OTEC
Ocean thermal energy conversion (OTEC) technology converts solar energy stored in the layers of the tropical and subtropical oceans. Thermal heat engines use the temperature difference between the sun-warmed surface water and cold water in the deep ocean. The temperature difference between surface waters and deeper water can reach over 25oC in summer months, although usually this temperature difference exists only over water with depths of 1,000 m or greater. Many different OTEC archetypes have been investigated, some on floating offshore platforms and some built onshore with pipelines to transport the water to and from the ocean. Each system uses one or a combination of thermodynamic processes to turn the temperature difference into mechanical energy. Both the open-cycle and closed-cycle plants use cold water pumped from the deep ocean to condense a working fluid. An ancillary benefit is that the condensate is freshwater that can have other uses such as agriculture and potable drinking water.
Photo: Okinawa Prefecture Industrial Policy Division