Urban photovoltaics reshape radiative–convective fluxes and cooling energy demand in cities

Abstract

The rapid urbanization and transition to renewable energy are driving the adoption of rooftop photovoltaic solar panels (RPVSPs) to meet local energy demands. While their potential for clean energy generation is well-recognized, their broader impacts on urban microclimates, building energy consumption, and system performance remain poorly understood. This study examines the effects of RPVSPs on urban temperatures, energy balances, and cooling demand in Lyon, France, using high-resolution simulations with the weather research and forecasting (WRF) model. Results show that citywide installation of RPVSPs increase daytime temperatures by up to 0.72 °C, primarily because RPVSPs have a lower albedo compared to conventional rooftop surfaces, which leads to increased solar heat absorption and enhanced thermal convection between the panels and the underlying roof surfaces. This elevates the net sensible heat flux to the urban atmosphere during the daytime. Conversely, the nocturnal cooling of up to −0.42 °C results from radiative heat losses facilitated by the air gap and reduced thermal storage in RPVSPs covered roofs, enabling more efficient surface cooling after sunset. This dual thermal behavior reflects the RPVSPs influence on altering both the radiative and convective energy fluxes at the urban surface. While these effects may not exceed the cooling capacity of dedicated reflective or radiative cooling materials, the innovation in our study lies in quantifying the net thermal impact of real-world RPVSPs deployment at an urban scale. This dimension remains inadequately addressed in existing literature for temperate cities, especially in terms of balancing energy production with local microclimatic alterations. Additionally, RPVSPs reduce roof surface temperatures, cutting daytime air conditioning (AC) demand by nearly 5 %, particularly in areas with high roof-to-surface ratios. Immediate RPVSPs utilization achieved 100 % at 25 % RPVSPs coverage, offsetting 26.8 % of AC demand. At 60 % RPVSPs coverage, utilization dropped to 91.2 % with a 59.9 % AC offset, but storage enabled 100 % utilization and a 50.1 % offset. At full (100 % RPVSPs) coverage, immediate utilization declined to 64.3 % with a 73.0 % AC offset, while storage restored 100 % utilization, achieving an 85.9 % AC offset. High-resolution simulations reveal that RPVSPs simultaneously alter urban radiative–convective fluxes and cooling energy demand, highlighting their dual role in shaping city climate and energy resilience. Such strategies are vital for creating sustainable, energy-efficient urban environments that optimize renewable energy use while ensuring thermal comfort and resilience.