Energy from thermal gradient

The first power plant for the conversion of ocean thermal energy was created in 1996 offshore the Hawaii islands and produces energy exploiting the temperature difference between the different layers of the ocean. The solar energy absorbed by the sea surface heats it, creating a temperature difference between the surface water, whose temperature is around 25-28°C, and deeper water, up to 600 m depth, and whose temperature does not exceed 6-7°C.
Superficial water, which is warmer, lets substances like ammonia and fluoride evaporate. High-pressure vapours activate a turbine and an electricity generator; they pass into a condenser, go back to a liquid state and are cooled down by the water, which is sucked from the bottom. A 20°C difference is sufficient to guarantee the production of an economically exploitable quantity of energy. At the moment there is a power of 50 kW/h, but it will probably be possible to reach 2 MW even though the costs are very high. (Many abandoned sea platforms for the extraction of hydrocarbons could be converted for the application of this technology).

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