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 TPP Busbar Mapping Ruling, 10/12/2026
• 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

Initial Mapping Results for the Proposed Base Case

The Initial Busbase Mapping Dashboard for the Base Case summarizes the initial mapping results, the mapped resources alignment with the busbar criteria, and the analysis used to assess that alignment.

• Full Dashboard - Initial Mapping for the 27-28 TPP Case, 10/12/2026
  • This workbook is ~60 MB and includes a summary of the initial mapping results as well as the full analysis, including the calculations, equations, and data used to conduct the mapping and assess the criteria alignment.  If an error occurs when downloading, staff recommends using Chrome or Firefox browsers.
• Compact Dashboard - Initial Mapping for the 27-28 TPP Case, 10/12/2026
  • This version of the dashboard is ~22MB and is the smaller compact version of the mapping results.  It includes only the results (fixed numbers) and not the equations, calculations, and supporting reference data that is used to conduct the busbar mapping analysis.
• Supplemental data workbooks for initial mapping effort.
  • Baseline Reconciliation and In-development resources, 10/12/2026
  • Interconnection Upgrade Criteria, 10/12/2026
  • Commercial Interest Analysis, 10/12/2026
  • Gas Capacity Not Retained, 10/12/2026

Webinar – 10/22/2026 - IRP Webinar on the Proposed 2027-28 Transmission Planning Process Portfolios and Preliminary Busbar Mapping Results

• Objectives
  • Familiarize stakeholders with proposed portfolios and busbar mapping process.
  • Review the preliminary mapping results for the proposed base case portfolio.
  • Provide an opportunity for stakeholders to ask clarifying questions about busbar mapping process and preliminary mapping results.
• Noticing Document 

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