Innovation for Climate-Resilient Cities: Synergies Between Green Spaces and Solar Power
The “GreenPV” project at the Georg Simon Ohm University of Applied Sciences in Nuremberg is investigating synergies between green facades and photovoltaics.
Green facades play a key role in regulating the urban climate in particular, thanks to adiabatic cooling processes. Decentralized, renewable energy generation is another important component in the ongoing transformation of the building stock toward climate neutrality. However, high temperatures can reduce the efficiency of crystalline photovoltaic (PV) modules. To ensure an efficient energy yield even during the summer months, GreenPV is investigating the potential for synergies between greening and PV.
Until now, these two facade systems have been used separately in the field of energy-efficient buildings. By combining green roof technologies with photovoltaics, the project aims to develop knowledge for the implementation of harmonious overall designs. While a combination has already been successfully tested on solar green roofs, the specific influence of plants on solar energy generation in vertical applications has largely been overlooked.
Based on preliminary work (see EnOB: GreenFaBS), measurements were conducted in the summers of 2022 and 2023 using three vegetation systems (wall-mounted vegetation, a mixed system with a horizontal growth plane, and climbing plants). In addition, the distance between the PV modules and the plant level was varied: a shorter variant 1 (33 cm) and a longer variant 2 (52 cm); in all cases, the PV modules were initially mounted vertically, parallel to the facade cladding (angle of incidence: 0°).
The individual greening systems result in a reduction in air temperatures (max. 1.6 K) between the photovoltaic modules and the plants compared to the unplanted reference case. It is evident that the two wall-mounted systems achieve a slightly greater reduction than the climbing plant. Surface temperatures on the back of the modules decrease by up to 4.0 K due to the cooler ambient conditions. Nevertheless, only minor increases in PV yield of up to approximately 0.5% were observed. However, it is confirmed that the PV modules reduce the heat stress on the plants, as virtually no negative effects on growth were observed in the experimental setups. Furthermore, it appears that the greenery also results in a slight reduction (up to 1.1 K) in perceived room temperatures.
However, when it comes to combining greenery and photovoltaics in the facade, another aspect is of central importance: the vertical evaporation rate of the plants, which has an effect on the urban environment. With a dense arrangement of PV modules parallel to the wall, this capacity is significantly reduced. Therefore, test setups were conducted with two different tilt angles for the PV modules (30° and 7.5°; hybrid system). For the measurements with the low-angle variant, an increase in yield of approximately 11% was observed. In the 30° variant, self-shading led to yield losses. However, an optimized configuration (module spacing and/or tilt) is expected to result in significant yield increases compared to a vertical installation.
