Multi-objective planning for integrated energy systems considering both exergy efficiency and economy

Improving the comprehensive utilization level of energy has been a core goal for the optimal design of the integrated energy system (IES), which requires an accurate assessment of energy efficiency. The widely used criterion of conventional energy efficiency derived from the first law of thermodynamics has gradually been criticized for its shortcomings of neglecting the quality of energy. As a concept considering both the quantity and quality of energy, exergy efficiency has been recognized as a more reasonable index in recent decades. Nevertheless, it is a complicated problem to calculate the exergy efficiency among multiple energy forms in an electricity-gas-heating-cooling coupled IES, limiting its application in IES planning. This paper hence proposes the method of calculating the exergy efficiency of an IES by using a black-box model, after defining the concept of energy quality coefficient (EQC) that values the quality of various energy forms involved. And then, a multi-objective planning model considering both exergy efficiency and economy is thus proposed for the joint planning of energy generators, storages and networks, wherein a five-tier energy hub is modeled to deal with the multi-energy couplings. To reduce the difficulty of optimizing, several convex relaxation measures are designed to transform the non-convex original problem into a convex one. The proposed framework is verified in a real-world study case located in Guangzhou, China.