The international community directs significant funding towards Pacific Small Island Developing States (PSIDS) for climate change allowing ambitious target setting. The Nationally Determined Contribution (NDC) of Fiji targets 81% of renewable energy share in grid electricity supply by 2020 and 100% by 2030. A model is developed to determine possible energy transitions to achieve those targets. The model uses installed capacities, capacity factors and electricity generated for each technology and calculates direct CO2 emissions, the Global Warming Potential and the Levelised Cost of Electricity. Eight energy mixes were assessed for electricity supply adequacy and the ability to achieve the NDC. The results demonstrate few realistic energy future options; a sole focus just on renewable energy generation is unlikely to be successful. Specifically, meeting the 2020 and 2030 NDC targets would require the installation of significant new renewable energy capacity accompanied by phasing out of fossil fuel plants, addition of baseload technology (e.g. geothermal, Ocean Thermal Energy Conversion), technological improvements (e.g. capacity factor) and minimizing electricity demand through energy savings and efficiency. All those determinants mean that there is a vital need for improved energy modelling and strategic planning, if NDCs are to be achieved in Fiji and other PSIDS.