A new study has disturbing news for India’s solar power industry. It claims that dust and particulate matter (often a by-product of diesel engines) can reduce solar panel efficiency by 17% to 25%. Half this reduction comes from dust and particles deposited on the surface of solar panels which form a physical barrier to the passage of sunlight.
That’s according to Duke University professor Mike Bergin, who led the study. The rest of the reduction comes from ambient haze from atmospheric pollution, a condition known as solar dimming. “This study thus shows that improving air quality can lead to a big improvement in solar energy yield,” says Bergin. “Cleaning panels is not enough.” Many solar power plants today include systems that periodically wash the solar panels to remove dust, dirt, pollen, and bird droppings.
Dust can have a significant effect on solar panel output. A 2016 study in Baghdad, for example, found an 18.74% decline in efficiency for solar modules left uncleaned for a month. Another 2014 paper from Colorado, found that up to 4.1% of light transmission was lost due to dust buildup.
But losses from air pollution have received less attention. In one 2013 study, researchers investigated the power output of ten PV systems in Singapore during a haze episode caused by forest fires in Indonesia. That study found that lower air quality caused system output to decline by up to 25% over a 10 week period. On one day in particular, output was reduced by a staggering 50% according to Andre Nobre, lead author and head of operations at Cleantech Solar in Singapore. The study did not look at particulate deposits because frequent rain keeps solar panels clean in Singapore, he noted. “For a city like New Delhi, you have the added effect [of] soiling on the panels from the fact that it is a much drier and dirtier city.”
The Bergin study is the first to quantify the combined impact of ambient particles and deposited matter. He and his colleagues analyzed deposits on solar panels at the IIT campus in Gandhinagar and tracked energy yield before and after cleaning. Power generation increased 50% after each cleaning, the study found.
Air pollution is now a factor in solar power plant business decisions, says Nobre, whose company has solar projects across Asia including India. “Developers like ourselves will be extra cautious when signing power purchase agreements with clients with facilities located in highly polluted zones,” Nobre said. “Our returns are impacted by air pollution, which in turn end up increasing electricity tariffs we are able to offer. As the fleet of PV systems is drastically growing in India, there could be millions of dollars in revenue being lost,” he says.