The main share of greenhouse gas emissions is related to energy production and usage. Therefore, meeting the climate targets of mitigating global warming, set by the United Nations and the European Union, requires a strong expansion of renewable energy production and using this energy efficiently. However, energy from wind and photovoltaic is not controllable and only partly predictable. Therefore, these energy sources are challenging the electrical energy transmission and storage systems. A sector coupling between electricity and gas infrastructure can make the transmission and storage capacities of the gas grid available for the balancing of spatial and temporal mismatch between renewable production and demand. The plans for transforming the natural gas grid to a hydrogen grid, the need for providing carbon free industry feedstock and high temperature heat makes hydrogen an important future energy carrier. Reversible Solid Oxide Cells (rSOC) are a bidirectional electrochemical conversion technology for converting electricity to hydrogen and back. Therefore, they can enable a coupling of electricity and gas grid. Furthermore, the operation at high temperatures allows for thermal coupling with industrial waste heat and district heating, which enables high conversion efficiencies of above 55%. Another strength of this technology is the fuel flexibility. This allows the fuel cell to operate with natural gas from current grids but also with hydrogen. In the present thesis, the energy conversion system based on rSOC cells and its application in energy systems is investigated. Firstly, the effect of system parameters in this rSOC system is studied based on a detailed system model. This allows for the determination of important parameters and their values of an optimally designed rSOC system. Secondly, the possibilities and benefits of thermal coupling for both conversion directions are investigated. It allows deriving the characteristics of good integration sites for this system. Thirdly, the application of the rSOC system is simulated, in different ambient energy systems and market conditions, by means of operational optimisation. This gives an understanding of the economic conditions that are necessary to allow rSOC systems to be profitable. Finally, the system¿s application potential is studied considering grid supportive operation. This makes the identification of most promising installation sites for large scale rSOC systems possible. Thereby, this thesis enables a deep understanding of processes within the rSOC system, proposes approaches for simplified models, shows a simulation option of its application and gives insights into the application potentials.