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CPUC will split CAISO zone into PG&E, SCE and SDG&E zones for Resolve; baseline resources and local constraints updated
Summary
CPUC staff will disaggregate the CAISO model zone into three IOU-specific zones (PG&E, SCE, SDG&E) in Resolve, representing baseline resources, thermal-retention constraints, load profiles and candidate resource regions per IOU; staff said the change will improve treatment of interzonal transmission and locational decisions.
CPUC staff and consultants said the Resolve capacity-expansion model will disaggregate the CAISO balancing area into three IOU zones — Pacific Gas & Electric (PG&E), Southern California Edison (SCE) and San Diego Gas & Electric (SDG&E) — to better reflect zonal transmission constraints and IOU-specific resource characteristics.
Angana (E3 consultant) described the change as a way to “better align with the CAISO topology” and to allow Resolve to capture interzonal transmission constraints and IOU-specific thermal-retention decisions. The split will also localize baseline resources, annual load profiles, candidate resource potentials and busbar mapping to each IOU zone.
The presenters said the combined CAISO baseline is roughly 95 gigawatts, of which about 13 gigawatts are in development; the 2028 snapshot presented showed approximately 29 GW of fossil-fueled generators, about 13 GW of nuclear/geothermal/biomass/biogas/hydro, roughly 9 GW of wind, 23 GW of solar, 16 GW of storage, and about 4 GW of demand response distributed across the three IOU zones.
Staff also said some baseline gas capacity (about 14.5 GW) is assumed to be required to meet CAISO local capacity needs (sourced from CAISO local capacity studies); an additional ~12.5 GW is economically retainable and subject to Resolve’s retention decisions.
Why it matters: Disaggregating the CAISO zone enables Resolve to optimize resource builds with attention to IOU-specific deliverability, local capacity needs and interzonal flows. It also allows transmission upgrades between IOU zones to be modeled as discrete, selectable elements rather than an undifferentiated CAISO transfer.
Technical notes and limits described in the workshop: - Baseline and in-development resource data sources: CAISO master generating capability list, retirement/mothball lists and IRP compliance filings (December 2023) for in-CAISO resources; WEC anchor datasets for external zones. - The disaggregation includes updating thermal-retention constraints, baseline resource mapping, annual and hourly load profiles, and candidate-resource potentials per IOU. Off-system external zones remain modeled as before but with forecasted future builds to avoid unrealistic export opportunities.
Ending: Staff said the disaggregation will also support closer alignment with CAISO transmission planning study areas and ease later busbar mapping work.
