• Electricity generation from RPS-eligible renewable sources and large hydroelectric made up 45.3 percent of the power mix in 2020, a slight decrease from 2019’s 46.3 percent. The decrease in generation from hydroelectric was mostly made up by generation from natural gas. When California is in a drought, hydroelectric’s shortfall has been replaced by natural generation before: the same trend was observed in 2012 to 2015, when California was in a previous drought.
  • The imminent decommissioning of the Diablo Canyon nuclear power plant84 may add further strain to the grid, though recent procurement commitments from the CPUC could go a long way in addressing this challenge. While a February 2021 Union of Concerned Scientists study85 found that at current trajectory, the retirement of Diablo would be replaced with energy from existing natural gas power plants—leading to higher GHG and air pollution emissions—a June 2021 CPUC decision aims to avoid this by requiring clean energy to replace Diablo. The CPUC procurement order called for at least 2,500 MW of zero-emitting energy resources to replace the retiring 2,200 MW Diablo Canyon power plant.86 To avoid that, the state must procure a diverse mix of resources and technology such as battery storage, pumped storage and demand response.

84 Diablo is the last nuclear power plant in California, which currently provides around 8 percent of the in-state generation or 6 percent of the power mix.

85 Specht, M. Countdown to Shutdown: California’s Clean Energy Future after Diablo Canyon. Union of Concerned Scientists. February 23, 2021. Retrieved from:

86 California Public Utilities Commission. Decision Requiring Procurement to Address Mid-Term Reliability (2023-2026. Source: