EDAM, Markets+ and Which Way Idaho Went

The power grid course explained the three Western markets in its lesson on who runs the grid: the real-time Western Energy Imbalance Market, CAISO's day-ahead EDAM, and SPP's competing Markets+. This lesson asks the Idaho question. Four organizations serve most Idaho customers. Each made a different choice, and each choice reaches a bill by a different road.

Where Idaho's utilities stand, October 2026

Utility	Serves in Idaho	Real-time (WEIM)	Day-ahead choice	Regulator of the choice
Idaho Power	Southern and southwest Idaho	Entered 2018	Listed as leaning toward EDAM since March 2024; no entry date listed	Company decides; Idaho PUC reviews costs; FERC approves tariffs
PacifiCorp (Rocky Mountain Power)	Eastern Idaho	Entered 2014	Entered EDAM in 2026, its first non-California participant	Six state commissions, including Idaho's, review its costs
Avista	North Idaho	Entered 2022	Not listed among EDAM participants or Markets+ phase two funders	Idaho and Washington commissions
Bonneville Power Administration	Wholesale supplier to many Idaho co-ops and city utilities	Entered 2022	Pursuing Markets+; its March 2026 proposal targets joining October 1, 2028	BPA's own process; FERC reviews its rates

Entry years and EDAM status come from the Western Energy Markets participant pages; BPA's dates come from its own documents. The EDAM page lists other participants too: Portland General Electric entered in 2026, four California and New Mexico entities plan to enter in 2027, and NV Energy, PowerWatch (formerly BHE Montana) and Imperial Irrigation District plan to enter in 2028. SPP's Markets+ page lists eleven phase two funders as of October 27, 2025, including BPA, Arizona Public Service, Puget Sound Energy, Salt River Project, Tri-State and Xcel's Colorado utility.

Look at the map that makes. PacifiCorp's eastern Idaho territory and Idaho Power's southern Idaho territory touch. If Idaho Power joins EDAM, most of southern and eastern Idaho trades day-ahead in one market. BPA, whose lines carry power for much of north and east Idaho's public power, heads to the other one. The seam between EDAM and Markets+ would run through the Northwest.

Why a seam costs money

Inside one market, the operator's software schedules generation across the whole footprint at once. It can see that a cheap hour of hydro in Idaho should displace a gas unit in Utah and schedule both. Across a seam, two operators run two optimizations. Trades between them need extra scheduling steps, transmission reservations and price differences. Some trades that would have saved money don't happen. Each market's backers have studies estimating the savings of their own option. When someone quotes a number at a meeting, ask who paid for the study.

How market results reach an Idaho bill

No market operator sends an Idaho customer a bill. The money runs through three steps.

1. The market settles with the utility. Idaho Power is paid for power it sells into the market and pays for power it buys, at market prices, every five minutes in the WEIM and by the hour day-ahead in EDAM.
2. Those net costs land in the utility's power supply costs.
3. Idaho Power's Power Cost Adjustment passes most of the change to customers. The PUC's 2026 PCA order describes 95 percent of the difference between actual and base power supply costs flowing to customers, up or down. The power grid course covers the PCA in How Your Power Bill Is Built.

Savings and costs from market participation also show up in general rate cases, where the commission resets base power costs, and in the costs of joining: software, staff, market fees. Those implementation costs go into rates only if the PUC finds them prudent.

What the Idaho PUC can do

FERC approves market tariffs. The utility decides whether to join. So what is left for Idaho?

More than it looks. The PUC decides whether the costs of joining go into rates, whether the utility managed its market participation prudently, and how benefits are credited to customers. In practice, a utility planning a major market move files a case or an update with its commission, and parties can intervene. Nevada's commission reviewed NV Energy's EDAM plan before approving it, according to trade press cited in Jeff Pierson's Feeding the Beast No. 4. As of October 2026 the market operator still lists Idaho Power only as leaning toward EDAM, so the Idaho version of that review is still ahead.

The Idaho Legislature has also spoken. House Concurrent Resolution 32, adopted by both chambers in March 2026 with Rep. David Leavitt as House floor sponsor, says Idaho "participates in interstate energy markets and benefits at times from cost-effective imported power." It also says transmission projects built in Idaho "must demonstrate a clear, measurable, and durable net benefit to Idaho ratepayers." A concurrent resolution states the Legislature's position. It does not change the law the PUC applies, though it names PUC cost recovery proceedings as a place the standard is meant to guide.

Feeding the Beast No. 4 argues the PUC should attach conditions to any Idaho Power EDAM authorization: participation contingent on ROWE actually gaining independent authority by a set date, written exit triggers, and an annual audited Idaho accounting of market costs and benefits. Supporters of joining answer that participation is voluntary and a utility can withdraw, so the right to leave is the protection, and that delay forfeits savings other utilities are already collecting. Both points can be tested in a docket, which is why the filing, when it comes, matters.

Dates worth having: BPA joined CAISO's Western Energy Imbalance Market on May 3, 2022, then chose SPP's Markets+ over CAISO's day-ahead market on May 9, 2025. Idaho Power said on March 21, 2024 it was "leaning towards" EDAM, which launched May 1, 2026.