The Extended Day-Ahead Market, CAISO's day-ahead extension of its western imbalance market, has now run for five full months. PacifiCorp's two balancing areas, PacifiCorp East (PACE) and PacifiCorp West (PACW), joined CAISO in the first live trading day on 1 May 2026. Portland General Electric followed on 1 October. The CAISO and the Western Energy Markets Governing Body published the third-quarter benefits report on 29 October, which gives a first summer of data, and CAISO's market analysis group has issued a monthly EDAM performance report for each month from May through September. The last of those, for September, came out on 23 October.
This piece reads those reports alongside the equivalent figures for the Western Energy Imbalance Market (WEIM) and EIA-930 hourly demand data, to put the early EDAM numbers in proportion. It also sums the settlement costs of the reserve and capacity products that launched with EDAM, which are larger than the benefit figure in the CAISO area.
What EDAM is and what FERC approved
The WEIM, which began in 2014, optimises dispatch across balancing areas in the 15-minute and 5-minute markets. Each participating utility still schedules its own resources a day ahead and only the real-time deviations are pooled. EDAM moves the pooling forward into the day-ahead timeframe. Participating balancing authorities submit their supply and demand into CAISO's integrated forward market, which commits and schedules resources across the whole footprint and produces transfers between areas where transmission is made available.
FERC accepted the EDAM tariff in part, subject to conditions, in its order of 20 December 2023 in Docket ER23-2686-000 (185 FERC ¶ 61,210). The same filing carried CAISO's Day-Ahead Market Enhancements (DAME), which created two products that matter for the cost story below: imbalance reserves, procured in the day-ahead market to cover uncertainty between day-ahead and real-time net load, in upward (IRU) and downward (IRD) directions; and reliability capacity, procured in the residual unit commitment process in place of the older RUC capacity, again in upward (RCU) and downward (RCD) forms. FERC accepted CAISO's compliance filing on 30 April 2024.
Each EDAM area keeps its own resource sufficiency evaluation, run before the day-ahead market, and an area that fails it can be limited in what it draws from the others. No area failed the evaluation in any of the five months, according to the monthly reports.
The benefit figures
CAISO's quarterly reports count EDAM's gross benefits in four parts: production cost savings, imbalance reserve savings, reliability capacity savings and greenhouse gas revenues. The method, set out in a draft methodology paper of 20 January 2026, estimates what each area's costs would have been without the day-ahead optimisation across the footprint. The figures are gross. They do not subtract implementation costs, administrative charges or any settlement uplift.
| Area | May | Jun | Jul | Aug | Sep | Total |
|---|---|---|---|---|---|---|
| CAISO | 3.00 | 2.96 | 6.26 | 2.58 | 1.32 | 16.11 |
| PACE | 1.93 | 1.29 | 2.58 | 2.61 | 2.17 | 10.58 |
| PACW | 1.39 | 0.81 | 1.38 | 1.40 | 1.10 | 6.08 |
| Total | 6.32 | 5.06 | 10.22 | 6.59 | 4.59 | 32.77 |
Gross EDAM benefits, $ million. Source: WEM quarterly benefits reports, Q2 and Q3 2026, Table 1. Rows may not add exactly because of rounding in the source.
July was the best month by a margin, and almost all of the jump came on the CAISO side, where the benefit more than doubled from June to $6.26 million. By September CAISO's share had fallen to $1.32 million, less than either PacifiCorp area. PACE was the steadiest of the three, between $1.29 million and $2.61 million every month.
Against the imbalance market
The obvious yardstick is the WEIM, which has been reported the same way for twelve years and whose cumulative gross benefits reached $9.60 billion at the end of September. TEI summed the WEIM's monthly figures for CAISO and PacifiCorp over May to September from the same two quarterly reports: $63.25 million for CAISO and $68.44 million for PacifiCorp, which the WEIM reports as a single participant.
EDAM's $32.77 million is 24.9% of that $131.69 million. The ratio is close to the same for each side: 25.5% for CAISO and 24.3% for PacifiCorp's two areas taken together. In the third quarter alone, both came out at about 25%.
A quarter is a reasonable showing for a market of this size. The WEIM benefit for an area reflects the whole western footprint of 24 participants, while EDAM has had three areas and a few hundred megawatts of transfer capability. The comparison does show where the money still is. For the same two utilities, real-time optimisation across the West continued to be worth about four times as much as day-ahead optimisation among themselves.
There was some concern before go-live that EDAM would draw value away from the WEIM by settling more of the trade in the day-ahead market. The third-quarter numbers do not show that for PacifiCorp. Its WEIM benefit was $44.43 million in Q3 2026 against $46.37 million in Q3 2025, down 4.2%, while its EDAM benefit added $11.24 million on top. CAISO's WEIM benefit doubled over the same comparison, from $19.91 million to $40.60 million, and total WEIM benefits rose 26.3% to $520.50 million. Market conditions, prices and the set of participants changed between the two summers, so the year-on-year figures say little about cause.
Transfers: California turned importer in July
The quarterly reports give EDAM transfer volumes between each pair of areas. Netting them by month gives each area's position in the day-ahead exchange.
| Month | CAISO net | PACE net | PACW net | Gross transfers (MWh) | Average MW |
|---|---|---|---|---|---|
| May | +96,944 | −61,663 | −35,281 | 379,040 | 509 |
| Jun | +113,425 | −25,348 | −88,077 | 375,041 | 521 |
| Jul | −62,948 | +97,619 | −34,671 | 442,380 | 595 |
| Aug | −78,928 | +161,985 | −83,057 | 417,630 | 561 |
| Sep | −121,237 | +175,487 | −54,250 | 385,531 | 535 |
Net EDAM transfer position, MWh; positive is net export. TEI calculation from WEM quarterly benefits reports Q2 and Q3 2026, Table 2.
In May and June, with California's solar output high and its load mild, the CAISO area sold into both PacifiCorp areas on a net basis. The Department of Market Monitoring's second-quarter report describes the pattern: the CAISO area exported about 300 MW to PACW in hours ending 8 through 18, and PACE exported about 140 MW to PACW in the other hours, while PACW was a net importer in every hour of the quarter.
From July the direction reversed. The CAISO area was a net importer in each of July, August and September, and the net import grew each month, to 121,237 MWh in September. PACE became the main net exporter, sending more to CAISO and starting to sell to PACW, a path with no flow at all in May. PACW stayed a net importer throughout. CAISO's own demand drove some of this: the CAISO balancing area peaked at 50,335 MW on 9 September, against a California Energy Commission forecast of 46,360 MW for the month.
The monthly benefit per megawatt-hour transferred moved between $11.91 in September and $23.10 in July, and averaged $16.39 over the five months. Benefits do not come only from transfers, since the imbalance reserve and reliability capacity savings also count, so this is a rough measure of value density rather than a price.
The volumes are small set against load. EIA-930 data put demand in the three areas at 141.8 TWh from May to September, 109.0 TWh of it in the CAISO area. Gross EDAM transfers were 2.0 TWh, or 1.41% of that load. Average transfers in the benefit reports ran at 509 MW to 595 MW per month. The DMM's Q2 report gives an average of about 670 MW for May and June, which may reflect a different counting basis. Either figure is a fraction of the roughly 4,800 MW the DMM reports for average WEIM transfers.
Per megawatt-hour of load
Divided by EIA-930 demand, EDAM's gross benefit comes to 23 cents per MWh across the three areas. The split is lopsided. CAISO's $16.11 million spread over 109.0 TWh is 15 cents per MWh. PACE's $10.58 million over 24.2 TWh is 44 cents, and PACW's $6.08 million over 8.7 TWh is 70 cents.
A small area joined to a large one gains more per unit of its own load, which was also the WEIM's pattern in its early years. For PacifiCorp's customers EDAM's gross benefits so far are close to half a dollar per MWh. For CAISO's load they are a rounding error on an average wholesale energy cost that the September report put at $51.4/MWh.
What the new products cost
The monthly reports also show settlements for the DAME products. These are payments to the resources providing the reserve or capacity, and they are costs to the load that is allocated them. TEI summed the IRU, IRD, RCU and RCD settlement tables in the September report (Tables 21 and 22) for May to September.
| Area | Imbalance reserves | Reliability capacity | Total |
|---|---|---|---|
| CAISO | 15.54 | 39.78 | 55.32 |
| PACE | 2.30 | 0.57 | 2.87 |
| PACW | 1.68 | 0.54 | 2.22 |
| Total | 19.52 | 40.89 | 60.41 |
Imbalance reserve and reliability capacity settlement costs, May–September 2026, $ million. TEI sum of CAISO Monthly EDAM Performance Report, September 2026, Tables 21 and 22.
The CAISO area carried 92% of these costs. Its upward reliability capacity alone cost $35.85 million, and $14.54 million of that came in August, a month when CAISO's EDAM benefit was $2.58 million. Across the five months the CAISO area's IR and RC settlements were 3.4 times its gross EDAM benefit.
That ratio should not be read as a net loss. The products are part of the CAISO day-ahead market design and would have existed for CAISO load with or without PacifiCorp; they replace procurement previously handled through RUC and operator adjustments; and EDAM's benefit figure already counts the savings from procuring reserves and capacity across the wider footprint. The CAISO report is explicit that costs before and after go-live are not like for like. It says total RUC costs since EDAM began reached $74.7 million, $73.8 million of it in the CAISO area, against $28.7 million in the same five months of 2025, and that part of the difference comes from design changes. Before EDAM, resource adequacy resources were excluded from RUC payments and received no compensation for that capacity.
The operational side looks better. RUC adjustments, which operators used to add capacity outside the market's own procurement, were applied 11% of the time in September against 65% in September 2025. July showed 19% against 61% a year earlier. CAISO describes this as a sign that the new reserve framework may be reducing the need for manual adjustments while saying it needs more experience to be sure.
Settlement is the open question
The September report draws a line between operations and settlement. Day-ahead energy offsets, the residual left when collections and payments do not match, required payments out of $91.09 million across the three areas from May to September, $78.17 million of it in the CAISO area. These offsets grew with summer loads and prices. CAISO notes that EDAM introduced area-specific marginal energy costs and revised greenhouse gas accounting, so the post-launch offsets cannot be compared directly with history.
Corrections have also been significant. The congestion revenue allocated to PacifiCorp areas, first reported at around $1.3 million a month, was revised after a settlement error to amounts between about −$680,000 and +$400,000. Bid cost recovery figures for August and September in PACE are still subject to correction. CAISO's October update to its board says previous EDAM settlement issues have been resolved and the dispute deadline was extended. The day-ahead market's timing has been uneven too: results were posted before 1:00 p.m. on 77% of September days, 46% in August and 53% in July.
None of this changes the benefit figures, which are computed separately from settlement. It does mean that what PacifiCorp's customers and CAISO's load actually pay under EDAM will not be settled for some months.
Greenhouse gas pricing
EDAM carries California's cap-and-trade obligation into the day-ahead market by attributing imports into California to specific resources and pricing them. The day-ahead GHG price averaged $4.4/MWh in June, about $8.9/MWh in July, $8.25/MWh in August and $9.33/MWh in September. GHG revenue, earned by resources outside California that are deemed delivered into the state, is one of the four benefit components. Washington's cap-and-invest programme is due to be represented in EDAM from 1 January 2027.
What comes next
Portland General Electric's first month, October, will appear in the Q4 report. PGE has said it expects about $14 million a year in customer savings once the market is fully built out. CAISO's onboarding roadmap shows BANC, LADWP, Turlock Irrigation District and PNM due to go live on 1 October 2027, and Imperial Irrigation District and Berkshire Hathaway Energy's Montana utility in 2028. With more participants, transfer capability between areas should rise above the roughly 600 MW the early reports describe.
A storage enhancement to the residual unit commitment process took effect on 1 October. CAISO says it will let the day-ahead market make more use of batteries, and will report on it in the October monthly report, which, on the pattern so far, should appear in late November.