Design models for the components of an energy system concept are used to extract the information relevant to the prediction of the cost and performance of the system. The information is directed towards seeking an optimal design point for the system and then redirected towards predicting its performance at off-design points. The design model of a heat exchanger is used as an example for information extraction. Few gas turbine power systems are considered for optimal design. The part-load operation of the optimized simple combined cycle is then computed. The methodology in more detail is referred to elsewhere.