Coordinated Transmission Planning Overview

In 2022, the California Energy Commission (CEC), California Public Utilities Commission (CPUC), and California Independent System Operator (California ISO) established a synchronized annual transmission planning process through a Memorandum of Understanding (MOU). This MOU signifies a commitment to tightly integrate electricity demand forecasting, resource planning and procurement, and transmission planning. The goal is to support the timely development of clean energy resources in the near and long term.

Graphic showing the coordinated roles for transmission planning.

The MOU coordinates the efforts of the CEC, CPUC, and CAISO in a multi-step approach:

  • The CEC forecasts long-term electricity demand, incorporating the state's goals for 100 percent clean electricity and economy-wide greenhouse gas emission reductions. This forecast also considers climate simulation data to account for extreme weather events.
  • The CEC's demand forecast informs the CPUC's Integrated Resource Planning (IRP) process. The IRP process results in a clean energy portfolio known as the “Preferred System Plan” designed to achieve emission reduction goals at least cost, while maintaining electric service reliability throughout the California ISO balancing authority area.
  • The CPUC’s Preferred System Plan then guides the California ISO's Transmission Planning Process (TPP). The TPP identifies the transmission enhancements needed to interconnect new clean generation and storage resources and meet the state’s growing electricity demand.

To further the state’s transmission system planning, California ISO prepared a 20-Year Transmission Outlook in May 2022 that builds off the synchronized annual transmission planning process to ensure that transmission investments fully align with anticipated clean energy development – procurement, permitting, and interconnection -- that are essential to achieving California’s long-term energy and climate goals.  The California ISO is leading a public process to update the 20-Year Transmission Outlook.

Transmission Project Development Overview

California ISO’s annual Transmission Planning Process (TPP) develops a comprehensive plan designed to assess the need for new transmission based on reliability, economic, and policy considerations, as required by the Federal Energy Regulatory Commission. The process considers non-wire alternatives such as energy storage resources, and the use of grid enhancing technologies. The annual transmission plan identifies the transmission facilities needed to strengthen and build out the transmission system, including new transmission lines, upgrades to existing lines, and new substations. The annual transmission plan is approved by the California ISO’s Board of Governors.

Following approval through the TPP process, some projects will be developed by a utility or an independent private developer through a competitive solicitation process. Other projects will be directly assigned to the incumbent utility or transmission owner. California ISO’s annual transmission plan includes only the functional requirements of transmission projects, such as the end points and capacity requirements, but it does not include detailed routing or engineering information.

Outside of the TPP, utilities and independent transmission owners pursue repair and replacement projects to maintain their transmission assets. These projects repair existing or replace aging transmission infrastructure with similar or upgraded materials or equipment, to ensure a reliable and safe electricity system. Some projects approved by California ISO in the annual transmission plan and some repair and replacement projects may require approval by the CPUC to construct, depending on the magnitude and complexity of the project. CPUC tracks transmission repair and replacement projects to projects approved in the California ISO transmission plan, regardless of the regulatory authorization process.

Projects approved through California ISO’s annual transmission plan entail limited and preliminary designs, including functional requirements such as transmission endpoints and capacity needs. Once a project is approved as part of the transmission plan, the transmission owner embarks on more detailed project design and engineering including the physical route and alternatives, environmental impact assessments, schedule, and cost estimates.

For transmission owner repair and replacement projects, the transmission owner is responsible for the design and engineering process, without California ISO approval.

The CPUC’s General Order 131-D determines conditions under which CPUC approval is required, depending on whether the project concerns new or existing infrastructure and other technical criteria.


Siting, Transmission, and Environmental Protection Division