NorthWestern Energy says it wants to acquire part of Puget Sound Energy's share of the coal-fired Colstrip Power Plant for $1.

The agreement would involve taking over the Washington utility's 25% ownership interest in Colstrip's Unit 4 and purchasing additional interest in the Colstrip Transmission System for between $2.5 and $3.75 million.

That would boost South Dakota-based NorthWestern's ownership interest in the unit to 55% amid questions about the plant's future with Puget Sound Energy and other utilities look to unload their coal-generated power.

Tuesday's announcement came a day after NorthWestern Energy officials told the PSC its 20-year power plan for the state leans toward building more natural gas-fired plants.