HELENA — NorthWestern Energy leaders say acquiring another large ownership share in the Colstrip power plant will give them much more control over the plant’s future.
On Tuesday, NorthWestern announced they would take over Puget Sound Energy’s share of the coal-fired plant, at no cost, as of Jan. 1, 2026. Last year, the company reached a deal to acquire Avista’s share, at the same time and on essentially the same terms. All together, NorthWestern will own 55% of the plant – giving them majority control.
“We can certainly influence votes on the overall plant expenditures,” said John Hines, NorthWestern’s vice president of supply and Montana government affairs. “That's not to say that we can have absolute control, but absent the Puget transaction, we had far less control in being able to dictate outcomes.”
Hines said PSE and Avista will both retain responsibility for decommissioning costs when the plant eventually closes.
Colstrip has a complex ownership structure, with six energy companies holding stakes. Both PSE and Avista, headquartered in Washington state, are seeking to end their investment in Colstrip in the next few years to comply with state utility regulators.
Hines said one key area where majority control could make a difference is in decisions surrounding a recent rule from the U.S. Environmental Protection Agency. Utility leaders have said the Mercury and Air Toxic Standards rule would likely require hundreds of millions of dollars in investment to install a “baghouse filter” at Colstrip to bring the plant into compliance.
“I feel much more comfortable that we can move forward on a bag house if that's what we ultimately need to do to keep the plant operational,” said Hines. “If you're a utility that's in Washington, for example, and your commission says you have to be out at the end of 2025, it'd be very, very difficult for you to support an investment of this magnitude.”
The MATS rule is currently facing litigation, and Hines said they won’t make a decision on how to move forward at the Colstrip plant until later this year or early next year. NorthWestern currently hopes to keep using the plant through at least 2042.
NorthWestern currently has authority to use 222 megawatts of power from Colstrip. With Avista’s 222 megawatts and PSE’s 370, they’ll nearly quadruple that authority. Hines said it would cost hundreds of millions of dollars and take years for NorthWestern to build the same generating capacity they’re adding in this deal.
“Given that we have an obligation – an absolute obligation – to ensure there's sufficient electricity to heat homes, to use their stoves, cool their food, this was a really easy decision for us to make in the context of affordability and reliability,” he said. “There's no other capacity out there that comes at a zero cost.”
NorthWestern has put a heavy emphasis in recent years on a need for fossil-fuel generation, which they say provides dependability that other energy sources still aren’t able to match. Hines called Colstrip a “bridge” to cleaner energy.
Environmental groups questioned the reliability of Colstrip and accused NorthWestern of not sufficiently planning for cleaner generation.
“If you see rats fleeing a sinking ship, it doesn’t make good business sense to invest billions into the sinking ship – it makes much more sense to divest of risky and outdated technology and instead invest in the next generation of energy generation, like every other utility in the country,” said Anne Hedges, policy and legislative director for Montana Environmental Information Center, in a statement. “Montana is falling decades behind and may never catch up to modern energy generation technologies if this acquisition comes to pass.”
MEIC also said the Colstrip plant has been down at some of the key periods of hot and cold weather when demand has been highest. They argued that went against the argument for this type of generation as a reliable backstop.
Hines said the plant’s two units were down over several days recently, but that didn’t show Colstrip wasn’t a necessary part of NorthWestern’s energy portfolio.
“The transmission system had to declare an energy emergency alert in order for us to serve load at that time period,” he said. “We were really close for a few hours of not being able to have enough power. There was no more transmission capability to bring power into the state – it was zero absent this energy emergency alert.”
Hines said NorthWestern’s current share of Colstrip comes primarily from Unit 4, but these additional acquisitions will give them a significant share in Unit 3 as well. He said that would reduce the risk of not being able to serve their demand if one unit went down.
