A pilot-scale oil/rock thermocline thermal energy storage (TES) system, consisting of a packed bed of two characteristic sizes rocks as storage material and thermal oil as heat transfer fluid, is experimentally studied. Exhaustive temperature instrumentation, with more than 250 imbedded thermocouples, shows that no significant inhomogeneity or by-pass exists in the rock bed and that the heat transfer process is mainly one-dimensional. Investigation of multiple charge/discharge cycles exhibits established behaviour quite different from single charge/discharge cycle and directly influenced by operating control of the TES system. A predictive approach of the packed bed pressure drops, based on hydraulic characteristics inside the rock-bed, has been developed and show very good agreement with the experimental measurements. A one dimensional numerical model based on two energy balances has been developed and validated with experimental data for both single and multiple charge/discharge. These experimental and numerical results confirm that dual-media thermocline storage is controllable and predictable and can be used as efficient storage solution for CSP plant. (C) 2014 Elsevier Ltd. All rights reserved.