​27 battery assets across 17 sites began commercial operations in CAISO in the first half of 2026, adding nearly 1.6 GW of grid-scale BESS capacity to the market. Energy capacity additions totaled 4.2 GWh, bringing total installed storage to 64 GWh.

Battery buildout has slowed in California. Additions in the first six months of 2026 ran 35% lower than H1 2025, the slowest half-year since 2023.

Key takeaways

• 18.9GW of utility-scale batteries are operating in CAISO as of June 30, 2026, across 150 sites and 64.3GWh of energy capacity.
• Additions slowed to 1.6 GW, 35% below H1 2025. Three sites delivered 58% of the half's capacity.
• SP15 took 1,337MW, or 85% of new capacity, and now holds 14.9GW.
• Co-located projects supplied 61% of additions, reversing the standalone concentration of late 2025. Standalone still holds 53% of installed capacity.
• California's first 8-hour battery reached full capacity in June, when REV Renewables completed the 125MW | 1000MWh Tumbleweed expansion in Kern County.

Throughout this report, "hybrid" refers to battery assets that share a DC-coupled connection to the grid with another generation source. "Co-located" BESS share a physical site with another generation asset but are registered as independently metered resources.

If you have any questions about our CAISO research, please reach out to ovais@modoenergy.com.

17 sites added 1.6 GW in the first half of 2026

27 assets across 17 sites reached commercial operations in the first half of the year. 16 were new sites; one was an augmentation of an existing site.

The largest was Intersect Power's solar-colocated Easley (350MW | 1400MWh) in Riverside County, commissioned on June 4.