Ocean Thermal Energy Conversion uses the temperature difference between surface and deep-sea water to generate electricity – and though it has an efficiency of just 1-3% – researchers believe an OTEC power plant could deliver up to 250MW of clean power, equivalent to one eighth of a large nuclear power plant, or one quarter of an average fossil fuel power plant. Architect and engineer Dominic Michaelis and his son Alex, along with Trevor Cooper-Chadwick
of Southampton University are developing the concept with plans of putting the theory to the test on an unprecedented scale by building a floating, hexagonal Energy Island that will harness energy from OTEC, as well as from winds, sea currents, waves, and the sun.

The US National Renewal Energy Laboratory estimates that the world’s tropical seas absorb the solar power equivalent of 250 billion barrels of oil per day. OTEC uses warm surface water to vaporize a fluid with a low boiling point, typically ammonia or propane, and pumps cooler water from depths of up to 1000 meters below the surface to re condense the fluid. The movement of the liquid through the system is enough to continually power a turbo-generator. The simplistic
nature of the station, which behaves almost like a gigantic internal combustion engine, allows OTEC power plants to be largely self-sufficient. And unlike wind and solar energy, which have a fluctuating output that changes according to the weather and the time of day, the regularity of ocean temperatures and movements provide a far more stable and consistent source of power. As the Energy Island site states, despite being 100 years old, OTEC is in its infancy.
But given the renewed interest, and the multitude of various benefits, it’s possible that the next 100 years of this concept could profoundly change the energy and environmental management of the Earth.

Dr.A.Jagadeesh Nellore(AP),India

http://www.lockheedmartin.com/content/dam/lockheed/data/ms2/documents/OTEC-brochure.pdf

In the case of Ocean Thermal Energy Conversion (OTEC) systems the so-to-speak boiler uses the unheated warm surface ocean water to boil a liquid like ammonia. This ammonia vapor then powers a typical turbine generator set. This is commonly referred to as the HOT side of a power plant. Not much different than a coal, natural gas or nuclear power plant – it just runs at a much lower temperature.

The COLD side of a OTEC power plant used deep ocean water to cool the ammonia vapor back into a liquid so the whole generation process can be repeated over and over again. The cold ocean water comes from a depth of about 2000-3000 feet below the oceans surface. In various locations around the world this can result in a 20-40 degree temperature difference which can makes OTEC financially feasible.

It is a good concept but requires massive amounts of water to work efficiently since there is such a small difference between the HOT side of the power plant and the COLD side. It is however, carbon free, works 24/7/365, and is fuel free renewable energy. Sometimes people forget that our oceans are just one gigantic solar panel since the sun heats the surface water. Finding economical ways to use that solar energy is the challenge but it can be done.

http://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion

If so they’re doing it wrong. The usual plan is to use some liquid with a low boiling point like ammonia for the working fluid.