Extensive biodiverse green roofs in combination with solar energy (PV) - innovative practice in Switzerland

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Solar renewable energy and green roofs renewable already has a long history in the Basel City (Switzerland) (Switzerland). This experience, through design and modification is part of the Swiss contribution to the biosolar roof project.

Green roof Capital – Basel City

The city of Basel in Switzerland has the highest area of green roofs per capita in the world. The use of green roofs has been stimulated by a combination of financial incentives and building regulations. Building regulations have required the use of vegetation on roofs since their instigation in 2002 (bylaw). Initiatives aiming to increase the provision of green roofs in Basel were initially driven by energy-saving programs, and subsequently by biodiversity conservation.

Since then there are many roofs in city which have automatically the combined of solar energy and green roofs.

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Biodiversity and Energy – the driver

Reducing energy consumption of buildings and protection of biodiversity have been thekey motivators behind expanding green roof coverage in Basel. Initially, the municipality explored green roofs as an energy-saving measure for buildings. Green roofs were funded by the city over a two-year period in the mid-1990s to stimulate interest and awareness. Encouraged by the success of this project, funds were allocated for a study documenting the biodiversity benefits of green roofs and that they do act as ecological compensation areas. It is now recognized that green roofs also provide climate change adaptation functions through limiting surface water runoff and reducing temperature in urban areas.

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Biodiversity improvement

In a study of the ZHAW (Zurich university of applied sciences) it was proven that, in particular, the diversity in the beetles species can be increased by combining extensive green roofs with solar panels (PVC). They installation of panels can provide better and more diverse living conditions for insects. Why? Because there are more surfaces with shadow (complete and mid) and varying moisture retention properties in the substrate below and behind the panels. This means that there is better and varied conditions for vegetation and therefore greater species diversity of invertebrates and in particular pollinators.

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Energy Improvement

The study also confirmed that greening also has a positive effect on the the production of solar energy. The evapotranspiration of the plants provides cooling for the PV panels. This cooling is important for as it increase the efficiency of the panels in the hot season – spring and summer.