Experimental Study of the Fire Behaviour on Flat Roof Constructions with Multiple Photovoltaic (PV) Panels

Fire experiments were conducted on four mock-up roof constructions with an array of six photovoltaic (PV) panels to study the fire dynamics and flame spread behaviour, so as to better characterise the fire risks of such a system. As it is customary to retrofit PV panels to existing warehouse roofs, where expanded polystyrene (EPS) and polyvinylchloride-based roofing membrane B-ROOF(t2) is a typical roofing, the experiments were carried out on such installations, but with a mitigation solution on top; 30mm mineral wool or 40mm polyisocyanurate (PIR). All mock-ups were 6.0m long, whereas the width was 2.4m (Experiments 1 and 2) and 4.8m (Experiments 3 and 4), respectively. A wood crib was placed under the PV panels and it ignited the roofing membrane after 7min to 8min, which in all four experiments resulted in fire spread under all the six PV panels covering an area of 5.1mx2.0m. However, no self-sustained fire was observed beyond the area below the PV array. Within the first hour, the maximum temperatures were measured to respectively 175 degrees C and 243 degrees C underneath the two mitigation solutions of PIR insulation and mineral wool, which is more than 100 degrees C below the piloted ignition temperature for the EPS insulation. However, the EPS was ignited in both experiments with the PIR insulation due to thermal degradation of the protective material after approximately 1h. These experiments confirm that a small initial fire underneath a PV installation can transform into a hazardous scenario due to the changed fire dynamics associated with adding the PV panels to the existing roof.