# Wind Power

## Power generated from the wind

Theoretically power in moving air - or wind - can be calculated

P =ρA v^{3}/ 2

=/ 8 (1)ρπ d^{2}v^{3}

where

P = power (W)

ρ = density of air (kg/m^{3})

A = wind mill area perpendicular to the wind (m^{2})

v = wind speed (m/s)

= 3.14....π

d = wind mill diameter (m)

Be aware that the density of air decreases with temperature and altitude and that the major factor in wind power generation is **wind speed**.

*20% increase in wind velocity will increase the power generation with 73%*

The theoretical and rated wind power generation from a typical windmill is 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.

### Actual Available Power

Actual available wind power can be calculated

P_{a}= ξρA v^{3}/ 2

(2)ξρπ d^{2}v^{3}/ 8

where

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

### Example - Wind Power

The actual available power from a wind mill with diameter *1 m*, efficiency *0.2 (20%) *- with wind velocity *10 m/s* - can be calculated as

*P _{a} = (0.2) (1.2 kg/m^{3}) π (1 m)^{2} (10 m/s)^{3} / 8*

* = 94.2 W*

### Related Mobile Apps from The Engineering ToolBox

- 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 of air (kg/mρ^{3})

- efficiency of windmillξ

v - wind speed (m/s)

d - windmill diameter (m)

### Generated Wind Energy

The energy generated over time depends on the wind mill potential 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 is indicated below.