In this paper the valorisation of an industrial and cheap by-product from the steel manufacturing, Electric Arc Furnace slag, is studied as new thermal energy storage material in a packed-bed system. For this application, the driving thermo-physical and the thermal and chemical stability of two different slags have been studied. The obtained results have revealed that this material presents similar properties to other materials typically studied as filler/thermal energy storage material in a packed-bed arrangement. The thermal stability and compatibility analysis have indicated that the slag is stable, at least up to 1000°C when working in direct contact with air as heat transfer fluid. In addition, in this work, a heat storage system based on air-packed bed configuration is proposed. In this frame, different operation methods have been computationally analysed in order to maximize the storage capacity and efficiency of the packed-bed design. Overall, this work has demonstrated the high potential of this waste material to obtain an efficient and cost-effective thermal energy storage solution. © 2015 The Authors. Published by Elsevier Ltd.