Challenge to use small hydropower by contrarotating small hydro turbine

Abstract

Small hydropower generation is alternative energy, and there is a significant potential for a small hydro turbine. Small hydropower facilities that generate about 100-1000 kW have spread widely; however, it causes environmental destructions by a foundation construction and a set up of a draft tube. On the other hand, there are a lot of places that can generate about 100 W-1 kW (pico-hydropower) in agricultural water and a small stream. Efficiency of small hydro turbines is lower than that of large ones, and it can be used in wide flow rates range. Then, there are demands for small hydro turbines to keep high performance in wide flow rates range. Therefore, we adopted contra-rotating rotors, which could be expected to achieve high performance. In this study, a significant compact hydro turbine is named as a small hydro turbine. Final goal on this study is development of a small hydro turbine-like electrical goods, which has high portability and makes an effective use of the unused small hydropower energy resource. In this research, we selected some places in Tokushima Prefecture in Japan, where a small hydropower could be generated, and conducted field tests of head, flow rate and water quality. Then, it was found that it was necessary to develop a small hydro turbine that could generate electricity in wide flow rates range because the small hydropower potential was different at each place. Therefore, we designed and manufactured an experimental apparatus to clarify the performance of our proposed contra-rotating small hydro turbine and investigated flow condition at the inlet of each front and rear rotor by the numerical analysis. Furthermore, the circumferential velocity distributions downstream of the rear rotor were also clarified.