Challenges and Future Perspectives in Thermal Energy Storage Systems: A Comprehensive Review

Thermal energy storage (TES) plays a vital role in enhancing the efficiency, flexibility, and sustainability of modern energy systems. A structured and critical synthesis of current TES technologies is provided, focusing on their classifications, working principles, material selection, integration strategies, and emerging innovations. Unlike previous TES review studies that focus on individual storage technologies or specific applications, this paper presents a unified, application-oriented comparison of sensible, latent, and thermochemical TES systems, integrating energy equations, efficiency metrics, and real-world project data across multiple energy sectors. TES is categorized in this paper into three primary types: sensible heat, latent heat, and thermochemical storage systems. Sensible heat TES systems typically operate over broad temperature ranges and exhibit relatively low energy densities, commonly below 200–300 MJ/m³, while latent heat TES systems offer moderate energy densities (200–800 MJ/ m³), with near-isothermal operation. Thermochemical TES systems demonstrate the highest energy densities, exceeding 5000 MJ/ m³ and suitable for high-temperature applications (800–1000 °C). A wide range of storage materials, including molten salts, phase change materials (PCMs), solid particles, and chemical reactants, are examined based on thermal properties, economic feasibility, and environmental impact. Applications of TES are outlined for different applications: renewable energy, nuclear power, buildings, district heating, and industrial processes. Key challenges such as low thermal conductivity, material degradation, corrosion, and high system cost are discussed alongside proposed mitigation strategies. Recent developments in artificial intelligence, materials science, and multifunctional system integration are identified as critical enablers for advancing the next generation of TES technologies.