Economic and environmental multi-optimal design and dispatch of solid oxide fuel cell based CCHP system

Combined cooling, heating and power system (CCHP) is an efficient alternative for building energy supply. Meanwhile, the advantages of high energy efficiency and low emission for solid oxide fuel cells (SOFCs) make the technology a promising prime mover for CCHP systems. In this study, a SOFC based CCHP system design and operation optimization model has been developed using the Mixed Integer Non-linear Programming (MINLP) approach. The model provides two capacity sizing options of the fixed size (user specified), and the optimal sizing. In the fixed size option, four dispatch strategies are considered, namely baseload, day/night, full-load, and electrical load following. In the optimal sizing option, the installed capacity of devices and the dispatch strategy are both optimized. Moreover, multi-objective optimizations are also conducted to optimize two conflicting objectives simultaneously by the epsilon-constraint method. The optimal results are displayed by Pareto frontiers and the most desired solutions have been identified and verified by two decision-making approaches of LINMAP and TOPSIS. To make the model applicable to real world operation, novel constraints including part-load efficiency, equipment on/off, and numbers of start constraints are applied, Finally, the proposed model is applied to a case study of a hospital in Shanghai, China considering state-of-the-art technical specifications, time-of-use energy pricing, and emission factors. The results indicate environmental advantages of SOFC based CCHP system. Moreover, the levelized cost of energy (LCOE) identified by the proposed optimal design and dispatch model would be 0.17 $/kWh, which is lower than the conventional energy system.