While renewable heat makes up only 13 % of overall German heat consumption, the share of renewable electricity produced from wind, solar, water, and geothermal power already reached 36 % of overall electricity consumption in 2017. One measure to support the integration of renewable heat in the German energy system is the use of heat storage systems. Although water-based heat storage systems for temperatures up to 100 degrees C are state of the art, systems for temperatures up to several hundred degrees Celsius are still under investigation or in the demonstration phase. Therefore, this work focuses on the development of a simulation model for analyzing and engineering fixed-bed thermal storage systems that are filled with an inert bulk material such as stone fragments.