New analytical approach for modelling effects of temperature and irradiance on physical parameters of photovoltaic solar module

In this paper, a new exact method has been presented to extract physical parameters of single diode equivalent circuit modelling a photovoltaic solar module operating at standard test conditions. The method uses four equations, three are linking output current to output voltage in short-circuit, maximum power and open-circuit points, the fourth equation is the first derivative of output power with regard to output voltage in maximal power point. According to this method, we used ideality factor eta as variation parameter and solved the system of four nonlinear equations to get values of photocurrent I-ph, saturation current I-s, series resistance R-s and shunt conductance G(p). We then varied ideality factor to minimize root mean square error and maximize the coefficient of determination. We assumed series resistance and shunt conductance constant, and derived analytical expressions describing effects of module temperature and incident solar irradiance on photocurrent, on ideality factor and also on saturation current using both temperature coefficients available as well as irradiance coefficients extracted from module datasheet. We considered standard test conditions numerical values of physical parameters as initial conditions and determined numerical models for I-ph(T,G), eta(T,G) and I-s(T,G). We also derived new mathematical expressions of maximum power point voltage and module efficiency. We tested these numerical models as well as mathematical expressions derived on Kyocera KC200GT and Shell SQ80 photovoltaic solar modules under different conditions of module temperature and incident solar irradiance and found good agreement between experimental and forecasted characteristics.