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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