In theory, solar electric panels on a rooftop should be good for many decades of trouble-free performance. In practice, however, panel performance is a function of manufacturing quality. And according to a May article in the New York Times, panel buyers may not be wise to take quality for granted ("Solar Industry Anxious Over Defective Panels," by Todd Woody).

"The solar panels covering a vast warehouse roof in the sun-soaked Inland Empire region east of Los Angeles were only two years into their expected 25-year life span when they began to fail," the Times reports. "Coatings that protect the panels disintegrated while other defects caused two fires that took the system offline for two years, costing hundreds of thousands of dollars in lost revenues. It was not an isolated incident. Worldwide, testing labs, developers, financiers and insurers are reporting similar problems and say the $77 billion solar industry is facing a quality crisis just as solar panels are on the verge of widespread adoption."

There are no global statistics on the problem, the Times reports, and no way of knowing yet how widespread the defects may be. But executives at top U.S. companies that manufacture panels or panel components told the Times that it's a significant worry.

"The question is whether things are deteriorating rapidly or whether it's a few isolated companies not doing so well on their quality control," Sarah Kurtz, a scientist with the Energy Department's National Renewable Energy Laboratory (NREL) who has studied the performance of solar panels. "I hear a lot of angst, but I haven't seen a lot of solid information."

Researchers are now trying to get ahead of the data curve — or at least catch up with it, reports Greentech Media ("Focusing on Solar Panel Durability, Not Bankability," by Herman K. Trabish).

"The Fraunhofer USA Center for Sustainable Energy Systems (CSE) began pursuing its Photovoltaic Durability Initiative (PVDI), a set of panel tests that go beyond safety and performance, in 2010, along with Germany's Fraunhofer Institute for Solar Energy Systems (ISE)," Greentech reports. "PVDI is 'a protocol to provide quantitative comparative data for modules in various operating environments,' explained Fraunhofer senior technical staff member David Meakin, and 'to identify the field performance capabilities necessary to reduce risk to investors.' Durability, which Fraunhofer focuses on instead of bankability, depends on a lifetime assessment of a panel's performance, Meakin said, and the data on that is inadequate. 'The best we could do is a probability because we don't have enough technical information -- nobody does -- to make lifetime predictions yet.'"