Emissions of greenhouse gases, radionuclides, and air pollution generated by production and use of solar cells are far lower than those generated by grid-supplied electricity, according to a new study led by Vasilis M. Fthenakis of Brookhaven National Laboratory (Environ. Sci. Technol., DOI; 10.1021/es071763q). The study found that 89% of air emissions associated with electricity generation could be prevented if electricity from photovoltaics (PV) displaced currently available grid-supplied electricity. The study looked at four major PV technologies-multicrystalline silicon, monocrystalline silicon, ribbon silicon, and thin-film cadmium telluride. The life-cycle emissions were quite similar, according to the report, but thin-film systems emitted the least harmful air emissions since they require the smallest amount of energy during manufacture. The report examined central PV systems and estimated that the emissions would be lower still for roof-based systems due to energy savings from eliminating transmission and distribution network losses.