CAISO May 2026: Battery revenues settle at $2.78/kW
Grid-scale batteries in CAISO earned $2.78/kW-month in May 2026. That is level with April's $2.77/kW, but $1.10/kW below May 2025's $3.88/kW, a 28.4% year-over-year decline.
What did CAISO batteries earn as TB4 spreads compressed in May?
Modo Energy's Benchmarks measure realised BESS revenue in CAISO and attribute it by service and strategy, from energy arbitrage to ancillary services.
Explore the CAISO benchmark →The fleet has now held a $2-3/kW spring base for three straight months.
Average daily highs reached 73.9°F against 75.4°F a year earlier, and average lows held at 49.2°F versus 49.4°F. With temperatures essentially flat, price compression came from the supply side.
Solar generation fell 3.9% year-over-year while wind rose 33.1%. The increase in wind tracks SunZia, the 3.5GW New Mexico project that reached commercial operation in May 2026. This step up led to a surplus of supply in the evening that flattened the discharge window batteries depend on.
​The month also opened with the Extended Day-Ahead Market going live on May 1, bringing PacifiCorp's two balancing authority areas and roughly 12 GW of generation into CAISO’s day-ahead optimization.
Read last month's report here.
Daily TB4 spreads compressed across the entire month
Daily average TB4 fell from $165/MW to $119/MW year-over-year. The strongest day of May 2026 was May 11 at $174/MW, which would have ranked as an average day in May 2025. The weakest day, May 26, posted just $82/MW.
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