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Tides are caused by the gravitational attraction of celestial bodies with the moon being a very major factor. Because of the changing positions of the Moon and Sun in relation to the Earth the magnitudes of the tides vary at various points on the Earth's surface, and it is the difference between the high tides and low tides that increases the potential for power generation.
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Dependability of Tidal Energy
A major advantage of tidal energy is that is that it is a source that can never be exhausted and is not dependent on climatic conditions that can affect wind energy and to some extent solar energy. It is also completely predictable and thus allows for complete dependability in its use. The disadvantage of tidal energy is that its maximum use rarely coincides with the times of peak power requirement, and thus its utility is restricted to serving as a backup power source for electric grids. This can change when advances are made in fields like superconductors that can allow electricity to be stored for long periods of time. This will allow the power from tidal energy to be produced whenever it is available and stored before use.
Image source: Wikimedia
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Methods to Generate Power From Tidal Energy
Like most forms of energy, tidal energy has two components: kinetic and potential. The kinetic energy is tapped by allowing generators to take advantage of the water rushing into coastal areas or running out of them due to the increase or decrease in tide levels. The potential energy is tapped after allowing the tides to build up behind barrages whose sluice gates are then closed . The stored water is used to drive generators just like in conventional hydropower plants. Tidal energy converters can be in the form of turbines that generate water when it passes through the foils, and such foils can be mounted either horizontally or vertically. Another method that is used to create energy from tidal differences is the oscillating hydrofoil. This is a moving arm that moves up and down with the tide and this movement allows a hydraulic system to achieve conversion to electricity. The venturi effect is used to good effect in tidal energy generators; a funnel allows in the tidal waters and the reduced area allows for higher speeds of water which can be helpful to drive the turbines more efficiently.
Another method to use tidal energy has been to install huge cylinders in the ocean. One cylinder is fixed to the ocean floor, while the other is allowed to take advantage of the tide to move up or down. This movement is then transformed into electricity through magnets. Tidal energy has also been used to force air through cylinders that then translate into movement for generators that are moved by the air pressure.
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Wave Energy and Other Methods to Produce Power From the Ocean
The constant movement of air currents in the atmosphere create winds that generate waves over the surface of the ocean. This is a form of energy from the ocean, though not as predictable as tidal energy. This movement can be tapped through mechanical devices to produce power. It is estimated that a four foot wave can produce 35,000 horsepower per mile of coast. There is almost no land requirement for the production of wave energy, which gives it a huge advantage over wind power and solar power which are land guzzlers.
The huge differences in surface temperatures in the ocean and low temperatures at ocean depths is another method being considered for production of power. Ocean thermal energy conversion has been an idea that has attracted a lot of attention because of the temperature differences of over 20 degrees Centigrade that can be found in most oceans. This temperature difference is used to condense ammonia and use this to generate power.
High construction costs have been the main hurdle to the exploitation of ocean energy. This has prevented it from being an area that can be exploited by utility companies. It is likely that higher costs of oil and other resources presently being exploited for cheap power will eventually force businesses to look at using ocean energy for producing power. Till then it will only be a subject for scientists , researchers and environmentalists.
Twenty four countries all over the world have developed systems for conversion of ocean energy using both tidal and wave energy. The estimates for power available from tidal energy alone is 200 to 400 TWH which can easily be scaled up if sufficient resources are allotted to such production.
Image source: Wikimedia