Generalized quantitative electroluminescence method for the performance evaluation of defective and unevenly degraded crystalline silicon photovoltaic module

Photovoltaic (PV) module experiences multiple cell defects and degradation in a field operation, which significantly reduces module output. Hence, quantitative assessment of a PV module is essential to ensure module operation within a desirable limit. This article proposes the generalized quantitative electroluminescence (g-QUEL) method to evaluate the performance of a defective and unevenly degraded PV module from the EL images. Four module classes are considered from the view of field applications, such as new, PID-s affected, field aged shunted, and nonshunted modules. The effects of defects and degradation on fundamental cell electroluminescence (EL) characteristics and constants are analyzed for each class. Based on this analysis, the g-QUEL method is developed, which utilizes module multiple EL images, datasheet information, and terminal voltage measurements for quantification. First, a test module is qualitatively assessed to identify the present defects and classified into one of four classes. In the second part, the g-QUEL algorithm is applied to a test module in a customized manner to extract five or seven parameters of a PV cell. Subsequently, a single or two diode model simulation is carried out at a module, submodule, or cell level to estimate module output by generating I-V curve. Experimental verification of the proposed method was conducted on five test modules of each class. Results demonstrate the accuracy and effectiveness of the g-QUEL method as it evaluates the output power of new to field-aged modules with a relative error <=+/- 3%.