Methodology for Predicting Flexible Photovoltaic Cell Life using Accelerated Tests
Venkata Bheemreddy& Bill J. J. Liu
MiaSole Hi-Tech Corp., Santa Clara, CA, United States

Long term stability is critical for maturing any photovoltaic (PV) technology. Among the several degradation mechanisms in a PV product, performance loss due to environmental stress is a major contributor. Currently, IEC61646 based accelerated tests are widely adopted in the industry as a metric to qualify a 25 year lifetime product. While this test standard enables assessing damp heat performance of a PV module, it is not suitable for evaluating an unencapsulated PV cell degradation performance. In this work, an accelerated test methodology has been developed to predict the degradation performance of an unencapsulated flexible PV cell under typical factory environment conditions. A semi-empirical model is proposed to predict the PV cell performance.  Model parameters were derived from accelerated damp heat test conditions. Finally, the model is validated using measured PV cell degradation performance data for a typical factory environment. Two types of polymer materials are also evaluated to assess their impact on the PV cell life. The framework developed in this work enables assessing the degradation state of a PV cell before it is laminated to a module. This information is critical to define appropriate storage conditions for the PV cell to avoid unintended degradation which can impact PV module performance.