J-Power has resumed commercial operation of Unit 1 at the Nagayama Hydroelectric Power Station in Kitagawa Village, Kochi Prefecture, following a comprehensive repowering project that concluded on October 31. The work began in January and involved a full renewal of major components, including turbines and generators.
The station has operated since 1960, and aging equipment prompted J-Power to replace all primary systems. Engineers applied updated analysis and design methods to improve the turbine runner blade shape, which contributed to higher operating efficiency. Unit 2 underwent the same process earlier, with work starting in 2023 and commercial operation resuming in October 2024.
With both units upgraded, the plant’s total output has increased from 37MW to 38.5MW. Unit 2’s output rose from 37MW to 37.75MW, and Unit 1 now brings the station to its final 38.5MW rating.
Nagayama uses up to 40 cubic meters of water per second supplied by the Hiranabe Dam, which is 124m in length and 38m high. The power station first entered service in July 1960.
J-Power says the project completes repowering efforts at eight of its hydropower plants and forms part of its longer-term plan to expand renewable energy under its “Blue Mission 2050” carbon-neutrality strategy.
