Numerical modelling of a thermocline energy storage system with internal electric resistances for CSP and PV hybrid plant

With the growing concerns regarding climate change and the need to move towards sustainable energy sources and stable energy supply, energy storage systems have become one of the main focuses of research. This thesis addresses this issue through the numerical modeling of a thermocline energy storage system (TES) integrated with internal electric resistances, designed for Concentrated Solar Power (CSP) and Photovoltaic (PV) hybrid plants. This research is done as a part of an ongoing project of Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA). The introduction describes the main environmental and technical issues that the energy sector faces. Additionally, in this paragraph main aspects relevant to this research are explained, including ways of harnessing solar energy, benefits of hybridization, as well as principles of energy storage systems, with a focus on thermocline systems. Following that, the theoretical framework explores the principles of thermal fluid dynamics and natural convection, offering the understanding necessary for the development of numerical models. The central focus of this study lies in the development of a numerical model for the thermocline energy storage system. The methodology includes benchmark case validation, grid and timestep independence studies, as well as parametric study for the improvement of heat transfer characteristics of the electric heater for two different heater configurations. All simulations are performed in STAR-CCM+, Computational Fluid Dynamics (CFD) software by Siemens. Results consist of a comparative analysis between two different electric heater models, highlighting the advantages and potential of each heater configuration. Based on the results of the simulations, perspectives for future research are proposed, and expected behaviors of the geometry improvement suggestions are described.