P = 0.5*ρAV3 - Morrisville State College

Residential and Farm-Scale Wind“You sure?”“Hi, I want a windmill.”“Yeah, I can’t wait to tell the utility company to go you-knowwhere.”“Hmm. Bet they’ll be glad to hear that. How much wind doyou have?”“Wind? Oh, we’ve got lots of wind. It’s always windy here.”Gipe (2004, p.23)

Checklist Wind speed Wind power Wind energy Siting Incentives

What is wind? Air is… 78% nitrogen 21% oxygen 1% argon Trace amounts of CO 2 (0.04%) and other gases Water vapor is variable; approximately 1% atany given time Wind is moving air, often caused by differentialheating

What is wind?Different surfaces lead to unequalheating at the Earth’s surface

Regional air currentsValley winds from late morning to evening

Regional air currentsValley winds from evening to morning

Griggs-Putnam IndexImage from Southwest Wind Power

Air speeds200%120%100% 50%

Global Air Currents:Coriolis EffectEarth RotationEarth Rotation

Global air currentsArctic Circle23.5 o66.5 o EquatorTropic of CancerTropic of CapricornAntarctic Circle

Wind PowerP = 0.5*ρAV 3P is power in wattsRho (ρ) is air density (kg/m 3 )A is windswept area (m 2 )V is wind velocity (m/s)1.Which of these variables is mostimportant?2.Which of these variables do we havethe most control over?

Wind Power: ρDensity of Air at Standard Atmospheric PressureTemperature °C Temperature ° F Density, i.e. mass of dry air kg/m 3-25 -13 1,423-20 -4 1,395-15 5 1,368-10 14 1,342-5 23 1,3170 32 1,2925 41 1,26910 50 1,24715 59 1,225 *20 68 1,20425 77 1,18430 86 1,16535 95 1,14640 104 1,127* The density of dry air at standard atmospheric pressure at sea level at 15° C is used as astandard in the wind industry.

Measuring windCup AnemometerWind VaneAt what height?

Tower height and wind speedV=V0⎛⎜⎝HH10α⎞⎟⎠VHHVαo1owind speed at new heightnew heightoriginal heightoriginal velocity(alpha) wind shear exponentImage from Southwest Wind Power

Tower height and wind speedWind Shear ExponentTerrainWind Shear Exponent (α)Ice 0.07Coastal waters 0.11Cut Grass 0.14Crops 0.19Hedges 0.21Trees, scattered buildings 0.29Woodlands 0.43

Wind shear: an example Assume we have a turbine mounted at a farm with aturbine height of 20 m, an anemometer height of 10 m,a wind speed of 6 m/s and a wind shear of 0.24. What is the wind speed at the turbine? V = 7.1 m/s (18% higher wind speed)

Surface Roughness

Wind Power: power extraction No energy conversion is 100% efficient Maximum theoretical wind turbine efficiency is 59.3%(Betz Limit) Most small wind systems operate at between 20%and 30% system efficiency So, our wind power equation becomes:P=½ηρAV 3

Turbine Efficiency“… you can’t beat Betz” Albert Betz calculated the theoretical maximumefficiency of a wind machine to be 59% No machine will ever come close to thismaximum› Drag› Blade tip losses› Rotor “wakes” Seek high rotor speeds and low torque (hightorque leaves a larger wake)

Solidity:ratio of blade area to swept areaLow solidity, low torqueHigh solidity, high torque

Wind Power: windswept area

Wind Power ExampleA 10 kW Bergey Excel has a 7m rotor diameter. Whatis the output power in a 4 m/s wind?• Air density is 1.225 kg/m 3• Efficiency of 25% Step 1: Windswept area Area = π*r 2 Area = 3.14 * (3.5 m) 2 Area = 38.5 m 2

Wind Power ExampleA 10 kW Bergey Excel has a 7m rotor diameter. What isthe output power in a 4 m/s wind?• Air density is 1.225 kg/m 3• Efficiency of 25% Step 2: Turbine Power Input Power = 0.5*ηρAV 3 Power = 0.5 * 0.25* 1.225 kg/m 3 * 38.5 m 2 * (4 m/s) 3 Power = 377.3 watts

Wind Power Example(original was 377 Watts)A 10 kW Bergey Excel has a 7m rotor diameter. What isthe potential power in a 4 m/s wind? What if the wind speed doubles? Power = 0.5*ηρAV 3 Power = 0.5 * 0.25* 1.225 kg/m 3 * 38.5 m 2 * (8 m/s) 3 Power = 3018 watts ; 3.0 kW

Power Density How do we know much wind is “enough” wind? Remember the influences of the solar resourceon annual energy output and, ultimately,system costs… Most people underestimate their solarresource and grossly overestimate their windresource

Wind power density Power density has units of W/m 2 (similar toirradiance in solar energy)Power class Power density (W/m 2 ) Wind speed (m/s)1 8.8

Wind Power

Wind Energy Wind is intermittent!DailySeasonally Power multiplied by time yields energy A mean wind velocity of 12 mph can yield verydifferent annual energy output in different locations

Wind Energy: Frequency distributions

Wind speed-power curveData for SWP Skystream 3.7

Wind speed-energy curveData for SWP Skystream 3.7

Skystream Energy example We have a Southwest Wind Power Skystream 3.7turbine.› Rotor diameter: 3.7 m› Average wind speed for the month of January: 5.5 m/s› System efficiency: 43%› How much electricity (kWh) is produced in January?

Skystream Energy example We have a Southwest Wind Power Skystream 3.7turbine. P = ½ηρAV 3 P = ½(0.43)(1.225)(π*1.85 2 )(5.5) 3 P = 471 Watts⎛ 24 hrs ⎞⎛31days ⎞⎛1kWh ⎞471 W ⎜ ⎟⎜⎟⎜⎟ =⎝ day ⎠⎝January ⎠⎝1000 Wh ⎠350 kWh in January

Siting a small wind turbine“30 : 300 rule”Image from Southwest Wind power

Siting a small wind turbineCoast or Lakeside Ridge top MesaImages from Southwest Wind power

Prevailing Wind Sites

Prevailing Wind Sites

Siting: Wind Power Maps An interactive wind explorer for New York Statehttp://nyswe.awstruewind.com/

Small Wind Incentives NYSERDA Power Naturally(http://www.powernaturally.org/programs/wind/incentives.asp) Database of State Incentives for Renewables andEfficiency (http://www.dsireusa.org) State incentives require a grid connect (and netmetering)

Zeeland Small Wind Test Site