Ocean Thermal Energy Conversion

Ocean Thermal Energy Conversion (OTEC) is a means of converting into useful energy the temperature difference between surface water of the oceans in tropical/sub-tropical areas and water at a depth of approximately 1,000 metres, the latter of which comes from the Polar Regions. For OTEC, a temperature difference of 20°C is adequate, thus it embraces very large ocean areas.

OTEC is a large resource, with 2,000 GW of potential capacity.

Oceans cover more than 70% of Earth’s surface, making them the world’s largest solar collectors. The sun’s heat warms the surface water a lot more than the deep ocean water, and this temperature difference creates thermal energy. OTECs can be sited anywhere across about 60 million square kilometres (23 million square miles) of tropical oceans-anywhere there is deep (and, therefore, cold) water lying under warm surface water. This generally means at latitudes within about 20 or 25 degrees of the equator-very roughly between the Tropic of Cancer and the Tropic of Capricorn. (For meteorological reasons this zone is somewhat contracted along the west coasts of continents and expanded along the east coasts.) Surface water in these regions, warmed by the sun, generally stays at 25 degrees Celsius (77 degrees Fahrenheit) or above. Ocean water more than 1,000 metres (0.6 miles) below the surface is generally at about four degrees C (39 degrees F). Since the average ocean depth is about 4,000 metres (2.5 miles), there is a vast reservoir of cold deep water under tropical skies, some 180 million cubic kilometres (43 million cubic miles). And even this inconceivably vast resource is constantly being renewed by deep cold-water flows from the Polar Regions.

Depending on the location of their cold and warm water supplies, OTEC plants can be land-based, floating, or as a longer term development, grazing.
OTEC plants have a significant advantage over other forms of ocean energy, in that they provide base-load electricity. The thermal resource of the ocean ensures the power source is available day or night and with only modest variation from summer to winter.

OTEC is environmentally benign, and some floating OTEC plants would actually result in net CO2 absorption.