Understanding the microenvironment of a PV module for better stress testing (Conference Presentation)

An understanding of the exposure environment of any material is necessary for the use of accelerated stress testing to evaluate different designs, materials, and configurations. For photovoltaic modules there is a wide range of environments and mounting conditions, each with a unique combination of temperature and humidity profiles. This is further compounded by differences in the microenvironment within a module, e.g. the humidity in the front EVA is not the same as the humidity in the backside EVA, and the presence of seasonal and diurnal changes in water content. We demonstrate how one can model the temperature and humidity environments of representative climates and use this to estimate the amount of moisture present in a PV module. To compare the relative degradation in different environments and to compare this to indoor testing, one must consider kinetically weighted parameters to characterize an environment. With some understanding of the kinetics, better choices for stress testing conditions can be made to minimize the uncertainty in correlating chamber results to the field allowing for better rank ordering of material and better service life prediction. This more general analysis highlights the fact that within reasonable limits a single humidity can represent a given climate. Thus, when a lower representative humidity is used, one can focus testing conditions on temperature effects and/or UV radiation. This can significantly simplify testing when very little is known about the humidity dependence of degradation processes.