Techno-economic analysis of thermochemical-integrated pumped thermal energy storage system

Energy storage technology can address the imbalance and mismatch between the supply and demand of renewable electricity. Pumped thermal energy storage technology has great developmental potential as it is not geographically limited and offers high energy density. For this technology, storing and utilizing thermal energy is the key to improve system efficiency and reduce thermal loss of the system. Thus, in this work, a pumped thermal energy storage system with air as the working medium, coupled with methanol decomposition technology, was proposed. Low-grade thermal energy can be converted into high-grade chemical energy for storage based on the endothermic chemical reaction during the charging process. An isothermal compression strategy was employed during the discharging process to simultaneously minimize the compression power consumption and achieve energy-efficient utilization. Thermodynamic, economic, and environmental theoretical models were also established in this work, then the sensitivity analysis and multi-objective optimization were conducted. It was found that the system required the optimal air-methanol ratio, low-pressure turbine-pressure ratio, and isentropic efficiency of the adiabatic compressor to obtain the optimal thermodynamic and economic performance. The multi-objective optimization results of the system showed that the round-trip efficiency, exergy efficiency, and energy storage density of the system under optimal design working conditions were 63.70 %, 61.62 %, and 8.10 kWh·m⁻³, respectively, which increased by 5.80 %, 5.88 %, and 6.30 %, respectively, compared with those under the base conditions. The levelized energy cost and carbon emission per unit energy of the system were 202.14 $·MWh⁻¹ and 199.03 kg·MWh⁻¹, respectively, which decreased by 0.61 % and 7.51 %, respectively, compared with those under the base conditions. This work can provide a theoretical basis for the technical and economic feasibilities of the pumped thermal energy storage systemand its applications.