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Do solar plants require backup from fossil fuels?

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 is responsive to quotes such as this one.

Sources

The Electricity JournalÿReliably integrating variable renewables: Moving grid flexibility resources from models to results

The Alliance for Climate Transition InstituteÿSolar energy requires 100% fossil fuel backup

Princeton UniversityÿNet-Zero America

University of VirginiaÿDecarbonization by 2050: Are We on Track?

California Energy CommissionÿCA Electric Generation 2001-25

California Energy CommissionÿCalifornia Energy Leaders Report Progress on Grid Reliability Ahead of Summer 2026

MITÿThe Future of Energy Storage

Columbia Law School Sabin Center for Climate Change LawÿRebutting 33 False Claims About Solar, Wind, and Electric Vehicles
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About fact briefs published on Gigafact

Fact briefs are short, credibly sourced summaries that offer "yes/no" answers in response to claims found online. They rely on publicly available, often primary source data and documents. Fact briefs are created by contributors to Gigafact - a nonprofit project looking to expand participation in fact-checking and protect the democratic process. See all of our published fact briefs here.

https://skepticalscience.com/fact-brief-solarunrel.html

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