Energy naturally present in water bodies or in their movement can be used for generation of electricity. This is achieved broadly in the following ways:
u Tidal energy: Using the "head" (height difference) between low and high tides to create a fall similar to that in a conventional hydropower project. This uses the potential energy of the water body.
u Wave energy: Using the kinetic (dynamic) energy of the waves to rotate an underwater power turbine and generate electricity thereon. This can be loosely described as an underwater wind farm.
u Thermal energy: Using the thermal energy of oceans to generate electricity. This is similar to geothermal power generation where heat trapped in the earth surface is converted into electrical energy.
The tidal energy method broadly works as follows. When a tide comes onto the shore, it is trapped in reservoirs constructed behind barrages (dams). When the tide drops, this collected water is released and is then used like in a regular hydropower project. For the tidal energy method to work effectively, the tidal difference (difference in the height of the high and low tides) should be at least 4m (around 13 ft)
Tidal energy projects are extremely site specific. The quality of the topography of the basin also needs to facilitate civil construction of the power plant.
Tidal energy is a clean mechanism and does not involve the use of fossil fuels. However, environmental concerns exist mainly to do with higher silt formation at the shore (due to preventing tides from reaching the shore and washing away silt) and disruption to marine life near the tidal basin. Wave energy projects have lesser ecological impact than tidal wave energy projects.
In terms of reliability, tidal energy projects are believed to be more predictable than those harnessing solar or wind energy, since occurrences of tides are fully predictable.
India being surrounded by sea on three sides has a high potential to harness tidal energy. The three most potential locations in this regard are Gulf of Cambay, Gulf of Kutch (west coast) and Ganges Delta, Sunderbans, West Bengal (east coast).
The total potential of tidal energy in India is estimated at 8,000 mw with Gulf of Cambay accounting for over 90 per cent.