An energy system as a complex system requires special methodology for evaluation.Because the complexity of the system is closely related to a multidimensional space with different scales, the methodology has to bear a multicriteria procedure to evaluate the energy system.The method for multicriteria evaluation and assessment of an energy system has proved to be a promising tool in order to determine the quality of the energy system.Even though it was shown that there are some deficiencies in the method, it was a new route in the tracing of future analysis of a complex system.Since the energy system is a good example to identify the potential sustainability development, it opens up a new field of research for those willing to make the effort to further understand the methods of evaluating complex systems.In demonstrating the examples of applying the multicriteria in evaluating potential options of energy systems, it is proved that evaluating an energy system as a complex system means engaging in sustainable development research with an associate uncertainty, suggesting that that the research should aim for general principles and guiding questions for new investigation.Sustainability comprises a complex system approach in evaluating the state of the energy system.By its definition, sustainability includes the definition of quality merits without compromising different aspects of the system's complexity [1,2].It is of paramount importance for any energy system as a complex system to quantify elements of complexity, taking into consideration various degrees of complexity.As regards complexity elements of an energy system, it can be codified as a specific structure reflecting different characteristics of the system [3,4].The complexity elements of the system should describe the interaction of internal parameters of the system and the system interaction with the different aspects of the socioeconomic environment of the ecosystem.Adopting an energy system to its surroundings leads to physical, social, and environmental interaction between the system and its environment.If there are a number of energy systems to be compared, taking into consideration the potential behavior of an individual system in the same environment, there must be a potential option that will give quantified quality priority among the systems under consideration.In order to define quality, which will be used as the