Where does Wind Energy come From?
All renewable energy (except tidal and geothermal power), and even the energy in fossil fuels, ultimately comes from the sun. The sun radiates 174,423,000,000,000 kilowatt hours of energy to the earth per hour. In other words, the earth receives 1.74 x 10 17 watts of power . 1)
About 1 to 2 per cent of the energy coming from the sun is converted into wind energy. That is about 50 to 100 times more than the energy converted into biomass by all plants on earth. 2)
Temperature Differences Drive Air Circulation
Sea Temperature World Map The regions around equator, at 0° latitude are heated more by the sun than the rest of the globe. These hot areas are indicated in the warm colours, red, orange and yellow in this infrared picture of sea surface temperatures (taken from a NASA satellite, NOAA-7 in July 1984).
Hot air is lighter than cold air and will rise into the sky until it reaches approximately 10 km (6 miles) altitude and will spread to the North and the South. If the globe did not rotate, the air would simply arrive at the North Pole and the South Pole, sink down, and return to the equator.
1) The power emission from the sun is 1.37 kW/m 2 on the surface of the sphere, which has the sun as its centre and the average radius of the earth trajectory. The power hits a circular disc with an area of of 1.27 x 10 14 m 2 . The power emitted to the earth is thus 1.74 x 10 17 W.
2) On average, plant net primary production is about 4.95 x 10 6 calories per square metre per year. This is global NPP, Global net primary production , i.e. the amount of energy available to all subsequent links in the food/energy chain. The earth's surface area is 5.09 x 10 14 m 2 . The net power output stored by plants is thus 1.91 x 10 13 W, or 0.011% of the power emitted to earth. You may find the conversion factor between the energy units calories and Joule in the reference manual .
© Copyright 1997-2003 Danish Wind Industry Association
Updated 1 June 2003
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