Impacts of Rooftop Photovoltaics on the Urban Thermal Microclimate: Metrological Investigations

Ambitious climate protection requires decentralized renewable energy production via building-related photovoltaics in cities. However, cities are also subject to the Urban Heat Island effect, which negatively impacts human health. In this context, the installation of PV modules in urban areas raises the question of how the energy-active building component affects its surrounding thermal microclimate. The topic is approached with a novel, twofold methodology: First, a horizontal ambient air temperature profile above a rooftop PV installation and the analysis of surface temperatures provide primal indications of the impacts of PV on the thermal microclimate. Secondly, establishing energy balances allows us to retrace the energy fluxes. The data required for the comparative analyses are gathered through metrological investigations of two rooftops with and without PVs in Munich, Germany. The results of the investigation show a daytime heating effect of photovoltaics on the ambient air temperature of up to +1.35 K and a nighttime cooling effect of up to −1.19 K. Cumulated daily, the daytime heating effect exceeds the impact of the nighttime cooling. The main driver of the heating and cooling is the additional convective heat transfer from the PV modules. However, the impacts of the PV modules are marginal and restricted to their direct surroundings.