Thermal Energy


Our oceans are vast, untapped and renewable collectors of heat from the sun. Through Ocean Thermal Energy Conversion (OTEC) technology, 1/10,000ths of the surface of our seas contains enough solar thermal energy to provide for our entire planet’s current energy needs, renewably and sufficient desalinated water for all water uses of a population of 7 billion.



OTEC can produce both power and desalinated water 24 hours a day and uninterrupted all year round. This is unlike most other forms of renewable energy sources, such as photovoltaic, wind and wave energies, which vary in output according to night/day cycles of weather conditions. An OTEC plant can be seen as a combined power plant and desalination plant: For every MW of power generated, 2.36 million litres/day of desalinated water will be created.



Additionally and where applicable, the cold water can be used as an inexpensive form of air conditioning, and the high-grade phytoplankton, drawn up during the process, as feed for aquaculture/fish farms surrounding the facility. As regards financing, the carbon credits generated would also be considered to be an output.


OTEC works in tropical and sub-tropical seas where surface waters are over 25°C and water at 1,000 meters depth is at 5°C, so that there is a difference in temperature of at least 20°C throughout the year.


In both cases, the surface temperature needs to be an average of approximately 25°C or more, which restricts the use of OTEC to tropical and sub-tropical waters around the equatorial belt.


In Open Cycle OTEC, solar heated tropical warm seawater is flash-evaporated in a vacuum chamber. The resulting low-pressure steam drives a turbine-generator, producing electricity.


Cold seawater drawn up from the depths condenses the steam on cold heat exchanger plates, after it has passed through the turbine, producing desalinated water.


In Closed Cycle OTEC, warm surface seawater and cold deep seawater are used to vapourise and condense a working fluid, such as anhydrous ammoniac, which drives a turbine generator in a closed loop producing only electricity. In Hybrid OTEC, various permutations of these cycles are used in order to create greater amounts of electricity and/or desalinated water, at greater overall efficiencies, achieved by greater system complexity.

With it’s dual outputs of both power and water, OTEC is a technology whose costs are hard to compare with those of generating any one of the two commodities, as the figure for one would preclude the provision of the other. The power produced by OTEC is base loaded/constant peak, whereas the majority of renewable technologies are variable in their rates of production.


With these two points in mind, the nearest comparable to OTEC would be a hybrid of a Reverse Osmosis desalination plant, powered by renewable power, for example, wind, working full time at peak capacity and producing a surplus of electricity.


In that case, and at 50MW and 118ML/day capacity, the costs of OTEC are over 25% less than that of the hybrid.