Rooftop boundary layer temperature effects of conventional and cool roof integrated photovoltaic systems

Rooftop photovoltaic (PV) deployment is expanding for urban decarbonization, yet the local climatic impacts of standard photovoltaic roofs (PVR) versus cool-roof-integrated systems (PVCR) in arid environments remain unresolved. This study presents a vertically-resolved observational analysis (30–200 cm) of both configurations on the typical Chinese arid urban rooftop (Lanzhou). Both systems achieved substantial daytime roof-surface cooling (PVR: 12.1 ± 1.2 °C; PVCR: 10.3 ± 1.5 °C), but their near-surface air temperature effects were highly stratified. While shading dominated roof cooling, substrate albedo played a decisive secondary role. Notably, PVCR produced warmer roof surfaces and adjacent air than PVR, as reflected shortwave radiation from the cool roof was partially re-absorbed by overlying bifacial panels—a “secondary heating” effect that increased panel thermal load and sensible heat flux. A distinct “thermal dipole” emerged: a shading-driven cooling layer at 30 cm and a sensible-heat-driven warming layer at 60 cm. At 150–200 cm, the signal attenuated; PVR maintained slight cooling, whereas PVCR induced minor daytime warming. Panel-to-air heating efficiency exhibited marked asymmetry between front and back surfaces. These findings demonstrate that rooftop PV restructures near-surface thermal gradients rather than uniformly cooling or warming the environment, suggesting that in high-insolation arid regions, maximizing shading may outweigh albedo enhancement for near-roof thermal regulation. The results are specific to bifacial modules and summer conditions.