Solar power curtailment continues to increase in California

CAISO solar curtailment

According to the U.S. Energy Information Administration (EIA), curtailments of solar 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 its utility-scale solar production. Solar curtailments in particular accounted for 94% of the total energy curtailed in CAISO.

Why does this happen? Grid operators curtail electricity production from solar and wind generators when supply exceeds demand. Solar curtailments tend to be greater in the spring months when electricity demand is relatively low 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.

Small-scale solar capacity has also continued to grow. These customer-sited solar PV systems decrease the need for CAISO-operated generation, which also leads to more solar curtailments.

Are there other solutions? EIA says CAISO has been exploring other options:

  • CAISO’s Energy Imbalance Market (EIM): CAISO’s EIM is a real-time market that allows participants outside of CAISO to buy and sell energy to balance demand and supply. In 2020, 16% of total possible curtailments were avoided by trade within the EIM, according to reports produced by the EIM operators.
  • Battery storage: CAISO is expecting to add 2.5 GW of battery storage capacity in 2021. Renewable generators can charge these batteries with electricity that would otherwise have been curtailed.
  • Other energy storage options: Hydrogen production and hydrogen-based energy storage could also help reduce solar curtailments.
  • Increasing demand response, which would adjust consumer demand when warranted
  • Encouraging time-of-use rates, which better match consumer prices with real-time energy prices
  • Reducing minimum generation levels for existing generators, which would allow greater opportunity for renewable energy production
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