OTEC: Ocean Thermal Energy Conversion

Non conventional sources of energy are turning out to be extremely important sources of energy for mankind. With global warming a certainty, it is imperative that we turn to non-polluting and renewable sources of energy. One such source of energy is Ocean Thermal Energy Conversion(OTEC).

Ocean Thermal Energy (OTEC)

Ocean Thermal Energy also called as Ocean Thermal Energy Conversion (OTEC) refers to a method of using the temperature difference between the deep parts of the sea which are cold and the shallow parts of the sea which are cold to run a heat engine and produce useful work. Basically, Ocean thermal energy conversion is an electricity generation system. The deeper parts of the ocean are cooler due to the fact that the heat of sunlight cannot penetrate very deep into the water. Here the efficiency of the system depends on the temperature difference. Greater the temperature difference, greater the efficiency. The temperature difference in the oceans between the deep and shallow parts is maximum in the tropics, 20 to 25o C. Tropics receive a lot of sunlight which warms the surface of the oceans, increasing the temperature gradient.

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OTEC and its By Products

The energy source of OTEC is abundantly available, free and will be so for as long as the sun shines and ocean currents exists. Estimates suggest that ocean thermal energy could contain more than twice the world’s electricity demand. This makes it necessary for us to give it a closer look.

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Types of Ocean Thermal Energy Conversion Systems

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Closed Cycle OTEC system

  • Closed Cycle:Closed cycle Ocean Thermal Energy Conversion systems use a working fluid with a low boiling point, Ammonia for example, and use it to power a turbine to generate electricity. Warm seawater is taken in from the surface of the oceans and cold water from the deep at 5o .The warm seawater vaporizes the fluid in the heat exchanger which then turns the turbines of the generator. The fluid now in the vapour state is brought in contact with cold water which turns it back into liquid. The fluid is recycled in the system which is why it is called a closed system.
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Open System OTEC system

  • Open Cycle: Open cycle OTEC directly uses the warm water from the surface to make electricity. The warm seawater is first pumped in a low pressure chamber where due to the drop in pressure, it under goes a drop in boiling point as well. This causes the water to boil. This steam drives a low pressure turbine which is attached to an electrical generator. The advantage this system has over closed system is that, in open cycle, desalinated water in the form of steam is obtained. Since it is steam, it is free from all impurities. This water can be used for domestic, industrial or agricultural purposes.

Ocean Thermal Energy (OTEC) is a real candidate as one of the future sources of energy. Its environment impact is negligible, in fact, the mixing of deep and shallow seawater brings up nutrients from the sea floor. The deep water is rich in nitrates and this can also be used in agriculture.

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Practise This Question

Floating generators are used in the sea to harness ___.