TIDAL ENERGY

WHAT IS TIDAL ENERGY?

Tidal energy is the utilization of the sun and moon's gravitational forces - as tides are formed by the gravitational pull of the sun and moon on the oceans of the rotating earth. Tides can be found with varying degrees of strength on any coastline, and sometimes even at sea, although these are better known as currents. A flood tide is one that is coming in or rising and an ebb tide is one that is going out. Tidal energy is one of the oldest forms of energy used as evidence of tide mills from before 1100AD have been found along the coast of France, Spain and the UK.

METHODS OF CONVERTING TIDAL ENERGY INTO ELECTRICITY

Tide mills existed more than nine hundreds years ago. When the tide comes in, water flows through a sluice into a storage pond. When the tides go back out, the water flows back into the sea through a water wheel. The difference between the tide mill and today's tidal power plant is the size of the unit and the amount of energy generated. The modern version of a tide mill is a semi-permeable barrage built across an estuary, allowing floodwaters to fill an impounded basin via a series of sluices. At high water the sluice gates are closed, creating a head of water on the ebb tide. Releasing the water through a series of conventional bulb turbines generates electricity. In future schemes the energy yield would be enhanced by pumping water into the estuary on the flood tide ('flood pumping'), thereby increasing the volume of water released through the turbines on the ebb tide.

Another method of utilizing tidal energy is to build a barrage or barrier with gates of some kind at the opening of a bay or a river system to create an estuary or a big basin. The gates create differences in the water levels between the estuary and the ocean, therefore enabling the generation of electricity. For example, when the tide falls, the receding water retreats back to the ocean by passing through a turbine located in the barrage; generating electricity. Electricity can also be generated when the open gate lets water flow into the estuary during peak periods of high tide. This is commonly called the barrage technique.

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ADVANTAGES OF TIDAL ENERGY

The most important advantage of tidal energy is its economical benefits, as tidal energy does not require any fuel. Tides rise and fall every day in a very consistent pattern. The economic life of a tidal plant is very high. A plant is expected to be in production for 75 to 100 years, in comparison with the 35 years of a conventional fossil fuel plant. Besides the economical factors, tidal energy is clean and renewable, unlike fossil fuels. Tidal energy offers a lot of potential to be a substitute for hydrocarbon and fossil fuels. A very important feature of tidal energy is that it is non-polluting. A tidal barrage can prevent approximately one million tons of CO₂ per TWH generated. A barrage can also safeguard coastlines from storms.

DISADVANTAGES OF TIDAL ENERGY

The altering of the ecosystem at the bay is the biggest drawback of tidal power. Damages like reduced flushing, winter icing and erosion can change the vegetation of the area and disrupt the balance. The alteration of tidal currents affects the habitat of the seabirds and the fish. Similar to other ocean energies, tidal energy has several prerequisites that make it only available in a small number of regions. For a tidal power plant to produce electricity effectively (about 85% efficiency), it requires a basin or a gulf that has a mean tidal amplitude (the differences between spring and neap tide) of 7 meters or above. It is also desirable to have semi-diurnal tides where there are two high and low tides everyday. Tides out in the ocean have maximum amplitude of about one meter. As you move closer to shore, this can increase to as high as 12 or more. This can depend on local features such as shelving or funneling meaning the tidal range can vary considerably along any given coastline. This can mean that a lot of places just aren't suitable. When planning the location major consideration has to be given to see whether the tides ar high enough and if there is a suitable place for building the site.