Pollution from coal-fired power plants is significantly reducing the output of solar panels around the world, according to new research that reveals a hidden cost of running fossil fuel and renewable energy systems side by side.
The study, led by the University of Oxford and University College London, mapped more than 140,000 solar installations worldwide using satellite data and combined this with atmospheric measurements to calculate how much electricity is being lost to air pollution.
It was found that in 2023, aerosols reduced global solar electricity output by 5.8%, equivalent to 111 terawatt-hours of lost energy. That’s roughly the same amount of electricity generated by 18 medium-sized coal-fired power plants.
The scale of the loss becomes even more significant when set against the pace of solar expansion. Between 2017 and 2023, new solar installations added an average of around 247 terawatt-hours of electricity per year, but aerosol-related losses from existing systems swallowed up the equivalent of nearly a third of those gains annually, a drain on clean energy that has largely gone unrecognised.
Lead author Dr Rui Song said: ‘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.
‘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.’
Coal-fired power generation emerged as a major source of these losses. The effect is most pronounced in China, where solar and coal capacity have expanded in parallel and are frequently located in the same regions.
China is the world’s largest solar producer, generating more than 40% of global solar electricity in 2023, but it also suffered the largest aerosol-related losses, with total solar output reduced by 7.7%. The researchers estimate that around 29% of those stem specifically from coal plants, whose emissions scatter and absorb sunlight before it can reach nearby panels.
That said, there is cause for cautious optimism regards Chinese. Aerosol-related solar losses in the country declined steadily between 2013 and 2023, likely due to stricter emissions standards and the adoption of cleaner technologies within coal plants, despite the fact the fact that coal capacity itself was not reduced.
Co-author Dr Chenchen Huang (University of Bath) said: ‘Our findings send a clear warning to the Sustainable Development Goals: overlooking pollution-induced solar energy losses can lead to a systematic overestimation of renewable energy output by governments, businesses and the broader community. To stay on track, policies must account for this hidden drag and shift fossil-fuel subsidies away from coal.’
The full research can be read here.
Photo: Wim van ‘t Einde