Evaluation of photovoltaic-green and other roofing systems by means of ReCiPe and multiple life cycle-based environmental indicators

The present study evaluates the environmental profile of a PV-green roof (PV panels over a soil/plant layer) and other roofing systems (PV-bitumen, PV-gravel, gravel, extensive green and intensive green). The analysis is based on multiple life-cycle impact assessment methodologies (ReCiPe, etc), several scenarios (for example with and without recycling) and it provides a deeper analysis as well as additional results to authors' previous investigation about PV-green roofs. The evaluation of the PV-green system (in terms of material manufacturing phase) shows that PV laminates (multi-Si) and steel components (joist, decking, balance of system) are responsible for the greatest part of the total footprint, based on GWP (global warming potential) and ReCiPe. Among the roofs which do not produce electricity, material manufacturing phase reveals that intensive green configuration has considerably higher impact in comparison with gravel and extensive green systems. Concerning PV roofs, PV-green configuration on a long-term basis (by considering material manufacturing, use phase, transportation and disposal), after a critical point, pays back its additional environmental impact (related with the “green layer”) and it becomes more eco-friendly than the other two PV roofs. Certainly, this is due to the benefits (cooling effect of evapotranspiration, etc) of the soil/plant layer which result in PV output increase. The above mentioned critical point is determined by means of ReCiPe payback time and greenhouse-gas payback time. Several environmental indicators are calculated and presented along with results from the literature. A critical discussion is also provided.