Multi-objective planning and sustainability assessment for integrated energy systems combining ORC and multi-energy storage: 4E (economic, environmental, exergy and emergy) analysis

Sustainability assessment and flexibility enhancement are the key to achieve efficient and economic, supply-demand matching and comprehensive evaluation of integrated energy systems (IES). Therefore, a joint optimization model of economic, environmental and exergy for IES combining waste heat driven organic Rankine cycle (ORC) power generation and multi-energy storage is developed, and the emergy theory is introduced for system sustainability assessment. Firstly, the mixed-integer nonlinear optimization models for three scenarios of gas turbine (GT) without ORC, GT with ORC (GT-ORC) and solid oxide fuel cell (SOFC) with ORC (SOFC-ORC) are established, and the Pareto curve is obtained by using the augmented ε constraint. Secondly, the economic, environmental and exergy efficiency of the optimal decision-making scheme are analyzed, and the system sustainability is evaluated by solar emergy. The results reveal that in the optimal scenario, the SOFC-ORC scenario reduces CO₂ emission by 33.2 %, but the annual cost is increased by 45.7 %, and exergy efficiency is lowered by 8.1 % compared to that of the GT-ORC scenario. Then, the emergy sustainability index of the optimal solution for SOFC-ORC scenario is 0.031, which is significantly lower than that in GT-ORC scenario, which is 0.152. The proposed emergy analysis method covers energy, economy, society and environment, and elucidate the developmental sustainability of the system.