Colstrip: Washington's coal-free deadline and the shares its utilities are giving up

What the 2025 deadline does, and does not do

If your electricity comes from Puget Sound Energy, Avista, or Pacific Power, the coal on your bill is on a countdown. Washington's Clean Energy Transformation Act, the 2019 law usually shortened to CETA, bars the state's private utilities from charging customers for coal-fired power after the end of 2025. That is roughly ten weeks away as this desk files. The coal in question is almost all one place: Colstrip, a large plant in eastern Montana, near the Rosebud County town of the same name.

CETA set three gates: no coal cost in rates after 2025, a carbon-neutral electricity supply by 2030, and fully non-emitting or renewable electricity by 2045. The first gate is the one arriving now. It does not require a utility to sell or shut its plant. It requires the utility to stop recovering coal costs from Washington customers, which for Colstrip's Washington owners amounts to the same practical thing. Think of it as a rate rule, not a demolition order. None of this closes the plant, since Montana can keep Colstrip running for its own grid.

The shares, and who is taking them

Colstrip runs two units today, Units 3 and 4; the older Units 1 and 2 closed in January 2020. Ownership of the surviving units is split among six utilities across four states. Among the Washington owners, Puget Sound Energy holds the largest piece, on the order of a quarter of the plant's remaining capacity, with Avista and Pacific Power holding smaller slices. Each unit is rated at roughly 740 megawatts at last public report, so the full running plant is on the order of 1,480 megawatts.

NorthWestern Energy, Montana's largest utility, is the main taker. Under agreements made public in recent years, NorthWestern would acquire the Washington utilities' interests around the end of 2025, with the shares changing hands at little or no purchase price rather than for a large payment. The logic is plain enough: a Washington ratepayer cannot be charged for coal, a Montana ratepayer can, and NorthWestern wants the capacity for its own winter peaks. Avista and Puget have both told the Washington Utilities and Transportation Commission, the state body that approves what utilities may charge, that they intend to be out by the deadline.

What stays on your bill after the coal is gone

Leaving a coal plant is not free, and the costs do not vanish at midnight on December 31. Washington's owners have been setting aside money for years for their share of Colstrip's eventual cleanup, the decommissioning and remediation of the site and its ash ponds, and those obligations survive the exit. Utilities recover that through rates over time, so the cleanup line can outlast the coal line by a decade or more.

This is what the UTC is weighing in the utilities' rate cases and clean energy plans: how much remaining Colstrip cost is prudent to recover, how fast, and how any transfer of shares is valued. Puget Sound Energy's clean energy implementation plan lays out its replacement path, mostly wind, solar, storage, and market purchases. If you want the numbers a utility is actually asking for, the rate case docket is where they live, line by line, open to public comment.

Worth watching this month

1. The December 31, 2025 coal-free deadline is the hard one, now about ten weeks out, so expect the Washington utilities' final exit filings at the UTC before year end.

2. Watch Puget Sound Energy's and Avista's rate cases at the UTC for how each proposes to treat its remaining Colstrip costs and any share transfer.

3. NorthWestern Energy's regulatory filings in Montana are the place to confirm whether and when it formally takes the Washington shares.

4. Colstrip's operating status, including any changes to its emissions controls or air permits, is worth a periodic check through Montana's environmental agency, though most such items are routine.

5. Puget Sound Energy's next clean energy implementation plan update will show what replaces the coal, and that one actually matters for future bills.