A heavy smog day in Bosnia in 2013.
Photo: AP

The solar industry is slowly chipping away at our dependence on oil, gas, and coal. But ironically enough, air pollution stemming from those same dirty energy sources may be making it harder for solar to gain a foothold.

That’s according to a new study that looked at how tiny air pollution particles known as PM 2.5 can reduce the energy output of solar photovoltaics by preventing sunlight from reaching them. The authors estimate this loss of light could translate to hundreds of millions of dollars of lost solar revenue (not to mention loads of carbon-free power) around the world each year.

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The researchers focused their analysis on the notoriously polluted city of Delhi. By correlating PM 2.5 data collected in 2016 and 2017 with data on solar insolation (i.e. sunlight) over the same period, they found that sunlight is diminished nearly 13 percent for every 100 micrograms of particles per cubic meter of air. On average, the study estimated photovoltaics in Delhi lost about 11.5 percent of their potentially useful sunlight to air pollution from 2016-2017.

In other words, if a million homes were powered by solar panels, 115,000 more could be powered just by cleaning up the air. Considering installation goals and local electricity prices, the authors estimated air pollution could be carving 20 million US dollars out of the solar industry’s bottom line in Delhi alone.

The authors extrapolated their results to 16 other cities using local air pollution data, and found that the loss of sunlight available for solar varied from just 2 percent in relatively smog-free Singapore to 9 percent in car-filled Beijing.

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Lead study author Ian Marius Peters, a photovoltaics researcher at the Massachusetts Institute of Technology, told Earther this extrapolation should be taken with a grain of salt, because different cities have different types of air pollution with varying effects on sunlight. Nevertheless, he expects the general pattern to hold elsewhere and that worldwide, the economic losses for solar could be in the hundreds of millions or even billions of dollars annually.

This study is far from the first to point out that airborne particles can blot out the Sun. Others have looked at the effects of desert dust storms or volcanic eruptions. Folks have also used satellites to look at air pollution over cities and try to estimate how this messes with the solar power potential.

But few studies have directly related measured levels of particle pollution near the ground to a loss of light and, well, money. Peters hopes that the work inspires copy-cat studies elsewhere so that “cities will be able to plan more accurately for future solar installations” as they transition to renewables.

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Overall, the study highlights an under-appreciated challenge the burgeoning renewable industry is facing. But it’s also a reminder of why we’re transitioning to cleaner energy sources in the first place: Air pollution sucks.

[Energy & Environment Science]