The California Independent System Operator's Extended Day-Ahead Market , or EDAM, went live on May 1 with PacifiCorp as its first outside participant. That may sound like a wholesale power market footnote, but for battery developers and operators it is a real shift in how revenue, dispatch, and curtailment management work across the western United States. Until now, most cross-border optimization in the region happened in real time through the Western Energy Imbalance Market. EDAM pushes that coordination into the day-ahead window, where utilities commit resources and transmission a full day before delivery. For batteries, that means more visibility, more products to bid into, and a better shot at getting paid for flexibility before the evening ramp hits. AI-generated image Regional day-ahead coordination gives battery operators more visibility into when and where flexibility is most valuable. A bigger market for battery flexibility CAISO and PacifiCorp describe EDAM as the next layer on top of the real-time Western Energy Imbalance Market, which has already produced more than $1.1 billion in benefits for PacifiCorp customers and more than $8.6 billion across WEIM participants since 2014. The difference is timing. Real-time balancing is useful, but batteries make money when operators can see the shape of the next day early enough to schedule charging, discharging, reserves, and transmission together. That is why CAISO chief executive Elliot Mainzer said batteries should play an important role in the new market. Storage can now participate in day-ahead energy scheduling while also offering frequency regulation, frequency response, and the new imbalance reserves product designed to manage uncertainty between day-ahead plans and actual real-time conditions. 42% Share of Western demand EDAM could cover after planned 2027 entrants 2.1M PacifiCorp customers now linked into the day-ahead footprint 8,500 MW Battery capacity already on non-California WEIM systems Oct. 2026 Portland General Electric's planned EDAM entry The practical effect is straightforward. A battery that used to react to price swings after they formed can now be positioned before they arrive. Midday solar oversupply, the classic California duck curve, becomes easier to capture. The evening ramp becomes easier to serve. Operators also get a larger geographic canvas, which matters when one balancing area is spilling solar while another is short on flexible capacity. Why this matters for storage margins Batteries do best when charging, discharging, and reserve commitments are coordinated instead of improvised. EDAM pushes more of that value stack into the day-ahead window, where revenue certainty is usually better and system operators can use storage with fewer surprises. Curtailment is turning into a battery opportunity AI-generated image Solar-heavy midday conditions are exactly where day-ahead battery scheduling can reduce waste and improve grid economics. The launch also lands at a time when western grids badly need better solar coordination. PV Magazine USA noted that CAISO curtailed 3.4 million MWh of utility-scale wind and solar in 2024 , up 29% from the year before, with solar responsible for the vast majority. Curtailment is not just a renewable problem. It is a market design problem, because spilled low-cost energy means batteries, transmission, and flexible loads are not being lined up well enough in advance. EDAM does not erase transmission bottlenecks or make every price spread disappear. What it does is give the region a better mechanism for moving surplus clean power before operators are trapped in five-minute firefighting. PacifiCorp's roughly 12 GW generation portfolio joins the footprint first, opening new pathways for exporting or absorbing excess energy across California, Oregon, Washington, Utah, Idaho, and Wyoming. Battery operators should care because curtailment is often the raw material for arbitrage. The more reliably they can see low-price hours forming, the better they can charge. The more confidence they have that the market will value evening discharge and contingency capacity later in the day, the stronger the case for bidding storage aggressively rather than holding back for uncertainty. Before EDAM With EDAM More dependence on real-time balancing after conditions tighten Day-ahead commitment of energy, transmission, and reserves across a broader footprint Batteries react to volatility that is already forming Batteries can position for midday charging and evening discharge sooner More renewable spill when one balancing area has excess supply Better chance to move energy or store it before curtailment becomes unavoidable A new revenue stack is taking shape The battery story here is not only about simple buy-low, sell-high arbitrage. EDAM expands the number of decisions that can be made coherently in one place. A storage asset can pursue day-ahead energy margins, support frequency products, and collect value for standing ready through imbalance reserves. That is a healthier setup than forcing every battery to chase the same evening peak with limited foresight. This matters even more as the West adds more storage outside California. Mainzer said balancing authorities outside California that already participate in WEIM now have 8,500 MW of batteries on their systems, on top of California's own massive fleet. That scale changes how storage behaves as a market participant. Batteries are no longer edge resources. They are becoming system resources. AI-generated image Regional transmission access is part of the battery value story, not a side issue. There is also a second-order effect for developers. If a broader day-ahead market reduces price volatility, lowers curtailment, and improves resource sufficiency, storage projects become easier to model. Revenue stacks are still merchant and still imperfect, but forecasting gets less chaotic when one operator can see more of the western grid and optimize around it. That helps utilities procure storage. It helps financiers underwrite it. It helps developers decide where a four-hour battery may be enough and where a longer-duration configuration might capture more value. What to watch next • Portland General Electric: Its planned October entry will show whether EDAM scales smoothly beyond the first participant. • Imbalance reserves pricing: Battery operators will be watching closely to see how much value the new product actually contributes. • Curtailment trends: If western day-ahead coordination works, midday renewable spill should become easier to monetize or reduce. • Longer-duration storage: Better day-ahead visibility may sharpen the case for assets that can move solar oversupply further into the evening or overnight hours. Why the western market buildout matters beyond California CAISO's release emphasizes that EDAM is voluntary and designed to preserve balancing authority autonomy while expanding coordination. That matters politically, but it also matters commercially. Utilities that were willing to join the real-time market but not a deeper regional structure now have a way to add day-ahead efficiency without giving up full control. If that compromise holds, storage owners could see a much larger western market assemble over the next two years. Planned 2027 participants include the Los Angeles Department of Water and Power, the Balancing Authority of Northern California, which includes SMUD, the Public Service Company of New Mexico, and Turlock Irrigation District. CAISO says that group would push EDAM to about 42% of western electricity demand . Once a market reaches that scale, storage bidding behavior, congestion patterns, and solar export paths all start to matter at a regional rather than local level. The battery industry has spent years talking about software, optimization, and stacked revenues. EDAM is one of the clearest signs yet that the market structure is finally catching up to that pitch. Hardware still