Wind.pdf

WIND ENERGY Dr.K.Ravi

HOW WIND IS GENERATED? • Wind is caused by the uneven energy distribution and rotation of the Earth.  Heat  Pressure gradients  Motion

Wind generation

• Wind is air in motion and derives from solar radiation. • About 2% of the total solar flux that reaches the earths surface is transformed to wind energy due to uneven heating of the atmosphere. • During daytime the air over the land heats up faster than the air over the oceans. • Hot air rises and expands while cool air from oceans Rushes to fill the space creating local winds.

Day time Night time

 Then in China wind mills were used to raise water for irrigation and sea water for production of salt.  In 1854 Daniel Halladay in US introduced a wind pump and used for irrigation and industrial applications.  In 1880 P. La’cour used wind mill as a source of electricity.  In 1929 French engineer Darreius built an aero generator.  In 1974 NASA constructed and operated a wind generator of 100kW capacity.  In 1987 US firms generated a 2.5MW generator

CLASSIFICATION OF WIND TURBINES 1.Based on alignment of rotor axis(depending upon the orientation of the axis of rotation of their rotors).

Horizontal axis turbine  Rotor axis is kept horizontal and aligned parallel in the direction of wind speed.

Vertical axis turbine  Rotor axis is kept vertical and aligned perpendicular in the direction of wind speed.

• Vertical-Axis Wind Turbines

• Vertical-Axis wind Turbines

Advantages o Omni-directional - Accepts wind from any direction o Components can be mounted at ground level - Ease of service - Lighter weight towers

o Can theoretically use less materials to capture the same amount of wind

Disadvantages o Rotors generally near ground where wind is poorer o Poor self-starting capabilities o Requires support at top of turbine rotor o Requires entire rotor to be removed to replace bearings o Overall poor performance and reliability

Horizontal -Axis wind Turbines HAWA

2.Based on the force utilised  Lift type wind turbine  Drag type wind turbine • Forces are transmitted from a moving fluid to an object in the flow stream Lift = the force component perpendicular to the original flow direction Drag = the force component in line with the original flow direction

α = low

DRAG TYPE

α = medium <10 degrees

α = High Stall!!

LIFT TYPE

DRAG TYPE

LIFT TYPE

Low speed turbines

High speed turbines

Rotor shaft torque is comparatively high which is of prime importance for mechanical applications such as water pumping

Rotor shaft torque is comparatively low . Electric power generation ,shaft of the generator requires to be driven at high speed

Greater blade area is required

Aerofoil type blades are required to minimize the effect of drag forces

Blades are fabricated using curved plates

Blades are having high thickness to chord ratio to produce high lift

Drag Design • For the drag design, the wind pushes the blades out of the way. • Drag powered wind turbines are characterized by slower rotational speed and high torque capability. • They are useful for the pumping, sawing or grinding

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LIFT Design • •

The blade is essentially an airfoil, or wing More efficient than drag device

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When air flows past the blade, a wind speed and pressure differential is created between the upper and lower blade surfaces.

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The pressure at the lower surface is greater and thus acts to "lift" the blade.

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When blades are attached to a central axis, like a wind turbine rotor, the lift is translated into rotational motion.

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Lift-powered wind turbines have much higher rotational speeds than drag types and therefore are well suited for electricity generation.

Terms Related to Wind Power

α V

Terms Related to Wind Power

Terms Related to Wind Power

Terms Related to Wind Power

Terms Related to Wind Power

Terms Related to Wind Power

Terms Related to Wind Power

Terms Related to Wind Power

by

Terms Related to Wind Power

Airfoil Shape Just like the wings of an airplane, wind turbine blades use the airfoil shape to create lift and maximize efficiency.

The phenomena

Angle of attack • • • • • • •

Angle of attack is the angle between the chord line of the airfoil and the free stream direction . Angle of attack has a large effect on the lift generated by an airfoil. Blade: extract wind energy Leading edge: front edge of the blade that faces towards direction of wind flow Trailing edge; Rear edge of the blade that faces away from the direction of wind flow Chord line: The line joining the leading edge and trailing edge. Camber; max distance between mean line and cord line which measure the curvature of airfoil

Angle Of Attack (blade angle)

Pitch angle: angle between the blade chord and the plane of the blade rotation. Swept area -area covered by the rotating rotor. Nacelle: The nacelle houses the generator, gear box, hydraulic system and yawing mechanism.

Twist & Taper • Speed through the air of a point on the blade changes with distance from hub • Therefore, tip speed ratio varies as well • To optimize angle of attack all along blade, it must twist from root to tip

Fastest Faster Fast

Tip-Speed Ratio ΩR

• Tip-speed ratio is the ratio of the speed of the outer blade tip to the speed of the undisturbed natural wind speed. • There is an optimum angle of attack which creates the highest lift to drag ratio. • Because angle of attack is dependant on wind speed, there is an optimum tipspeed ratio

ΩR TSR = V Where, Ω = rotational speed in radians /sec

R = Rotor Radius V = Wind “Free Stream” Velocity

R

Performance Over Range of Tip Speed Ratios • Power Coefficient Varies with Tip Speed Ratio • Characterized by Cp vs Tip Speed Ratio Curve

Capacity Factor

Tip Speed Ratio

Multiblade and savonius type rotors have low value of TSR while Propeller and darries have TSR from 3 to 7. Max value of Cp under ideal conditions is 0.593(Bitz limit)

Betz Limit All wind power cannot be captured by rotor or air would be completely still behind rotor and not allow more wind to pass through. Theoretical limit of rotor efficiency is 59% Most modern wind turbines are in the 35 – 45% range

Rotor Solidity Solidity :- is the ratio of blade area to circumference of the rotor. Low solidity (0.10) = high speed, low torque

Nb  2R N  no of blade b  blade width

R a

A

High solidity (> 0.80) = low speed, high torque

Solidity = 3a/A

Yawing – Facing the Wind • Active Yaw (all medium & large turbines produced today, & some small turbines from Europe) • Anemometer on nacelle tells controller which way to point rotor into the wind • Yaw drive turns gears to point rotor into wind

• Passive Yaw (Most small turbines) • Wind forces alone direct rotor

• Tail vanes • Downwind turbines

3. Based on generation Small (10 kW) • Homes • Farms • Remote Applications (e.g. water pumping, telecom sites)

Intermediate (10-250 kW) • Village Power • Hybrid Systems • Distributed Power

Large (250 kW - 2+MW) • Central Station Wind Farms • Distributed Power

Kid Wind Proj ect | www .kidw

WIND TURBINEMAIN COMPONENTS

Wind Farms

DIFFERENT TYPES OF ROTORS Multiblade Type Propeller Type Savonious Type Darrieus type

MULTIBLADE TYPE ROTOR • • • •

Sheet metal blades. Width of blade increases outward. Blade is fixed at inner and outer end. No. of blades 12-18.

PROPELLER TYPE • • •

2 or 3 aerodynamic blades. Blades made od fibre glass reinforced plastic. Diameter of rotor 2-25 m.

SAVONIOUS TYPE •

• •

•

It has 2 or more identical hollow semi cylinders fixed to vertical axis. Rotor rotates due to pressure difference Driving torque is drag type, so large starting torque. Suitable for water pumping.

DARRIEUS TYPE • • • • •

2 or 3 thin curved blades. Both end of blade attached to vertical shaft. Operates for wind from any direction. Driving force is lift torque. Used for electricity generation.

IMPORTANT TERMS RELATED TO WIND TURBINE • • • •

Rotor Blades Hub Propeller

• Leading edge • Trailing edge • Chord line

Aerofoil shape of blade

• Mean line • Angle of attack • Pitch angle

WIND ENERGY EXTRACTION  Extract energy from wind stream by converting the KE of wind to rotational motion required to operate an electric generator.  On interaction of free wind on turbine rotor, the wind transfers part of energy into rotor and speed of wind reduces.

AERODYNAMIC OPERATION OF WIND TURBINE Airfoil:Cross section of wind turbine blades Lift:Pressure difference between top and the bottom surface of blade result in a force called aerodynamic lift that cause airfoil to rise. This lift cause rotation of blade about the hub Drag:A Force perpendicular to lift force also act on blades which impede the blade rotation .this force is called drag force.

WIND POWER Power in the Wind = ½ρAV3 Effect of air density,  Effect of swept area, A Effect of wind speed, V

Swept Area: A = πR2 Area of the circle swept by the rotor (m2). • Wind power would increase four times if rotor diameter is doubled. • Wind power increases eight times if wind speed is doubled.

R

 More wind speeds  Less noise pollution  Less visual impact  Difficult to install and maintain  Energy losses due long distance transport

TURBINE DESIGN AND CONSTRUCTION

Blades: Important part that extract wind Energy Light weight and good strength Fabricated with aircraft industry technique. Made of Fiberglass reinforced polyester Structured for creating optimum lift. Rotor: Combination of blade and hub assembly Pitch control of blades: A system where the pitch angle of blade changes according to the wind speed for efficient operation Brakes: Aerodynamic and Mechanical braking are used for over speed protection , speed control , power control and emergency stop. Low speed shaft: shaft connected directly to rotor to the gear.

Gear box:  Mechanical power generated by rotor blade is transmitted to the generator through two stage gear box  Provided for increasing shaft speed. Generator:  Used for converting mechanical power to electric power.  Commonly used generators are PMSG,SEIG,DFIG. Controller:  Microprocessor based controller monitor wind speed , direction of wind , power output and take proper yaw , pitch rotations. Anemometer & wind wane:  Used for wind speed and direction monitoring. Nacelle:  Housing of generator, the gear box, yawing mechanism,etc.

High speed shaft:  Shaft connected between gear box and generator Yaw drive and yaw motor :  Yawing is done using two yawing motors meshed with big toothed wheel mounted on tower.  Yaw control continuously tracks and keep rotor axis in wind direction.  At high wind machine is stopped by turning the rotor axis right angle to wind direction.

Tower:  Modern turbine are mounted on tubular towers

MODES OF WIND POWER GENERATION 1) Standalone mode 2) Backup mode like wind diesel 3) Grid connected mode

STANDALONE MODE

 Decentralized application of wind energy  Individual consumer install their own wind turbine  Used for powering domestic appliances battery charging, water pump etc.  Capacity ranges between 2.5—5Kw  Most suited for remote mountainous areas.

BACK UP MODE LIKE WIND-DIESEL

 DG is used for maintaining 24 hrs. power supply ,since wind power is intermitted  Used in areas in accessible to grid, hospitals, military installations

GRID CONNECTED WIND TURBINE GENERATORS

 Generated power is distributed among nearby customers and excess power exported to grid.  Electric energy is purchased from grid when there is no wind

Energy Production Terms • Rated Power : Maximum power the generator can produce.

• Cut-in wind speed where energy production begins

• Cut-out wind speed where energy production ends.

Typical Power Curve Cut-in: 3-4 m/s Rated: 12-25 m/s

Cut-out: 25 m/s

WIND POWER GENERATION CURVE

Cut in Speed: It is the wind speed(14m/s) at which the turbine output begins. Rated Speed: It is the Speed at which the turbine is designed to generate rated power Cut out Speed: When the speed reaches upper limit (25m/s) the turbine stops to generate power

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Renewable source of energy

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Free of fuel cost

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Supply power to remote areas

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Public opinion is in favor of wind power generation rather than nuclear generation

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Cost effective

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Economically competitive with other modes of generation

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Reliable and has been used for ages

DISADVANTAGES OF WIND ENERGY SYSTEM

 Low energy density.  Available at selected graphical location.  Wind speed being variable , wind energy is irregular.  Wind turbine design is complex.  Requires storage batteries which contribute environmental pollution.  Capital intensive.

REFERENCES 1. Renewable Energy Sources And Emerging Technologies, D.P Kothari,K.C Singal,Rakesh Ranjan 2. www.renewableenergyworld.com.

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