Grid-scale batteries in CAISO earned $2.25/kW-month in September 2026, down 12% from September 2025's $2.54/kW and 13% below August's $2.59/kW.

In a relatively cool September, 13% of the month’s revenue was earned during a price spike on 9 September, when demand rose to 50 GW and the fleet earned $300/MW-day.

The National Weather Service put most of Los Angeles County under an extreme heat warning for 9 and 10 September, and CAISO declared Restricted Maintenance Operations for Southern California on 9 September and for the whole grid on 10 September. Demand on the day ran 2.6 GW above the day-ahead forecast.

The same temperatures produced far lower prices on 10 September. Demand peaked at 47.4 GW, within 260 MW of the day-ahead forecast, and real time settled below day-ahead through the evening, with northern real-time prices well above southern ones.

Read last month's report here.

Key takeaways

• CAISO battery revenues fell 12% year-over-year to $2.25/kW-month, and sat 13% below August.
• 9 September delivered $300.15/MW, 13% of the month. Without it, the index would have read $1.95/kW-month.
• Real-time TB4 spreads rose 11% to $3.88/kW-month and day-ahead spreads 5% to $3.58/kW-month.
• Wind rose 62% and gas generation fell 23%, while average demand held flat at 27.8GW.
• Ancillary services rose 50% to $0.38/kW-month, while fifteen-minute energy revenue turned negative at -$0.22/kW-month.

TB4 is the spread between the four highest and four lowest hourly prices in a day, reported here as a monthly total in $/kW-month so it compares directly with revenue. IFM is the Integrated Forward Market (day-ahead), FMM the Fifteen-Minute Market, and RTD Real-Time Dispatch (five-minute).

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

Real-time TB4 spreads rose 11% while day-ahead rose 5%

Real-time TB4 spreads at the CAISO system hub reached $3.88/kW-month in September 2026, up 11% from $3.50/kW-month a year earlier. Day-ahead spreads rose 5% on the same basis, from $3.41/kW-month to $3.58/kW-month.

But the average peak held flat at 34.4GW, and gas generation fell 23%. Both these should have deterred spreads.