Electrical Characterization of Fresh and Degraded Photovoltaic Backsheets Based on Temperature and Humidity-Dependent DC Conductivity

The operating environment conditions significantly impact the insulation resistance of photovoltaic (PV) modules. The equivalent insulation resistance of the strings connected to an inverter should be above the manufacturer’s recommended threshold limit, or else the inverter will trip. The DC conductivity values of the packaging materials decide the module insulation resistance at a given operating condition. Characterizing the backsheet conductivities requires sophisticated facilities, including open electrode fixtures, very low current measurement devices, and environments with controlled temperature and relative humidity (RH). Hence, such studies are not widely reported in the literature. This paper quantitatively determines the temperature and RH-dependent DC conductivities of different types of commonly used backsheets in PV modules. The RH-dependent Arrhenius behavior of DC conductivities can vary from material to material. The objective is also to electrically characterize the PV backsheet insulation properties of fresh and degraded backsheets, which is the preliminary step to understanding the insulation degradation mechanism comprehensively.