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Northwestern Energy to double ownership in Colstrip plant

The Colstrip Generating Station near Colstrip, Mont., is the second-largest coal-fired power plant in the West.

Montana's largest utility on Monday announced it will acquire 222 megawatts of the Colstrip coal-fired power plant from Washington-based Avista Utilities. The acquisition would take effect in 2026.

NorthWestern Energy buys about 40%of customers’ electricity on the open market.

CEO Brian Bird said the added Colstrip share, plus a natural gas plant under construction, will help the utility move toward generating more electricity locally.

“The combination of those two moves us from a capacity deficit in terms of serving our customers to a slight surplus,” said Bird.

The transfer itself comes without a price tag. Avista remains responsible for environmental and decommissioning costs. NorthWestern will take on operational and capital expenses starting in 2026.

Montana’s GOP political leaders including U.S. Sen Steve Daines, Gov. Greg Gianforte and Congressman Rep. Matt Rosendale voiced their support of the agreement this week. Conservation groups like the Montana Environmental Information Center have been vocal opponents of further investment in the plant, citing greenhouse gas emissions and the growing advancement of clean energy technologies.

Northwestern tried to acquire Puget Sound Energy’s share of Colstrip in 2020, but the agreement fell through. Both Puget and Avista are transitioning away from coal-fired generation as required under Washington state law.

Kayla writes about energy policy, the oil and gas industry and new electricity developments.