Data is presented on the field test of amorphous silicon photovoltaic modules. The modules have been obtained by SERI under the field test and performance evaluation program to track the changes in performance following the continuing development of improvements in their manufacture. The data have been gathered for up to five years. Procurement time intervals are used to distinguish between the sets of modules under test. The results show that more recent technogies have a more rapid initial loss of performance but that stability sets in at an earlier time than that observed for the earlier modules. Data are presented to show efficiency and fill factor degradation from both the date of deployment and a date selected for post initial degradation(pi). Performance models are presented and compared, including models which account for annual variations in insolation and temperature and, therefore, generation of light induced defects and annealing.