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Abstract: Solar photovoltaic (PV) technology is expected as one of the ideal renewable energy resources which can be used in large scale in Hong Kong. This paper presents an in-depth investigation into the development potential of rooftop PV system in Hong Kong and its environmental benefits as well. The potential installation capacity of rooftop PV systems is estimated to be 5.97GW p , and the annual potential energy output is predicted to be 5981GWh accordingly. The annual energy yield can account for 14.2% of the total electricity used in Hong Kong in 2011. In addition, about 3,732,000t of greenhouse gas (GHG) emissions could be avoided yearly by the replacement of the equivalent local electricity mix. For environmental benefits, the investigation results showed that the energy payback time (EPBT) and the GHG emission payback time (GPBT) of different types of rooftop PV systems in Hong Kong ranged from 1.9 to 3.0 and 1.4 to 2.1 years, respectively, both of which are far less than the systems' lifespan of 30 years. The energy yield ratio (EYR) ranged from 10.0 to 15.8, which indicates that the rooftop PV systems could generate at least 10 times the energy requirement during the system's lifetime. Although the current PV system installation cost is relatively high in Hong Kong, PV electricity is expected to fully compete with traditional electricity modes in the near future if appropriate subsidies are provided by the local government, carbon credits benefits are considered and installation cost can be further reduced. Thus, more proactive energy policies and aggressive development targets for PV technology should be set by the government. The findings presented in this paper are expected to provide a theoretical basis for local policy makers to set reasonable renewable energy policies, development targets as well as subsidies for PV technology in Hong Kong. [Copyright &y& Elsevier]