Various types of degradations and failures occur in photovoltaic (PV) modules during their outdoor operation, such as cell cracks and an increase in series resistance. Sensitive detection of them is essential to improve the efficiency and reliability of the PV modules and systems. Previous detection techniques such as the Iâ€“V curve measurement had a problem because they needed to interrupt the maximum power point tracking (MPPT) operation of the PV system. This study proposes a new method to detect those degradations and failures without interrupting the MPPT operation by using the time-series data of the voltage and current at the maximum power point (Vmp and Imp, respectively). The Vmp and Imp are corrected for temperature using recently developed temperature correction formulas, and are analyzed as the Impâ€“Vmp curves. It is shown that the existence of a cracked cell in a PV module can be sensitively detected from the Impâ€“Vmp curve, since the decrease in the photocurrent of a cracked cell tends to shift a part of the Impâ€“Vmp curve of the module toward high voltage. The experimental and simulation results indicate that a small cell crack less than 10% of a cell area can be detected. In addition, the simulation results also reveal that the increase in series resistance can be detected by the distortion of the Impâ€“Vmp curve toward a lower voltage in the high Imp, or high irradiance, region. These simulation results indicate that the present method is very powerful for detecting the degradation and failure of PV modules and systems.
Keywords cell-crack, series resistance, voltage at maximum power point, current at maximum power point, temperature correction, crystalline silicon photovoltaics