J-POWER began repowering Japan’s third-largest conventional hydropower plant, the 350MW Sakuma Power Station in Hamamatsu City, Shizuoka Prefecture, the company announced on July 6, 2026.
According to the statement, the company will completely replace major equipment such as turbines and generators, rebuild the power plant buildings, and install surface water intake facilities. The upgrades will increase the asset’s maximum water usage from 306m3 to 350m3 per second, increasing its capacity by 50MW to 400MW and adding approximately 55GWh per year of generation.
The construction will take about 10 years and be carried out in two phases, with Phase 1 running from July 2026 through FY2030 and Phase 2 from FY2031 through FY2035. Two of the plant’s four generators will be replaced in each phase, with each of the sets remaining offline for approximately 48 months.
Sakuma Power Station was commissioned in 1956. It has been generating approximately 1.4TWh per year and is capable of operating at both 50Hz and 60Hz, allowing it to supply both eastern and western Japan.
The project follows J-POWER’s upgrade of Unit 3 at the 566MW Okutadami Power Station, which is Japan’s largest conventional hydro asset, and refurbishments of several smaller hydropower plants. At 400MW, Sakuma Power Station will match the company’s Tagokura Power Station in Fukushima Prefecture, which currently ranks second.
In total, J-POWER operates 61 hydropower plants totaling over 8.5GW, including seven pumped storage facilities with a combined output of about 5GW.
