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Clean Energy From An Unlikely Source: Lukewarm Oceans

The sun pours down a lot of energy onto the surface of the ocean every day. Now scientists are figuring out a way to get that energy onto the grid, with only seawater as a waste product. It just requires a really, really long pipe.

There is a lot of seawater on the planet. And that seawater is warmed, daily by the sun. If only we could tap it, warm seawater offers a virtually limitless source of pollution-free energy. Good news, we can.

Ocean thermal energy conversion (OTEC) converts the energy stored in warm seawater into electricity. It works much like any other power plant that burns coal or gas to create steam and turn turbines. OTEC just works at much lower temperatures and pressures, with seawater as the only heat source and the only by-product.

The mechanics are relatively simple. Typically, warm surface water is pumped into a heat exchanger to vaporize a fluid, such as ammonia, with a low boiling point. The vapor rushes through a network of sealed pipes to spin turbines and generate power before it is condensed back into a liquid using cold water pumped up from more than 1 kilometer below. Theoretically, OTEC works anywhere ocean temperatures differ by more than 36 degrees.

After decades of rock bottom oil prices, OTEC is looking profitable as prices rise, says Robert Varley at Lockheed Martin, one of several companies pursuing the technology. "The challenge is to pick the best and most efficient technologies together in one system, and then you’ll have the birth of a new industry," he says. 

Most of the technology to build a 100-megawatt (MW) plant already exists. Deep-water floating ocean platforms, pioneered by the oil and gas industry, are common, and rugged aluminum heat exchangers exist. The holdup is the massive cold-water plumbing. The process requires a 10-meter diameter tube at least one kilometer long and able to survive the open ocean to pump billions of gallons of cold water. No such pipe has been manufactured, although most engineers say this is just a matter of time.

For now, there are a handful of organizations such as OTEC International, Ocean Thermal Energy Corporation, and a joint effort between Makai Engineering and Lockheed Martin—to build smaller or demonstration plants on their way to a full scale of 100 MW or more. "There is no more R&D needed to build a power plant of 10 megawatts," says Jeremy Feakins, CEO of Ocean Thermal Energy Corporation, which plans to build the world’s first commercial OTEC plant for the Bahamian government. "The company that is first to market with OTEC will be the market leader."  

Now it’s about who can find the investment, and refine the technology first. Governments from Africa to the Caribbean, as well as the U.S. military, are all keen to see the first megawatts generated by nothing more than the clear, blue ocean.

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  • Mike Straub

    Clean ocean power is ready to roll.  Forget demonstration plants, there's been one off the coast of Hawaii's big island for more than 3 decades.  Commercial OTEC is ready to go, and The Bahamas are leading the way.  They committed to building 2 OTEC plants, plus a huge resort is building a smaller OTEC system just for their air conditioning.  It will be the cleanest air conditioning system in the world.  This article leaves out one of the most dynamic aspects of OTEC's impact on millions of lives.  Every OTEC plant will produce millions of gallons of clean drinking water.  So endless clean power, and life changing clean water.  This is the energy future we can all get behind.

    Here's more info on the OTEC plants in the Bahamas...

  • Kcquek Sin

    energy/electricity generated is able to cover the operation cost ? if yes, what is stopping people from building it now?

  • la_cunae

    We are talking about a 10m diameter, 1000m long pipe, free hanging off of a floating vessel. Then there is the issue of transmitting that power back to shore, as well as maintenance of heat exchangers etc. (sea water is pretty nasty stuff)