Posts tagged ‘OTEC’

November 16, 2011

OTEC, Energy From the Sea

OTEC is an emerging technology that harvests energy from the ocean but does not involve waves or tides. OTEC stands for Ocean Thermal Energy Conversion.

This technology is actually not that new, as first attempts for developing an OTEC solution took place at the end of the 19th century and it has been more seriously researched since the 1970s, however the increasing focus on fossil fuels paused these developments.

Today, Japan is one of the most interested countries in the technology having started tests in 1970 with a 100 kW plant by the Tokyo Electric Power Company, while nowadays the Saga University runs a dedicated laboratory. India has also recently joined the group of key researchers, while the US has its main experimental site on the technology in Hawaii, at the National Energy Laboratory.

OTEC - Lockheed

How does it work?

The system utilizes the temperature difference of the deep cold water and the warm surface waters, producing electricity through heat engine systems.

There are three types: open, closed and hybrid cycle technology.

In the open-cycle system the seawater is pumped into a low-pressure chamber so it boils, vaporises and powers the turbine, thus generates electricity. Later the cold seawater helps in condensation, and the seawater will become pure water, which can then be used for various purposes or re-cycled.

The closed-cycle system differs in that a low-boiling-point fluid is used, usually ammonia or freon, which is heated through a heat exchanger by the warm seawater. Another heat exchanger helps at the condensation phase.

Hybrid systems combine the two technologies.

Where can it be used?

As with all heat engines the greater the temperature difference the better the results. Thus the OTEC technology could be used best in the tropical waters with about 20 degrees difference between warm surface (typically about 25C) and cold deep water (about 5-10C at one kilometre depth). This means it could be promising for islands, especially those facing regular challenges with constant electricity supply.

Systems can set up on land, on continental shelves or they can float to provide easy access to deep cold water.

Two new facilities are planned now in the Bahamas as agreed between Ocean Thermal Energy and Bahamas Electricity. These are expected to be the first commercially operating ones, not only providing electricity but also fresh water and would support sustainable food production.

The Maldives is planning to also investigate the technology in the rush to improve renewable energy usage in the country.

Also, the DCNS Group focuses on various marine energy resources and plans to build OTEC systems on the La Reunion Island, in the Indian Ocean. They have also been working on a feasibility study for Tahiti, and a 10 MW-factory is planned for Martinique.

Pros and Cons

Advantages of OTEC include its continuous operation, as it is not prone to changing weather conditions like wind, waves or tides, and it can support desalination processes hence offering clean water. The system can also help in areas where cooling is needed, for instance for agriculture or air-conditioning.

One of the main disadvantages is the difficulty of finding the right location, efficiency and so feasibility.

As issues with fossil fuels grow it seems that research on OTEC technology may be gaining momentum again.

Written for the Energy Saving Warehouse

Image: Lockheed Martin


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