Across the world urban skies have cleared as nations have gone into lockdown due to the pandemic, only to rise again in those countries moving towards business as usual. Scientists saw a perfect opportunity to examine the effects of pollution on solar energy systems, and have been startled at how much difference smoggy air makes.
"Delhi is one of the most polluted cities on the planet," said Dr Ian Marius Peters of Helmholtz-Institut Erlangen-Nürnberg for Renewable Energies in a statement. "Moreover, India enacted a drastic and sudden lockdown at the start of the pandemic. That means that reductions in air pollution happened very suddenly, making them easier to detect."
Peters was already studying how much pollution and natural haze can interfere with solar production, with instruments at the US embassy in Delhi providing essential baseline data.
In the journal Joule, Peters reports under cloudless conditions 950 Watts/square meter of solar energy reached the solar panels in late March 2020 compared to 880 W/m2 on equivalent dates in 2017-2019. An 8 percent difference may sound minor, but it's “Equivalent to the difference between what a PV installation in Houston would produce compared with one in Toronto," Peters noted.
That's particularly remarkable because Delhi's pollution fell by half, rather than disappearing entirely.
"I expected to see some difference, but I was surprised by how clearly the effect was visible," Peters said.
Solar power has set records in Europe in recent months, but reduced pollution needs to be disentangled from an unusually sunny spring.
Peters' work reveals a vicious spiral. By reducing the electricity roof-top solar panels produce, urban smog maintains demand for electricity from other sources, much of which ends up coming from coal plants, adding more pollution. Solar farms located within a city's pollution catchment suffer a similar effect.
Moreover, anything that reduces solar production also undermines panels' economics, quite possibly a larger obstacle to powering cities cleanly than the direct loss of production.
Few cities may be as badly affected as Dehli, but most are affected to a lesser degree.
Another paper in the same edition of the journal paints a depressing portrait of how the pandemic may slow the shift to cleaner energy by affecting many companies' capacity to invest in new technologies. However, the authors of that work stress this can be avoided with the right policy settings. Research like Peters' demonstrates just how much the world has to gain from renewable energy. In this case, it can turn the cycle from vicious to virtuous, with each shuttered polluter making it easier for solar to thrive, closing more coal-burners in their wake.