Method for quantifying optical parasitic absorptance loss of glass and encapsulant materials of silicon wafer based photovoltaic modules

Optical losses in a photovoltaic (PV) module consist of reflectance losses and parasitic absorptance losses in the front layers of the module. A method for quantifying the optical losses associated with the cover glass and encapsulant material of silicon wafer based PV modules is presented. The method involves measuring the spectral reflectance (R) and the external quantum efficiency (EQE) of a silicon wafer solar cell before and after encapsulation. The approach used is to first obtain the 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 multicrystalline silicon wafer PV modules with two different ethylene vinyl acetate (EVA) encapsulants (conventional and super-clear EVA) are investigated and compared. Compared to conventional EVA, the module encapsulated with super-clear EVA is found to have much lower Apara.mod at short wavelengths.