The California Independent System Operator (CAISO) Board of Governors approved the organization's 2025-2026 Transmission Plan this week, recommending 38 infrastructure projects at an estimated total cost of $6.7 billion at full buildout over the next decade. The plan had originally carried a $7 billion price tag in April draft estimates; updated assumptions from transmission owners reduced that figure before final approval.
More than half of the projects, and more than half of the total cost, are tied to forecasted load growth. The California Energy Commission (CEC) projects California's electricity demand will increase by 15 gigawatts (GW) by 2035 and 20 GW by 2040, driven by building and transportation electrification, manufacturing expansion, and large loads including data centers.
The approved plan includes 12 reconductoring projects that increase transmission capacity without requiring new transmission corridors to be built from scratch. Three of those will use advanced conductors, which the ISO classifies among its suite of grid-enhancing technologies (GETs). The plan also identifies the need for a new 500-kilovolt (kV) line to relieve congestion along the Path 15 corridor, a major north-south transmission route. That recommendation will require additional engineering before a final decision is made in the next planning cycle.
One previously approved project did not survive the update. The Serrano-Del Amo-Mesa 500 kV Transmission Reinforcement project in the Los Angeles Basin, originally approved in the 2022-2023 planning cycle, was cancelled after updated cost data from transmission owners made it no longer the most cost-effective option. Reliability needs will be addressed instead through smaller upgrades and energy storage development in affected grid areas.
Beyond load, the plan targets transmission access to resource development basins identified by the California Public Utilities Commission (CPUC) in its Integrated Resource Plan. The buildout is intended to accommodate 45 GW of solar development across the Central Valley, Tehachapi, and portions of Nevada and Arizona; 8 GW of in-state wind in Tehachapi; over 2 GW of geothermal primarily in the Imperial Valley; and more than 10 GW of wind imports from Idaho, Wyoming, and New Mexico. Offshore wind access for over 4.5 GW along the Central and North coasts is also included in the scope.
