The renewable curtailment narrative has been present within California over the years as the growth of behind-the-meter and utility-scaled solar capacity has been noted and Mother Nature is working on her third consecutive good Water Year.  This led to the CAISO real-time auction prices moving into negative territory starting in February 2025, which is the first indicator that the system is over-supplied in a region.  That region happens to be Southern California, or better known as SP15, as S to N congestion is a common theme along the Path 15 transmission corridor during the middle of the day.  The month of May (2025) has alleviated the constraint a bit as Mother Nature delivered two sprint-like warm weather periods with the first tapping the market prior to Memorial Day weekend and the second rounding out the month.

Figure 1 | CAISO Peak Load Summary – Daily Actuals and Forecast

The graph above illustrates the current weather event through the lens of CAISO peak load numbers where the chart on the left represents the grid with May 30^th tapping 36.0 GW in for the forecast while the actuals came in slightly lower.  Saturday, May 31^st, is showing the highest weekend peak demand for the month and it was reflected in the day-ahead auction results as both NP15 and SP15 cleared within $1.05 of each other across the heavy load block while the light load pushed upward as the increased demand played out across all hours and the solar volume is non-existent.