Experimental and Numerical Analysis of Hybrid Silica Sand–Basalt Rock Thermal Energy Storage for Enhanced Heat Retention and Discharge Control

In order to guarantee energy sustainability, effective thermal energy storage (TES) systems are required due to the volatile nature of renewable energy sources. In order to optimize energy storage capacity and reduce thermal losses, this study addresses a hybrid TES system that combines basalt rocks and silica sand. Using ANSYS, a computational transient thermal analysis was conducted to compare conduction and convection heat transfer modes, revealing convection as the more effective mechanism. Six sand–rock mixtures were tested experimentally; the 70% sand and 30% rock combination produced the highest temperature increase (52.38 °C), the highest heat storage capacity (3.21 ± 0.19 MJ), alongside an efficiency of 80.5%. This hybrid system had a very low discharge rate (0.24 ± 0.036 MJ lost in one hour), outlining its potential for integration with renewable energy. The results show that hybrid sand–rock TES systems are a cheap and green alternative to solutions that rely on fossil fuels. They can be used for large-scale energy storage.