Rooftop photovoltaic impacts on outdoor and indoor urban microclimate: Summer and winter simulations by local climate zones using LES

Rooftop photovoltaic (PV) systems are increasingly shaping urban environments, serving not only as sources of renewable energy but also altering the surface properties of cities. By modifying how rooftops store and release heat, they affect roof-level temperatures and, consequently, the surrounding indoor and outdoor microclimate. However, the overall impact of rooftop PV remains uncertain, with previous studies reporting conflicting findings depending on system design, building characteristics, weather conditions, and, importantly, the modeling approaches employed. Prior studies used simplified representations (e.g., effective-albedo methods), site-specific energy-balance models not coupled to the atmosphere, or mesoscale atmospheric models, which capture surface-atmosphere interactions but cannot resolve building-scale flows crucial for momentum and thermal exchange. In our previous work, we implemented a parametrization for building-applied PV into the large-eddy simulation (LES) model PALM and validated it against a five-month measurement campaign. The PV parametrization captures key physical processes, including radiative exchange, heat transfer, ventilation within the PV–roof gap, and material-specific properties. In this study, we apply PALM in building-resolving simulations to investigate impacts of area-wide rooftop PV on outdoor thermal comfort, indoor temperatures, and building energy demand. Simulations are conducted for summer and winter conditions across all built Local Climate Zones (LCZ1 - LCZ10), ensuring comparability and broader applicability. This study provides the first systematic microscale assessment of rooftop PV impacts using building-resolving LES. By disentangling the underlying heat transfer processes, it clarifies under which urban and climatic conditions rooftop PV may either exacerbate local heat stress or contribute to its mitigation. These findings offer actionable insights for climate-sensitive urban design and support more informed integration of PV systems into sustainable and resilient cities.