A certain form of energy is available due to the difference in the temperature of water at the surface of the ocean and its deeper levels.
(a) Name the form of energy.
(b) Is this energy ultimately derived from the sun or not?
(c) Explain how this form of energy can be converted into electricity.
(d) What is the minimum temperature difference in water at the surface of ocean and its deeper level which is required to operate power plants based on this energy?

(a) Ocean thermal energy

Explanation

The energy that is generated due to the difference between the temperatures of water at the upper surface and the deeper layers of the ocean, is known as ocean thermal energy.

(b) Yes, this energy is ultimately derived from the sun. The water at the upper surface of an ocean gets heated by the heat of the sun and attains a higher temperature than the colder water at deeper levels. Thus, ocean thermal energy is derived from the sun.

(c) Ocean thermal energy can be converted into electricity, with the help of 'Ocean Thermal Energy Conversion' (OTEC) power plants, in which a temperature difference of 20℃ or more between the surface water and the water at deeper levels is needed. In this process, the warm surface water of the ocean is used to boil a liquid, like ammonia or chlorofluorocarbons. The high-pressure vapours obtained are used to rotate the turbine of a generator to produce electricity.

(d) To operate power plants based on this energy, minimum of 20℃ temperature difference is required between the water at the surface of ocean and its deeper level.