High operating temperatures have a negative impact on photovoltaic (PV) modules. Hence, lowering the temperature of commercial crystalline silicon modules during their operation becomes an increasingly attractive prospect, as it increases the system's energy yield and prolongs the module's lifespan. In this work, we experimentally and numerically investigated two phenomena that could lead to a potentially costeffective passive cooling method for PV modules, one being the effect of roof structure on the convective flows, and the other being installation of an array of vortex generators (VGs) on the surface of the roof. The shape and positioning of the vortex generators is optimized for free convection conditions (in the absence of wind) which are the worst-case scenario for overheating of the modules. Infrared thermography was employed to assess the cooling ability of the VGs with different spacing for the flat, corrugated, and squared roof structures. Particle Tracking Velocimetry (PTV) measurements have been employed to obtain flow fields. The experimental data have been compared against numerical simulations of the flow dynamics and heat transfer. Numerical studies have adopted the unsteady URANS turbulence modelling and S2S radiation modelling, with the aim of analyzing flow structures and selecting the best configurations. It has been found that the VG-induced mixing in the boundary layer is responsible for enhancing the convective flux on the rear module surface as well as on the surface of the roof. We observed both that the formation of vortices is strongly dependent on the aerodynamic shape of the VG and that the placement of the VGs is important for improving the cooling of the rooftop modules. The cooling provided by VGs appears to be more pronounced in narrower roof gaps when the PV module is closer to the roof. Moreover, VGs appear to cool the PV module better on wavy roofs with riblets parallel to the long edge of the module, compared with other roof shapes.