Consolidating exergoeconomic and exergoenvironmental analyses using the emergy concept for better understanding energy conversion systems

This paper aims at reformulating exergoeconomic and exergoenvironmental analyses using the emergy concept for a better understanding of the sustainable level of energy systems in the biophysical context. The proposed approaches substitute the solar emergy joule (sej) for the monetary term and the environmental impact score in the conventional exergoeconomic and exergoenvironmental analyses, respectively, to harmonize the dimension and scale of their outputs. This improves understanding and interpretations of the results obtained from these analyses. In both approaches, the emergy value is interfaced with exergy analysis in order to establish emergy-based exergoeconomic and exergoenvironmental balances for components of a given energy conversion system. The specific exergy costing (SPECO) methodology is then used to determine the solar emergy joule for each stream of the system. As a case study, a gas turbine-based cogeneration system is analyzed using the proposed methodologies. The results show that emergy-based exergoeconomic and exergoenvironmental analyses can be practical and powerful tools for appraising the long-term sustainability of energy systems compared with monetary- and life cycle assessment (LCA)-based exergetic approaches. Overall, the proposed emergy-based exergetic approaches are suggested as complements to available exergy-based techniques to help understand better and link thermodynamic, financial, and ecological aspects of energy systems.