Severe air pollution is significantly reducing China’s solar energy potential, particularly in the northern and eastern parts of the country, according to a study from Princeton University.

The issue is worst in the winter when air pollution in these regions blocks about 20% of sunlight from reaching solar panel arrays. This makes air pollution’s wintertime effect on solar energy production as significant as that of clouds, which have long been considered the main hurdle to solar energy production, according to the study, which was published in the Proceedings of the National Academy of Sciences.

The study shows that in the most polluted parts of northern and eastern China, aerosol pollution reduces the potential for solar electricity generation by as much as one and a half kilowatt-hours per square meter per day, or up to 35 percent. That is enough to power a vacuum cleaner for one hour, wash 12 pounds of laundry or work on a laptop for five to 10 hours, the study noted.

Burning fossil fuels increases aerosol concentrations in the atmosphere. Other researchers have recognized that these aerosols, which include sulfate, nitrate, black carbon particulates and brown organic compounds, are contributing to solar dimming over large parts of China. But no previous research had calculated just how much aerosols in the atmosphere are reducing China’s solar energy-generating efficiency.

To calculate how much of the sun’s radiation is reaching solar arrays on the ground, the scientists used what’s called a solar photovoltaic performance model, combined with satellite data from NASA instruments that measure irradiance from the sun and analyze aerosol components and clouds in the atmosphere. They conducted nine separate analyses, which spanned 2003 to 2014 and covered all of China, to compare the impact of aerosols compared to clouds on solar power generation with and without technology that tracks the sun as it moves across the sky.

Xiaoyuan (Charles) Li, a Ph.D. candidate in Princeton’s Department of Civil and Environmental Engineering and the study’s lead author, said the findings should further spur countries like China and India to cut aerosol emissions so they reduce pollution and thereby increase their solar electricity generation more rapidly.

The findings can also help determine where to build new solar arrays, the authors said. Aerosol pollution in China is heavily concentrated in industrialized, urbanized regions, while remote, thinly populated areas have much cleaner air. If research can quantify how much air pollution is reducing solar power output, policymakers can weigh the costs of transmitting electricity from cleaner regions to dirtier ones against the benefits of producing more power by building arrays where more sunlight reaches the ground.