This Master's thesis concerns the design, modelling and analysis of a thermal energy storage (TES) system using Heatcrete as storage material and water/steam as heat transfer fluid (HTF). The discharge process of the TES system has been investigated, and the output has been coupled to a simple power plant turbine. Two dynamic models have been developed: a Lumped-Mass-Model and a FVM-Model. The Lumped-Mass-Model simulates the discharge temperatures of the concrete and HTF elements in the pipes. The FVM-Model simulates the temperature gradient throughout the concrete and calculates an average temperature efficiency. The two models are coupled in order to implement the concrete temperature gradient in the Lumped-Mass-Model. Furthermore, different discharge scenarios have been investigated. The thesis concludes that the concrete and HTF temperatures decrease over time, as the TES system is discharged. It is also concluded that the efficiency of the concrete does not affect the heat transfer rate significantly, however it decreases, as the efficiency decreases. Finally, different TES system and turbine outputs are obtained when different scenarios of time and temperature are investigated, and a double size TES system corresponds approximately to the doubled heat transfer rate and turbine output.