Climate change and energy security are forcing Hong Kong to shift from a fossil fuel-based to a clean and low-carbon energy structure. In this article, a simulation model for Hong Kong's energy system is developed to examine the present energy structure and analyse alternative future sustainable energy strategies. First, a reference model is established and validated based on year 2009 data. Secondly, three scenarios are modelled. The BAU (business-as-usual) scenario for Hong Kong's energy system in 2020 is presented and simulated. To address the energy security and environmental sustainability challenges posed by the BAU outcomes, two alternative scenarios are then studied. The first alternative is a fuel mix for 2020 proposed by the government which is characterized by importing more nuclear power from the mainland. As a result of the Fukushima nuclear incident, however, this proposal has been held in abeyance. Therefore, a second alternative for Hong Kong in 2020 is proposed in this study, using more RE (renewable energy) to replace nuclear power. The results show that both the governmentally proposed scenario and the RE scenario can achieve the carbon reduction target. However, the RE scenario would be much better than the government scenario in terms of environmental, social benefits and long-term sustainability. (C) 2014 Elsevier Ltd. All rights reserved.