In the fall of 2020, smoke blanketed most of the contiguous United States as megafires scorched swaths of forests in the West. The haze blocked some of the Sun’s rays from reaching nearby solar panels, dampening California’s solar energy production in the first 2 weeks of September by one third.
To meet the country’s growing energy demand, the U.S. government is seeking to quickly ramp up solar energy production from 3% to 45% by 2050. Over the coming decades, wildfires like those that rampaged in 2020 are expected to burn longer, larger, and throughout more of the year than ever before.
Scientists are finding in an ongoing study that despite the haze from far-off blazes, enough indirect sunlight was available to fuel the nation’s burgeoning solar panel industry in 2020.
“This could be good news for photovoltaic solar production,” said lead author and Colorado State University doctoral candidate Kimberley Corwin. The work, which has not yet been peer reviewed, was presented at AGU’s Fall Meeting 2022 last month.
Sun Versus Smoke
Earlier research on wildfires’ smoky effects largely focused on areas near the blazes. To take a nationwide view, Corwin created maps of solar irradiance—the power per unit area of the Sun’s electromagnetic radiation—across the contiguous United States using the National Renewable Energy Laboratory’s National Solar Radiation Database. Then, she overlaid daily satellite observations of smoke plumes from NOAA’s Hazard Mapping System.
Corwin compared two dramatically different years to start: 2019 and 2020. Wildfires in 2020 burned more than 40,000 square kilometers (10 million acres), whereas blazes the year prior burned less than half that.
These data show that although sunlight was more scattered and hazier on smokey days, about the same amount of light still hit Earth’s surface.
In a month-to-month comparison, the study found that the amount of the Sun’s direct beams of light that hit a square meter of the surface on a cloudless day dropped an average of 8% nationwide between September 2019 and 2020. But the amount of direct and diffuse light hitting a square meter of Earth’s surface on a cloudless day dipped by only 2% on average during the same time.
Atmospheric scientist Elizabeth Weatherhead at the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder, who was not involved in the research, compared this effect to reaching out your hand and blocking the Sun from your eyes. Although direct beams won’t reach your eyes, indirect light still will.
“Solar panels don’t care whether [they’re] getting photons from the direct beam or the diffuse radiation,” Weatherhead said.
The findings are slightly less positive for solar energy operations that concentrate solar energy using mirrors and other methods, said Corwin. These technologies rely more on direct sunlight than photovoltaics.
Corwin analyzed direct and diffuse light hitting different regions of the United States. Even in areas in the West and Southwest blanketed by smoke in 2020, the monthly global horizontal irradiance for each region decreased minimally on average from the year prior.
Past studies offered a more localized or short-term view. During a controlled fire near one of Australia’s government science laboratories in 2014, the amount of direct and diffuse light striking the laboratory fell by 6.5% on average over 2 hours. In some parts of California, it dropped by 20% on average over September 2020, when much of the state was burning, according to a report by Clean Power Solutions.
Knowing both local and national impacts is important, Weatherhead said. “It’s somewhat comforting to know that the impacts of smoke on energy production are only notable if the solar panels are right near the fires.”
That said, Corwin still needs to extend the analysis for 2006–2021, and the recent work doesn’t consider the tilt of solar panels or directly estimate solar energy generation. “We’re hoping to pull in actual utility-scale energy production,” she said.
Corwin and her colleagues plan to look at solar photovoltaic plant data collected by the U.S. Energy Information Administration. She hopes to describe how much energy a solar plant can produce in smokey conditions compared with normal conditions.
Her main goal is to provide more information for developing solar forecasts, which help grid operators improve the cost-effectiveness and reliability of solar energy by mitigating intermittency.
Though 2020 may have been an unusual fire year, it could become the new normal, said Corwin. The Fourth National Climate Assessment projects that the annual area burned by lightning-sparked wildfires in the Southeast could increase by around one third by 2060. In the West, the area burned annually could be 2 to 6 times higher than present by midcentury.
The latest study demonstrates the significance of cross-disciplinary research, said Weatherhead. “This is an example of Earth sciences using observations and modeling approaches developed over the decades to address this very practical concern.”
—Jenessa Duncombe (@jrdscience), Staff Writer