Effects of rooftop parapet walls on airflow and dust deposition on photovoltaic arrays: A CFD–DPM study

Rooftop photovoltaic (PV) systems are increasingly deployed in dense urban environments, where parapet walls are common architectural features that alter rooftop airflow patterns. However, the resulting effects on particle transport and dust deposition, which can significantly reduce PV energy yield, remain insufficiently understood. This study employs three-dimensional computational fluid dynamics (CFD) coupled with a discrete phase model (DPM) to investigate airflow characteristics and first-contact particle capture on individual rows of rooftop PV arrays with parapet walls. The airflow model is assessed against wind-tunnel measurements of the approach flow and of surface pressures on the PV array. Results show that parapet walls significantly alter rooftop airflow by reducing near-surface velocity, displacing the separated shear layer, and modifying recirculation around the PV array. The effect of parapet height is conditional rather than monotonic, and the influence of wind speed is strongly particle-size dependent. The particle diameter associated with the highest capture varies with operating conditions, with peaks near 100 μm at U He = 1.3 m/s, 150–200 μm at U He = 2.6 m/s, and 200–300 μm at U He = 3.9 m/s. Capture is highly non-uniform across the PV rows: upstream rows intercept particles with greater inertia, whereas medium-sized particles bypass the front rows and show enhanced capture on downstream modules at higher wind speeds.