Thermal Energy Storage for Flexible, Low-Carbon Energy Systems: Materials, Architectures, Design Metrics, and Deployment Pathways

Abstract

Thermal energy storage (TES) is a cornerstone technology for decarbonizing heating and cooling, increasing renewable penetration, and improving grid flexibility by shifting thermal demand in time. This review consolidates TES fundamentals and deployment practice across sensible, latent, and thermochemical pathways, emphasizing how material properties and system architectures translate into practical metrics such as energy density, power density, round-trip efficiency, cycling durability, and levelized cost. Sensible TES remains the most mature and widely deployed, ranging from chilled-water tanks and ice storage in buildings to packed-bed rock, concrete, and molten-salt systems for industrial heat and concentrating solar power. Latent TES (phase change materials, PCMs) enables quasi-isothermal operation and compactness but is constrained by low thermal conductivity, phase segregation, subcooling, and packaging complexity. Thermochemical TES offers the highest theoretical energy density and the possibility of long-duration storage with limited standing losses, yet faces challenges in reactor/contactor design, kinetics, cycling stability, and integration. The review proposes a consistent framework for material screening, component sizing, and system-level evaluation, and summarizes emerging enhancement strategies including encapsulation, finned heat exchangers, metal foams, graphite additives, and cascading temperature stages. Six illustrative figures and three design-oriented tables are provided to connect key concepts: technology classification, energy-density ranges, temperature signatures, PCM property trade-space, suitability scoring, and multi-criteria comparison.