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Western wildfires suppressed solar output in 2020

Wildfires exacerbated by climate change darkened the skies above solar projects across the U.S. West last year.

Emma Foehringer Merchant
Emma Foehringer Merchant
4 min read
Western wildfires suppressed solar output in 2020

In the Western U.S., quantifying which wildfires rank as the region’s worst has become an increasingly overwhelming chore. In 2020, blazes across several states caused the sky to glow an eerie orange, and California logged yet another record fire season.

“We’ve broken almost every record there is to break,” climate scientist Daniel Swain of UCLA told The New York Times in September.

Worsening wildfires are fueled by climate change, which is making the West hotter and drying out vegetation, heightening ignition risk. Wildfires are also affecting one of the technologies that is best positioned to help solve the problem: solar energy.

In parts of the West, some of the most productive months for solar energy overlap with the traditional wildfire season — and that season is now getting longer and more brutal. Last year ranked as the worst for solar production since 2001 in parts of California’s Central Valley, according to recently released analysis from Clean Power Research, which sells solar performance and forecasting software and maintains solar irradiance data dating back to 1998.

In the Central Valley, where roughly 40 percent of California’s large-scale solar is located, 2020 output for one PV system dropped nearly 6 percent below the annual average as wildfire smoke blotted out the sun and then rained down soot that tarnished panels. In the first two weeks of September, solar electricity generation on the power grid of the California Independent System Operator (CAISO) dropped 30 percent below the summer average. And in the early weeks of October, California's daily solar output dropped as much as 20 percent compared to the same dates in 2018 and 2019, said BloombergNEF analyst Brianna Lazerwitz.

Over the whole of September 2020, the Central Valley and Oregon’s Columbia River Basin experienced a 20 percent drop in insolation, a measure of the amount of sun reaching solar panels. “That’s a very big number,” said Patrick Keelin, Clean Power Research’s lead product manager. “You do have months where you can have a 20 percent below normal amount [of solar production] due to cloud cover. But in the middle of the Central Valley in August or September, that might be a little bit unusual.” Keelin compares the reduction to the production declines seen in an “extremely, extremely cloudy” month.

Clean Power Research found that even the few months of lowered production in 2020 due to wildfires reduced annual solar output totals to levels comparable to the cloudiest of years.

The solar sector lacks data on wildfire risks

The overall impact of wildfires on the clean energy industry remains as hazy as last year’s smoky skies, largely because little research has been done on the problem.

Hotter temperatures and other environmental changes will lead to increasingly severe and more prevalent wildfires in the West in coming years and decades, scientists say, but the solar industry has little understanding of how those risks will affect its installed equipment.

In the planning process for a solar plant, developers, funders and insurers examine historical risk reports and analysis that estimate how an installation will perform using data that stretches back about three decades. But as climate change advances, the future is expected to look less and less like the recent past.

Currently, project stakeholders do their best to assess project risk in order to determine expected output, financing and insurance. That process, says Matthew Muller of the National Renewable Energy Laboratory, is “very imperfect right now.” And while it’s being refined as the industry grows, some of the variables — including climate change and wildfires — are changing.

“How do you take something like wildfires and bring that into the picture when you don’t have a very good picture in the first place?” said Muller, an engineer with the lab’s photovoltaic performance and reliability group.

Clean Power Research is working with a group studying aerosols and air quality at NASA to understand the problem. NREL is collecting solar plant operation data from solar providers across the U.S.

But both Keelin and Muller said the amount of data available to help understand fire's impact on solar is limited. As developers and other project partners begin to better understand the challenges, climate risks may need to filter into power plant contracts.

“[Solar] might not be as constant as once thought,” said Keelin. “We need to be looking at the trends in the solar resource and understanding [whether] there are significant trends that the industry needs to pay attention to.”

Generally speaking, any type of extreme weather is not a friend to solar power. Clean Power Research pointed to the potential for solar output to be affected by periods of heavy snowfall in areas where that type of weather is uncommon.

"I've watched extreme weather events cause an increasing number of power market disruptions over the past several years. Power markets will need to adapt to a rapidly changing world," said Lazerwitz in an email. "Solar is an important piece of that puzzle."

One answer: Build more solar

In 2019, researchers at the Massachusetts Institute of Technology published a paper suggesting that warmer temperatures would curtail energy output from solar cells. Ian Marius Peters, an author of the MIT study, argued that we should install even more solar to compensate: “Decarbonizing electricity is probably the first thing we should do to put a lid on global warming.”

In September of last year, California Gov. Gavin Newsom also called for an acceleration in the state’s decarbonization plans as it coped with 28 "major wildfires" (according to Department of Forestry and Fire Protection classification) burning simultaneously throughout the state.

“We are experiencing weather conditions the likes of which we’ve never experienced in our lifetime,” said Newsom, standing amid debris from Northern California’s North Complex fire. “While [California is] leading the nation in low-carbon, green growth…we’re going to have to do more, and we’re going to have to fast-track our efforts.”

(Article image courtesy of James Todd)

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Emma Foehringer Merchant

Emma is a contributing writer at Canary Media. She has covered clean energy and climate change at publications including Greentech Media, Grist and The New Republic.