​On May 1st 2026, CAISO’s Extended Day-Ahead Market (EDAM) and accompanying Day-Ahead Market Enhancements (DAME) extend wholesale day-ahead operations across the historically regulated Western Interconnection.

EDAM follows a month after SPP’s expansion into the Western Interconnection with RTO West. With their competing Markets+ launching in 2027, Balancing Areas in the West are drawing lines to join SPP or CAISO’s constructs by the end of the decade.

​For batteries and renewables, these expansions introduce new market products, and increase the liquidity of bilateral contracting opportunities across the region.

​This article covers what investors need to know about EDAM’s launch: two new market products, larger cross-BA contracting opportunities, and the expected impact on price dynamics. The next article in the series will cover SPP and Markets+.

Key takeaways

• EDAM goes live May 1st 2026. PacifiCorp joins as the day-one participant, adding roughly 12 GW of generation across coal, gas, hydro, wind and solar.
• DAME adds two new day-ahead product pairs to CAISO's procurement stack: Imbalance Reserves Up and Down, and Reliability Capacity Up and Down.
• Wheeling charges between EDAM Balancing Authorities go to zero, opening up economic contracting opportunities to BESS sited inside the EDAM footprint.
• Day-Ahead pricing at generator nodes means capacity swaps and tolling agreements can now be written against actual settlement points.
• Ancillary services stay siloed by Balancing Authority at launch. Resource Adequacy stays fragmented across CPUC RA for CAISO, and the optional Western Resource Adequacy Program (WRAP) for WECC BAs.

To learn how the Extended Day Ahead Market works, read CAISO’s presentation on DAME and EDAM.

PacifiCorp anchors EDAM at launch, with the timeline running to 2029

PacifiCorp joins as the EDAM’s day-one participant, adding roughly 12 GW of generation across coal, gas, hydro, wind and solar.

The first entrant operates two service territories. Pacific Power (PACW) covers Northern California, Oregon and Washington and is a net importer. Rocky Mountain Power (PACE) covers Utah, Wyoming and Idaho and is a coal-dominant net exporter. Two intra-PacifiCorp transfer points, Mona and Crag View, handle the bulk of EDAM-CAISO settlements at launch.

Most CAISO imports already come from these areas. CAISO's Western Energy Imbalance Market (WEIM), live since 2014, has optimized real-time power flows across PacifiCorp and 21 other balancing authorities. EDAM is the day-ahead extension of WEIM. Where WEIM cleared real-time imbalance only, EDAM and DAME bring day-ahead commitment, the market process that clears the bulk of CAISO's energy.

The launch sequence runs through the end of the decade. The following balancing areas plan to join EDAM in the next three years:

• October 2026: Portland General Electric (PGE)
• 2027: BANC, LADWP, PNM, Turlock Irrigation District (TIDC)
• 2028: Imperial Irrigation District (IID), Nevada Power Company, PowerWatch (BHE Montana)
• 2029: Seattle City Light (SCL)

Bonneville Power Administration (BPA), currently a WEIM participant, chose Markets+ over EDAM in March 2025. That keeps the Northwest federal hydro pool, which BPA operates across 31 federal dams and 75% of the Northwest's high-voltage transmission, outside EDAM. Wheeling charges still apply for any EDAM resource serving load through BPA territory.

What EDAM does to CAISO's price formation

​EDAM brings with it variants of gas-, hydro-, coal- and solar-heavy grids, but each mix is only a fraction of CAISO’s existing grid. Any changes in price dynamics will happen on the margin.

CAISO clears a net load that bottoms near 2 GW at midday and peaks near 21 GW in the evening. The footprint runs almost entirely on solar and wind for several midday hours, with the renewable share of supply peaking at 90% at HE11.

Adding PacifiCorp and the rest of the committed EDAM cohort raises the combined midday net load floor to 12.5 GW, against a peak near 40.6 GW. The min-to-max ratio rises from 10% to 31%. The resulting impact is a similar flattening of prices throughout the day.

For a CAISO BESS, the practical consequence is fewer hours of zero-or-negative pricing. Negative wholesale prices offer greater spreads for batteries to arbitrage. This is especially true in the spring, solar penetration starts to rise approaching summer, but cooler temperatures keep load comparatively low

PacifiCorp's thermal floor sets a higher marginal cost than CAISO's curtailed solar. Charging windows narrow in availability but widen in geographic reach. A battery in PACE can charge against PACW's wind or CAISO's solar depending on which is cheaper hour-by-hour, instead of a single regional reference.

What EDAM changes for battery investors

For BESS investors, EDAM and DAME introduce two new wholesale market products and increase the liquidity in regional energy contracts. The latter is a result of generator-level Day-Ahead LMPs and reduced wheeling costs across regions.

1. Two new day-ahead products create slim new revenue streams

DAME adds four new biddable products to CAISO's day-ahead market, in two pairs.

Imbalance Reserves

Imbalance Reserves Up and Down (IRU/IRD**)** manage uncertainty between the day-ahead and real-time net load forecasts. The market pays for 30-minute ramp capability across the entire EDAM footprint.