POTENTIAL-INDUCED DEGRADATION: AN IMPROVED UNDERSTANDING OF MECHANISM AND INFLUENCE FACTORS

摘要

Potential-induced degradation (PID) is a critical failure mode in today's photovoltaic (PV) system architecture with very large to catastrophic impact on PV-module performance and energy yield. Potential-induced shunting (PID-s) is one of the most severe types of PID leading to shunting of p-type crystalline silicon solar cells. In previous works a preliminary phenomenological model was developed describing the progression of shunt resistance (R_(sh)) under realistic field conditions. Comparison between measured and predicted R_(sh) progressions revealed good qualitative agreement. Nevertheless quantitatively some differences between measured and simulated R_(sh) progressions were found. In order to better understand these differences various aspects of R_(sh) - measurement and - modelling are investigated in this paper. Firstly a cell-type and temperature dependence of the temperature coefficient of R_(sh) was found revealing a possible source of error in the correction of the temperature influence. In addition for a temperature of 70°C the grounded module-frame is found to influence the R_(sh) progression of the investigated one-cell mini-module even under dry conditions, which is not yet part of the preliminary model. Finally a physical model based on a description of the shunting and recovery process as a combination of drift and diffusion of sodium ions and atoms is presented improving upon the preliminary model.