J-POWER increased the output of Okutadami Power Plant, which is Japan’s largest conventional hydropower plant, from 560MW to 566MW by upgrading Unit 3, the company announced on December 4, 2025.
According to the statement, J-POWER replaced the unit’s turbine runner, enabling an output increase from 120MW to 126MW without the need to change water flow conditions.
Okutadami Power Plant’s first three units, all originally 120MW, were commissioned in December 1960. The fourth, 200MW unit was added to the power plant in Hinoemata Village, Fukushima Prefecture, in June 2003.
The company said that going forward it plans to upgrade the other units, as well as other power plants, to improve their efficiency and increase their output. Okutadami Unit 3’s refurbishment follows the repowerings of its Nagayama, Suesawa, and Okamigo hydropower plants.
In total, J-POWER operates 61 hydropower plants totaling over 8.5GW, including seven pumped storage facilities with a combined output of about 5GW. Its portfolio also includes Japan’s second- and third-largest conventional hydro assets, the 400MW Tagokura in Fukushima Prefecture and the 350MW Sakuma in Shizuoka Prefecture.
