Comparison of green ammonia and green hydrogen pathways in terms of energy efficiency

The global energy system transition necessitates new energy carriers with low greenhouse gas emissions. Chemical energy storage technologies provide a viable basis for long-term energy storage. Ammonia is a promising approach in this regard. This study takes a closer look on the energetic potential of ammonia as energy carrier compared to hydrogen. The efficiencies of five green ammonia and four green hydrogen pathways are evaluated for production, storage and utilisation on a power-to-X-to-power basis. The round-trip efficiency for each pathway is calculated by comparing the energy demand that each individual technology requires along the pathways and the usable electric energy that is provided at the end of the pathways. The most efficient pathway for ammonia turns out to be a combination of a decomposition-unit and a solid-oxide fuel cell with a round-trip efficiency of 28 +/- 5 % for 30-day storage duration. This is similar to the value for the most efficient pathway using hydrogen. Pathways utilising ammonia are energetically particularly beneficial compared to the hydrogen pathways in case of long storage duration.