Curtailments of solar-powered electricity generation have increased in the California Independent System Operator (CAISO) region. In 2020, CAISO curtailed 1.5 million MWh of utility-scale solar, or 5% of the state’s utility-scale solar production, according to the U.S. Energy Information Administration.
Grid operators curtail electricity production from solar and wind generators when supply exceeds demand. In 2020, solar curtailments accounted for 94% of the total energy curtailed in CAISO. Solar curtailments tend to be greater in the spring months when electricity demand is relatively low (because of moderate temperatures decreasing heating and cooling demand) and solar output is relatively high. In the early afternoon hours of March 2021, CAISO curtailed an average of 15% of its utility-scale solar output.
Increases in renewable generation and curtailments of solar and wind have followed an increase in new renewable capacity additions. To help meet California’s target of 50% renewable generation by 2025, CAISO plans to add another 1.6 GW of utility-scale solar capacity and 0.4 GW of onshore wind turbine capacity in 2021. Combined, these two technologies represent 44% of CAISO’s total capacity additions in 2021.
Small-scale solar capacity has also continued to grow. Customer-sited solar generation decreases the need for CAISO-operated generation, leading to more solar curtailments.
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