Optimising solar green roofs
Solar green roofs utilise the roof in multiple ways. They are a combination of photovoltaics (PV) and green roofs. This has several advantages: for the energy transition, rainwater management and the preservation of biodiversity, among others. What needs to be considered when planning and installing a solar green roof? And what are the pitfalls?
A 4-page brochure from the Bundesverband GebäudeGrün e.V. (BuGG) gives you important tips for getting started:
Background knowledge
In order to achieve the climate targets and ensure security of supply, it is essential not to place the urgently needed roof areas in competition with each other, but to utilise them multiple times wherever possible. Solar green roofs (combination of photovoltaics (PV) and green roofs) are a tried-and-tested form of multiple utilisation and represent a holistic approach to energy transition, climate and environmental protection.
(Solar) green roofs utilise the roof surface in several ways. They are an established technology that has been used in various forms for decades. Dual utilisation has potential.
Multiple use of roof surfaces - but what about politics?
The coalition agreement of the German government between the SPD, Bündnis 90/Die Grünen and FDP and the opening statement announce a solar obligation for new commercial roofs and a standardised use for residential buildings. This calls into question green roofs as an option for climate adaptation (heat and flood protection), preservation of biodiversity and conservation of resources (protection of the roof cladding from damage) that is already in use today and is mandatory in many cities.
Check the funding opportunities for green roofs and solar green roofs: at KfW and in your city/municipality.
Advantages of solar green roofs
There are numerous advantages and synergy effects in favour of solar green roofs on suitable flat roofs.
- Heat protection for more efficiency and a better quality of life
Green solar roofs heat up less than roofs on which only photovoltaic modules are installed. Among other things, this leads to a higher efficiency of the solar cells. In addition, solar green roofs lower or cool the ambient temperature, bind dust, improve the microclimate and provide better sound insulation. This significantly improves the quality of life for residents, especially during heatwaves.
- Insulation of the building
A solar green roof acts like a natural air conditioning and thermal insulation system. The need for air conditioning and heating in the building is reduced and energy can be saved.
- Conserving resources by protecting the roof waterproofing
With solar green roofs, the installed green roof structure serves as a ballast for the wind suction protection of the PV system. Roof penetrations or other interventions in the roof waterproofing and building fabric can then be omitted. The green roof also protects the roof from UV radiation and mechanical damage.
- Low repair and renovation costs
Compared to roofs with PV systems without green roofs, the susceptibility to repair and renovation is significantly lower. According to an online survey by the Central Association of the German Roofing Trade and the Federal Association of Green Buildings, solar green roofs only require major repairs after more than 20 years. In comparison: PV roofs are already due for repairs after 10 - 15 years. In addition, repairing a PV roof is very time-consuming and cost-intensive.
- Protection against flooding and relief for public drainage systems
Solar green roofs store rainwater, delay water run-off and help to protect against high peak flows, particularly in the event of increasing heavy rainfall. Green roofs store at least 40 - 50 % of the annual precipitation. For this reason, green roofs on flat roofs are already prescribed in the building regulations in many cities.
- Saving space
If the local authority's discharge restrictions for rainwater runoff are not complied with via a green roof, other solutions such as rainwater retention basins or cisterns must be used. These require additional space, which is expensive in times of rising land prices. As green roofs can also be counted as a mitigation measure in the impact on nature, compensation areas are saved.
- Protecting and increasing species diversity (biodiversity)
Green roofs have a positive effect on biodiversity and help to reduce the decline in flower-pollinating insects. Green roofs are an important habitat for plants and animals. The solar system provides different light/shade and moisture conditions. The resulting varied site conditions also promote the diversity of flora and fauna.
Conclusion
(Solar) green roofs make multiple use of the roof surface. They are an established technology that has been used in various forms for decades. Dual use has potential. Check the possibilities: Over 100 cities (> 20,000 inhabitants) have already set up their own funding programs for green roofs. Cities such as Hamburg, Freiburg and Hanover even specifically promote solar green roofs. KfW also supports green roofs in its efficiency promotion programs. German companies are among the global market leaders, install tried-and-tested systems and are constantly working on their further development.
Further information:
This knowledge was donated by:
Dr. Gunter Mann gunter.mann@bugg.de
info@bugg.de
www.gebaeudegruen.info