A Dual PCM Thermal Battery Delivering More than 80 kW of Discharge Power Despite the Low Thermal Conductivity of Organic PCM

The increasing deployment of decentralized renewable energy systems requires sus-tainable, affordable, and high-energy-density storage technologies. While thermal en-ergy storage using phase change materials (PCMs) represents a promising solution, its widespread adoption remains limited by the low thermal conductivity of most PCMs, which restricts (dis)charge power. This work demonstrates that high discharge powers can be achieved through optimized heat-exchanger design without enhancing the in-trinsic thermal conductivity of the PCM. After dimensioning simulations for individual homes, a thermal storage demonstrator integrating water heat exchangers immersed in two PCM reservoirs for domestic hot water and space heating was designed and ex-perimentally investigated. The prototype achieved discharge powers exceeding 80 kW, while maintaining 65 kW at breakthrough, within a compact volume of 0.78 m³ despite the low PCM thermal conductivity of only 0.16 Wm⁻¹K⁻¹. This performance is enabled by a global heat-exchanger design providing 80 m² of heat-transfer area while limiting the PCM conduction path to about 1 mm. Thermosiphon-driven natural convection was also observed during melting and may further enhance heat transfer. These results demonstrate that heat-exchanger geometry, rather than enhanced PCM conductivity, is the key design parameter for achieving compact, high-power PCM thermal energy storage.