What are BioSolar roofs?

Green roofs and photovoltaic systems are increasingly combined on flat roofs, as the two technologies offer considerable synergy benefits. The low surface temperature of the green roof reduces the ambient temperature around the solar panels, which helps increase their efficiency. Roof systems that combine photovoltaics and green roofs within the same space have become known as Biosolar roofs.

Biosolar roofs roofs provide a distinct advantage because they allow the roof space to serve a dual purpose. In the past, roof areas had to remain separate, which restricted the amount of green roof and photovoltaic provision that could be achieved. BioSolar roof systems typically do not require mechanical fixing to the roof. Instead, the green roof build-up provides the necessary ballast weight, or superimposed load, to resist wind suction loads. This avoids the need for hundreds of roof penetrations, reducing the potential for leaks through the roofing membrane.

Careful planning needs to be considered when designing a Biosolar roof.

Vegetation must not shade the solar panels. At the same time, enough light and water must reach the underside of the panels to support plant growth. The distance between the lower edge of the panel and the green roof surface needs particular attention. For extensive green roofs, this minimum distance should be 200mm.

The correct superimposed load also needs to be calculated. This calculation should consider the dry weight of the system build-up rather than the saturated weight. However, the saturated weight should still be considered when assessing the load-bearing capacity of the roof construction.

Ballasted biosolar systems should only be used on roofs with an inclination of up to 5°.