Accurately extracting the shunt resistance of photovoltaic cells in installed module strings

A straightforward non-invasive method is proposed to accurately evaluate the shunt resistance of an elementary cell of a photovoltaic module connected in an installed string without the need of preliminary knowledge of the intrinsic diode parameters. The approach relies on the measurement of the current-voltage characteristic of the whole string after intentionally shading the selected cell. Calibrated PSPICE simulations are employed to both illustrate and test the method. As a case study, the shunt resistances of several cells belonging to a series array of 10 commercial modules are determined.