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WIND ENEGRY

Introduction

Nature of Wind

Energy and Power in the Wind

Forces on the Blades and Trust

on the Turbine

Aerodynamics of Wind turbines

Basic Components of WECS

Horizontal Axis Wind Turbines

Vertical Axis Wind Turbines

Performance of Wind Turbines

Environmental Impacts


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INTRODUCTION

Wind power

Fastest growing renewable energy technology

Propelling ships ,pumping water, irrigation, milling grains Clean, safe, pollution free Indirect solar electric technologyWind power

All renewable energy (except tidal and geothermal power),ultimately comes from the sun

The earth receives 1.74 x 1017 watts of power (per hour) fromthe sun

About one or 2 percent of this energy is converted to windenergy (which is about 50-100 times more than the energyconverted to biomass by all plants on earth


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Wind-Turbine Generators Functional similar to steam and gas turbines to generate

electricity Wind energy conversion system (WECS) Aero generators (turbine/generator combination) Very small 0.5-1 KW Small 1-15 KW Medium 15-200 Large 250-1000 KW Very large 1000-6000 KW

A largest wind generator built 800 kW unit operated in France Flexible 3 blades propeller - 35 m in diameter Produced rated power in a 60 km/hr wind with rotation speed of

47 rpm. Wind energy is one of Americas greatest natural resources. Netherland & Denmark Wind mill - NAL Bangalore, CSMCRI, Bhavnagar CAZRI, Jodhpur


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Nature of Wind Wind results from air in motion arises from pressure gradient

Local winds are caused by two mechanism.Differential heating of land and water.Due to hills and mountains

2% of all solar radiation falling on the face of the earth isconverted to K.E. in the atmosphere.

30% of K.E. occurs in the lowest 1000m of elevation.

Solar radiation heats the air near the equator and this low densityheated air is buoyed up.

At the surface it is displayed by cooler more dense higher pressureair flowing from the poles

In the upper atmosphere near the equator the air thus tends to flowback toward the pole and away from the equator

The net resultant is a global convective circulation with surfacewinds from north to south in northern hemisphere


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Energy and power in the wind

Conversion of the KE of the wind into mechanicalenergy that can be utilized to perform useful workor to generate electricity

When the wind blows against the vanes or blades,

they rotate about the axis and the rotation motionthat can be made to perform useful work .

Wind energy power depends on

1. Wind speed

2. Cross-sectional area of the windswept by the rotor3. Conversion efficiency of the rotor, transmission

system and generator


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Wind machines intended for generating substantial amount ofpower should have large rotor and be located in the area of

high wind speeds.


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Unlike the old-fashioned Dutch windmilldesign, which relied mostly on the wind's

force to push the blades into motion, modern

turbines use more sophisticated principles

to capture the wind's energy most effectively.

The two primary aerodynamic forces at

work in wind-turbine rotors are lift whichacts perpendicular to the direction of wind

flow; and drag which acts parallel to the

direction of wind flow.

TURBINE AERODYNAMICSWhen fluids passes through an inclinedstreamlined body, it is subjected to lift

and drag forcesD, drag forces parallel to flowL, lift forces perpendicular to flow


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LIFT & DRAG

Primary mechanisms for producing forces from wind Lift forces are perpendicular to the air flow.

Drag forces act in the direction of flow.

Lift forces are produced by changing the velocity of the air streamflowing over either side of the lifting surface

Due pressure drop- change in velocity The pressure difference produces a forces that begins to act on the high

and moves towards the low pressure side of the lifting surface which iscalled aerofoil.

Good aerofoil has high lift /drag ratio

Stalling phenomena

drag more than the lift. Magnus effect- spinning a cylinder in air stream at high speed of rotation


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Basic components of a wind energy

conversion system (WECS)

Aero generator: Consist of Wind turbine Or rotor

Wind mill head

Transmission and control

Supporting structure


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Rotors

Horizontal axis rotorVertical axis rotor

Wind mill head: supports the rotor , housing the rotor bearing

Transmission: Normally blade rotates 40-50rpm but generator requires1800rpm. Transmission increase the rotor speed to generator speed

Generator: constant speed, synchronous and permanent magnet types.

Controls: It has following componentsa)sensormechanical , electricalb)decision elements-relays ,analog circuit, microprocessorc)actuators-hydraulic ,electric

towers: reinforced concrete towerpole tower

shell tube towerTruss tower-widely adaptable, low cost


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Classification of Wind Turbine

horizontal axis machinesvertical axis machinessize: small size up to 2kW)-farms

Medium size(2-100kW)-residenceLarge size(100kW)-power grid

DC out putAC outputconstant speedVariable speed


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Wind energy collectors (aero generator)

A wind mill is a machine for wind energy conversion,a wind turbine converts the K.E of wind motion tomechanical energy transmitted by the shaft andgenerator further converts it to electrical energy .

Aero generator: turbine and generator

Two types - horizontal axis type - vertical axis type

Horizontal axial machine-sub-classified into

Single blade , Multi blade


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Horizontal axis using two aerodynamic blades

Rotor drives a generator through step-up

gear box.

Components are mounted on a bed oftower.

Because of light cost of blade rotor, more

than two blades are not recommended.


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Horizontal Axis propelled type usingsingle blade

Long blade is mounted on rigid hub. Ithas induction generator and gear box toreduce rotor cost, low cost counterweight is recommended for balancing.

Advantages of one blade rotorLower blade with and cost, lower gearbox cost.Counters wt cost is less than a secondblade

DisadvantagesVibration produced due to aerodynamictorqueUn conventional appearanceLarge blade root bending moment


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Horizontal axis multiblade type

Blades are made from sheet metal or aluminum

Rotor has high strength to weight ratio

Good power coefficient high starting torque

simplicity , low costHorizontal axis wind mill Dutch type

Blade surface are made from an array of wooden

slats.


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Sail typeThe blade surface are made fromcloth, nylon or plastic are

arranged as sail wingsHorizontal axis types generallyhave better performance. Theapplications are inElectric power generatorPumping water


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VerticalAxis machines

Savonious or S type rotor (low velocity wind)

Darrious type rotor (high velocity wind)

Vertical axis machines are of simple design as compared tohorizontal axis type.

Advantages of vertical type

They will react to wind from any direction and therefore doesnot need yawing equipment to turn rotor into wind

It requires less structural support since the gear box andgenerator are located at the ground level .

The rotor is not subjected to continuous cyclic gravity load.


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Savonius rotor Works like a cup anemometer

It requires low velocity winds

Two semi circular drums are mounted on a verticalaxis on a vertical axis perpendicular to winddirection.

Characteristics

Self starting

Low speed

Low efficiency


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Advantages

Elimination expressive power transmission system

Produce power effectively even at low wind speed 8km/hour Cost is lower

It has simple structure

Since generator ,gearbox at ground level, easy access formaintenance

Disadvantages

It is not useful for tall installation, because a long drive shaftproblems.


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Darrieus type machine It has two or three thin curved blades with aerofoil

cross section and constant chord length

both end of the blades attached to vertical shaft.

Shaft torque is transmitted to generator for power generator

Characteristics

High speed

High efficiency

Potentially low capital cpst

Advantages

The rotor blades can accept the wind fromany direction

It eliminates yaw control requirement for its rotor

to capture wind energy

Disadvantages

Efficiency is lower than conventional horizontal rotor

Vibratory stresses are encountered which will affect the rotor life


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Performance of wind machines

The parameter involve in estimation of performance :

Power coefficient Tip speed ratio

Solidity

Power coefficient cp = power extracted by rotor/power available in the wind

= Tip- speed ratio =blade speed/

free stream wind speed

=R/Vi R is the tip radius

is the angular velocity

solidity =blade area /

swept frontal area (face area)


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Environmental effects

Environmental benefits of electricity generation by wind energy:-

The generation of electricity by wind turbine does not involve the release of

Carbon dioxide (or) pollutants

Acid rain

smog

radioactive contaminationsIt does not require consumption of water supply

Environmental impacts of wind turbines:

Possible impacts are

Noise

Electromagnetic interference

Mechanical noise due to mechanical or electrical equipment (gear box,generator)

Aerodynamic noise due to interaction of air flow with the blades

El t ti I t f


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Electromagnetic Interference

When the turbine is positioned between thetransmitter and receiver, some of the

electromagnetic radiation can be received signal tobe distorted significantly . This interference dependsmainly on turbine blade materials and surface shapeof tower.


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Problem 1Wind at 1 standard atmospheric pressure and 15 degree C has velocity

of 15 m/sec calculate:a) The total power density in the wind stream

b) The maximum attainable power densityc) A reasonable obtained power densityd) The total powere) The torque and axial trustThe turbine has diameter of 120m , speed 40 rpm at maximumefficiency

Air density =1.226kg/m3 from given p R and T, =

a)total power in the wind stream Ptot=AVi3/2

power density =Ptot/A =Vi3/2 =1.226x153/2 = 2068.87W/m2

b)maximum Power density=Pmax/A=(8/27)Vi3

=8/27x1.226x153

=1226W/m2

RT

p

)15273(287

100132.15

x

x


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c) assume = 35%

Power density, P/A = (Ptot/A)= 0.35x2068.87 =724 w/m2

d) Total power P = power density x Area= 724x (/4)D2= 724x(/4)x(120)2

=8184 kwe) Torque at maximum efficiency:

Tmax= (2/27)(DVi3/N)

=2/27x(1.226x120x153/(40/60))

=55.17kNd) Total power P = power density x Area= 724x (/4)D2= 724x(/4)x(120)2

=8184 kwe) Torque at maximum efficiency:

Tmax= (2/27)(DVi3/N)

=2/27x(1.226x120x153

/(40/60))=55.17kN

Maximum axial thrustFx,max=/9 D

2Vi2

= /9x1.226x1202x152

=1385.87kN


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Problem:A wind mill with multiblade lifts 3.03 m3/hr ofwater through a head of 28 m when the wind speed is3.3 m/s. Calculate the power coefficient for a rotordiameter of 9 m. Assume transmission efficiency as0.95 and pump efficiency as 0.70

Ideal power needed to pump the water P = QgH

= 1000x(3.03/3600)x9.81x28 =231.19 watt

Power required at rotor efficiency=231.19/overall = 231.19/(.95x.70) =347.65

watt

P tot = AVi3 = =1370.92 watt

Power Coefficient = power required at rotor/ P tot

= 347.65/1370.92 = 0.253


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Date post:	04-Apr-2018
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