An exploratory study on road tunnel with semi-transparent photovoltaic canopy—From energy saving and fire safety perspectives

Road tunnels consume a large amount of energy, especially in the Canadian cold climate, where the roads are heated electrically or deicing during the winter. For a more sustainable and resilient road tunnel energy system, we conducted an exploratory study on installing a semi-transparent photovoltaic (STPV) canopy at the entrances and exits of a tunnel under a river. The proposed system generates solar-powered electricity, improves thermal and visual conditions, and reduces energy loads. In this study, field measurements of road surface temperature and air temperature were conducted, and numerical simulations with and without STPV were performed to study air and road surface temperatures under different traffic speeds. The field measurements show the road surface temperatures are higher than the air temperature on average. The interior air and road surface temperature were measured to be above 0 ℃, even though the outdoor temperature is far below 0 ℃, thus significantly reducing the need for deicing in winter using salts. The simulations show that the air and surface temperatures elevate due to the solar transmission heat through the STPV canopy, thus reducing deicing energy consumption significantly. The fire safety analysis also showed that the proposed system's top opening should be located near the tunnel entrance instead of the canopy entrance for better smoke exhaust during a fire.