Green hydrogen & electricity production via geothermal-driven multi-generation system: Thermodynamic modeling and optimization

Concerning limited sources of fossil fuels, humankind should ensue new avenues to meet its energy demands. Towards this, geothermal energy is acknowledged as a promising, reliable, safe, and clean means for this aim. In the present study, a multi-generation system driven by geothermal energy, which produces electrical power, hydrogen, oxygen, and cooling, is proposed, appraised from thermodynamic and economic standpoints. Due to today's importance of hydrogen production, pure hydrogen production is one of the primary purposes of the system here described and analyzed. The subsystems include an organic Rankine cycle (ORC), a polymer electrolyte membrane (PEM) electrolyzer, and a lithium/bromide absorption refrigeration cycle. The model is implemented in the Engineering Equation Solver software and a multi-objective optimization is performed with NSGA-II. The results indicate that the parameters mostly affecting system performance include geothermal fluid mass flow rate, geothermal fluid temperature, ORC turbines inlet temperature, and evaporator pinch-point. The highest exergy destruction is pertinent to evaporators and the PEM electrolyzer, respectively. Moreover, the results reveal that the higher the geothermal well temperature, the higher the output parameters of the system. Also, a case study was carried out to implement the proposed system in Sabalan geothermal wells; the results indicate that the system can support the energy need of 160 families during one year by producing 4,696 MWh of electrical power. Lastly, the multi-objective optimization lead to a optimal scenario with 37.85 % exergy efficiency and 15.09 USD/h system cost rate.