This paper presents a complete robust optimization framework to deal with a large range of uncertainties in optimization-based energy models. Robust formulations are proposed to address specific features of long- term energy models – such as multiplied uncertain parameters in the objective and many uncertainties in the constraints. Then, we introduce an original approach to make use of the obtained robust formulations for decision support and provide a real case study of a national energy system for validation. It is demonstrated that, by first ensuring feasibility and then evaluating cost-optimality, the proposed method offers solutions which are both reliable and cost-effective, while limiting the computational requirements.