Eco-thermodynamics of hydrogen production by high-temperature electrolysis using solid oxide cells

Abstract

In this study, Solar Energy Demand (SED), Cumulative Exergy Extraction from the Natural Environment (CEENE), and LCA-ReCiPe 2016 (using both midpoint and endpoint modeling) life cycle impact assessment methods has been used to assess the performance of hydrogen (H2) production with renewable and non-renewable electricity sources via high-temperature Solid Oxide Electrolysis Cells. The analysis identified most relevant impact categories, life cycle stages, and processes, both from a thermodynamic and an environmental viewpoint. Electrolysis with non-renewable energy is characterized by the greatest environmental burdens, however, renewable energy systems also have considerable environmental impacts, some of which are significant. While no perfect electricity source exists, a growing portion of the renewable-based electricity production in the grid mix is an attractive option to lower environmental impacts of H2 production. Irrespective of the evaluation method, the contribution analysis from different life-cycle stages shows and confirm that the major contributor to the environmental burdens is the electricity supply. The manufacturing stage has high relevance for mineral and metal resources and toxicity-related impacts. Calculations of grid-based electrolysis life cycle environmental impacts in some European countries showed that significant variations. For example, global warming potential per kgH2 produced vary between 3.31 and 48.24 kgCO2. Trade-off analysis between the midpoint and endpoint indicators revealed that water consumption, global warming, and particulate matter formation, play a major role in the ranking of electricity supply options. The findings suggest that all potential impacts both at the midpoint and endpoint level should be considered to ensure robust results of the LCA evaluation, a fair comparison between pathways towards more transparent and evidence-based decisions. Towards that end, a further country site-specific assessment with optimization strategies and integration of traditional LCA with resource accounting (thermodynamic metrics) will need to be developed to explore additional valuable insights towards sustainable electrolytic H2 production systems.