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
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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
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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
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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