Fire‐induced reradiation underneath photovoltaic arrays on flat roofs

Abstract

The impact of the reflection of fire-induced heat from a gas burner was studied experimentally to gain knowledge on the interaction between photovoltaic (PV) panels and a fire on flat roofs. The heat flux was measured in a total of eight points at the same level as the top of the gas burner. The gas burner was placed underneath the centre of a PV panel, installed in a geometry similar to a commercial EastWest orientated mounting system, and the eight points were symmetrical pairs of two at four different distances from the burner. Measurements were compared to tests with no PV panel, and thereby without the reflection from the PV panel. A significant increase of the received heat flux was recorded, with ascending percentage-wise difference for increased heat release rates. This indicates that PV panels can have a significant contribution in roof fires, primarily because they stimulate fire spread over the roof on which they have been mounted. The received heat flux is higher underneath the most elevated part of the PV panel, due to two important, flame-related reasons: 1) the flame deflection towards the most elevated part of the panel; 2) a non-homogeneous temperature distribution on the PV panel surface, due to the deflected flame, and thereby a non-homogeneous emission from the heated PV panel. Finally, the results were very similar for a brand new PV panel and a PV panel tested for the fourth time, except during the period when the thin combustible film underneath the new PV panel is burning, supporting that it is the fire dynamics and not the fire load associated with the PV panels that is promoting fire spread associated with PV panels on flat roofs. With this in mind, the current results are not only relevant for PV panels, but also for any inclined roof covering panel with limited combustibility.

Impact of flat roof–integrated solar photovoltaic installation mode on building fire safety

“…Next, as aforementioned, Kristensen et al have corroborated that the heat flux component from the combustible part of the PV panel contributes little to the total reradiated heat flux. Meanwhile, it was seen that the emission from the PV panel is limited to less than 1 kW/m 2 immediately after interruption of the gas flow (and thereby the almost immediate disappearance of the flame).…”

“…This study focuses on the cases in which H f is greater than H to further characterize the flame extension geometry underneath the PV panel. In previous researches on the impact of PV installation on roof fire safety, the values of h were set to about 10 cm. Therefore, h was defined as 5, 10, and 15 cm in this work.…”

“…Both IEC 61730‐2 and UL 1703 present sets of methods to address fire hazards of PV modules, including thermal cycling, hot spot endurance, and temperature tests. Even so, Ref . indicates that the fuel load of a PV panel does not represent a large fire hazard for a roof construction.…”

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

“…The four backsheets obtained respectively the best and second best reaction to fire rating on a scale with five steps. Likewise, recent parametric studies [19] have showed that the PV panel itself only contains a limited amount of combustible materials such as a thin polymer based backsheet and combustible encapsulate materials. When ignited, the materials increase the heat flux towards the subjacent roof surface for a very short period because of the thin combustible layers and thereby limited time of combustion [19].…”

“…Likewise, recent parametric studies [19] have showed that the PV panel itself only contains a limited amount of combustible materials such as a thin polymer based backsheet and combustible encapsulate materials. When ignited, the materials increase the heat flux towards the subjacent roof surface for a very short period because of the thin combustible layers and thereby limited time of combustion [19]. Given these points, the importance of the combustible materials in the main PV panel might be insignificant with respect to the propagation of the fire, -not to be mistaken with the fact that the PV panels probably are the main cause for the ignition, which leads to the fire.…”