As Grids Reach 100% Renewable at Peak, Growing Curtailment of 8 Gigawatts Looms as a Challenge to Decarbonization

Abstract

In April 2022, the California Independent System Operator (CAISO) power grid reached momentary peaks of 100% renewable energy for the first time. After a year, momentary 100% supply from renewables isn't a news any more, and CAISO reported record wind and solar renewable curtailment of 606 GWh (March 2023) and 686 GWh (April 2023). In addition, peak renewable coincided with curtailment rates of 8 GW in April 2023. Our prior studies documented monthly-peak renewable curtailment growth of 40% annually (23 GWh in March 2015 growing to 82 GWh in March 2017). Updating for 2018-2023 shows that 40% annual growth has continued through April 2023 and with it, CAISO has reached an average sunlight hours curtailment rate of 2 GW. If this 9-year trend continues unchecked for the next 5 years, monthly curtailment is projected to reach 3.3 TWh in both March and April of 2028, an average sunlight curtailment rate of nearly 11 GW. We analyze causes of increased curtailment, and discuss its likely future trajectory (growth). We also discuss the challenges its growth represents for grid decarbonization. Finally we outline the difficulties in reducing curtailment growth and highlight several new opportunities for power grids and computing systems.