Solar power is on the rise around the world as the cost of solar panels goes down and societal acceptance of the technology rises. The world added record-breaking solar power installations in 2025, and capacity is expected to more than double in the next five years, according to the International Energy Agency.
But there’s one inescapable issue darkening the skies for the transition to clean solar energy: dirty coal plants. Researchers in the UK have found that pollution from coal is significantly reducing the amount of power we could be getting from solar panels.
From 2017 to 2023, annual solar energy losses “from existing systems were, on average, equivalent to one-third of the energy added by new PV installations,” the researchers write in a paper published in the journal Nature Sustainability.
When power plant furnaces burn coal, it releases not just carbon dioxide but also sulfur dioxide. This gas reacts with other molecules to become small particles called sulfates. Called aerosols, these tiny particles get suspended in the air and reflect sunlight.
For their new study, the researchers used satellite data to map and assess more than 140,000 solar installations worldwide. They combined this data with air pollution data to calculate how much sunlight dims and how this reduces electricity generation. The researchers traced the origins of the aerosols and found that they came mainly from coal-fired power plants.
They found that in 2023 aerosols reduced global solar electricity output by 5.8%, or 111 terawatt-hours of energy; that is equal to the amount generated by 18 medium-sized coal-fired power plants. The losses were highest in China, where solar and coal are expanding and are often located close to each other. China had the largest aerosol-related solar energy losses worldwide, reducing national solar power generation by 7.7% in 2023.
The phase-out of coal power around the world has been slow, the researchers write, and this study presents yet another way that coal could interfere with the world’s clean-energy transition. “Looking forward, the physical interaction between coal-based aerosols and solar PV performance is likely to become an increasingly critical constraint on the global energy transition,” they say.
Source: Rui Song et al. Coal plants persist as a large barrier to the global solar energy transition. Nature Sustainability, 2026.
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