This paper reports the method of electric power generation from tidal currents and test results of the system which is specially designed for this purpose. The system consists of a vertical axis turbine, a gear box, an electric generator, and a control unit. The turbine is the vertical axis Darrieus rotor, and has three blades. The authors have studied on power generation from the tidal currents with out blocking the bay or strait. Also the real test in tidal currents was conducted from 1983 to 1988, at Kurushima straits in Ehime prefecture, and its results are discussed.
Attention is focused on the use of renewable energy as a substitute of fossil fuels. Among others, tidal energy has been studied for 50 years. Most of such studies, however, were related to optimum location of tidal power stations. A typical example of the tidal power generation is La Rance Tidal Power Station in Franc which supplies power at the maximum rate of 240MW. Tidal power generation requires a very large amount of money for construction of the dam and associated facilities. It is believed that an average tidal range of 5m of more is required for effective tidal power generation. It has also been accepted that the energy effectively recovered from the tidal motion is in proportion to the square of tidal range. The tidal range is lower than 5m at any place in Japan due to the topography. Power generation by tidal current, on the other hand, is likely to be feasible in Japan since the maximum speed of the tidal current exceeds 5m/s at some locations of Akasi and Kurusima narrows in the Seto Inland Sea. So the authors have conducted experiments on tidal power generation from the tidal current without blocking the bay or strait. This method may be effectively applicable to power generation by the river flow with low head.