Solar projects are getting more reliable over time

Newer solar power projects are degrading more slowly than older ones, according to research from the US Department of Energy.

The finding, published in the Journal of Renewable and Sustainable Energy, demonstrates how photovoltaic technology in solar panels has improved over time, and could help investors in new solar projects better understand long-term risk. 

Researchers from Department of Energy’s Lawrence Berkeley National Laboratory and the National Renewable Energy Laboratory assessed the performance of 411 utility-scale photovoltaic projects built in the United States between 2007 and 2016 – together they were responsible for more than half of all the solar electricity generated within the country in 2017.

After correcting for weather variations and other factors, the researchers found that the newer projects had degraded at a slower rate than older ones. They also found that projects in hotter climates tend to degrade faster than ones in cooler areas.

"A large and rapidly growing market that lacks a lengthy operating history means that investors are fronting a lot of money – $6.5 billion for projects built within the US in 2018 alone – based on as-yet untested assumptions about the long-term performance of these projects," says Mark Bolinger, one of the researchers.

There are a variety of factors that influence how quickly photovoltaic cells degrade in efficiency and performance. "Most photovoltaic module manufacturers warrant that their modules' performance won't degrade by more than a certain percentage, for example, losing 0.5% per year, during a 25-year period," Bolinger says. "But module degradation is only part of the story, because the other components of a utility-scale photovoltaic system – the inverter, tracking system, fuses, wiring – can also negatively affect output."

Because the study focuses on system-level risk rather than the individual photovoltaic cells themselves, Bolinger says it offers a more holistic and realistic estimate of the long-term risk for potential investors in new solar projects.