A new report has found that thin-film cadmium telluride solar cells have the lowest life-cycle emissions primarily because they consume the least amount of energy during the module production of the four types of major commercial PV systems: multicrystalline silicon, monocrystalline silicon, ribbon silicon, and thin-film cadmium telluride (CdTe).
The study, published in the Environmental Science & Technology journal, based on PV production data of 2004–2006, presents the life-cycle greenhouse gas emissions, criteria pollutant emissions, and heavy metal emissions of the four types of PV systems considered. Life-cycle emissions were determined by employing average electricity mixtures in Europe and the United States during the materials and module production for each PV system.
They found that thin-film cadmium-telluride solar cells had the best life-cycle profile. Even though the process emitted heavy metal cadmium, it still had a lower overall level of “harmful air emissions” than the other PV technologies in the study.
The report stated that "Overall, all PV technologies generate far less life-cycle air emissions per GWh than conventional fossil-fuel-based electricity generation technologies. At least 89% of air emissions associated with electricity generation could be prevented if electrity from photovoltaics displaces electricity from the grid."
The fact that Cd-Te technology was found to have the lowest emissions profile is interesting, but the main point, to me, is that all technologies had low emissions profiles, that are insignificant when compared to the emissions of the fossil fuel technologies that they replace. While I do not find it suprising that all solar PV systems have a low emissions profile, I find it suprising that the authors did not include thin-film silicon or copper indium gallium selenide (CIGS) cells in their study. I assume the overall results would have been the similar, but it woud have given a fairer comparison to the technologies now in use. One problem with scientific research is that it takes so much time to do the study and get it published that by that time the information is made public it is sometimes outdated.