A robust optimal design method of energy supply systems under uncertain energy demands is revised so that it can be applied to systems with complex configurations and large numbers of periods for variations in energy demands. First, a robust optimal design problem is described by using the minimax regret criterion and considering the hierarchical relationship among design variables, energy demands, and operation variables, which is followed by a solution method. Especially, a novel solution method is proposed for efficiently evaluating an upper bound for the optimal value of the maximum regret. Then, a method of comparing two energy supply systems under uncertain energy demands is proposed by utilizing a part of the revised robust optimal design method. Finally, through a case study on a gas turbine cogeneration system for district energy supply, the validity and effectiveness of the revised optimal design method and features of the robust optimal design are clarified. In addition, the gas turbine cogeneration system is compared with a conventional energy supply system using the proposed comparison method. (C) 2014 Elsevier Ltd. All rights reserved.