Ocean thermal energy conversions - An alternative source of energy
What is OTEC?
Three-fourth of the earth’s surface is covered by water bodies, which continuously gets heated due to the heat from the sun. This vast amount of solar energy in the form of heated water if harnessed can form an excellent source of renewable energy. It has been stated that the amount of energy generated by such method will be more than twice the energy generated by using other means of harnessing ocean energy.
OTEC or Ocean Thermal energy conversion is a way of generating electricity by using the temperature difference that exists between the two layers of water. The technology uses a heat engine to generate electricity. The temperature of water is more towards decreasing latitudes, i.e. towards the center of the earth. Higher the temperature difference more the electricity generated.
The system
The system uses the ocean’s thermal gradient to convert solar energy to electrical energy. It is a known fact that the different water layers of oceans have different temperature.Till the time the difference in temperatures is more than 20 degree Celsius, the OTEC system can generate a significant amount of power. The system uses a power producing cycle to generate electricity.
The plant should be established in such an area where consistent output of energy can be acquired. The natural ocean thermal gradient is generally found in between 20 degree North and 20 degree South latitudes. The plant can also be established on an offshore platform or on land near a shore. Nowadays there are vessels that carry OTEC plants to procure energy where it is available the most.
Working
In order to generate the desired temperature different, the cold sea water layer should be brought to the surface using a pumping system utilizing centrifugal or screw pumps. One more method of bringing the cold sea water to the surface is by desalinating the cold water and hence reducing the density. This will bring the cold layer at the top without the help of a pumping system.
The OTEC system consists of a low boiling point fluid such as ammonia, which is used to run a turbine that generates electricity. The high temperature water layer is made to pass through a heat exchanger that consist ammonia. Due to heat from the high temperature water, ammonia vaporizes. The expanding vapors are forced on a turbo generator. Ammonia vapors are then passed through another heat exchanger wherein it transfers the heat to a cold sea water layer thereby again getting converted to fluid. The heated sea water is passed to the first heat exchanger where it again evaporates ammonia. In this way the power generation cycle goes on continuously to generate the necessary energy.
It is said that if only one tenth of this solar energy is utilized by the OTEC system, the amount of energy produced will be 20 times the total power consumed by the United States in a single day.
References
Images taken from the website of Institute of Ocean Energy, Saga University, Japan
