Multi-layered thermal energy storage using phase change materials and molten salt for high-temperature waste heat recovery

Industrial high-temperature waste heat remains a largely underused high-grade energy source due to the limited techno-economic performance of conventional thermal energy storage (TES) systems. This paper proposes a novel multi-layered hybrid TES concept that combines phase change materials (PCMs) and molten salts to achieve high energy storage density while maintaining adequate heat transfer performance and stable charging-discharging behavior. The design incorporates two concentric layers filled with different melting temperature PCMs and a central core filled with molten salt, which serves as the heat transfer fluid and a high-temperature thermal buffer. The paper analyzes the thermal response, cycling behavior, and techno-economic performance of the hybrid TES for a given PCM pair. It benchmarks it against the two-tank TES across three scenarios: electricity generation with a power block, heat supply to an industrial process, and standalone energy storage. The optimized hybrid design reduces the levelized cost of electricity (LCOE), heat (LCOH), and storage (LCOS) by up to 2.6%, 12.4%, and 33.2%, respectively. The optimization also provides guidelines for the internal tube configuration, tube pitch, and energy storage allocation between the PCM layers. This article demonstrates the strong potential of our hybrid TES approach for cost-effective high-temperature energy storage.