Wind Power

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The theoretically available power in the wind can be expressed as

P = 1/2 ρ A v³         (1)

where

P = power (W)

ρ = density of air (kg/m³)

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

v = wind velocity (m/s)

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

• 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

P_a = 1/2 ξ ρ A v³         (2)

where

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

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.

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Related Topics

• Environment - Climate, Meteorology, Sun, Wind and environmental resources ..
• Fluid Mechanics - The study of fluids - liquids and gases. Involves various properties of the fluid, such as velocity, pressure, density and temperature, as functions of space and time.

Related Documents

• Air - Altitude, Density and Specific Volume - The density and the specific volume of air varies with the elevation above sea level
• Air - Density and Specific Weight - Density and specific weight of air at temperatures ranging -40 - 1000 ^oC (-40 - 1500 ^oF) at standard atmospheric pressure - Imperial and SI Units
• Air - Temperature, Pressure and Density - Air density for pressures and temperatures ranging 0 - 1000 psi and 30 - 600 deg F
• Air Properties - Temperature, density, specific heat, thermal conductivity, expansion coefficient, kinematic viscosity and Prandtl's number for temperatures ranging -150 - 400 ^oC
• Power - Power is a measure of the rate at which work is done or energy converted
• Wind Energy - Available wind energy
• Wind Load - Wind load on a surface
• Wind Shear - Wind is slowed down at the surface by trees and obstructions
• Wind Turbine Power Calculator - Online wind turbine calculator