Novel Method for Quantifying Optical Losses of Glass and Encapsulant Materials of Silicon Wafer Based PV Modules

Optical losses in a photovoltaic (PV) module consist of reflectance (R) losses and parasitic absorptance losses (Apara.mod) in the front layers of the module. In this paper, a method for quantifying the optical losses associated with the cover glass and the encapsulant material of silicon wafer based PV modules is presented. The method involves measuring the spectral reflectance (R) and the full-area external quantum efficiency (EQE) of a silicon wafer solar cell before and after encapsulation. The approach used is to first obtain the full-area internal quantum efficiency (IQE) of the cell using R and EQE of the cell before encapsulation. Assuming that the IQE of the cell is not changed by the encapsulation process, the spectrally resolved parasitic absorptance loss (Apara.mod) associated with the cover glass and the encapsulant material is calculated with the aid of EQE and R measurements of the encapsulated cell. Using this method, the optical losses (at near normal incidence) of single-cell monocrystalline silicon wafer PV modules with various glass structures (textured, planar, antireflection coated) and encapsulant materials (EVA, ionomer) are investigated and compared. Ionomer encapsulated modules are found to show higher Apara.mod because of a higher absorption coefficient of the material. Modules with textured glass show a higher Apara.mod due to the longer optical pathlength resulting from refraction of light at the glass-air interface.