Design and optimization of a geothermal-driven polygeneration system with cascade utilization for green hydrogen production

A polygeneration system is proposed to cascade geothermal heat and liquefied natural gas cold energy for power generation, refrigeration, desalination, and hot water production, while internal electricity drives green hydrogen production. An integrated thermodynamic and exergoeconomic model is developed to evaluate the performance, followed by parametric sensitivity analyses. A scenario-based multi-objective optimization is implemented using NSGA-II coupled with TOPSIS and LINMAP decision-making methods, aiming to simultaneously maximize efficiency, minimize cost, and enhance diverse product yields. Results show that under design-point conditions, the system achieves an exergy efficiency of 34.32% and a unit cost of 28.24 $/GJ. At the optimal configuration, hydrogen production rate is enhanced from 5.86 kg/h to 11.31 kg/h with a levelized cost of 3.29 $/kg, while increasing exergy efficiency by 6.70% and reducing unit cost by 8.96%. These findings confirm the high effectiveness of the optimization approach in upgrading green hydrogen production and overall performance.