Using Power-to-Ammonia to Transform Fluctuating Wind Power into Base-Load

The energy revolution in Europe is focused on the installation of renewable energies, which are mainly wind power and solar power. Due to their strong dependence on wind and sun, their production is highly fluctuating and not matching the consumption profiles of industry and households. With the on-going shut-down of base-load power plants, like e.g. coal fired power plants, the renewable energies have to be transformed into base-load by means of energy storages.

In this case study, a 3 MW wind turbine is combined with a Power-to-Ammonia process as an energy storage. In times of high electricity production, hydrogen is produced by an electrolyser. Due to the low volumetric energy density of hydrogen, it is not directly used as the energy storage. Instead, it is mixed with nitrogen to react to ammonia in a modified of Haber-Bosch-process. The reaction parameters for this exothermic reaction are chosen to be about 155 bar and 420 °C. Ammonia is separated by condensation at the reactor outlet and, since it can be stored as a liquid, it shows a huge advantage in terms of energy density (approx. 3150 kWh/m³). In times of low electricity production, the energy storage is discharged, i.e. ammonia is fed to the same reactor but at a low pressure and a higher temperature. Thus, ammonia is split up into nitrogen and hydrogen, which can be used in a fuel cell. The heat for the reverse reaction is delivered by the combustion of a part of the hydrogen. The overall efficiency of this Power-to-Ammonia process is found to be about 30%. The results are compared to other storage technologies in terms of efficiencies, storage size, investment costs and finally electricity generation costs. For a long-term energy storage, which is capable of transforming a wind turbine into base-load, the Power-to-Ammonia process is looking very promising.