Hydrogen Production from Low-temperature Geothermal Energy - A Review of Opportunities, Challenges, and Mitigating Solutions

This study aims to provide a comprehensive review of the potential of geothermal energy for producing hydrogen, with a focus on the Australian context where low-temperature geothermal reservoirs, particularly hot sedimentary aquifers (HSAs), are prevalent. The work includes an overview of various geothermal technologies and hydrogen production routes, and evaluates potential alternatives for hydrogen production in terms of energy and exergy efficiency, economic performance, and hydrogen production rate. Values for energy efficiency are reported in the literature to range from 3.51 to 47.04%, 7.4–67.5% for exergy efficiency, a cost ranging from 0.59 to 5.97 USD/kg of hydrogen produced, and a hydrogen production rate ranging from 0.11 to 5857 kg/h. In addition, the article suggests and evaluates multiple metrics to appraise the feasibility of HSAs geothermal reservoirs, with results tailored to Australia but that can be extended to jurisdictions with similar conditions worldwide. Furthermore, the performance of various hydrogen production systems is investigated by considering important operating conditions. Lastly, the key factors and possible solutions associated with the hydrogeological and financial conditions that must be considered in developing hydrogen production using lowtemperature geothermal energy are summarised. This study shows that low-temperature HSAs (~100 ◦C) can still be used for hydrogen generation via supplying power to conventional electrolysis processes by implementing several improvements in heat source temperature and energy conversion efficiency of Organic Rankine Cycle (ORC) power plants. Geothermal production from depleted or even active oilfields can reduce the capital cost of a hydrogen production system by up to 50% due to the use of pre-existing wellbores, under the right operating conditions. Thus, the results of this study bring novel insights in terms of both the opportunities and the challenges in producing clean hydrogen from geothermal energy, applicable not only to the hydro-geological and socio-economic conditions in Australia but also worldwide, exploring the applicability of geothermal energy for clean hydrogen production with similar geothermal potential.