Japan is a country that relies heavily on imported fossil fuels to generate a good part of its energy. Faced with a public opinion that, after the Fukushima nuclear disaster in 2011, is against nuclear energy, the Japanese country is looking for ways to take advantage of renewable energy sources .
Installing wind turbines or solar panel fields is out of the question, as the mountainous archipelago does not offer enough space for it. Being remote from neighboring countries, there are also fewer opportunities to balance fluctuations in renewable energy through energy trading. What Japan does have is vast expanses of coastal water. To the east, the ocean swirls under the power of the North Pacific gyre. Where the gyre meets Japan, it channels into a relatively strong flow called the Kuroshio Current.
It is precisely the Kuroshio currents that a team of engineers wants to take advantage of to generate practically unlimited electricity. Kairyu, which translates to “ocean current” is a prototype 330-ton turbine. Its structure consists of a 20-meter-long fuselage flanked by a pair of similarly sized cylinders, each housing a power generation system attached to an 11-meter-long turbine blade. When tethered to the ocean floor by an anchor line and power cables, the device can be oriented to find the most efficient position to generate power from the thrust of a deep-sea current , and funnel it into a network.
IHI Corporation, which is behind the prototype, partnered in 2017 with the New Energy and Industrial Technology Development Organization (NEDO) to test its designs. In February of this year, a test period of the turbine prototype that lasted three and a half years successfully ended, managing to generate 100 kilowatts of stable power.
IHI calculates that if the energy present in the stream could be harnessed, some 205 gigawatts of electricity could be generated , an amount it says is equivalent to the country’s current power generation. However, things are not that easy.
Despite the enormous interest in this relatively underutilized renewable energy reserve, attempts to extract watts from the tides, waves, and currents of the open ocean often end in failure . One of the difficulties that arise for the commercialization of the turbine is the high engineering costs that it has.
Another important obstacle is the place where it works best, that is, where the waters flow the fastest. And where are these waters? Near the surface, which is right where typhoons can easily destroy power plants. To what we have discussed are added more difficulties: environmental limitations, the proximity of coastal areas to the electricity grid…
Kairyu was designed to float about 50 meters below the waves and as it floats towards the surface, the resistance created provides the necessary torque to the turbines. Each of the blades also rotates in the opposite direction, which keeps the device relatively stable. At a flow of two to four knots (about one to two meters per second), Kairyu is capable of producing a total of 100 kilowatts of power. Compared to the 3.6 megawatts of an average offshore wind turbine, that may not seem like much. However, if the prototype has withstood the harsh conditions of the currents during the testing period, who says it can’t have a brother that swings the 20 meter long turbines and generates a more than respectable 2 megawatts?
Precisely generating 2 megawatts is IHI’s objective as a preliminary step to be able to market Kairyu in 2030. The company has reported that it has carried out a study of the environmental impact of the turbine to see how it affects marine fauna and fishing.
