An Analysis of Greenhouse Gas Emissions in Electrolysis for Certifying Clean Hydrogen

The drive for carbon neutrality has led to legislative measures targeting reduced greenhouse gas emissions across the transportation, construction, and industry sectors. Renewable energy sources, especially solar and wind power, play a pivotal role in this transition. However, their intermittent nature necessitates effective storage solutions. Green hydrogen and ammonia have gained attention for their potential to store renewable energy while producing minimal emissions. Despite their theoretical promise of zero greenhouse gas emissions during production, real-world emissions vary based on system configurations and lifecycle assessments, highlighting the need for detailed evaluations of their environmental impact. Therefore, in this study, calculations were performed for the actual amount of produced greenhouse gas emissions that are associated with the production of green hydrogen using electrolysis, from raw material extraction and processing to hydrogen production, with these assessed from well-to-gate emission estimates. Emissions were also evaluated based on various types of renewable energy sources in South Korea, as well as hydrogen production volumes, capacities, and types. Using these data, the following factors were examined in this study: carbon dioxide emissions from the manufacturing stage of electrolysis equipment production, the correlation between materials and carbon dioxide emissions, and process emissions. Current grades of clean hydrogen were verified, and the greenhouse gas reduction effects of green hydrogen were confirmed. These findings are significant against the backdrop of a country such as South Korea, where the proportion of renewable energy in total electricity production is very low at 5.51%. Based on the domestic greenhouse gas emission efficiency standard of 55 kWh/kgH2, it was found that producing 1 kg of hydrogen emits 0.076 kg of carbon dioxide for hydropower, 0.283 kg for wind power, and 0.924 kg for solar power. The carbon dioxide emissions for AWE and PEM stacks were 8434 kg CO2 and 3695 kg CO2, respectively, demonstrating that an alkaline water electrolysis (AWE) system emits about 2.3 times more greenhouse gasses than a proton exchange membrane (PEM) system. This indicates that the total carbon dioxide emissions of green hydrogen are significantly influenced by the type of renewable energy and the type of electrolysis used.