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Japan Is Building Underwater Kites to Harness the Power of Ocean Currents

The new year will see at least one fresh, promising, and experimental cleantech idea put to the test: deploying fleets of underwater kite turbines that can harness ocean currents for power.
January 2, 2015, 9:35pm
Image: Toshiba

The new year will see at least one fresh, promising, and experimental cleantech idea put to the test: deploying fleets of underwater kite turbines that can harness ocean currents for power.

Eager to seek out energy alternatives in ​the long ugly wake of the nation's nuclear crisis at ​Fukushima, Japan's New Energy and Industrial Technology Development Organization (NEDO) was keen to examine its ocean energy prospects. So it turned to Toshiba and partner company IHI to launch a research program that will investigate current power by floating kite turbines in the Kuroshio Current.


"The unique 'underwater floating type ocean current turbine system' will demonstrate power generation in a real ocean environment, in a project expected to continue until 2017," Toshiba explains. "The research work is expected to prove the viability of ocean energy power generation and to create the framework for an industry, and also to contribute to improved energy security for Japan."

Mere miles off the coast of Japan, the Kuroshio is one of the world's most powerful ocean currents. As such, it holds a great potential as a very stable, very reliable renewable energy source.

The idea of harnessing the energy of these ocean currents isn't entirely new (though NEDO's kite-based approach is). But it's one of the least-explored and least-developed clean energy ideas out there, as the US Bureau of Ocean Energy Management (BOEM) notes ​in a white paper that urges further research. BOEM suggests examining more traditional turbines built on poles fixed to the ground, underwater wind farms that would look something like this:

Tidal power—which harnesses the energy of tidal currents nearer the coast—is more developed, and is even close to commercialization in some places. Same goes with ​wave power.

But ocean current power has largely remained on the drawing board, largely because building, deploying, and maintaining power-generating equipment underwater, in the middle of a major current, would be costly. Still, the potential is huge, largely because ocean currents are predictable, stable, and carry a lot of energy.


"Ocean currents are relatively constant and flow in one direction, in contrast to tidal currents along the shore," the BOEM explains. "While ocean currents move slowly relative to typical wind speeds, they carry a great deal of energy because of the density of water. Water is more than 800 times denser than air. So for the same surface area, water moving 12 miles per hour exerts the same amount of force as a constant 110 mph wind." The Kuroshio moves about three miles per hour, according ​to the US Navy.

That's why Japan is aiming to see how feasible it would be to plug into the Kuroshiro, and why, if it does, other companies and governments will likely take note.

"Because of this physical property, ocean currents contain an enormous amount of energy that can be captured and converted to a usable form," the BOEM continues. "It has been estimated that taking just 1/1000th the available energy from the Gulf Stream would supply Florida with 35 percent of its electrical needs."

Details on how the proposed technology will work are scarce, but Toshiba provides some of the basics: "The underwater floating type ocean current turbine system is a power generation device with two counter-rotating turbines. It is anchored to the sea floor and floats like a kite carried and driven by the ocean current." IHI will build the turbines and the floating body, and Toshiba will supply the necessary electric devices like the generator and the transformer.

The project should consider the technology's impact on marine ecology; the turbines likely won't be spinning fast enough to slice up fish outright, but the alterations to the current and lengthy tethers may have unintended consequences.

Still, it's an exciting prospect, and the kites may prove nimbler—and easier to deploy and cheaper to maintain—than traditional turbines. And in 2015, off the back of the ​hottest year on record, and on the cusp of ​a serious global agreement to combat climate change, we're going to need all the firepower we can get.