12 Water INTRODUCTIONEnergy 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 to 500 W, for grinding grain are still in use in remote mountains and hilly regions in the develop- ing world. There are an estimated 500,000 in the Himalayas, with around 200,000 in India [1,2]. Of the 25,000 to 30,000 watermills in Nepal, 2,767 mills were upgraded between 2003 and 2007 [3]. Paddle wheels and buckets powered by moving water were and are still used in some parts of the world for lifting water for irrigation. Water provided mechanical power for the textile and industrial mills of the 1800s as small dams were built, and mill buildings are found along the edges of rivers throughout the United States and Europe. Then, starting in the late 1800s, water stored behind dams was used for the generation of electricity. For example, in Switzerland in the 1920s there were nearly 7,000 small-scale hydropower plants.The energy in water can be potential energy from a height difference, which is what most people think of in terms of hydro; the most common example is the gen- eration of electricity (hydroelectric) from water stored in dams. However, there is also kinetic energy due to water flow in rivers and ocean currents. Finally, there is energy due to tides, which is due to gravitational attraction of the moon and the sun, and energy from waves, which is due to wind. In the final analysis, water energy is just another transformation from solar energy, except for tides.
đang được dịch, vui lòng đợi..
