ENERGY
Ocean Thermal Energy Conversion (OTEC)
The energy from the sun heats the surface water of the ocean. In tropical regions, the surface water can be 40 or more degrees warmer than the deep water. The Ocean Thermal Energy Conversion (OTEC) technologies utilises this temperature difference between warm surface water of the oceans and cold water at a depth of approximately 1000 meters to drive power plants for electricity. It is believed that OTEC is potentially capable to produce more energy than conventional tidal, wave, and wind energy combined.
The OTEC technologies, in principle, is to turn warm surface water into steam, or used to heat another fluid (e.g. ammonia) into vapour and spins a turbine to produce electricity. At the same time, pumps bring cold, deep seawater to the surface, cools the steam or vapour back into liquid form and restarts the cycle again. In an alternative design steam is turned into fresh water while new surface water is added to the system.
At the moment the efficiency of an OTEC system is generally low, as pumping water across the cycle or transportation of electricity to land are both energy-intensive. In addition, to make the technology efficient the OTEC system needs a temperature difference of at least 20 oC to operate. This limits OTEC’s use to tropical regions where the surface waters are very warm.
References:
- [1] Avery W.H., Wu C. Renewable energy from the ocean: a guide to OTEC. Oxford University Press, NY, 1994.
- [2] US DoE, National Renewable Energy Laboratory