As the world races to curb greenhouse gas emissions and mitigate climate change, hydrogen is emerging as a potential low-carbon fuel, particularly for energy-intensive industries like steel production. However, the environmental impact of hydrogen production is far from straightforward, as new research highlights. The climate friendliness of hydrogen hinges critically on its production method and associated infrastructure.
Currently, most hydrogen is produced from natural gas via steam reforming, generating "grey hydrogen." This process releases significant carbon dioxide â approximately 13.7 kilograms of CO2 per kilogram of hydrogen. "Blue hydrogen," utilising carbon capture and storage (CCS), aims to reduce emissions to around 6 kilograms of CO2 per kilogram. However, CCS technology remains expensive and often fails to achieve its promised capture rates.
The favoured alternative is "green hydrogen," produced by electrolysing water using renewable energy sources like solar or wind power. While electrolysis itself generates minimal greenhouse gases, a complete assessment must account for the "embodied emissions" associated with the entire lifecycle, from infrastructure construction and hydrogen storage to transportation.
A study led by Kiane de Kleijne at Eindhoven University of Technology examined embodied emissions from over 1,000 planned green hydrogen projects by 2030. The analysis considered factors such as electricity source, plant design, and hydrogen transportation methods, including the energy-intensive process of converting hydrogen to ammonia for shipping, which can result in up to 30% hydrogen loss.
The research revealed that even green hydrogen production generates emissions. The team estimated a minimum of 2.9 kilograms of CO2-equivalent pollution per kilogram of hydrogen produced. Transportation adds further emissions â 1.5 kilograms for pipeline transport and 1.8 kilograms for shipping. Considering these embodied emissions, many green hydrogen projects might struggle to meet climate targets, such as the EU's renewable fuel threshold of less than 3.4 kilograms of CO2 per kilogram of hydrogen.
Mark Winfield of York University emphasised that this study reinforces concerns about the potential for lifecycle emissions to outweigh anticipated benefits. De Kleijne's findings indicate that while green hydrogen remains significantly cleaner than grey and blue hydrogen, the environmental impact varies substantially depending on production methods and location.
The study pinpointed key factors influencing green hydrogen's carbon footprint. Wind power generally proves more sustainable than solar due to lower embodied emissions in turbine construction. Connecting plants to the wider electricity grid allows for efficient energy management, reducing emissions compared to stand-alone facilities. Furthermore, minimising transportation distances is crucial, with pipelines offering lower emissions for shorter distances and shipping becoming preferable for longer distances.
Zane McDonald of the Open Hydrogen Initiative acknowledges the industry's awareness of embodied emissions and the development of standardised emission estimation methods. Financial incentives, such as the US 45V tax credit, promote cleaner production methods.
Both Winfield and de Kleijne advocate for a project-specific approach, emphasising that direct electrification should be prioritised wherever feasible. Green hydrogen should only be considered when a compelling use case exists, avoiding unnecessary transportation and complex conversion processes. The research strongly suggests a nuanced view of hydrogen's role in a sustainable future, moving away from generalised claims of green credentials towards a more precise, project-by-project assessment.