Ocean thermal energy is a reliable source of offshore ocean energy. The difference between the temperature of warm and cold sea water at around 800-1000 meters depth is used to run heat engine and hence produces electricity. This technology needs an environment where the thermal gradient between the surface and depth is at least 22 degree Celsius, which makes it only viable in tropical seas. The difference in temperature is converted into electrical power through turbines. On one hand, vapors from the warm sea water are used as working fluid to drive the turbine, on the other hand, cold water is used to condense the vapor. This difference in vapor pressure drives the turbine, hence produces energy. The resource can be utilized in either side of the equator (latitude 0 to 30 degrees). The capacity factor of OTEC is in between 90-95 per cent which is among the highest in all power generation technologies in both renewable and non-renewable sector. Ocean thermal energy can also be used for seawater air conditioning, seawater district cooling and aquaculture. Moreover, OTEC plants can also produce fresh water with the desalination technologies.