Performance test of amorphous silicon modules in different climates - year four: Progress in understanding exposure history stabilization effects

In a round robin outdoor exposure experiment carried out in three different climates, we have previously demonstrated that amorphous silicon (a-Si) PV modules reach higher stabilized performance levels in warmer climates. The four-year experiment involved three identical sets of thin-film a-Si modules from various manufacturers deployed outdoors simultaneously in three sites with distinct climates. Each PV module set spent a one-year period at each site before a final period at the original site where it was first deployed. The experiment aimed to determine the light-induced degradation and stabilization characteristics of a-Si regarding specific history of exposure, and to compare degradation rates in different climates. We propose that after the initial sharp degradation associated with the Stabler-Wronski effect (SWE) has passed, the subsequent stabilized performance levels attained will depend largely on light exposure and a characteristic temperature associated within a coherent time-scale. PV modules which were first deployed at the lowest-temperature site for one year, reaching a stabilized state, and were then further deployed at higher temperature sites for two more years, experienced considerable recovery in output parameters (Pmax and FF). However, when further deployed back at the original, lowest-temperature site, performance degraded back to the first year, original level.