Comparative short term/long term field test performance and stability of tandem and single junction a-Si modules

Short-term and long-term data obtained for thin film modules under test in the Solar Energy Research Institute´s module field test performance and stability evaluation program are presented and analyzed. A comparison is made between the short-term performance data of amorphous silicon modules placed under test during 1985 and 1988-9. The module sets include both single-junction and and tandem modules. The 1988-9 sets show degradation which is initially faster on the average than that of the 1985 sets. The rate of degradation of later vintage modules is considerably lower following the initial degradation than that of the earlier vintage. Data for the 1985 single-junction modules have been gathered for a sufficiently long period for life predictions. Staebler-Wronski effects are readily demonstrated. A set of models for analyzing the long-term field test data for the 1985 modules are presented to bracket the expected life performance. These models are compared to a stretched exponential model and a model which accounts for the seasonal data variations introduced by changing annealing rates. The linear term, model continues to represent the data better than the other models