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Since 1978, the Agency of Industrial Science and Technology (AIST) of MITI has promoted research and development of “Large-Scale Energy Conservation Technology” popularly known as the “Moonlight Project”. As the first step, “system technology tests” using improved lead acid batteries started at Kansai Electric's Tatsumi Electric Energy Storage System Test Plant on October 1, 1986. The results showed that this system can work not only as a load-leveling apparatus but also as a high-quality power source which can support the utility power system with its load frequency control and voltage regulation capabilities. As the second step of these R&D activities, a 1MW/8MWh sodium-sulfur battery pilot plant was constructed at the same Tatsumi site. On July 11, 1991, 1000 kW× 8H facility, the largest of its type in the world, was completed and started operation. This paper describes the construction experience and operation results of the pilot plant.

Since 1985, we have been developing the redox flow battery, which is a kind of new-model secondary battery for stationary energy storage. In 1986 we manufactured the 10kW class system and evaluated it by using the iron/chromium electrolyte. Furthermore, we installed a 60kW class system on Kansai Electric Power Company's Tatsumi substation. This system was connected to a 6.6kV power distribution system and tested for five years. It achieved 1,819 charge/discharge cycles, exceeding the target of 1,500 cycles. On the other hand, we also developed the cell which used the vanadium electrolyte whose electromotive force was higher than the iron/chromium electrolyte. This paper reports the principles and configuration of the redox flow battery, the test results of the 450kW battery system and the improved 20kW-8h battery system. The steps toward the realization of the redox flow battery are shown.