Ocean thermal energy conversion

Ocean Thermal Energy Conversion (OTEC) is a clean, zero-emission and renewable energy technology. OTEC takes the heat from tropical oceans and converts it to electricity. OTEC is capable of generating electricity day and night, throughout the year, providing a reliable source of electricity. Although still largely untapped, OTEC is one of the world’s largest renewable energy resources and is available to around 100 countries within their nautical economical zone.

The ocean comprises an enormous energy source. Covering almost two-third of the surface of the earth, the ocean captures 70% of the solar energy that irradiates on earth. It is estimated that the solar energy that is absorbed by the ocean per year, exceeds the human energy consumption more than 4000 times. Recent research concludes that there is between 7 and 30 terawatt of electric potential energy available without having an adverse impact on natural thermal currents and ocean temperatures, this equals three to ten times the global electricity demand. This vast resource has been recognized worldwide in recent reports from the International Institute for Applied Systems Analysis (IIASA) and the International Panel on Climate Change.

An advantage of OTEC compared to other renewable energy sources is the reliable and predictable energy production. Since tropical oceans hardly encounter fluctuations in their surface temperature (neither per day, nor per season), the temperature difference between the various oceanic layers remains nearly constant. This enables OTEC to provide a base-load electricity supply with a capacity factor of 80% - 100%.

The oceans cover almost two-third of the surface of the earth and capture a majority of the solar energy that reaches the earth. Especially in tropical regions, solar energy is absorbed by the ocean and stored as heat. The balance between the incoming solar radiation and the heat loss due to evaporation and convection accounts for a constant temperature of the oceanic surface water.

As depth increases, the ocean water becomes colder, due to the accumulation of ice-cold water that has melted from the polar regions. Because of its higher density, this cold water flows along the bottom of the ocean from the poles towards the equator, displacing the lower-density water above. These two phenomena provide for a layered oceanic structure in deep, tropical oceans with a reservoir of warm water at the surface and a reservoir of cold water deeper in the ocean. The temperature difference between these layers varies between 22 °C and 25 °C. Until today this vast sustainable energy reservoir remains largely unused.

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