Effects of clouds, aerosols and shadows on solar energy potential on urban rooftops using earth observation data and digital surface models

This study combines high-frequency Earth observation data (Copernicus Atmosphere Monitoring Service) and very-high-resolution digital surface models, to explore the effects of clouds and aerosols in conjunction with shadows on solar energy potential on urban rooftops. We focus on the assessment of two municipalities in the city of Athens (Greece). Besides quantifying the shadowing effect from the adjacent buildings and constructions, the previously scarcely considered effects of clouds and aerosols on the solar radiation availability on the rooftops and their inter-annual variability are investigated. Important results of this investigation include that the atmosphere and building shadows cause monthly 30–60 kWhm−2 of solar radiation loss on urban rooftops in Athens. The mean monthly cloud effect ranges from 5 % in summer to >30 % in winter; the mean aerosol effect has its peak of 8 % in August and <3 % in winter months; shadows account for 5 %–10 % of the solar radiation reduction in winter, but <5 % in other seasons. Compared to clean-sky conditions, the shadowing effect on radiation is suppressed when clouds or aerosols are present. All-sky shadowing effect on city-center rooftops on average stays stably <10 % during the ten-year span from 2012 to 2021, and mostly <5 % from April to October. The main contribution of our findings is the demonstration of using radiative transfer modeling in quantifying atmospheric and building shadowing effects on urban rooftop solar energy systems.