How a battery earns in California (CAISO)

California runs an energy-only wholesale market under the CAISO ISO — there is no centralized capacity auction; instead the CPUC's Resource Adequacy program and SB 100 (100% clean electricity by 2045) shape investment. A battery lives off California's famous duck curve: a solar fleet so large that in the first five months of 2026 solar out-generated natural gas pushed midday day-ahead prices toward zero or negative, then a steep evening ramp lifts them again. Over the last 30 days the SP15 hub showed a day-ahead spread of about $21/MWh — roughly 105% of the average price — the raw material for charge-low, discharge-high arbitrage. That signal, plus the federal 30% investment tax credit for standalone storage and the state SGIP rebate, has driven the CAISO battery fleet past 15 GW, with a ~101 GW interconnection queue behind it.

$21/MWh

SP15 day-ahead spread — ~105% of the average price (30-day arbitrage window)

~15GW

CAISO utility-scale battery fleet — after a record 4.7 GW added in 2025 (Modo Energy)

>50%

Solar out-generated natural gas in CAISO over Jan–May 2026 — the duck curve driving daily price swings (EIA)