BIG ISLAND, HAWAII — Can you imagine a 100-megawatt renewable energy power plant capable of running this entire island of 185,000 people? I can, because I’ve seen a scale model.

I’m on the Big Island of Hawaii, which has an energy problem. Although solar energy is abundant, most of the island runs on expensive imported fossil fuel. Gasoline is $5 a gallon, electricity as much as 46 cents a kilowatt hour. There has to be a better way, and maybe there is.

I’m at the Natural Energy Laboratory of Hawaii, the largest tech park on the islands with 870 acres on Keahole Point. NELHA is capable of pumping 14,000 gallons of cold  seawater (41 degrees Fahrenheit) per minute, and that icy H2O is used by all kinds of aquaculture businesses here — there’s even a seahorse farm! But one very useful application is for ocean thermal energy conversion (OTEC), a way of creating energy from the temperature differences between cold water at the bottom of the ocean and warmer surface water.

According to Dr. Joseph Huang, a senior scientist at the National Oceanic and Atmospheric Administration, “If we can use one percent of the energy [generated by OTEC] for electricity and other things, the potential is so big. It is more than 100 to 1,000 times more than the current consumption of worldwide energy. The potential is huge. There is not any other renewable energy that can compare with OTEC.”

We are standing on a platform at the point, atop Makai Ocean Engineering’s 100-kilowatt demonstration plant, which will use heat exchangers and steam rising from tubes of anhydrous ammonia to run a turbine and produce electricity. Now, 100 kilowatts is not going to make a huge difference for Hawaii — it can power some NELHA operations. But the 100-meg plant will cost $1 billion, and that’s not immediately on the horizon.

The demonstration plant, started in 2011, isn’t operating yet, but the single-bladed turbine (modeled after the unit in a torpedo) should be in place next year. We went up on the platform with engineer Robert Loudon, and here he explains how the plant will work on video:

There’s a smaller but working OTEC plant on an island in Okinawa, and the technology definitely has its adherents. I asked Loudon if he can imagine thousands of OTEC plants powering the world, and he said, sure, but it’s only going to work well in the tropics, where there’s a huge temperature difference between surface and deep-sea water. “There’s only so much ocean thermal energy,” he said.

A neat thing is that the electricity generated can run the deep-sea pumps — the operating costs are mostly maintenance. It’s a very clean energy loop.

“This 100-kilowatt plant will tell us how an OTEC plant will affect the grid,” Loudon said. “We’re still working on the 100-megawatt unit—nobody’s every built heat exchangers that big,” he said. “But we see a lot of promise — wave energy is interesting, too, but usually the units tear each other apart.”

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