Energy storage systems are an emerging field of interest for the future of electrical grids. With the rapid growth of renewable but intermittent sources of electricity, energy storage systems can help smooth the variations, making the grid more stable and reducing the need for maintaining an overcapacity of power production infrastructure. Among energy storage solutions, power-to-chemical storage is of particular interest due to the high energy density of chemicals and seasonal storage capabilities. Developments made in power-to-chemical technologies can also go a long way towards making the transportation and chemical industries sustainable. The chemical considered in this work is ammonia (NH3), which has advantages of being an easily liquefiable fuel, and has also been in industrial use for over a century. This thesis project aims towards the development of an efficient power-to-ammonia energy storage system using reversible solid oxide cells. The system designed in this thesis is based on direct ammonia utilisation in fuel cell mode, and steam electrolysis coupled with Haber-Bosch ammonia synthesis in the electrolysis mode. A steady state process model is designed in Aspen Plus. This is followed by extensive thermodynamic exergy analysis, used as the basis for the further design and optimisation of the system, with a goal to maximise the round trip efficiency. Exergy analysis is used to identify the sources with most scope for improvement.
The final system can attain a maximum round trip efficiency of 61.20 %, improved from a basic system efficiency of 19.79 %. The maximum round trip efficiency is comparable to values reported in recent times for thermodynamically studied models from literature using other fuels, such as 56.72 % for methanol. The optimised system attains high efficiencies without the need for thermal energy storage or an afterburner. Further, it is demonstrated that the designed system is efficient enough that heat integration across modes with high temperature energy storage does not provide any significant benefit.