Two-thirds of Earth's surface is covered by oceans. These bodies of water are vast reservoirs of renewable energy. In a four-day period, the planet's oceans absorb an amount of thermal energy from the sun and kinetic energy from the wind equivalent to the world's known oil reserves. Several technologies exist for harnessing these vast reserves of energy for useful purposes. The most promising are ocean thermal energy conversion (OTEC), wave power plants, and tidal power plants. All of these produce electricity from the oceans' reserves of renewable energy. Because the ultimate source of energy from the oceans is solar radiation (or the gravitational force of the sun and the moon in the case of tidal energy), ocean energy systems are renewable, have no fuel costs, and are relatively nonpolluting when compared to conventional sources of energy, such as fossil fuels. To date, the technologies...