Assumptions for the 2027-2028 TPP

The Integrated Resource Planning (IRP) process develops a resource portfolio(s) annually as a key input to the California Independent System Operator's (CAISO) Transmission Planning Process (TPP) base case studies, which includes a reliability base case portfolio and a policy-driven base case portfolio.  The California Public Utilities Commission (CPUC) may also transmit additional resource portfolios as inputs for sensitivity studies that test the implications of various policy futures.  This page contains documentation relevant to the development and mapping of resource portfolios for the 2027-2028 TPP.

Transmission Planning Process Ruling and Ruling Development Materials

• 2027-2028 Transmission Planning Process Portfolio Ruling, 8/31/2026
  • Fact Sheet on 2027-2028 Transmission Planning Process Portfolio Ruling,8/31/2026
  • 2027-2028 Transmission Planning Process RESOLVE Analysis Slide Deck, 8/31/2026
  • 2027-2028 Transmission Planning Process RESOLVE Package analysis, 8/31/2026. Note: These zip files are big, it is advised to download and open locally
    • Raw RESOLVE Outputs 
      • Unprocessed RESOLVE outputs for Recommended Base Case with 0 GW OSW and 38MMT by 2030, 2025 IEPR load forecast case, Limited out-of-state resources case, 4.5 GW OSW and 30 MMT GHG target by 2030 case, 4.5 GW OSW and 38 MMT GHG target by 2030 case)
    • RESOLVE Code Base and Inputs
      • Code base and template Scenario Tool and Results Viewer, and inputs used for RESOLVE modeling
    • RESOLVE Upstream Data Workbooks and Public Case Results Viewers
      • Workbooks upstream of the RESOLVE Scenario Tool, Baseline Resources and Transmission Workbook, and Results Viewer for published cases

Methodology for Resource-to-Busbar Mapping

The busbar mapping methodology states guiding principles, establishes mapping criteria, and outlines the iterative inter-agency mapping process.

• Methodology for Resource-to-Busbar Mapping for the Annual TPP, Ruling version, 8/31/2026
  • Red--lined Methodology for Resource-to-Busbar Mapping for the Annual TPP (red-lined from the 2026-2027 TPP version), 8/31/2026

Webinar – 06/16/2026 – IRP MAG Webinar on Potential Updates to the Busbar Mapping Methodology

• Objectives
  • Provide an overview of the busbar mapping process and its role in the TPP
  • Familiarize stakeholders with the updates to the criteria and the criteria alignment thresholds. 
  • Give opportunity to stakeholders to ask questions and provide comments on the busbar mapping methodology and the proposed criteria. 
  • Request stakeholders’ informal written feedback to be incorporated in the final updated methodology
• Noticing Document 
• CPUC slides
• CEC slides
• Webinar Q&A
• Webinar Recording