High efficiency, environmental friendliness, low operation and maintenance costs, and the lowest possible impact on the environment are some of the requirements of sustainable energy production. In the selection of new power generation systems, a number of steps have to be taken into account in order to meet these requirements. Here, the first law analysis has been implemented and investigated, followed by a combination of the first and second law analyses (exergy analysis), and thermoeconomics. Finally, an exergetic life cycle assessment (ELCA) has been carried out for two different power cycles to show how the irreversibility of a process is coupled to environmental issues. The study involves two cycles, a two-pressure level combined cycle and a humid cycle, to demonstrate the usefulness of the three methods mentioned above in a pre-purchase process. The main goal of this study is to point out the advantages and the difficulties related to the implementation of each and every method, and to identify the target groups that can gain knowledge and information by using these methods. Since the operators of power plants often do not have access to detailed information about component materials, characteristics, etc., of the power cycle, assumptions have to be made when comparing different cycle configurations with each other. These limited types of data and information have also been used here to create a plausible scenario of how different pre-purchase methods can differ from each other.