The progressive decarbonisation process and the increased share of renewable energy sources in the grid has increased the need for the development of new approaches to store energy and to increase the efficiency of industrial processes. Increasingly, latent heat thermal energy storage systems are being used, which exploit phase change materials to store a large amount of energy during the phase change. A novel approach to increasing the efficiency of the commonly used Ruths steam storage is currently being investigated in the project HyStEPs, a project funded by the Austrian Research Promotion Agency (FFG) with grant number 868842. In this concept, a container filled with phase change material is placed at the shell surface of the Ruths steam storage.In this diploma thesis, and in contribution to the HyStEPs project, the phase change material of this hybrid storage is modelled in two dimensions using the finite element method. The apparent heat capacity method is applied in aMATLAB implementation and considers heat transfer by both conduction and natural convection. Furthermore, the developed code can handle any desired layout of materials arranged on a rectangular domain. The model was successfully validated using an analytical solution and experimental data, and a cross-validation showed corroboration with the results of the CFD software ANSYS Fluent. A parameter study was conducted and the behaviour of different dimensions and orientations of the phase change material cavity was investigated. The effect of natural convection was found to cause significantly varying behaviour of the studied cavities with different orientation during the charging process, while the effect was found to be negligible during the discharging process.weiterlesen