Wind Turbine Calculator

Use this calculator when you are sizing a small wind turbine or want a back-of-envelope check before talking to a supplier.

Power is ½ × air density (1.225 kg/m³) × the disc the blades sweep × wind speed cubed × Cp. The disc comes from the rotor diameter. Diameter can be entered in metres (m) or feet (ft); it is converted to metres before the formula. Wind speed stays in metres per second (not km/h). Hours are equivalent full-load hours, not clock hours. Yearly energy is kW × those hours; profit is that energy × the price you type, minus yearly running cost. Cp cannot go above about 0.59 (the Betz limit). This is not a bankable yield study.

Rotor diameter: Tip-to-tip diameter of the rotor, in m or ft. A small turbine is often 3–15 m.

Wind speed (m/s): Average wind at hub height in m/s. 8 m/s is a decent site; 4 m/s is weak.

Power coefficient Cp: How much of the wind’s power the machine actually captures. Try 0.4; the physics cap is about 0.59.

Full-load hours / year: Equivalent hours at full power in a year, often 2,000–4,000, not 8,760 clock hours.

Price / kWh: What you are paid (or save) per kWh, e.g. 0.12.

Yearly running cost: Yearly upkeep in the same currency as the kWh price.

kW: Instantaneous power at the entered wind speed.

kWh / year: Energy from those full-load hours.

Profit / year: Energy revenue minus opex.