LOS ANGELES — 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.
Executives at companies that inspect Chinese factories on behalf of developers and financiers said that over the last 18 months they have found that even the most reputable companies are substituting cheaper, untested materials. Other brand-name manufacturers, they said, have shut down production lines and subcontracted the assembly of modules to smaller makers.
“We have inspectors in a lot of factories, and it’s not rare to see some big brands being produced in those smaller workshops where they have no control over quality,” said Thibaut Lemoine, general manager of STS Certified, a French-owned testing service. When STS evaluated 215,000 photovoltaic modules at its Shanghai laboratory in 2011 and 2012, it found the defect rate had jumped from 7.8 percent to 13 percent.
In one case, an entire batch of modules from one brand-name manufacturer listed on the New York Stock Exchange proved defective, Mr. Lemoine said. He declined to identify the manufacturer, citing confidentiality agreements.
