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Wind energyFrom Wikipedia, the free encyclopedia

Wind energy is the kinetic energy of air in motion; see also wind power.

Total wind energy flowing through an imaginary area A during the time tis:

where v is the wind speed; is the air density; Avtis the volume of air passingthrough A (which is considered perpendicular to the direction of the wind); Avt is

therefore the mass m passing per unit time. Note that v2 is the kinetic energyof the moving air per unit volume.

Power is energy per unit time, so the wind power incident on A (e.g. equal to therotor area of a wind turbine) is:

Wind power in an open air stream is thus proportional tothe third power of the wind speed; the available powerincreases eightfold when the wind speed doubles. Windturbines for grid electricity therefore need to be especiallyefficient at greater wind speeds.

History of usage by humans

The wind has been used for thousands of years as a sourceof energy. Sailors capture it in the sails of their ships, and weather has therefore had important historicalconsequences, for example, the Spanish Armada was defeated with the help of stormy weather aroundthe British Isles. The Netherlands are famous for the use of windmills with four cloth sails. These wereused for pumping water to drain polders forming agricultural land. In the UK, Norfolk borrowed thisDutch expertise to do the same, leaving distinctive features on the flat lowland landscape.

Electric energy

Renewable energy

Biofuel

BiomassGeothermal

HydroelectricitySolar energy

Tidal power

Wave powerWind power

Windsock

Contents

1 History of usage by humans 2 Electric energy

2.1 Theoretical power captured by a wind turbine 2.2 Practical wind turbine power

3 References 4 See also 5 External links

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Main articles: Wind power, Wind turbine, and Electricenergy

Theoretical power captured by a wind turbine

Total wind power could be captured only if the windvelocity is reduced to zero. In a realistic wind turbine this isimpossible, as the captured air must also leave the turbine. Arelation between the input and output wind velocity must beconsidered. Using the concept of stream tube, the maximalachievable extraction of wind power by a wind turbine is

59% of the total theoretical wind power[1] (see: Betz' law).

Practical wind turbine power

Further insufficiencies, such as rotor blade friction and drag, gearbox losses, generator and converterlosses, reduce the power delivered by a wind turbine. The basic relation that the turbine power is(approximately) proportional to the third power of velocity remains.

References

1. ^ The Physics of Wind Turbines Kira Grogg Carleton College,2005, p.8

See also

Wind power

External links

- Wind Energy Resource Atlas of the United States

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Map of available wind power for the

United States.

Example of a horizontal axis machine

Wind TurbineSustainable energy Wind power

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