Sunday, January 13, 2008

More on OTEC and Energy Island

Ocean Thermal Energy Conversion (OTEC) is at the center of the Energy Island concept. OTEC was invented by Frenchman Georges Claude in the 1920s. The idea is simple: use the approximately 20 degrees C difference in temperature between the deep ocean and tropical surface ocean to drive a heat engine. Besides producing megawatts of electric power, the byproducts of the process include clean freshwater for drinking and growing crops, and plenty of air conditioning.
There are two basic versions of the technology. The first operates in a "closed cycle", using warm surface water to heat ammonia, which boils at a low temperature. This expands into vapour, driving a turbine that produces electricity. Cold water from the depths is used to cool the ammonia, returning it to its liquid state so the process can start again.

The "open cycle" version offers the added benefit of producing drinking water as a by-product.

Warm seawater is introduced into a vacuum chamber, in which it will boil more easily, leaving behind salt and generating steam to turn a turbine. Once it has left the turbine, the steam enters a condensing chamber cooled by water from the depths, in which large quantities of desalinated water are produced - 1.2 million litres for every megawatt of energy.

A 250MW plant (a sixth of the capacity of the new coal-fired power station that has just won planning permission in Kent) could produce 300 million litres of drinking water a day, enough to fill a supertanker. Using electrolysis, it would also be possible to produce hydrogen fuel.
The map below displays the ocean area where the temperature difference between surface waters and the deep ocean is great enough to allow large scale economical OTEC . By placing a site close to an arid coastline, an OTEC energy island could make a huge difference in quality of life--by providing reliable electric power, plentiful fresh water for drinking and crop irrigation, and chiller-based air conditioning.
Energy island based seasteads could also provide a nucleus for burgeoning aquaculture--based upon the nutrient-rich deep ocean water routinely pumped into the OTEC generator.

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