Abstract:
Green roofs are sustainable infrastructures used widely to reduce stormwater runoff, decrease urban heat island, improve air quality, and increase the aesthetic value of the urban environment. The hypothesis tested in this work is that the performance of green roofs can be enhanced if solar power panels are placed on top of the vegetated green roofs to provide shading and lower surface temperature and sun exposure. A research experiment was designed at the George Mason University campus in Fairfax, VA, to assess and quantify the impact of different rooftop configurations on stormwater with and without the presence of solar panels. Roof configurations included vegetated roofs, bare soil pallets, and experimental controls, i.e., traditional flat surfaces used for both residential and commercial building. Four water quality indicators – temperature, conductivity, pH, and Total Dissolved Solids (TDS) – were sampled during mid-May – mid-November 2017. Vegetated green roofs were able to reduce stormwater runoff when compared to any conventional roof and bare soil surfaces, thanks to leaf interception and root uptake. In terms of stormwater quality, bare soil and vegetated roofs showed a small decrease in stormwater temperature and a large increase in conductivity and TDS concentration, due to the fact that stormwater carries nutrients, metals, and suspended solids present in the soil through infiltration. However, vegetated green roofs were shown to decrease both conductivity and TDS with respect to the bare soil pallets and the deeper the soil substrate layer in the green roof, the larger improvement was observed. Moreover, vegetated roofs equipped with solar panels were able to overall reduce both conductivity and TDS. Thus, equipping vegetated roofs with solar panels has the potential to improve stormwater quality.
