Japan has successfully tested a huge system of turbines on the seabed that harnesses energy in deep ocean currents and turns it into a stable, reliable source of electricity.
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For more than a decade, Japanese heavy machinery maker IHI Corp. has been working on building a deep-sea turbine to harness energy, according to Bloomberg News.
The system is a giant aircraft-like machine, with two counter-rotating turbine fans, and a central "fuselage" containing a buoyancy control system.
The machine called Kairyu, weighing 330 tons, is designed to anchor to the seabed at a depth of 30-50m.
According to the commercial production plan, the turbines are placed in the Kuroshio flow. It is one of the strongest currents in the world, running along the east coast of Japan and transmitting electricity through cables on the seabed.
"Japan has the advantage of having access to strong ocean currents," said Ken Takagi, a professor of ocean technology policy at the University of Tokyo.
Japan's New Energy and Technology Development Organization (NEDO) estimates the Kuroshio flow could generate 200 gigawatts - about 60% of Japan's current electricity generation capacity.
The advantage of ocean currents is stability. Their flow has little fluctuation in speed and direction, yielding a power factor - a measure of how often the system generates it - of 50-70%. This is quite impressive compared to about 29% for onshore wind and 15% for solar.
In February, the team tested the system in the waters around the Tokara Islands in southwestern Japan. The team hooked up the Kairyu system to a ship, and the generated electricity was also directed back to the ship.
Tests have demonstrated that the Kairyu system can produce a steady 100 kilowatts of power as expected.
The company now plans to scale up the 2-megawatt system, which could go into commercial operation in the 2030s or beyond.
However, the potential for ocean energy depends on location, magnitude of currents, network or market access, maintenance costs, transportation, marine life, and other factors.
With the cost of wind, solar and storage batteries falling, IHI will also need to demonstrate price competitiveness for ocean currents.
Currently, IHI aims to generate electricity at 20 yen/kilowatt from large-scale deployment. Prices are still high compared to about 17 yen for domestic solar and about 12-16 yen for offshore wind.
If successful on a large scale, deep ocean currents could make an important contribution to the supply of green energy in the global effort to phase out fossil fuels.