Can Stimulated Geological Hydrogen Generation Systems be Circular?

Abstract Stimulated Geological Hydrogen is currently being studied as a potential energy resource. However, the process involves the use of injected fluid (water) to induce serpentinization – a pathway to hydrogen generation. If hydrogen is generated, water is produced alongside the hydrogen. Both fluids are expected to be associated with large temperatures. The objective of this study is to evaluate the feasibility of recovering heat from stimulated hydrogen generation systems as well as reuse the produced water for the reaction. If this waste heat recovery and produced water reuse is deemed possible, it has the potential to position stimulated geological hydrogen as a low cost, sustainable fuel. This study uses a combination of experiments, numerical model and data analysis to evaluate the circularity of stimulated geological hydrogen. The experiments were used to determine what the properties of the reacted water are, and what its condition would be after treatment. Hydrogen generation with deionized water and with the treated water were compared. The energy and cost associated were documented. Numerical models were used to predict the temperature and rates of hydrogen and water. These were fed into a model for estimating the power output if the fluids are used in an Organic Rankine Cycle. The power potential of the hydrogen was estimated assuming it was used for power generation. The net power generated from the system, ie power from hydrogen and the Organic Rankine Cycle minus the power used for injection, water treatment, and separation, was computed as one of the metrics to measure circularity. The results of this study indicate that stimulated geological hydrogen generation has the potential to be a self-sustaining, low-cost, and energy-efficient system. The heat extracted from the reaction can be harnessed for electricity generation through an Organic Rankine Cycle (ORC), particularly when hydrogen and water production rates are high. In scenarios with significant hydrogen generation, the combined power output from hydrogen combustion and ORC-generated electricity exceeded the energy required for water injection, separation, and treatment, confirming the system's energy viability. Furthermore, analysis of the reacted water revealed that, with proper treatment, it can be recycled back into the system for further hydrogen generation, minimizing freshwater consumption. The composition of the produced water was found to be within treatable limits using conventional filtration and chemical treatment processes. Water reuse significantly reduces operational costs associated with sourcing fresh injection water and improves the sustainability of the process. Overall, the findings suggest that stimulated geological hydrogen systems can function as a circular energy resource, maximizing energy recovery while minimizing waste. This provides a promising outlook for hydrogen as a scalable, low-carbon alternative fuel, especially when integrated with waste heat recovery and water recycling strategies. This study presents a novel evaluation of the circularity of stimulated geological hydrogen by integrating waste heat recovery and water reuse. Unlike previous studies that primarily focused on hydrogen yield, this work quantifies the energy balance of the entire system, demonstrating that power recovery can exceed operational energy consumption. Additionally, the study establishes a framework for water recycling, ensuring that hydrogen generation does not compete with critical freshwater resources. Combining experimental validation, numerical modeling, and process integration, provides a foundation for developing self-sustaining hydrogen systems, positioning stimulated geological hydrogen as a viable, cost-effective, and scalable clean energy source.