Energy-hungry Japan that relies on fossil fuels has successfully tested a system that can provide a stable, consistent form of renewable energy, regardless of wind or sun.
For more than a decade, Japanese heavy machinery maker IHI Corp has been developing subsea turbines that harness power in deep-ocean currents and turn it into a stable, reliable source of electricity. The giant machine resembles an airplane, with two reversing turbine propellers rotating instead of jets, and a central “fuselage” housing a buoyancy adjustment system. The prototype called Kairyu, which weighs 330 tons, is designed to be anchored to the seabed at a depth of 30-50 meters (100-160 feet).
In commercial production, the plan is to place the turbines in the Kuroshio Stream, one of the most powerful turbines in the world, which runs along the east coast of Japan, transmitting power via seafloor cables.
“Ocean currents have an advantage in terms of their accessibility in Japan,” said Ken Takagi, professor of ocean technology policy at the University of Tokyo’s Graduate School of Frontier Sciences. “Wind energy is more geographically suitable for Europe, which is exposed to prevailing westerly winds and is located at higher latitudes.” The Japan New Energy and Industrial Technology Organization (NEDO) estimates that the Kuroshio Stream can generate up to 200 gigawatts – about 60% of Japan’s current generation capacity.
Like other countries, the lion’s share of investment in renewables has gone into wind and solar power, especially after the Fukushima nuclear disaster that curbed that country’s appetite for atomic energy. Japan is already the world’s third largest solar generator and is investing heavily in offshore wind, but harnessing ocean currents can provide the reliable base energy needed to reduce the need for energy storage or fossil fuels.
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The advantage of ocean currents is their stability. It flows with little fluctuation in speed and direction, giving it a power factor – a measure of how much a system is generating – of 50-70%, compared to about 29% for onshore wind and 15% for solar.
In February, IHI completed a 3-year technology demonstration study with NEDO. Her team tested the system in the waters around the Tokara Islands in southwest Japan by suspending Kairyu from a ship and returning power to the ship. The ship was initially driven to generate an artificial current, and then the turbines were suspended in Kuroshio.
Tests have proven that the prototype can generate 100 kilowatts of expected stable power and the company is now planning to expand to a full 2 megawatt system that could be in commercial operation in 2030 or later.
Like other developed maritime nations, Japan is exploring various ways to harness energy from the sea, including tidal and wave energy and ocean thermal energy conversion (OTEC), which exploits the temperature difference between the surface and the deep ocean. Mitsui OSK Lines Ltd. invested at UK-based Bombora Wave Power to explore the potential of technology in Japan and Europe. The company is also promoting OTEC and began operating a 100-kilowatt pilot facility in Okinawa in April, according to Yasuo Suzuki, general manager of the corporate marketing division. The renewable energy unit Kyushu Electric Kyuden Mirai Energy will begin a 650 million yen ($5.1 million) feasibility test this year to produce 1 megawatt of tidal power around the Goto Islands in the East China Sea. This month the government also proposed changes to offshore wind auctions that could speed development.
Among marine energy technologies, it is the tidal current that is advancing the fastest toward cost-effectiveness, as “technology has advanced a lot and is definitely working,” said Angus Macron, former Bloomberg NEF editor-in-chief and marine energy analyst. Orbital Marine Power, based in Scotland, is one of several companies building tidal systems around Orkney, the site of the European Marine Energy Centre. Other companies include SIMEC Atlantis Energy’s MeyGen group and California-based Aquantis, founded by American wind pioneer James Delsen, which are said to plan to begin testing the tidal system there next year.
While tidal flows do not run for 24 hours, they tend to be stronger than currents deep in the ocean. The Kuroshio current flows at 1 to 1.5 meters per second, compared to 3 meters per second for some tidal systems. “The biggest problem for current ocean turbines is whether they can produce a device that generates energy economically from currents that are not particularly strong,” Macron said.
Ocean Energy Systems, an intergovernmental collaboration set up by the International Energy Agency, sees the potential to deploy more than 300 gigawatts of ocean energy globally by 2050.
But ocean energy potential depends on location, taking into account the strength of currents, access to networks or markets, maintenance costs, shipping, marine life and other factors. Takagi said that Japan’s wave energy is moderate and unstable during the year, while areas with strong tidal currents tend to have higher sea freight traffic. The OTEC is more suitable for tropical regions where the temperature gradient is greater. One advantage of the deep-ocean current, IHI said, is that it does not restrict ship navigation.
The Japanese company still has a long way to go. Compared to land installations, the installation of an underwater system is much more complicated. “Unlike Europe, which has a long history of drilling for North Sea oil, Japan has little experience in offshore construction,” Takagi said. There are significant engineering challenges to building a system strong enough to withstand the hostile conditions of deep ocean currents and to reduce maintenance costs.
“Japan is not blessed with many alternative energy sources,” he said. “People might say this is just a dream, but we need to try everything to achieve zero carbon.”
With the cost of wind, solar, and battery storage falling, IHI will also need to demonstrate that the overall project costs for current ocean energy are competitive. IHI aims to generate power at 20 yen per kilowatt-hour from widespread deployment. That compares to about 17 yen for solar in the country and about 12-16 yen for offshore wind. IHI also said it had conducted an environmental assessment before launching the project and would use the test results to examine any impact on the marine environment and the fishing industry.
If successful on a large scale, deep ocean currents could add a vital role in providing green essential energy in the global effort to phase out fossil fuels. Macron said IHI’s work could help Japanese engineering take a leading role with government support.
He said IHI has to make a convincing case that “Japan can benefit from being a technology leader in this field.”
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