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Integrating photovoltaic (PV) panels with different tilt angles in building envelopes or roofs is widely employed for environmental sustainability. However, little is known about the influence of different tilt angles on the thermal failure of the photovoltaic façades or roofs in fire conditions. A total of 15 four-edge shielded PV panels (300 × 300 × 4.7 mm3), with five different inclinations of 0°, 15°, 30°, 45° and 60°, were heated to fail using a uniform radiant panel. Measurements were taken to track glass thermal breakage, surface temperatures, incident heat flux and failure characteristics. The glass fracture and pyrolysis of the internal thermoplastic materials were observed under thermal radiation. The average breakage time of glass in PV panels showed an increasing trend with increasing inclination of the PV panels. Moreover, when the PV panels were tilted beyond 30°, the time to failure increased more significantly. The maximum temperature difference and heat flux that the PV panels can withstand were primarily measured within the range of 61–84 °C and 8–15 kW/m2, respectively. Finally, the test results were simulated by a finite element method (FEM) model, calculating the heat transfer and thermal stress of PV panels: the average errors concerning temperature distributions and failure times were smaller than 15 % compared with the experimental results. [ABSTRACT FROM AUTHOR]

Summary This paper quantifies experimentally the fire‐induced reradiation to roof surface created by flame extension on the back of the flat roof–integrated photovoltaic (PV) array. A gas burner underneath the tilted PV panels was employed as the fire source. The effects of the PV tilt angle, distance from PV panel to roof, and fire heat release rate (HRR) were investigated. The flame extension geometries and flame reradiation heat flux distribution were recorded. The results show that the flame extension length and vertical thickness (ie, the vertical distance from the back surface of the PV panel to the extension flame profile) are reduced with the increase of PV tilt angle and panel‐roof distance but are increased with increases in the fire HRR. A unified nondimensional HRR coupled with all these factors is proposed to quantify the flame extension geometry. Furthermore, a general equation based on the physical relationship between flame radiation and flame geometry is developed to characterize the distribution of reradiation heat flux on the roof surface with the nondimensional local flame thickness. Finally, suggestions regarding PV installations on flat roofs and the selection of roofing materials are given to decrease the possibility of flame propagation underneath the PV arrays. [ABSTRACT FROM AUTHOR]

Summary: 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 center of a PV panel, installed in a geometry similar to a commercial east‐west orientated mounting system, and the eight points were symmetrical pairs of two at four different distances from the burner. Measurements were compared with 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 toward the most elevated part of the panel and 2) a nonhomogeneous temperature distribution on the PV panel surface, due to the deflected flame, and thereby a nonhomogeneous 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 relevant not only for PV panels but also for any inclined roof covering panel with limited combustibility. [ABSTRACT FROM AUTHOR]