A novel procedure to adjust the equivalent circuit parameters of photovoltaic modules under shading

Commercial PhotoVoltaic (PV) modules generally consist of a number of PV cells ranging between 60 and 96. The solar cells in a PV module are connected in series and partitioned in 3 or 4 strings, each protected by a bypass diode. In general, the terminals of each string are available by opening the junction box but, in case of partial shading, the current-voltage (I-V) curves of a single defective solar cell cannot be directly measured and only the I-V curve of the PV string can be obtained by experimental tests. In the present work, a novel indirect procedure to extract the parameters of shaded PV cells using models generally adjusted for irradiated cells is proposed. It is defined "One Module (or One String), Two Tests"and it requires two tests performed as close as possible: in the first step, all the Ns cells of a PV module or a string are irradiated while, in the second step, the PV module or string have a shaded cell and Ns-1 irradiated cells. In the present work, the procedure is applied to a string of a p-Si module consisting of 20 solar cells.