Green-Hydrogen Energy Share: An Intuitive Metric to Compare Energy Density and H₂ Efficiency in Biofuels and E‑Fuels

This communication proposes two indices to quantify hydrogen utilization efficiency and compare biofuels and e-fuels on a common energy basis: Hydrogen-Energy Share coefficient, HES [MJ_H2/kg_fuel], and its complementary, Hydrogen Energy fraction, HES% [MJ_H2/MJ_fuel]. Mass- and energy-balanced data sets are normalized to 1 MJ of produced-fuel (lower heating value). External-energy demand is disaggregated into feedstock provision, synthesis-plant operation, and renewable power for green hydrogen (G-H2) electrolysis. Then, the metrics are applied across 11 industrially relevant pathways, 5 e-fuels, and 6 biomass-to-liquids biofuels, as a compact demonstration data set. The analysis is restricted to liquid fuel routes; hydrogen storage vectors (e.g., ammonia and LOHCs) are outside the present scope. Total energy input spans an order of magnitude, from 0.19 MJ_H2/MJ_HVO to 2.62 MJ_H2/MJ_e‑FT. In e-fuel pathways, most input is the electricity used to produce G-H₂ (1.6-2.0 MJ_H2/MJ_e‑fuel) with HES up to 60 MJ_H2/kg_e‑CH4 and HES% ≥ 100%. Bioroutes use little electrolytic hydrogen but depend on sustainable biomass y (0.08-1.06 MJ_biomass/MJ_biofuel); HES ranges 3-38 MJ_H2/kg_biofuel and HES% ≤ 80%. Defined purely from energy balances, HES/HES% are proposed as first-order hydrogen-energy metrics to be used alongside, rather than instead of, detailed techno-economic and environmental assessments. These indexes make the electricity-versus-biomass trade-off explicit and intuitive in the deployment discussion: bioroutes where low-carbon power is scarce but biomass is available, electrofuels where cheap clean power and concentrated CO₂ are colocated.