Calculate wind turbine power coefficient Cp, Betz limit percentage and electrical efficiency from rotor size, wind speed, air density and measured output.
A wind turbine efficiency calculator estimates how effectively a turbine converts wind power into rotor power and electrical power. The main aerodynamic value is power coefficient Cp, while the final electrical output also depends on generator, controller and inverter efficiency.
Wind turbine Cp vs efficiency
Cp is the fraction of available wind power captured by the rotor. Electrical efficiency is the fraction retained after generator and power electronics losses. Overall efficiency is usually Cp multiplied by electrical conversion efficiency.
Why Betz limit matters
The Betz limit is the theoretical maximum rotor power coefficient. If a calculation gives a Cp higher than 59.3%, the input data is likely wrong, the wind speed is underestimated, rotor diameter is wrong, or measured power is not being compared correctly.
Cp means power coefficient. It shows how much of the available wind power passing through the rotor area is captured by the rotor as mechanical power.
For small practical turbines, Cp around 25–40% is common depending on blade design and operating point. Well-designed rotors may go higher, but no real rotor can exceed the Betz limit.
The Betz limit is the theoretical maximum rotor efficiency, about 59.3% of the kinetic wind power through the rotor area.
Rotor Cp cannot be more than 59.3% under the ideal Betz model. If your calculated Cp is above this, check wind speed, diameter, air density, unit conversion and whether the power value is electrical or mechanical.
No. Cp is an instant aerodynamic efficiency value. Capacity factor is an energy production value over time, usually annual energy compared with rated power running all year.
Calculate available wind power using 0.5 × air density × swept area × wind speed cubed. Then divide measured rotor power by available wind power for Cp, or divide electrical output by available wind power for overall efficiency.
The most common causes are underestimated wind speed, wrong rotor diameter, using peak power instead of steady measured power, unit conversion mistakes, or measuring in gusts rather than average wind.
No. Each blade design has an optimum tip speed ratio. Too low or too high TSR can reduce Cp, increase noise, cause stall or create unnecessary drag losses.