The wind power is utilised by the wind mill stations which have many large wind mills equipped with large multiple fan blades which are rotated by the wind, thus these wind mills convert wind energy to electrical energy. The hydroelectric power stations contribute fifteen percent of the global generation of electricity. The hydroelectric power stations consist of hydro turbines which convert the mechanical energy produced by the falling of water on the blades of turbine into electrical energy with the help of alternators coupled to it. The solar energy obtained from the sunlight can be used to charge large amount of photovoltaic cells which further converts the light energy into electrical energy. This solar energy can be used to light up the street lights, operate fans and solar air conditioners. This solar energy can also be used to cook food with the help of solar cookers. The other types of renewable sources of energy are the bio fuels which contribute about 11 to 13 percent of generation of electricity. These bio fuels are obtained from the biomasses formed by plants, trees and other green vegetations. The bio fuels like ethanol, biodiesel etc can be used as fuels in internal combustion engines and boilers. The bio gases can be used as natural gas fuels. There also exist geothermal power stations which uses the hot air and team present deep inside the earth to produce electricity.