EVEN by the standards of American bureaucracy, an organisation that operated for 13 years without achieving anything is impressive. Yet that was the fate of the Ocean Thermal Energy Conversion (OTEC) permit office, which opened its doors in 1981 and closed them in 1994, having issued not a single OTEC permit. The office was part of NOAA, America’s National Oceanic and Atmospheric Administration—a marine counterpart of the country’s space agency, NASA. And the idea of OTEC was to exploit the difference in temperature between the top of the ocean and the bottom, in order to drive turbines and generate electricity... the idea of a power station whose fuel is free is attractive, as long as the capital cost is not too high. The most common OTEC design uses a fluid with a low boiling point—typically ammonia—which circulates through a network of pipes. First, it is vaporised in a heat exchanger that is warmed by surface water with a temperature of around 25°C. That puts the gas under sufficient pressure to spin a turbine and thus generate electricity. When it has done so, the gas is sent to a second heat exchanger, where it is cooled by seawater that has been pumped from a depth of a kilometre or so, where the temperature is about 5°C. That condenses it back into a liquid, and the whole process can be repeated. Theoretically, then, an OTEC plant can be built anywhere that the ocean has a surface temperature above 25°C and is more than 1km deep. The actual experiment, though, is on Hawaii, where Lockheed is collaborating with a smaller firm, Makai Ocean Engineering, to build a ten megawatt (MW) pilot plant that should be operational by 2015. If that goes well, the idea is to follow it with a 100MW power station by 2020. Please read more from: http://www.economist.com/node/21542381
