Universal analytical solution to the optimum load of the solar cell

Accurate performance model of solar cells is very crucial for embedded power applications. At low irradiance levels, the two-diode model for PV model is well known for its excellent accuracy. Using the two-diode model, we provide the generic expression of the optimum load RmL which holds for both the single-diode and two-diode model. Also, we obtain an explicit solution based on elementary analytical functions to seek the optimum diode-voltage VmD using dichotomy method. Furthermore, the values of Im and RmL can be calculated based on the explicit expression of Im and RmL in terms of VmD. However, the computation for RmL is difficult, so we create a user-friendly program by Matlab/GUI to make it easier. As predicted, the results computed by the proposed method agree well with the experimental data of four real solar cells. Finally, the impacts of the series and shunt resistance on the optimum load are studied. It turns out that the results of the single-diode model in literature have the same tendency as that of the two-diode model.