Experimental Study of the Fire Dynamics in a Semi-enclosure Formed by Photovoltaic (PV) Installations on Flat Roof Constructions

Abstract

Flame spread experiments upon a BROOF(t4) compliant flat roof mock-up located below a vertical barrier were carried out for variations in gap height, inclination, subjacent insulation material, and the barrier type (stainless-steel board or photovoltaic (PV) module). A binary flame spread scenario was identified, where re-radiation from the flame facilitated self-sustained flame spread if the gap height to the horizontal panel was below 10 cm for the stainless-steel board and 11 cm for PV modules. These were defined as the critical gap heights. Inclination of the PV modules increased the critical gap height and caused a 25% faster flame spread rate (FSR) than the FSR below horizontal modules with the same gap height at the location of ignition. The faster FSR for inclined modules caused a 40% reduction of the maximum temperature measured at a depth of 70 mm in the insulation materials (242°C). Based on temperatures measured in the insulation materials, the 60 mm polyisocyanurate (PIR) insulation performed slightly better than the 50 mm mineral wool insulation. However, it is expected that the mineral wool would outperform the PIR insulation if tested with the same thickness, as it insulates significantly better at high temperatures. Finally, no sustained flame spread was observed on the back side polymer sheet of the PV modules, but one of the three PV module brands produced burning droplets. Based on the experiments, it can be concluded that the current standards are inadequate as the introduction of a PV system on a compliant roof construction enables flame spread.