Analysis of the Applicability of the Diode Equivalent Model for GIGS Thin-Film Photovoltaic Modules

Equivalent electrical models, either single or double diode, of photovoltaic (PV) cells and modules can be very useful tools when predicting performance of PV devices to be operated in natural, changeable conditions. Additionally, such models may also be very helpful when analyzing even basic physical processes occurring in the devices, e.g. recombination/diffusion processes. In the paper results of numerical simulations with use of equivalent diode model applied for the analysis of Cu(In,Ga)Se₂ (CI(G)S) thin-film solar cells are presented. For that purpose I-V curves systematically acquired in the outdoor monitoring system have been used. To fit large amount of I-V curves to one of the commonly used diode models special PC program has been developed. Its role is fast and effective importing of I-V curves from database, immediate performing fitting procedure with subsequent storing and graphical presentation of the calculated results. The choice which of the models, i.e. either single model or two-diode, is more appropriate for a specific I-V curve, depended on better approximation of the calculated curve to measured one according to defined criteria. Presented examples show results of using developed program and effect of chosen model on resulting module performance parameters. It is shown which model seems to be more reliable for Cu(In,Ga)Se₂ thin-film solar cells, including analysis of the approximation errors