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Tial power - energy from the sea
Tidal Power Plants can be used to make electricity.
From Popular Mechanics http://www.popularmechanics.com/
Tide, periodic rise and fall of all ocean waters, including those of open sea, gulfs, and bays, resulting from the gravitational attraction of the moon and the sun upon the water and upon the earth itself.
The moon, being much nearer to the earth than the sun, is the principal cause of tides. When the moon is directly over a given point on the surface of the earth, it exerts a powerful pull on the water, which therefore rises above its normal level.
Water covering the portion of the earth farthest from the moon is also subject to this pull, so that another distinct dome of water is formed on the farther side of the earth providing the basis for a second wave.
The lunar wave crest directly beneath the moon is called direct tide, and the crest on the side of the earth diametrically opposite is called opposite tide.
At both crests, the condition known as high water prevails, while along the circumference of the earth perpendicular to the direct-opposite tidal axis, phases of low water occur.
Tides are the daily movements of large bodies of water
caused by the attraction of the sun and moon on the rotating Earth. Tides have a regular schedule, they rise and fall twice each day. Tides can be effected by seasons and storms.
Tides are lower in the winter and late fall when the sun's pull on the tides is not as strong. The sun and the moon help make tidal power but in some places it is to weak to be useful and in others it is strong enough to be used.
The energy of the tides comes from the rotational energy of the Earth. The gathering of tidal energy will not have an effect on the Earth's rotation The first known Tidal Power Plant was built in England 70 years ago.
Tidal Generating Plants are being used in China, Norway, The Soviet Republic, Great Britain, The United States, Canada, Argentina and the Cambridge Gulf of Western Australia.
The most successfully Tidal Power Plant is the Rance River Project in St. Malo in Brittany, France. During 1987 the possibility of building a Tidal Power Dam across the bay of Fundy in Nova Scotia was studied.
The tides there are the highest ones in the world 39 to 56 feet(12 to 17 meters) from low to high tide. Tidal Power Plants need special turbines that turn in two directions to help make electricity.
They turn in two directions to take advantage of the tides as they rise and fall. A dam is used to make a pool of water. The water in one pool would be kept at a high level by allowing the pool would be kept at a low level by allowing the pool to drain as the tide falls.
To build a tidal power plant you need a lot of money. You also need a site with Bays or Estuaries that can be easily dammed, plus very large tides.
The number of areas with these things are very small so tidal energy cannot be found very often. Tidal power Plants can effect the movement of ships because the dams do not let the ships go by.
This problem can be solved by using locks. Tidal Power Plant can have an effect on the enviorment. Tidal Power Plants effect delicate sea life and injured shell fishbeds already harmed by pollution and overhavesting.
Tidal Power Plants effect the food chain which causes schools of fish to move to different waters which makes people who fish for a living lose there jobs. The French have developed a new type of Tidal Power Plant that is cheaper than a dam. The systems works on a principle called siphoning.
The tide moves a huge amount of water twice each day, and harnessing it could provide a great deal of energy - around 20% of Britain's needs.
Although the energy supply is reliable and plentiful, converting it into useful electrical power is not easy.
There are eight main sites around Britain where tidal power stations could usefully be built, including the Severn, Dee, Solway and Humber estuaries.
Only around 20 sites in the world have been identified as possible tidal power stations.
Tidal power works rather like a hydro-electric scheme, except that the dam is much bigger.
A huge dam (called a "barrage") is built across a river estuary. When the tide goes in and out, the water flows through tunnels in the dam.
The ebb and flow of the tides can be used to turn a turbine, or it can be used to push air through a pipe, which then turns a turbine. Large lock gates, like the ones used on canals, allow ships to pass.
If one was built across the Severn Estuary, the tides at Weston-super-Mare would not go out nearly as far - there'd be water to play in for most of the time.
But the Severn Estuary carries sewage and other wastes from many places (e.g. Bristol & Gloucester) out to sea. A tidal barrage would mean that this stuff would hang around Weston-super-Mare an awful lot longer!
ST.-MALO, FRANCE
Considered an engineering marvel, the 31-year-old power plant consists of a nearly half-mile-long dam that also serves as a highway bridge linking St.-Malo and Dinard. At high tide, the dam traps Atlantic waters in the bay. At low tide, the water flows back to the sea. En route, it passes through 24 turbines connected to generators that produce enough electricity for a city of 300,000.
The largest tidal power station in the world (and the only one in Europe) is in the Rance estuary in northern France. It was built in 1966.
A major drawback of tidal power stations is that they can only generate when the tide is flowing in or out - in other words, only for 10 hours each day. However, tides are totally predictable, so we can plan to have other power stations generating at those times when the tidal station is out of action.
There have been plans for a "Severn Barrage" from Brean Down in Somerset to Lavernock Point in Wales.
It may have over 200 large turbines, and provide over 8,000 MegaWatts of power (that's over 12 nuclear power station's worth). It would take 7 years to build, and could provide 7% of the energy needs for England and Wales.
There may be a number of benefits, including protecting a large stretch of coastline against damage from high storm tides, and providing a ready-made road bridge. However, the drastic changes to the currents in the estuary could have huge effects on the ecosystem.
Advantages
Once you've built the dam, tidal power is free.
It produces no greenhouse gases or other waste.
It needs no fuel.
It produces electricity reliably.
Not expensive to maintain.
Tides are totally predictable.
Disadvantages
Very expensive to build.
Affects a very wide area - the environment is changed for many miles upstream and downstream.
Many birds rely on the tide uncovering the mud flats so that they can feed.
Only provides power for around 10 hours each day, when the tide is actually moving in or out.
There are very few suitable sites for tidal power stations.
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