What is OTEC?

Ocean Thermal Energy Conversion (OTEC) is 

“… a method of converting part of the heat from the Sun which is stored in the surface layers of a body of water into electrical energy or energy product equivalent”

[Pub. L. 96-310, Sec. 9, July 17, 1980, 94 Stst. 946.]

Principles of OTEC

The basis of OTEC technology is that water near the surface is heated by sunlight while seawater, deep in the dark, is much colder. This technology is viable, primarily, in equatorial areas where the year-round temperature differential is at least 20°C (36°F).

OTEC plants work by using warm surface water to heat ammonia, or some other fluid that boils at a low temperature, to produce gas used to drive the turbines needed to produce electricity. The gas is then cooled by cold water pumped up from the ocean depths and the resulting fluid is recycled to help generate power.

The oceans cover more than 70% of the Earth’s surface and capture a large part of the sun’s heat in the upper layers, making them the world’s largest solar collectors and energy storage system. Utilizing just a small portion of this energy can cover the global energy need.

The energy source of OTEC is free, available abundantly, and is continually being replenished as long as the sun shines and the natural ocean currents exist. Various renowned parties estimate the amount of energy that can be practically harvested to be in the order of 3 to 5 terawatts (1 terawatt is 112 watts) of baseload power generation, without affecting the temperature of the ocean or the world’s environment. That’s about twice the global electricity demand.

The oceans are thus a vast renewable resource, with the potential to contribute to the future energy mix, offering a sustainable electricity production method.

(otecfoundation, published October 25, 2012)

Benefits of OTEC


It has the potential to provide a continuous baseload, day and night (24/7) and all year-round. This is advantageous for (remote) tropical and subtropical islands that have smaller electricity networks and/or experience intermittent power. This will help them become more self-sufficient, energy wise.


Clean and safe water for drinking, nutrients to enhance the quality of fish farming, and cool greenhouses which enable food production in arid regions are some of its by-products.


Energy savings of up to 90% can be achieved by using the cold, deep seawater in building air-conditioning systems.

By-Products of OTEC

1) Clean and Safe Drinking Water:

A small 1MW hybrid OTEC plant is capable of producing, approximately, 4500 m³ of water per day, an amount enough for a population of 20,000 people. OTEC-produced water compares favourably to those from standard desalination plants, in terms of quality and production costs.

 2) Food:

Nutrient-rich, cold, deep seawater from the OTEC plant can be discharged into large ponds, near shore or on land, where it can be used for multispecies mariculture, producing high yields.

3) A Coolant:

The cold, deep seawater can be used to cool greenhouses, as seen in the Seawater Greenhouse project, and can be used for cold-bed agriculture. This water can also be used in air-conditioning systems and food refrigeration systems.

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