New research led by the University of Oxford and University College London (UCL) has revealed that pollution from coal-fired power plants is significantly reducing the energy output of solar photovoltaic (PV) installations, particularly where these are expanding side by side.
The new study mapped and assessed more than 140,000 solar PV installations worldwide using satellite data. By combining this with atmospheric data on air pollution, the researchers calculated how much sunlight is lost and how this reduces electricity generation. They found that aerosols—tiny particles suspended in the air—reduced global solar electricity output by 5.8% in 2023. This is equivalent to 111TWh of lost energy—the amount generated by 18 medium-sized coal-fired power plants.
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Crucially, these losses represent a significant and often overlooked constraint on the clean energy transition. Between 2017 and 2023, new PV installations added an average of 246.6TWh of electricity each year, while aerosol-related losses from existing systems reached 74.0TWh annually—equivalent to nearly one-third of the gains from new capacity. This highlights a previously unrecognised interaction between fossil fuel use and renewable energy, where emissions from one system directly reduce the performance of the other.
“We are seeing rapid global expansion of renewable energy, but the effectiveness of that transition is lower than often assumed. As coal and solar expand in parallel, emissions alter the radiation environment, directly undermining the performance of solar generation,” said lead author Dr Rui Song from the Department of Physics at University of Oxford and Mullard Space Science Laboratory at UCL.
To identify the sources of these aerosol-related losses, the researchers traced their origins and found coal-fired power generation to be a major contributor. This effect is particularly evident in China, where solar and coal capacity have expanded in parallel and are often co-located. Regions with high coal capacity aligned closely with areas experiencing the greatest solar PV losses.
China is the world’s largest solar producer, and generated 793.5TWh of solar PV electricity in 2023 (41.5% of the global total). But it also experienced the largest losses from aerosols, with total output reduced by 7.7%. The researchers estimate that around 29% of aerosol-related solar PV losses in China come specifically from coal-fired power plants. Coal plants emit fine pollution particles that scatter and absorb sunlight, reducing the amount that reaches nearby solar panels. As a result, the panels generate less electricity than they otherwise could.
“Air pollution doesn’t just block sunlight—it also changes clouds, which can cut solar power even further. That means the real impact is likely to be bigger than we’ve measured, so we may be overestimating how much solar power can contribute to reducing emissions if we do not get pollution from coal power under control,” Dr Song said.
Interestingly, China was found to be the only major region showing a sustained improvement. Aerosol-related solar PV losses declined by an average of 0.96TWh per year (-1.4% annually) between 2013 and 2023. This is likely due to stricter emission standards and widespread adoption of ultra-low-emission technologies within coal-fired power plants, rather than a reduction in coal capacity itself.
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To carry out the analysis, the researchers combined satellite imagery and machine learning to identify and map more than 140,000 solar installations worldwide. They then integrated these data with atmospheric observations and a validated solar energy model to estimate how much electricity each site generates and how much is lost due to air pollution.
Dr Song has also developed an interactive dashboard that shows where solar installations are located, when they were built, and how much energy they generate under real-world atmospheric conditions.
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