Phase change materials (PCMs) are among the most promising candidates for thermal energy storage (TES) applications. However, their low thermal conductivity and slow phase change phenomena are major restricting factors for efficient TES applications. This work investigates a novel thermal energy storage aggregate (TSA) composite based on butyl stearate (BS), a low-cost, commercially available, supported by graphene nanoparticles (GN) as high conductive agents stabilized in the porous media of expanded clay (EC) aggregates. Based on GN's high thermal conductivity, adding 2% GN in the composite shows enhanced heat transfer, while the composite TSA containing 2% GN, compared to plain EC, decreases the maximum temperature peaks up to 5 ℃ in heating cycles. Furthermore, the leakage test demonstrates that the developed TSA exhibits excellent thermal stability, indicating the potential to maintain its thermal performance even after multiple thermal cycles. Finally, the thermal performance of a TES concrete (TSC) containing TSA with 3.5% PCM-2GN by weight of TSC decreased the peak ambient temperature fluctuations up to 3.5 ℃ for a test in complete insulation condition. This reduction on TSC surface was between 9 ℃ to 10.8 ℃ in 1D heat transfer condition with 0% and 50% humidity, respectively. The novel-designed TSA composites pave the way for a practical and effective solution to enhance internal building comfort and energy efficiency.