One of the most common solutions currently available to meet future energy needs in the world is concentrated solar power
(CSP) plants combined with thermocline thermal energy storage (TES) tank subsystems. The air rock thermocline TES
tank asserts to be an effective and inexpensive TES subsystem for CSP plants. In this study, a discrete element method
(DEM) combined with a numerical model of computational fluid dynamics (CFD) was adopted to investigate the thermal
performance of a scale model of an air rock thermocline TES tank. The study is carried out to optimize TES thermocline
tank’s thermal behavior by changing the heat transfer fluid (HTF) inlet velocity. The DEM–CFD coupled model is validated
against analytical and experimental data. The results show that the use of the distributor reduced the influence of the wall
effect by distributing the HTF in a regular way as the fluid passes through it, especially at high inlet velocity. Moreover, the
results show that each TES tank subsystem has a critical velocity at which the tank operates most efficiently. Furthermore,
the results demonstrated that the maximum value of the overall cycle efficiency was equal to 70.15% at 10 m/s, while the
minimum value was equal to 42.5% at 2 m/s. The highest capacity and utilization ratio are 81.31 and 72.81% at 16 m/s,
while the lowest capacity and utilization ratio are 52.01 and 44.75% at 2 m/s. The pumping energy needed to overwhelm
the pressure drop rises when the HTF inlet velocity increases. This study can provide an effective reference for the efficient
operation regulation and optimal design of the thermocline tank.