Energy and environmental impacts of buildings: the role of the biosolar roofs

Considering the prevailing demand for sustainable solutions to combat climate change and biodiversity loss in urban areas, the PROOF (Photovoltaic and greenROOF) collaborative project was initiated. The objective of the project was to evaluate the multi-scale performance of biosolar roofs, regarding energy consumption, CO2 emissions, and the various ecosystem services offered by green roofing solutions.

To this end, the performance of biosolar roofs at the building scale was compared with that of their alternatives: gravel and cool roofs. The evaluation of the seven configurations was conducted according to three criteria: energy consumption, carbon emissions and in-situ biodiversity support.

A dedicated tool has been developed to address the biosolar roofs' particularities in the context of the carbon emission assessment, employing the Life Cycle Assessment (LCA) approach. The ecosystem service of biodiversity support was assessed based on the HIBOU 2030 methodology, developed by the CSTB.

The results indicate that, when considered only one criterion, the performance of biosolar roofs is comparable to other configurations. For instance, about the carbon criteria at the building scale, the emissions from the configuration with a biosolar roof are equal or up to a maximum of 5% higher than those from other configurations. However, it is crucial to recognise that biosolar roofs offer a multifaceted functionality, encompassing not only the primary function of covering the building, but also secondary benefits such as local energy production, support for biodiversity, and enhanced rainwater management. In contrast, other configurations typically possess only one or two functions. Consequently, when evaluated using a multi-criteria approach, biosolar roofs are identified as a multifunctional device that merits promotion.