Hawaii Taps the Ocean to Generate Carbon-Free Power

Ocean thermal energy conversion technology heralds a new wave of renewable energy projects.
Makai Ocean Engineering's ocean thermal power plant in Kailua-Kona on the Big Island. (Photo: Makai Ocean Engineering)
Sep 15, 2015· 2 MIN READ
Katharine Gammon has written for Nature, Wired, Discover, and Popular Science. A new mom, she lives in Santa Monica.

The world’s most abundant source of energy is solar—the sun shines everywhere—and most of that potential power falls on the ocean.

Now, a Hawaii-based company has built the world’s largest power plant to harvest that energy from the ocean and convert it into electricity. The 105-kilowatt ocean thermal energy conversion demonstration plant went online last month in Kailua-Kona on the Big Island. It cost about $5 million to build and only generates enough electricity to power 120 homes. But the project is a big step toward a future where ocean thermal energy could replace carbon-spewing fossil fuel power plants.

“The ocean is the world’s largest energy storage system, the largest solar collector—and all we have to do is figure out how to extract it,” said Duke Hartman, vice president for business development at Makai Ocean Engineering, the company that developed the plant.

Ocean thermal energy has several advantages over solar, wind, and other intermittent sources of renewable energy. “It’s stable, constant, and available around the clock,” said Hartman.

(Photo: Makai Ocean Engineering)

The system works by pumping cold deep-sea water and warm surface seawater into a heat exchanger. The warm seawater heats ammonia until it becomes high-pressure vapor. The vapor then drives a turbine that generates electricity. Leaving the turbine, the vapor is condensed by the relative cold of the deep seawater and repeats the cycle. The only environmental impact is a small change in the temperature of water discharged from the system.

(Graphic: Makai Ocean Engineering)

Ocean thermal systems can ramp up and down quickly to respond to electricity demands. That may make them an attractive technology to complement less reliable solar and wind energy. Hawaii has set a target of obtaining 100 percent of its electricity from renewable sources by 2045, and Hartman said ocean thermal energy conversion will be an important piece of the mix.

The technology’s real promise may be in tropical countries where the differential between deep ocean and surface temperatures is great enough to make the technology work.

“Most of the world’s population is in coastal zones, and there are many developing nations located in good areas where there are OTEC resources,” said Hartman.

While the current plant is onshore, Hartman said much larger plants would be built offshore because it would be more cost-effective to place pipes vertically into cold seawater rather than run them to land. Some plants could be built on floating platforms that could be moved if necessary.

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“If you have a floating power plant, you can tow it around the world with a renewable always-on power source,” said Hartman, noting the facilities could run autonomously.

Makai Energy is building a larger power plant in Hawaii in collaboration with a Japanese consortium. China, Korea, the Philippines, Malaysia, France, and the Netherlands are all putting money into ocean thermal energy research and development, and Makai estimates that global investments have surpassed $100 million since 2009.

“If people are serious about reducing and mitigating global warming, OTEC is a perfect option,” Hartman said.