Photovoltaic and green ROOF – PROOF

The PROOF project (Photovoltaic and Green ROOF) aims to compare roofing systems and their energy-environment impacts and performance with contrasting urban development scenarios, linked to the associated territorial challenges. It is particularly interesting to study an innovative combined system, combining an extensive green roof and a photovoltaic panel. To address this problem, PROOF brings together a consortium composed of Cerema, LEMTA, LMOPS, LSE, CSTB and Efficacity. It bases its scientific approach on four hypotheses that it intends to verify during the project: 1) Incident solar energy in summer dissipated by a green roof mainly in the form of latent heat fluxes, creates a decrease in the localized air temperature providing conditions favourable to the increase in electrical efficiency of a photovoltaic panel; 2) an extensive green roof with a structure capable of storing rainwater, promotes evapotranspiration flows and can therefore further improve the panel's efficiency; 3) at the building level, we assume that the overall energy balance (production/energy consumption per use + grey energy) is more advantageous for a combined system than for a standard bare or green flat roof; 4) compared to a conventional roof configuration, a combined system provides additional ecosystem services that can be assessed and valued at the neighbourhood level. To address these different hypotheses, PROOF is divided into four scientific tasks. The first is to provide all the data and characterizations needed for modelling heat exchange between the panel and the green roof, as well as for modelling heat transfer in the panel and its impact on performance. This task also provides comparison data for other roof configurations (standard, cool-roof and extensive green roof with rainwater storage). Both models are studied in detail in Task 2: contribution of radiative, convective and latent heat fluxes; evaluation of the temperature at the rear of the panel on the delivered power. The transition from system scale to building scale is addressed by Task 3, which assesses the thermal performance of different configurations at the building scale, but also the energy-environmental and ecological performance at both scales (devices and building) under different climatic conditions. The aim is to highlight the savings on consumption at the handset scale, improved efficiency, increased service life and at the building scale. Finally, Task 4 seeks to identify and evaluate the impacts and benefits associated with the types of devices tested, which are to be compared with the local challenges of the neighbourhoods, settings and urban areas in which they will be located.