Energy, exergy and economic (3E) evaluation and multi-objective optimization of a CHP system with geothermal-assisted high-temperature PEMFC and self-condensing transcritical CO₂ cycle

Geothermal energy, with its abundant reserves, continuous and stable energy supply, as well as low-carbon and clean properties, is one of the key solutions to promoting the low-carbon transformation of energy systems. To advance the efficient utilization of geothermal energy and the low-carbon transformation of energy systems, a thermodynamic and economic performance model for the combined heat and power (CHP) system integrating a geothermal-assisted high-temperature PEMFC (HT-PEMFC) and a self-condensing transcritical CO₂ (TCO₂) cycle is established. The distribution of exergy destruction and equipment costs within the system is analyzed, and performance benchmarking is conducted against other similar energy systems to demonstrate the performance superiority of the proposed system. Through sensitivity analysis, the influence mechanism of key parameters on system performance is revealed, and a multi-objective genetic algorithm is applied to optimize the system with energy efficiency, exergy efficiency and levelized cost of product (LCOP) as the objectives. The results show that exergy destruction mainly occurs in the fuel cell stack, combustion chamber and cooler, while the major costs are associated with the fuel cell stack, turbine and gas heater. Under optimized operating conditions, the system achieves an energy efficiency of 79.35%, exergy efficiency of 53.76% and LCOP of 0.0439 $·kWh⁻¹. This study not only provides theoretical and technical support for the design and optimization of geothermal-assisted integrated systems combining HT-PEMFC and self-condensing TCO₂ cycles, but also demonstrates the feasibility of deep cascade utilization of geothermal energy through multi-energy complementary supply (electricity, heat and space heating).