Structural Safety of Photovoltaic Modules in the Building Envelope
The mechanical performance of photovoltaic modules has not been adequately characterized for use as glazing product in the building envelope. As a result, the modules are subject to individual approval by the building authorities in many building-integrated applications. This paper presents experimental research on glass based photovoltaic modules, analyzing their mechanical properties in comparison with regulated construction products. The focus is on the influence of photovoltaic thin-film coatings on the bending strength of the float glass used as a substrate or superstrate and on the post-breakage behavior of glass-glass modules. The four-point bending test according to EN 1288-3 was modified in terms of specimen dimensions in order to test full-size photovoltaic glass panes. The modified set-up was verified as a suitable and simple test method to determine and confirm strength values. Edge ablation was found to reduce glass strength rather than the PV coating and cell scribing processes, but the reduction is less than 10 % and the minimum strength value of float glass can still be met. Residual strength testing of glass-glass photovoltaic modules in different load and temperature scenarios showed that the integration of crystalline silicon cells as well as thin-film solar cells improves the post-breakage behavior of glazings. A critical point may be mechanical failure within the layers of thin-film cells on glass associated with the potential danger of broken glass pieces falling down. Standard glass-glass module configurations appear to provide the same or higher residual strength performance as laminated safety glass, if the interlayer material is approved for use in laminated safety glass.