I-V curves for detecting faults of operating photovoltaic modules

The present paper focuses on I-V curves for localizing possible defects in a photovoltaic module. The study considers the response of a photovoltaic module to changes in external and internal factors of the urban environment in Chelyabinsk, Russian Federation. To carry out measurements and control the module condition, we use the IV Swinger 2 software package reading data from the module to plot I-V curves and determine the maximum power point in real time. Changes in the internal parameters of the module are simulated by connecting additional resistances of different values to the external terminals of the experimental module. The conducted research has demonstrated additional resistance changing the shape of the I-V curve of the photovoltaic module regardless the type of connection and electrical circuit section of the module. This resistance simulates the main faults according to the given classification. Additional resistance in the cell circuit makes the shunt diode a conductor in the range of values from 0.71 to 1.06 Ohm. If additional resistance is installed between modules, the resistance can increase in a wide range of values without the diode transition to the conducting state. Additional resistance can reduce the power generation of a photovoltaic module. Therefore, we have assessed the impact of different cell shading levels on the module power generation. Given the resulting shunt resistance for all cells of one module, the slope of the I-V curve is inversely proportional to resistance due to the increased current leakage. Thus, the data of the I-V curve and the slope angle near the maximum power points is appropriate to identify and analyze the emerging faults of the photovoltaic module by evaluating its resistance.