Power generated from the wind
The theoretically available power in the wind can be expressed as
P = 1/2 ρ A v3 (1)
P = power (W)
ρ = density of air (kg/m3)
A = area wind passing through perpendicular to the wind (m2)
v = wind velocity (m/s)
- a 20% increase in the wind velocity - increases the power generated with 73%
Theoretical and rated wind power generation for 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.
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%)
- free apps for offline use on mobile devices.
Online Wind Power Calculator
The calculator below can be used to calculate available power from a windmill:
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.