March 7, 2011 — Electricity generated by the ocean is gaining steam with a demonstration plant off the coast of Kona, Hawaii. The technology, Ocean Thermal Energy Conversion, is based on using solar energy stored in the world's tropical oceans and takes advantage of the temperature gradient from surface to depth. At the plant in Hawaii, cold water is pumped from 900-plus meters to the surface using a 1.4-meter in diameter pipe. "OTEC uses this water in conjunction with the warm surface water to drive turbines in a Rankine cycle power plant," said James Klett of Oak Ridge National Laboratory's Materials Science and Technology Division. The OTEC cycle runs warm water through a heat exchanger to boil ammonia, which becomes a vapor and drives the turbine to generate power. Deep ocean cold water runs through condenser heat exchangers to return the ammonia to liquid state and complete the cycle. If the demonstration proves to be as successful as expected, the next step will be to build a 5-to 10-megawatt floating plant offshore. The technology is of special interest to the military.