A Reliability-Based Framework for Phase Change Material Thermal Energy Storage under Renewable Intermittency: Linking Phase-Change Dynamics, Energy Availability and Load Matching
DOI:
https://doi.org/10.65582/ec.2026.005Keywords:
Phase change materials, PCM thermal energy storage, Renewable energy intermittency, Energy Reliability Index, Energy availability, Load Matching Index, Enthalpy–porosity method, Demand-side reliability, Natural convection meltingAbstract
Phase change material (PCM)-based thermal energy storage is widely recognized as a key technology for integrating intermittent renewable energy into energy systems. However, most existing studies evaluate performance using temperature- or heat-transfer-based indicators, which do not directly quantify the system’s ability to meet time-dependent energy demand. This limitation becomes critical under realistic renewable operating conditions, where temporal mismatch between supply and demand governs system performance. This study develops a reliability-oriented evaluation framework for PCM-based thermal energy storage under intermittent renewable forcing. The model is applied to an n-octadecane storage system subjected to three forcing scenarios with identical daily input energy (103.13 kJ) and increasing fluctuation intensity (σ = 0.00, 0.20, 0.40). The results show that increasing intermittency leads to a systematic degradation in system performance, with ERI decreased by 10.5%, while LMI declined by 14.0% under strong intermittency and LMI decreasing from 0.931 to 0.801. At the same time, the unmet-energy deficit increased by approximately 5.10 kJ, while the critical duration of unmet demand extends from 2.1 h to 5.6 h. Despite nearly identical final liquid fraction values (0.933 to 0.904), the system exhibits significantly different reliability characteristics, highlighting the limitation of conventional thermal indicators. The results demonstrate that temporal variability affects not only the magnitude of stored energy but also its availability during critical demand periods. The proposed framework establishes a direct link between internal phase-change behavior and system-level energy reliability, providing a physically consistent basis for evaluating and designing thermal energy storage systems under intermittent renewable conditions.
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