Now, two U.S. companies have signed an agreement to build the first two floors of the world ocean thermal energy conversion (OTEC) on two islands in the Bahamas. The aim is that this technology will spread and become a sustainable energy alternative, and increasingly, economically viable for more than 100 tropical regions worldwide.
The power supply on the islands is a real problem. Granted, you can have enough wind and solar, but that supply is not always constant. On the mainland you can use the electricity transmission network itself as a store that dampens the fluctuations in power. But in the islands, are forced to invest in expensive batteries to store electricity or continue to receive supplies of fossil fuels. Tropical islands have, unknowingly, another huge potential. This is the difference between the temperature of the water surface and deeper layers, sometimes up to 20 º C cooler.
A thermal power plant uses a heat source to boil water. The heat source can come from coal, nuclear reactor or a solar concentrator tower (CHP). The steam drives a generator that produces electricity. This is what is called the Rankine cycle.
OTEC uses the temperature gradient of the ocean to produce electricity. It is based on organic Rankine cycle, a variation of the above where the water is replaced by a fluid with a very low boiling point, for example, ammonia. To cool the liquid and restart the cycle, using the colder water of the ocean. What is the source of heat? The sun heats the ocean surface and this heat is used by OTEC.
Obviously, the efficiency of OTEC system falls far short when compared to other technologies that use water vapor, so that, until now, was not economically viable. But now, OTEC plants have new and exciting benefits:
Potable water supply. Theoretically, an OTEC plant can generate up to 2MW of clean electricity, and produce 4,300 m3 of desalinated water from the ocean every day.
Cooling that can take advantage of the areas near the plant. Cold water may be used to cool buildings or the ground, allowing the cultivation of own cooler climates.