Sun optimism. SolarWorld’s ratings aim to keep the photovoltaic industry on the sunny side.So which is the sunniest solar manufacturer of them all?

I don’t mean companies whose photovoltaic panels generate the most carbon-free electricity, but which are the most environmentally friendly in their manufacturing, labor, and recycling practices.

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Solar modules can contain toxic materials, and they have a finite life cycle. As the industry booms — the number of megawatts installed in the United States in 2010, for instance, spiked 67 percent — photovoltaic trash eventually will become an issue.

The Silicon Valley Toxics Coalition this week released its annual Solar Scorecard to rate photovoltaic manufacturers according to four criteria: recycling, green jobs, toxics, and disclosure.

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The toxics coalition looked at whether companies had programs to take back and recycle their old solar panels, whether they performed chemical use and life-cycle analysis, and whether they monitor their suppliers to ensure they adhere to health, safety, environmental, and labor standards.

“The Silicon Valley Toxics Coalition (SVTC) believes that we still have time to ensure that the PV sector is safe for the environment, workers, and communities,” the report states. “We need to take action now to reduce the use of toxic chemicals in PV, develop responsible recycling systems, and protect workers throughout the global PV supply chain.”

Of the top 10 solar manufacturers, six responded to the toxics coalition’s survey. SolarWorld scored the highest, earning 91 points out of a possible 100. The German manufacturer was awarded “sunny” designations for its recycling and green jobs and “partly sunny” for toxics and disclosure.

Other sunny companies: Trina Solar of China took the No. 2 spot with 89 points and the United States’ First Solar and Norway’s REC tied with 87 points. The other big U.S. solar manufacturer, SunPower, scored 85 points. China’s Yingli earned 72 points but was labeled “cloudy” on disclosure and partly sunny overall.

Four of the top 10 solar manufacturers did not respond to the survey — Canadian Solar, Sharp, Hanwa SolarOne, and Suntech, the world’s biggest module maker.

“Sharp and Suntech contacted SVTC and worked to have a constructive dialogue, but did not complete the survey,” the report noted.

So will homeowners care whose solar panels are installed on their roofs?

They should, according to the toxics coalition.

“If you plan to own your home for 20-25 years, or to pass it down to your children, the PV modules will become your burden to recycle if they are not covered by a manufacturer take back program,” the reports warned.