Object dependent properties of mirrors for PV applications studied under accelerated weathering protocols

Abstract

Abstract-Lifetime and degradation science (L&DS) has been implemented over the past two years to explore exposure protocols for accelerated weathering of back-surface aluminum mirrors for photovoltaic applications and to apprise PV developers of their implications. Using weathering protocols that induce degradation through heat, humidity, ultraviolet light and exposure to corrosive environments, a variety of degradation modes have been observed. In order to characterize changes in the object-dependent optical properties of these mirrors, a careful accounting of reflected, absorbed and scattered light was performed. Metrics for comparing the degradation observed in various sets of samples with different protective coatings were developed. These metrics can be used to track, correlate and predict performance of systems exposed in real-world conditions. Using a stress and response framework, observations of sample performance were made at multiple steps of exposure in order to monitor the progression of damage accumulation. This allows for correlation to outdoor exposure results and provides a pathway for system lifetime performance prediction. Acrylic back surface mirrors exposed to accelerated weathering protocols showed an increase in scatter, interfacial absorptance and a reduction in specularity. This L&DS approach to technology development allows for confidence when entering new markets and mitigates risks associated with premature failure due to improper material substitution.