 MJ ml 10.8 3 × 94 min m

Measured value Pload (W)

Calculated total

0.00

0.00

0.60

0.04

2.60

0.13

5.40

0.20

8.20

0.25

10.70

0.28

15.40

0.30

24.20

0.32

31.60

0.32

36.90

0.29

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Solutions 7

4.2

Efficiency of a fuel cell power supply

C.7

Transfer the values from the table in 4.1 to the following diagram and draw the graph of total = f(Pload). Overall efficiency 1.0

Efficiency

total

0.8

0.6

0.4

0.2

0.0 0

5

10

15

20

25

30

35

40

Power Pload (W) 4.3

Describe the course of the overall efficiency in the resulting characteristic curve. What is a favorable power range? The characteristic curve has a clear positive rise for small powers, beginning in the origin. With rising power the curve flattens gradually and for large powers has a negative slope. The maximum is at approximately 25 W, where the efficiency is 32 %. Because much of the curve is flat the efficiency changes only slightly over a wide range of powers. Therefore we can declare the favorable power range to be about 10 W to the maximum for this fuel cell system. The minimum efficiency in this range is about 27 %.

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Solutions 8

Efficiency of a fuel cell power supply

C.7

5

Calculation of stack and system efficiency

5.1

Using the appropriate power ratios and the measured values in 3.2 determine the stack efficiency stack and the system efficiency sys the fuel cell system. Perform an example calculation for a selected measuring point (other than the no-load operation point) and then calculate all values for the table. Also transfer the delivered electrical power of the EL200 Pload into the table. Note: The measured values of the hydrogen flow rate are converted to standard conditions (0 °C, 1.01325 bar). The lower heating value of hydrogen at standard conditions is LHV = 10.8 MJ/m3. Example calculation for the second measuring point (Istack = 1.2 A): The stack efficiency (over the hydrogen):

is the ratio of delivered power (from the stack) to absorbed power

stack

Pout,stack

Vstack ⋅ Istack = LHV ⋅ V&

7.48 V × 1.2 A = 0.53 . MJ ml H2 10.8 3 × 94 min m 7KHV\VWHPHIILFLHQF\ sys is the ratio of delivered power (from the entire system) to delivered stack power:

ηstack =

Pin

ηsys =

=

Pout,total Pout,stack

=

Measured value Pload (W)

Pload 0.6 W = = 0.07 . Vstack ⋅ Istack 7.48 V × 1.2 A

Calculated stack

sys

0.00

0.53

0.00

0.60

0.53

0.07

2.60

0.53

0.24

5.40

0.52

0.39

8.20

0.51

0.49

10.70

0.50

0.55

15.40

0.49

0.62

24.20

0.46

0.70

31.60

0.44

0.72

36.90

0.41

0.72

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Solutions 9

5.2

Efficiency of a fuel cell power supply

C.7

Transfer the values from the table in 5.1 to the following diagram and draw the graphs of stack = f(Pload) and sys = f(Pload). Stack and system efficiency 1,0 stack Stack sys System

Efficiency

0,8

0,6

0,4

0,2

0,0 0

5

10

15

20

25

30

35

40

Power Pload (W) 5.3

Describe the characteristic curves of stack and system efficiency and compare them with one another. Where do the optimum operating points of the fuel cell system lie, related to each efficiency?

7KHVWDFNHIILFLHQF\ stack reaches its maximum in the no-load operation (Pload = 0 W), because here the internal requirement of the system is covered by the stack (see experiment C.5). That is, the entire curve is shifted to the left, with the zero point lying in the negative range. In the measured range a constant loss is apparent, thus the optimal operating point occurs at low power. The system efficiency sys behaves the opposite: it reaches its maximum and optimum operating point at maximum power. The system efficiency curve rises over the entire measured range, however with evident flattening at high power.

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Solutions 10

5.4

Efficiency of a fuel cell power supply

C.7

What is the relationship between system, stack and overall efficiency? Demonstrate this relationship using the individual efficiencies in 4.1 and 5.1 for any measuring point except the no-load point. The overall efficiency is the product of the stack and the system efficiency:

total  stack • sys. This can be demonstrated from the second measuring point (Istack = 1.2 A). With the values for stack and system efficiency from 5.1 and the above equation the total efficiency results: total = 0.53 × 0.07 = 0.04. This calculated value agrees with the value determined in 4.1.

5.5

Consider which losses affect the individual efficiencies. Which of the individual losses are particular to a laboratory system and thus would not occur in an actual grid-independent power supply? Since the overall efficiency depends on stack and system efficiency, relevant losses can be divided as: All losses which affect the stack efficiency (see experiment C.5). All other losses belonging to the system which affect the system efficiency (see experiment C.6). For a laboratory system specific losses include those resulting from the collection and visualization of measured data. In addition the digital displays and lighting and integrated measuring instruments are part of a laboratory system. (Safety monitoring of the system is another matter.) In addition a power supply fuel cell system would be compactly built, reducing internal line losses.

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Solutions 1

Fuel cell application I: Remote traffic light

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

Voltage converter VC100

621

Traffic light TL10

622

Hydrogen supply (alternates)

I II III

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Traffic Light TL10

Voltage Converter VC100

Electronic Load EL200

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C.8

Solutions 2

Fuel cell application I: Remote traffic light

C.8

Task: When using a fuel cell system as a stand-alone power supply it is necessary to anticipate fuel consumption over a planned interval. Knowing the amount of fuel, the required storage volume can be computed. Using the example of a traffic light, this experiment attempts to determine its fuel requirement for a certain period and the needed storage volume. In addition, different hydrogen storage methods are compared, and a further comparison made with battery operation.

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Power to operate the FC50 Fuel Cell module will be provided by the VC100 Voltage Converter. Use the provided 3-pin cable to connect the Parasitic Load output on the VC100 Voltage Converter to the 12V= DC power input on the FC50 Fuel Cell.

1.2

On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.3

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.4

Use two test leads to additionally connect the FC50 with the input of the VC100, paying attention to the polarity.

1.5

Use two short test leads to connect Available Power on the VC100 with the TL10 traffic light, paying attention to the polarity. Place the toggle switch on the front panel of the TL10 in its middle position.

1.6

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.7

It is necessary to use the provided software program to perform the experiment. Make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Solutions 3

2

Fuel cell application I: Remote traffic light

C.8

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: You must use the provided software program to assist with this experiment. Start the FC50 software on your PC and select experiment C.8. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

2.5

Voltage converter VC100: The module starts automatically. When voltage is applied at its input, a constant 12 V appears at the Available Power output. If no voltage is applied at its input, the internal battery provides 12 V at the Parasitic Load output.

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Solutions 4

Fuel cell application I: Remote traffic light

C.8

3

Data acquisition

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Use the control software to set a load current of approximately 5 amperes. To further cause stack temperature to rise, set the FC50 fan power at 10%. After the temperature reaches 40 °C, the software switches off the EL200 and returns the fan power to AUTO. The system is ready for use.

3.2

With the help of the FC50 software hydrogen consumption and supplied power can be determined. Any arbitrary load could be attached to the Available power terminals of the VC100. However the following measurement is done with the TL10 Traffic Light in order to make the results of measurement consistent. Data for ten traffic light intervals will be taken. The TL10 front panel toggle switch must be set to AUTO. The software will read the instantaneous values of the output and the hydrogen flow rate. Subsequently, the consumption measurement is started and stopped after exactly ten cycles. The indicated instantaneous values are integrated (also visibly) at a 200 ms sampling rate in a named tabular data file. At the end of the measurement the integrated values are automatically written the end of the table. All measured values necessary for the evaluation are stored in the named file.

3.3

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

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Solutions 5

Fuel cell application I: Remote traffic light

C.8

4

Evaluation of the measured values

4.1

To evaluate the measurements open the tab-separated data file in a spreadsheet program such as MS Excel.

4.2

Using these tabular measured values make a power-time diagram of the available power over a traffic light interval. Mark in the diagram the individual traffic light phases and read the duration and the power of each individual phase. Determine with the data of the measured value table the duration and the average power of a traffic light interval Pusable . Power demand in a traffic-light cycle 8 Yel

Red

Red - Yel

Green

Power Pusable (W)

7 6 5 4 3 2 1 0 32

33

34

35

36

37

38

39

40

41

42

43

44

Time (s) For the individual traffic light phases the following values are observed: Tyellow = 0.8 s Pyellow = 4 W Tred = 4.9 s Pred =3W Tred-yellow = 0.6 s Pred-yellow = 6.9 W Tgreen = 4.6 s Pgreen = 0.9 W. The duration of a cycle is: Tcycle  7 10.9 s. The mean power Pusable can be determined by a summation of the individual measured values:

Pusable =

1 ⋅ n

n

∑ P = 2.36 W . i

i =1

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Solutions 6

4.3

Fuel cell application I: Remote traffic light

C.8

Compute the performed electrical work Wusable of the entire traffic light interval using the mean power Pusable . Also compute the performed electrical work using the sum of individual phases. The performed electrical work can be computed: 1. With the help of the mean power Pusable and the cycle time Tcycle: Wusable = Pusable • Tcycle = 25.7 Ws. 2. Calculating the individual electrical work of each traffic light phase: Wusable = Wyellow + Wred + Wred-yellow + Wgreen = Pyellow • Tyellow +… = 26.2 Ws.

4.4

Compare the computed values in 4.3 with the noted value over ten measurements from the measured value file. Explain the difference and describe the advantages of performing the measurement over several intervals. The value from the measured value file is 261.5 Ws, thus 26.15 Ws work over one cycle. The deviations result from the different accuracy of the various computation variants. The measured values over several intervals results in a more meaningful average value of the power used and decreases the error in the interval duration. The measurement of the electrical work this way is the most accurate. The two values in 4.3 for the performed electrical work differ since with the computation using the average power Pusable all measured values of the cycle were considered. Thus the actual average value of the power was obtained. Reading the electrical power and the duration of the traffic light phases off the diagram produces unavoidable errors. Determining the performed electrical work is quite inaccurate over the individual traffic light phases, however this method is sometimes necessary.

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Solutions 7

C.8

Produce a diagram of V&H 2 = f(t) over the same time interval as the diagram in 4.2 and compare them. How do you explain the differences of the courses of the curves? Hydrogen flow rate in a traffic-light cycle Hydrogen flow rate VH2 (ml/min)

4.5

Fuel cell application I: Remote traffic light

140 120 100 80 60 40 20 0 32

33

34

35

36

37

38

39

40

41

42

43

44

Time (s)

In the diagram of 4.2 the electrical power of the traffic light changes in discrete jumps as the individual consumers (LEDs in this instance) use constant power. However the hydrogen flow rate shows a continuous process since the fuel cell (within a limited range) exhibits a capacitive character: the stack sees the change in load (corresponding to the hydrogen flow rate) occurring over a certain time. The convergence of the taken-up and the available power takes place gradually. However an average value can be determined.

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Solutions 8

Fuel cell application I: Remote traffic light

C.8

5

Interpretation of hydrogen reservoirs

5.1

In the following, we will use measured values to specify different hydrogen reservoir systems for a building-site traffic light. The building-site traffic light is to operate for two weeks. It will need hydrogen at twice the rate of the FC50 system. How much hydrogen will be needed for continuous operation? A hydrogen demand of 192.46 ml was recorded over 111 s (see the measured value file). Converted to 2 weeks and double consumption, the total requirement of hydrogen would be 4.2 3 m.

5.2

To store the hydrogen volume computed in 5.1 three different possibilities exist: compressed gas storage, liquid gas storage and metal hydride storage. Compute volumes and mass of the different storage methods for the necessary hydrogen. Then examine the results regarding their targeted application from a technical and economic viewpoint. For the computation use the following volumetric and gravimetric memory densities for hydrogen: Compressed gas storage (350 bar): Liquid gas storage (20 K): Metal hydride storage (298 K):

22.3 g+/L, 45 g+/L, 63 g+/L,

With the density of hydrogen at VWDQGDUGFRQGLWLRQV results from the hydrogen demand calculated in 5.1: m+ 

+

+

40 g+/kg 112 g+/kg 14 g+/kg. 3

= 0.0899 kg/m the following mass

• V+ = 377.2 g.

Thus the volumes and masses can be computed for each storage method: Compressed gas storage: 16.9 L, Liquid gas storage: 8.4 L, Metal hydride storage: 6.0 L,

9.43 kg 3.4 kg 26.9 kg.

Depending upon storage type, volume- and mass-referred storage densities vary substantially. The most favorable is liquid gas storage. Both values are below those for compressed gas storage. Volume-referred is more than twice as high storage density For metal hydride storage, the volume density is more than twice that of compressed gas, but the mass density is only about a tenth of liquid gas. If one made a selection according to these criteria only, the choice would be liquid gas storage. This storage method is however very complex and energy-intensive because of the extremely low temperatures, incurring high acquisition and operating costs. Metal hydride storage is simple to handle, but compared with compressed gas storage has higher initial costs. Considering these criteria one would not choose liquid gas storage, but depending upon priority of costs and size, would choose the compressed gas or metal hydride storage.

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Solutions 9

5.3

Fuel cell application I: Remote traffic light

C.8

A conventional building-site traffic light operates with a lead storage battery. It has a volumetric memory density of 75 Wh/l, and gravimetric memory density of 30 Wh/kg. Compute the volume and mass of a lead storage battery that could store the same energy as the hydrogen storage in 5.2. Compare the result with the calculation from 5.2. What should be considered in this comparison? 3

Computing the energy with the lower heat value LHV = 3 kWh/m as determined in 5.1, we obtain: E+ = LHV • V+ = 30.47 kWh. With the given memory densities, a lead storage battery requires a volume of Volbattery = 470 L and a mass of 1016 kg. It is evident in this result that accumulators (batteries) have a significantly smaller power density (memory density) than fuel cells. It is thus desirable to use fuel cell systems both from the volume, and from the mass considerations. In this comparison however only the fuel cell storage, was considered, not the fuel cell stack (including system components). However in applications with large storage capacities, only a small portion of the volume and the mass would be the stack and the comparison would not change fundamentally. Additionally cost must also be considered. The accumulators, particularly lead storage batteries today are still priced more favorably than fuel cell systems. However further developments will enormously reduce the price of fuel cells in the future making the technology competitive.

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Solutions 1

Fuel cell application II: Fuel cell car

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

Voltage converter VC100

621

Hydrogen supply (alternates)

I II III

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Voltage Converter VC100

Electronic Load EL200

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C.9

Solutions 2

Fuel cell application II: Fuel cell car

C.9

Task: The fuel cell is predicted to have a strong future in the motoring industry. There is consequently much interest in quickly examining and optimizing the fuel cell for this application. In this experiment we examine the behavior of the system using different load profiles and by extension the use of fuel cells in motor vehicles. The advantages and disadvantages of various fuels are pointed out.

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Power to operate the FC50 Fuel Cell module will be provided by the VC100 Voltage Converter. Use the provided 3-pin cable to connect the Parasitic Load output on the VC100 Voltage Converter to the 12V= DC power input on the FC50 Fuel Cell.

1.2

On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.3

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.4

Use two test leads to additionally connect the FC50 with the input of the VC100, paying attention to the polarity.

1.5

Use two short test leads to connect Available Power on the VC100 with the TL10 traffic light, paying attention to the polarity. Place the toggle switch on the front panel of the TL10 in its central position.

1.6

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.7

It is necessary to use the provided software program to perform the experiment. Make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Solutions 3

2

Fuel cell application II: Fuel cell car

C.9

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: You must use the provided software program to assist with this experiment. Start the FC50 software on your PC and select experiment C.9. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

2.5

Voltage converter VC100: The module starts automatically. When voltage is applied at its input, a constant 12 V appears at the Available Power output. If no voltage is applied at its input, the internal battery provides 12 V at the Parasitic Load output.

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Solutions 4

Fuel cell application II: Fuel cell car

C.9

3

Data acquisition

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Use the control software to set a load current of approximately 5 amperes. To further cause stack temperature to rise, set the FC50 fan power at 10%. After the temperature reaches 40 °C, the software switches off the EL200 and returns the fan power to AUTO. The system is ready for use.

3.2

The "FC50 software" now automatically runs through two different load profiles. As a basis for comparison, the system operates as long in each profile as it takes for the EL200 to consume 2500 Ws. Additionally the consumed hydrogen volume for each load profile is indicated. The first profile represents a constant load within the range of the efficiency optimum. For comparison a repeating changing-load cycle will execute, consisting of full load, partial load and no-load operation sections. The delivered power and the associated hydrogen flow rate can be seen in the diagram over the time. Both tabular values are additionally stored at 200 ms intervals in a measured value file. At the conclusion of both load profiles the hydrogen volumes used in each case and the performed electrical work of the table are appended. These data are the basis of the following evaluation.

3.3

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

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Solutions 5

Fuel cell application II: Fuel cell car

C.9

4

Evaluation of the measured values

4.1

To evaluate the measurements open the tab-separated data file in a spreadsheet program such as MS Excel.

4.2

Compare the consumed hydrogen volume of both load profiles. What causes the differences, although about the same electrical work was performed? The hydrogen requirement in the changing-load trials is about three times that in the constant load trial. Higher consumption results from the lower efficiency, at which the changing-load system works. That is, more power must be supplied, in order to deliver the same power (definition of the efficiency). The supplied power corresponds to the hydrogen flow rate from higher consumption.

Using the spreadsheet program transfer the collected values to a diagram of the delivered electrical power Pdel and the hydrogen flow rate V&H 2 over the time t for a load change cycle. Describe and justify the processes of both characteristics.

Operation with a changing load 35

700 Pdel V&

600

H2

25

500

20

400

15

300

10

200

5

100

0

Flow rate VH2 (ml/min)

30 Delivered power Pdel (W)

4.3

0 60

65

70

75

80

85

90

Time (s)

The delivered electrical power follows the given rectangle profile. Only in the full load range is a small rise seen. A gradual "recovering" of the stack voltage occurs after the load change. The hydrogen flow rate approaches its final value after the load change with PT1-behavior. We see clearly the capacitive character of the fuel cell. Additionally it is noticeable that the characteristic has an offset, which is to due to the internal requirement of the system.

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Solutions 6

4.4

Fuel cell application II: Fuel cell car

C.9

Compute the efficiency using the delivered (electrical) and supplied (hydrogen) power for each load range in the changing-load trial. Compare these values with the efficiency in the constant-load trial. In which load range does the different hydrogen consumption of each load profile become particularly clear? What saving potential exists here? 3

If we compute the efficiencies with the lower heat value of hydrogen LHV = 3 kWh/m , we receive for the individual load ranges (computation see experiments C.5 and C.7): constant load: full load: partial load: no-load operation:

   

0.35 0.28 0.25 0.

In the constant-load trial the system works at its efficiency optimum. The efficiencies in the changing-load trials are always lower, from which the increased consumption noted in 4.2 results. The different hydrogen requirement of each load profile becomes particularly clear by viewing the no-load operation section in the changing-load trial: No electrical power is delivered by the system, although to cover the internal requirement of the system, power (that is, hydrogen) must be supplied; the efficiency is thus zero. If the system exclusively runs in the no-load operation, hydrogen is used, but delivers no power. The system could therefore be optimized by switching it off in the no-load operation. However a faster start of the system would be necessary, in order to react to sudden load changes. Further saving potential lies in the improvement of the efficiency. See also experiment C.7.

4.5

What are load profiles good for generally? Then consider in which connection the used load profiles in the automotive sector could to be used and justify your answer. Load profiles are used to simulate the employment of technical devices under different conditions in line with standard usage. Using a load profile it is possible to compare different devices with one another in order to find suitable equipment for a certain targeted application. Use different load profiles to assign an optimal area of operation to equipment or test the behavior with different modes of operation. If we refer this experiment to the automotive sector, the constant load enterprise could simulate a highway trip at constant speed. With this mode of operation the best overall efficiencies can be achieved by vehicles if the selected speed is not too high. Consequently fuel consumption would be low. If one operates an automobile in city traffic, within a short time different loads from no-load to full load are demanded. This mode of operation corresponds to the previous changing-load trial, which demands high dynamics from the system. The load cycle could simulate the operation of a fuel cell vehicle in stop-and-go traffic. The full load section corresponds to starting, the partial load section brief driving at constant speed, and the no-load operation section corresponds to waiting, perhaps at a traffic light.

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Solutions 7

Fuel cell application II: Fuel cell car

C.9

5

Comparison: Fuel cell – combustion engine

5.1

The fuel cell, in connection with an electric motor, represents a feasible replacement for the combustion engine (e.g. in the automobile). Describe the advantages of the combination of fuel cell and electric motor as against the combustion engine on the basis of energy transformation chains. Discuss the relevant efficiencies, to which the respective transformation chain is subject. Which advantages concerning the operating temperature result for the fuel cell? In both cases the chemical energy of the fuel is to be converted into mechanical energy to the drive of the vehicle. In the combustion engine this takes place through the intermediate step of the thermal energy (warmth), with the fuel cell this occurs through electricity. The energy transformation chains are subject however to different efficiencies: The transformation of the chemical energy into electrical with the help of the fuel cell is subject to the Gibbs efficiency (theoretical electrical efficiency of a fuel cell), which indicates the R R relationship of free reaction enthalpy G to the reaction enthalpy H:

∆R G

. ∆R H With the usual operating temperature of 50 °C – 120 °C this theoretical efficiency is above 90% (for gaseous product water) and decreases linearly with rising temperature. The energy transformation in the combustion engine is subject to the Carnot efficiency, which is computed from the upper process temperature T1 and lower process temperature T2: T ηCarnot = 1 − 2 . T1

ηGibbs =

The higher this temperature difference, the higher is the efficiency. However the breakdown of materials limits the temperature spread and a maximum Carnot efficiency of 40 % – 50 % results. The Carnot efficiency is like the Gibbs efficiency only a theoretical value, thus a maximally attainable upper limit. Still all losses arising in the system must be taken off from this maximum value. There the Gibbs efficiency like the Carnot efficiency, lies in the use of the fuel cell technology that has the potential of about twice as large an initial efficiency. Additionally the materials used by fuel cells lie in a more favorable operating temperature range, substantially reducing the thermal stress.

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Solutions 8

C.9

With the use of fuel cells in motor vehicles the required fuels will change. List different storage possibilities for hydrogen and compare these with conventional fuels for combustion engines using characteristic data and suitable graphics. Hydrogen can be stored in its pure form (compressed gas, liquid gas, metal hydride storage), or stored chemically, in technically reproducible hydrogen-rich substances (e.g. methanol). Depending upon storage type different gravimetric and volumetric energy densities are reached. We should always consider expenditure on production and storage. For example with the storage of the hydrogen in liquid form about 30% of the stored energy is needed for cooling. In the following table the gravimetric and volumetric energy densities of the specified hydrogen reservoirs are compared to the corresponding values of gasoline and diesel. The following graphic shows the differences clearly.

Fuel

Volumetric energy density (kWh/L)

Gravimetric energy density (kWh/kg)

Gasoline

9.1

11.67

Diesel

10

11.39

Methanol

4.29

5.42

H2 (g) 350 bar

0.74

1.33

H2 (l)

1.5

3.73

H2 (metal hydride)

2.1

0.47

Energy density comparison 12 Energy density (kWh/l and kWh/kg)

5.2

Fuel cell application II: Fuel cell car

Volumetric energy density Gravimetric energy density

10 8 6 4 2 0 Gasoline

Diesel

Methanol

H2 (g) 350 bar

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H2 (l)

H2 Metal hydride

Solutions 9

Fuel cell application II: Fuel cell car

C.9

Gasoline and diesel have the highest energy densities, thus the most energy per volume and/or per mass. Methanol compares favorably, however demands a complex reformation to obtain the hydrogen. The disadvantages of the energy-intensive storage of liquid hydrogen have already been mentioned. A possibility of storing hydrogen in a simple manner is metal hydride storage. Because of its high weight it is suitable however only for small applications; too heavy for use in the automobile. In the end compressed gas storage, which does not have a particularly high power density, remains a technically simply and developed method.

5.3

On a fuel cell vehicle a fuel storage is to be specified so that the vehicle with a single tank filling can travel the same distance as a vehicle with combustion engine (gasoline) with 30 L of fuel in its tank . The overall efficiency of the fuel cell vehicle is 40 %, that of the vehicle with combustion engine 20 %. Compare the mass and volume of compressed gas, liquid gas and metal hydride storage for hydrogen, as well as a methanol tank, and the equivalent values of a gasoline tank. Discuss your result and then choose a suitable storage. Under which simplifications, related to the hydrogen reservoirs, did you perform the calculations and how does this affect the result? Assume the volume of the gasoline tank itself is negligible: Vgasoline = Vtank = 30 L :LWKWKHHPSW\ZHLJKWRIWKHWDQNDUELWUDULO\FKRVHQWREHNJDQGWKHGHQVLW\ gasoline = 0.78 kg/dm³ a total mass results: mtotal = mtank gasoline • Vgasoline = 25.9 kg. Using the lower heat value LHV = 42 MJ/kgDQGWKHGHQVLW\ gasoline the energy content of the gasoline can be determined simply as: Egasoline  gasoline • Vgasoline • LHVgasoline = 273 kWh Considering the efficiency differences of both propulsion principles the masses and volumes of the storage can be computed using the power densities specified in 5.2. For the methanol tank, similar to the gasoline tank, the volume of the tank itself is ignored and an empty weight of 2.5 kg was used.

Fuel

Volume (L)

Mass (kg)

Gasoline

30

25.9

Methanol

31.8

27.7

H2 (g) 350 bar

184.5

102.6

H2 (l)

91

36.6

H2 metal hydride

65

290.4

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Solutions 10

Fuel cell application II: Fuel cell car

C.9

Comparison of fuel storage methods

Volume (L) and mass (kg)

300 250

Storage volume Storage mass

200 150 100 50 0 Gasoline

Methanol

H2 (gas) 350 bar

H2 (liquid)

H2 Metal hydride

Storage volumes and mass are lowest for the vehicle with a combustion engine. Due to the significantly better efficiency of the fuel cell vehicle, the methanol tank is however only a little larger and heavier. Also liquid storage of hydrogen represents a practical alternative. In the case of compressed gas storage the range of the vehicle would have to be reduced or a much larger storage chosen. The relatively small volume of a metal hydride storage is favorable, but the mass of the system is so high as to make it impractical. With this comparison the energies needed by the respective storage methods were neglected. To maintain liquid hydrogen storage significant energy expenditure is necessary, for example to guarantee cooling. When using methanol, energy is needed to loosen bound hydrogen from the molecular lattice (reformation). Therefore additional fuel is necessary, in order to meet such power requirements. In summary to select a suitable storage system, you would consider volumes and mass for the methanol method. If one wants to avoid the reformation, the choice is clearly for the liquid gas storage. But because this is achieved at high technical cost, it may be appropriate to return to the larger, heavier, but more simple compressed gas storage.

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Solutions 11

5.4

Fuel cell application II: Fuel cell car

C.9

Compare the structure of the drive train of a fuel cell vehicle with that of a combustion engine vehicle. Which advantages result for the fuel cell vehicle? To operate a vehicle with a combustion engine a clutch as well as a transmission is necessary, since with the combustion engine only a limited range of engine speeds can be used. Since at rotational speed 0 no torque is delivered, at least an idling speed must always be maintained. In order to move in the optimal speed range of the engine, a complex transmission is necessary. The power transmission to the wheels must be through shafts. Different distribution of forces or different numbers of revolutions of individual wheels can be realized only through powerabsorbing differentials. In a fuel cell vehicle the drive is achieved by electric motors. Since these produce high torque over the entire speed range of the motor, a clutch and transmission are not necessary. Thus wear-intensive units can be omitted, and the structure of the engine will be significantly simpler and more durable. An additional advantage is that each wheel can be propelled individually, thus shafts and differentials in the power transmission would be unnecessary, the distribution of forces being regulated electronically. Many years of experience already exist, e.g. in building rail-mounted vehicles. The larger volumes and masses for hydrogen storage could be compensated by savings in the power train.

5.5

A fuel cell vehicle is to be propelled with an asynchronous engine. How would you control the rotational speed and how could the power be delivered? To control the number of revolutions of asynchronous machines the frequency voltage control is best suited. With this control it is possible to accelerate away from a stop in minimal time up to the rated speed. A further increase of the number of revolutions is possible, however with a reduction of the torque. To implement this control a variable DC voltage is necessary, over which the working force level can be stepped. In addition a DC—DC transducer is necessary, which converts a variable input voltage into a variable output voltage. The output voltage should always correspond to a pre-set value. For the frequency control an inverter must be used, which sets the desired frequency and thus the number of revolutions of the motor.

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Work sheet 1

The basic functions of the fuel cell system

D.1

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

Voltage converter VC100 (optional)

621

Traffic light TL10 (optional)

622

Hydrogen supply (alternates)

I II III

Arrange the devices as in the following diagram:

Fuel cell Cell FC50 Hydrogen supply

Traffic light Light TL10 (optional)

Voltage Converter Spannungswandler VC100 (optional)

Electronic Load Elektronische Last EL200

Name

Grade / Course

© Heliocentris - Energizing education

Date

Work sheet 2

The basic functions of the fuel cell system

D.1

Task: Learn about the FC50 Fuel Cell System and its components by stepping through their operation. Notice how the system reports operation errors and learn how to correct them.

Execution: Note: This procedure shows you the operating modes of the individual components and later helps you to easily recognize and correct errors. You should follow the sequence step by step as indicated here. If you notice a mistake or omission in the procedure steps, you should nevertheless do the steps as indicated in order to learn the behavior of the system in the event of an error. To solve the following problems and answer the questions it will be necessary to refer to the Component Descriptions of the devices used. 1

Installation and start-up of FC50, EL200 and hydrogen supply: When setting up and starting the equipment, follow the instructions provided in Part A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Place the modules into the mounting frame arranged as shown in the above illustration. Use the AC power cord to connect the EL200 Electronic Load to the source of AC power. (Connection is on the right side behind the front panel.) Ensure the toggle switch on the EL200 front panel is OFF. Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.2

On the FC50, set the main (toggle) switch to ON and press the START button. Which problem occurs and how can it be corrected?

Name

Grade / Course

© Heliocentris - Energizing education

Date

Work sheet 3

1.3

The basic functions of the fuel cell system

D.1

After you have corrected the problem, press the START button again. Which problem now occurs and how can it be corrected? Use the error list in A.3 Fuel Cell Module FC50 to explain.

1.4

Press the START button again. For approx.10 seconds a system test is performed. If this is successful, the displays are illuminated. The FC50 is now ready for use.

1.5

Turn the main power switch located behind the EL200 front panel on. The ‘Power’ display is illuminated. Turn the 10-turn potentiometer, in order to apply a load current. What does this show?

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Work sheet 4

The basic functions of the fuel cell system

D.1

1.6

The load current previously set on the potentiometer is drawn from the Fuel cell and can be read on the appropriate display. The power Pload absorbed by the electronic load is shown in the EL200 display window.

1.7

Cooling fans supply air necessary for the operation of the fuel cell. The speed of the fans can be adjusted to suit the load current automatically or manually. Use the knob beside the display ’ Fan Power ’, to set a fan power between 5 % and 100 %. Try setting different operating points on the EL200 and try to set an appropriate fan power. Watch how the system reacts when you change these settings.

1.8

Now apply a load current of 9 A and reduce the fan power slowly to 5 %. Watch the stack voltage display. What did you observe? Use the “Error messages” list (see A.3 Fuel Cell Module FC50) in order to explain why the FC50 shut off.

1.9

Switch the FC50 off. Ensure that the potentiometer of the EL200 is set to zero and the toggle switch on the front panel is OFF.

1.10 If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

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Work sheet 5

2

The basic functions of the fuel cell system

D.1

Installation and start-up of COMPUTER-SUPPORTED Operations To operate the FC50 in the COMPUTER-SUPPORTED mode, it is necessary to have a computer with RS232 interface on which you have installed the provided software. Refer to operation of the software in the section A.7 "Control Software".

2.1

Connect the port ’ RS232 ’ of the FC50 to the appropriate interface on your computer using the provided long 9-pin data cable. Start the program ’FC50 software’ on your computer selecting the menu option ’user Interface’ and click the ’START’ button. Follow the instructions in the reporting window of the control software.

2.2

When you are requested from the software, switch on the FC50 and start it. Which problem occurs and how can it be corrected?

2.3

The measured values of the FC50 are now shown on both the module and on your computer. But you can adjust the fan power only through the software.

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Work sheet 6

2.4

The basic functions of the fuel cell system

D.1

Also, setting the load current is only possible through the software. Set a value of Iload = 2 A Why doesn’t the EL200 react?

2.5

In the ’user Interface’ of the FC50 software click the label ’data display’. Observe the behavior of the different fuel cell parameters when you change the load current.

2.6

When you are through with the system, proceed to shut down and switch off the system as follows: •

Terminate the FC50 software. The FC50 sees the interruption of communication and displays an error.

•

Turn the potentiometer of the EL200 to zero, set the toggle switch to OFF and switch off the main switch behind the front panel.

•

Turn the knob for the fan power to AUTO and turn the FC50 main switch OFF.

•

Put the hydrogen supply out of operation correctly.

•

Remove the hydrogen inlet to the FC50 by disconnecting the quick-coupler.

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Work sheet 7

3

The basic functions of the fuel cell system

D.1

Installation and start-up of VC100 and TL10 (optional) This part can only be performed if the voltage converter VC100 and the traffic light TL10 is available. It does not matter if the FC50 is operating in COMPUTERSUPPORTED mode or in manual mode. Follow the safety instructions provided in section A: Component Descriptions for the individual components.

3.1

In the following the fuel cell system is self-powered. Switch the FC50 off and remove the AC power pack. Instead connect the 12 V DC input of the FC50 to the “Parasitic Load” output of the VC100 using the provided 3-pin cable. From the “Available Power” output of the VC100, the traffic light TL10 or other loads can be supplied. Use the provided short 9-pin RS485 data cable to connect the VC100 to the unused interface port of the EL200, to provide communication in the COMPUTERSUPPORTED mode. Start the FC50. Which error occurs?

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Work sheet 8

3.2

The basic functions of the fuel cell system

D.1

Restart the FC50 and wait for the system test to complete. In the VC100 display ‘parasitic load' see the power consumed by the FC50. In the display 'available power' see the power consumed by the attached load. Briefly try out the traffic light TL10 and observe the ‘available power’ display: At switch position ON all lamps shine; at position AUTO, a normal traffic light sequence occurs. In the middle position the device is off.

3.3

The electronic load EL200 can be operated in parallel with the traffic light. Gradually increase the load current of the fuel cell using the EL200 potentiometer. Try to reach the maximum EL200 load current. Explain why the FC50 switches off. What has to be considered when restarting?

3.4

When you are through with the system, proceed to shut down and switch off the system as follows: •

Turn the potentiometer of the EL200 to zero, set the toggle switch to OFF and switch off the main switch behind the front panel.

•

Turn the knob for the fan power to AUTO and turn the FC50 main switch OFF.

•

Put the hydrogen supply out of operation correctly.

•

Remove the hydrogen inlet to the FC50 by disconnecting the quick-coupler.

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Work sheet 9

4

The basic functions of the fuel cell system

D.1

Summary Considering the problems and the associated error messages again, look at the error list in section A.3 Fuel Cell Module FC50. Explain why it is useful to divide the errors into two groups: start-up errors and operating errors. Give at least one example of each group.

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Work sheet 1

The characteristic curve of a fuel cell

D.2

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

I II III

Hydrogen supply (alternates)

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Electronic Load EL200

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Work sheet 2

The characteristic curve of a fuel cell

D.2

Task: In this experiment we determine the voltage-current characteristic of a fuel cell and plot a power-current diagram. This provides a basic knowledge of the behavior of a fuel cell. The results can be used to size and design fuel cell stacks.

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Connect the AC power pack cable to the 12V= DC power input on the FC50 Fuel Cell. Connect the other end of the AC power pack to a source of AC power. On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.2

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.3

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.4

If you want to use the provided software program to help perform the experiment, make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Work sheet 3

2

The characteristic curve of a fuel cell

D.2

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: If you want to use the provided software program to assist with the experiment, start the FC50 software on your PC and select experiment C.2. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

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Work sheet 4

The characteristic curve of a fuel cell

D.2

3

Data acquisition

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Using the potentiometer of the EL200, increase the load current until the Current display on the FC50 shows approximately 5 amperes. To further cause stack temperature to rise, turn the fan control knob on the FC50 so the Fan Power display indicates 10%. After the temperature reaches 40 °C, ensure the load potentiometer is turned back to zero and set fan control knob to AUTO.

3.2

Using the EL200 potentiometer, set in turn each load current listed in the following table. After waiting at least 15 seconds at each point, record the measured values of stack current Istack and stack voltage Vstack in the table. When measuring the first point (no-load operation) turn the toggle switch on the EL200 to OFF to ensure that there is no load on the fuel cell. Nominal current Istack (A)

Measured values Istack (A)

Vstack (V)

Calculated Pstack (W)

0.0 0.2 0.5 1.0 1.5 2.0 3.0 5.0 7.0 10.0 3.3

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

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Work sheet 5

The characteristic curve of a fuel cell

D.2

4

Data interpretation

4.1

Draw the fuel cell voltage-current relation Vstack = f (Istack) and describe the characteristic curve. Voltage-Current Characteristic 10

Stack Voltage Vstack (V)

9 8 7 6 5 4 3 2 1 0 0

1

2

3

4

5

6

7

8

9

10

Current Istack (A)

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Work sheet 6

4.2

The characteristic curve of a fuel cell

D.2

How do you explain the characteristic curve?

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Work sheet 7

D.2

Also draw the fuel cell power-current relation Pstack = f (Istack). Use the calculated electrical power from table 3.2. Then considering the characteristic curve, make a statement about the maximum power of the fuel cell. Power-Current Characteristic 60 50 40 Power Pstack (W)

4.3

The characteristic curve of a fuel cell

30 20 10 0 0

1

2

3

4

5

6

7

8

9

10

Current Istack (A)

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Work sheet 8

4.4

The characteristic curve of a fuel cell

D.2

For the power of fuel cell stacks two parameters are significant: the number of cells and the current density (in A/cm2). From the results of your measurement of the stack at a load current of 10 A, determine the voltage and the current density of an individual cell. Note: The active surface of these cells (surface of the electrodes) is 25 cm2. Assuming these values are transferable to larger fuel cells, use your results to specify two fuel cell stacks: •

a 1 kW el rated stack with a working voltage Vstack = 24 V

•

a 5 kW el rated stack with a working voltage Vstack = 42 V

For both stacks give the following values: cell current, number of cells and active cell surface.

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Work sheet 9

4.5

The characteristic curve of a fuel cell

D.2

The power density of a fuel cell (in W/L) is an important characteristic for the capacity of a fuel cell, for example for use in a motor vehicle. Calculate this value for the experimental fuel cell (without fan and end plates) for a power of 50 W. Then compare this value with fuel cells that are used today in automobile prototypes. Here values of 1 to 2 kW/L are being reached. How might the power density of the experimental fuel cell stack be optimized? State some ideas.

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Work sheet 1

Parameters influencing the characteristic curve

D.3

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

I II III

Hydrogen supply (alternates)

External voltmeter

-

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Electronic Load EL200

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Work sheet 2

Parameters influencing the characteristic curve

D.3

Task: In this experiment we investigate the effects of reduced air supply, increased internal resistance, and fuel cell temperature on the characteristic curve of the fuel cell.

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Connect the AC power pack cable to the 12V= DC power input on the FC50 Fuel Cell. Connect the other end of the AC power pack to a source of AC power. On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.2

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.3

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.4

If you want to use the provided software program to help perform the experiment, make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Work sheet 3

2

Parameters influencing the characteristic curve

D.3

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: If you want to use the provided software program to assist with the parts of the experiment described in section 3 and 5 (automated support for section 4 is not possible), start the FC50 software on your PC and select experiment C.3. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

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Work sheet 4

Parameters influencing the characteristic curve

D.3

3

Effect of the air supply on the characteristic curve of a fuel cell

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Using the potentiometer of the EL200, increase the load current until the Current display on the FC50 shows approximately 5 amperes. To further cause stack temperature to rise, turn the fan control knob on the FC50 so the Fan Power display indicates 10%. After the temperature reaches 40 °C, ensure the load potentiometer is turned back to zero and set fan control knob to AUTO.

3.2

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 15 s at each current setting before copying the measured values of stack current Istack and stack voltage Vstack to the measured value table. For the first series of measurements place the fan setting at AUTO. For the second series, adjust the control so that Fan Power is 6%. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Note: The last measured values of the second series of measurements should be taken quickly, because inadequate cooling will cause the fuel cell temperature to rise. If necessary, you can cool the stack by temporarily removing the load and increasing fan power. If the temperature does rise above 50 °C, for safety the FC50 automatically switches off and will not restart until the temperature falls below 45 °C.

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Work sheet 5

Parameters influencing the characteristic curve

Nominal current 1 Istack (A)

Measured values, Fan at AUTO Istack (A)

Vstack (V)

Nominal current 2 Istack (A)

0.0

0.0

0.2

0.2

0.5

0.5

1.0

1.0

1.5

1.5

2.0

2.0

3.0

3.0

5.0

5.0

7.0

7.0

10.0

7.4

D.3

Measured values, Fan at 6% Istack (A)

Vstack (V)

7.6 7.8 8.0 8.2

3.3

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

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Work sheet 6

D.3

Use the measured values to draw on the following diagram the voltage-current characteristic Vstack = f( Istack) of the fuel cell for both fan settings. Briefly describe the shape of the resulting characteristic curve. Effect of air supply 10 9 Stack voltage Vstack (V)

3.4

Parameters influencing the characteristic curve

8 7 6 5 4 3 2 1 0 0

1

2

3

4

5

6

7

8

9

10

Stack current Istack (A)

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Work sheet 7

3.5

Parameters influencing the characteristic curve

D.3

How do you explain the divergence of the reduced-air characteristic curve? On the diagram mark the individual ranges of the reduced-air characteristic.

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Work sheet 8

3.6

Parameters influencing the characteristic curve

D.3

Transfer from 3.2 the measured values for the stack current Istack to the following table and calculate the associated stack power Pstack. Then use the calculated values to draw on the following diagram the characteristic Pstack = f( Istack) of the fuel cell with the two air supplies and briefly describe the shape of the characteristic curve. Fan at ’AUTO’

Fan at ’6%’

Measured value Calculated Measured value Calculated Istack (A)

Pstack (W)

Istack (A)

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Pstack (W)

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Work sheet 9

Parameters influencing the characteristic curve

D.3

Effect of air supply on the power curve

Stack power Pstack (W)

60 50 40 30 20 10 0 0

1

2

3

4

5

6

7

8

9

10

Stack current Istack (A)

3.7

What do you observe about the operation of fuel cells from the shape of the performance curve at reduced air supply?

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Work sheet 10

3.8

Parameters influencing the characteristic curve

D.3

Calculate the oxygen flow rate needed at an individual cell and the rate of water formation in order to produce an electric current of 10 A. Use a formula derived from Faraday’s laws for the determination of the substance change. Then determine the theoretically needed volumetric air flow for the entire stack on the assumption that the usable oxygen portion in air is 20 %. Consider the number of cells of the stack. Note: Perform the calculation at standard conditions (0 °C, 1.01325 bar). The molecular standard volume is Vm = 22.4 L/mol; the Faraday constant F = 9.648 × 104 C/mol.

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Work sheet 11

3.9

Parameters influencing the characteristic curve

The fuel cell stack actually operates with excess air mean and why is it necessary?

D.3

= 10. What does “excess air”

Note: Also consider the temperature behavior of the fuel cell at reduced fan power.

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Work sheet 12

Parameters influencing the characteristic curve

D.3

4

Effect of internal resistance on the characteristic curve of a fuel cell

4.1

In this part of the experiment software support is not possible, because an external voltage measurement is necessary. Connect a suitable voltmeter to measure the terminal voltage Vterminal at the output of the FC50.

4.2

The recommended operating temperature is the same as in the previous part, 40 °C. If the fuel cell has cooled, heat it again as described in 3.1.

4.3

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 15 s at each current setting before copying the measured values of stack current Istack, stack voltage Vstack and terminal voltage Vterminal to the measured value table. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Nominal Istack (A)

Measured values Istack (A)

Vstack (V)

Vterminal (V)

0.0 0.2 0.5 1.0 1.5 2.0 3.0 5.0 7.0 10.0

4.4

If you are not making further measurements with the system, proceed to shut down and switch off the system as described in 3.3.

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Work sheet 13

D.3

Draw the two voltage-current characteristics Vstack = f(Istack) and Vterminal = f(Istack) and describe the shapes of both characteristic curve.

Effect of internal resistance 10 9 8 Voltage (V)

4.5

Parameters influencing the characteristic curve

7 6 5 4 3 2 1 0 0

1

2

3

4 5 6 7 Stack current Istack (A)

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8

9

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Work sheet 14

4.6

Parameters influencing the characteristic curve

D.3

Describe the diverging shape of the characteristic curve with the FC50 fuel cell structure and suggest causes for it.

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Work sheet 15

4.7

Parameters influencing the characteristic curve

D.3

Consider the FC50 as a real power supply and describe the make-up of internal resistance Rint. Divide it into two partial resistances and draw an appropriate schematic diagram.

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Work sheet 16

4.8

Parameters influencing the characteristic curve

D.3

Determine with the help of the curves in 4.5 the size of the resistances in the diagram of 4.7. Calculate the power losses due to these resistances at a stack current of 10 A.

4.9

To which physical causes can the Ohmic resistance be attributed within the fuel cell stacks? What optimization possibilities exist?

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Work sheet 17

Parameters influencing the characteristic curve

D.3

5

Effect of the temperature on the characteristic curve of a fuel cell

5.1

In this part of the experiment two series of measurements are taken at different fuel cell temperatures. The recommended temperatures at the beginning of each series are approximately 28 °C and 44 °C. During the experiment temperatures will unavoidably drift. In order to keep the deviations small, currents and voltages should be measured and recorded as quickly as possible.

5.2

If you want to use the provided software program to assist with this part of the experiment, you must now switch off the FC50 and start the FC50 software on your PC. Select the appropriate experiment and wait until the program requests you to press the FC50 START button.

5.3

It is recommended to take first the series of measurements at the lower temperature. If the temperature is already too high, you can use the fan to lower it. Cool the fuel cell as quickly as possible to avoid drying the membranes. After reaching the desired operating temperature, reset the fan control to AUTO. To reach the fuel cell temperature of the second series of measurements load the fuel cell for a few minutes with a current of approximately 7 A. Using the potentiometer of the EL200, increase the load current until the Current display on the FC50 shows approximately 7 amperes. To further cause stack temperature to rise, turn the fan control knob on the FC50 so the Fan Power display indicates 12%. After the temperature reaches 44 °C, ensure the load potentiometer is turned back to zero and set fan control knob to AUTO.

5.4

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 15 s at each current setting before copying the measured values of stack current Istack and stack voltage Vstack to the measured value table. Begin the first series of measurements at a stack temperature of approx. 28 °C, the second series of measurements at approx. 44 °C. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Note: The last measured values of the first series of measurements should be taken quickly, because high current will cause the fuel cell temperature to rise. If necessary, you can cool the stack by temporarily removing the load and increasing fan power.

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Work sheet 18

Parameters influencing the characteristic curve

Nominal Istack (A)

D.3

Measured values Tstack = 28 °C Istack (A)

Vstack (V)

Tstack = 44 °C Istack (A)

Vstack (V)

0.00 0.20 0.50 1.00 1.50 2.00 3.00 5.00 7.00 10.00

5.5

If you are not making further measurements with the system, proceed to shut down and switch off the system as described in 3.3.

5.6

Draw the voltage-current characteristic curve for each operating temperature and describe the shape of the curve.

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Work sheet 19

Parameters influencing the characteristic curve

D.3

Effect of stack temperature 10 9 Stack voltage Vstack (V)

8 7 6 5 4 3 2 1 0 0

1

2

3 4 5 6 Stack current Istack (A)

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9

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Work sheet 20

5.7

Parameters influencing the characteristic curve

D.3

Explain the described characteristic curves considering the electrochemical reaction occurring here and the electrical conductivity.

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Work sheet 21

Parameters influencing the characteristic curve

D.3

5.8

Draw conclusions about the optimum operating temperature.

5.9

By which measure can the optimal operating temperature be increased? Draw on your conclusions in 5.7 and consider whether the effect is applicable in every case.

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Work sheet 1

Determination of the hydrogen current curve

D.4

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

Hydrogen supply (alternates)

I II III

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Electronic Load EL200

Name

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Work sheet 2

Determination of the hydrogen current curve

D.4

Task: In this experiment we determine the relationship between the hydrogen flow rate and electrical current, and how this is expressed in Faraday’s first law.

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Connect the AC power pack cable to the 12V= DC power input on the FC50 Fuel Cell. Connect the other end of the AC power pack to a source of AC power. On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.2

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.3

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.4

If you want to use the provided software program to help perform the experiment, make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Work sheet 3

2

Determination of the hydrogen current curve

D.4

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: If you want to use the provided software program to assist with the experiment, start the FC50 software on your PC and select experiment C.4. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

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Work sheet 4

Determination of the hydrogen current curve

D.4

3

Determination of the hydrogen-current relation

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Using the potentiometer of the EL200, increase the load current until the Current display on the FC50 shows approximately 5 amperes. To further cause stack temperature to rise, turn the fan control knob on the FC50 so the Fan Power display indicates 10%. After the temperature reaches 40 °C, ensure the load potentiometer is turned back to zero and set fan control knob to AUTO. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system.

3.2

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 60 s at each current setting before copying the measured values of stack current Istack and hydrogen flow rate V&H 2 to the measured value table. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Note: For reaching even hydrogen concentration at all membranes it is necessary to purge the hydrogen channels of the fuel cell. This takes place automatically and for a brief time visibly increases the hydrogen flow rate. If a purging occurs during the measurement, you should restart the 60 s waiting period for that operating point. The previously measured values are still valid.

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Work sheet 5

Determination of the hydrogen current curve

Nominal Istack (A)

D.4

Measured values Istack (A)

V&H 2 (ml/min)

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 3.3

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

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Work sheet 6

3.4

Determination of the hydrogen current curve

D.4

Plot the measured hydrogen consumption as a function of current in a diagram: ) V&H 2 = f (I VWDFN

Hydrogen - current curve Rate of hydrogen flow VolH2 (ml/min)

800 700 600 500 400 300 200 100 0 1

0

3.5

2

3 4 5 6 Stack current Istack (A)

7

8

9

10

Describe and explain the characteristic curve, using the First Faraday Law. Then explain the observed behavior in no-load operation (I = 0 A). VWDFN

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Work sheet 7

3.6

Determination of the hydrogen current curve

D.4

When specifying fuel cell systems it is important to know the current-dependent hydrogen flow rate of a stack. This indicates how much hydrogen the stack needs to supply a given current. Determine this value from the diagram in 3.4 neglecting the leakage rate. Then with the help of Faraday’s laws calculate the theoretical value and compare it to the observed value. Note: The displayed values of hydrogen flow rate have been converted to the equivalent ml/min at standard conditions (0 °C, 1.01325 bar). Calculate the theoretical value of the hydrogen flow rate at standard conditions. The molecular standard volume is Vm = 22.4 L/mol; the Faraday constant F = 9.648 × 104 C/mol.

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Work sheet 8

3.7

Determination of the hydrogen current curve

D.4

The current-dependent hydrogen flow rate determined in 3.6 is valid only for this stack. Express the hydrogen flow rate as a function of the number of cells a of a fuel cell stack and develop a general formula for the required hydrogen volume of a stack related to current, number of cells and time. Use this formula to calculate how much hydrogen is needed to draw 30 A from a 25cell stack for 8 hours. What is the required hydrogen flow rate?

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Work sheet 1

Efficiency of the fuel cell stack

D.5

Required devices: Description Hydrogen supply (alternates)

I II III

Item 630 642 652

Fuel cell FC50

610

Electronic load EL200

620

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Electronic Load EL200

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Work sheet 2

Efficiency of the fuel cell stack

D.5

Task: In this experiment we determine the efficiency of the fuel cell stack. By analyzing the power efficiency characteristic you will gain important knowledge about sizing a fuel cell. Two additional methods are used to measure efficiency in different ways: •

Stack efficiency as determined from voltage and current efficiency;

•

Efficiency calculation using the free reaction enthalpy, lower heat value (LHV) or higher heat value (HHV).

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Connect the AC power pack cable to the 12V= DC power input on the FC50 Fuel Cell. Connect the other end of the AC power pack to a source of AC power. On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.2

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.3

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.4

If you want to use the provided software program to help perform the experiment, make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Work sheet 3

2

Efficiency of the fuel cell stack

D.5

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: If you want to use the provided software program to assist with the experiment, start the FC50 software on your PC and select experiment C.5. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

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Work sheet 4

Efficiency of the fuel cell stack

D.5

3

Data acquisition

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Using the potentiometer of the EL200, increase the load current until the Current display on the FC50 shows approximately 5 amperes. To further cause stack temperature to rise, turn the fan control knob on the FC50 so the Fan Power display indicates 10%. After the temperature reaches 40 °C, ensure the load potentiometer is turned back to zero and set fan control knob to AUTO.

3.2

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 60 s at each current setting before copying the measured values of stack current Istack, stack voltage Vstack and hydrogen flow V&H 2 to the measured value table. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Note: For reaching even hydrogen concentration at all membranes it is necessary to purge the hydrogen channels of the fuel cell. This takes place automatically and for a brief time visibly increases the hydrogen flow rate. If a purging occurs during the measurement, you should restart the 60 s waiting period for that operating point. The previously measured values are still valid.

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Work sheet 5

Efficiency of the fuel cell stack

Nominal Istack (A)

D.5

Measured values Istack (A)

Vstack (V)

V&H 2  (ml/min)

0.0 0.2 0.5 1.0 1.5 2.0 3.0 5.0 7.0 10.0 3.3

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

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Work sheet 6

Efficiency of the fuel cell stack

D.5

4

Determination of the stack efficiency of the fuel cell

4.1

Determine the stack efficiency stack of this fuel cell by power balance (the ratio of delivered power to the power used). Perform an example calculation for a selected measuring point (other than the no-load operation point) and then calculate all values for the table. Also note the delivered stack power Pstack in the table. Note: The displayed values of hydrogen flow rate have been converted to the equivalent ml/min at standard conditions (0 °C, 1.01325 bar). The heat value of hydrogen at standard conditions is LHV = 10.8 MJ/m3.

Measured value Istack (A)

Calculation stack

Pstack (W)

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Work sheet 7

D.5

Transfer the calculated data from the table into the following diagram and draw the graphs of the functions stack = f(Istack) and Pstack = f(Istack) Briefly describe the shape of both characteristics.

1,2

60

1,0

50

0,8

40

0,6

30

0,4

20

0,2

10

Power Pstack (W)

Efficiency-Power comparison

Efficiency

4.2

Efficiency of the fuel cell stack

P 0,0

0 0

1

2

3

4 5 6 7 Stack current Istack (A)

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8

9

10

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Work sheet 8

4.3

Efficiency of the fuel cell stack

D.5

What important principles for the optimum design of fuel cells can be learned from these characteristic curves of power and efficiency? Consider for each principle a possible area of application, and an example of use.

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Work sheet 9

Efficiency of the fuel cell stack

D.5

5

Determination of the stack efficiency from current and voltage efficiency

5.1

Determine the voltage efficiency V of the fuel cell from the measured values of 3.2. Perform the calculation with the reversible thermodynamic voltage related to the lower heat value (LHV) of hydrogen. Also determine the current efficiency I and then calculate the stack efficiency stack from both. Perform an example calculation for a selected measuring point (other than the no-load operation point) and then calculate all values for the table. Note: The values of the hydrogen flow rate are converted to standard conditions (0 °C, 1.01325 bar). The reversible thermodynamic voltage related to the lower heat value LHV of hydrogen is Vrev LHV = 1.254 V, the Faraday constant F = 9.648 x 104 C/mol and the molecular standard volume Vm = 22.4 L/mol.

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Work sheet 10

Efficiency of the fuel cell stack

Measured value

Computation

Istack (A)

V

I

stack

Transfer the calculated data from the table into the following diagram and draw the graphs of the functions V f(Istack), I = f(Istack) and stack = f(Istack) Briefly describe the characteristic curves and the mutual influence of the graphs on one another. Note: Consider and compare the characteristic processes particularly for small and large currents.

Efficiencies of the fuel cell 1,2 1,0 Efficiency

5.2

D.5

0,8 0,6 0,4 0,2 0,0 0

1

2

3

4 5 6 7 Stack current Istack (A)

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8

9

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10

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Work sheet 11

5.3

Efficiency of the fuel cell stack

D.5

What determines the current efficiency and which losses decrease it? Why is the efficiency for large currents nearly 1?

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Work sheet 12

5.4

Efficiency of the fuel cell stack

D.5

Now consider the voltage efficiency more exactly. What does it affect and which losses decrease it? Why isn’t it 1 also in the no-load operation?

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Work sheet 13

Efficiency of the fuel cell stack

D.5

6

Thermodynamic view of the reference voltage

6.1

For the determination of the voltage efficiency a reference voltage is necessary. What different ways are there to calculate this reference voltage and how might they be used?

6.2

Briefly describe the theoretical determination of the reference voltages sought in 6.1. Use the thermodynamic terms "formation enthalpy", "reaction enthalpy", "reaction entropy" and "free reaction enthalpy".

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Work sheet 14

6.3

Efficiency of the fuel cell stack

D.5

Calculate the voltage efficiencies based on the reference voltages in 6.1. Use them with selected measured values from 3.2. Discuss the results and interpret the meaning. Which calculation is most meaningful, in order to determine the electrical efficiency of the fuel cell compared with a conventional power station? Note: If you don’t know the reference voltages mentioned in 6.1, you can use the values V1 = 1.23 V, V2 = 1.254 V and V3 = 1.482 V.

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Work sheet 15

6.4

Efficiency of the fuel cell stack

D.5

In step 5.4 the different losses which affect the voltage efficiency should be listed. Even neglecting all losses which directly affect the characteristic, the voltage efficiency does not become 1.0. Which additional deviation from the theoretical occurs in this system? Note: Consider which thermal boundary conditions affect the formation enthalpy of the materials.

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Work sheet 1

Set-up of a fuel cell power supply

D.6

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

Voltage converter VC100

621

Traffic light TL10

622

Hydrogen supply (alternates)

I II III

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Traffic Light TL10

Voltage Converter VC100

Electronic Load EL200

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Work sheet 2

Set-up of a fuel cell power supply

D.6

Task: In this experiment a grid-independent power supply is assembled and examined. We examine the parasitic load and the available power of the entire system as a function of the stack current.

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Power to operate the FC50 Fuel Cell module will be provided by the VC100 Voltage Converter. Use the provided 3-pin cable to connect the Parasitic Load output on the VC100 Voltage Converter to the 12V= DC power input on the FC50 Fuel Cell.

1.2

On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.3

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.4

Use two test leads to additionally connect the FC50 with the input of the VC100, paying attention to the polarity.

1.5

Use two medium test leads to connect Available Power on the VC100 with the TL10 traffic light, paying attention to the polarity. Place the toggle switch on the front panel of the TL10 in its middle position.

1.6

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.7

If you want to use the provided software program to help perform the experiment, make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Work sheet 3

2

Set-up of a fuel cell power supply

D.6

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: If you want to use the provided software program to assist with the experiment, start the FC50 software on your PC and select experiment C.6. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

2.5

Voltage converter VC100: The module starts automatically. When voltage is applied at the VC100 input, a constant 12 V appears at the Available Power output. During start-up, when no voltage is applied at its input, the internal battery temporarily provides 12 V at the Parasitic Load output.

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Work sheet 4

Set-up of a fuel cell power supply

D.6

3

Grid-independent fuel cell system for traffic light supply

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Using the potentiometer of the EL200, increase the load current until the Current display on the FC50 shows approximately 5 amperes. To further cause stack temperature to rise, turn the fan control knob on the FC50 so the Fan Power display indicates 10%. After the temperature reaches 40 °C, ensure the load potentiometer is turned back to zero and set fan control knob to AUTO.

3.2

For this part of the test leave the TL10 traffic light switch in its middle position, so it consumes no power. Then record the displayed FC50 and VC100 values in the following table.

Size

Measured value

Parasitic load Pself Stack voltage Vstack Stack current Istack

3.3

Although no power is taken from the Available Power output of the VC100, the fuel cell is producing a current (see Current display on the FC50). Where is this power being used? Mention at least two consumers.

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Work sheet 5

3.4

Set-up of a fuel cell power supply

D.6

Compare the parasitic load PSelf indicated by the VC100 with the stack power Pstack = Vstack · Istack, which is being generated by the fuel cell. Explain the difference of these values. What is the actual power consumed by the entire system?

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Work sheet 6

3.5

Set-up of a fuel cell power supply

D.6

In the following part the internal requirement Pself of the FC50, and the available power Pusable of the traffic light are measured during the different traffic light phases. Switch the toggle switch on the front panel of the TL10 to AUTO (lower position). Record the displayed values of the VC100 in the following table of measured values. Note: Because of the short duration of traffic light phases, it may be necessary to repeat some of the measurements. Measured values Traffic light phase Pself (W)

Pusable (W)

Green Yellow Red Red-yellow

3.6

3.7

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

Compare the internal requirement Pself with the available power Pusable for each phase of the light and describe the differences between phases.

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Work sheet 7

3.8

Set-up of a fuel cell power supply

D.6

At which measuring point does the fuel cell system work most efficiently and what conclusions can you draw from this? Justify your statements and refer if necessary to questions already answered.

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Work sheet 8

Set-up of a fuel cell power supply

D.6

4

Determination of the parasitic load characteristic of a fuel cell system

4.1

For the determination of the parasitic load characteristic, the traffic light module is not needed. Set the toggle switch on the front panel of the TL10 to its middle position (OFF) and remove the test leads between the VC100 and TL10.

4.2

If you want to use the provided software program to assist with this part of the experiment, you must now switch off the FC50 and start the FC50 software on your PC. Select the appropriate experiment and wait until the program requests you to press the FC50 START button.

4.3

The recommended operating temperature is the same as in the previous part, 40 °C. If the fuel cell has cooled, heat it again as described in 3.1.

4.4

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 15 s at each current setting before copying the measured values of stack current Istack stack voltage Vstack, internal requirement Pself and power of the electronic load Pload into the measured value table. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Note: Although you are adjusting the load current of the EL200, make sure that the preset values and displayed values you record are actually the FC50 stack current Istack. Also be aware of the automatic safety disconnect at stack currents > 10.5 A. Nominal Istack (A)

Measured values Istack (A)

Vstack (V)

Pself (W)

calculated Pload (W)

Pstack (W)

min 2 3 4 5 6 7 8 9 10 4.5

If you are not making further measurements with the system, proceed to shut down and switch off the system as described in 3.6.

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Work sheet 9

D.6

Transfer the function Pself = f(Istack) onto the diagram. Transfer in addition the appropriate measured values from the table in 4.4 to the following diagram and describe briefly the behavior of the characteristic.

Internal power requirement of the fuel cell system 8

7 Power Pself (W)

4.6

Set-up of a fuel cell power supply

6

5

4 0

1

2

3

4

5

6

7

8

9

10

Stack current Istack (A)

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Work sheet 10

4.7

Set-up of a fuel cell power supply

D.6

The internal requirement of the fuel cell system can be attributed to different peripheral devices (see 3.3). These internal consumers can be divided into two groups. Identify and describe this division on the basis the characteristic curve as described in 4.6 and identify at least one consumer in each group.

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Work sheet 11

4.8

Set-up of a fuel cell power supply

D.6

Compute the stack powers Pstack in the table in 4.4. Transfer onto the diagram values from the table in 4.4 showing the difference between usable power and the calculated power produced at the stack. Draw the characteristics Pstack = f(Istack) and Pload = f(Istack). Note: The available power corresponds to the EL200 load Pload.

Stack power – Usable power comparison 60

Power P (W)

50 40 30 20 10 0 0

4.9

1

2

3

4 5 6 7 Stack current Istack (A)

8

9

10

Describe and explain the process of the characteristics in diagram 4.8. Consider the two characteristics with the internal requirement characteristic in diagram 4.6 and explain the observed deviations.

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Work sheet 12

Set-up of a fuel cell power supply

D.6

5

Determination of the losses of the potential transformer

5.1

In this part of the experiment the losses which arise during the DC voltage transformation in the VC100 are determined. The EL200 must be attached to the Available Power output of the VC100. Switch the FC50 and EL200 off before you change these connections. Make sure that the potentiometer of the EL200 is set to zero.

5.2

The recommended operating temperature is the same as in the previous part, 40 °C. If the fuel cell has cooled, heat it again as described in 3.1.

5.3

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 15 s at each current setting before copying the measured values of stack current Istack, and power of the electronic load Pload to the measured value table. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Carefully increase the stack current Istack greater than 8 A and note the behavior of the system. Note: Although you are adjusting the load current of the EL200, make sure that the preset values and displayed values you record are actually the FC50 stack current Istack. Also be aware of the automatic safety disconnect at stack currents > 10.5 A. Nominal Istack (A)

Measured values Istack (A)

Pload (W)

min 2 3 4 5 6 7 8 9 10

5.4

If you are not making further measurements with the system, proceed to shut down and switch off the system as described in 3.6.

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Work sheet 13

5.5

Set-up of a fuel cell power supply

D.6

Transfer the measured values from the table in 5.3 to draw a characteristic curve for the available power of the fuel cell system with voltage converter. Also transfer the characteristic curve for available power without transducer losses from the diagram in 4.8. Note: The usable power corresponds to the EL200 load power.

Converter Losses 60

Power P (W)

50 40 30 20 10 0 0

5.6

1

2

3

4 5 6 7 Stack current Istack (A)

8

9

10

Describe and explain the process of the characteristic curves. Describe the differences between the curves, and refer to the diagram in 4.8.

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Work sheet 14

Set-up of a fuel cell power supply

D.6

5.7

What is the function of a voltage converter in a fuel cell system; is it possible to operate without it?

5.8

Summarize your conclusions from this experiment. How can one increase the available power of a fuel cell system during continuous stack power? Suggest at least two optimization possibilities.

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Work sheet 1

Efficiency of a fuel cell power supply

D.7

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

Voltage converter VC100

621

Hydrogen supply (alternates)

I II III

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Voltage Converter VC100

Electronic Load EL200

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Work sheet 2

Efficiency of a fuel cell power supply

D.7

Task: The goal of this experiment is to determine the efficiency of a grid-independent fuel cell system. The terms system efficiency and stack efficiency are explained and measured for the experimental system. In addition the effect of parasitic load on the system efficiency is examined.

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Power to operate the FC50 Fuel Cell module will be provided by the VC100 Voltage Converter. Use the provided 3-pin cable to connect the Parasitic Load output on the VC100 Voltage Converter to the 12V= DC power input on the FC50 Fuel Cell.

1.2

On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.3

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.4

Use two test leads to additionally connect the FC50 with the input of the VC100, paying attention to the polarity.

1.5

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.6

If you want to use the provided software program to help perform the experiment, make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Work sheet 3

2

Efficiency of a fuel cell power supply

D.7

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: If you want to use the provided software program to assist with the experiment, start the FC50 software on your PC and select experiment C.7. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

2.5

Voltage converter VC100: The module starts automatically. When voltage is applied at its input, a constant 12 V appears at the Available Power output. If no voltage is applied at its input, the internal battery provides 12 V at the Parasitic Load output.

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Work sheet 4

Efficiency of a fuel cell power supply

D.7

3

Data acquisition

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Using the potentiometer of the EL200, increase the load current until the Current display on the FC50 shows approximately 5 amperes. To further cause stack temperature to rise, turn the fan control knob on the FC50 so the Fan Power display indicates 10%. After the temperature reaches 40 °C, ensure the load potentiometer is turned back to zero and set fan control knob to AUTO.

3.2

Use the load potentiometer of the EL200 to set in sequence the current values given in the following table. Wait for at least 60 s at each current setting before copying the measured values of stack current Istack, stack voltage Vstack and hydrogen flow rate V&H 2  to the measured value table. In each series, for the first measuring point of zero-amperes, you can simply turn the EL200 toggle switch OFF, to ensure no load is applied to the system. Note: For reaching even hydrogen concentration at all membranes it is necessary to purge the hydrogen channels of the fuel cell. This takes place automatically and for a brief time visibly increases the hydrogen flow rate. If a purging occurs during the measurement, you should restart the 60 s waiting period for that operating point. The previously measured values are still valid. Note: Although you are adjusting the load current of the EL200, make sure that the preset values and displayed values you record are actually the FC50 stack current Istack. Also be aware of the automatic safety shut-down at stack currents > 10.5 A.

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Work sheet 5

Efficiency of a fuel cell power supply

Nominal Istack (A)

D.7

Measured values Istack (A)

Vstack (V)

V&H 2 (ml/min)

Pload (W)

min 1.2 1.5 2.0 2.5 3.0 4.0 6.0 8.0 10.0

3.3

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

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Work sheet 6

Efficiency of a fuel cell power supply

D.7

4

Calculation of the overall efficiency

4.1

Using the measured values in 3.2 determine the ratio of delivered power to consumed power (the overall efficiency) total of this fuel cell system. Perform an example calculation for a selected measuring point (other than the no-load operation point) and then calculate all values for the table. Also transfer the delivered electrical power of the EL200 Pload into the table. Note: The measured values of the hydrogen flow rate are converted to standard conditions (0 °C, 1.01325 bar). The lower heating value of hydrogen at standard conditions is LHV = 10.8 MJ/m3.

Measured value Pload (W)

Calculated total

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Work sheet 7

4.2

Efficiency of a fuel cell power supply

D.7

Transfer the values from the table in 4.1 to the following diagram and draw the graph of total = f(Pload). Overall efficiency 1.0

Efficiency

total

0.8

0.6

0.4

0.2

0.0 0

5

10

15

20

25

30

35

40

Power Pload (W) 4.3

Describe the course of the overall efficiency in the resulting characteristic curve. What is a favorable power range?

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Work sheet 8

Efficiency of a fuel cell power supply

D.7

5

Calculation of stack and system efficiency

5.1

Using the appropriate power ratios and the measured values in 3.2 determine the stack efficiency stack and the system efficiency sys the fuel cell system. Perform an example calculation for a selected measuring point (other than the no-load operation point) and then calculate all values for the table. Also transfer the delivered electrical power of the EL200 Pload into the table. Note: The measured values of the hydrogen flow rate are converted to standard conditions (0 °C, 1.01325 bar). The lower heating value of hydrogen at standard conditions is LHV = 10.8 MJ/m3.

Measured value Pload (W)

Calculated stack

sys

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Work sheet 9

5.2

Efficiency of a fuel cell power supply

D.7

Transfer the values from the table in 5.1 to the following diagram and draw the graphs of stack = f(Pload) and sys = f(Pload). Stack and system efficiency 1,0

Efficiency

0,8

0,6

0,4

0,2

0,0 0

5

10

15

20

25

30

35

40

Power Pload (W) 5.3

Describe the characteristic curves of stack and system efficiency and compare them with one another. Where do the optimum operating points of the fuel cell system lie, related to each efficiency?

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Work sheet 10

5.4

Efficiency of a fuel cell power supply

D.7

What is the relationship between system, stack and overall efficiency? Demonstrate this relationship using the individual efficiencies in 4.1 and 5.1 for any measuring point except the no-load point.

5.5

Consider which losses affect the individual efficiencies. Which of the individual losses are particular to a laboratory system and thus would not occur in an actual grid-independent power supply?

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Work sheet 1

Fuel cell application I: Remote traffic light

D.8

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

Voltage converter VC100

621

Traffic light TL10

622

Hydrogen supply (alternates)

I II III

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Traffic Light TL10

Voltage Converter VC100

Electronic Load EL200

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Work sheet 2

Fuel cell application I: Remote traffic light

D.8

Task: When using a fuel cell system as a stand-alone power supply it is necessary to anticipate fuel consumption over a planned interval. Knowing the amount of fuel, the required storage volume can be computed. Using the example of a traffic light, this experiment attempts to determine its fuel requirement for a certain period and the needed storage volume. In addition, different hydrogen storage methods are compared, and a further comparison made with battery operation.

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Power to operate the FC50 Fuel Cell module will be provided by the VC100 Voltage Converter. Use the provided 3-pin cable to connect the Parasitic Load output on the VC100 Voltage Converter to the 12V= DC power input on the FC50 Fuel Cell.

1.2

On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.3

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.4

Use two test leads to additionally connect the FC50 with the input of the VC100, paying attention to the polarity.

1.5

Use two short test leads to connect Available Power on the VC100 with the TL10 traffic light, paying attention to the polarity. Place the toggle switch on the front panel of the TL10 in its middle position.

1.6

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.7

It is necessary to use the provided software program to perform the experiment. Make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Work sheet 3

2

Fuel cell application I: Remote traffic light

D.8

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: You must use the provided software program to assist with this experiment. Start the FC50 software on your PC and select experiment C.8. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

2.5

Voltage converter VC100: The module starts automatically. When voltage is applied at its input, a constant 12 V appears at the Available Power output. If no voltage is applied at its input, the internal battery provides 12 V at the Parasitic Load output.

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Work sheet 4

Fuel cell application I: Remote traffic light

D.8

3

Data acquisition

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Use the control software to set a load current of approximately 5 amperes. To further cause stack temperature to rise, set the FC50 fan power at 10%. After the temperature reaches 40 °C, the software switches off the EL200 and returns the fan power to AUTO. The system is ready for use.

3.2

With the help of the FC50 software hydrogen consumption and supplied power can be determined. Any arbitrary load could be attached to the Available power terminals of the VC100. However the following measurement is done with the TL10 Traffic Light in order to make the results of measurement consistent. Data for ten traffic light intervals will be taken. The TL10 front panel toggle switch must be set to AUTO. The software will read the instantaneous values of the output and the hydrogen flow rate. Subsequently, the consumption measurement is started and stopped after exactly ten cycles. The indicated instantaneous values are integrated (also visibly) at a 200 ms sampling rate in a named tabular data file. At the end of the measurement the integrated values are automatically written the end of the table. All measured values necessary for the evaluation are stored in the named file.

3.3

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

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Work sheet 5

Fuel cell application I: Remote traffic light

D.8

4

Evaluation of the measured values

4.1

To evaluate the measurements open the tab-separated data file in a spreadsheet program such as MS Excel.

4.2

Using these tabular measured values make a power-time diagram of the available power over a traffic light interval. Mark in the diagram the individual traffic light phases and read the duration and the power of each individual phase. Determine with the data of the measured value table the duration and the average power of a traffic light interval Pusable . Power demand in a traffic-light cycle

F

8

Power Pusable (W)

7 6 5 4 3 2 1 0 Time (s)

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Work sheet 6

4.3

Fuel cell application I: Remote traffic light

D.8

Compute the performed electrical work Wusable of the entire traffic light interval using the mean power Pusable . Also compute the performed electrical work using the sum of individual phases.

4.4

Compare the computed values in 4.3 with the noted value over ten measurements from the measured value file. Explain the difference and describe the advantages of performing the measurement over several intervals.

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Work sheet 7

D.8

Produce a diagram of V&H 2 = f(t) over the same time interval as the diagram in 4.2 and compare them. How do you explain the differences of the courses of the curves? Hydrogen flow rate in a traffic-light cycle Hydrogen flow rate VH2 (ml/min)

4.5

Fuel cell application I: Remote traffic light

140 120 100 80 60 40 20 0 Time (s)

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Work sheet 8

Fuel cell application I: Remote traffic light

D.8

5

Interpretation of hydrogen reservoirs

5.1

In the following, we will use measured values to specify different hydrogen reservoir systems for a building-site traffic light. The building-site traffic light is to operate for two weeks. It will need hydrogen at twice the rate of the FC50 system. How much hydrogen will be needed for continuous operation?

5.2

To store the hydrogen volume computed in 5.1 three different possibilities exist: compressed gas storage, liquid gas storage and metal hydride storage. Compute volumes and mass of the different storage methods for the necessary hydrogen. Then examine the results regarding their targeted application from a technical and economic viewpoint. For the computation use the following volumetric and gravimetric memory densities for hydrogen: Compressed gas storage (350 bar): Liquid gas storage (20 K): Metal hydride storage (298 K):

22.3 g+/L, 45 g+/L, 63 g+/L,

40 g+/kg 112 g+/kg 14 g+/kg.

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Work sheet 9

5.3

Fuel cell application I: Remote traffic light

D.8

A conventional building-site traffic light operates with a lead storage battery. It has a volumetric memory density of 75 Wh/l, and gravimetric memory density of 30 Wh/kg. Compute the volume and mass of a lead storage battery that could store the same energy as the hydrogen storage in 5.2. Compare the result with the calculation from 5.2. What should be considered in this comparison?

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Work sheet 1

Fuel cell application II: Fuel cell car

D.9

Required devices: Description

Fuel cell FC50

Item 630 642 652 610

Electronic load EL200

620

Voltage converter VC100

621

Hydrogen supply (alternates)

I II III

Arrange the devices as in the following diagram:

Fuel Cell FC50 Hydrogen supply

Voltage Converter VC100

Electronic Load EL200

Name

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Work sheet 2

Fuel cell application II: Fuel cell car

D.9

Task: The fuel cell is predicted to have a strong future in the motoring industry. There is consequently much interest in quickly examining and optimizing the fuel cell for this application. In this experiment we examine the behavior of the system using different load profiles and by extension the use of fuel cells in motor vehicles. The advantages and disadvantages of various fuels are pointed out.

Execution: 1

Set-up When setting up and starting the equipment, follow the instructions provided in section A: Component Descriptions for the individual components, especially the safety instructions. During experiments, ensure the area has adequate ventilation and keep away from sources of ignition.

1.1

Power to operate the FC50 Fuel Cell module will be provided by the VC100 Voltage Converter. Use the provided 3-pin cable to connect the Parasitic Load output on the VC100 Voltage Converter to the 12V= DC power input on the FC50 Fuel Cell.

1.2

On the front panel of the EL200 Electronic Load ensure the toggle switch is OFF. Use the AC power cord to connect the EL200 to a source of AC power; then turn on the main power switch located behind the EL200 front panel.

1.3

Use two short test leads to connect the FC50 with the EL200, paying attention to the polarity.

1.4

Use two test leads to additionally connect the FC50 with the input of the VC100, paying attention to the polarity.

1.5

Use two short test leads to connect Available Power on the VC100 with the TL10 traffic light, paying attention to the polarity. Place the toggle switch on the front panel of the TL10 in its central position.

1.6

Attach the hydrogen supply quick-coupler to the FC50. Connect the 9-pin plug of the hydrogen supply’s solenoid valve to the H2 SUPPLY connector on the FC50.

1.7

It is necessary to use the provided software program to perform the experiment. Make the appropriate connections now. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

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Work sheet 3

2

Fuel cell application II: Fuel cell car

D.9

Start-up Start each component as directed.

2.1

Hydrogen supply: To start your hydrogen supply, refer to sections A.8, A.9 or A.10 of the Component Descriptions, as appropriate for the supply you are using.

2.2

Electronic load EL200: Ensure the 10-turn potentiometer is set to zero. Then turn ON the toggle switch on the front panel.

2.3

FC50 software: You must use the provided software program to assist with this experiment. Start the FC50 software on your PC and select experiment C.9. Wait until the program requests you to press the FC50 START button. You will find instructions in section A.3 Fuel Cell Module FC50 under the heading “Start-up” and in section A.7 Control Software.

2.4

Fuel cell FC50: Ensure the fan control knob is at AUTO. Set the main switch to ON and press the START button. After completing a system test, the green OPERATION light comes on and the FC50 is ready for use. If an error occurs, the error code will appear in the H2 Flow display. You will find descriptions of the errors in section A.3 Fuel Cell Module FC50 under the heading “Error Messages and Causes”.

2.5

Voltage converter VC100: The module starts automatically. When voltage is applied at its input, a constant 12 V appears at the Available Power output. If no voltage is applied at its input, the internal battery provides 12 V at the Parasitic Load output.

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Work sheet 4

Fuel cell application II: Fuel cell car

D.9

3

Data acquisition

3.1

For these measurements, the fuel cell should be at a temperature of 40 °C. You can reach this temperature by loading the fuel cell for a few minutes with a current of approximately 5 A. Use the control software to set a load current of approximately 5 amperes. To further cause stack temperature to rise, set the FC50 fan power at 10%. After the temperature reaches 40 °C, the software switches off the EL200 and returns the fan power to AUTO. The system is ready for use.

3.2

The "FC50 software" now automatically runs through two different load profiles. As a basis for comparison, the system operates as long in each profile as it takes for the EL200 to consume 2500 Ws. Additionally the consumed hydrogen volume for each load profile is indicated. The first profile represents a constant load within the range of the efficiency optimum. For comparison a repeating changing-load cycle will execute, consisting of full load, partial load and no-load operation sections. The delivered power and the associated hydrogen flow rate can be seen in the diagram over the time. Both tabular values are additionally stored at 200 ms intervals in a measured value file. At the conclusion of both load profiles the hydrogen volumes used in each case and the performed electrical work of the table are appended. These data are the basis of the following evaluation.

3.3

If you are not making further measurements with the system, proceed to shut down and switch off the system as follows: •

On the EL200, turn the potentiometer to zero, set the toggle switch to OFF, and turn off the main power switch behind the front panel.

•

On the FC50, turn the fan control knob to AUTO and turn the main switch OFF.

•

Follow the correct procedure to shut down your hydrogen supply, as described in sections A.8, A.9 or A.10 as appropriate.

•

Remove the hydrogen supply from the FC50 by opening the quick-coupler.

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Work sheet 5

Fuel cell application II: Fuel cell car

D.9

4

Evaluation of the measured values

4.1

To evaluate the measurements open the tab-separated data file in a spreadsheet program such as MS Excel.

4.2

Compare the consumed hydrogen volume of both load profiles. What causes the differences, although about the same electrical work was performed?

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Work sheet 6

D.9

Using the spreadsheet program transfer the collected values to a diagram of the delivered electrical power Pdel and the hydrogen flow rate V&H 2 over the time t for a load change cycle. Describe and justify the processes of both characteristics.

35

700

30

600

25

500

20

400

15

300

10

200

5

100

0

0

Flow rate VH2 (ml/min)

Operation with a changing load

Delivered power Pdel (W)

4.3

Fuel cell application II: Fuel cell car

Time (s)

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Work sheet 7

4.4

Fuel cell application II: Fuel cell car

D.9

Compute the efficiency using the delivered (electrical) and supplied (hydrogen) power for each load range in the changing-load trial. Compare these values with the efficiency in the constant-load trial. In which load range does the different hydrogen consumption of each load profile become particularly clear? What saving potential exists here?

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Work sheet 8

4.5

Fuel cell application II: Fuel cell car

D.9

What are load profiles good for generally? Then consider in which connection the used load profiles in the automotive sector could to be used and justify your answer.

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Work sheet 9

Fuel cell application II: Fuel cell car

D.9

5

Comparison: Fuel cell – combustion engine

5.1

The fuel cell, in connection with an electric motor, represents a feasible replacement for the combustion engine (e.g. in the automobile). Describe the advantages of the combination of fuel cell and electric motor as against the combustion engine on the basis of energy transformation chains. Discuss the relevant efficiencies, to which the respective transformation chain is subject. Which advantages concerning the operating temperature result for the fuel cell?

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Work sheet 10

5.2

Fuel cell application II: Fuel cell car

D.9

With the use of fuel cells in motor vehicles the required fuels will change. List different storage possibilities for hydrogen and compare these with conventional fuels for combustion engines using characteristic data and suitable graphics. Volumetric energy density (kWh/L)

Fuel

Gravimetric energy density (kWh/kg)

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Work sheet 11

5.3

Fuel cell application II: Fuel cell car

D.9

On a fuel cell vehicle a fuel storage is to be specified so that the vehicle with a single tank filling can travel the same distance as a vehicle with combustion engine (gasoline) with 30 L of fuel in its tank . The overall efficiency of the fuel cell vehicle is 40 %, that of the vehicle with combustion engine 20 %. Compare the mass and volume of compressed gas, liquid gas and metal hydride storage for hydrogen, as well as a methanol tank, and the equivalent values of a gasoline tank. Discuss your result and then choose a suitable storage. Under which simplifications, related to the hydrogen reservoirs, did you perform the calculations and how does this affect the result? Fuel

Volume (L)

Mass (kg)

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Work sheet 12

5.4

Fuel cell application II: Fuel cell car

D.9

Compare the structure of the drive train of a fuel cell vehicle with that of a combustion engine vehicle. Which advantages result for the fuel cell vehicle?

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Work sheet 13

5.5

Fuel cell application II: Fuel cell car

D.9

A fuel cell vehicle is to be propelled with an asynchronous engine. How would you control the rotational speed and how could the power be delivered?

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