Life-cycle greenhouse gas effects of introducing nano-crystalline materials in thin-film silicon solar cells

Solar PV is widely considered as a green technology. This paper, however, investigates the environmental impact of the production of solar modules made from thin-film silicon. We focus on novel applications of nano-crystalline Silicon materials (nc-Si) into current amorphous Silicon (a-Si) devices. Two nc-Si specific details concerning the environmental performance can be identified, when we want to compare to a-Si modules. First, in how far the extra (and thicker) silicon layer (s) affects upstream material requirements and energy use. Second, in how far depositing an extra silicon layer may increase emissions of greenhouse gases as additional emissions of Fluor gases (F-gases) are associated to this step. The much larger global warming potential of F-gases (17 200-22 800 times that of CO2) may lead to higher environmental burdens. To date, no study has yet analyzed the effect of F-gas usage on the environmental profile of thin-film silicon solar modules. We performed a life-cycle assessment (LCA) to investigate the current environmental usefulness of pursuing this novel micromorph concept. The switch to the new micromorph technology will result in a 60-85% increase in greenhouse gas emissions (per generated kWh solar electricity) in case of NF3 based clean processing, and 15-100% when SF6 is used. We conclude that F-gas usage has a substantial environmental impact on both module types, in particular the micromorph one. Also, micromorph module efficiencies need to be improved from the current 8-9% (stabilized efficiency) toward 12-16% (stab. eff.) in order to compensate for the increased environmental impacts. Copyright (C) 2010 John Wiley & Sons, Ltd.