A thermal energy storage (TES) approach is the primary technology for ensuring the continuous supply of electricity from solar power plants. In solar power research and development, selecting the best storage device and the right thermal storage content remains a major challenge. As compared to the liquid storage substance in a two-tank TES system, the thermocline TES system is a more cost-effective alternative for storing sensible heat. Centred on the concept of using a thermocline tank in concentrated solar power plants, the current study utilizes a range of solid storage materials as filling materials, with air acting as the heat transfer fluid. The major contribution of this research is to directly compare the thermo-economic efficiency potential of four storage materials (Quartzite, BOF-slag, Magnetite, and River rock) used in the thermocline storage tank in order to meet some design criteria of a CSP plant without the need for parametric studies. The thermo-economic performance of an air rock thermocline TES tank was investigated using a discrete element system combined with a numerical approach of computational fluid dynamics. The Quartzite presents the highest overall efficiency of 70 %, followed by the River rock with 61 %, and BOF-Slag equals 54 %, while Magnetite is the least in a row with 52 % overall efficacy. Based on thermal-economic performance evaluation, the results showed that the storage capacity of the Quartzite is greater by 37.5 %, 51.2 %, 21.2 % than BOF-Slag, River rock, and Magnetite.