Dust, particulate matter in air reducing solar energy output by 25 per cent: study

Global solar energy production is taking a major hit due to dust and atmospheric particulate matter, according to a new study. The airborne particles and their accumulation on solar cells are cutting energy output by more than 25 per cent in certain parts of the world.

The study, which appeared in Environmental Science and Technology Letters journal on June 23, said that the regions that are hit the hardest are also the regions that have invested the most in solar energy installation. The regions include: China. India and Arabian Peninsula.

"We always knew these pollutants were bad for human health and climate change, but now we've shown how bad they are for solar energy as well," says Michael Bergin, professor of civil and environmental engineering at Duke University and lead author of the study.

"My colleagues in India were showing off some of their rooftop solar installations, and I was blown away by how dirty the panels were. 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," continues Bergin.

How much does dirt affect solar panel’s efficiency?

Along with colleagues at the Indian Institute of Technology Gandhinagar (IITGN) and the University of Wisconsin at Madison, Bergin measured the decrease in solar energy gathered by the IITGN’s solar panels as they became dirtier over time.

The data showed a 50 per cent jump in efficiency each time the  solar panels were cleaned after being left alone for several weeks. The study also showed that when the sample of grime was analysed to see its composition, 92 per cent of it was dust, while the remaining fraction was composed of carbon and ion pollutants from human activity.

While this may seem to be a small amount, the carbon and ion pollutants block light more effectively than natural dust. Thus, human contributions to energy loss are much greater than those from dust, making the two sources roughly equal antagonists in this case.

"The man-made particles are also small and sticky, making them much more difficult to clean off," says 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."

Having previously analysed pollutants discolouring the Taj Mahal, Bergin already had an idea of how these different particles react to sunlight. Using his earlier work as a base, he created an equation that accurately estimates the amount of sunlight blocked by different compositions of solar panel dust and pollution buildup.

Pollution as a major factor

But the grimy build up isn’t the only thing that is blocking the sunlight. The ambient particles in air also have a screening effect.

NASA’s GISS Global Climate Model not only calculates the amount of sun’s energy blocked by the airborne pollutants but also estimates the amount of particular matter deposited on surface worldwide.

This provides a basis for Bergin's equation to calculate how much sunlight would be blocked by accumulated dust and pollution.

The resulting calculations estimate the total loss of solar energy production in every part of the world. While the US has relatively little migratory dust, more arid regions such as the Arabian Peninsula, Northern India and Eastern China are looking at heavy losses—17 to 25 per cent or more—assuming monthly cleanings. If cleanings take place every two months, those numbers jump to 25 or 35 per cent.

The Arabian Peninsula loses much more solar power to dust than to man-made pollutants, Bergin said. But the reverse is true for China and India.

"China is already looking at tens of billions of dollars being lost each year, with more than 80 per cent of that coming from losses due to pollution," says 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."

This study was supported by the US Agency for International Development and the Office of the Vice Provost for Research at Duke University.

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