Locked in on RFNBOs – Will EU mandates for drop-in synthetic aviation fuels lead to decreased energy- and cost-efficiency?

• Comparison of methanol synthesis based on combustion or gasification of biomass. • Gasification outperforms combustion options in terms of cost and energy efficiency. • Policies requiring CO 2 -based fuel synthesis create lock-in in sub-optimal system. • RFNBO rules are in conflict with energy efficiency directive and waste hierarchy. • Regulatory inconsistency increases investment risk that could slow down deployment. Decarbonization of the transportation sector implies that fossil fuels must be substituted with sustainable alternatives. Current EU policies incentivize large-scale deployment of synthetic aviation fuel production that can be classified as Renewable Fuel of Non-Biological Origin (RFNBO). Synthetic aviation fuel can be produced from methanol and this work presents a techno-economic assessment of three pathways (two combustion-based and one gasification-based) to produce synthetic methanol from biomass residues and renewable hydrogen. The results show that the gasification-based pathway can produce methanol at a lower cost (820 €/t methanol) and higher energy efficiency (46 %, for conversion of biomass, electricity and heat inputs to methanol) compared to combustion-based options (1,050–1,500 €/t methanol and ∼37 % efficiency). The gasifier route requires less renewable hydrogen, resulting in a 30 % lower electricity demand. However, only 55 % of the gasification-based methanol is compliant with the RFNBO definition, since the regulation stipulates that biofuel cannot be counted towards the drop-in quotas. Furthermore, the findings indicate that RFNBO policies that favor production using CO 2 from combustion processes that supply energy to utility systems (e.g., district heating) risk leading to lock-in in inefficient systems, as electrification of heat supply could be a more efficient option. This work identifies such regulatory inconsistencies that increase risk related to investment decisions.