ABSTRACT
Energy from water is one of the oldest sources of energy, as paddle wheels were used to rotate a millstone to grind grain. A large number of watermills, 200–500 W, for grinding grain are in use in remote mountains and hilly regions in the developing world. Around one-quarter of the solar energy incident on the Earth goes to the evaporation of water; however, as this water vapor condenses, most of the energy goes into the atmosphere as heat. Only 0.06% is rain and snow, and that power and energy of the water flow is the world resource, estimated at around 40,000 TWh/year. In terms of renewable energy, large-scale hydropower is a major contributor to electric generation in the world, over 3000 TWh/year. The world installed capacity for large-scale hydroelectricity has increased around 2% per year, from 462 GW in 1980 to around 850 GW in 2009. Large-scale hydroelectric plants have been constructed all across the world.
