Abstract: There is provided a modular and high-temperature thermal energy storage system, which withstands temperature and mechanical conditions. The disclosed thermal energy storage system comprises a thermal energy storage assembly to adapt to storage capacity requirements of an energy consumer comprises a plurality of thermal energy storage modules are stacked on top of each other to increase energy storage capacity, wherein the stack of thermal energy storage modules acts as a single thermal energy storage unit. Also disclosed is a regenerator manufactured using a plurality of thermal energy storage modules comprises a first chamber to store heat from a hot source resulting in charging operation, and a second chamber to transfer the stored heat to air resulting in discharging. A parallel configuration of the thermal energy storage modules allows for simultaneous charging and discharging operations.