Report: Thick wildfire smoke dimmed the sun in 2020

AUSTIN (KXAN) — A new government report shows that wildfire smoke from the intense California fires in September 2020 darkened the skies enough to slash the state's solar power production by 10-30%.

The study, led by scientists at the National Center for Environmental Research (NCAR), found that solar energy forecasts substantially overestimated the amount of power that would be generated by the sun for the electric grid, and illustrates the opportunity for better energy forecasts in the future.

“The key takeaway from this research is that wildfire smoke can have a substantial and negative impact on solar energy production in areas near major wildfires,” said NCAR scientist Timothy Juliano, the lead author. “This is something that utilities should keep in mind when wildfires occur.”

How the Study Worked

Researchers at NCAR used advanced computer models of wildfire smoke and meteorological conditions, along with records of solar irradiance and energy production.

The 2020 wildfire season brought California five of the 10 largest wildfires in state history, including the August Complex Fire which burned more than one million acres — a new state record. Smoke plumes were clearly visible from space as severe drought conditions and windy weather set the stage for the dangerous fires.

The study focused on the period between Sept. 7-16, 2020, when the fires were peaking. To determine the amount of solar energy generated at various sites across the state, they drew on data from the California Independent System Operator. Researchers compared the energy output from the 2020 period with the same period in September during the two previous years, when solar arrays produced far more energy.

During heavy smoke days, researchers found that solar power production dropped 10-30% during peak production hours of 12 p.m. to 4 p.m. But on days when winds blew smoke out of the region, solar power production at utility operations declined by less than 7%. Although the study focused on California solar power impact, NCAR mentions that smaller declines in solar power production may have occurred elsewhere in the country where smoke dispersed.

Better Forecasting in the Future

To determine if power production forecasts can be improved, the scientists next turned to an NCAR-based computer known as Weather Research and Forecasting-Solar (WRF-Solar), which is able to calculate how various airborne particles known as aerosols block sunlight. By running simulations on their supercomputer, they were able to better approximate the magnitude and timing of solar irradiance during smoke events.

Authors of the study note that as wildfires become more common and smoke plumes extending over large parts of the nation, scientists need to continue working toward better-predicting smoke impacts across disciplines of fire behavior, weather forecasting and renewable energy.

"Wildfire smoke can be quite an important factor in energy production,” Juliano said. “Given the increase in large wildfires and society’s greater reliance on solar energy, even regions far downwind of fires may need to consider the potential impacts of smoke.”