Work upgrading Madison Dam’s four turbines and generators that’s expected to increase the facility’s peak capacity from 8 MW to 12 MW is slated to start in the fall, NorthWestern Energy said July 29 in a release.

NorthWestern expects the upgrades to harness 95 percent of power available from flows used under the hydroelectric facility’s existing FERC license. In an average water year, the upgrades will add almost 15,000 MWh to the dam’s current annual budgeted generation of 59,348 MWh.

The work will also be more fish friendly, the company said.

Madison is scheduled to be off line between in October 2019 and May 2021. NWE plans to replace the plant’s 109-year-old turbines with Francis turbines made by Voith Hydro and 4.1 kVA cylindrical-rotor generators by Končar Generators and Motors. The project is estimated to cost $11 million.

The hydroelectric facility is one of nine plants comprising the 334 MW Missouri-Madison hydroelectric project.

NorthWestern acquired Madison Dam as part of its $900 million purchase of 11 PPL Montana hydroelectric plants in 2014.