The Use of Two-Diode Substitute Model in Predicting the Efficiency of PV Conversion in Low Solar Conditions

The article presents theoretical foundations of a two-diode equivalent model of a photovoltaic cell/module (PV), together with calculation procedures. A physical interpretation of individual components of an equivalent model was presented. Its practical application in predicting efficiency of operation of various PV cells and modules in low insulation conditions was demonstrated. The obtained predictions were verified with the actual results of their operation in open space (outdoor). The practical suitability of the “model” in early detection of ageing phenomena, such as, for example, absorber degradation taking place in PV modules, was demonstrated. The article was prepared on the basis of the results of testing five different PV modules with various constructions, made of different materials and absorbers, such as: c-Si, mc-Si, CIS, a-Si_SJ, a-Si_TJ. The used measurement data were collected during the 16-year period of the experimental PV modules testing system operation in University of Opole, equipped with a data acquisition system.