Ocean Thermal Energy Conversion [OTEC] uses the temperature differential between the warm water at the surface of the ocean and the cold water in the deep. It is essentially the reverse of a heat transfer device, something like a giant air conditioner in reverse. The working fluid is in a closed loop system. Warm water vaporizes the fluid in a heat exchanger [evaporator] which expands to feed a turbine to generate electricity. Cool water from the deep ocean then condenses the fluid in another heat exchanger so that it can make the circuit again.
Provided that the temperature differential is fairly constant, OTEC should run on its own. The world’s biggest Ocean Thermal Energy Conversion plant will be built off the coast of China by Lockheed Martin. The 10MW offshore plant will be built to power a new green resort and test the system as a whole. Data from this plant will be used to make adjustments for efficiency and power output, which will make future installations, up to 100MW, easier to design and implement. Lockheed Martin estimates that a 100MW OTEC plant could offset 1.3 million barrels of oil and cut carbon dioxide emissions by 500,000 tons.