Japan Digs Deep Into The Ocean For A New Stream Of RE

For the Island country, renewable energy from Ocean currents is an idea well worth pursuing, for its proximity as well as abundance, if the effort can be cracked.
Kairyu, On land. Pic Courtesy: IHI Corp.

Japan has finally found a steady source of renewable energy deep into the ocean regardless of the wind or sun. Working for more than a decade, Japanese heavy machinery maker IHI Corp. has developed a subsea turbine that harnesses the energy in deep ocean currents to convert it into a steady and reliable source of electricity. The prototype could generate the expected 100 kilowatts of stable power.

Called Kairyu, the developed machine resembles an airplane, with two counter-rotating turbine fans in place of jets, and a central ‘fuselage’ housing a buoyancy adjustment system and is designed to be anchored to the sea floor at a depth of 30-50 meters (100-160 feet). Japan’s New Energy and Industrial Technology Development Organization (NEDO) estimates the Kuroshio Current could potentially generate as much as 200 gigawatts — about 60% of Japan’s present generating capacity. While tidal flows don’t run 24 hours, they tend to be stronger than deep ocean currents. The Kuroshio current flows at 1 to 1.5 meters per second, compared with 3 meters per second for some tidal systems.

A variety of approaches to the realization of ocean renewable energy have been proposed. Approaches include ocean current power generation, which uses a big ocean current in the open sea, such as the Kuroshio, to rotate turbine rotors; tidal flow power generation, which uses tidal flow in a strait or the like to rotate turbine rotors; wave activated power generation, which uses the vertical motion of waves; ocean thermal energy conversion, which uses the temperature difference between surface and bottom; tidal (level difference) power generation; and seawater concentration difference power generation.

“Ocean currents have an advantage in terms of their accessibility in Japan,” said Ken Takagi, a professor of ocean technology policy at the University of Tokyo Graduate School of Frontier Sciences.

The ocean currents flow with little fluctuation in speed and direction, giving them a capacity factor — a measure of how often the system is generating — of 50-70%, compared with around 29% for onshore wind and 15% for solar. Among marine-energy technologies, the one advancing fastest towards cost-effectiveness is tidal stream, where “the technology has advanced quite a long way and it definitely works. “The biggest issue for ocean current turbines is whether they could produce a device that would generate power economically out of currents that are not particularly strong,” said Angus McCrone, a marine energy analyst.

Ocean Energy Systems, an intergovernmental collaboration established by the International Energy Agency, sees the potential to deploy more than 300 gigawatts of ocean energy globally by 2050.

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