Pollution from coal-fired power plants can significantly limit the energy output from solar installations, particularly in areas where plants are located nearby, according to new research.
A UK-based research team led by the University of Oxford and University College London used satellite data to map over 140,000 solar installations worldwide, combining their dataset with atmospheric data on air pollution to calculate aerosol-induced losses from solar plants.
The team found aerosols reduced global solar electricity output by 5.8% in 2023, equivalent to 111 TWh of lost energy.
For the same year, the team calculated the average PV energy loss of potential output under optimal conditions at 26.9%, with the remaining 21.1% coming from clouds. “While clouds are the dominant source of atmospheric reduction in insolation, aerosols have a disproportionate impact in densely populated, industrialized regions where PV deployment is concentrated,” the research paper explains.
The researchers also calculated that, between 2017 to 2023, aerosol-related losses from existing PV systems reached 74.0 TWh, while capacity gains from new solar installations stood at an average of 246.6 TWh annually.
In order to compare quantities across regions and years, the team used a loss-to-growth ratio, a calculation of the annual aerosol-induced energy loss from existing systems divided by the annual energy generations from new PV capacity, which averaged 30% during the study period.
“Aerosol-induced losses from the existing PV fleet are equivalent to nearly one-third of the annual energy generated by new PV installations globally, representing a magnitude not previously quantified and unexpectedly high,” the research paper says.
Rui Song, an academic based at the University of Oxford and corresponding author of the paper, told pv magazine one of the most important findings was that coal and solar are increasingly expanding side by side in some regions and are often co-located.
“Emissions from coal-fired power plants directly reduce the amount of sunlight reaching nearby solar panels, creating a previously under-quantified drag on solar energy generation,” he explained.
Aerosol-induced losses are highest in China, the research found, which the research paper attributes to persistent pollution and dense PV deployment. Losses caused by aerosols in China amounted to 61.3 TWh in 2023, equivalent to 54.9% of the global total and exceeding all other countries combined, reducing national PV generation by 7.7%.
For comparison the USA, which is home to limited co-location of solar and coal plants, experienced 3.1% aerosol-induced PV loss.
Despite recording the most total aerosol-induced losses, China was found to be the only major PV-producing region with evidence of a sustained decline in such losses over the study period.
Figures in the paper highlight losses falling by 0.96 TWh a year in China. In comparison, losses trended upwards by 0.15 TWh and 0.12 TWh in the USA and Europe while India continues to experience “persistently high losses due to severe air pollution”, the research paper says.
“The modest global decline of −0.72 TWh annually was therefore driven almost entirely by the improvements in China,” the paper continues. “The observed decline in pollutants over China’s PV sites does not reflect a coal phase-out, but rather the effectiveness of aggressive emission controls on a growing coal fleet.”
Song said this finding suggests stricter pollution controls and ultra-low-emission technologies can partially reduce the atmospheric impacts of coal in the short term. “But ultimately, maximizing the climate and energy benefits of solar power still requires a transition away from coal itself,” he added.
Song told pv magazine the results suggest that energy policy should account not only for installed solar capacity but also the atmospheric conditions that influence how much electricity solar systems actually deliver.
“In practical terms, this could include reducing fossil-fuel subsidies that continue to support coal generation, strengthening carbon pricing and emissions trading schemes and creating stronger incentives for coal plant retirement,” he said. “Policies that better account for the air-quality and health costs of coal pollution would also help address the hidden impacts of fossil fuels on renewable energy performance.”
Song added that investment in grid infrastructure, transmission capacity and energy storage is also essential for reducing the continued dependence on coal-fired power plants as backup for renewable energy systems. “Better spatial planning of solar infrastructure could also help minimize avoidable performance losses where coal and solar facilities are closely co-located,” the researchers explained.
Their findings are presented in the research paper “Coal plants persist as a large barrier to the global solar energy transition,” available in the journal nature sustainability.
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