Severe smoke from the wildfires that have been sweeping parts of California reduced power output from the state’s utility-scale solar installations by 13% in the first two weeks of September, even after factoring in a significant gain in solar capacity compared to the previous year.

Data from the U.S. Energy Information Administration and the California Independent System Operator (CAISO) showed that “particulate matter from fires sparked in August and early September blotted out the sun enough to cause quantifiable differences in solar output,” Greentech Media reports, even though the state added 659 megawatts of new grid-scale solar between 2019 and 2020. Its total grid-scale solar capacity now stands at 13 gigawatts.

“California’s recent experience is not the first time researchers have pointed out the challenges that climate change poses to solar energy, ironically one of the technologies held up as an integral tool to coping with the crisis,” Greentech writes. “Last year, analysis from the Massachusetts Institute of Technology suggested warmer temperatures would curtail solar output.”

Wade Schauer, research director at Wood Mackenzie Power & Renewables, said the direct impact of climate-fuelled wildfires on solar generation will likely be limited. “But the effect may become more pronounced as solar grows to make up a larger portion of California’s overall generation, or if the uncertainty impacts deal-making in the sector,” Greentech writes. It’s already “become a critical consideration” for one asset management company that owns 4.6 GW of solar capacity, affecting credit risk and the location of assets.

“There are two things at play,” explained WoodMac senior solar analyst Colin Smith. “Does it affect production enough to change revenues short-term and make a project not profitable? And does it change project assumptions long-term if we expect lots of wildfires?”

But while the state’s 9.8 GW of small solar installations don’t figure into the EIA’s analysis, Greentech says home solar panels may see the worst impact.

“One thing I’ve noticed in my local neighbourhood south of Sacramento: The ash and dust has caked on many homes’ rooftop solar panels and likely won’t be cleaned off until our first rain, which is nowhere in sight,” Schauer told Greentech’s Emma Foehringer-Merchant. “I’ve got to believe that rooftop solar output, in general, is lower than normal, even on days with little smoke, due to the ash buildup.”