Environmentally exposed thin-film a-Si modules were tested using Auger spectroscopy and electron and optical microscopy. The results seem to indicate that there is a serious corrosion problem associated with thin-film PV (photovoltaic) modules. This is considered to be primarily due to the permeation of water through the organic protective encapsulations. Such materials are all water permeable to some extent. If the module life expectancy is to be fixed in the 20-to-30 year range, then it is felt that further research is needed to find encapsulant materials that will act as effective water barriers for this period of time.<<ETX>>