Martin Kidston

(Missoula Current) While NorthWestern Energy was able to secure electricity on the regional market to meet demand in Montana during last week's deep freeze, utility watchdogs are asking why it's coal-fired generating station was offline.

NorthWestern this week said it was able to meet a significant spike in customer demand by entering the regional market, where prices are volatile. During the cold snap, other generating sources within the utility's portfolio, such as wind and solar, weren't available.

But industry watchdogs said the utility's Colstrip power station was also offline, and the timing could be costly for rate payers. NorthWestern has kept the issue quiet, saying only that Unit 4 was down for “scheduled maintenance.”

“Last week, as the storm was approaching, one of the units at the Colstrip plant went offline,” said Anne Hedges with the Montana Environment Information Center. “Despite cold temperatures starting on Thursday and continuing into Friday, that power remained offline for unknown reasons. The storm was well predicted so I'm guessing that there was some type of problem at the plant.”

According to Hedges, the operating unit didn't return to full service until around 2 a.m. on Saturday morning. By that point, temperatures across Montana had been below zero degrees for nearly two days.

Hedges said NorthWestern was lucky the outside energy market could backfill the utility's inability to meet customer demand during critical weather conditions.

“It's important for people to understand that an old coal plant isn't as reliable as NorthWestern wants us to believe and during the time that unit was offline, NorthWestern customers were paying for Colstrip and paying for market purchases,” Hedges said.

As the cold air pushed in last Friday and temperatures in Missoula fell to -30 degrees, the demand for electricity across Montana jumped to nearly 1,100 megawatts. At the same time, wind generation died back, forcing NorthWestern to import electricity from outside markets.

At the time, it needed to secure nearly 600 megawatts of power at peak demand. When asked about the spike in demand, the utility didn't say that its primary generating plant was offline. It's spokesperson told the Missoula Current instead that the utility was pushing for reliable, on-demand generation.

“On the energy market, prices are volatile. There's a lot of companies in the market at the same time looking to serve capacity for their customers,” said Jo Dee Black, the company's spokesperson. “It's why we're working to close that capacity gap and add more capacity dedicated to serving our Montana customers.”

Black praised NorthWestern crews and said the utility plans for such weather events “throughout the year so our systems are ready to serve our customers during these extreme conditions.” But such statements have watchdogs asking why Colstrip was offline at a critical moment.

“We need to know what caused the outage so we can understand if this is just a function of an aging coal plant prone to breakdowns,” Hedges said. “If so, we need to plan our energy future accordingly.”

NorthWestern told the Daily Montanan that Colstrip 4 was down for “scheduled maintenance.” However, it hasn't addressed what that maintenance was, and why it was scheduled during a record-breaking cold spell.