The spatio-temporal patterns of the existing rooftop photovoltaic (PV) production can provide valuable insights for the design of effective strategies for PV integration at large scale. In this work, we quantify the hourly production of existing rooftop PV installations by combining two large-scale methods, for detecting rooftop solar panels and for estimating their hourly PV generation, which are both applicable at the Swiss national scale. A validation against measured data of PV installations from 16 roofs in the Swiss Canton of Aargau shows that the existing PV area is detected accurately, while the hourly profiles overestimate the PV production, with higher errors in winter than in summer. These errors result in a mean overestimation of the annual PV production by 16%, assuming a triangular panel placement at low tilt (15 degrees) on flat roofs.