The “PV Rooftop Garden”: Providing Recreational Green Roofs and Renewable Energy as a Multifunctional System within One Surface Area

In urban areas, summer temperatures are continuously increasing, and cities are aiming at implementing measures to mitigate the urban heat island (UHI) effect. Reducing sealed surfaces and adding plants have been shown to be beneficial for urban microclimates. Green roofs are thus a viable alternative to standard roofs made out of materials that completely seal the top layer. However, roofs are, at the same time, also ideal for the integration of photovoltaics (PVs), as they are mostly unshaded. With both applications competing for the same surface area, solutions must be found that symbiotically combine the benefits of vegetation and renewable energy. Using an interdisciplinary study, various designs were developed for prototypical applications to integrate PV systems into rooftop gardens, with a specific focus on retrofitting flat roofs. The prototypes were analyzed and tested based on structural design aspects, suitable plant choices, and energy output. The results showed that the concurrent integration of PVs and green roofs into the same surface area can be achieved with lightweight construction, which is particularly suitable for existing buildings. The system can contribute to much-needed urban renewable energy generation, the mitigation of the UHI effect, and the provision of recreational spaces.