Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy Operating limitation and degradation modeling of micro solid oxide fuel cell-combined heat and power system Wangying Shi a , Jianzhong Zhu a , Minfang Han a,b, ⁎ , Zaihong Sun c , Yaming Guo d a Department of Energy and Power Engineering, State Key Laboratory of Control and Simulation of Power System and Generation Equipment, Tsinghua University, Beijing 100084, PR China b Tsinghua Innovation in Dongguan, Guangdong 523808, PR China c Suzhou Huatsing Power Co., Ltd., Jiangsu 215314, PR China d Nanjing Clear Power Co., Ltd., Jiangsu 210032, PR China HIGHLIGHTS • A 5 kW micro SOFC-CHP system was simulated combined with a SOFC degradation model. • A real SOFC stack was tested under CH 4 &H 2 showing 262 W output and 600 h lifetime. • The most appropriate parameter range was illustrated to be limited in a shape of a small triangle. • The calculated system electrical efciency could reach 44.9% (HHV) at 120 A. • The constant current operating pattern had the longest lifetime and constant power followed. ARTICLE INFO Keywords: Solid oxide fuel cell Combined heat and power Operating limitation Degradation model ABSTRACT The micro Solid Oxide Fuel Cell-Combined Heat and Power (SOFC-CHP) System is one of the most promising technologies of distributed generation and has been commercialized in Japan and Europe. However, the per- formance degradation of an SOFC stack still exists, causing the ratio of power and heat to change and the Joule heat to increase in the stack. This phenomenon should not have been neglected. A zero-dimension SOFC model including basic Nernst, ohmic, activation and concentration voltage loss was used to simulate the micro SOFC- CHP system, and a degradation model was also applied to modeling the power change with respect to operating time in diferent situations. Both of the models were verifed by real stacks experiment data and the efectiveness was proved in system-level modeling. Three key operating parameters of the system were promoted: stack current I, excess air factor α and fuel utilization U f . Given the safe temperature ranges of an SOFC stack, com- bustor and reformer, the most appropriate parameter range was illustrated to be limited in a shape of a small triangle. Within the safe parameter range, while the excess air factor α was fxed at 2.64, the electrical efciency reached a maximum 44.9% (HHV) at 120 A, while the electric power output of SOFC and hot water were both 5.58 kW. As for the dynamic modeling, by comparing constant current, constant voltage and constant power three operating patterns, results showed that the constant current pattern had the longest lifetime and the constant power pattern followed. 1. Introduction As the largest developing country, China emitted 9.76 billion tonnes CO 2 in 2014, accounting for 27.5% of the world total and ranked 1st in the word [1]. Besides, China has been facing a rapid urbanization process since the 1980s, which is likely to boost the energy consump- tion and CO 2 emission [2]. To meet the high growth rate of energy consumption [3] and to reduce greenhouse gas emission [4], Distributed Generation (DG) is attracting more attention globally [3–8]. Based on the advantages of abundant renewable resources reserves, the EU 2020 target of 20% of energy consumption produced from renewable resources, and the main driving force is the expansion of DG [9]. The United States has more than 12 million DG units, which is about one-sixth of the capacity of the nation’s existing centralized power plants [10]. In Japan, developing DG technology is more for energy security reasons, and after the Great https://doi.org/10.1016/j.apenergy.2019.113444 Received 15 January 2019; Received in revised form 21 May 2019; Accepted 6 June 2019 ⁎ Corresponding author. E-mail address: hanminfang@mail.tsinghua.edu.cn (M. Han). Applied Energy 252 (2019) 113444 0306-2619/ © 2019 Published by Elsevier Ltd. T