POTENTIAL-INDUCED DEGRADATION (PID) – COMPARISON OF DIFFERENT TEST METHODS SHUNT RESISTANCE MEASUREMENTS OF INDIVIDUAL CELLS INSIDE A MODULE AND INFRARED IMAGING OF PV MODULES

摘要

The degree of PID degradation of a module can be measured quantitatively by maximum power determination at standard test conditions or low irradiance but without information of the individual cells. Electroluminescence (EL) imaging with test currents close to short circuit current or low test currents shows details but no qualitative values. Additional analysis methods are used to get further information: 1. The shunt resistance (Rsh) of individual cells can be determined by shading of single cells in the module. The comparison of the I-V curves of the unshaded module and the module with one shaded cell enables to measure the individual shunt resistance of the shaded cell. With this method it is possible to early detect PID and to quantify EL images for simulating the degradation and regeneration process. 2. Infrared (IR) imaging of modules in the direct sunlight is the most suitable method for getting an estimation of the degree of PID degradation during the operation of modules in the system. Typical PID IR patterns (warmer cells close to the bottom frame or patchwork patterns) and the position of the module close to the negative end of the module string are strong hints for PID effects. The aim of this work is to show different test methods and to arrive at a test procedure for early detection and characterization of the PID effects on degraded modules in the field and in the laboratory.