HomeMy WebLinkAboutFundamentals of Wind Energy Ian-Baring-Gould NREL 2005Fundamentals of Wind EnergyAlaska Wind Energy Applications Training Symposium Bethel, AlaskaE. Ian Baring-GouldNational Renewable Energy Laboratory
TOPICSIntroductionEnergy and PowerWind CharacteristicsWind Power PotentialBasic Wind Turbine Theory Types of Wind TurbinesBasic Wind Turbine CalculationsFurther Information
What is Wind Power800-900 years ago, in Europe140 years ago,water-pumpingwind mills70 years ago, electric power1400-1800 years go,in the Middle EastThe ability to harness the power available in the wind and put it to useful work.
ENERGY AND POWERENERGY: The Ability to do workENERGY = FORCE * DISTANCEElectrical energy is reported in kWh and may be used to describe a potential, such as in stored energyPOWER: Force without timePOWER = ENERGY / TIMEGenerator Size or an instantaneous load which is measured in kW
P = 0.5 ρv3P: power, Wattρ:density of air, kg/m3V: wind speed, m/sWe call this the Wind Power Density(W/m2)If we include the area through which the wind flows (m2), we get the collectable power in Watts.Power in the Wind
Power from the WindCp = Coefficient of Performance (an efficiency term)AS= The swept area of the wind turbine bladesMultiplied by time give youEnergy…P = 0.5 ρCpv3AS
Critical Aspects of Wind Energy V3: Doubling of the wind speed results in an 8 fold increase in powerρ: High density air results in more power (altitude and temperature)As: A slight increase in blade length, increases the area greatlyCp: Different types of wind turbines have different maximum theoretical efficiencies (Betz limit ≈0.593) but usually between .4 and .5P = 0.5 ρCpv3AS
Impact on Increasing Wind SpeedA small increase in wind speed can increase the power greatly 0.00.10.20.30.40.53456789Average Wind Speed, m/sAnnual Energy, MW h0%10%20%30%40%50%Annual Energy OutputCapacity Factor (%)
Air Density Changes with Elevation-40-30-20-10010203040506070809010011090 95 100 105 110 115 120 125Density Change Compared to 59 F, %Temperature, FAir Density Changes with Temperature01,0002,0003,0004,0005,0006,0007,0008,0009,00010,00070 75 80 85 90 95 100Density Change Compared to Sea Level, %Elevation, ft
10 kW38 m21 kW 6 m2500 kW1257 m2300 kW415 m225 kW 78 m21000 kW2400 m2A=(πD2)4
Wind Characteristics and ResourcesUnderstanding the wind resource at your location is critical to understanding the potential for using wind energy• 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• Turbulence Intensity• Usually has patterns– 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.
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 time2. A location where the wind that blows all of the time at 5 m/sBoth have exactly the same annual average wind speed…P = 0.5 ρCpv3AS
Wind Maps and ClassCareful:Wind class is defined at a specific height
Wind Speed Data Collection and ReportingCollection•Measured every 2 second •Averaged every 10 minutes•Reported as hour averagesWind Speed Frequency of Occurrence Histogram based on hour average data for a year020040060080010001200140016000123456789 10111213141516171819202122232425Wind Speed (m/s)Time (Hours)
Wind DirectionCONTINENTAL TRADE WINDSWind RoseWind Speed Rose
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 slower• 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.140120100806040200Height, m1086420Wind Speed, m/s 12:10 12:20 12:30 12:40 12:50 Pow er Law Log Law
Wind Shear• The type of surface (grass, trees) impacts the wind shear• Real vs. apparent heightWind Speed, m/sHeightm504030201050SURFACE12.612.211.711108.8
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.------------------------------------------------------------------------------------------------------------------------NONONhhVV=NONONhhVV=VN: Wind speed at new height,VO: Wind speed at original height,hN: New height,hO: Original height,N: Power law exponent.
Height Impacts on Power1.001.502.002.503.003.500 50 100 150 200 250Tower Height, ftIncrease Compared to 30 ftWind Speed IncreaseWind Power Increase
Micro-Siting Example:Obstruction of the Wind by a Small BuildingPrevailing windH2H20H2HRegionof highlydisturbedflow02770346
Basic Wind Turbine TheoryLift and Drag – The different types of wind turbinesAerodynamics – How turbines workPower Curves – The performance of wind turbinesPower Availability - Power your can get from the windDifferent types of lift turbines
WINDPANEMONE TURBINECUPFLAP PLATEshieldrotationAerodynamic Drag
Classic Drag Devices
Some Modified Drag Devices
Aerodynamic Lift
Lift Wind Turbines
WTG Power Curve
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 manufacture• 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
Wind Turbine Power CurveBergey 1500 (manufacturer’s data)00.20.40.60.811.21.41.61.80 1 2 3 4 5 6 7 8 9 1011121314151617181920212323 24 25Wind Speed (m/s)Power (kW)
Wind Speed Frequency of OccurrenceAverage Wind Speed: 5 m/s (11 mph)020040060080010001200140016000123456789 10111213141516171819202122232425Wind Speed (m/s)Time (Hours)
Annual Energy Production: 2643 kWh/yearBergey 1500 @ 5 m/s (11 mph) average wind speed0501001502002503003504004501 2 3 4 5 6 7 8 9 10111213141516171819202122232425Wind Speed (m/s)Energy (kWh)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• Large grid connected turbines
Parts of a Wind TurbineRotor
Basic Motion of a Wind TurbineYawPitchRotation
•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)•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)Different Types of Wind Turbines1,500 kW10 kW
Sizes and ApplicationsSmall (≤10 kW)HomesFarmsRemote Applications (e.g. water pumping, telecom sites, icemaking)Intermediate(10-250 kW)Village PowerHybrid SystemsDistributed PowerLarge (250 kW – 2+ MW)Central Station Wind FarmsDistributed Power
Permanent Magnet WTGTail VaneTail BoomNacelleTower Adapter(contains slip rings)Alternator(Permanent Magnet)Turbine BladeNose ConeTower• Permanent magnet alternator• Generates wild AC (variable voltage and frequency) power that must be treated. • Can provide AC or DC power• Passively controlled
Overspeed Protection of Small WTGDuring High WindsFurling: The rotor turns up or too one side under high winds•Used to control rotor speed and power output•Dynamic activity
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 needed for the guy wires and their anchors• Free-standing towers are used where space is limited
Tilt-Up TowersTurbine 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 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 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 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 wind02770345
AC WTG• Induction or variable speed generator• Create AC power supplied to the grid•Actively controlled
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 liftYaw: 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.
Characteristics of Large WTGPower 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
A 27 m BladeRotor Area = 2460 m2for a 1MW wind turbine • 1.5 MW turbine is now “standard”• 5 MW Turbines in prototype
Other Large (and Small) Turbines Considerations• Policy•Siting• Transmission• External Conditions• Intermittency
Policy• Encourage economic development and use of local resources• facilitate “green”markets• Federal, state and local incentives (Production Tax Credit (PTC) and Renewable Portfolio Standards (RPS)Siting• Avian and other wildlife•Noise• Visual Impact • Land Ownership
Transmission • Grid Access• System studies• Allocation of available capacity• Scheduling and costs for usage–firm– non-firmExternal Conditions • Lightening • Extreme Winds• Corrosion• Extreme temperaturesIntermittency• 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 a 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 availability– 25-40% is typical, up to 60% has been reported– Reason for the “only works 1/3 of the time” quote.
Basic WTG CalculationsBack of the envelope calculations for wind turbine sizing1. Turbine size or energy production2. Cost of energy3. Turbine capital cost Note: Designing a power system that includes wind turbines is not a simple issue and should not be taken lightly.
Determining Turbine SizeThere is a direct tradeoff between the size of the generator and the amount of power that it will produce. If you know one, you can get the other.AKWH= CF * AV * GS* 8760AKWH Annual energy production, kWh/yrCF Capacity Factor (25 to 50%)AV Turbine Availability (~95 to 98%)GS Generator Size (rated power), kW8760# of hours in a year
Example – What Sized Turbine?Your community/home/building/business uses 11,250 kWh / year and you want ~ 25% of that to come from wind.AEP = CF * GS * AV * 8760CF 30% = 0.30 (~ 6 mps annual average)AV 97% = .97AEP 11,250 kWh8760 # of hours in a yearGS = 11250 / ( 0.30 * .97 * 8760 )GS = 4.5 kWOf course there are many other factors…
Quick calculation of Annual Energy Production using densityAKWH = CF * Ar * WM * 8.76AKWH Annual energy production, kWh/yrCF Capacity factor (efficiency factor)Ar Rotor Area, m2WM Wind Map Power, W/m28.76 1000 hours in a yearconverts W to kW
Levelized Cost of EnergyCOE = (FCR * ICC) + LRC + AOMCOE = LEVELIZED COST OF ENERGY, $/kWhLRC = LEVELIZED REPLACEMENT COST, $/yr (major repairs)ICC = INITIAL CAPITAL COST, $FCR = FIXED CHARGE RATE, per yearAEP = ANNUAL ENERGY PRODUCTION, kWhA0M = ANNUAL OPERATION & MAINTENANCE, $/kWhAEP
Turbine Capital CostHardware Cost $670/kWturbine $550/kWtower $120/kWInstallation Cost $100/kWfoundation, erection, interconnectionShipping $70/kWOther $100/kWROUND NUMBER $1000/kWCosts however are impacted by the market. In 2005 the cost of installed wind turbines has increased to between $1300 and $1400 per kW due to high steel prices and demand caused by the Production Tax Incentive
COE Example1 MW TURBINEFCR = 10% = 0.10ICC = $1000/kW = $1,000,000LRC = $5,500AOM = $0.01/kWh availability elevationAEP = 2,600,000 98% 1000 mCOE = (0.1 * 1,000,000) + 10,000 + 0.012,700,000COE = $0.051 / kWh
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 time2. A location where the wind that blows all of the time at 5 m/s
Bergey 1500 (manufacturer’s data)00.20.40.60.811.21.41.61.80 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 212323 24 25Wind Speed (m/s)Power (kW)
Make the calculationAEP = expected power * availability * timeCase 1: 10 m/s 50% of the timeAEP = 1.15 kW * 0.97 * (8760 *0.5)= 4,886 kWh / yearCase 2: 5 m/s all of the timeAEP = 0.15 kW * 0.97 * (8760 * 1.0)= 1,275 kWh / year
Further Information / ReferencesWeb Based:• American Wind Energy Association http://www.awea.org/• Wind Powering America http://www.eere.energy.gov/windpoweringamerica/• European Commission's Atlas Project: http://europa.eu.int/comm/energy_transport/atlas/homeu.html• Solar Access: http://www.solaraccess.comPublications:• Ackermann, T. (Ed’s): (2005), Wind Power in Power Systems, John Wiley and Sons, west Sussex, England, p299-330 (2005).• Hunter, R., Elliot, G. (Ed’s) (1994) Wind-Diesel Systems. Cambridge, UK: Cambridge University Press, 1994.• Paul Gipe, Wind Energy Comes of Age, John Wiley and Sons Inc, 1995.• AWS Scientific Inc. “Wind Resource Assessment Handbook”produced by for the National Renewable Energy Laboratory, Subcontract number TAT-5-15283-01, 1997