Monitoring of Photovoltaic System Performance Using Outdoor Suns-VOC

In-field characterization of photovoltaics is crucial to understand performance and degradation mechanisms, subsequently improving overall reliability and lifespans. Current outdoor characterization is limited by logistical difficulties, variable weather, and requirements to measure during peak production hours. We capitalize on Suns-VOC, which is widely used for laboratory measurements of single solar cells and discuss the barriers in extending the technique to outdoor systems. We demonstrate the normalization of measurements using both backsheet temperature sensors and on-site weather stations. Despite weather variation, VOC, ideality factor, and pseudo fill factor all fall within 1% of the laboratory measurements. It is also demonstrated that monitoring the system VOC at 0.05 to 0.1 suns, during minimal power production, provides a figure of merit that can indicate early degradation of the system. Extensive simulations show that shading portions of a system has minimal effect on measurements, allowing the technique to be used in all weather conditions.