The Kannagawa Hydroelectric Power Plant is an pumped-storage hydroelectric power plant near Minamiaiki in Nagano Prefecture and Gunma Prefecture, Japan. The power plant utilizes the Minamiaiki River along with an upper and lower reservoir created by two dams, the upper Minamiaiki Dam and the lower Ueno Dam. The power station in between the two dams will contain six 470 MW pump-generators for a total installed capacity of 2,820 MW. Only Unit 1 has commenced commercial operation and did so in 2005. When completed, the plant will have the largest pumped-storage power capacity in the world.

The Kannagawa Hydroelectric Power Plant is 1,600 ft (490 m) underground and measures 708 ft (216 m) long, 108 ft (33 m) wide, and 169 ft (52 m) high. It will contain 6 x 470 MW pump generators for a total capacity of 2,820 MW. Water from the upper Minamiaiki Reservoir is transferred through the power house and after producing electricity, it is brought to the lower Ueno Reservoir. The pump-generators can then pump water from the lower reservoir back up to the upper reservoir for re-use in hydroelectric power production. The water tunnel connecting the two reservoirs is 3.8 mi (6.1 km) long. The power station also has an effective hydraulic head of 653 m (2,142 ft) and maximum discharge of 510 m3/s (18,000 cu ft/s). Unit 1 commenced commercial operation in 2005 and Unit 2 is expected for 2012. The other four units are expected to be operational by 2020 or later.
Kannagawa Hydropower Plant
Country Japan
Locale Nagano Prefecture and Gunma Prefecture
Status In partial operation
Commission date 2005 (Unit 1)
Owner(s) Tokyo Electric Power Company

Power station information
Primary fuel Hydroelectric
Generation units 6 x 470 MW

Power generation information
Installed capacity 2,820 MW