Daylight Photoluminescence Imaging: Quantitative Analysis of String Voltage Mismatch and Balancing Currents

Abstract

Large-scale daylight photoluminescence imaging of crystalline silicon solar panels in utility-scale solar farms, whereby luminescence images of several hundred to thousands of panels are acquired simultaneously, was demonstrated by our group recently. Here, we demonstrate that photoluminescence images of large solar farm sections that are connected to the same central inverter uniquely contain quantitative information about voltage mismatch between series-connected strings of modules resulting from voltage variations between groups of modules. These voltage variations cause significant balancing currents between module strings when no or only low power is extracted from the solar farm. The impact of these balancing currents on the luminescence intensity is discussed. An analytical model to correct daylight photoluminescence images for these balancing currents is proposed and validated using experimental data.