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Deep Ocean Current Turbines To Find New Renewable Energy Sources.

The potential for renewable energy is not evenly distributed. For example, Japan's solar potential is modest, and its wind potential is ...

The potential for renewable energy is not evenly distributed. For example, Japan's solar potential is modest, and its wind potential is nowhere near that of Western Europe or the United States. Japan currently ranks fifth globally in electricity consumption, and adding nuclear power is politically difficult after Fukushima, meaning its race to zero emissions will need more than most countries if it hopes to remain energy independent innovation.

Japan does have a large amount of coastline, with the sixth-largest territorial waters in the world, making the idea of ​​ocean-based alternative energy particularly attractive. Tidal current generators like the 2 MW Orbital O2 currently exporting power to the grid on the Scottish island of Orkney might provide reliable baseload generation, but Japan sees a lot of shipping traffic passing through areas with decent tidal potential, and the idea is off the table. Too likely to succeed.

So the Japanese company IHI and the New Energy and Industrial Technology Development Organization (NEDO) have been experimenting with another reliable energy source that, if harnessed, could provide an especially reliable source of energy: ocean currents.

Ocean currents generally provide slower manageable flows than well-chosen tidal stream locations. For example, O2 can provide its rated power output at a water velocity of 2.5-4.5 m/s. On the other hand, the Kuroshio Current is more like 1-2 m/s. But it's massive, up to 100 kilometers (62 miles) wide in some places, and is estimated to move 65 million cubic meters of water per second at its strongest point, off Japan's southeastern coast.

As a result, it would be possible to connect a large number of ocean current turbines, share transmission lines, and draw some of the energy that IHI estimates to be around 205 gigawatts. IHI and NEDO have been studying this opportunity since 2011, and the two companies have had a small-scale 100 kW tidal generator under test since 2017.

The demonstration generator, called Kairyu, is anchored to the ocean floor and is very similar to the Orbital O2. But while the Orbital O2 harnesses the current a few meters below the surface and switches direction with the tides, Kairyu remains steady, about 50 meters (164 feet) below the waves. The IHI says this is not the most efficient place to harvest energy from ocean currents – closer to the surface would be better, but the typhoon conditions experienced in the area can cause waves to exceed 20m in height, so keeping them deep underwater is mainly a matter of safety consider.

Each of Kairyu's three cylindrical pontoons is about 20 meters long and the entire pontoon is about this wide. The two outer buoys feature variable-pitch two-bladed turbine rotors, 11 meters in diameter, set to counter-rotate to balance torque forces. Each rotor spins a 50-kilowatt generator.

Water pressure sensors let the machine know its depth, and it manages its position autonomously through a buoyancy adjustment system. Likewise, current speed sensors inform Kairyu about blade pitch decisions, which are managed for maximum efficiency, and other position sensors allow it to control its pitch, yaw and roll angles using attitude controls on the rear end of the buoys. Where maintenance is required, the Kairyu simply raises its buoyancy and floats to the surface, where it can do the work – so it doesn't need an articulating arm like the Orbital O2.

With Kairyu successfully tested in about three and a half years, IHI says it hopes to scale the thing up to 2 megawatts, with blades about 40 meters long, for a full-scale production version that can be deployed in large numbers. IHI is targeting 2030, when it expects current energy prices from the ocean to be close to competitive with solar prices in Japan, according to Bloomberg. In fact, the company says, as it scales up, it could be a powerful solution as a low-cost energy source for remote islands.

The key is, and always will be, funding. If this thing works economically at scale, it could provide a very reliable source of green energy that could make a huge contribution to Japan's decarbonization efforts. In Japan, solar typically operates at a capacity factor of 15% – that is, over the course of a year it tends to generate 15% of what it would generate under always perfect conditions – while onshore wind has a capacity factor of about At 29%, Ocean Current operates at a capacity factor of 70%, which is almost on par with coal-fired power plants at 80%.

What's more, climate change studies predict that the Kuroshio Current will become stronger as the planet warms, potentially boosting the output of these devices in the coming decades. Regardless, the potential is enormous, and this project represents yet another ingenious way humans are trying to extract energy from nature with minimal adverse consequences.

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