Renewable energy is a remarkable developing potential in Vietnam, in which solar photovoltaic (PV) energy is rapidly invested by investors in and out of the country in recent years. Specially, the solar radiation in Southern area is more tremendous comparing with other parts in Vietnam. Developing the PV energy is very essential and results to national economic, social and technical benefits. However, the state of uncontrollable developing rooftop PV in residential households and entrepreneurs affects national power system in the area. In this study, the potentials of rooftop PV energy in Hau Giang province – being located in Southern part and occupying about 0.5% of total area in Vietnam (1,608km2) - is evaluated by statistical methods, analysist methods and online map-based applications. As a results, total rooftop suitable area and the average peak capacity PV power potential in Hau Giang province are approximately 15.79km2 and 1,882.3MW/year, respectively. Besides, power system steady state stability is analysed via commercial software ETAP when connecting rooftop PV power station in Hau Giang province and a study case is proposed to verify economic and social effects of a pilot project.