Several news stories have asserted that California has a “glut” of solar power that is being wasted and sold at a loss to other states. The problem is that the stories mischaracterize the situation, both in cause and magnitude.

The Diablo Canyon nuclear power units were scheduled to be retired in 2024 and 2025 due to having reached the end of their license and concerns around public safety from the aging plant. As a result, state energy regulators launched an aggressive renewable energy and battery storage procurement process in 2018 following the decision to close Diablo Canyon. Those added resources are now coming online to offset the anticipated loss of energy output from Diablo Canyon’s closure.

However, despite those additional renewable resources, the state legislature and Governor Newsom then extended the life of Diablo Canyon in 2022 to 2030. Diablo Canyon’s 2,200 megawatts of around-the-clock energy production – which adds up to 18 million megawatt hours a year – is the true source of grid management issues, particularly during the spring when the majority of energy curtailments occur.

This imbalance is exacerbated by the large swings in the state’s hydropower production, from 17 million megawatt hours during a dry 2022 to 30 million megawatt hours in a wet 2023. These swings are inherent in California’s power system, and related curtailments were common for decades before solar was on the scene. In other words, California will always need to have excess energy in wet years if it wants sufficient power in the other two-thirds of the years that are average or dry. Diablo Canyon’s year-round, around the clock output only makes that glut worse.

Not only is Diablo Canyon’s extension clogging up transmission lines and driving curtailment, it is also a high cost energy resource. PG&E initially claimed the Diablo Canyon power would cost about 5.5 cent per kilowatt hour, which is near the average cost of the California Independent System Operator’s (CAISO) energy purchases. Instead, PG&E is asking the California Public Utilities Commission to charge more than 9 cents per kilowatt hour, nearly double the cost of the average energy purchase.

Instead of blaming and halting California’s clean energy progress, an easier solution that would solve most of the curtailment issue would be to shut down Diablo Canyon from March to May, when energy demand is lowest in the state. This is when loads are lowest and hydro output the highest. Reducing at least some of Diablo Canyon’s 18 million megawatt hours per year, would more than offset the 3.2 million megawatt hours of solar energy that were curtailed in 2024. Diablo Canyon would still be available to meet summertime peaks. That would save ratepayers money and reduce the need to sell excess generation at a loss. 

California is already addressing other causes of curtailments by installing more storage capacity. It would be foolish to reduce solar generation now when we will need it in the near future to match the additional storage capacity.