The assessment of the solar potential in urban areas relies on a geometrical model that can be defined at different levels of detail (LOD). In this work we compare the solar irradiation simulated on the surfaces of four sample buildings, which were modeled at three different LODs as defined by the CityGML standard. Results indicate a general overestimation of the solar irradiation when using LOD1 and LOD2 models, if we consider LOD3 (i.e. the finer model) as the ground truth. However, results show also that the error varies significantly between the analyzed buildings and the considered minimum irradiation thresholds and, if we take into account only rooftops, the effect of added elements might result either in an overestimation or an underestimation of the annual total irradiation. We conclude by discussing how such findings should influence current practices in the assessment of the solar potential at the urban scale.