During 1977, MIT/Lincoln Laboratory, in conjunction with the Department of Energy, placed 41.5 kilowatts of photovoltaic modules at various experimental test sites in the United States. The largest of these was a 25-kW array in Mead, Nebraska, which is used for corn irrigation and crop drying. This report serves to summarize the performance of these modules and to describe the physical and electrical changes which have occurred due to weathering during that time period. To date, the performance has exceeded all expectations as only 6 modules amounting to 0.07 kW have failed during the operational period starting in July. MIT/Lincoln Laboratory has initiated a module degradation analysis program involving field inspection and measurements of modules, in-house inspection and analysis of modules returned from the field and soil accumulation studies. To date, 58 modules from 4 manufacturers have been analyzed, and a detailed description of the observations made is presented.