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California fuel mix changes in response to September heat wave

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September 21, 2022

California electricity supply by source



Data source: California Independent System Operator


An extreme heat wave affected California the week of September 4, 2022, driving record-breaking demand for electricity to meet increased air-conditioning use. On September 6, a new record was set in the California Independent System Operator’s (CAISO) territory.

CAISO, the grid operator for most of the state, issued appeals for consumer energy conservation throughout the week, as well as Energy Emergency Alerts each day, to help reduce electricity demand and prevent rolling power outages. CAISO predominately used natural gas, electricity imports, and hydroelectric sources during the highest demand hours to meet the record-breaking demand, which was a change from the typical mix.

For brief periods during the week of September 4, CAISO used natural gas for as much as 60%—and never less than 30%—of the generation mix to meet electricity demand. California typically uses a mix of solar, wind, imports, hydroelectric, and natural gas sources for electricity generation. The exact mix depends on the time of day, the availability of sources, and the price that power plants set to sell electricity to the grid.

This year, up to the record-setting demand week in September, CAISO’s generation mix included:

  • 40% from solar, wind, nuclear, batteries, and other sources
  • 32% from natural gas
  • 20% from imports
  • 7% from hydroelectric

The mix relies slightly more on natural gas during the evening hours from 6:00 p.m. to 9:00 p.m., when electricity demand peaks and solar generation wanes. During the week of September 4, 2022, however, natural gas contributed nearly one-half of the resource mix in CAISO; nuclear, solar, wind, batteries, and other resources decreased to a 24% share. In California, natural gas units are often the last resource turned on to meet demand because they can be turned on after the sun sets in the evening when cooling demand remains high. When demand reaches record highs, seldom-used (less efficient, more expensive) natural gas units are needed to meet demand.

CAISO's electricity generation mix so far...



Data source: California Independent System Operator


Principal contributor: M. Tyson Brown

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