In this work steel slag, one of the main by-products of the steelmaking industry, is proposed as a competitive and effective heat storage material. The implemented storage design suggested for this material is a solid packed bed arrangement based in the temperature stratification (thermocline) phenomena. In particular, two different solutions based on different storage tank geometries, cylindrical and conical, have been modeled by using computational fluid dynamic (CFD) methods. In addition, both geometries have been simulated under two different operation modes as a function of the used heat transfer fluid: solar salt and air. This selection permitted to investigate the operation of the proposed storage for current CSP technologies which make use of molten salt as storage/heat transfer fluid and also the analysis of the system when the operation parameters are potentially associated to new generation CSP plants at higher temperatures, above 600 °C. The comparison between the simulated systems has allowed to determine the influence of the driving parameters on the proposed storage solution, such as the operation temperature range, nature of the heat transfer fluid or geometrical implications. The thermal management of the storage unit has also been shown during a transient operation up to a reproducible behavior. Overall, the selected parameters for the presented modeling analysis have revealed the high potential of steel slag as heat storage material and the suitability and flexibility of the implemented packed bed solution. © Copyright 2015 by ASME.