Alternative Energy Sources

Although there are several ways of utilizing energy from the oceans, the most promising ones are the harnessing of tidal power and ocean thermal energy conversion. The power of oceanic tides is based on the difference between the (usually) twice-daily high and low water levels. In order for tidal power to be effective, this difference in height must exceed about 15 ft (3 m). There are only a few places in the world where such differences exist, however, including the Bay of Fundy in Canada and a few sites in China.

Oceanic thermal energy conversion utilizes temperature differences rather than tides. Ocean temperature is commonly stratified, especially near the tropics; that is, the ocean is warmer at the surface and cooler at depth. Thermal energy conversion takes advantage of this fact by using a fluid with a low boiling point, such as ammonia. Vapor boiled from this fluid by warm surface water drives a turbine, with cold water from lower depths being pumped up to condense the vapor back into liquid. The electrical power thus generated can be shipped to shore over transmission lines or used to operate a floating industrial operation such as a cannery.

It is unlikely, however, that ocean-derived energy will ever make a large contribution to world energy use; the number of suitable sites for tidal power is small, and the large-scale use of thermal energy conversion would likely cause unacceptable environmental damage.