Techno-economic assessment of Power-to-Ammonia-to-Power for long-term energy storage

Hydrogen produced via electrolysis represents a promising solution for renewable energy storage due to its high gravimetric energy density. However, its low volumetric density requires storage under extreme conditions, raising costs and safety concerns. An alternative approach involves converting hydrogen into other chemicals. Among them, ammonia offers higher volumetric energy density and lower tanks cost than hydrogen, stability under ambient conditions, and an existing transport infrastructure. This study evaluates the techno-economic feasibility of green ammonia as an energy storage medium compared to green hydrogen. Green ammonia is synthesized using renewable electricity to power an electrolyzer, an air separation unit, and a Haber-Bosch reactor. Stored ammonia is later reconverted into electricity via a combined cycle gas turbine. The system is modeled using MESS, an open-source software developed at the University of Florence. The ammonia synthesis plant model includes reaction kinetics and flexible operation. System sizing is performed by minimizing the Levelized Cost of Electricity (LCOE), assuming a 4 MW electricity demand at each hourly step over a year, fully supplied by photovoltaics coupled with ammonia or hydrogen storage. A sensitivity analysis on the load profile reveals that ammonia is more cost-effective for long-duration storage, provided reactor operation is properly controlled. Under constant and winter–peaked demand, ammonia achieves LCOEs of 0.529 €/kWh and 0.666 €/kWh, outperforming hydrogen at 0.575 €/kWh and 1.209 €/kWh. With summer-peaked demand, characterized by short–term storage needs, hydrogen reaches 0.343 €/kWh, whereas ammonia 0.483 €/kWh. Battery-integrated variants are also assessed, reducing LCOE in all scenarios except for the hydrogen-based system under summer-peaked demand.