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The water at the surface of an ocean gets heated by the heat of the sun and attains a higher temperature than the colder water at deeper levels in the ocean. So, there is always a temperature difference between the water "at the surface of ocean" and "at deeper levels." At many places in the ocean, this difference in temperatures of water is up to 20oC. The energy available due to the difference in the temperature of water at the surface of the ocean and at deeper levels is called ocean thermal energy (OTE). The ocean thermal energy can be converted into "usable form" of energy like electricity. This can be done as follows:
The devices used to harness ocean thermal energy are called Ocean Thermal Energy Conversion power plants (or OTEC power plants). In one type of OTEC power plants, the warm surface water of ocean is used to boil a liquid like ammonia or a chlorofluorocarbon (CFC). The high pressure vapours of the liquid (formed by boiling) are then used to turn the turbine of a generator and produce electricity. The colder water from the deeper ocean is pumped up to cool the used up vapours and convert them again into a liquid. This process is repeated again and again.
A greater advantage of the ocean thermal energy is that it can be used continuously for 24 hours throughout the year.
Ocean thermal energy is a renewable source of energy and its use does not cause any pollution. Sea-wave energy and ocean thermal energy are the two forms in which solar energy manifests itself in oceans.
The installation and maintenance of an OTEC power plant is very high and efficient commercial exploitation is difficult.
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