In the case of building surfaces, the installation of green roofs or green facades can be used to reduce the temperature of the environment and the building. In addition, introducing photovoltaic energy production will help to reduce CO₂ emissions. Both approaches (building greenery and photovoltaic energy production) compete, as both of them are located on the exterior of buildings. This paper aims to give an overview of solutions for the combination of building greenery (BG) systems and photovoltaic (PV) panels. Planning principles for different applications are outlined in a guideline for planning a sustainable surface on contemporary buildings. A comprehensive literature review was done. Identified solutions of combinations were systematically analysed and discussed in comparison with additional relevant literature. The main findings of this paper were: (A) BG and PV systems with low sub-construction heights require shallow substrates/low growing plants, whereas in the case of the combination of (a semi)-intensive GR system, a distance of a minimum 60 cm between the substrate surface and lower panel edge is recommended; (B) The cooling effect of the greenery depends on the distance between the PV and the air velocity; (C) if the substrate is dry, there is no evapotranspiration and therefore no cooling effect; (D) A spectrum of different PV systems, sub-constructions, and plants for the combination of BG and PV is necessary and suitable for different applications shown within the publication.

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.

Vertical greenery systems (VGS) are promoted as a nature-based solution to mitigate the urban heat island effect. In order to ensure the long-term provision of this function, sufficiently available irrigation water is the key element. Currently, potable water is one of the main resources for irrigation of VGS. While rainwater is often mentioned as an alternative, only a few studies investigate the actual application of rainwater for irrigation. In this study a conceptual model is developed to present the processes and influencing factors for a holistic investigation of rainwater use for irrigation. In this model, five sub-modules are identified: the atmospheric, hydraulic, quality, rainwater harvesting and VGS sub-module. The conceptual model depicts which processes and influencing factors are involved in the water demand of VGS. Thus, the conceptual model supports a holistic understanding of the interrelations between the identified sub-modules and their relevance for VGS irrigation with harvested rainwater. The results of this study support the implementation of rainwater harvesting as a sustainable resource for VGS irrigation.