This project aims at evaluating the sustainability of the joint project’s “Reduction and reuse of CO2” value chain, i.e. the carbon dioxide methanation value chain – from the production of hydrogen through photoelectrochemical (PEC) water splitting (partner project 2), through the methanation of carbon dioxide from the cement industry with renewable hydrogen using a catalyst (partner project 1), to using the methane generated as fuel for electricity generation in novel stationary and mobile fuel cells (partner projects 3 and 4). Achieving the potential benefits of such a hydrogen/methane system requires careful integration of production, storage and end-use components with minimised cost and maximised efficiency, and a strong understanding of environmental impacts and opportunities. System models combined with comprehensive sustainability assessments, including life cycle assessments and technology assessments, provide a platform for comparisons of energy systems for specific applications. Environmental, economic and social benefits and drawbacks will be demonstrated for the different technologies mentioned above along the value chain.