Experimental characterisation and numerical modelling of a structured thermocline energy storage system under different operating conditions

This paper presents the first pilot-scale experimental demonstration of a molten salt structured thermocline thermal energy storage system. The study combines both experimental and numerical approaches to assess the performance and feasibility of this novel configuration. The experimental campaign was conducted at the thermal energy storage in molten salts (TESIS) facility at the DLR, where the storage tank consists of three vertically stacked baskets filled with clinker bricks. A series of dynamic cycling tests were carried out to evaluate the system's response under realistic operating conditions. In parallel, an unsteady and one-dimensional model was developed to simulate the thermal behaviour of the structured thermocline consisting of different layers of material. The model was validated against experimental data, showing good agreement across various charging and discharging cycles with different cutoff temperatures and mass flow rates. The experiments showed that allowed cut-off temperature affected the thermocline thickness much more than the mass flow rate. Moreover, the experiments successfully demonstrated the feasibility of the thermocline storage concept with refractory bricks, as it was possible to establish a stable thermocline for multiple cycles, confirming the potential of structured configurations for large-scale thermal storage applications. • First pilot-scale demonstration of a structured thermocline thermal energy storage system. • Experimental campaign conducted at DLR's TESIS facility with refractory ceramic bricks as a filler material. • One-dimensional unsteady model validated against dynamic charging/discharging experiments. • Cut-off temperature has a stronger effect on thermocline thickness than mass flow rate. • Demonstrates the feasibility and stability of structured thermoclines for large-scale TES applications.