The development of wave and tidal resources as a source of energy is the subject of growing international investigation. Irelandís offshore renewable energy resources have significant development potential and are considered as being among the best in the world, with the practicable wave energy resource estimated at more than 6000MW.Oceans cover up more than 70% of Earth's surface, causing them to the world's greatest solar collectors. The sun's heat warms the surface water a lot more than the deep ocean water, and this temperature difference produces thermal energy. Just a small element of the heat trapped in the ocean could power the world. Workers install equipment for an sea thermal energy conversion experiment in 1994 at Hawaii's Natural Energy Laboratory. Credit: A. Resnick, Makai Ocean Engineering, Inc.

Ocean thermal energy is used for a lot of applications, including electricity generation. There are three types of electricity conversion systems: closed-cycle, open-cycle, and hybrid. Closed-cycle systems use the ocean's warm surface water to vaporize a working fluid, which has a low-boiling point, that include ammonia. The vapor expands and turns a turbine. The turbine then activates a generator to produce electricity. Open-cycle systems actually boil the seawater by operating at low pressures. This produces steam that transmits through a turbine/generator. And hybrid systems combine both closed-cycle and open-cycle systems.