Kazunogawa Pumped Storage Power Station

The Kazunogawa Pumped Storage Power Station is a pumped-storage hydroelectric power station near Kōshū in Yamanashi Prefecture, Japan. The station is designed to have an installed capacity of 1600 MW and three of the four 400 MW generators are currently operational, for a total operational capacity of 1200 MW. Construction on the power station began in 1993 and the first generator was commissioned on 3 December 1999. The second was commissioned on 8 June 2000. The third one became operational on 9 June 2014, six year early due to post-power demand from the Great East Japan earthquake. The fourth and final generator is slated to be commissioned by 2024. It is owned by TEPCO and was constructed at a cost of US$2.2 billion.

Design and operation
The upper reservoir for the power station is created by the Kamihikawa Dam at 35.71611°N, 138.8325°W which is a 87 m tall and 494 m long rock-fill embankment type. It has a fill volume of 4110000 m3. The upper reservoir's capacity is 11470000 m3 of which 8300000 m3 is active (or "useful) for power generation. The lower reservoir is formed by the Kazunogawa Dam (葛野川ダム), which uses water from the Sagami River system. The Kazunogawa Dam is 105.2 m tall and 263.5 m long roller-compacted concrete gravity dam. It has a structural volume of 622000 m3. The lower reservoir's capacity is 11500000 m3 of which 8300000 m3 is active (or "useful) for pumping into the upper reservoir.

When energy demand is high, water from the upper reservoir is released down to the underground power station via a single 3.3 km long headrace tunnel which splits into two 1.8 km tunnels before each separate into two 620 m long penstocks. Each penstock feeds a single reversible 400 MW Francis turbine-generator with water before it is released into a 3.3 km long tailrace tunnel which discharges into the lower reservoir. When energy demand is low and therefore inexpensive, the turbines reverse into pumps and send water from the lower reservoir back to the upper reservoir. The process is repeated when necessary to help balance electricity loads. The difference in elevation between the upper and lower reservoirs affords an effective hydraulic head of 714 m and maximum of 779 m.