OTEC: The Time is Now

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Ever since French physicist Jacques Arsene d'Arsonval first proposed tapping the ocean’s thermal energy for power in 1881, the “experts” proclaimed Ocean Thermal Energy Conversion (OTEC) was an idea whose time would never come.

While there were some small successes along the way, the skeptics believed OTEC pioneers were tilting at windmills in their quest to make this environmentally friendly, endless energy source on a large enough scale to help quench the world’s thirst for electricity. The sheer size and economics of developing an off-shore facility that could affordably and efficiently generate significant power would prevent d’Arsonval’s dream from becoming a reality.

But the tide is finally turning.

The high cost of fossil fuels, the push toward renewable energy and advances in ocean technology are bringing OTEC’s boundless power potential closer to reality than ever before.  

Oceans serve as the world’s largest solar panels, every day absorbing the energy equivalent to 250 million barrels of oil.  That’s three times the earth’s daily consumption rate. The ocean thermal conditions needed for OTEC are favorable in more than 80 countries in tropical areas of the world, including the southeastern United States, Central America, much of South America, southeast Asia, China, Australia and many Pacific and Caribbean islands. Resource constraints and high fuel costs in a number of these areas, make achieving grid parity for OTEC closer than people might think.

The theory behind OTEC is straight forward.  OTEC systems require at least a 36⁰F (20⁰C) difference between surface and deep ocean temperature. This temperature difference drives the OTEC system, much like a steam engine. Warm surface water pumped through a heat exchanger vaporizes a working fluid with a low boiling point, such as ammonia, to drive a turbine generator that produces electricity. The cold deep sea water then condenses the vapor back into a liquid, creating a repeating cycle.

Tapping into a renewable energy source that produces no greenhouse gases, offers virtually no visual impacts from shore and operates consistently with minimal maintenance further strengths the OTEC case. Perhaps the biggest advantage of OTEC is that it produces the constant, base-load power necessary to maintain stability in a country’s or region’s electrical grid. Renewable energy sources such as wind and solar require a back-up source to ensure there’s power even on calm days or when there are too many clouds in the sky.

OTEC’s challenges include that of building a facility large enough to generate significant power, robust enough to withstand the constant pounding of the ocean, as well as the forces of major storms, and reducing the capital expense to build such a facility. Improvements in composite materials, fabrication and modeling, along with related technology advances in the offshore oil industry, are facilitating OTEC’s development.

Still, various small-scale demonstrations projects have been successful.  In 1979, for instance, a Lockheed Martin-led consortium successfully deployed a net power producing ocean-based OTEC plant. Known as Mini-OTEC , the plant was operated for a three-month period off of the Big Island of Hawaii, producing 50 kilowatts of net power. In addition, Japan has demonstrated a shore-based, closed-cycle plant in the Republic of Nauru in the Pacific Ocean that generated 31.5 kilowatts of net power during continuous operating tests.  In the Bahamas and Hawaii, other OTEC-related projects are under way. 

Working with the U.S. Navy and the Department of Energy, Lockheed Martin has invested $15 million over the past three years toward the technology need for and the design of a 10 megawatt  prototype plant to  validating the technologies necessary for small to large scale (100 MW or greater) commercial sized OTEC power plants.  The pilot plant would also provide vital information on the cost of constructing and maintaining a full-scale OTEC facility and validate assumptions about its performance and negligible environmental impact. As the OTEC technology matures and more plants are built, costs for the energy they generate will decrease.  Labor efficiencies, improved technology, quantity and capacity, size and incentives would reduce the cost of future plants.

Beyond the obvious energy and environmental advantages, OTEC offers additional benefits as well. With the world economy struggling, wide spread OTEC development would create an entire new industry. A University of California, Berkley study estimates that each commercial OTEC plant would create 3,500 to 4,000 direct jobs. With the potential for thousands of OTEC plants, the economic impact would be enormous.

OTEC plants can also be configured to produce fresh water by evaporating warm sea water and condensing the resulting clean vapor into potable water using cold sea water. This additional capability would prove invaluable in areas of the world where fresh water is a dwindling resource.

OTEC’s future has never been brighter, and it looks like d'Arsonval’s vision may just be an idea whose time has come.

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highlights
  • The high cost of fossil fuels, the push toward renewable energy and advances in ocean technology are bringing OTEC’s boundless power potential closer to reality than ever before. 
  • Oceans serve as the world’s largest solar panels, every day absorbing the energy equivalent to 250 million barrels of oil.
  • Perhaps the biggest advantage of OTEC is that it produces the constant, base-load power necessary to maintain stability in a country’s or region’s electrical grid.

 Lockheed Martin’s heat exchanger is the first to use friction stir welding, which minimizes ocean corrosion and ultimately drives down cost.

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