CAISO is proposing a set of tariff changes for submission to FERC early in 2026 to help ease participants into the ISO’s new Extended Day-Ahead Market.
The planned tariff revisions range from formatting changes to rule adjustments that affect the overall market design, said Andrew Ulmer, CAISO assistant general counsel, at a Dec. 17 joint meeting of the ISO Board of Governors and Western Energy Markets (WEM) Governing Body. CAISO plans to file the proposed revisions with FERC in the first quarter of 2026 to keep EDAM’s May 2026 opening date on track.
The first proposed revision is associated with CAISO’s rules for intertie modeling and scheduling. Intertie resources in CAISO are currently modeled at specific scheduling points, but the ISO in 2025 proposed to model intertie resources under EDAM at generation aggregation points (GAPs). A GAP is the collection of supply resources in a balancing authority area or group of BAAs.
The GAP approach would have significantly improved power flow and market accuracy, improved alignment with actual power flows by reducing phantom congestion and reduced operator conformance of transmission limits in real-time, CAISO staff wrote in a November white paper. (See EDAM Intertie Scheduling Processes Raise Stakeholder Concerns.)
But many stakeholders raised concerns about the GAP approach, saying it could lead to a market with multiple prices for the same intertie.
CAISO therefore adjusted its approach in its tariff revisions proposal: The ISO plans to price and model schedules at intertie scheduling points as it does today, CAISO Vice President of Market Design and Analysis Anna McKenna said in a memo presented at the Dec. 17 meeting.
“This [proposed approach] will enable market participants to transition to EDAM without impacting existing commercial arrangements for transactions at the ISO balancing area interties,” McKenna wrote in the letter. “Management will work with stakeholders to determine when the market should transition to modeling and pricing the ISO balancing area intertie scheduling points using the aggregate modeling locations.”
Sticking with the current intertie scheduling approach largely preserves intertie scheduling and modeling practices for ISO interties, McKenna wrote. The current approach represents a reasonable compromise to implement EDAM and reflect the congestion impacts of intertie transactions, she wrote.
“I want to make sure I really understand this. … The generation aggregation points [approach] is being deferred,” Robert Kondziolka, WEM Governing Body member, said at the meeting. “Is it your understanding that stakeholders support how GAP should be implemented, whether it’s 2027 or sometime after that?”
“I think there are questions about how GAPs are modeled,” CAISO Regional Markets Section Manager replied. “That’s where [future] stakeholder workshops … will help tease out those questions.”
“It sounds like what we are moving toward is a model that prices electricity differently depending how it got there,” added Board of Governors Chair Severin Borenstein. “This is sort of moving away from a nodal pricing model, which … worries me because of gaming [opportunities].”
For resource adequacy imports, CAISO’s proposed tariff changes would allow certain scheduling coordinators to reassign their system resource capacities prior to the day-ahead market — specifically when the resource supporting that import is in the EDAM area.
The RA tariff revisions would also allow participants to continue to bid RA imports at CAISO interties that are also EDAM transfer locations, specifically when those imports are sourced from outside the EDAM area, McKenna said in the memo. This approach is similar to how the market treats RA imports today, Bosanac said.
At the Board of Governors’ Dec. 18 general session, board members nominated Joe Eto to be the board’s new chair in 2026, replacing Borenstein. Eto joined the board in 2023 after retiring from the Lawrence Berkeley National Laboratory after 40 years.
