wind energy.pptx

8/13/2019 Wind Energy.pptx

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What is wind?

The uneven heating of the earths surface causes

wind. Simply, wind can be defined as moving air.

The winds energy has been used to do work

throughout history from moving sailboats to

generating electricity. Today, wind is harnessed primarily to generate electricity.


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Global winds At equator, a low pressure belt

is created because of strongsolar radiation. At the surface,this region is calleddoldrums .

The air cools until it reacheslatitudes of about 30degreeswhere it sinks back to thesurface, creating a high

pressure belt. Some are forced back towards

low pressure zone (tradewinds).


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generation of windThe wind, for examplethe shoreline breeze, isthe result of unevenheating of the earth bythe sun.

Sea Breezes, result of theseas ability to maintaintemperature.

Daytime land heats Sea iscool & ..

Nighttime land cools

faster than sea.


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Merits 1. The primary energy (wind) is cost-free;

2. The primary energy is renewable and never runs out;3.There is an abundant resource, nobody can cut access/supply.4. Stable life-cycle-cost of its use can be guaranteed;5. Wind power is competitive with other new power sources;

6. Operating wind turbines cause no carbon emissions, no air pollution and no hazardous waste;

7. No water for cooling is needed;8.Wind has a short energy payback of energy invested, normally

less than one year;9. There is a global, easy access to wind technology, compared to

nuclear and others;10. Time to market is very short, erection of entire wind farms

within one year possible;


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11. The project is environment friendly.12. Good wind potential to harness wind energy.

13. Operation and Maintenance (O&M) costs are low.14.No marketing risks, as the product is electrical

energy.

Photo Courtesy Burbo Bank wind farm (Photo:

Wind Power Works) UK


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Limitations of Wind energy

Low energy density. Favorable winds are available only in few

geographical location that is away from the citiesand forests.

Direction of wind changes it will never remainconstant.

Requires energy storage batteries or back updiesel power generator for constant availability ofthe power to load.


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Cont

Solar can be directly converted in to heat whilethe wind energy can be converted in tomechanical and then into electrical.

Wind farm locations are away from the cities thatis power generation medium.

Only in kW and MW range. Presently higher cost per MWh.


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World Wind power totalinstalled Capacity

Current CapacityOF RENEWABLE POWER IN INDIA

18,454.52MW 10.63%(Source: Electrical India)


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Estimated Wind power Potential in worldand INDIA


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Sr.No.

States of India Wind powergeneration in

MW

Sr.No.

States of India Wind powergeneration in

MW

1 Andhra Pradesh 5394 17 Maharashtra 5439

2 Arunachal Pradesh 201 18 Manipur 73 Assam 53 19 Meghalaya 44

4 Bihar 0 20 Mizoram 0

5 Chhattisgarh 23 21 Nagaland 3

6 Goa 0 22 Orrisa 910

7 Gujarat 10609 23 Punjab 08 Haryana 0 24 Rajasthan 5005

9 Himachal Pradesh 20 25 Sikkim 98

10 Jammu & Kashmir 5311 26 Tamil Nadu 5374

11 Jharkhand 0 27 Tripura 0

12 Karnataka 8591 28 Uttar Pradesh 137

13 Kerala 790 29 Uttaranchal 161

14 Madhya Pradesh 920 30 West Bengal 22

15 Lakshadweep 16 31 Andaman & Nicobar

2

16 Delhi 0 32 Others 0


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Newinstallations


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Wind Speed Classification ofThe Beaufort Wind Scale


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Wind turbine arts


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Parts

Anemometer : Measures the wind speed andtransmits wind speed data to the controller.

Blades : Most turbines have either two or three

blades. Wind blowing over the blades causes the

blades to "lift" and rotate.

Brake : A disc brake which can be appliedmechanically, electrically, or hydraulically to stop

the rotor in emergencies.


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Parts

Wind vane: Measures wind direction andcommunicates with the yaw drive to orient theturbine properly with respect to the wind.

Yaw drive: Upwind turbines face into the wind;the yaw drive is used to keep the rotor facing intothe wind as the wind direction changes.

Downwind turbines don't require a yaw drive, thewind blows the rotor downwind.

Yaw motor: Powers the yaw drive.


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Power and torque equations

P=Power developed byWind turbineT=Torque produced by

Wind turbine

Cp=The power-coefficient=Air density=1.225 kg/m 3 A=Area of wind turbine

blades in m 2

V=Velocity of WindT=Output torque N.m = Tip Speed Ratio

Tip Speed Ratio Number of blades

~6-7 2 ~5-6 3 ~2-3 5


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Derivation of Power

The kinetic energy in air of mass m moving with speed V isgiven by the following in joules:

The power in moving air is the flow rate of kinetic energy persecond in watts:

IfP = mechanical power in the moving air (watts), = air density (kg/m 3),A = area swept by the rotor blades (m 2), andV = velocity of the air (m/sec).


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The Energy Extracting Stream- tube of a Wind Turbine


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W HAT IS OUR GOAL ????

The maximum efficiency can be extract from thewind.

So we can categorized the entire scenario in three

cases: Case I: no wind no power and max wind

max power Case II: V passing through wind w/o hindrance

or thrust at that time.V=v=V =V 2

So how much power has been extracted???


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Case III: suppose the surface consists of verylarge power extraction like a wall so that V stopped over here. So power extracted isagain????

So in between this some value is there from

that maximum power can be extracted. Logically this phenomenon is called Axial

Interference Factor. a so if a=0 no

interference and a=1 complete blockage. So lets define v in terms of a and V . Try it????


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Defining a

So if defining a with different velocities;v = V (1-a)

Similarly putting value of v;

So power extracted is dropping of energy.)21(

)(21

)1(

2

2

aV V

V V aV


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In form of power

))21(1)(1(21

))21()(1(21

)(2

1

*21

23

222

22

2

2

aa AV P

aV V a AV P

V V Av P

v Av P

Simplify and Differentiate wrt a


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Power contained in windultimate maximum efficiency

Putting a = 1/3,

]2716[

21 3 Av P


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BETZ LIMIT FOR WT

No wind turbine could convert more than 59.2% of the kineticenergy of the wind into mechanical energy turning a rotor.


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Terms related to wind energy

Cut-in wind speed : the speed at which the wind turbinestarts to operate.Cut-out wind speed : is the wind speed where the windturbine stops production and turns out of the main wind

direction.Tip Speed Ratio : TSR is the speed of the blade at its tipdivided by the speed of the wind.The design wind speed : when the windmill reaches itsmaximum efficiency.The rated wind speed : when the machine reaches itsmaximum output power.


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Tip Speed Ratio (TSR)

By definition, TSR is the speed of the blade atits tip divided by the speed of the wind. For example, if the tip of a blade is traveling at100 mph (161 kph) and the wind speed is 20mph (32 kph or 9 m/s), then the TSR is 5 (100mph/20 mph). Simply put, the tip of the bladeis traveling five times faster than the speed ofthe wind.


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Importance of TSR

If the rotor of the windturbine spins too slowly, mostof the wind will pass straight

through the gap between the blades, therefore giving it no power! But if the rotor spinstoo fast, the blades will blur

(make or become lessdistinct) and act like a solidwall to the wind.


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How Do You Know The Perfect TipSpeed Ratio???

The optimum Tip Speed Ratio for maximum power output, this formula has beenempirically proven: (max power) = 4 / n

where n (n = number of blades)


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Wind Turbine Blade Aerodynamics:

Wind turbine blades are shaped to generate themaximum power from the wind at the minimumcost.

Primarily the design is driven by the aerodynamicrequirements, but economics mean that the bladeshape is a compromise to keep the cost ofconstruction reasonable.

In particular, the blade tends to be thicker thanthe aerodynamic optimum close to the root,where the stresses due to bending are greatest.


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No of Blades:

The limitation on the available power in the wind meansthat the more blades there are, the less power each canextract.

Narrow blade gives maximum aerodynamic efficiency Minimum solidity In practice the optimum solidity is low (only a few percent)

which means that even with only three blades, each onemust be very narrow


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How blades capture wind power


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Effect of angle of attack


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Twist of wind turbine blades

Typically the twist is around 0-20 from root to tip.


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Rotational speed of Turbine wheel

Depends on Tip-Speed ratio


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Power coefficient vs Tip speed ratio

Draw an involute of a circular arc whichsubtends an angle of 90o at thecentre of the circle of diameter 120 mm.


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Pitch Control & YAW CONTROL

Blade pitch control is the system which monitors and adjuststhe inclination angle of the blades and thus control the rotationspeed of the blades.Lower wind speeds the pitching system leads to an

acceleration of the hub rotation speed and at higher speeds blade pitch control reduces the wind load on the blades andstructure of turbine.Over a certain wind speed the blade pitch control starts torotate blades out of the wind, there by slowing and stoppingthe blade to avoid the complete damage.The wind turbine yaw mechanism is used to turn the windturbine rotor against the wind.The wind turbine is said to have a yaw error, if the rotor is not

perpendicular to the wind.


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Classifications


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According to size

Size in terms of determine the useful outputpower:

Small Scale (Up to 2kW) Medium size Machines (2-100kW) Large size (100kW and up)


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General types

HAWT:The propeller-type rotor is mounted on a horizontal axis.The rotor needs to be positioned into the wind direction

by means of a tail or active yawing by a yaw motor.

HAWTs are sensitive to the changes in wind direction andturbulence which have a negative effect on performancedue to the required repositioning of the turbine into thewind flow.The best locations for HAWTs are open areas withsmooth air flow and few obstacles.

l d b


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Horizontal Axis Wind Turbine(HAWT)

Advantages:

Higher efficiency due to variable blade pitch.

Consistent wind loading over the course of arotation reduces vibration and noise. Established manufacturing know-how and market

acceptability .


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Disadvantages

Increased costs of transporting tall towers and long blades. Installation requires very tall and expensive cranes and

skilled operators. Massive tower and heavy foundation to support blades,

gearbox, and generator. Complex design of twisted blades is difficult and

expensive to fabricate. Large size may disrupt the landscape and create local

opposition. Requires yaw control to turn the blades and nacelle

toward the wind. Difficult, expensive, and frequent maintenance

required.

H i l i i d i


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Horizontal axis using two aerodynamic blades

Rotor drives generator to step upgear box.

Rotor is usually designed fordownwind of the tower.

The rotor blades are continuouslyflexed by unsteady aerodynamics,

gravitational and inertia loads. Tail vane is required for balancing

the force.


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l ll


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Horizontal axis propeller typewith single blade

A blade is mounted on rigid hub.Induction generator and gear

box are shown. To reduce the rotor cost use of

low cost counter weight isrecommended which balance

the long blade centrifugally.


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One blade rotating veryfast can essentially

extract as much energyfrom the wind as many

blades rotating slowly.

A wind turbine withone blade would saveon material; however, acounter weight isneeded for balance.


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Horizontal axis multi bladed type

These type of design is made ofsheet of metal or aluminum.The rotors have high strength toweight ratios.

They have higher startingtorque and good power co-

efficient.


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VAWTVertical axis wind turbines VAWTs aretypically developed only for the urbandeployment.Changes in wind direction have fewernegative effects on this type of turbine becauseit does not need to be positioned into the winddirection. However, the overall efficiency of

these turbines in producing electricity is lowerthan HAWTs.


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Shape v/s dragco-efficient

Vertical Axis Wind Turbine


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Vertical Axis Wind Turbine(VAWT)

Smaller tower structure, since lower bearings are mounted nearthe ground.

The generator and gearbox are installed near the ground. Suitable for low speed winds, due to lower wind start up speed.

May be built at locations where taller structures are prohibited. Can take advantage of locations where landscape increases wind

speed near the ground. May have a lower noise signature.

Needs less space than HAWT to generate the same amount of power.

Straight blades are much easier and economical to fabricate orextrude.

Lower overall maintenance and transportation costs.


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Disadvantages

Lower aerodynamic efficiency compared toHAWT.

Blade fatigue failure due to change in stresssign during each revolution.

May require dismantling the entire structure tofix the generator or gearbox.


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HAWT v/s VAWT

Most wind turbines built at present have a horizontal axis. The vertical axis Darrieus machine has several advantages. First of all, it is omnidirectional and requires no yaw

mechanism to continuously orient itself toward the winddirection. Secondly, its vertical drive shaft simplifiesthe installation of the gearbox and the electrical generatoron the ground, making the structure much simpler. On the

negative side, it normally requires guy wires attached tothe top for support.


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This could limit its applications, particularly for theoffshore sites. Overall, the vertical axis machine hasnot been widely used because its output power cannot

be easily controlled in high winds simply by changingthe blade pitch. With modern low-cost, variable-speed power

electronics emerging in the wind power industry, the

Darrieus configuration may revive, particularly forlarge capacity applications.

HAWT Suitable for both small and large systems and


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HAWT Suitable for both small and large systems andmost commercial wind turbines are HAWT.

Advantages: High wind speed at a greater height, Highefficiency

Disadvantages: Complex system, High installation cost forlarge systems (Generator and gearbox installed on top oftower) (control ckts, panels etc)

VAWT Suitable for small systemsAdvantages: Gearbox and generator can be placed on the

ground; Do not need a yaw system to turn the rotor

against windDisadvantages: Wind speed is low near the ground, Low

efficiency; May need guy wires to hold the turbine, anddifficult maintenance.


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Savonius rotor

The Savonius wind turbine, invented by S.J. Savonius, is

a vertical axis machine consisting of two half cylindrical

(or elliptical) blades arranged in S shape. Convex side ofone of the half cylinder and the concave side of the other

are facing the wind at a time.

The drag coefficient of a concave surface is more than the

convex surface.


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Being drag machines, Savonius rotors have relatively

lower power coefficient.

However, some experimental rotors have shown power

coefficient up to 35 percent. These rotors have high

solidity and thus high starting torque. They work at low tip speed ratios, with the maximum of

about 1. They are very simple in construction-even can be

made from oil barrels cut in two halves lengthwise.

Hence they are preferred for high torque-low speed

applications like water pumping.


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Characteristics

Self starting Low speed Low efficiency


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Advantages As it is vertical axis it direction of the wind doesnt

matter. Machine performs on the low wind speeds too. Low cut in speed and produce power effectively in

wind as slow as 8 km/hr. Cost of the wind turbine is lower compared to standard

wind turbine. Simple structure and hence easy to manufacture. Yaw and pitch control are not needed to bring into the

wind or operate at high speeds. Ground level mounting Overall weight of the turbine.


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Disadvantages

This type of machine is too solid having somuch metal or other material surface comparedwith the amount of wind intercepted. Weight is

excessive. It is not useful for a very tall installation

because a long drive shaft problems and also

bracing of the topmost bearing above the rotorof very tall vawt is awkward.


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Darrieus type rotor / wind machine


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Darrieus type rotor / wind machine The term Darrieus describes a class of Vertical Axis

Wind Turbines (VAWT) that is powered by the phenomenon of lift. This class consists of two types ofturbines, eggbeater -type .

This lift is created because of the airfoil shape of theturbines blades. These blades cut through the air withan angle of attack to the wind causing a pressure

differential. The resulting pressure differentials cause aforce called lift, which propels the blade forward.

The Darrieus has several attractive features


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The Darrieus has several attractive features.One is that the machine rotates about a vertical

axis, hence does not need to be turned into thewind. Another is that the blades take the shape of a

jumping rope experiencing high centrifugalforces. This shape is called troposkein, fromthe Greek for turning rope.

Since the blade operates in almost puretension, a relatively light, inexpensive blade issufficient.


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Another advantage is that the power train,generator, and controls are all located nearground level, hence are easier to construct and

maintain. The efficiency is nearly as good as that of the

horizontal axis propeller turbine, so the

Darrieus holds considerable promise as a costeffective turbine.


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One disadvantage of the Darrieus is that it isnot normally self starting. That is, if theturbine has stopped during a period of low

wind speeds, it will not usually start when thewind speed increases. Starting is usually accomplished by an

induction motor connected to the local utilitynetwork. Not the disadvantage once it isstarted it works as induction generator.


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Darrious rotors are lift devices andcharacterized by the curve of the airfoil crosssections.

Characteristics: Not self starting High speed High efficiency Potentially low capital cost


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Site Selection

Understand Your Wind Resource Wind speed Optimum power generation

High annual average wind speed survey of historical data contour maps of terrain and wind are consulted potential sites are visited best sites are instrumented for approx 1 year choose optimal site.


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wind energy.pptx

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