Solar and wind curtailment has increased by 29% between 2023 and 2024 in California, according to the US Energy Information Administration (EIA).
Solar PV accounted for nearly the entirety of the curtailed capacity last year, making 93% of all energy curtailed in the California Independent System Operator (CAISO) territory, which covers most of the US state of California.
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The first quarter of 2025 has continued to see curtailed capacity increase, as shown in the chart below, with March 2025 registering a record 919GWh of solar and wind curtailed that month alone.
The increased curtailment between 2020 and 2025 has been more notable in the first half of the year, while the difference between 2020-2024 in H2 is less pronounced.
According to the US EIA: “CAISO curtailed the most solar in the spring, when solar output was relatively high and electricity demand was relatively low, because moderate spring temperatures meant less demand for space heating or air conditioning.”
Moreover, CAISO also curtails solar PV capacity to leave space for natural gas generation, according to the EIA. This is due to the fact that a certain amount of natural gas must remain online throughout the day to comply with the North American Electric Reliability Corporation (NERC) reliability standards.
As solar PV curtailment keeps rising, year after year, CAISO aims to reduce these curtailments in several ways, including trading with neighbouring balancing authorities; including curtailment reduction in transmission planning; and incorporating battery storage in ancillary services, energy and capacity markets.
As of the first half of May 2025, the CAISO territory had 21GW of installed solar PV capacity. Solar PV currently generates nearly half of CAISO’s electricity demand between daylight hours of 8am and 4pm.
Energy storage systems have often been pointed to as a way to reduce curtailment, and their deployment has grown in California. A recent survey from the California Energy Commission highlighted that the state had nearly 16GW of installed battery storage, as covered by our sister site Energy-storage.news. The state aims to deploy 52GW of energy storage by 2045, 4GW of which will be from long-duration energy storage.
