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.

Fire safety of building integrated photovoltaic systems—State of the art

“…The worst option in this case is a roof insulated only with polystyrene foam. Such a structure will require a layer that mitigates the effects of fire to prevent serious consequences (Kristensen et al, 2022).…”

“…PV systems are available in all sizes, from a single PV cell mounted on the wall of a power bank, to domestic and commercial installations on buildings, to ground installations of nearly 1 GW, such as the Longyangxia Dam Solar Park in China (Voiland, 2017). The increased number of photovoltaic systems is associated with a continuous reduction in the cost of photovoltaic modules and thus the cost of energy, which makes them attractive to commercial and family property owners (Kristensen et al, 2022).…”

“…After the initial expenditure of planning and financing costs, the multifunctionality of BIPV thus has a favorable effect on the total costs of the construction project and on the amortization of the PV system itself (Prume and Viehweg, 2015). However, it should be noted that PV installations cause an increased probability of ignition (Kristensen et al, 2022;Prume and Vieweg, 2015) and the physical presence of PV modules changes the fire dynamics of the existing roof structure (Ju et al, 2019;Kristensen et al, 2018;Kristensen et al, 2020).…”

“…For example, the flame spread caused by PV panels on the roof is related to the height of the gap, the slope and the insulation material (Kristensen et al, 2022). Moreover, PV panels have been shown to be flammable structures causing fires in buildings (Iringova, 2022).…”

A Review on Safety Practices for Firefighters During Photovoltaic (PV) Fire

“…The experiment conducted by Kristensen and Jomaas [ 12 ] indicated that the flame propagation is influenced substantially by the geometry of PV installations with additional heat reflected underneath panels that fuels fire to propagate. The inclination of the PV modules also affects the flame spread rate [ 17 ].…”