5/27/2009

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E. Ian Baring-Gould,

Fundamentals of Wind EnergyFundamentals of Wind Energy(Wind(Wind--Diesel 101)Diesel 101)

NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy operated by the Alliance for Sustainable Energy, LLC

National Wind Technology Center & Deployment & Industrial Partnerships Centers

May 31st 2009

TOPICS

IntroductionEnergy and PowerWind CharacteristicsWind Power PotentialBasic Wind Turbine Theory Types of Wind TurbinesReview of Small and Large TurbinesReview of the Current Wind MarketFurther Information

What is Wind Power800-900 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 to harness the power available in the wind and put it to useful work.

ENERGY AND POWER

ENERGY: The Ability to do workElectrical energy is reported in kWh and may be used to describe a potential, such as in stored energy or the amount of energy used over a time period, like 1000 kWh per day

POWER: Force at any instantThe amount of energy needed at any instant in time. Represents current generation and constraints such as Generator Size or an instantaneous load which is measured in kW

P = 0.5 ρ v3

P: power, Watt

ρ: density of air kg/m3

Power in the Wind

ρ: density of air, kg/m3

V: wind speed, m/sWe call this the Wind Power Density (W/m2) which is a measure of the power available in the wind at a specific point or as an average over a longer period of time

Power from the Wind

Cp = Coefficient of Performance (an

P = 0.5 ρ v3 Cp AS

Performance (an efficiency term)

AS = The swept area of the wind turbine blades

Multiplied by time give you

Energy…

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Critical Aspects of Wind Energy

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

ρ: High density air results in more power

P = 0.5 ρ Cp v3 AS

ρ: 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 have different maximum theoretical efficiencies (Betz limit ≈0.593) but usually between .4 and .5

Velocity – The Impact on Increasing Wind Speed

A small increase in wind speed

i0.3

0.4

0.5

rgy,

MW

h

30%

40%

50%

Annual Energy Output

Capacity Factor (%)

can increase the power greatly

0.0

0.1

0.2

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

Ann

ual E

ne

0%

10%

20%

Air Density -Changes with

Elevation0

1,0002,000

3,000

4,000

5,000

6,0007,000

8,000

9,000

10,000

70 75 80 85 90 95 100

Density Change Compared to Sea Level, %

Elev

atio

n, ft

-40-30-20-10

0102030405060708090

100110

90 95 100 105 110 115 120 125

Density Change Compared to 59 F, %

Tem

pera

ture

, F

Changes with Temperature

500 kW1257 m 2

300 kW

1000 kW

2400 m2

Swept Area

10 kW 38 m 2

1 kW 6 m 2

300 kW

415 m 2

25 kW 78 m 2

A = (π D2 )4

Wind Characteristics and Resources

Understanding the wind resource at your location is critical to understanding the potential for using wind energy

• Wind Speed• Wind Speed– Wind Profile– Wind classes – Collection and reporting

• Wind Direction• Wind speed change with height

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

hourly, daily, seasonally and year to year

• Usually has patternsDi l it l bl i– Diurnal - it always blows in the morning

– Seasonal – The winter winds are stronger

– Characteristics – Winds from the sea are always stronger and are storm driven.

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So, which is better… 1. A location where the wind that blows only

50% of the time at 10 m/s but is calm the rest 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 average wind speed…

P = 0.5 ρ Cp v3 AS

Wind Maps and Class

Careful:Wind class is defined

at a specific height

Wind Speed Data Collection and Reporting

Collection• Measured every 1

or 2 seconds • Averaged every 10

or 15 minutes• Reported as hour1000

1200

1400

1600

s) Reported as hour averages

Turbulence Intensity Wind Speed

Frequency of Occurrence Histogram based on hour average data for a year

0

200

400

600

800

0 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)

Tim

e (H

our

Wind DirectionWind Rose

Wind Speed Rose

CONTINENTAL TRADE WINDS

Can also have a wind direction change intensity – similar to turbulence

Impacts on Wind Speed Many things impact the

speed and direction of the wind at any specific

location, making local measurements important

Wind Speed Increases with Height

• Because of friction with the earth, air closer to the surface moves more slowly

140

120

100

m

12:10 12:20 12:30 12:40 12:50Pow er Lawmoves more slowly

• The farther we get away from the earth (increase in altitude) the higher the wind speed gets until it is no longer effected by the earths surface

80

60

40

20

0

Hei

ght,

m

1086420Wind Speed, m/s

Pow er Law Log Law

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Wind Shear

• The type of surface (grass, trees) impacts the

Wind Speed, m/sHeightm50

40

30

12.6

12.2

11.7 impacts the wind shear

• Real vs. apparent height

30

201050

SURFACE

11

108.8

Factoring in Measurement HeightThe Power Law

N

O

NON h

hVV ⎥⎦

⎤⎢⎣

⎡=

N

O

NON h

hVV ⎥⎦

⎤⎢⎣

⎡=

VN: Wind speed at new height,VO: Wind speed at original height,hN: New height,hO: Original height,N: Power law exponent

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.

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

N: Power law exponent.

Height Impacts on Power

2 50

3.00

3.50

red

to 3

0 ft Wind Speed Increase

Wind Power Increase

1.00

1.50

2.00

2.50

0 50 100 150 200 250

Tower Height, ft

Incr

ease

Com

par

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

Prevailing wind

H

2H 20H

2HRegionof highlydisturbed

flow

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Basic Wind Turbine Theory

Lift and Drag – The different types of wind turbines

Aerodynamics – How turbines workPower Curves – The performance of

wind turbinesPower Availability - Power your can

get from the windDifferent types of lift turbines

Aerodynamic Drag

WIND

PANEMONE TURBINECUPFLAP PLATE

shield

rotation

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Classic Drag DevicesSome Modified Drag Devices

Aerodynamic LiftLift Wind Turbines

WTG Power Curve

68

1012141618

rbin

e Po

wer

(kW

)

Cut in wind speed

Rated wind speed

Cut out wind speed

0246

0 5 10 15 20 25 30

Wind Speed (m/s)

Win

d Tu

r wind speed

Important Terms

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

• Rated Wind Speed: The wind speed at which the turbine is producing “rated power” – though “rated power” is defined by the manufacturep y

• Cut out wind speed: The wind speed at which the turbine stops producing power

• Shut down wind speed: The wind speed at which the turbine stops to prevent damage

• Survival wind speed: Wind speed that the turbine is designed to withstand without falling over

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Wind Turbine Power CurveBergey 1500 (manufacturer’s data)

1.2

1.4

1.6

1.8

W)

0

0.2

0.4

0.6

0.8

1

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)

Pow

er (k

W

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

1000

1200

1400

1600

urs)

0

200

400

600

800

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25Wind Speed (m/s)

Tim

e (H

ou

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

250

300

350

400

450

y (k

Wh)

0

50

100

150

200

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)

Ener

gy

All available energy may not be captured

Types of Lift TurbinesHAWT VAWT

Basic Properties of HAWT

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

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Parts of a Wind Turbine

Rotor

Basic Motion of a Wind Turbine

Pitch

Yaw

Rotation

• Utility-Scale Wind Power600 - 5,000 kW wind turbines

– Installed on wind farms, 10 – 300 MW– Professional maintenance crews– Classes 5 and 6 (> 6 m/s average)

Different Types of Wind Turbines

1,500 kW

• Distributed Wind Power300 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)

10 kW

Sizes and Applications

Small (≤10 kW)HomesFarmsRemote Applications

(e.g. water pumping, telecom sites icemaking)

Intermediate(10-250 kW)Village PowerHybrid

sites, icemaking) SystemsDistributed Power

Large (250 kW – 2+ MW)Central Station Wind FarmsDistributed Power

Small wind turbines

Tail Vane

Tail Boom

Nacelle

Tower Adapter(contains slip rings)

Alternator(Permanent Magnet)

Turbine Blade

Nose Cone

Tower

• Typically use a permanent magnet alternator

• Generates wild AC (variable voltage and f ) th tTower frequency) power that must be treated.

• Can provide AC or DC power

• Passively controlled

Overspeed Protection of Small WTGDuring High Winds

Furling: The rotor turns out of the

wind during high winds to reduce

power

• Used to control rotor speed and power output

• Dynamic activity

• Can cause noise issues (flutter)

• Not all small wind turbines do this

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Small Wind Turbine Towers

• Guyed lattice and tube towers are the least expensive and most commonly used towers for small wind turbines

• Adequate space is neededAdequate space is needed for the guy wires and their anchors

• Free-standing towers are used where space is limited

Tilt-Up Towers

Turbine installation in remote areas can be a

problem.To solve this problem:• Tilt-up versions of guyed towers are available for easier installation and maintenance.

• Self erecting technology also used wisely

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 nloaded and allo ed to• 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

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• Between 2 and 4 years: blade leading edge tape may need replacement

• Beyond 5-10 years: blade or bearing replacement may be needed

• Lifetimes of 10 to 20 years are possible• Some Jacobs wind turbines have

been operating for more than 60 years with periodic maintenance!

“Hot Tips” on Small Wind Energy

• “Buy Reliability”“Based on experience, I side with the ‘school of heavy metal,’ those who believe that beefiness of components is directly related to the longevity of the equipment.” M. Sagrillo, small wind turbine expert“Taller is Better”• “Taller is Better”Taller towers give better performance due to smoother wind and higher wind speeds

• “Micro-Siting”For best performance, locate wind turbines above and away from obstructions to the wind

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Small turbines – the Wild West of Wind

• Small Wind Turbine industry is unorganized & lacks working standards– Currently, Third party certification is typically limited to the

inverter (UL 1740)– Limited 3rd party testing & certification

• Current IEC small turbine testing standard generally• Current IEC small turbine testing standard generally not used due to the expense

• Small wind turbine testing & certification schemes for North America are under development (Small Wind Certification Council [SWCC, AWEA Small Wind Test Standard (in draft stage)]

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Questions to Ask about SWT• What level of certification does

the turbine have?• Is a power curve available? If

so, how was it developed?• Has the turbine been previously

installed? (In the U.S., near the proposed site)

Vertikalrotor 500

Loopwing Tromc

Hush Turbine 3000

• How many units have been deployed?

• Is there any sort of dealer infrastructure?

• How long has the manufacturer been in business? (What is the experience of the company key personnel?)

• Is the inverter UL listed? (Grid tied systems)

Skystream 2400

Vertikalrotor 500

Windport 5000

Windkraft 500

http://www.allsmallwindturbines.com/

Large Wind Turbines• Typically

induction or variable speed permanent magnet generators

• Create AC power supplied to the grid

• Actively controlled

Nacelle

Boeing 747-200

Blades

Parts of a Wind Turbine Power Plant

Tower

Characteristics of Large WTGPower Types• Induction (Constant speed)• Permanent Magnet (Variable

speed) using power electronicsPower System Efficienciesy• Aerodynamic• Rotor• Drive train / gear box• Generator• Power Conversion (if applicable)

Control of Large WTGFixed Pitch (Stall regulated): The shape of the blade

varies over its length so that as wind speed increase parts of the blade stop producing lift and limit power.

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

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

Brake: All wind turbines are required to have two of them 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.

Other Large (and Small) Turbines Considerations

• Policy• Siting• Transmission• Transmission• External Conditions• Intermittency

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Policy• Encourage economic

development and use of local resources

• facilitate “green” markets

Siting• Avian and other

wildlife• Noise• Visual Impact markets

• Federal, state and local incentives such as the Production Tax Credit (PTC) and Renewable Portfolio Standards (RPS)

• Land Ownership

Avian (Bird) Research• Over 200 projects, two problem sites.

• Biggest problem was in the Altamont Pass.

• Managed by careful site selection.

Nysted Windfarm - Denmark

Are Wind Turbines Noisy?

What is the sound level of a utility-scale turbine?

45 decibels at 350 meters

Transmission• Grid Access• System studies• Allocation of available

capacity• Scheduling and costs

for usage (firm and fi )

External Conditions • Lightening • Extreme Winds• Corrosion• Extreme temperatures

Remote Systemsnon-firm) • Amount of energy

from wind• Control of system

voltage and frequency• Use of excess wind

energy

Intermittency• Operational Impacts

(ancillary services)– voltage/VAR control,

load following, etc.

• 10-20% of system capacity is reasonable

Other General Wind Terms

• Availability: The amount of time that the wind turbine is available to produce power (Maintenance parameter)

• Capacity Factor: The annual energy production of i d t bi di id d b th th ti l d ti ifa wind turbine divided by the theoretical production if

it ran at full rated power all of the time (Resource parameter)– 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.

Current Status of the Wind Industry

60000

70000

80000

90000

100000

110000

120000

acity

(MW

)

1. United States: 25,408 MW2. Germany: 23,600 MW3. Spain: 16,000 MW4. India: 9,522 MW5. China: 9,500 MW

Total Total Global Installed Global Installed Wind CapacityWind Capacity

0

10000

20000

30000

40000

50000

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

Cap

United States Europe Rest of World

,

Source: WindPower Monthly

World total 2008: 115,254 MW

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Major Source of New Generation Capacity Additions

• 2008: 42%• 2007: 35%• 2006: 18%• 2005: 12%• 2000-04: <5%40%

50%60%

70%

80%

90%

100%

of A

nnua

l Cap

acity

Ad

ditio

ns

40

60

80

100

Annu

al C

apac

ity

dditi

ons

(GW

)

0%

10%

20%30%

2000 2001 2002 2003 2004 2005 2006 2007 2008

Perc

ent

0

20 Tota

l Ad

Wind Other RenewableGas (CCGT) Gas (non-CCGT)Coal Other non-RenewableTotal Capacity Additions (right axis)

Source: EIA, Ventyx, AWEA, IREC, Berkeley Lab

Wind Has Been Competitive with Wholesale Power Prices in Recent Years

20

30

40

50

60

70

80

90

2008

$/M

Wh

Wind project sample includes projects built from 1998-2008

Note: Wholesale price range reflects flat block of power across 23 pricing locations; wind costs represent capacity-weighted average price for wind power for entire sample of projects built from 1998-2008

0

10

20

2003 2004 2005 2006 2007 2008

53 projects 66 projects 87 projects 107 projects 127 projects 159 projects

2,467 MW 3,268 MW 4,397 MW 5,810 MW 8,341 MW 11,091 MW

Nationwide Wholesale Power Price Range (for a flat block of power)

Cumulative Capacity-Weighted Average Wind Power Price

Source: FERC 2006 and 2004 "State of the Market" reports, Berkeley Lab database, Ventyx, ICE

Wind Prices Have Been Rising Since 2002-03…

• Wind power prices bottomed out with projects built in 2002-03• Projects built in 2008 are ~$15-20/MWh higher on average

The Near-Term Wind has Become Somewhat Less Attractive

40

50

60

70

80

90

ower

Pric

e (2

008

$/M

Wh)

Note: Prices include the value of the PTC

• Wind prices are likely to increase further in 2009 as installed costs will remain high as developers work through turbines ordered at peak prices, and given higher equity yields.

• Wholesale price’s are also likely to increase as the economic depression reverses course

0

10

20

30

2000-01 2002-03 2004-05 2006 2007 2008902 MW 1,801 MW 1,717 MW 766 MW 3,425 MW 1,856 MW

Capacity-Weighted Average 2008 Wind Power Price (by project vintage) Individual Project 2008 Wind Power Price (by project vintage)

2008

Po

2008 2009 Wholesale Price

Range

Drivers for Wind Power

• Declining Wind Costs• Fuel Price Uncertainty• Federal and State Policies• Economic DevelopmentEconomic Development• Public Support• Green Power• Energy Security• Carbon Risk

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. (Ed’s), Wind Power in Power Systems, John Wiley and

Sons west Sussex England (2005)Sons, west Sussex, England, (2005).• Hunter, R., Elliot, G. (Ed’s), 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 number TAT-5-15283-01, 1997

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

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Carpe Ventem

NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy operated by the Alliance for Sustainable Energy, LLC

E. Ian Baring-GouldNational Wind Technology Center & Deployment & Industrial Partnerships Centers303-384-7021Ian.baring-gould@nrel.gov