Understanding the thermodynamic behaviors of integrated system including solid oxide fuel cell and Carnot battery based on finite time thermodynamics

Finite time thermodynamics is applied to carry out the thermodynamic analysis of integrated system including solid oxide fuel cell (SOFC) and supercritical CO₂ Brayton Carnot battery (CB). SOFC-CB integration can keep SOFC-based system high flexibility in terms of load changing, but research methods used in the past studies focus on classical equilibrium thermodynamics. The large deviations have been caused from calculated and practical points. Therefore, this paper considers finite time of thermodynamic process and finite size of heat exchangers to find out the realistic regulations from pinch point and performances. The comparison results show the finite time thermodynamic model shows more precise, in which the average error of finite time thermodynamic model can reach 4.08%, 2.02 times smaller than that of classical equilibrium thermodynamic model. It can be significantly observed that the increase of power output can lead to the decrease of efficiency. In addition, the finite time thermodynamic analysis of CB system is also performed. The results show that in the finite time thermodynamic theoretical framework, optimization round-trip electric efficiency of CB can reach 214.8%. Meanwhile, the multi-objective optimization based on TOPSIS combined with weight entropy method and non-dominated sorting genetic algorithm-II is performed. The optimal results show that the net efficiency, net power output and charging power of SOFC system can be achieved by 47.82%, 3159 kW, and 402 kW, while the overall energy utilization efficiency during the whole operation can reach 60.89% at fuel utilization of 0.70. Furthermore, the configuration optimization results show that the net efficiency, net power output and charging power of SOFC system can be achieved by 59.01%, 3989 kW, and 128 kW, while the overall efficiency can reach 62.88%. The improved system can show more feasibility of the actual application.