Development of a twin-flapping-foils unit to generate hydroelectric power from a water current

Most of the conventional hydraulic turbines have been used for those sites having the static head larger than around 1 m. To extensively utilize not only large hydro-power but small one, which is one of renewable energy resources, development of an energy conversion system being operable under an extremely low head stream is crucial. A twin-flapping-foils unit which works based on the lift acting on the flapping foils in a stream is proposed. The foils oscillate in the transverse direction of the flow due to the lift. The pitching motion of the foils is caused by their own transverse movement through the mechanism consisting of crankshafts and con-rods. In the unit, each foil is supported vertically with a shaft in a manner of a cantilever so that no other parts need to be submerged in a water current. An experimental model with symmetric foils of 100 mm chord and 300 mm span was designed to generate average power output of 10 W at a flow velocity of 1 m/s. Through the tests carried out in the circulating water channel, the performance of the unit was verified to satisfy the design specifications. Further, the demonstration tests by using an irrigation stream performed for over a half year clarified the performance equivalent to that in the in-door water channel and the durability to a certain extent, and showed the applicability to the practical use of lighting a LED street lamp during night even at this scale model