Japanese Tidal Generator Prototype Completes Testing

Renewable energy has come on leaps and bounds over the last decade. Designs for solar and wind power especially have been refined until the main gains we see now are more incremental than revolutionary, and we still require more generation to replace fossil fuel sources. As suitable land has been used up for renewable generation, we have turned to the sea to try to supply our needs. Windfarms are moving further offshore to try capture the strong reliable winds there. Various projects are ongoing, but perhaps the most ambitious is one from Denmark that hopes to build a giant offshore island that will serve as a hub for 200 offshore wind turbines. The installation is expected to come online by 2033 and when operational it will supply 3 million homes. Another smaller island is planned in the Baltic sea. Solar installations are also set to move offshore and there are a number of projects trying to iron out any difficulties.

One renewable resource that has not been successfully exploited to date and has great potential for suitable areas is tidal energy. Tidal power is very predictable, and doesn’t suffer from the downsides of some other renewable generation. Solar panels don’t work when there is no sun, and windmills don’t work if there is no wind, but tides are active 24/7. The big downside of tidal power at the moment is developing a method of extracting it. Salt water is very corrosive to metals, and huge underwater installations would be hard to access for maintenance. If that hurdle could be overcome, then tides would be a huge provider of clean energy over the long term.

There are particular regions that could greatly benefit from tidal power if it could be tapped. In Scotland for instance, the country’s marine area potentially has 25% of Europe’s tidal energy resource, an estimated 32 TWh per year. There is similar potential for tidal power in the seas off the Japanese coast. The Kuroshio ocean current is one of the world’s most powerful and an estimate of the total energy present in the Kuroshio is approximately 205 GW. While researchers in Europe are trialling different methods of capturing tidal power, scientists from IHI Corporation in Japan are also working on the problem and have just completed a large scale test.

Water near the surface flows faster and has the potential to generate more energy. However, Japan is often hit by typhoons, so placing the generators too near the surface would expose them to damage. The Japanese scientists designed the generator to be moored at around 50m below the surface, anchored to the ocean floor. Two turbine rotors, on the left and right of the generator, are rotated in opposite directions to each other to cancel rotary torques and maintain the devices position. The ocean current generator can be brought to the surface for maintenance.

A prototype of the device was developed in 2017. It uses three cylindrical floats, having a total length of approximately 20 m, a width of approximately 20 m, and a turbine rotor diameter of approximately 11 m. The rated flow speed is 1.5 m/s (approximately 3 knots) and the rated output capacity is around 100 kW. The device has been in testing and validated for performance. IHI is now working on a full-scale production turbine with a rated output of 2 MW (1 MW × 2 units) and a turbine rotor blade diameter of approximately 40 m.

https://www.ihi.co.jp/var/ezwebin_site/storage/original/application/5a7bd9898dee90868aa1e1e085beb50b.pdf