Exergetic life cycle assessment for green hydrogen production

Life cycle assessment (LCA) is a method for assessing the environmental impacts of products and processes. The life cycle inventory provides a measure of the quantitative throughput of a process, but it cannot measure the intrinsic quality of that throughput. Exergy is a measure of the quantity and quality of energy. When combining LCA and exergy analysis in an exergy-based life cycle assessment (ExLCA) a powerful tool for the quantification of resource efficiency can be established. This study performs a detailed bottom-up cradle-to-grave ExLCA based on cumulative exergy consumption and exergy analysis of the use phase for a state-of-the-art (SoA) and a future plant 5 MW proton exchange membrane (PEM) electrolyzer plant. Three scenarios are implemented, i.e. SoA plant operated in the German grid mix of 2018, SoA plant operated in a defossilized grid, and a future plant operated in a defossilized grid. In every scenario, more than 98 % of the resource demand originates from electricity generation alone and decreases significantly with renewable electricity operation. In plant construction, the anode catalyst material iridium causes approximately half of the resource demand and bears the largest lever for the resource reduction potential of the plant construction of 65 %.