Hydroelectricity in Japan

Hydroelectricity is the second most important renewable energy source after solar energy in Japan with an installed capacity of 50.0 gigawatt (GW) as of 2019.^[1] According to the International Hydropower Association Japan was the world's sixth largest producer of hydroelectricity in 2020. Most of Japanese hydroelectric power plants are pumped-storage plants. Conventional hydropower plants account for about 20 GW out of the total installed capacity as of 2007.^[2]

Conventional hydropower potential of Japan is considered to be almost fully developed, with little opportunity for further capacity increase.^[3] In recent years, almost exclusively pumped storage plants were commissioned, significantly increasing the ratio of pumped storage capacity over conventional hydro.^[3] The large capacity of pumped storage hydropower was built to store energy from nuclear power plants, which until the Fukushima disaster constituted a large part of Japan electricity generation. As of 2015, Japan is the country with the highest capacity of pumped-storage hydroelectricity in the world, with 26 GW of power installed.^[4] After the 2011 nuclear power shutdowns, pumped-storage plants have been increasingly used to balance the variable generation of renewable energy sources such as solar, which have been growing rapidly in recent years.^[4]

As of September 2011, Japan had 1,198 small hydropower plants with a total capacity of 3,225 megawatt (MW). The smaller plants accounted for 6.6% of Japan's total hydropower capacity. The remaining capacity was filled by large and medium hydropower stations, typically sited at large dams. Cost per kilowatt-hour for power from smaller plants was high at ¥15-100, hindering further development of the energy source.^[5]