PacifiCorp East's 17% negative-hour rate points to bearish CAISO day-ahead summer
First month of EDAM data shows eastern PacifiCorp clearing negative in 17% of hours, reinforcing storage-driven bearish pressure on CAISO day-ahead prices.
PacifiCorp's eastern system cleared negative prices in 17% of all hours during May, against just 2% for its western counterpart, according to PCI Energy Solutions senior product manager Tapas Peshin — the sharpest early signal from California Independent System Operator's Extended Day-Ahead Market since it launched.6
The east cleared an average of about 5,600 MW in May, nearly three times PacifiCorp West's roughly 2,200 MW, and peaked near 7,650 MW against the west's 2,830 MW.6 That gap is not weather noise. It is the shape of two grids running under one market design, with storage-saturated solar supply hitting a day-ahead auction built to clear volume. CAISO NP15 spot power stood at $56.83/MWh and SP15 at $43.10/MWh on Tuesday (2026-08-11), but the EDAM negative-hour data is the number day-ahead traders are tracking.6
The EDAM launch is the first time CAISO's day-ahead optimization has extended across a control area with meaningful thermal and renewable diversity. One month of data is thin. But the east-west split aligns with what the summer assessment flagged before EDAM went live: solar saturation in the midday window pushes prices toward zero or below, and storage charging absorbs the excess only until batteries fill.6,1
The storage build is accelerating into the same trough. REV Renewables, an LS Power company, brought its Tumbleweed Energy Storage facility in Kern County online on June 18, and commissioning across California continues to add battery capacity into the midday window that EDAM now prices more transparently.5 More storage means more hours where the day-ahead curve prices the charge cycle, not the discharge.
The supply backdrop reinforces the bearish read. Utility-scale solar generation in CAISO over the first five months of 2026 increased 21% compared with the same period in 2024, and solar has already surpassed natural gas generation in the operator's footprint.4 Every incremental megawatt of mid-day solar lands directly on the curve that EDAM now clears with greater granularity.
California power sector CO2 emissions rose roughly 1.6% year-on-year in April even as the natural gas generation share declined, per grid operator data.2 Gas units are running fewer hours but cycling more aggressively, ramping around the storage charge window rather than serving load directly. Day-ahead price depression from storage does not eliminate gas dispatch; it shifts it to the shoulder hours.
On the gas side, the broader supply picture adds to that neutral-to-bearish pressure. Feedgas flows hit 18.6 billion cubic feet per day, up 9.3% week-on-week, with LNG exports absorbing the incremental supply as domestic storage builds run about 6% above the five-year average.3 That surplus is not shrinking. NYMEX Henry Hub front-month gas was at $2.76/MMBtu on Tuesday (2026-08-11), with little in the prompt strip to support a meaningful premium for California gas-fired generation during solar hours.
Qatar's Ras Laffan Industrial City remains damaged, with 17% of the world's largest natural gas export plant offline.3 That is a global supply story. The Atlantic arbitrage keeps the marginal LNG molecule heading to export terminals rather than displacing domestic gas in California's generation stack — but feedgas data shows the domestic market remains well-supplied regardless.
The contrarian case rests on how storage operators bid. If batteries clear as price-takers during the charge window, they will accept negative prices repeatedly, deepening the 17% figure. If operators instead withhold charge capacity until prices recover above a threshold, negative-hour frequency compresses. One month of data cannot settle that question.6
The next concrete check is June EDAM settlement data, expected in coming weeks. If PacifiCorp East's negative-hour share holds above 15% through a month with longer days and higher solar output, the bearish day-ahead curve is confirmed. If it compresses toward single digits, battery bidding behaviour is already adapting to the new market structure.6,1