Solar radiation is the largest source of renewable energy and, at urban scale, photovoltaic (PV) is expected to contribute significantly to its exploitation through the use of building rooftops. Although single building installations are well studied, the potential benefices of diffused PV systems deployment at urban scale are less investigated, being, in fact, the estimation of cities solar energy potential challenging task due to the complexity of the urban morphology. In this study, we propose an innovative method to assess the solar energy potential at urban scale able to provide the PV potential for each single building rooftop within the city by means of high resolution 3D maps. The method is based on a detailed 3D city model, including buildings and trees, from high resolution LiDAR data. On the basis of that 3D model and taking advantage of a comprehensive set of suitable factors, properly defined, a high spatial resolution solar energy potential map, in the viable buildings’ rooftop area, is realized taking into account the characteristics of each single building rooftop, the rooftop obstructions on the , the influence of the urban context, and the spatial variability of selected reduction factors, including air pollution. As a case study the City of Portici (South Italy), characterized by a high urban density and a complex urban canopy, has been studied and a high resolution PV buildings’ rooftop potential map has been generated.