Regional energy self-sufficiency based on microgeneration from clean, local energy sources is essential and strategic for meeting growing electricity demand. In this context, initiatives driven by local governments are decisive in achieving such progress. This study proposes a methodology for sizing photovoltaic (PV) capacity at the parish level, which is the basic political–administrative unit in Ecuador. Rooftop-based microgeneration and self-supply are considered to entail minimal environmental impact while offering significant potential to meet the basic energy demands of buildings in the Andean equatorial climate. The results demonstrate that, using accessible tools such as drones, computer-aided design software, and Agisoft Metashape, and through low-labour processes, it is feasible to estimate the PV potential of buildings at the parish scale. A total of 1698 rooftops were surveyed, and after discarding those with precarious construction materials, the estimated solar potential was found to be between ten and twenty-three times higher than the electrical demand of the analysed parishes. The estimated annual generation potential reaches 28,101 MWh, compared to an annual demand of 1827 MWh for both parishes combined. The proposed process enables the incorporation of rooftop-based technological capacity, relying on a low-technology, affordable methodological approach and instruments for low-income parish governance offices, with low-density populated areas as the main novelty, providing clear information to both authorities and the local population.