Chapter 10 Powerpoint

Energy for Sustainability Randolph & Masters, 2008 Chapter 10: Decentralized Energy Systems

Distributed generation technologies and electricity storage systems can be owned and operated by customers or the utilities that serve them.

100

Relative Carbon Emissions, compared to Coal

100 Relative Carbon Emissions (%)

90

79

80 70 60 50

34

40

23

30

19

20 10 0

AVERAGE AVERAGE COAL COAL 33% eff

BEST BEST COAL COAL 42% eff

N. GAS N.COMB-CYCLE GAS CC 49% eff

N. GAS, CHP N. GAS CHP N. GAS N. GAS CC SIMPLE-CYCLE COMB-CYCLE CHP CHP 30% Elect eff 41% Elect eff 49% Thermal eff

44% Thermal eff

Demand Side Management 1. Conservation/energy efficiency programs that have the effect of reducing consumption during most or all hours of the day. 2. Load management programs that have the effect of reducing peak demand through conservation or by shifting the demand to nonpeak hours. 3. Fuel substitution programs that encourage a customer to replace electricity with another energy source. For example, replacing a standard air conditioner with one based on absorption cooling can shift the load from electricity to natural gas.

Energy storage is an emerging load management strategy. Storage can absorb power during periods of low demand in order to provide it during peak periods. 45

Original load curve

Discharge storage

40

System load (GW)

35

Charge storage

30 Leveled load

25 20 15

Night time

Daytime

10 5 0 0 MN

66 am

12 Noon

618pm

24 MN

A vanadium redox battery energy storage system seems well suited to stationary applications such as power line voltage and power support

A Duracell in the Desert: The Castle Valley VRB Project

Battery Energy Storage, Castle Valley, Utah (www.vrbjpower.com)

Feeder power with and without battery storage

180 180

Battery Energy Density

Energy Density (Wh/kg)

160 140 120

90

100 80 60

35

45

40 20 0

Pb-acid

NiCd

NiMH

Li-ion

Current lithium-ion batteries have energy densities a little below 200 Wh/kg, but future materials may make much higher densities possible e(-) Load (+)

Cu contact Li anode Polymer electrolyte LiMOX cathode Cu contact

Anode (­):         Li  → Li+ + e− Cathode (+):      Li+ +   e− + Lix CoO 2 →Li1+x CoO 2      current   <<  300 Wh / kg                            Li+ + 2e− + Lix NiO 2 →Li1+x NiO 2         future?   <  540 Wh / kg                            Li+ + 3e− + Lix CrO 3 →Li1+x CrO 3         future?    <  700 Wh / kg

Plug-In Hybrid Vehicle: simply add an extra battery bank

Retrofit packages: Hymotion

PHEV offer certain advantages  With greater use of the electric drive, the vehicle

uses less gasoline and is more efficient than conventional HEV on a mpg of gasoline basis. Some PHEV Prius retrofits have achieved 100 mpg over 1000 miles of travel.  With greater use of the electric drive in city driving, the PHEV is a zero emission vehicle (ZEV) that can reduce emissions and improve urban air quality.

All Electric Vehicles

The Tesla Roadster

Electric Drive Vehicles: Gas-equivalent “Price per Gallon” and CO2 Emissions

One-quarter the cost of gasoline (at 10¢/kWh, $3/gal) One-half the CO2 emissions as gasoline (at average U.S. electricity sources: 52% coal)

Where do you get the electricity?  Vehicles charged at night by grid power during

off-peak hours  Plug-in Vehicles can enhance Distributed

Renewable Generation Your PV garage roof is your filling station  Night-time demand provides a market for grid wind power or other intermittent generation. 

Typical electricity system load in California showing impacts of night charging for electric vehicles with fraction of total vehicle miles provided by electricity as a parameter. Based 3 miles/kWh and 280 billion vehicle-miles/yr. 45 40 System load (GW)

40% vehicle-miles EV 35 20% EV 30 No EVs 25 20 15 0 Noon

66 pm

12 MN

18am 6

24 Noon

The PV Garage could easily charge a vehicle for 30-45 all-electric miles per day

A vehicle-to-grid system would require careful control and accounting to manage large numbers of vehicles supplying high-value, quick response grid services

Residential 120V/240V electrical system

Reading Your Electric Meter

kWh dials

Rotating Disk 7.2 Wh/ Revolution

Electricity Rates Inverted Tier 1 0 - 255 11.43

kWh ¢/kWh

Tier 2 256-331 12.99

Tier 3 332 - 510 17.81

Tier 4 > 510 kWh 21.94

Time-of use rates On Peak Off Peak

SUMMER: May - October 2 - 8 pm 29.4 ¢/kWh All other times 8.7 ¢/kWh

WINTER: Nov - Apr 7-10 am, 5-8 pm 11.5 ¢/kWh All other times 9.0 ¢/kwh

Demand Charges

Energy charge Demand charge

General Service < 7500 kWh/mo 6.56 ¢/kWh

Medium Service > 7500 kWh/mo 2.60 ¢/kWh

-

$11.85 /mo-kW

Medium Service TOU Rate 2.32 ¢/kWh $13.20/mo-kW ON PEAK $3.87/mo-kW OFF PEAK

Net-metering for Grid-Connected Systems  “Bank” excess energy with the local utility  Meter spins backward; customer receives full

retail value for each kWh produced  Net excess generation (NEG) credited monthly or annually

Synchronous Inverter

Utility

Utility

Buy

Sell

Buy

Sell

Customer (a) Ratcheted meters • •

Customer (b) Net metering

Ratcheted meters allow different prices for selling and buying electricity; with net metering a single meter runs in either direction

Cogeneration: aka Combined heat and power (CHP) Micro- gas turbines with heat recovery

Basic configuration for a PEM fuel cell

Stationary Fuel Cell System Clean exhaust Natural gas

Useful heat

H2 Fuel Processor (reformer)

DC Power Fuel Cell Stack

AC Power Power Conditioner

Steam Air

A complete fuel cell system consists of a reformer to produce hydrogen-rich fuel, the fuel cell stack itself, and a power conditioner to convert dc to ac

One way to provide reliable electric power from a renewable source such as wind or solar is with a reversible fuel cell with hydrogen storage