Draft transmission plan now available; recommends 38 infrastructure upgrades to meet growing electricity demand

FOLSOM, Calif. – To accommodate growing demand for electricity and help meet the state’s clean energy goals, the California Independent System Operator (ISO) has recommended 38 transmission upgrades in its draft 2025-2026 Transmission Plan, with an estimated cost of $7 billion at full buildout over the next decade.

As shown in California Energy Commission forecasts, the increasing demand is driven by building and transportation electrification, manufacturing, and large loads including data centers.

“We recognize the concerns around electricity affordability and are committed in our annual transmission planning process to find ways to meet system needs efficiently and cost-effectively while also providing the best customer value over the long term,” said Neil Millar, the ISO’s Vice President, Transmission Planning and Infrastructure Development.

As part of that commitment, the plan analyzed where reconductoring and other grid-enhancing technologies could be used to increase transmission capacity without having to construct new lines. The draft recommends 12 projects that include reconductoring, three of which are using advanced conductors as the most efficient and cost-effective solution to meeting capacity needs.

The ISO’s transmission planning process also consistently monitors and reports on when and where congestion is expected on the grid and higher priced generation must be dispatched to serve load because of transmission limitations in accessing lower cost generation. The transmission planning process does this by using production cost modeling that takes into account evolving load and generation patterns, and planned transmission system development.

As part of its analysis, the ISO compares the savings in energy costs that would benefit customers by reducing or eliminating the transmission limitation with the cost of building new transmission to relieve that congestion. This helps determine when it is more economical to reinforce the system rather than continue operating with recurring bottlenecks.

The analysis in this year’s plan determined the need for a new extra high-voltage 500 kilovolt line to relieve congestion on the Path 15 corridor, one of the state’s major north-south transmission corridors. However, as the plan explains, the recommended alternative needs additional engineering refinement, which the ISO will conduct in next year’s planning cycle prior to recommending approval of the solution. This upgrade will also support renewable development in the Westlands area in Fresno and Kings counties and southern California.

This year’s transmission plan is based on the state’s projections provided to the ISO in 2025 indicating that California’s load will grow by 15 gigawatts (GW) by 2035 and 20 GW by 2040 while the installed resource capacity will need to increase by more than 74 GW and 107 GW, respectively.

The 2025-2026 plan, which the ISO’s Board of Governors will consider at a virtual Board meeting on May 19, will, together with transmission identified in previous transmission plans, enable the grid to accommodate forecasted load growth and critical resource development identified in the California Public Utilities Commission Integrated Resource Plan, including:

• 45 GW of solar generation in the Westlands area in the Central Valley, Tehachapi, the Kramer area in San Bernardino County, Riverside County, as well as southern Nevada and western Arizona;
• 8 GW of in-state wind generation in Tehachapi;
• Over 2 GW of geothermal development, primarily in the Imperial Valley and in southern Nevada;
• Access for battery storage projects co-located with renewable generation projects across the state, as well as stand-alone storage located closer to major load centers in the LA Basin, greater Bay Area, and San Diego;
• The import of over 10 GW of wind generation from Idaho, Wyoming and New Mexico, largely over out-of-state transmission that is already in development, by enhancing corridors from the ISO border in southeastern Nevada and from western Arizona into California load centers. (The in-development transmission projects include SWIP North and Subscriber Participating Transmission Owner projects); and
• Over 4.5 GW of offshore wind with 2.9 GW in Central Coast Morro Bay and 1.6 GW in the North Coast Humboldt.

Specific transmission upgrades in the current plan, most notably related to load growth in the Greater Bay area, include:

• Greater Bay Area Tesla – Trimble – Metcalf 230 kV Corridor Expansion to supply the south Greater Bay area;
• Trout Canyon – Lugo 500 kV Line to access resources in the East of Pisgah area;
• Short-circuit duty upgrades at a number of stations to accommodate increases in resources in the CPUC portfolio;
• Gates – Los Banos #3 500 kV Line Series Compensation to address congestion on Path 15; and
• A host of smaller upgrades improving supply of load and access to other smaller resource zones.

To read the draft plan, please visit the ISO's 2025-2026 Transmission Planning Process webpage. Please see details to take part in the April 15 public meeting.

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California ISO | 250 Outcropping Way | Folsom, CA 95630 | www.caiso.com

The California Independent System Operator (ISO) is a nonprofit public-benefit corporation dedicated with its partners to continuous improvement and secure operation of a reliable grid operated for the benefit of electricity consumers. 

The ISO provides comprehensive grid planning, open and nondiscriminatory access to one of the largest networks of high-voltage transmission power lines in the world and operates a competitive electricity market that in 2024 included $16.1 billion in transactions. In helping to carry out California’s energy policy objectives, the ISO is at the forefront of integrating renewable power and advanced technologies that will help provide a reliable and sustainable energy future efficiently and cleanly. 

The Western Energy Imbalance Market (WEIM) is a real-time wholesale energy trading market that enables participants throughout the West to buy and sell energy when needed. Since its inception in 2014, it has resulted in more than $7 billion in financial benefits to market participants and their customers and has enhanced reliability across the region by sharing diverse resources and optimizing inter-connected transmission. The Western Energy Markets Governing Body, designed by regional stakeholders, has primary decision-making authority regarding rules specific to participation in the WEIM and Extended Day-Ahead Market.