OREANDA-NEWS. Washington state regulators have launched a review of costs associated with the potential retirement of 614MW of capacity that utility Puget Sound Energy co-owns at the Colstrip coal-fired power plant in Montana.

Colstrip's four units have 2,090MW of capacity. Utilities in the west rely on the plant extensively. In recent years it ran at an average of 75pc capacity factor.

But political pressure is building in the Pacific northwest to require local utilities to drop their stakes in Colstrip or to use their ownership claims to force the plant into retirement.

"We want to be sure we know what costs Puget Sound Energy's customers may face when the day comes for these older units to close," Washington's Utilities and Transportation Commission chairman David Danner said. Puget Sound co-owns units 1 and 2 with independent power producer Talen Energy, which operates the facility.

Washington state lawmakers in the past year considered bills to require Puget Sound to force the closure of units 1 and 2 and to finance the shutdown and alternative supply costs by issuing state-backed bonds. The legislation did not pass. But the state utility commission expects the measure to eventually succeed and wants to preempt such legislation by investigating the potential cost to customers of the retirement.

"We need to know that money is set aside to comply with environmental regulations and meet other obligations," Danner said.

Utilities Portland General Electric, Avista, PacifiCorp and NorthWestern Energy are among other owners of Colstrip.

Talen, which owns 529MW of capacity at units 1 through 3, has no immediate plans to shut down the plant. The merchant generator said earlier this year it would prefer to buy out northwest utilities' stakes rather than accept a retirement mandate.

Power grid planners in the west already are planning for the eventual retirement of Colstrip units 1 and 2. The units are older than the larger units 3 and 4.

Transmission planners at ColumbiaGrid see no impacts from the retirements so long as an equivalent natural gas-fired capacity is built closer to demand centers along the Pacific coast. But renewables advocates and some lawmakers want wind farms to replace Colstrip, and grid planning agency Northern Tier Transmission Group is looking at new transmission needs if the coal-to-wind switch occurs.

Montana lawmakers earlier this year mounted an effort to discourage out-of-state utilities to drop Colstrip stakes, by proposing a fee on any company that shuts a coal plant. Montana legislators dropped the effort after the Colstrip bill failed in the Washington state legislature.

The plant took 8.7mn short tons (7.9mn metric tonnes) of coal from Westmoreland Coal's 8,550 Btu/lb Rosebud mine in Montana last year, according to Energy Information Administration fuel receipts. The mine, which is adjacent to the power plant, produced 9mn st in 2014, according to Mine Safety and Health Administration data.

Puget Sound Energy next year plans to join the California-led energy imbalance market, hoping to capitalize on the excess of solar capacity in that state.