Wind Power Extraction by Wind Turbines
There is a limit, only a partial extraction of power available in the wind is possible. The amount of extracted wind power in percentages is termed the Power Coefficient (Cp). For example, 25% Cp indicates that only 25% out of 100% available wind power is extracted.
The limit for power extraction from wind is 59.3%, which is Betz's law. A wind turbine extracts wind power by slowing down incoming wind velocity through the rotor blades and letting pass through. The maximum power is extracted when the incoming wind velocity is reduced by one-third at the rotor.
The actual Power Coefficient (Cp) of a wind turbine is below 59.3% due to aerodynamic, generator, and cable losses.
Modern wind turbines operate at a certain Tip Speed Ratio (TSR) to optimize the power output. TSR is the ratio between the velocity of the tip of the blade and the incoming wind speed. The rotor of a wind turbine rotates at a certain rpm (revolutions per minute) for a given wind speed to keep the ratio.
