Ocean thermal energy’s big selling point is that it’s always on, and it’s always available. “Once you get the system going, it runs twenty-four/seven,” says Harry Jackson, president of Ocean Engineering and Energy Systems (OCEES), a company based in Honolulu, Hawaii, that designs OTEC plants. It’s consistent because the oceans act like a giant battery, storing up sunlight. “As an alternative energy source, it’s one of the few to provide baseload power,” says Reb Bellinger, vice president of Makai Ocean Engineering, also based in Honolulu, a firm that designs deep water pipes for OTEC.

The oceans’ thermal energy can be effectively harnessed wherever the temperature difference between the warm surface water and the cold deep water is at least 20°C — which covers about one-third of oceans’ area. OTEC’s major downside, however, is that most of the resource is marooned far from land and far from people. But scores of specially outfitted ships could float in the open ocean, grazing on the energy and using it to synthesize fuels and chemicals that get shipped to shore — a futuristic dream that could be the key to unlocking the technology’s potential.

Trial Niche

It won’t be easy. Even a simple test of OTEC, if it’s realistic, requires a huge system. “Unlike other renewables, it cannot be tested in small sizes,” says Girard Nihous of the Hawaii Natural Energy Institute. For one thing, even a proof-of-concept power plant still needs a wide pipe that reaches about a kilometer deep into the ocean. The up-front capital costs are also high, partly because of the sheer scale but also because of the difficulty of working with the sea. These systems have to contend with corrosive salt water and a slime of microorganisms that can grow inside the plumbing and clog it up. Violent weather can wreak havoc with the long cold-water pipes, especially if a storm hits when they’re in the midst of being installed. “The part that brings the risk is the ocean engineering,” Nihous says.

These obstacles have deep-sixed all efforts to date to build a practical OTEC system, though engineers have been trying for over a hundred years. Since the five-year run of an experimental plant in Hawaii ended in 1998, there hasn’t been a functioning OTEC plant anywhere in the world. However, several new plants are in various states of planning and the first could be switched on as soon as 2012.

That could be the plant the U.S. Navy has commissioned for its remote base on the island of Diego Garcia, in the middle of the Indian Ocean. The 8-megawatt plant — about 40 times bigger than any built so far — would float on a platform like those used for offshore oil drilling, about five kilometers from the coast. As a byproduct of the process of creating electricity, it would also desalinate nearly 5 million liters of drinkable water each day. “This is the first commercial project,” says Jackson of OCEES, the firm designing the plant. “A lot of people are watching to see how that goes. I think we’re going to learn a lot in this first project, and the technology will advance extremely fast.”

The base in Diego Garcia is now powered almost entirely by diesel fuel brought in by tanker. “There’s definitely an energy security issue,” says Christopher Tindal of the Navy’s Energy Policy Office. “Also, because of the price of energy these days, it’s prudent to go with alternative energy.” The new OTEC plant will save the Navy $290 million over 30 years, according to OCEES’s estimates — and that’s the main reason the Navy is going for it. “We won’t pay more for green power than for brown power,” Tindal says. “Any of the renewable projects we’re doing have to be cost-effective.” Getting the first commercial plant installed will be a major milestone, according to all the players in this field. “This is the golden egg,” as Tindal puts it. “Whether the Navy does it, or whether Lockheed Martin does it first, it doesn’t matter. I think it’s a wonderful concept.”

Other plants are in the works as well. The U.S. Navy is exploring the feasibility of an OTEC plant for its base on Guam, a South Pacific island. In November, the state of Hawaii concluded a deal with the Taiwan Industrial Technology Research Institute and Lockheed Martin that could pave the way for a 10-megawatt OTEC plant there. And the National Energy Laboratory of Hawaii Authority (NELHA) is also looking for companies interested in building an OTEC plant. “We’re issuing a request for proposals to build a 1-megawatt OTEC scale-up plant,” says Ronald Baird, NELHA’s chief executive officer. “The last one [at this site] was about 200 kilowatts, so this is five times bigger.”

Baird argues that OTEC is ideal for remote tropical islands like Hawaii, which gets over 90 percent of its energy from imported fossil fuels. “And our major sources of imported petroleum are very stable countries — Vietnam, Iraq, Iran, Yemen,” he adds sarcastically. “Hawaii’s electricity price is 44 cents per kilowat-thour — the highest in the U.S., and probably one of the highest electricity costs in the world.” But with a 1-megawatt OTEC plant, he said, the cost would be about half that, 22 cents per kilowatthour.

Serving this niche market of remote islands, where energy and drinking water are at a premium, could help OTEC get over a hump and move toward more widespread application, many of the technology’s supporters hope. “Great hope has been placed in military-controlled small islands, because the Department of Defense of the United States is richer than most countries, and they have discretion to do things that others can’t,” Nihous says. “So it makes sense to approach OTEC development this way.”

In part 3 of this series, we’ll explore other benfits of OTEC.

Mason Inman is a freelance science journalist currently based in Karachi, Pakistan.

This article originally appeared in World Watch Magazine May/June 2009 and is reprinted by permission.