fundamentals wind

8/10/2019 Fundamentals Wind

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Fundamentals of Wind Energy

E. Ian Baring-GouldSenior Engineer

National Wind Technology Center National Renewable Energy [email protected]


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TOPICS

IntroductionEnergy and Power Wind CharacteristicsWind Power PotentialBasic Wind Turbine TheoryTypes of Wind TurbinesBasic Wind Turbine CalculationsFurther Information


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What is Wind Power 800-900 years ago,in Europe

140 years ago,water-pumpingwind mills

70 years ago,electric power

1400-1800 years go,in the Middle East

The ability toharness the poweravailable in thewind and put it touseful work.


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ENERGY AND POWER

ENERGY: The Ability to do workENERGY = FORCE * DISTANCE

Electrical energy is reported in kWh and maybe used to describe a potential, such as instored energy

POWER: Force without timePOWER = ENERGY / TIMEGenerator Size or an instantaneous loadwhich is measured in kW


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P = 0.5 v 3P: power, Watt

density of air, kg/m 3

V: wind speed, m/s

We call this the Wind Power Density (W/m 2)If we include the area through which thewind flows (m 2), we get the collectable power

in Watts.

Power in the Wind
http://localhost/var/www/apps/conversion/tmp/Conferences/WEATS/2005%20Alaska%20WEATS/Video/Ht%20of%20Obstacles.mpg


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Power from the Wind

Cp = Coefficient ofPerformance (anefficiency term)

AS = The swept area of the

wind turbine bladesMultiplied by time give you

Energy

P = 0.5 v 3 Cp AS


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Critical Aspects of Wind Energy

V3: Doubling of the wind speed results inan 8 fold increase in power

: High density air results in more power(altitude and temperature)

As: A slight increase in blade length,increases the area greatly

Cp: Different types of wind turbines havedifferent maximum theoreticalefficiencies (Betz limit 0.593) butusually between .4 and .5

P = 0.5 Cp v3 AS


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Velocity The Impact on Increasing

Wind Speed A smallincrease in

wind speedcan increasethe powergreatly

0.0

0.1

0.2

0.3

0.4

0.5

3 4 5 6 7 8 9 Average Wind Speed, m/s

A n n u a

l E n e r g y , M

W h

0%

10%

20%

30%

40%

50%

Annual Energy Output

Capacity Factor (%)


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Air Density -Changes with

Elevation

-40-30-20-10

0102030405060708090

100110

90 95 100 105 110 115 120 125

Density Change Compared to 59 F, %

T e m p e r a

t u r e , F

Changes withTemperature

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

70 75 80 85 90 95 100

Density Change Compared to Sea Level, %

E l e v a t i o n , f

t


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10 kW 38 m2

1 kW 6 m 2

500 kW1257 m 2

300 kW

415 m 2

25 kW 78 m 2

1000 kW2400 m 2

A = (p D2 )

4

SweptArea


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Wind Characteristics andResources

Understanding the wind resource at yourlocation is critical to understanding thepotential for using wind energy

Wind Speed Wind Profile Wind classes Collection and reporting

Wind Direction Wind speed change with height


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Wind Speed Measured in m/s or mph Varies by the second,

hourly, daily, seasonallyand year to year

Usually has patterns Diurnal - it always blows inthe morning

Seasonal The winterwinds are stronger

Characteristics Windsfrom the sea are alwaysstronger and are stormdriven.


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So, which is better

1. A location where the wind that blows only50% of the time at 10 m/s but is calm therest of the time

2. A location where the wind that blows all of

the time at 5 m/s

Both have exactly the same annual averagewind speed

P = 0.5 Cp v3 AS


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Wind Maps and Class

Careful:Wind class is defined

at a specific height


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Wind Speed Data Collection andReporting

Collection Measured every 1

or 2 seconds Averaged every 10

or 15 minutes Reported as hour

averagesTurbulence IntensityWind Speed

Frequency ofOccurrenceHistogram basedon hour averagedata for a year

0

200

400

600

800

1000

1200

1400

1600

0 1 2 3 4 5 6 7 8 9 10 11 12 1 3 1 4 1 5 1 6 1 7 18 19 2 0 2 1 2 2 2 3 2 4 25

Wind Speed (m/s)

T i m e

( H o u r s

)


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Wind Direction

CONTINENTAL TRADE WINDS

Wind Rose

Wind Speed Rose

Can also have a winddirection change intensity

similar to turbulence


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Impacts on Wind Speed

Many things impact thespeed and direction of thewind at any specific

location, making localmeasurements important


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Wind Speed Increases with Height

Because of frictionwith the earth, aircloser to the surfacemoves more slowly

The farther we getaway from the earth(increase in altitude)the higher the windspeed gets until it isno longer effected bythe earths surface

140

120

100

80

60

40

20

0

H e

i g h t , m

1086420Wind Speed, m/s

12:10 12:20 12:30 12:40 12:50 Pow er LawLog Law


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Wind Shear

The type ofsurface(grass,trees)impacts thewind shear

Real vs.

apparentheight

Wind Speed, m/sHeightm50

40

30

20

1050

SURFACE

12.6

12.2

11.7

11

10

8.8

N

h


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Factoring in Measurement HeightThe Power Law

Terrain Power Law ExponentWater or ice 0.1Low grass or steppe 0.14Rural with obstacles 0.2Suburb and woodlands 0.25

----------------------------------------------------------------------------------------------------------------------Source: Paul Gipe, Wind Energy Comes of Age, John Wiley and Sons Inc, 1995, pp 536.

------------------------------------------------------------------------------------------------------------------------

O

N O N

h

hV V

N

O

N O N

h

hV V

VN: Wind speed at new height,VO: Wind speed at original height,hN: New height,

hO: Original height,N: Power law exponent.


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Height Impacts on Power

1.00

1.50

2.00

2.50

3.00

3.50

0 50 100 150 200 250

Tower Height, ft

I n c r e a s e

C o m p a r e d

t o 3 0 f t

Wind Speed IncreaseWind Power Increase


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Micro-Siting Example:Obstruction of the Wind by a Small Building

Prevailing wind

H

2H 20H

2HRegion

of highlydisturbed

flow

02770346


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Basic Wind Turbine Theory

Lift and Drag The different types ofwind turbines

Aerodynamics How turbines workPower Curves The performance ofwind turbines

Power Availability - Power your canget from the wind

Different types of lift turbines


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WIND

PANEMONE TURBINECUPFLAP PLATE

shield

rotation

Aerodynamic Drag


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Classic Drag Devices


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Some Modified Drag Devices


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Aerodynamic Lift


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Lift Wind Turbines


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WTG Power Curve

02468

1012141618

0 5 10 15 20 25 30

Wind Speed (m/s)

W i n d T u r b i n e

P o w e r

( k W )

Cut inwind speed

Ratedwind speed

Cut outwind speed


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Important Terms

Cut in wind speed: The wind speed that the turbinestarts producing power (may be different than thespeed at which the turbine starts spinning)

Rated Wind Speed: The wind speed at which theturbine is producing rated power though ratedpower is defined by the manufacture

Cut out wind speed: The wind speed at which theturbine stops producing power

Shut down wind speed: The wind speed at which theturbine stops to prevent damage

Survival wind speed: Wind speed that the turbine isdesigned to withstand without falling over


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Wind Turbine Power CurveBergey 1500 (manufacturers data)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 23 23 24 25

Wind Speed (m/s)

P o w e r

( k W )


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Wind Speed Frequency of OccurrenceAverage Wind Speed: 5 m/s (11 mph)

0

200

400

600

800

1000

1200

1400

1600

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 2 0 2 1 2 2 23 24 2 5

Wind Speed (m/s)

T i m e

( H o u r s

)


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Annual Energy Production: 2643 kWh/year Bergey 1500 @ 5 m/s (11 mph) average wind speed

0

50

100

150

200

250

300

350

400

450

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Wind Speed (m/s)

E n e r g y ( k

W h )

All available energy may not be captured


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Types of Lift TurbinesHAWT VAWT


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Basic Properties of HAWT

Basics of a horizontal axis wind turbine Types of turbines Small distributed turbines Large grid connected turbines


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Parts of a Wind Turbine

Rotor


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Utility-Scale Wind Power 600 - 5,000 kW wind turbines Installed on wind farms, 10 300 MW Professional maintenance crews

Classes 5 and 6 (> 6 m/s average) Distributed Wind Power

300 W - 600 kW wind turbines Installed at individual homes, farms,

businesses, schools, etc. On the customer side of the meter High reliability, low maintenance Classes 2 and 3 (5 m/s average)

Different Types of Wind Turbines

1,500 kW

10 kW


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Sizes and Applications

Small ( 10 kW)HomesFarmsRemote Applications

(e.g. water

pumping, telecomsites, icemaking)

Intermediate(10-250 kW)Village Power

HybridSystemsDistributedPower

Large (250 kW 2+MW)Central Station WindFarmsDistributed Power


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PermanentMagnet WTG

Tail Vane

Tail Boom

Nacelle

Tower Adapter (contains slip rings)

Alternator (Permanent Magnet)

Turbine Blade

Nose Cone

Tower

Permanent magnetalternator

Generates wild AC(variable voltageand frequency)power that must betreated.

Can provide AC orDC power Passively

controlled


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Overspeed Protection of Small WTGDuring High Winds

Furling : Therotor turns up

or too one side

under highwinds

Used to controlrotor speed

and poweroutput

Dynamicactivity


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Small Wind Turbine Towers

Guyed lattice and tubetowers are the leastexpensive andmost commonly used towersfor small wind turbines

Adequate space is neededfor the guy wires and theiranchors

Free-standing towers are

used where space is limited


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Tilt-Up Towers

Turbine installation inremote areas can be a

problem.

To solve this problem: Tilt-up versions of guyed

towers are available foreasier installation andmaintenance.

Self erecting technologyalso used wisely


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The Wind Turbine Controller Battery-Charging

Converts AC power to DC for battery-charging Regulates the battery voltage to prevent over-

charging When the battery is fully charged:

Power is diverted to another load, or The rotor is unloaded and allowed to

freewheel

Grid Interconnection Inverter, converts the power to

constant frequency 60 Hz AC Water Pumping

Direct connection to the pump


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Small Wind TurbineMaintenance and Lifetime

Low maintenance not no maintenance Inspection and maintenance every year: tightening bolts

and electrical connections, inspecting slip ring brushes,checking for corrosion, etc.

Between 2 and 4 years: blade leading edge tape mayneed replacement

Beyond 5-10 years: blade or bearing replacement maybe needed

Lifetimes of 10 to 20 years are possible Some Jacobs wind turbines have been operating for

more than 60 years with periodic maintenance!


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Hot Tips on Small Wind Energy

Buy ReliabilityBased on experience, I side with the school of heavymetal, those who believe that beefiness ofcomponents is directly related to the longevity of theequipment. M. Sagrillo, small wind turbine expert

Taller is BetterTaller towers give better performance due to smootherwind and higher wind speeds

Micro-SitingFor best performance, locate wind turbines above andaway from obstructions to the wind

0277034

5


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AC WTG Induction or

variablespeedgenerator

Create ACpowersupplied tothe grid

Activelycontrolled


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Control of Large WTG

Fixed Pitch (Stall regulated) : The shape of the bladevaries over its length so that as wind speed increaseparts of the blade stop producing lift and limit power.

Variable Pitch : The rotation (pitch) of each blade isindividually controlled to control lift

Yaw : Motors control yaw behavior based on a winddirection vain, used to shut down wind turbine in highwinds but can also be a source of problems.

Brake : All wind turbines are required to have two ofthem but there are several types: Aerodynamic: Flaps on the blades that cause drag.Mechanical: Disks or calipers, like your car.Electrical: using the generator to cause electrical resistance.


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Characteristics of Large WTG

Power Types Induction (Constant speed) Variable Speed (uses power electronics)Power System Efficiencies

Aerodynamic Rotor Drive train / gear box

Generator Power Conversion (if applicable)

1MW WTG Nacelle


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1MW WTG Nacelle

A 27 m Blade


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A 27 m Blade

Rotor Area = 2460 m 2 for a 1MW wind turbine

1.5 MW turbine is now standard

5 MW Turbines in prototype


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Policy Encourage economicdevelopment and use

of local resources facilitate green

markets Federal, state and

local incentives suchas the Production TaxCredit (PTC) andRenewable PortfolioStandards (RPS)

Siting Avian and other

wildlife Noise

Visual Impact Land Ownership


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Transmission Grid Access

System studies Allocation of availablecapacity

Scheduling and costs

for usage (firm andnon-firm)

External Conditions Lightening Extreme Winds Corrosion Extreme temperatures

Remote Systems Amount of energyfrom wind

Control of system

voltage and frequency Use of excess windenergy

Intermittency Operational Impacts

(ancillary services) voltage/VAR control,

load following, etc.

10-20% of systemcapacity is reasonable


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Other General Wind Terms

Availability : The amount of time that the windturbine is available to produce power (Maintenanceparameter)

Capacity Factor : The annual energy production ofa wind turbine divided by the theoretical production ifit ran at full rated power all of the time (Resourceparameter) The stronger the resource the higher the Capacity Factor Usually reported monthly or yearly 25-40% is typical, up to 60% has been reported Reason for the only works 1/3 of the time quote.


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Basic WTG Calculations

Back of the envelope calculations for windturbine sizing

1. Turbine size or energy production

2. Cost of energy3. Turbine capital cost

Note: Designing a power system that includeswind turbines is not a simple issue andshould not be taken lightly.

i i bi Si


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Determining Turbine Size

There is a direct tradeoff between the size of thegenerator and the amount of power that it will

produce. If you know one, you can get the other.

AKWH = CF * AV * GS * 8760 AKWH Annual energy production, kWh/yr CF Capacity Factor (20 to 50%)

AV Turbine Availability (~95 to 98%)GS Generator Size (rated power), kW8760# of hours in a year

E l Wh Si d T bi ?


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Example What Sized Turbine?Your community/home/building/business uses11,250 kWh / year and you want ~ 25% of thatto come from wind.

AEP = CF * GS * AV * 8760CF 30% = 0.30 (~ 6 mps annual average)

AV 97% = .97 AEP 11,250 kWh8760 # of hours in a year

GS = 11250 / ( 0.30 * .97 * 8760 )GS = 4.5 kW

Of course there are many other factors

Quick calculation of Annual Energy


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Quick calculation of Annual EnergyProduction using density

AKWH = CF * Ar * WM * 8.76 AKWH Annual energy production, kWh/yr

CF Capacity factor (efficiency factor) Ar Rotor Area, m 2

WM Wind Map Power, W/m 2

8.76 1000 hours in a year converts W to kW


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Levelized Cost of Energy

COE = (FCR * ICC) + LRC + AOM

COE = LEVELIZED COST OF ENERGY, $/kWh

LRC = LEVELIZED REPLACEMENT COST, $/yr(major repairs)

ICC = INITIAL CAPITAL COST, $FCR = FIXED CHARGE RATE, per year

AEP = ANNUAL ENERGY PRODUCTION, kWh

A0M = ANNUAL OPERATION & MAINTENANCE, $/kWh

AEP

Turbine Capital Cost


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Turbine Capital CostHardware Cost $670/kW

turbine $550/kWtower $120/kW

Installation Cost $100/kWfoundation, erection, interconnection

Shipping $70/kW

Other $100/kWROUND NUMBER $1000/kW

Costs however are impacted by the market. In 2005the cost of installed wind turbines has increasedto between $1300 and $1400 per kW due to highsteel prices and demand caused by the

Production Tax Incentive

COE E l


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COE Example

1 MW TURBINEFCR = 10% = 0.10ICC = $1000/kW = $1,000,000LRC = $5,500

AOM = $0.01/kWh availability elevation AEP = 2,600,000 98% 1000 mCOE = (0.1 * 1,000,000) + 10,000 + 0.01

2,700,000COE = $0.051 / kWh


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So, which is better

1. A location where the wind that blowsonly 50% of the time at 10 m/s but is

calm the rest of the time2. A location where the wind that blows

all of the time at 5 m/s

B 1500 ( f t d t )


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Bergey 1500 (manufacturers data)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 23 23 24 25

Wind Speed (m/s)

P o w e r

( k W )


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Further Information / ReferencesWeb Based:

American Wind Energy Association http://www.awea.org/ Wind Powering America

http://www.eere.energy.gov/windpoweringamerica/ Danish Wind Industry Association guided tour and information.

http://www.windpower.org/en/tour/Publications:

Ackermann, T. (Eds), Wind Power in Power Systems , John Wiley andSons, west Sussex, England, p299-330 (2005). Hunter, R., Elliot, G. (Eds), Wind-Diesel Systems . Cambridge, UK:

Cambridge University Press, 1994. Wind Energy Explained, J. F. Manwell, J. G. McGowan, A. L. Rogers

John Wiley & Sons Ltd. 2002. Paul Gipe, Wind Energy Basics: A Guide to Small and Micro Wind

Systems, Real Goods Solar Living Book. AWS Scientific Inc. Wind Resource Assessment Handbook produced

by for the National Renewable Energy Laboratory, Subcontract numberTAT-5-15283-01, 1997

Thanks to: Ken Starcher, Alternative Energy Institute, West Texas A&M University

fundamentals wind

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