Wind power is simple physics with one steep curve in it. This tool shows the kinetic-energy equation at work so an engineer, a developer or a student can judge a site and a rotor in a minute.
Power goes with the cube of the speed
Double the wind speed and the available power goes up eight times. That is why siting dominates wind economics: a small difference in average speed between two sites is a large difference in annual energy.
The Betz limit
Albert Betz showed in 1919 that no rotor can extract more than 59.3 % of the energy in the wind, because the air must keep enough speed to clear the turbine. Commercial machines reach a power coefficient between 0.35 and 0.45, which is 59 to 76 % of that ceiling.
Capacity factor
Wind is not constant, so the capacity factor relates real annual energy to a turbine running at rated power all year. Onshore farms achieve 25 to 40 %, offshore 40 to 55 %. The capacity factor is defined against the turbine’s nameplate rating, so it needs the manufacturer’s power curve and cannot be applied to the power at the average wind speed. This tool multiplies that power by 8,760 hours and stops there.
What it does not do
Real assessments model the wind as a Weibull distribution, correct for shear up to hub height, and use the turbine’s power curve with its cut-in, rated and cut-out speeds. A year of on-site anemometer data is standard before a project is financed.
