Marine energy technologies harness the natural movement or temperature of bodies of water to produce energy, and include wave, tidal, marine current, and ocean thermal energy conversion (OTEC). The technical potential for marine energy is very large, though most technologies are in development stages.
Tidal Energy: Tidal energy installations come in two general forms: tidal barrage energy and tidal stream generators. A tidal barrage is usually a structure constructed at the mouth of a bay or in a river estuary that captures water during high tide and pushes it through a hydro turbine during low tide, generating electricity. The basic principles of hydropower apply, even though tidal energy deals with a massive volume of water moving very slowly. Tidal stream generators convert the kinetic energy of moving water into electricity through the use of horizontal, vertical, and oscillating turbines, which can resemble underwater wind turbines. Electricity is generated by tidal water flowing both into and out of a bay, and the flow of water is not restricted.
Marine Current Energy: As with tidal stream generators, marine current power utilizes submerged turbines to capture energy from the movement of ocean water, but only within marine currents where water moves in just one direction. In the U.S., the Florida Current and the Gulf Stream are reasonably swift and continuous currents moving close to shore in areas where there is a demand for power.
Wave Energy: Wave energy devices either float on the surface of the ocean or are fixed to the ocean floor, and can be employed both on the shoreline and in deep waters. A number of technologies have emerged to capture energy from the movement of waves, including floating devices that bend with the waves and others that utilize pressure fluctuations in tubes caused by waves going up and down.
Ocean Thermal Energy Conversion (OTEC): OTEC uses the temperature difference from the warmer surface of a body of water to its cooler, lower depths for electricity generation, water desalinization, air conditioning, and other purposes. There are three general forms of OTEC technologies, including open cycle, closed cycle, and hybrid cycle systems.