Potential methods for geothermal-based hydrogen production

In this study, four potential methods are identified for geothermal-based hydrogen production, namely: i) direct production of hydrogen from the geothermal steam, ii) through conventional water electrolysis using the electricity generated through geothermal power plant, iii) by using both geothermal heat and electricity for high temperature steam electrolysis and/or hybrid processes, iv) by using the heat available from geothermal resource in thermochemical processes. Here we focus on low-temperature thermochemical and hybrid cycles, due to their greater application possibility, and examine them as a potential option for hydrogen production using geothermal heat. We also assess their thermodynamic performance through energy and exergy efficiencies. The results show that these cycles have good potential and attractive overall system efficiencies over 50%. The copper-chlorine cycle is identified as a highly promising cycle for geothermal-hydrogen production. Furthermore, three types of industrial electrolysis methods, which are generally considered for hydrogen production currently, are also discussed and compared with the mentioned cycles. It may be concluded that the current technological status of all pathways of hydrogen production from geothermal requires further research and development on how to implement these first and how to make them more cost effective and efficient. (author)