Wind Power

Power generated from the wind


The theoretically available power in air moving - wind - can be expressed as

P = 1/2 ρ A v3         (1)


P = power (W)

ρ = density of air (kg/m3)

A = area the wind is passing through the wind mill - perpendicular to the wind (m2)

v = wind velocity (m/s)

Be aware that density of air decrease with temperature and altitude and that the major factor in power generation is the wind velocity.

  • 20% increase in wind velocity - increases power generation with 73%

Theoretical and rated wind power generation from typical windmills are indicated in the "wind speed-power curve" below. Cut-in wind speed, rated wind speed, shut-down wind speed and rated power for windmills with 20% and 40% efficiency are indicated.

wind speed power curve

Actual Available Power

can be expressed as

Pa = 1/2 ξ ρ A v3         (2)


ξ = efficiency of the windmill (in general less than 0.4 - or 40%)

Related Mobile Apps from The Engineering ToolBox Engineering Toolbox Apps

- free apps for offline use on mobile devices.

Online Wind Power Calculator

The calculator below can be used to calculate the available power from a windmill:

Density (kg/m3)

Efficiency - ξ

Wind velocity (m/s)

Windmill diameter (m)

Generated Wind Energy

The energy generated by a windmill depends on the power generation as indicated above - and how often, or how many hours the wind blows - or more scientifically - the "wind speed frequency distribution" at the actual location.

The total energy generated over a year can be calculated by summarizing the power generation for all velocities (ranging from the actual windmill cut-in speed to the shut-down speed) multiplied with the no. of hours the wind blows at the actual speeds.

A typical wind speed frequency distribution diagram with energy produced at the different velocities are indicated below.

wind speed frequency distribution diagram

Related Topics

  • Environment - Climate, meteorology, sun, wind and environmental resources
  • Fluid Mechanics - The study of fluids - liquids and gases. Involves velocity, pressure, density and temperature as functions of space and time

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