Dennis Schroeder/ Department Of Energy/National Renewable Energy Laboratory GREEN OR GREENHOUSE Research-industry team says nitrogen trifluoride emissions during solar-panel production can be offset within four months of power generation.

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Two years ago, the first atmospheric measurements of a rare but potent greenhouse gas used by solar panel manufacturers alarmed many climate scientists. The concentration of the man-made gas, nitrogen trifluoride, was four times greater than scientists had expected and growing by 11% a year. Now a study offers some encouraging news: The greenhouse-gas-free power generated by solar cells offsets in less than four months the potential climate-warming impact of the NF 3 released during their production (Environ. Sci. Technol., DOI: 10.1021/es100401y).

During the past 15 years, manufacturers have adopted NF 3 for cleaning during electronics manufacturing, because it creates fewer overall emissions than previous cleaners. But in 2008, Michael Prather, lead author of the 2007 Intergovernmental Panel on Climate Change assessment, called NF 3 "the greenhouse gas missing from Kyoto."

Scientists estimate that the gas lingers in the atmosphere for about 550 years, and its global-warming potential is about 17,000 times greater than that of carbon dioxide. The solar power industry accounts for 5% of the global NF 3 demand, with the rest coming largely from integrated circuit manufacturing. However, for the past decade, the solar industry has grown by more than 45% annually.

Vasilis Fthenakis, an expert in life-cycle analysis at Columbia University and Brookhaven National Laboratory, and colleagues from Air Products and Chemicals, a major supplier of NF 3 , examined solar panels' life-cycle NF 3 emissions from production to end use. They measured emissions from Air Products' factories and six solar panel manufacturing plants around the world. Then, by accounting for the greenhouse gases released per energy output by the U.S. grid, the researchers compared the emissions saved by solar panel operation to emissions generated from their manufacture. A typical solar panel must operate for at most four months for the greenhouse gas savings to balance out its fabrication emissions, the researchers concluded.

Prather, an atmospheric chemist at the University of California, Irvine, says that this study provides much-needed hard figures and detailed analysis, but cautions that it examines only one product. He hopes that the study will prompt groups independent of NF 3 producers and users to evaluate it, and to do similar measurements for other electronic products.