The earth gets unevenly heated by the sun. During the day when sun shines, the air over landmasses gets heated more quickly than the air over water. Since this air is warm it expands and rises, and the heavier cool air, over the water, moves to take its place creating local winds. During night time, this process gets reversed. The wind that blows is called a renewable energy source because wind will be produced as long as the sun shines over the earth.
Wind renewable power has been used as an alternative energy source since long in traditional forms but its sophisticated use was first made in Netherlands. Wind mills are used to generate wind renewable power. The wind mills capture the renewable wind energy that is used to rotate turbines to generate electricity. This generated electricity can be used as an alternative energy source to pump water in wells for irrigation, for lighting houses and streets and for use in small units of industries.
The amount of electricity generated by wind renewable power from a single wind mill cannot be used for commercial purposes. Therefore, to generate wind power or electricity for commercial use a number of wind mills are erected over a large area known as a Wind Energy Farm.
The calculation of average wind speeds is required since different wind mills are suitable for different speeds in different terrains. The design and construction of wind mills or machines that use wind renewable power can be adapted to suit a specific location and the end use of the electricity generated by wind power.