OTEC
OTEC stands for Ocean Thermal Energy Conversion. The basic idea is that you use the temperature difference between warm surface water and cold deep water to power a heat engine to generate power. Because the temperature difference between these two heat reservoirs is small, the efficiency tends to be quite low. The technology required is not at all unlike the technology in your refrigerator. Furthermore, the lower temperatures make it easier to design than traditional heat engines that operate at much higher temperatures.
