A sewage aeration system powered by a wind-photovoltaic hybrid power generation system has been installed by Nippon Electric Industry Co Ltd at its main factory in Tsukuba-south First Industrial Park. The system will improve the quality of water in the sewage plant's regulating pool before it is discharged into the Seimei River. As a manufacturer of power conditioners for photovoltaic systems and Savonius type wind turbines, Nippon decided to generate power for the water purification system using environmentally clean wind and solar energy. The hybrid unit consists of a 2.7 kW Savonius type vertical axis wind turbine and a 3.25 kW photovoltaic unit. The Savonius rotor has a cut in wind speed of 2 m/s and cuts out at 20 m/s. "It is clear that the aeration system produces appropriate dissolved oxygen levels and improves water quality in the reservoir. Excessive dissolved oxygen in water causes algae to bloom, leading to illness amongst the fish. In contrast, water with too little dissolved oxygen exudes a bad odour and also provides a poor environment for fish," explains the Japanese government's New Energy Development Organisation in the International Energy Association's renewable energy newsletter, Caddet. "The significance of this project is that the environment can be successfully improved and restored by using clean natural energy, without placing any additional load on the environment."