Life Cycle Assessment of synthetic fuel production from renewable hydrogen: Process contribution and impact assessment considering different 2030 energy mixes

Renewable energy source generation has been increasing drastically for the last decades. In order to avoid grid congestions or overloads and energy curtailments, it is necessary to envisage energy storage technologies. Converting surplus electricity into hydrogen or eventually other synthetic fuels through Powerto- X technologies is regarded as a promising solution for the mid and long-term storage and for its potential of providing sector interconnection. However, synthetic fuel production consists of energy-intensive conversion steps, for which it is of importance to assess its environmental impacts before large scale plant development. This work aims at modeling and assessing the impacts of different alternative fuel synthesis based on renewable hydrogen in a life cycle assessment perspective. The analyzed fuels are chosen among the ones that can rely on a reliable and extensive infrastructure and, likewise, feed emerging and innovative technologies (e.g., fuel cells); in particular, methane, methanol, ammonia are selected as promising hydrogen carriers. The plant models developed in previous works are assessed regarding several environmental impacts in the software SimaPro. The data used in the present study included both data from ecoinvent database version 3.5, data from literature, and assumptions based on engineering practice for electricity generation, electrolysis, and concerning carbon dioxide sources. From a process contribution analysis, the sub-optimal and critical steps are pointed out and an outlook is provided. Since electricity production proved to be one of the most critical parameters, a sensitivity analysis over different 2030 energy mixes and renewable energy sources is carried out.