Keywords:Photovoltaics, glazing, laminated safety glass, approval, energy payback time, carbon footprint
The majority of the photovoltaic (PV) modules used in building skins contains glass, but does not entirely comply with the product standards and design rules for glass in building. As a result, structural applications are subject to individual approval by the building authorities in many cases. This paper presents experimental research on glass based photovoltaic modules, analysing their mechanical properties in comparison with approved construction products. The focus is on glass-glass modules and on the question whether the most common module configurations can be classified as laminated safety glass. Testing included residual resistance testing to study the potential to provide residual load-bearing capacity and shear testing to examine the interaction of photovoltaic cells and interlayer material as well as adhesion characteristics. If approved interlayers are used, glass-glass modules correspond to the safety level of laminated safety glass, because the PV integration does not impair breakage behaviour and improves residual resistance, while the observed reduced adhesive bond does not imply a higher injury risk. Formal classification of photovoltaic products within the product and design standards for glass in building could facilitate the use of building-integrated photovoltaics. Life-cycle assessments of photovoltaic systems so far concentrated on roof-top and ground-mounted installations. Based on these studies, the specific environmental performance of building-integrated systems was analysed. Constructive integration of the PV modules associated with the substitution of conventional materials in the building skin reduce the life-cycle environmental impacts like primary energy demand and greenhouse gas emissions, especially in those areas with suboptimal solar irradiation like façades. The net energy payback times calculated for Central European range from 0.8 and 5.6 years and the net carbon footprint varies between 12 and 192 g CO2-eq/kWh.