Harmonizing the assessment of (green) hydrogen supply chain: a modular and parametrized life cycle assessment framework

Despite a growing number of life cycle assessment (LCA) studies on green hydrogen technologies, a lack of harmonization in how to scope the LCA modeling framework and transparently disseminate results prevents the field from fully capitalizing on this expanding body of knowledge. This paper presents a harmonized LCA framework to support a consistent assessment of green hydrogen supply chains and comparison with functionally equivalent alternatives. The framework guides the practitioners to define the functional unit, tailored to six identified end-use applications of hydrogen. The process tree is developed as a unified and agile modular structure applicable to describe the value chain of any green hydrogen technology, each module representing a standalone building block that can be modified or replaced within the product system. It provides a parametrized inventory model linking the flows of the product systems to key parameters characterizing their design or performance. The framework has been implemented in a dedicated LCA tool (the HTWOL), supported by a library of modules representing pre-set configurations of elementary processes (e.g., electrolyser technologies), enhancing accessibility for users with varying levels of expertise. The framework has been successively applied to representative use cases. Results show the importance of ensuring low-impact energy supply and always striving to maximize the overall energy-efficiency in delivering the functional units. Environmentally relevant deployment of green hydrogen technologies would target end-use applications with no viable fossil substitutions (e.g., production of ammonia) and long-term renewable electricity storage. Efforts toward direct electrification and demand reduction must continue in parallel.