3E multi-objective optimization of Organic Rankine Cycle configurations for a geothermal off-grid system: Power, DHW, and hydrogen production

This study investigates the optimization of an off-grid system for supplying electrical load and domestic hot water (DHW) to a building using geothermal energy. The system generates power through an Organic Rankine Cycle (ORC), with excess energy directed to an electrolyzer for hydrogen production. A residential complex in Tabriz, Iran, with 408 occupants, was selected as the case study, leveraging the availability of geothermal power. Three ORC configurations—basic ORC, ORC with reheater (RHORC), and regenerative ORC (RORC) were optimized in terms of energy, exergy, and economy. The optimization process utilized the Non-Dominated Sorting Genetic Algorithm II (NSGA-II), aiming to maximize energy and exergy efficiency, hydrogen production, and minimize levelized costs of electricity (LCOE) and hydrogen (LCOH), while ensuring that electrical and DHW demands are met. The results demonstrate that the RORC configuration outperforms the other two cycles in all aspects: it produces 44.45 % more power than RHORC and 47.86 % more than ORC, with energy and exergy efficiencies of 49.03 % and 47.01 %, respectively. Furthermore, RORC generates significantly more hydrogen 63.81 % more than RHORC and 69.37 % more than ORC. Additionally, RORC has the lowest LCOE (4.52 cent. kWh⁻¹) and LCOH (2.69 cent. kWh⁻¹).