New research shows that solar power output increases as skies clear

As the air cleared after lockdowns, solar installations in Delhi produced 8% more power, study shows.

According to findings published in the journal Joule, researchers from MIT have demonstrated that clearer skies have an impact on the output from solar PV panels, leading to an 8% increase in the power output from installations in Delhi after shutdowns and stay-at-home orders took effect. Mechanical engineer, Tonio Buonassisi, research scientist Ian Marius Peters, and three others in Singapore and Germany, conducted the research.

The scientists said that this is the first study to demonstrate and quantify the impact of the reduced air pollution on solar output. The effect should apply to solar installations worldwide but would normally be very difficult to measure against a background of natural variations. The conditions triggered by COVID-19, with its sudden cessation of normal activities, combined with high-quality air-pollution data from one of the world’s smoggiest cities, afforded the opportunity to harness data from an unprecedented, unplanned natural experiment.

The study was an extension of previous research in Delhi. The impetus for the work came after an unusual weather pattern in 2013 swept a concentrated plume of smoke from forest fires in Indonesia across a vast swath of Indonesia, Malaysia, and Singapore, where Peters, who had just arrived in the region, found “it was so bad that you couldn’t see the buildings on the other side of the street.”

Peters decided to investigate the effects of air pollution on solar panel output. The team had data on both solar panel output and solar insolation, and they saw that during the 18-day-long haze event, the performance of some types of solar panels decreased, while others stayed the same or increased slightly.

Peters later learned that a high-quality, years-long record of actual measurements of fine particulate air pollution (particles less than 2.5 micrometers in size) had been collected every hour, year after year, at the U.S. Embassy in Delhi. That provided the necessary baseline for determining the actual effects of pollution on solar panel output; the researchers compared the air pollution data from the embassy with meteorological data on cloudiness and the solar irradiation data from the sensors.

They identified a roughly 10% overall reduction in output from the solar installations in Delhi because of pollution.

To see the impact of COVID-19, researchers used the mathematical tools they had developed, along with the embassy’s ongoing data collection, to see the impact of reductions in travel and factory operations. They compared the data from before and after India went into mandatory lockdown on March 24 and compared this with data from the previous three years.

Pollution levels were down by 50% after the shutdown, they found. As a result, the total output from the solar panels increased by 8.3% in late March, and by 5.9% in April.

“These deviations are much larger than the typical variations we have” within a year or from year to year, Peters says — three to four times greater. “So, we can’t explain this with just fluctuations.” The amount of difference, he says, is roughly the difference between the expected performance of a solar panel in Houston versus one in Toronto.

An 8% increase in output might not sound like much, Buonassisi says, but “the margins of profit are very small for these businesses.” If a solar company was expecting to get a 2% profit margin out of their expected 100% panel output, and suddenly they are getting 108% output, that means their margin has increased fivefold, from 2% to 10%.

“This is the first real quantitative evaluation where you almost have a switch that you can turn on and off for air pollution, and you can see the effect,” he says. “You have an opportunity to baseline these models with and without air pollution.”

By doing so, he states, “it gives a glimpse into a world with significantly less air pollution.” It also demonstrates that increasing the usage of solar electricity, and thus displacing fossil-fuel generation pollution, makes those panels more efficient.

The research team included C. Brabec and J. Hauch at the Helmholtz-Institute Erlangen-Nuremberg for Renewable Energies, in Germany, where Peters also now works, and A. Nobre at Cleantech Solar in Singapore. The work was supported by the Bavarian State Government.

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