CAISO continues to see growth in renewables, particularly in its solar and battery fleets, but the effects of renewable expansion to the CAISO grid have been muted this spring compared to last year, and especially so during the month of May.  Real-time prices rose from April to May at both the NP15 and SP15 hubs, while the latter moved up $5.08 month-on-month and averaged more than $13 higher this May than in May of 2024 at $22.19 for the month.  Oversupply issues were not as pronounced; only 18% of hour intervals during May had a price below $0 at SP15, down from a full third of hours in April and a whopping 38% of hours in May of last year.  Only 40% of solar potential generation occurred during these negatively priced intervals this past month, compared to 79% the prior year and 75% this past April.  This resulted in more of CAISO’s solar generation making its way onto the grid.  Solar curtailments dropped from 675.8 GWh this April to just 371.8 GWh in May (compared to 625 GWh in May 2024).  Wind curtailments were impacted as well, dropping to just 45 GWh this past month from 143 GWh and 161 GWh in April 2025 and May 2024, respectively. 

Figure 1. California Daily Average Temperature and Difference from Normal (F)