The photovoltaic heat island effect in Tokyo: Morphological dependence and spatiotemporal dynamics of PV-induced urban warming

• Quantified spatial distribution of PVHI in Tokyo under two rooftop PV scenarios. • Residential neighborhoods consistently showed stronger PVHI than other areas in Tokyo. • PVHI intensity depends strongly on urban morphology, especially building height and street width. • Found consistent pattern of daytime warming and nighttime cooling across all seasons. • Diurnal thermal behavior of PV panels drives seasonal variability of PVHI. Rooftop photovoltaics (PV) play a central role in urban decarbonization, yet their unintended thermal impacts—known as the photovoltaic heat island (PVHI) effect—raise growing concerns. This study exposes the PVHI effect in Tokyo, revealing a significant trade-off between clean energy generation and urban microclimate management. Using a high-resolution urban canopy-building energy model, we provide the first quantitative analysis linking PVHI directly to urban morphology. Our simulations reveal a peak warming of 0.20°C on summer afternoons, a burden disproportionately borne by residential neighborhoods. By systematically quantifying the relationship between PVHI and urban morphology, we demonstrate that lower building heights and narrower street widths significantly intensify local warming. Furthermore, we identify the underlying mechanism: rooftop PV panels, due to their low thermal capacity, induce a pronounced diurnal cycle of daytime warming and nighttime cooling, which in turn shapes seasonal temperature impacts. These findings highlight a critical trade-off between clean energy deployment and thermal resilience, especially in densely built residential areas. This research provides a crucial framework for climate-sensitive urban planning, necessitating an integrated approach that balances decarbonization goals with the imperative to mitigate localized heat risks.