Renewable Energy: Navy Taps Oceans for Power

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* As the Navy dives headlong into the challenge of meeting its alternative energy goals within the next decade, technologists are striving to help the service harness solar power trapped in ocean waters to generate electricity for its shore-side bases.

Facilities ashore consume a quarter of the Navy's annual energy resources. Most are powered by the U.S. electrical grid, which relies on fossil fuel generators. In addition to being tied to the turbulent prices of foreign oil, the grid infrastructure is vulnerable to hacker attacks, says R. James Woolsey, senior advisor at Vantage Point and former co-chair of the Defense Science Board's study on energy and defense.

Naval installations are shifting to grids powered by renewable energy sources, says Rear Adm. Philip Cullom, director of the Navy's fleet readiness division. Within the next 10 years, officials plan to generate half of the service's shore-based installation energy requirements from alternative sources.

"This is where renewables make a huge difference," says Cullom, who is leading the Navy's task force on energy. Officials intend to boost the use of solar, wind, ocean and geothermal energy sources on bases and in some cases also supply power to the U.S. grid.

At China Lake Naval Station, Calif., a geothermal plant produces 270 megawatts of power. A megawatt powers about 1,000 homes.

Solar and wind power too have become sources of renewable energy. But there are limitations: The sun does not always shine and the wind does not blow constantly. Grids that are powered by these resources often have to supplement the system with electricity made by conventional fuel-burning generators.

Thermal energy from the ocean is gaining interest because seawater is readily available around the clock to provide utilities with a consistent output of power, experts say.

Ocean thermal energy is a form of solar energy that is trapped in the upper layers of the sea. In tropical areas of the world, the water temperatures can be as warm as 80 degrees Fahrenheit. Several thousand feet below the surface, the water temperature drops below 40 degrees Fahrenheit.

The warm and cold waters can be used in an energy conversion system that drives turbine generators to produce electricity.

The Navy last fall awarded an $8.1 million contract to Lockheed Martin Corp. to continue development of a 10-megawatt ocean thermal energy conversion pilot plant.

"OTEC is essentially a very large heat pump," explains Robert Varley, program manager of the contract, which was awarded through the naval facilities engineering support center in Port Hueneme, Calif. Warm ocean water drawn up through a pipe evaporates liquid ammonia. The gaseous ammonia turns the turbine generators that produce electricity. Cold ocean water condenses the generator exhaust back into liquid form. The ammonia is pumped back to the evaporator to start the cycle anew.

"We need to pump a lot of water to extract enough energy to produce a utility-scale power plant," says Varley. Unlike fossil fuel plants, the fuel is free and carbon dioxide is not produced as a byproduct.

The company is not a newcomer to the field. In 1979, it demonstrated a floating 50-kilowatt OTEC plant off Hawaii's big island. The plant ran for three months and produced net power of 15 kilowatts. The Department of Energy had planned to initiate the construction of a pilot plant afterwards, but government funding for renewable energy took a hit and the industry fell dormant.

In recent years, renewed interest in clean energy has spurred a resurrection of the industry. Lockheed Martin in 2008 won a grant from the Energy Department to develop and demonstrate the tooling necessary to build a large cold water pipe to suck up ocean water from depths of several thousand feet below the surface, says Dennis Cooper, OTEC business manager for Lockheed Martin. …