Concentrating Solar Power (CSP) technology is a promising alternative to fossil-fuelled power plants, yet its transition to a reliable energy source is hindered by the high investment costs of the system. The integration of packed-bed thermocline storage offers a viable solution to enhance affordability and thermal efficiency. This configuration is implemented to increase energy density, enhance thermal stratification and reduce the required mass of heat transfer fluid. This study presents the development of a system-level numerical model in Modelica to simulate the charge and discharge processes of a thermocline tank. The model employs a transient, two-phase, 1D approach to characterize the thermal and fluid dynamic behaviour of the heat storage fluid along the tank’s vertical axis.