Water Power
Energy in water can be harnessed and used in the form of motive energy or temperature differences. Since water is about a thousand times heavier than air, even a slow flowing stream of water, or moderate sea swell, can yield great amounts of energy.
There are many forms. Hydroelectric energy is a term usually reserved for hydroelectric dams. Tidal power captures energy from the tides in vertical direction. Tides come in, raise water levels in a basin, and tides roll out. The water must pass through a turbine to get out of the basin. If the basin is a river delta then silt will block the turbine. Tidal stream power captures a stream of water as it is pushed horizontally around the world by tides. Wave power uses the energy in waves. The waves will usually make large pontoons go up and down in the water, leaving an area with no waves in the "shadow". Ocean thermal energy conversion (OTEC) uses the temperature difference between the warmer surface of the ocean and the cool (or cold) lower recesses. To this end, it employs a cyclic heat engine. Deep lake water cooling, although not technically an energy generation method, can save a lot of energy in summer. It uses submerged pipes as a heat sink for climate control systems. Lake-bottom water is a year-round local constant of about 4 °C. Blue energy is the reverse of desalination.
US Hydroelectric Resources |
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