ERCOT's Ancillary Services Market Is Sized by Forecast Error, Not Load

ERCOT's battery fleet grew nearly 80% to over 17 GW and 31,500 MWh, yet the volume of ancillary services procured stayed roughly flat and their cost to consumers fell 60% to $0.39 per MWh. Because requirements are sized by historical net load forecast error rather than grid size, ancillary services' share of battery revenue dropped from 97% to 28%.

• ERCOT battery fleet grew nearly 80% to 17 GW and 31,500 MWh
• Ancillary service cost fell 60% to $0.39 per MWh
• Ancillary services' share of battery revenue dropped from 97% to 28%
• Independent Market Monitor: ERCOT buys more than double the reserves reliability requires