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Energy oversupply - managing a greener grid

How western EIM works video

​Managing oversupply

The California ISO is working to implement the state's renewable energy objectives, and supports California's leadership in a worldwide movement to decarbonize the electric sector. The ISO stands ready to integrate additional renewable energy resources onto the grid, while maintaining safety, cost effectiveness and reliability.

​Oversupply and curtailments


The shift to a clean, efficient and modern grid is essential to California's economy and its environment. This transition to a low-carbon grid provides challenges and opportunities, as the state incorporates increasing amounts of renewable energy on to the electric system. Sometimes, during the middle of the day, California's renewable resources can generate more electricity than is needed.

During these periods of surplus energy, the ISO's market automatically reduces the production of energy from renewable resources, or “curtail" generation. In rare instances, when economic bids from generators are insufficient, ISO operators manually curtail production to maintain the balance between supply and demand.

While curtailment is an acceptable operational tool, as increasing amounts of renewable resources, oversupply conditions are expected to occur more often. The ISO is seeking solutions to avoid or reduce the amount of curtailment of renewable power to maximize the use of clean energy sources.

Wind and solar curtailment totals by month



Wind and solar curtailment by day

  • May 2024
  • April 2024
  • Daily wind and solar curtailment reports 2024
  • Daily wind and solar curtailment reports 2023
  • Daily wind and solar curtailment reports 2022
  • Daily wind and solar curtailment reports 2021
  • Daily wind and solar curtailment reports 2020
  • Daily wind and solar curtailment reports 2019

Production and curtailment data


There are several promising concepts and technologies being explored to minimize oversupply and curtailment including:

Today's Outlook

Curtailment Fast Facts

Renewables Watch

Managing oversupply - solutions

Monthly renewables performance reports

Flexible Resources Help Renewables - Fast Facts