2008 年 24 巻 p. 13-18
A feasibility study on the tidal current power generation by making use of a bridge pier in the narrow strait is introduced. Current velocity increases near the pier, therefore the tidal power generation becomes more efficient because the power is proportional to the cubic of the current velocity. Furthermore, the pier is convenient for the maintenance of the hydraulic turbine and the power unit. The project is now underway at the Ikitsuki Bridge in Tatsuno-Seto Strait of Nagasaki Prefecture. A Darrieus turbine is adopted for tidal current power generation because it is simple in structure with straight wings rotating around a vertical axis, so that it has no directionality against the motion of tidal flow which changes its direction twice a day. However, there is one defect in the Darrieus turbine; its small starting torque. Once it stops, a Darrieus turbine is hard to re-start until a fairly fast current is exerted on it. To improve the starting torque of the Darrieus turbine, a hybrid turbine, composed of a Darrieus turbine and a Savonius rotor is proposed. A combined Darrieus and Savonius turbine was tested in the circulating water channel. Finally, power generation experiments using a 48 pole electric generator were conducted in a towing tank and the power coefficients were compared with the results of experiments obtained in the circulating water channel.