CAISO's EDAM load-balancing math is under CPUC scrutiny as 2 GW of demand resources eye Wednesday entry
The Extended Day-Ahead Market's first month shows two very different grids, and California regulators aren't satisfied with how the balancing arithmetic works.
A revised demand response framework due from the California Independent System Operator on Wednesday (2026-08-19) could pull upwards of 2 gigawatts of behind-the-meter energy resources into CAISO's wholesale power market, according to Advanced Energy United's lead regulatory officer.4 Day-ahead participants are positioned heavily bearish, with consensus sentiment at 71% bearish on CAISO day-ahead, but the accounting assumptions behind that view may be shakier than the positioning implies.
California Public Utilities Commission staff have raised questions about whether EDAM's load-balancing mathematics hold up under scrutiny, and the first month of Extended Day-Ahead Market data suggests their skepticism has a basis. One month in, PacifiCorp's eastern and western systems are clearing like two separate grids. PacifiCorp East cleared at negative prices in 17% of all hours in May (2026-05), while PacifiCorp West went negative only 2% of the time, Utility Dive reported.3 That gap is not a rounding error. It reflects supply surpluses in the eastern system that EDAM's cross-regional balancing is failing to absorb.
The scale of the mismatch reinforces the concern. PacifiCorp East's day-ahead schedule averaged approximately 5,600 MW in May (2026-05), against roughly 2,200 MW for PacifiCorp West, and peaked near 7,650 MW versus the western system's 2,830 MW.3 If EDAM's mechanism is not moving surplus power efficiently between those zones, the price signals CAISO is generating in its day-ahead market reflect accounting artefacts as much as actual supply and demand.
CAISO spot prices already show a notable regional split. NP15 spot cleared at $56.83 per megawatt-hour on Tuesday (2026-08-18), with SP15 settling at $43.10 per megawatt-hour. A north-south gap of more than $13 per megawatt-hour sits uncomfortably against a market reform designed to improve cross-regional price convergence.
The potential entry of 2 GW of demand resources adds a further complication. Advanced Energy United has argued that the CAISO accounting change expected Wednesday (2026-08-19) would open a path for behind-the-meter batteries, rooftop solar, and smart loads to compete in the wholesale day-ahead stack.4 If that volume materialises, it adds both supply-side flexibility and demand-side optionality to a market where bearish positioning rests heavily on load suppression. Whether 2 GW of new DER participation reduces peak clearing prices or simply shifts which resources set the clearing price is not obvious from the rule text alone.
California's underlying supply picture has also shifted materially. EIA data show utility-scale solar generation in CAISO surpassed natural gas output in the first five months of 2026, with solar up 21% compared with the same period in 2024 and gas generation declining.1 More solar means deeper midday suppression and steeper evening ramps, a pattern that makes demand response timing critical and day-ahead forecasting harder precisely when participation rules are changing.
In June (2026-06), FERC voted unanimously to issue show-cause orders to all six RTOs and ISOs, directing them to justify or rewrite their large-load interconnection tariffs.2 FERC staff described the action as addressing a pressing need affecting more than 200 million Americans in more than 30 states. For CAISO, that process is running concurrently with EDAM's ramp-up and the DER accounting review, piling three parallel regulatory proceedings onto a market already generating anomalous price signals.
The bearish case on CAISO day-ahead rests on demand suppression from solar overgeneration and moderate summer load. But if CPUC staff's concerns about EDAM load-balancing math prove substantive, the settlement-price signals that participants are responding to may not reflect actual clearing economics. PacifiCorp East's 17% negative-price-hour rate in a single month is the sharpest empirical test of that concern available so far.3
CAISO's formal response to the CPUC staff critique, the initial DER participation rate following Wednesday's (2026-08-19) rule publication, and the trajectory of the NP15-SP15 spread across EDAM's second month will each provide a cleaner read on whether the bearish consensus has correctly weighed the accounting risk.4