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Energy oversupply - managing a greener grid

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​Managing oversupply

The California ISO is working to implement the state's 50-percent renewable energy objective, which was specified in Senate Bill 350 of 2015. The ISO supports California's leadership in a worldwide movement to decarbonize the electric sector and 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 can be consumed by customer demand.

During these periods of surplus energy, the ISO's market will automatically reduce the production of energy from renewable resources, ensuring that supply and demand remain in balance. This is often called “curtailment.” In rare instances, when economic bids from generators are insufficient, ISO operators manually curtail production to maintain the important balance between supply and demand.

Curtailment is an operational tool that works well in today's energy market. But as the state introduces 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 sources thus enabling the state to maximize the use of clean energy sources.

Curtailment totals by month

Figures for 2018 updated on 10/9/2018


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

Wind and solar daily curtailment report

Curtailment Fast Facts

Renewables Watch

Managing oversupply - solutions

Monthly renewables performance reports

Flexible Resources Help Renewables - Fast Facts

Today's Outlook