Ocean thermal energy conversion (OTEC) systems use the temperature difference of surface and deep water to make energy. This idea is not new but actually dates back to 1881, when a French engineer by the name of Jacques D'Arsonval first thought of OTEC. Ocean water gets colder the deeper you go from the surface, and at a great depth the ocean gets very cold. It is warmer on the surface because sunlight warms the water.
Power plants can be built that use this difference in temperature to make energy. A difference of at least 21°C is needed between the warmer surface water and the colder deep ocean water. Using this type of energy source, an OTEC system is being demonstrated in Hawaii.
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