Renewable energies are eco-friendly and sustainable. However, their development faces two critical issues: the uncontrollable generation variability, and the high levelized cost. These two issues impede the development of renewables substitution for a government from lacking of clearly argument of how to promote renewables substitution, and what is the role of traditional generation resources should play to back up the renewable energies in a target year. This study aims to depict the possibility of the concerned topic from the aspects of economy, security, and environment, taking a top-down viewpoint of policy making to address an energy supply problem, and proposes an Energy Supply-Mix Model by considering the complimentary and substitution possibilities between renewable and non-renewable energies, and also among the renewable energies. The solution provides an overall assessment of three aspects under the conditions of supply and demand balance, desired generation percentage of renewable energies, and also ensure no shortage in peak-hour demand. Parametric analysis on the carbon tax is particularly conducted for policy making reference. This study takes Taiwan as a case and performs the scenario analysis according to the recent energy policies. The results have shown that the proposed model can effectively support a decision body for policy formulation. (C) 2015 Elsevier Ltd. All rights reserved.