Ocean Thermal Energy Conversion: Renewable Ocean Power & Air Conditioning Research Receives Federal Funding

napali coast kauai hawaii photo

Unlike other ocean power technologies, which use the movement of water to generate power, Ocean Thermal Energy Conversion uses differences in water temperature to create electricity. Napali Coast of Kauai, photo: Jean-Phillipe Rebuffet.

The US Department of Energy has just been doling out the money lately. The most recent announcement being that the DOE has awarded Lockheed Martin a cooperative agreement contract worth up to $1.2 million to "demonstrate innovative technologies to enable ocean thermal energy power generation." The technology in question is Ocean Thermal Energy Conversion (OTEC), which uses differences in ocean temperature to drive a heat engine. Lockheed Martin has worked on the technology since the early 1970s but has yet to demonstrate a commercial version of the technology, they hope to soon change that:OTEC Offers Promise of Clean Baseload Electricity: Lockheed Martin
Under the agreement, Lockheed Martin will "demonstrate a cold water pipe fabrication approach using modern fiberglass technology and recent low-cost composite material manufacturing methods at prototype and pilot plant scales." The company, citing Hawaii as an example, says that OTEC has the promise of "providing clean, base-load electricity to energy markets that today rely almost exclusively on fossil fuels."

The DOE describes three different types of OTEC systems:

Closed Cycle

These systems use fluid with a low-boiling point, such as ammonia, to rotate a turbine to generate electricity. Warm surface seawater is pumped through a heat exchanger where the low-boiling-point fluid is vaporized. The expanding vapor turns the turbo-generator. Cold deep-seawater—pumped through a second heat exchanger—condenses the vapor back into a liquid, which is then recycled through the system.

Open Cycle
These systems use the tropical oceans' warm surface water to make electricity. When warm seawater is placed in a low-pressure container, it boils. The expanding steam drives a low-pressure turbine attached to an electrical generator. The steam, which has left its salt behind in the low-pressure container, is almost pure fresh water. It is condensed back into a liquid by exposure to cold temperatures from deep-ocean water.

These systems combine the features of both the closed-cycle and open-cycle systems. In a hybrid system, warm seawater enters a vacuum chamber where it is flash-evaporated into steam, similar to the open-cycle evaporation process. The steam vaporizes a low-boiling-point fluid (in a closed-cycle loop) that drives a turbine to produce electricity.

OTEC History
The first work on this sort of technology dates back to 1881 when a French physicist proposed the concept, but it wasn't until 1930 when Cuba developed two pilot scale plants, which were unfortunately destroyed by "weather and waves" before becoming net energy emitters. Another plant was developed in 1956 in the Ivory Coast, but it was abandoned after being deemed to expensive to complete.

Seawater Air Conditioning
In addition to generating power, the DOE says that ocean-powered air conditioning systems are a potential other application of OTEC. In fact just such a sea water air conditioning system has been proposed for Honolulu, Hawaii, and completed funding earlier this summer.

More about OTEC from the :: US Department of Energy.

via :: PR Newswire
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