Useful life prediction for first generation a-Si photovoltaic modules using outdoor test data

The authors present an analysis of field-test data for first-/generation a-Si modules under the Solar Energy Research Institute´s ongoing field test and performance evaluation program. The program goal is to establish baseline data against which future development can be compared. To that end, models are discussed which represent the data and which begin to correlate basic cell and material studies to module field performance. Two sets of first-generation modules have been placed in the field test. The test configuration for most of the modules is maximum power. Short-circuit and open-circuit configurations are also used. The modules show rapid initial degradation during the first year of field testing. Typical efficiency loss for the test period is over 30%. The data for efficiency degradation are modeled by exponential fit, and the deviance from ideal is discussed. Fill factor data are compared to the model of Z.E. Smith et al. (1985), and in most cases they show a log (t) dependence. Both models are used to predict 30-year performance.