Modular high-temperature geopolymer thermal energy storage: experimental validation and 3D modelling

This work presents the development and validation of a modular high-temperature geopolymer-based thermal energy storage (GeoTES) system operating above 600 °C. The prototype consists of a 3 × 3 assembly of geopolymer modules produced from industrial brick/roof tiles waste and equipped with electrical heating and external insulation. Thermal performance was assessed through two consecutive charging–discharging cycles under controlled laboratory conditions. The heated-heated interface reached a mean peak temperature of 614 °C with highly reproducible heating dynamics, while boundary temperatures remained limited to a mean of 75 °C, confirming effective thermal containment. Heat penetration into the central passive module was uniform, and a comparison between axis-aligned and corner interfaces showed no clear directional dependence under the tested conditions. Differences between axis-aligned and corner interfaces were small relative to overall gradients. Cooling profiles were smooth and repeatable, demonstrating short-term stability under cyclic high-temperature exposure. A three-dimensional transient heat conduction model reproduced the main experimental trends, including internal gradients and boundary attenuation. The simulation and measurement support the conduction-dominated behaviour and the scalability of the modular concept toward larger high-temperature thermal energy storage systems.