Thermo-economic analysis of a NG-fueled SOFC-HCCI engine hybrid energy conversion system as distributed power plant with high efficiency

Solid oxide fuel cell (SOFC) was integrated with internal combustion engine (ICE) due to its high operating temperature for improving the energy conversion efficiency in this work. In the SOFC-ICE hybrid energy conversion system, the SOFC anode off-gas with high temperature and combustible fuels is used as the ICE fuel for additional power generation. To evaluate the thermo-economic performance, the thermo-economic model of the hybrid system is developed for the economic analysis. The results showed that the specific electric energy cost (SEEC) of the hybrid system is 3.75 kWh, which is lower than that of a standard power plant. Through the further analysis, the capital investment cost of the system with the net output power of 470 kW is 50.5 k$, which includes the capital cost of auxiliary devices such as heat exchanger and compressors. In addition, the SOFC accounts for about 35% of the system's capital cost. The annual cost of the system under the cycle life of 10 years is calculated to be approximately 15.6 k$. Moreover, the influence of operating parameters on thermo-economic performance of the hybrid system is also investigated to optimize the thermo-economic performance. Finally, the corresponding payback period of this system is approximately 6.8 years and the annual return on investment is 4.6%. These results reveal that the proposed NG-fueled SOFC-HCCI engine hybrid system presents a broad market prospect in the practical applications.