Encapsulant for glass-glass PV modules for minimum optical losses: gas or EVA?

Abstract

Our simulation work aims at analyzing optical loss mechanisms for two types of glass-glass modules: laminated modules, using for example EVA (ethylene vinyl acetate) as encapsulant, and modules without encapsulant that are filled with neutral gas. The simulation results give arguments in favor of the use of gas as encapsulant in glass-glass PV modules instead EVA. Indeed, with an anti-reflection coating (ARC) on both sides of the front glass of the module and an appropriate ARC on the cell, the collected current of a cell encapsulated with gas is almost equal than the one obtained for a standard EVA module with a single side ARC on the glass and an appropriate ARC on the cell under an AM1.5G spectrum.Because of the different spectral behavior of the two materials, a careful filtering of lamps used in solar simulators is mandatory due to the high-infrared content, in order to compare gas filled modules to EVA laminated ones. Low UV content in the incident spectrum underestimates the optical losses in the EVA module and high-infrared content overestimates the optical losses in the gas filled module. This analysis shows that the refractive index of SiN of industrial solar cells and the current spectral distribution of solar simulators defined according to the norm IEC 60904-9 could penalize gas filled modules in comparison to EVA laminated ones.