The power in the wave is proportional to the square of the amplitude and to the period of motion. Therefor, the waves having long period (~10 s) and large amplitude (~ 2 m) are of considerable interest for power generation. Eventhough the engineering problems associated with wave-power are formidable, the amount of energy that can be harnessed is large and development work is in progress. On an average, it is estimated that about 10 kW of power is available in ocean waves and that the total amount of wave power is of the order of 2 x 106 MW.
2. Ocean Thermal Energy Conversion (OTEC)
Tropical oceans collect and store very large amount of solar energy. Utilization of this energy with associated temperature difference and conversion of this thermal energy into work and hence into electricity is the basis of ocean thermal energy conversion (OTEC) systems.
3. Tidal Energy
Tides are generated by the gravitation attraction between the earth and the moon. They arise twice a day. In mid-ocean, the tidal range is only a meter or less, but in some coastal estuaries, it is much greater.
In a tidal power station, water at high tide is first trapped in an artificial basin and then allowed to escape at low tide. The escaping water is used to drive water turbines which in turn drive electrical generators.
4. Geothermal energy
The geothermal resources is the heat stored locally at depths of 1 or 2 km in the earth's mantle in hot dry rocks having no contact with water. When ground water comes in contact with these hot rocks, either dry steam or wet steam and water are formed. After drilling such locations, the dry or wet steam emerges at the surface where its energy can be utilized either for generating electricity or for space heating.
5. Biofuels
Biomass is nothing but the material of all plants and animals. This cab transformed by chemical and biological processes into intermediate products like methane gas, ethanol liquid or charcoal solid.
Biofuels can be used to produce electricity in below mentioned two ways : a) By burning the biomass in a furnace to generate steam which will be used to drive turbines.
b) By allowing fermentation in sites or in special anaerobic tanks, to produce methane gas. This can be used as a fuel for household stores or in gas turbines.
Biofuels have a potential to meet about 5 % of the electricity requirements by exploiting all forms of these household and industrial wastes, sewerage, sledge and agriculture wastes like cow dung, sugarcane, chicken litter etc.
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