Experimental study of flame spread underneath photovoltaic (PV) modules

The horizontal flame spread underneath a photovoltaic (PV) module (or a plate) was studied for various gap heights to understand the fundamental fire dynamics between it and a flat roof construction. In a number of experiments, an opaque black polymethyl methacrylate (PMMA) and a black stainless-steel plate were used as surrogate fuel and module, respectively. Additional experiments were conducted with actual PV modules to analyse the reproducibility of the surrogate results and to study the potential effect of the small fuel contribution from the PV modules. PMMA samples (70 cm long) of varying widths (20 cm, 30 cm and 40 cm) were ignited at one end, and flame spread rate, mass loss, radiative heat flux and temperatures were recorded. For the 30 cm wide samples, a reduction in gap height from 20 cm to 17 cm resulted in a significant increase in the flame spread rate (from 0.37 mm/s to 2.41 mm/s). A similar critical gap height (transition into a much faster flame spread rate) was identified for all widths. Thus, introducing gap height requirements into PV installation standards could offer an inexpensive and elegant design that could reduce the fire risk associated with PV modules on flat roofs significantly.