Short-term outages caused by extreme weather have a minimal impact on most solar panels, but further work is needed to develop a clearer picture of the potential impacts, according to research by the National Renewable Energy Laboratory.
In 2022, researchers at NREL’s PV Fleet team found a national median loss in solar cell performance of 0.75 percent per year, a finding that was confirmed by previous studies. NREL’s analysis also discovered that solar systems in hotter temperature zones exhibited about twice as much performance loss as those in cooler climates.
"This median loss in performance is a crucial number," Chris Deline, a group manager for photovoltaic field performance at NREL, said in a statement. "First, it shows that our fleet of PV systems, on the whole, is not failing catastrophically, but rather degrading at a modest rate within expectations. It's important that we quantify this rate as accurately as we can, because this small but tangible number is used in almost all financing agreements that fund solar projects and provides critical guidance for the industry."
To improve their knowledge of solar cell vulnerability to extreme weather, the NREL researchers compared the performance of solar systems in their data set with a National Oceanic and Atmospheric Administration map of extreme weather events to study how each system's performance was affected when an extreme weather event occurred within 10 kilometers of its location.
The findings, published in the IEEE Journal of Photovoltaics, showed that, overall, the short-term outages caused by extreme weather have a minimal impact on most solar systems. Over the 2008–2022 time range studied, the NREL researchers found that the median outage length after an extreme weather event was two to four days, resulting in only a 1 percent median loss in annual performance with a small number of solar systems – 12 out of 6,400 – experiencing longer outages of two weeks or more. Most of the outages were the result of flooding and rain, followed by high wind events.
However, the research also showed a “clear trend emerged,” the NREL researchers wrote, noting that after weather events above certain thresholds — hail greater than 25 millimeters in diameter, winds in excess of 90 kilometers per hour (56 miles per hour), or snow depths greater than 1 meter (3 feet) — systems showed greater annual performance losses than the baseline established in the 2022 data.
"We don't feel any of this analysis suggests that PV systems are unreliable or especially vulnerable to extreme weather," Dirk Jordan, a member of the research staff and author on the PV Fleet publications at NREL, said in a statement. "PV has demonstrated that it can provide backup power and save lives when surrounding infrastructure is damaged by extreme weather events. Yet, there are further measures we can take to improve the quality of equipment and especially installation best practices to increase resilience to these weather events."
To harden PV systems against the impacts of extreme weather, module manufacturers and PV testing organizations need to first understand the thresholds at which damage can occur, NREL said, adding that industry can then begin to design for those conditions and create tests that subject panels to realistic stresses.
NREL said the findings suggest a need for more stringent hail testing, As well as more rigorous testing standards for wind and snow loading.