The buildup of dust and grime on solar panels do their efficiencies no good, indeed we've seen some creative maintenance solutions such as using autonomous drones to brush them off. But what role does manmade pollution play in this, including the particles that hang in the air? A new study has found that this is taking a sizable chunk out of the world's solar energy production, with big investors such as India and China being hit the hardest.

The research was carried out by engineers from Duke University in collaboration with scientists from the Indian Institute of Technology-Gandhinagar, and sought to answer a key question: How much is dust buildup and airborne pollutants impacting the efficiency of solar panels?

"My colleagues in India were showing off some of their rooftop solar installations, and I was blown away by how dirty the panels were," said Michael Bergin, professor of civil and environmental engineering at Duke University and lead author of the study. "I thought the dirt had to affect their efficiencies, but there weren't any studies out there estimating the losses. So we put together a comprehensive model to do just that."

This first involved measuring the decline in solar energy gathered by the solar panels as the dust built up. The team found that each time they wiped the panels clean after a period of several weeks, a 50 percent jump in efficiency followed. A closer examination of this grime found that 92 percent of it was dust, while the remainder was carbon and ion pollutants from human activity. While these particles make up a small fraction of the total dust coverage, they happen to be much better at blocking sunlight – so much so, that they account for around half of the total energy loss.

"The manmade particles are also small and sticky, making them much more difficult to clean off," said Bergin. "You might think you could just clean the solar panels more often, but the more you clean them, the higher your risk of damaging them."

For the second part of their study looking at airborne pollutants, the researchers drew on data from NASA's GISS Global Climate Model. This tool includes information on how much of the sun's energy is blocked by various airborne particles, along with estimates on how much particulate matter gathers on surfaces across the world. From this, the team could gain insights into how much sunlight was being blocked by both airborne pollution and the pollution that gathers in the form of dust on solar panels.

According to the modelling, the team found that in the world's more arid regions like the Arabian Peninsula, Northern India and Eastern China, both airborne and accumulated surface dust reduced solar energy production by 17 to 25 percent. Those figures are based on the assumption that the panels are cleaned once a month. If they are cleaned once every two months, the losses shoot up to 25 to 35 percent.

How much of a role airborne particles play compared to dust varies between regions. Much more solar power is lost to dust in the Arabian Peninsula, but in parts of China it is air pollution that is the main culprit, with India following suit. The researchers calculate that particulate matter accounts for around 780 MW of solar power loss in India, and around a 7,400 MW loss in China.

"China is already looking at tens of billions of dollars being lost each year, with more than 80 percent of that coming from losses due to pollution," said Bergin. "With the explosion of renewables taking place in China and their recent commitment to expanding their solar power capacity, that number is only going to go up."

The research was published in the journal Environmental Science & Technology Letters.