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| Water Power |
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| 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.
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