EESS talk on "Evaluating the performance of vegetated and reflective roofs to cool cities and increase solar panel yield"


Event details

Date and time 27.04.2021 12:1513:00  
Place and room
Speaker Dr Lauren Cook, PATT and Group leader, Dept. Urban Water Management, EAWAG
Category Conferences - Seminars
Due to their ability to reduce the surface temperature of rooftops, sustainable roofing configurations, such as vegetated and reflective roofs, are a promising way to mitigate urban heat and increase urban resilience. More recently, due to their cooling effect, these sustainable rooftops are also gaining attention for their ability to increase solar panel yield. Photovoltaic (PV) panel efficiency is reduced as temperatures rise, and cooler roofs can hinder heat exchanged with the PV panel on hot days. While evidence is growing that these integrated systems can increase solar energy generation, especially in warmer climates, they are rarely selected and designed with this objective in mind. It remains unclear whether these systems are effective in cooler climates, like Switzerland, and whether targeted design practices could improve their performance to meet this and other objectives, including heat mitigation. This study quantifies the ability of sustainable green and reflective roofs to reduce temperatures and increase solar panel yield in cooler climates, compared to traditional black and gravel roofs. This study also explores how the design properties of the roof (e.g., vegetation or membrane type) could be altered to better achieve both of these goals.

Simulated results for a rooftop near Zurich, Switzerland, show that peak roof temperatures are, on average, 10 to 16 deg C cooler on green and white roofs, respectively, than gravel roofs, leading to an increase in annual (2019) PV electricity yield from 1.5 % to 4%, depending on the rooftop design characteristics. Experimental results from a different study site show that a green roof planted with Silene Vulgaris (a plant with high transpiration) can reduce air temperatures and increase PV panel yield more than other green roofs with different vegetation (e.g., Sedum album) and nearly as much as a light colored, sponge roof. Overall, reflective roofs are generally more effective than green roofs at mitigating urban temperatures and increasing PV yield; however, vegetated roofs provide additional benefits, such as stormwater attenuation and habitat for threatened species, that are important to recognize when considering different sustainable roofing configurations. Future research will use decision analysis to evaluate rooftop choices with respect to cost and multiple co-benefits, including using vegetation to increase habitat for improved biodiversity.

Short biography:
Dr. Lauren Cook is a group leader at Swiss Federal Institute of Aquatic Science and Technology (Eawag) in the Department of Urban Water Management. With her background in hydrologic engineering, energy, and climate impacts modeling, her research focuses on quantitative approaches for the design of multifunctional blue-green stormwater infrastructure to create more sustainable and resilient cities. She received her Ph.D. in 2018 in Department of Civil and Environmental Engineering at Carnegie Mellon University (Pittsburgh, USA) and her B.S. in Civil & Environmental Engineering in 2010 from the University of Maryland, College Park (USA).

Practical information

  • General public
  • Free
  • This event is internal


  • EESS - IIE



rooftop PV heat mitigation green roofs reflective roofs energy balance