The 4th Local Stakeholder Workshop in Bolzano and Merano

Solar green roofs are innovative solutions for the sustainable development of urbanised areas as they combine rainwater management, thermal mitigation and renaturalisation with renewable energy without further land consumption. This topic was the focus of the JUSTNature fourth local stakeholder workshop, which was held on the 12th December 2023 at Eurac Research headquarters in Bozen and brought together the cities of Merano and Bolzano.

The workshop was open to experts from the sector and local administrators, to discuss the technical and strategic aspects related photovoltaics and green solutions.

Several voices from the administrations remarked that South Tyrol can be an open-air laboratory for the experimentation of innovative technologies such as photovoltaic green roofs, capable of combining the preservation of greenery and biodiversity with the production of renewable energy, promoting a new futuristic and necessary vision of a green city for the Province's cities. However, even though photovoltaic green roofs are technologies that have been in the field for almost two decades, adoption in the province is minimal. Requests for installation on roofs (especially on barns in peri-urban and peripheral areas) prefer photovoltaic systems to green roofs, due to a higher incentive for the former than for the latter. Integration between the two is hindered by technical barriers (clear indication of structural aspects), economic barriers (companies building integrated systems), cultural barriers (lack of knowledge of integrated solutions and preference for one or the other technology) and political barriers (lack of clear legislation on the matter).

The Municipalities of Bozen/Bolzano and the Municipality of Meran/Merano are striving to give more space to photovoltaic green roofs within their municipal building regulations (through instruments such as the RIE in Bozen/Bolzano and the Ecological Functionality Index in Meran/Merano), including them as measures to reduce the impact on soil and greenery in the construction or renovation of buildings, and to adapt buildings to the effects of urban changes such as summer heat waves and loss of biodiversity in cities.

Key insights from speakers include the eighteen years of experiments conducted by Helga Salchegger at the Laimburg Research Centre. Her experiments have shown the positive effect on biodiversity of designing green roofs that explicitly take into account the creation of species habitats on roofs and the use of new varieties of plant species beyond the classic sedum to allow for greater ecological functionality of roofs.

Interesting insights came from the analysis carried out by ENEA with the Municipality of Bolzano on several buildings in the industrial area, using Sentinel 2 satellite data to measure the effects of green roofs on heat islands and the area's microclimate. The benefits of photovoltaic green roofs could be helpful especially in large industrial areas for the huge energy requests of industries.

The experiences of Susanne Formanek of GRÜNSTATTGRAU emphasized the importance of the multifunctionality of surfaces and roofs, which will no longer only be 'solar' or 'green' but also 'blue': capable of retaining and managing water and with great attention to biodiversity and climate adaptation of buildings. GRÜNSTATTGRAU also recently studied a green solar pergola in the INFINITE project.

Multifunctionality is part of a broader discourse on how we intend to live in cities in the future, how we intend to create a quality of life, not only based on the exploitation of surfaces for energy production but a vision based on green, on biodiversity, on sustainability, for the current and future generations.

From a political point of view, for the promotion of photovoltaic green roofs the importance of developing a strategy that is in line/integrated with provincial strategies such as, for example, KlimaPlan 2040 is emphasized. Integration with existing certifications (such as Casa Cima and REI) is suggested as an opportunity.

From a social/economic point of view, there is a fear of the high costs of a photovoltaic green roof, both for installation and maintenance. When thinking about renovating/constructing a building, it is most obvious that the photovoltaic roof costs money but brings savings (in terms of utility bills), as well as being heavily financed. However, there is a lack of quantification of the benefits of green roofs: this lack of stakeholder awareness of the benefits of green roofs is one of the main barriers to their adoption. Being able to easily calculate the benefits of solar and green roofing with apps even for non-experts could be an opportunity. In addition, these technologies require new integrated skills (between solar and green) that can generate new professional opportunities and attract qualified professionals to the province.

In addition to the stakeholders' lack of awareness of the benefits, there is also a knowledge gap from a technical point of view and in terms of construction methods (substrate height, choice of green roof substrate, structural aspects). The balance between photovoltaics and green roofs depends on proper design: for example, if you choose a type of vegetation that grows too high, you risk reducing the performance of the panels. This is why it will be important to build up professional skills/qualifications in the province so that the design can be integrated.

From an environmental point of view, the choice of plants and substrate was discussed: while it may be possible to favor substrates from local materials, it is more difficult to choose native plants because they do not always present the most suitable characteristics for the green roof. Furthermore, one must consider that in the cities of South Tyrol (Merano, Bolzano), there is now a strong presence of non-native plants, so choosing local plants would not bring any added value.

From an environmental/economic point of view, the green roof could also be attractive for tourism: for example, imagine a picture of a South Tyrolean village with its roofs covered in vegetation.

It was emphasised by several participants that utility should be the guiding principle: the photovoltaic green roof should not be imposed by law, it should bring benefits to the user (and the user should be aware of the benefits).