Estimate a wind turbine's power output and annual energy production from its rotor size, wind speed, and efficiency.
A wind turbine converts the kinetic energy of moving air passing through its rotor into electrical power. The theoretical maximum efficiency is capped at about 59% (the Betz limit), and real turbines typically achieve a power coefficient (Cp) of roughly 0.35-0.45 once mechanical and electrical losses are included.
Swept Area = π × (Diameter ÷ 2)²
Power (watts) = 0.5 × Air Density × Swept Area × Wind Speed³ × Cp
Annual Energy (kWh) = Power (kW) × Operating Hours per Year
Enter the turbine's rotor diameter, the average wind speed at hub height, air density (1.225 kg/m³ at sea level is a reasonable default), and the power coefficient (0.35-0.45 is typical for modern turbines). Add estimated annual operating hours to project yearly energy output.
A 50-meter rotor at an 8 m/s wind speed, standard air density, and a 0.40 power coefficient produces roughly 251 kW of power. Running for an estimated 2,500 hours a year at full output equivalent, that's about 627,000 kWh of annual energy production.
Power = 0.5 × air density × swept rotor area × wind speed³ × efficiency.
Because it's cubed in the formula, small increases produce large power gains.
Larger blades capture more wind energy, since output scales with swept area.