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

Abstract

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.

The Combination of Building Greenery and Photovoltaic Energy Production—A Discussion of Challenges and Opportunities in Design

“…In consideration of the limed urban roof area, both technologies (BG and PV energy production) are often viewed as competitors [6], a combination of both technologies (BG and PV energy production) appears to be important when striving for a holistic design of contemporary buildings [33].…”

“…(Estimated) energy output/thermal behaviour: No information was given in the paper. The vision of the PV rooftop garden project was to add an extra benefit to the combination of roof greenery and PV panels by providing space for human interaction under the PV panels [33]. In this design approach, the roof is constructed as a (semi)-intensive garden with a pergola-like sub-construction holding the PV panels.…”

“…The influence of translucent PV panels on plants were investigated [33,[52][53][54][55]. A summary of the findings, a documentation of the design process and visualizations of potential applications on buildings were carried out by Sattler et al [33] The increased thermal comfort of this solution for users of the rooftop was investigated by Weixelbaumer et al [56,57] Type of GR: The vegetation layer of the rooftop garden is constructed as semi-extensive GR using 4 cm drainage layer (lava substrate), filter fleece and 16 cm of lightweight green roof substrate. Climbing plants, annuals, edible plants, perennials, herbs and grasses were planted.…”

“…Only a few publications [7,33,47,54,55] were investigating the development of specific plant species under the PV panels. Certainly, more research should be done in this sector for different climate zones.…”

“…The species can be selected regarding the needs of the users (low maintenance, food production, ornamental roof garden etc.) For the selection of the plants, it is important to be informed about the light distribution on the roof [33].…”