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Tidal Energy

Tidal cycles are caused by rise and fall of the tides occurring every 12 hours due to gravitational force of the moon. Water flowing in and out of estuaries carries energy and the amount of energy extractable depends on the area intercepted and speed of flowing stream. Tidal range can be forecasted with a high level of accuracy and is highly predictable when compared to wave, solar and wind energy. The current in tidal flows is constant over the water depth, hence it makes tidal energy to be a greatest opportunity to harness energy. There are mainly two methods for generating energy from tidal: Tidal Barrages and Tidal Stream Turbines. Variation in tides ranges from 4.5m to 12.4m; however, to harness tidal energy economically at least 7m high tide is required to head start the turbine. The cost efficiency of tidal power plant depends on the ‘Gibrat’ ratio, which is the ratio of the length of the barrage (in meters) to annual energy production in kWh. The smaller the ratio the better the site is for harnessing energy. The harvestable tidal energy resource is estimated at 1 terawatts (TW) globally. Extensive plans exist for tidal barrage projects in India, Korea, the Philippines and Russia adding up to around 115 gigawatts (GW). The sites such as Severn Estuary between Southwest England and South Wales are examples of favorable sites which could provide 12 GW (approximately 10% electricity need of the country) of energy. Several sites in the Bay of Fundy, Cook Inlet in Alaska, and the White Sea in Russia are found to have the potential to