A new study from the University of Oxford and University College London has found that coal pollution reduces the amount of energy that solar power can generate. 

Coal plants emit aerosols, which are tiny particles of pollutants that float in the air, scattering and absorbing sunlight. This reduces the amount of sunlight that can reach the solar panels, lowering their energy output. In addition to this, these aerosols can also modify clouds, increasing reflectivity, which further reduces sunlight reaching the panels, and therefore further reduces the energy output

In 2023, aerosols reduced total solar generation by 5.8%. This is a loss equivalent to the annual output of 18 medium-size coal plants. From 2017 to 2023, these energy losses were on average one-third of the energy added by new solar plants. The extent of these losses varies depending on the country. While China is the largest generator of solar energy, it had the largest global energy loss with 7.7% lost to aerosols, a result of their reliance on coal for  61% of its electricity generation in 2023.

The results were published in Nature on the 15th May. Over 140,000 solar power facilities were studied, identifying them through analysing satellite imagery. They estimated how much electricity could be produced at each site if there was no pollution or clouds, and then looked at atmospheric data to see how much sunlight reached the panels. Through comparing these values, they calculated how much energy was lost. 

Solar energy is extremely important in the renewable energy transition, with solar energy accounting for nearly 80% of all new renewable electricity capacity growth globally and capacity set to more than double between 2025 and 2030 compared to the 2019 to 2024 period. This is due to lower costs and efficiency increases. This research highlights the importance of continuing the phase-out of coal power plants- showing that when positioned close to solar panels, they could significantly reduce their contributions to renewable energy generation. 

Lead author Dr Rui Song (Department of Physics, University of Oxford, and Mullard Space Science Laboratory, UCL) highlights the implications of this pollution on emission reduction data, saying in a press release statement that this “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”. 

These findings provide further evidence for the need for pollution-control measures such as retrofitting coal power plants, a policy which has resulted in losses declining 1.4% per year since 2017 in China, alongside accelerating the coal phase out pledged by 46 countries in COP26. Whilst coal’s share in the energy mix decreases, in real terms coal power generation continues to grow, with an increase of 1.2% in 2024. It remains the largest source of power generation, which emphasises the importance of sustaining pressure on their phase-out.

Corresponding author Professor Jan-Petter (Mullard Space Science Laboratory at UCL)  said that in the future this approach can be used to “observe the impacts of dust and smoke particles on reducing solar energy at the Earth’s surface in real-time every 10 minutes”. This increased frequency is significant as it would lead to more accurate estimations of solar energy as well as helping us to position solar farms where pollution is less likely to affect them. 
Read their full findings here: www.nature.com/articles/s41893-026-01836-5