Progress and Prospects in Thermal Energy Storage Systems

Dear Colleagues,

As the global energy landscape shifts toward decarbonization and sustainability, the need for efficient, flexible, and scalable energy storage technologies has become increasingly critical. Among the various storage options, thermal energy storage (TES) systems have emerged as a key enabler for integrating renewable energy sources, improving grid stability, and enhancing energy efficiency.

TES systems function by storing thermal energy—either as heat or cold—for later use. This can be achieved through three main mechanisms: sensible heat storage, where energy is stored by increasing the temperature of a medium (e.g., water and molten salts); latent heat storage, which exploits the phase change of materials (e.g., paraffin wax and salt hydrates); and thermochemical storage, which relies on reversible chemical reactions to absorb and release heat. These approaches enable TES systems to bridge the temporal gap between energy supply and demand, making them particularly valuable in applications such as concentrated solar power (CSP), district heating and cooling, industrial waste heat recovery, and building climate control.

The scientific basis of TES lies in thermodynamics, heat transfer, fluid flow, and materials science. Progress in these fields has driven the development of advanced storage media with higher energy densities, better thermal conductivity, and material stability. Innovations in system design—such as cascaded storage, hybrid configurations, and integration with heat pumps—have further expanded the flexibility and economic feasibility of TES technologies. Pumped thermal energy storage is an emerging technology that represents a promising application of TES.

Despite these advancements, several challenges persist, including material degradation, energy and exergy losses, hysteresis effects, response time for charging/discharging operations, cost constraints, and system integration complexities. Confronting these challenges necessitates interdisciplinary collaboration and coordinated efforts among researchers and industry stakeholders. The objective of this Special Issue is to highlight research endeavors aimed at overcoming these challenges.

Consequently, this Special Issue aims to is to highlight research aimed at overcoming the identified challenges and showcase cutting-edge advancements in the study, development, and deployment of TES technologies. Theoretical frameworks, methodological innovations, empirical investigations, and comprehensive reviews that critically assess the current state of thermal energy storage systems are welcoming.

Within the scope of heat storage, the general research themes of the invited papers may include, but are not limited to, the following areas:

• Novel Materials and Architectures: Advancing innovative materials and system topologies to improve energy density and transfer efficiency, enhance thermal cycling performance (charging and discharging), and ensure greater safety and scalability.
• Fluid dynamics and heat transfer in thermal energy storage (TES) systems using conventional or phase change materials (PCMs), including thermocline-based configurations.
• Next-Generation Devices and Techniques: Emerging battery chemistries, hybrid systems, pumped thermal electricity storage, high-temperature and unconventional storage mechanisms for diverse applications.
• Modeling, Simulation, and Aging Analysis: Multi-scale modeling, predictive simulations, and experimental validation of degradation and performance over time.
• Smart Management and Control Systems: AI-driven energy management, fault detection, and real-time condition monitoring for optimized system reliability.
• Deployment and Business Models: Thermo-economic frameworks, policy implications, and innovative deployment strategies for on-grid and off-grid integration of local and/or large-scale energy storage.
• Sustainability and Circular Economy: Lifecycle assessments, second-life applications, and advanced recycling technologies for environmental stewardship.

Dr. Abdelhamid Kheiri
Prof. Dr. Ahmed Elgafy
Guest Editors

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