Fabricating the panels requires caustic chemicals such as sodium hydroxide and hydrofluoric acid, and the process uses water as well as electricity, the production of which emits greenhouse gases. It also creates waste. These problems could undercut solar's ability to fight climate change and reduce environmental toxics.

A new ranking of 37 solar manufacturers, the Solar Scorecard, shows that some companies are doing better than others. Chinese manufacturer Trina scored best, followed by California-based SunPower.

The annual scorecard was created by the Silicon Valley Toxics Coalition (SVTC), a San Francisco-based nonprofit that has tracked the environmental impact of the high-tech industry since 1982. It's the group's fifth scorecard, and it shows that the industry is becoming more—not less—opaque