“The SOD stack analysis is a critical planning tool that visualizes how California’s available power resources compare to projected electricity demand.”
RA Supply and Demand Stack Analysis
Introduction
Resource adequacy (RA) supplies in the California Independent System Operator (CAISO) balancing area have been tight in recent years. CalCCA’s RA White Paper demonstrated razor–thin margins when comparing RA requirements with the available RA supply for 2023 and 2024. The “stack” analysis presented below compares RA requirements with available supply under California’s new slice-of-day (SOD) program to reveal the current conditions of the market, with a focus on overall grid reliability. Although there are enough total resources to meet system-wide needs, community choice aggregators (CCAs) and other load-serving entities (LSEs) may still face challenges to meet their hourly SOD obligations. This is because the program doesn’t allow trading of hourly RA obligations, which creates artificial shortages and raises prices. CalCCA’s hourly RA trading proposal aligns RA obligations more precisely with actual resource availability and system needs, providing LSEs with the tools to optimize RA procurement and reduce customer costs — without compromising reliability. More on the push to improve RA SOD trading here.
Interactive Dashboard
Explore our interactive PowerBI dashboard to examine the complete SOD stack analysis across all months of 2026 and 2027. The dashboard allows users to investigate various scenarios, including potential delays in new resource development, adjustments to the market supply, and changes to PRM in future years. Users can visualize hourly resource contributions, identify critical constraint periods, and assess how different planning assumptions affect reliability margins on a month-to-month basis. Download the complete dataset (CSV) or access the interactive dashboard.
How to Use
- Click to select different variables such as Year, Month, Type, Delay, or Adjustments for Resources not available for purchase.
- Hover over any bar in the stacked chart to get more details and explore the data.
- Play around with different variables to see the differences!
- Navigate to page 2 by clicking the right arrow at the bottom middle of the screen.
- You can use the options at the bottom right of the screen to zoom in on data or make the analysis full-screen.
- Share to social media or other sites at the bottom right.
- Scroll down for a breakdown of data sources and assumptions.
Interactive Dashboard
Stack Analysis Explained
Understanding the SOD Stack Analysis
The SOD stack analysis is a critical planning tool that visualizes how California’s available power resources compare to projected electricity demand. By stacking various resource types (thermal generation, renewables, imports, demand response, etc.) against forecasted demand plus planning reserve margins, the analysis identifies potential shortfalls or surpluses in the resources participating in the RA market. This assessment is crucial for understanding the feasibility of meeting reliability targets, especially as California navigates its clean energy transition during extreme weather events and peak demand periods.
September 2026 Stack Analysis
The September 2026 stack analysis reveals several critical insights about California’s energy landscape. Solar resources provide substantial contributions during daylight hours but diminish as evening demand peaks. Due to the increased reliance on storage in peak hours (17-21), we see that later hours in the day when storage resources are depleted become tight. Hours 22-24 show the tightest supply-demand balance. Overall, we see that available resources exceed demand by approximately 6-7 GW during these critical periods, assuming that 40% of expected new resources are delayed. The analysis indicates that unexpected resource retirements and further project delays, particularly for storage projects, could quickly transform the current margin into a tight market similar to 2023-2024.
Data Sources and Assumptions
The SOD stack analysis relies on several key data sources and methodological assumptions:
- Demand with PRM:
- Demand: 2026 and 2027 monthly peak load day managed net load forecasts are from CAISO’s California Energy Demand Planning Scenario (2023 and 2024 Hourly Forecasts, respectively)
- PRM: The planning reserve margin for 2026 and 2027 is 18 percent.
- Resources:
- Supply resources inside of the CAISO system are composed of Online Resources and Contracted Resources that are expected to come online prior to the RA month.
- Online Resources: Master Resource Database and NQC list published March 2026.
- Contracted Resources: CAISO Interconnection Report last updated April 19, 2026 used to project expected resources to come online by 45 days before the 1st of RA eligible month based on the reported commercial online date.
- Delay scenarios reduce the amount of Contracted Resources that come online in time to be RA eligible.
- Storage Dispatch:
- Storage dispatch is constrained based on the SOD accounting rules from the CPUC. Storage power is limited by the nameplate capacity (MW) rating, storage energy is limited by the energy (MWh) rating, and sufficient charging energy must be available to charge storage, including efficiency losses. Within these constraints storage is dispatched after accounting for all other resources, imports, and adjustments, to maximize the minimum planning reserve margin.
- Imports:
- RA imports for each month are based on the actual RA imports reported by the CAISO in 2025. The hourly shape of the RA imports follows the assumptions from the CPUC using confidential RA showing data. The CPUC’s hourly shapes achieve the full RA import level in hours 6 through 22 but are as much as 50% lower in the other hours of the day.
- Demand Response:
- Demand response quantities are from the CPUC’s Resource Adequacy Compliance Materials; applied to 5 contiguous hours with highest difference between demand and supply. Demand response totals include avoided losses and are from event-based programs at PG&E, SCE, and SDG&E.
Negative Adjustments to Market Supply
- Thermal Plant Derate:
- Many thermal generators cannot produce maximum output during periods with high ambient temperatures, leading to plant derates. For this reason, resource owners may not sell their full nameplate capacity as RA capacity. For thermal plants whose NQC is listed as equivalent to their Net Dependable Capacity, we apply a technology-specific thermal derate estimated from historical ambient temperature derates within the CAISO. CalCCA’s approach parallels CPUC discussions regarding the need to include thermal derates in reliability modeling.
- Excess IOU Procurement for a Higher Effective PRM:
- CPUC’s authorization of IOUs to procure excess resources to achieve a higher effective PRM continues through 2027. The quantity of excess procurement is estimated for respective months using an average of actual achieved IOU excess procurement of RA-eligible resources from 2022-2026.
- Retention for Substitution:
- IOUs are entitled to retain RA beyond their bundled needs for substitution during planned outages. This assessment relies on the 2021 resources retained by IOUs as reported in the 2021 IOU Excess Resource reports.
Have questions or feedback about the Stack Analysis or Dashboard?
We’d love to hear from you. Please reach out to us at info@cal-cca.org.
