Comparing photovoltaic and reflective shade surfaces in the urban environment: Effects on surface sensible heat flux and pedestrian thermal comfort

Photovoltaic (PV) arrays are increasingly being used to provide shade for parking lots and walkways. These structures introduce convective surfaces that have potentially significant thermal effects on the urban environment. This investigation uses a scale-model shade structure to provide a quantitative comparison of surface temperature, sensible heat flux, and pedestrian thermal comfort of a PV structure and a reflective shade structure to those of an unshaded asphalt surface during summer in Phoenix, AZ. Measurements were used to calculate the sensible heat flux and mean radiant temperature for a pedestrian for each test case. The results indicate that the overall sensible heat flux of the PV structure during the day was 80% higher than the unshaded (asphalt) ground, while the non-PV reflective shade structure case has 50% lower sensible flux than the unshaded ground. At night, we observed a consistent, albeit small, negative heat flux from both shade cases. Furthermore, while the thermal comfort beneath the PV and reflective shade structures was significantly improved compared with an unshaded lot, the reflective shade structure performed better than the PV shade. Under peak radiation, the mean radiant temperature underneath the reflective shade structure was 12 K less than that of the PV structure.