Environmental performance of Power-to-X fuels based on life cycle assessment

Abstract

This thesis covers a cradle-to-gate life cycle assessment of five Power-to-X fuels-e-methanol, e-methane, e-ammonia, e-diesel and e-kerosene-produced under three electricity-supply scenarios representative of current and future Finnish conditions. The environmental impacts of the fuels were quantified using the following four ReCiPe 2016 midpoint categories climate change, terrestrial acidification, freshwater eutrophication and marine eutrophication. The results indicated that across pathways, hydrogen production dominates the total impacts, ranging from 70% to 95% of burdens. It was also determined that decarbonising electricity reduces impacts by up to two orders of magnitude. Under the Finnish grid mix, due to hydrogen demand and simpler synthesis routes, e-methanol and e-methane showed low impacts, while Fischer-Tropsch fuels had higher burdens. However, with the supply of wind electricity, among all fuels, FT-derived e-diesel and e-kerosene reached the lowest absolute impacts at 0.58-0.98 g CO₂-eq/MJ and outperformed methanol, methane and ammonia in every impact category. E-ammonia exhibited a reduction from 34.7 g CO₂-eq/MJ under the grid to 6.56 g CO₂-eq/MJ under wind but remained an intermediate performance fuel. Comparison with literature confirmed that model results are within or below the established ranges for renewable-powered PtX systems, while all wind-based fuels satisfy the RED III greenhouse-gas threshold for renewable fuels of non-biological origin. Overall, the study concluded that PtX fuels can achieve extremely low environmental impacts powered by renewable electricity, whereby in highly decarbonised systems, FT fuels become the most favorable pathways, but methanol and methane remain attractive options under partially decarbonised grids.