Physics

(b) Energy From Sea :
(i) Tidal energy : Due to the gravitational pull of mainly the moon on the spinning earth, the level of water in the sea rises and falls.This phenomenon is called high and low tides and the difference in sea-levels gives us tidal energy. Tidal energy is harnessed by constructing a dam across a narrow opening to the sea.
A turbine fixed at the opening of the dam converts tidal energy to electricity.
(ii) Wave Energy : The kinetic energy possessed by huge waves near the seashore can be trapped in a similar manner to generate electricity.
The waves are generated by strong winds blowing across the sea. Wave energy would be a viable
proposition only where waves are very strong. A wide variety of devices have been developed to trap wave energy for rotation of turbine and production of electricity.
(iii) Ocean Thermal Energy :
The water at the surface of the sea or ocean is heated by the Sun while the water in deeper sections is relatively cold. This difference in temperature is exploited to obtain energy in ocean-thermal-energy conversion plants. These plants can operate if the temperature difference between the water at the surface and water at depths up to 2 km is 293 K (20°C) or more. The warm surface-water is used to boil a volatile liquid like ammonia. The vapours of the liquid are then used to run the turbine of generator. The cold water from the depth of the ocean is pumped up and condense vapour again to liquid.
The energy potential from the sea (tidal energy, wave energy and ocean thermal energy) is quite large, but efficient commercial exploitation is difficult.