Laveet Kumar, Bilawal A. Bhayo
Thermal energy storage (TES) plays a pivotal role in enhancing energy efficiency, supporting renewable energy integration, and decarbonizing energy-intensive sectors. This chapter provides a comprehensive overview of TES technologies across three distinct temperature ranges: low, medium, and high. Low-temperature TES (<100°C) is explored in the context of building heating and cooling, refrigeration, and district energy systems, with a focus on sensible heat, phase change materials, and chilled water/ice storage. Medium-temperature TES (100–400°C) is examined through industrial process heat applications, combined heat and power systems, and solar thermal plants, emphasizing the use of oils, molten salts, and eutectic salts. High-temperature TES (>400°C) is analyzed in the framework of concentrated solar power, heavy industries, and long-duration grid storage, highlighting molten salts, ceramics, graphite, and thermochemical systems. A comparative analysis is provided to evaluate performance, costs, and maturity across these ranges. The chapter concludes with insights into future research directions, including advanced materials, hybrid storage systems, and policy drivers, underscoring TES as a critical enabler of sustainable and flexible energy systems.