Hawaii and Taiwan Ink 10 MW OTEC Deal

The state of Hawaii is partnering with the Industrial Technology Research Institute of Taiwan to build a 10 MW OTEC plant off the shores of Hawaii.

OTEC could provide renewable electricity generated from the difference in temperature between the ocean’s warm surface and its chilly depths.

The ocean temperatures and the subsea terrain make the waters surrounding both Taiwan and Hawai‘i superior locations for this technology. Lockheed Martin Corporation has developed and studied OTEC technology for over 30 years. Its plans for a 10-MW OTEC pilot plant in Hawai‘i are already underway. _Source

OTEC takes advantage of warm solar heated surface waters in combination with cold deep ocean waters, to provide the necessary heat differential to drive a heat engine. Besides generating electricity, OTEC can also create fresh water, and provide abundant air conditioning for the tropics. Aquaculture promotion from nutrient-rich deep seawater is another benefit.

Closed-cycle OTEC uses a refrigerant/heat exchange material to drive the power turbine. Alternatively, open-cycle OTEC uses vacuum "flash distillation" to create fresh-water "steam" to drive the turbine and to provide fresh water.

Both forms of OTEC provide power and air conditioning, although only the open-cycle form provides fresh water directly. Closed-cycle OTEC can provide fresh water via condensation on surfaces cooled by the deep cool seawater.

OTEC is a relatively small scale power source, but should suit large numbers of tropical island communities that have access to deep seawater.

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.

Telegraph
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.

Ocean Thermal Energy Conversion--OTEC

A very nice video illustrating Earth's thermohaline circulation, and the OTEC method of extracting electrical energy from the temperature differential of the tropical ocean. Definitely worth four minutes of your time.