Do solar plants require backup from fossil fuels?
No.
Solar plants require backup, but it doesn’t have to be from fossil fuels.
A combination of renewables, energy storage, and long-distance transmission can reliably power the majority of the U.S. without relying on coal, oil, or natural gas, as one 2017 research paper describes. Renewables like wind can generate under cloudy conditions, while surplus solar from brighter weather can be stored in utility-scale batteries for rainy days. Additionally, transmission from neighboring regions can assist solar capacity drops.
The Department of Energy and Princeton have outlined decarbonization scenarios projecting expansion of solar and decrease in fossil fuels while maintaining reliability. Analysis of real-world outcomes has found that renewables growth has actually outperformed projections.
California is an example of improving reliability while transitioning from fossil fuels to solar. From 2015 to 2025, in-state generation saw a jump in solar reliance from 8% to 27%, while natural gas dropped from 60% to 36%.
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This Fact Brief was written by Sue Bin Park and originally published by our Gigafact partner, Skeptical Science. See a full discussion of this at Skeptical Science.
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Fact Briefs are bite-sized, well-sourced explanations that offer clear "yes" or "no" answers to questions, confusions, and unsupported claims circulating online. They rely on publicly available data and documents, often from the original source. Fact Briefs are written and published by newsrooms in the Gigafact network. Each brief is limited to 150 words or fewer and is not intended to provide an in-depth analysis, but rather to deliver concise, definitive answers grounded in verified information.
Sources
- The Electricity Journal Reliably integrating variable renewables: Moving grid flexibility resources from models to results
- The Alliance for Climate Transition Institute Solar energy requires 100% fossil fuel backup
- Princeton University Net-Zero America
- University of Virginia Decarbonization by 2050: Are We on Track?
- California Energy Commission CA Electric Generation 2001-25
- California Energy Commission California Energy Leaders Report Progress on Grid Reliability Ahead of Summer 2026
- MIT The Future of Energy Storage
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