Cities are facing two challenges in view of the climate crisis. On the one hand, there is an increasing risk that urban centres will become veritable heat islands. On the other hand, they have to cope with the energy transition with a different property ownership structure than in the countryside.
In addition, with longer and longer dry periods, particulate matter pollution increases and biodiversity decreases drastically, especially with regard to insects.
Solar yield increases, ambient temperature decreases
To solve these problems, the NRW consumer advice centre advises green roofs in combination with solar systems. In this way, property owners no longer have to decide on a solution for just one of the many challenges, but can tackle everything in combination and actually benefit.
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This is because the green roof provides cooling for the solar modules. This not only prevents the area around the modules from heating up during the day - at night, the modules with their large glass surfaces provide more cooling for the cities anyway. It also increases the solar yield because the modules are cooled.
Consider the statics
However, the statics of the roof must also be taken into account. This applies both without and with a solar system. It is true that the photovoltaic generator then stands freely on the roof and the substrate of the green roof also serves as ballast, so that the systems can be built with optimised weight.
But you have to reckon with 80 to 180 kilograms of weight per square metre for a green roof when wet. Add another 25 kilograms per square metre for the solar system. If you do not know the load-bearing capacity of your roof, you should consult a structural engineer when planning a solar green roof, consumer protection experts advise.
Choose a high enough mounting system
Property owners should also make sure that the mounting system is high enough so that the plants under the modules get enough light to grow. In addition, a larger distance between the roof surface and the solar modules prevents the plants from shading the panels.
Special subsidies for solar green roofs
Consumer advocates also point to special subsidies that are available for combining a green roof with a solar system. Many cities and municipalities subsidise such solutions over and above the EEG. In addition, the German KfW-Bank offers low-interest loans for the construction of solar green roofs. "When installing a solar green roof, you should coordinate one specialist company for solar technology and one for green roofs, who must work hand in hand," advise the consumer protectors. (su/mfo)
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