The Sea Energy :
The energy obtained from sea can be classified into three parts:
(1) Tidal Energy
(2) Wave Enrgy
(3) Ocean Thermal Energy
1. Tidal Energy : The energy produced due to high and low tides is called tidal energy.
Tidal energy obtained from rising and falling of the level of sea water during tides.
Tide : The phenomenom of changing the level of the water of sea during the day is called tide.
Cause of tide :
(i) Rotation of the Earth
(ii) The gravitational pull of the moon
Tapping of 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.
2. 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. A wide variety of devices have been developed to trap wave energy for rotation of turbine and production of electricity.
Limitation of wave energy :
(i) Wave energy would be a viable proposition only where waves are very strong.
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 (OTEC) plants.
Ocean-thermal-energy conversion (OTEC) plants : This is a device which is used to produce electric energy to use the heat from the difference of the temperature of top of ocean and the deeeper section.
Tapping of Ocean Thermal Energy :
OTEC plant is used for tapping this energy. This plant works when 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.
Limitation of Ocean Thermal Energy :
(i) The difference in temperature of the top and deeper section should be 20०C.
(ii) Efficient commercial exploitation is difficult.
Geothermal energy : When underground water comes in contact with the hot spot, steam is generated. The steam trapped in rocks is routed through a pipe to a turbine and used to generate electricity.
Hot spots: Due to geological changes, molten rocks formed in the deeper hot regions of earth’s crust are pushed upward and trapped in certain regions called
Hot Springs : Sometimes hot water from that region finds outlets at the surface. Such outlets are known as hot springs.
(i) The cost of production would not be much.
(ii) Tapping of this energy is practically better for commercial use.
(i) There are very less regions of geothermal energy on the Earth.
(ii) Reaching in such hot spots is very defficult and costly.