A grey box model for shunting-type potential induced degradation in silicon photovoltaic cells under environmental stress

Abstract

This paper proposes a grey box model for cell-level simulation of potential induced degradation of the shunting type (PID-s) by extending a physics-based energy yield simulation framework. The leakage current is first computed using a physics-based approach based on an equivalent frame-to-cell electric circuit composed of temperature and humidity dependent resistances. Then, the increase of PID-s degradation due to leakage current is retrieved from measurements of PID-s evolution performed on poly-cSi cells. Finally, IV-curves of cells affected by PID-s are approximated by modifying the IV-curve of a PID-free cell using measurements of short circuit current and open-circuit voltage decrease with PID-s. A first comparison of simulated versus measured final PID-s levels is reported for a PV string after nine years of operation. The advantage of our grey box model over an empirical model is the possibility to investigate changes in material properties without the need for new measurements and to provide quantitative energy yield loss estimates depending on climate and system design.