Sustainable development and optimization of a geothermal–biomass hybrid energy system for green hydrogen production

Abstract

Fossil fuels remain the primary contributors to greenhouse gas emissions, particularly carbon dioxide. Transitioning toward renewable energy sources and adopting clean fuels, such as hydrogen, constitute effective strategies for mitigating CO₂ emissions and decreasing global dependence on fossil-based energy systems. In this study, a carbon–neutral hybrid energy system was designed and developed to produce electricity, medium-pressure steam, hot water, and green hydrogen. The designed system utilizes municipal solid waste and geothermal energy as primary energy sources, offering an innovative solution for sustainable energy production. The proposed configuration integrates four principal subsystems: biomass steam gasification, a water electrolysis, a desalination unit, and a combined flash-binary geothermal system coupled with a cascaded organic Rankine cycle. A comprehensive evaluation was carried out, including thermodynamic analysis, sustainability assessment, environmental impact evaluation, and thermo-economic analysis. Furthermore, a detailed parametric study was conducted to assess the effects of key independent operating variables on the overall system performance. Subsequently, a multi-objective optimization was performed using the weighted sum method, aiming to minimize the TUCP and maximize the hydrogen production rate. The optimized system yielded useful outputs, including 230 kg/h of hydrogen, 31,217 kW of net electrical power, 18,488 kg/h of hot water, 1,981 kg/h of MP steam, and oxygen of 1054 kg/h. Thermodynamic analysis revealed an energetic efficiency of 78.57 % and an exergetic efficiency of 65.4 %, accompanied by a sustainability index of 2.89 and a TUCP of $3.70/GJ. The environmental assessment of the developed near-zero-carbon emission process highlighted substantial benefits, including an annual petroleum savings of 66,428 L/year and a reduction in annual CO₂ emissions by 223,260 kg/year. Consequently, this study demonstrates an efficient, sustainable, and environmentally friendly process that effectively addresses energy and environmental challenges while outperforming comparable systems.