Renewable Energy - Water Power
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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 is, even a slow flowing stream of water can yield great amounts of energy.
There are many forms:
Hydroelectric energy, a term usually reserved for hydroelectric dams.
Tidal power, which captures energy from the tides in horizontal direction.
Tides come in, raise waterlevels in a basin, and tides roll out. The water
must pass through a turbine to get out of the basin.
Tidal stream power, which does the same vertically, capturing the stream of
water as it is moved around the world by the tides.
Wave power, which uses the energy in waves. The waves will usually move large
pontoons up and down.
Ocean thermal energy conversion (OTEC), which 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, not technically an energy generation method, though
it 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.
Drawbacks
Hydroelectric power is probably not a major option for the future of energy production in the developed nations because most major sites within these nations with the potential for harnessing gravity in this way are either already being exploited or are unavailable for other reasons such as environmental considerations. Building a dam often involves flooding large areas of land, changing habitats, and while hydroelectric energy produces essentially no carbon dioxide, recent reports have linked hydroelectric power to methane, which forms out of decaying submerged plants which grow in the dried up parts of the basis in times of drought. Methane is a potent greenhouse gas.
The other methods of energy generation (and cooling) have had varying degrees of success in the field. Wave and tidal power prove hard to tap, while OTEC has not been field tested on a large scale.
The general public mostly considers water power energy to be renewable.
From Wikipedia.