Thermodynamic performance analysis of a novel PEMEC-SOFC-based poly-generation system integrated mechanical compression and thermal energy storage

Abstract

The issues arising from the intermittent nature and extreme weather conditions of renewable energy must be addressed urgently. Green hydrogen produced from electrolysis powered by renewable energy has been widely regarded as an ideal energy storage scheme in the energy revolution of the 21st century. A novel proton exchange membrane electrolysis cell (PEMEC)-solid oxide fuel cell (SOFC)-based poly-generation system integrated mechanical compression energy storage (MCES) and thermal energy storage (TES) is proposed. The MCES-assisted PEMEC efficiently produces and stores green hydrogen, while hydrogen-fueled SOFC is employed to generate electricity, achieving higher efficiency and zero greenhouse gas emission. The energy from compression heat and gas turbine exhaust gas is enormously recovered by TES and then utilized by absorption chiller/heater in the cascade way to produce heating, cooling, and domestic hot water. Thermodynamic models and operating strategies are constructed. The energy and exergy analyses are performed to evaluate the system performance and the effects of key parameters of SOFC and PEMEC on performance. The results show that under design conditions, the energy efficiencies of the novel system for summer, transitional season, and winter are 82.61%, 79.36%, and 87.30%, meanwhile, the exergy efficiencies are 43.85%, 44.47%, and 45.58%, respectively. Finally, sensitivity analysis results show that properly increasing the operating pressure or temperature can significantly improve the total exergy output and exergy efficiencies of SOFC and the hybrid system. When the pressure varies from 1 bar to 13 bar, the total exergy outputs are increased by 27.08%, 26.33%, and 20.78% in the summer, transitional season and winter, respectively. The SOFC energy efficiency is improved from 34.19% at 800 ℃ to 53.72% at 1000 ℃. The system exergy efficiency enhances when the PEMEC operating pressure ranges from 1 bar to 20 bar or the temperature varies from 50 ℃ to 90 ℃, furthermore, the optimal operating condition is 5 bar and 67 ℃.