A new multi-objective optimization model for an integrated energy system based on life-cycle composite technical, economic and environmental indices

Integrated energy systems offer higher energy, environmental, and economic benefits than conventional separate systems. To comprehensively assess the performance of the integrated energy systems, applying life cycle assessment methods, the life-cycle primary energy saving ratio, renewable energy supply ratio, and electricity supply ratio are aggregated into a composite technical index, the life-cycle carbon dioxide emissions reduction ratio and life-cycle sulfur dioxide emissions reduction ratio are aggregated into a composite environmental index, and the life-cycle annual total costs and life-cycle annual costs saving ratio are aggregated into a composite economic index to fully assess the economic, technical, and environmental performances of the system. A new multi-objective optimization model is constructed with composite technical, economic, and environmental indices as objective functions. Optimization results indicate that under the optimal configuration, the composite technical, economic, and environmental indices of the system reach 0.894, 0.909, and 0.915. Compared to the reference system, the highest life-cycle primary energy saving ratio, life-cycle annual costs saving ratio, life-cycle carbon dioxide emissions reduction ratio, and life-cycle sulfur dioxide emissions reduction ratio are 31.20 %, 22.13 %, 52.70 %, and 88.90 %, respectively. The lowest life-cycle annual total costs are 67750.47 $, and the highest renewable energy supply ratio and electricity supply ratio are 59.22 % and 91.70 %, respectively. The multi-objective optimization model presented in this work offers a different viewpoint for comprehensively evaluating the technical, economic, and environmental performances of the integrated energy systems, which is predicted to guide the design of the integrated energy systems.