Ocean Thermal Energy Conversion

Our oceans cover over 70% of the globe’s surface. The solar energy that is received by the oceans is mainly absorbed and converted into heat, due to the low reflectivity, or albedo, of the ocean. This heat is trapped in the upper layer of the ocean, above the thermocline, which is the transition layer between the mixed layer at the surface and the deep water layer. The ocean is very cold below the thermocline. This cold water is replenished by the global ocean conveyor belt, the thermohaline cycle, bringing the cold water all the way from the artics. As such, the tropical ocean can be seen as a huge, constantly charging, thermal battery.

Ocean Thermal Energy Conversion (OTEC) uses the temperature difference between the surface and deep layers to generate electricity. The energy production with OTEC is very constant, as the temperatures in the ocean hardly vary between day and night or even between the seasons. This makes OTEC a very reliable source of energy that can be easily integrated into the electricity grid.

The basic working principle of OTEC is quite simple. The warm water is used to evaporate a working fluid with a low boiling point. The high pressure vapour that is produced drives a turbine-generator to produce electricity. The cold deep seawater is used to condense the working fluid vapour back into a liquid. Finally, a pump drives the working fluid back into the evaporator, to complete the fully closed cycle. In essence, this is similar to how power is produced with a steam cycle found in thermal baseload plants such as coal or nuclear plants, but then in a completely clean and sustainable manner.

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