The National Renewable Energy Laboratory (NREL) has been testing amorphous silicon (a-Si) Photovoltaic (PV) modules for more than a decade. NREL has been conducting controlled light-soak testing of multijunction a-Si modules to characterize their performance for stability evaluation as well as to benchmark the technology status. Some of the test modules, after controlled light-soak testing, have been installed outdoors. We have observed that under outdoor exposure, the modules further degrade in performance, possibly due to lower outdoor temperatures and varying spectra. The paper presents data on the light-induced degradation for the third controlled light-soak test on multijunction a-Si modules as well as outdoor performance data on single-and multijunction modules under prevailing conditions.
I n t h i s outdoor performance study, a comparison was made o f various a-Si a l l o y photovoltaic devices --singles, tandems, and t r i p l e s --under i n c i d e n t solar irradiance w i t h widely d i f f e r e n t spectral content. The spectral i r r a d i a n c e was varied over a range o f t h e three most c r u c i a l atmospheric paramet e r s which a f f e c t t h e i n c i d e n t spectrum: a i r mass, water vapor, and t u r b i d i t y . A multi-source s o l a r simulator was used t o simulate t h e spectrum throughout t h e day f o r each o f f i v e d i f f e r e n t days. I -V curves of t h e s o l a r c e l l s were then measured under these various spectral conditions and t h e i r performance compared.The r e s u l t s reveal t h a t t h e power output o f t h e m u l t i -j u n c t i o n devices, when normalized a t s o l a r noon and integrated over t h e
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