Symbolic algebra for the calculation of the series and parallel resistances in PV module model

In this paper a symbolic analysis of the equations that allow to calculate the values of the series and parallel resistances appearing in the single diode model of a photovoltaic module is presented. Such a model requires the identification of five values, that are the photo-induced current, the diode ideality factor and saturation current, the series and parallel resistances. This calculation can be done on the basis of the few data taken from the module data sheet or by using a fitting process starting from experimental measurements. In this paper the first case is considered: it allows to identify the parameters´ values in the standard test conditions and requires a solution of a non linear system of equations. In this paper the problem is afforded by using symbolic calculations only: the main result is the explicit expressions giving the values of all the five parameters. The explicit formulas allow to avoid the convergence problems that are typical of the methods based on the solution of a non linear system of equations. Nonetheless, the values obtained by using the proposed procedure can be used as guess solution for a more accurate calculation.