Photovoltaic-green roofs: An experimental evaluation of system performance

The research focused on the experimental evaluation of Photovoltaic (PV) - green roofs under Mediterranean climate summer conditions. Two autochthonous plants, Gazania rigens and Sedum clavatum, were selected for the PV-green systems while a PV-gravel configuration was used as the reference roof. The above mentioned roofing systems were developed and tested at the University of Lleida, in Spain. Research focused on electrical differential performances. In addition, thermal and irradiance analysis were also conducted. The results obtained for a sunny, five-day time period revealed an average increase of the maximum power output of the PVs (ranging from 1.29% to 3.33% depending on the plant), verifying the positive synergy between the PVs and the plants. Another positive effect of the plant/PV interaction was the fact that the PV-green systems showed considerably lower roof surface temperature in comparison with the PV-gravel configuration. Conclusively, the present work demonstrates the benefits of the PV-green roofs and fills the gap which exists in the literature in terms of the experimental evaluation of PV-green systems, especially under Mediterranean climatic conditions.