CAISO Approves $6.7 Billion Transmission Plan to Meet California Load Growth and Clean Energy Targets

The Board of Governors of the California Independent System Operator (CAISO) has approved the organization’s 2025-2026 Transmission Plan, advancing 38 infrastructure projects designed to support rising electricity demand, integrate new renewable energy resources and maintain grid reliability across California.

The approved portfolio carries an estimated cost of $6.7 billion over the next decade, down from an initial $7 billion estimate released in April after updated cost assumptions from transmission owners reduced projected expenses.

According to CAISO, more than half of the projects — and more than half of the total investment — are tied directly to forecasted load growth driven by transportation electrification, building electrification, manufacturing expansion and the rapid growth of large energy-intensive facilities such as data centers.

“We are constantly striving to find ways to meet system needs in the most affordable way possible,” said Neil Millar, CAISO vice president of transmission planning and infrastructure development. “This year’s plan does that in a number of different ways while also making sure we have the right infrastructure in place to accommodate all of the new resources that are being added to the system.”

Reconductoring and Grid-Enhancing Technologies Featured

The transmission plan emphasizes the use of existing infrastructure where possible, including 12 reconductoring projects aimed at increasing transmission capacity without constructing entirely new lines. Three of those projects will deploy advanced conductors as part of a broader suite of grid-enhancing technologies (GETs) that CAISO is incorporating into its planning process.

The ISO also approved a significant shift in the Los Angeles Basin. The previously approved Serrano-Del Amo-Mesa 500-kV Transmission Reinforcement project, first authorized during the 2022-2023 planning cycle, has now been canceled following updated cost information from transmission owners.

Instead, CAISO plans to address reliability needs in the region through a combination of smaller, lower-cost upgrades and expanded deployment of battery energy storage resources in key grid locations.

Path 15 Congestion Drives New 500-kV Recommendation

A major focus of the 2025-2026 plan is transmission congestion management. CAISO said ongoing production-cost modeling identified the need for a new 500-kV transmission line along the Path 15 corridor, one of California’s primary north-south transmission pathways.

The proposed upgrade is intended to reduce congestion costs that can force grid operators to dispatch more expensive generation when transmission bottlenecks limit access to lower-cost power resources. The project would also support renewable energy development in the Westlands region spanning Fresno and Kings counties.

CAISO noted that the recommended Path 15 solution still requires additional engineering analysis and will be further refined during the next transmission planning cycle before receiving final approval.

Plan Supports Major Renewable Energy Buildout

The transmission expansion strategy is based on projections from the California Energy Commission showing statewide electric load increasing by 15 GW by 2035 and 20 GW by 2040. At the same time, resource portfolios provided by the California Public Utilities Commission indicate installed generation capacity will need to grow by more than 74 GW by 2035 and 107 GW by 2040.

CAISO said the plan will support the integration of a broad range of renewable and storage resources identified in the CPUC’s Integrated Resource Plan, including:

• 45 GW of solar generation across the Central Valley, Tehachapi, San Bernardino County, Riverside County, southern Nevada and western Arizona;
• 8 GW of in-state wind generation in the Tehachapi region;
• More than 2 GW of geothermal resources, primarily in the Imperial Valley and southern Nevada;
• Battery energy storage projects both co-located with renewable generation and installed near major load centers;
• More than 10 GW of imported wind generation from Idaho, Wyoming and New Mexico using new and existing interstate transmission corridors; and
• More than 4.5 GW of offshore wind generation, including projects planned near Morro Bay and Humboldt County.

Bay Area and Regional Reliability Projects Included

Among the major transmission upgrades identified in the plan are several projects tied to accelerating load growth in the Greater Bay Area, including the Tesla–Trimble–Metcalf 230-kV corridor expansion intended to strengthen supply to the southern Bay region.

Other key projects include the Trout Canyon–Lugo 500-kV line to improve access to renewable resources in the East of Pisgah area, short-circuit duty upgrades at multiple substations, and additional upgrades aimed at reducing congestion along Path 15.

CAISO said the approved projects, combined with transmission investments from prior planning cycles, are intended to ensure the grid can reliably support California’s long-term decarbonization and electrification goals while maintaining affordable electric service.