Mechanical Stability of PV Modules

Analyses of the Influence of the Glass Quality

Abstract

A significant increase in reported glass breakages from the field was recognized during the past three years, where a disproportionately high number of modules were affected by glass breakage. Different substructures and module designs are affected, framed and unframed modules, tracked and fixed systems. What all inquiries have in common, however, is that modules with a double-glazed design with ≤ 2.5 mm glass thicknesses are affected and the problems were observed after just a few months in field operation. Various factors such as heavy weather events, faulty installation or errors in the structural design could be excluded as root causes and our experience points on additional, more fundamental problems that are associated in particular with the continuing trend towards larger modules > 3 m² and thinner module glass ≤ 2mm. Furthermore, it seems that the residual compressive surface stress of the glass as one major parameter that determines the stability of glass panes has not been considered in this context in the PV module industry yet. In this work, we focus on the glass thickness in combination with the compressive surface stress. Besides qualitative methods, one possibility to investigate the surface stress quantitatively is a scattered light polariscope (SCALP), previously used in the glass industry. In particular, the aim is to validate the SCALP measurement method for the use on PV modules. Furthermore, a potential correlation between the surface compressive stress and the mechanical stability of various common module designs with 2 mm and 1.6 mm glass is investigated.