Optical model for multilayer glazing systems: Experimental validation through the analytical prediction of encapsulation-induced variation of PV modules efficiency

Abstract

A simple analytical calculation based on a transfer matrix method for incoherent optics, allowing the prediction of photovoltaic module efficiencies in different encapsulation conditions is presented. This approach is used for the experimental validation of the main features of the optical model for multilayer glazing systems considered, through the relation between the external quantum efficiency of the module and its optical modeling. The theoretical procedure avoids the need to manufacture and characterize by solar simulator or external quantum efficiency measurements all the variety of photovoltaic module configurations, which is of interest at research and manufacturing levels, especially for building-integrated photovoltaics. The absorptivity of encapsulated solar cells is not directly accessible from direct air-bare cell or air-encapsulated cell optical measurements, and therefore analytical or numerical methods are generally needed. The calculations presented in this work provide closed analytical expressions for the layer-by-layer absorption of the different components of a photovoltaic module. From a small set of experimental measurements of a particular encapsulation configuration, and the theoretical expressions for spectral absorptivities, the short-circuit current of a module can be predicted for any other encapsulation scheme. It will be proved that the method accurately matches short-circuit current density of the modules as obtained from experimental measurements. Results will be presented for crystalline silicon and CIGS thin film cell technologies with several glass and encapsulation material combinations.