Table 3 presents commonly used materials for sensible heat storage (SHS), selected based on their specific heat capacity, operating temperature range, thermal conductivity, and density. These properties directly influence the energy storage capacity, charging/discharging rate, and system compactness. Water remains one of the most efficient SHS media due to its high specific heat capacity (4.18 kJ/kg·K), high density (∼1,000 kg/m³), and excellent thermal conductivity (0.6 W/m·K). However, its use is restricted to applications within 0°C–100°C due to phase change limitations. Concrete, widely used in building-integrated storage, has a specific heat between 0.88 and 1.0 kJ/kg·K and operates effectively up to 400°C. Its density (2,300–2,400 kg/m³) and moderate thermal conductivity (1.1–1.4 W/m·K) make it ideal for stationary systems. Cast iron offers a compact thermal storage solution with its high density (∼7,200 kg/m³), decent thermal conductivity (∼55 W/m·K), and operational stability up to 500°C, although its specific heat is relatively low at 0.46 kJ/kg·K. Molten salts such as sodium nitrate (NaNO₃) and potassium nitrate (KNO₃) are widely adopted in solar thermal plants due to their specific heat (1.5–1.6 kJ/kg·K), high operating range (200°C–600°C), and adequate thermal conductivity (0.5–0.6 W/m·K). Their densities typically range from 1,800 to 2,100 kg/m³. Rocks like basalt are valued for high-temperature storage, sustaining up to 1,000°C. With a specific heat of approximately 0.79 kJ/kg·K, density around 3,000 kg/m³, and thermal conductivity ranging from 1.5 to 3.0 W/m·K, they are ideal for packed-bed systems in industrial heat recovery and CSP plants.

Tank-based sensible heat storage (SHS) systems are well-established and widely used in residential and industrial applications. These systems typically employ fluids such as water, thermal oils, or molten salts contained within heavily insulated tanks to minimize heat losses (Khan et al., 2024). Without a phase change, the storing mechanism depends on raising or lowering the fluid’s temperature throughout cycles of charging and discharging. The development of efficient intake diffuser designs brought about by advances in computational fluid dynamics (CFD) has greatly improved thermal stratification and achieved stratification efficiencies surpassing 90%, which in turn has reduced mixing losses (Barrak et al., 2024; Chekifi and Boukraa, 2023). Water-based tank systems are commonly used in residential heating due to their low cost and their suitability for low-to-moderate temperature ranges (Kousksou et al., 2014). Synthetic thermal oils are frequently used as heat transfer fluids (HTFs) in industrial settings because of their capacity to function at higher temperatures, usually up to 400°C https://doi.org/10.3390/en14227486. Eutectic mixes of diphenyl and diphenyl oxide, marketed as Therminol VP-1 or Dowtherm A, are common synthetic thermal oils in the 12°C–400°C temperature range (Alva et al., 2018). They are stable and effective. In concentrated solar power (CSP) facilities and other industrial operations that need high-temperature heat transfer, these oils are very common. Innovations like polymer liners and ceramic internal coatings have been introduced to increase the longevity and durability of storage tanks operating at elevated temperatures. These materials improve resistance to corrosion and material degradation, guaranteeing the tanks’ structural integrity over extended periods of operation (Magliano et al., 2024). Overall, tank-based thermal energy storage systems offer the advantages of operational simplicity, high technology readiness levels, and cost-competitiveness. However, their energy density is generally lower compared to latent heat and thermochemical storage systems, which can limit their applicability in scenarios where space and weight are critical considerations (Mohammad, 2024). Figure 4 depicts a tank storage system integrated with a solar collector and boiler for supplying domestic hot water and space heating.

The main heat storage medium of packed bed thermal energy storage (TES) systems is made of solid materials like alumina, ceramics, or natural rocks. As shown in Figure 5 these systems transmit thermal energy to or from the solid materials without causing a phase transition by passing a heat transfer fluid usually air or thermal oil through the packed bed. The inexpensive cost of materials and straightforward construction of packed bed systems make them especially appealing (Hrifech et al., 2020). According to Strasser and Selvam (2014), these systems typically operate in the 120°C–325°C temperature range, and they cost about $30 per kWh. The design configuration and operating factors, like flow rates and bed packing configurations, have a significant impact on efficiency.

TES systems based on concrete heat vast amounts of specially prepared high-temperature concrete to store thermal energy. Concrete is suited for medium-to high-temperature applications because of its high specific heat capacity, which allows it to absorb and hold onto large amounts of thermal energy (Carrillo et al., 2019). At temperatures as high as 400°C, concrete storage systems have proven to operate dependably. Using concrete materials for storage has a relatively cheap cost of about $1 per kWh (Panneer Selvam et al., 2013). Depending on the insulation quality and system design, these systems can also have significant thermal efficiency. Concrete’s mechanical strength and thermal stability have been improved recently for long-term use (Hoivik et al., 2019). Figure 6 illustrates a smart home energy system incorporating concrete thermal energy storage for storing and distributing heat collected from solar tiles and a combined heat and power (CHP) unit.

Molten salt systems represent a mature and highly efficient technology for large-scale thermal energy storage, particularly in concentrated solar power (CSP) applications. These systems typically employ mixtures of sodium nitrate (NaNO₃), potassium nitrate (KNO₃), and lithium nitrate (LiNO₃) as the storage medium (Ayinla et al., 2024). The salts are heated to a molten state, allowing thermal storage at operational temperatures typically between 290°C and 565°C. At commercial stage, the cost of molten salt storage is estimated between $15–25 per kWh, offering a highly competitive solution relative to alternative storage technologies (Roper et al., 2022). Thermal efficiencies of molten salt systems are remarkably high, often ranging from 90% to 99%, depending on the heat exchange and insulation strategies employed (Roper et al., 2022). Figure 7 shows a molten salt thermal energy storage system integrated with a solar tower and Rankine cycle for efficient solar power generation.

Phase Change Materials (PCMs) are compounds that can undergo reversible phase changes, mainly between solid and liquid states, to store and release significant amounts of thermal energy. A PCM is very useful for thermal energy storage (TES) applications because it collects or releases a sizable amount of latent heat at a virtually constant temperature as it goes through a phase shift.

Phase Change Materials (PCMs) are substances that store and release thermal energy during phase transitions, such as melting or freezing. They are classified into three main categories: Organic, Inorganic, and Eutectic. Organic PCMs include Paraffins and Non-Paraffins, with the latter further divided into Fatty Acids and Bio-Based PCMs like Plant Oils (e.g., coconut, soy), Animal Fats (e.g., beeswax), and Sugar Alcohols (e.g., erythritol). Inorganic PCMs consist of Salt Hydrates and Metallics, known for their high thermal conductivity. Eutectic PCMs are mixtures with a single melting point, categorized as Organic-Organic, Inorganic-Inorganic, Inorganic-Organic, and Bio-Based Eutectics. This classification highlights the diversity of PCMs for various applications, such as thermal energy storage and temperature regulation. Figure 9 effectively illustrates the various classifications of PCMs, providing a clear and structured overview of their categories and subcategories.

The performance of Latent Heat Storage can be hindered by factors such as slow heat transfer rates, low thermal conductivity, phase segregation, and subcooling. Several strategies have been developed to address these challenges and enhance the efficiency and effectiveness of latent heat storage systems.

Materials such as Materials such as salt hydrates (e.g., CaCl₂·6H₂O), metal oxides (e.g., MgO/Mg(OH)₂), and carbonates (e.g., CaCO₃/CaO) are commonly used due to their high reaction enthalpies and well-understood behavior. Table 6 presents a comparison of key thermochemical energy storage materials based on their reaction types and performance characteristics. While materials like Ca(OH)₂ and Mg(OH)₂ are relatively mature and low-cost, they suffer from issues such as sintering and agglomeration, which limit their cycle life. CaCO₃ offers higher energy density but requires very high decomposition temperatures, making it less practical for some applications. Co₃O₄, though promising due to its high energy density, faces challenges related to cost, toxicity, and limited cycle life, indicating it is still largely at the research stage.

Thermochemical energy storage (TCES) reactors are critical components that facilitate reversible heat storage and release through chemical reactions. Effective reactor design must optimize heat and mass transfer, reaction kinetics, cyclability, and integration with energy systems. Table 7 compares different reactor types (fixed-bed, fluidized-bed, and moving-bed) based on their thermochemical materials, temperature ranges, energy density, and cycling stability for energy storage applications.

The efficiency of thermochemical energy storage (TCES) systems largely hinges on the reaction kinetics of their reversible chemical processes. This kinetics dictate the pace at which thermal energy is either stored or released during the system’s charge and discharge phases, thus directly influencing its dynamic response and operational efficiency. In gas-solid based TCES configurations, transport phenomena both mass and thermal are equally vital. Maintaining steady gas diffusion through the reactive bed is crucial to sustaining the reaction, especially for processes like hydration/dehydration and carbonation/decarbonation. In parallel, the thermal conductivity of the material and the heat transfer coefficient between system components determine the effectiveness of thermal energy delivery and extraction.

To better understand and optimize the interaction between reaction kinetics and transport mechanisms, researchers frequently employ simulation tools such as Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA). CFD helps visualize gas flow, temperature profiles, and species distributions within the system, enabling insight into reaction rates and thermal limitations. FEA, on the other hand, is instrumental in evaluating temperature-induced stress, material deformation, and structural reliability under repeated thermal cycles. These modeling approaches play a crucial role in refining TCES system designs and predicting their real-world performance under varied operating scenarios. A notable example is the work by Jiang et al. (2025) who formulated a numerical model to examine heat transfer and conversion dynamics in calcium carbonate (CaCO₃) particles for TCES applications. Their study also assessed the potential of silicon carbide (SiC) additives in improving energy storage capacity and reaction behavior. Also, a study by Yaïci et al. (2013) developed a three-dimensional unsteady CFD model using COMSOL Multiphysics to simulate a seasonal solar thermochemical heat storage system for buildings.

Recent progress in thermochemical energy storage (TCES) has been largely driven by innovations in composite materials and nanotechnology, which effectively tackle critical issues such as material stability, thermal conductivity, and reaction kinetics.

Concentrated solar power (CSP) plants produce electricity by using mirrors or lenses to focus sunlight onto a central receiver, where a heat transfer fluid captures and carries the thermal energy. As shown in Figure 16, this heat is then used to produce steam that drives a turbine connected to a generator. Thermal energy storage (TES) is pivotal in enhancing the performance and reliability of concentrated solar power (CSP) systems by decoupling solar energy collection from electricity generation. Among the TES technologies employed in CSP, sensible heat storage remains the most widely adopted, particularly in commercial systems that use molten salt mixtures such as sodium nitrate and potassium nitrate. These salts exhibit high specific heat capacity and thermal stability, typically operating at temperatures up to 565°C. However, recent advancements have focused on replacing or enhancing molten salts with higher-temperature alternatives, including molten chlorides like magnesium chloride and potassium chloride, which can function above 700°C and offer improved cost-effectiveness and thermal efficiency. Caldwell et al. (2021) demonstrated that certain MgCl₂-KCl-based molten salts are air-stable and less corrosive, enabling CSP systems to operate at temperatures exceeding 750°C without significant degradation, a notable improvement over traditional nitrate salt. Complementing these material developments, innovative diagnostic techniques have emerged to assess thermal properties in real time. Chung et al. (2023) introduced an in-situ method using modulated photothermal radiometry to measure the thermal conductivity of flowing molten chloride salts, providing key insights for optimizing heat transfer performance under operational conditions. Solid particle TES systems, using materials such as ceramic and sand particles, have also gained traction. These systems can operate at temperatures exceeding 1,000°C and serve as both heat transfer and storage media, making them especially suitable for next-generation CSP plants targeting higher thermodynamic efficiencies. Such systems offer high energy density and thermal stability, and their integration into CSP plants is increasingly being explored due to their scalability and cost-effectiveness (Barrasso et al., 2023).

Thermochemical energy storage (TCES) stands out as a highly promising thermal energy storage (TES) approach for concentrated solar power (CSP) due to its superior energy density and capability for long-duration storage with minimal thermal losses. TES is critical for CSP plants, enabling consistent electricity generation by storing thermal energy during peak solar periods for use during low or no sunlight hours. For example, the Andasol CSP plant in Spain employs a two-tank molten salt system (60% NaNO₃, 40% KNO₃) to store 7.5 h of thermal energy at 565°C, providing 50 MW of dispatchable power with a round-trip efficiency of ∼93–98% and reducing the Levelized Cost of Electricity (LCOE) by ∼10–15% compared to CSP plants without TES. Emerging innovations, such as the solid particle TES system tested at Sandia National Laboratories’ Falling Particle Receiver, utilize ceramic particles to reach temperatures exceeding 1,000°C, boosting thermodynamic efficiency by ∼20% over conventional molten salts. However, issues like particle attrition and high capital costs (∼$20–30/kWh) remain. TCES systems, such as the CaO/CaCO₃ looping in the GLASUNTES project, deliver high energy density (∼1.5–3.0 GJ/m³) but require advancements in catalysts to overcome slow reaction kinetics. Systems based on calcium looping (CaO/CaCO₃) and magnesium-based redox cycles are under active development. For example, the GLASUNTES project recently demonstrated the use of molten glass in thermochemical systems at temperatures up to 1,300°C, significantly pushing the boundaries of operational temperature ranges in TES (GLASUNTES, 2016). Moreover, recent advancements include cascaded TCES configurations designed to optimize round-trip efficiency and exergy performance Lu et al. (2024) investigated such systems using coupled redox reactions, achieving better temperature control and reduced thermal degradation. System integration strategies have also seen significant refinement. Thermosyphon-based charging mechanisms in stratified single-medium storage tanks have shown enhanced efficiency in preserving thermal stratification without requiring mechanical pumps. Parida and Basu (2022) experimentally validated the efficacy of this approach in achieving rapid and uniform heat distribution, reducing exergy losses and simplifying system design.

From an economic perspective, integrating TES into CSP plants contributes significantly to lowering the Levelized Cost of Electricity (LCOE) by increasing plant capacity factors and reducing dependence on auxiliary fossil fuel systems Borge-Diez et al. (2022) conducted an economic assessment showing that TES-enhanced CSP plants are better equipped to respond to electricity price volatility, offering both technical and market-driven resilience. Additionally, life cycle assessments of CSP plants equipped with TES have indicated significant reductions in greenhouse gas emissions and water usage, reinforcing their role as a sustainable energy technology (Kuravi et al., 2013).

Looking ahead, hybrid CSP systems that integrate photovoltaic (PV) modules with TES are being investigated to enhance flexibility and dispatchability (Sumayli et al., 2023; Zapater and Vicente, 2023). These hybrid configurations allow for optimized use of solar resources across varying conditions, bolstering grid reliability. Continued research into novel high-temperature materials, cost-effective thermochemical cycles, and hybrid energy systems is expected to further solidify TES as a cornerstone of future CSP technologies and global renewable energy strategies.

Thermal Energy Storage (TES) systems are pivotal in enhancing the efficiency of fossil fuel and nuclear power plants by capturing and reusing waste heat, thereby reducing fuel consumption and greenhouse gas emissions. These systems store surplus thermal energy from high-temperature exhaust gases or steam cycles, enabling better alignment of energy supply with demand, especially during peak loads or rapid fluctuations. For instance, a pilot TES system at the Drax Power Station in the UK utilizes molten salts to capture exhaust heat at ∼500°C, cutting coal use by ∼5% and CO₂ emissions by ∼50,000 tons annually. At Iran’s Bushehr Nuclear Power Plant, integrating Organic Rankine Cycle (ORC) with TES boosts electrical output by 0.077% and reduces thermal discharge by 15%–20%. However, challenges such as corrosion in high-temperature systems and retrofit costs (∼$25–40/kWh) persist. Ongoing research focuses on optimizing heat exchanger designs and exploring cost-effective materials like basalt rocks to enhance TES scalability and adoption in power plants for a sustainable energy future.

Figure 17 depicts a thermal energy storage (TES) system integrated into fossil/fuel plants, where high-temperature exhaust gases (1,200°C) are captured, stored, and later discharged to preheat scrap, produce steam, or supply heat-demanding processes, improving energy efficiency and waste heat recovery.

Recent advancements have highlighted the integration of Thermal Energy Storage (TES) with Combined Heat and Power (CHP) systems and innovative thermodynamic cycles to optimize energy recovery in nuclear power plants. For instance, Salaudeen et al. (2025) explored the feasibility of using Organic Rankine Cycle (ORC) technology for waste heat recovery at Iran’s Bushehr Nuclear Power Plant. Their study demonstrated a modest 0.077% increase in electrical output and a significant 15%–20% reduction in thermal discharge into the Persian Gulf, showcasing both performance improvements and environmental benefits. In the nuclear sector, TES also contributes to peak shaving and enhances load-following capabilities. (Obara and Tanaka (2021) proposed a gas hydrate heat cycle for waste heat recovery, which showed higher conversion efficiency compared to conventional systems, indicating a promising approach for future energy recovery. Additionally Srivastava et al. (2024) conducted a thermo-economic feasibility study on ORC technology for waste heat recovery in Indian nuclear power plants. Their findings demonstrated improved efficiency and economic viability, further emphasizing the potential of advanced thermodynamic cycles in enhancing the sustainability of nuclear energy production. These studies demonstrate that Thermal Energy Storage (TES) technologies are increasingly being adopted in fossil fuel and nuclear power plants to capture waste heat, enhance efficiency, and reduce environmental impact. The integration of advanced thermodynamic cycles, such as Organic Rankine Cycle (ORC) and gas hydrate systems, has shown significant operational and ecological benefits, underscoring the potential of TES to improve both plant performance and sustainability.

Thermal energy storage (TES) is increasingly vital for enhancing energy efficiency and lowering emissions in energy-intensive industrial processes such as steel production, cement manufacturing, and chemical processing. Innovative TES solutions are transforming these sectors. For example, at Sweden’s SSAB steel plant, a packed-bed TES system utilizing basalt rocks captures waste heat at 600°C to preheat scrap metal, reducing energy consumption by ∼10%. In cement production, Heidelberg Cement’s Lixhe plant employs calcium-based thermochemical energy storage (TCES) to store heat at 850°C, achieving ∼15% lower CO₂ emissions. In chemical processing, metal hydride TES systems, such as those using MgH₂, offer high energy density (∼2 GJ/m³) but are limited by slow hydrogen release kinetics. Ongoing research aims to improve reaction rates and reduce material costs to enhance the scalability and adoption of these emerging TES technologies, driving sustainable industrial operations toward a low-carbon future.

In the steel industry, molten salt TES systems are employed to capture and store waste heat from electric arc furnaces. This stored heat can be used to preheat raw materials or generate steam, which enhances the overall energy efficiency of steelmaking operations and reduces energy consumption (Klopčič et al., 2023). In the cement industry, calcium-based thermochemical energy storage (TCES) systems are gaining traction. These systems use calcium oxide (CaO) in reversible chemical reactions to store and release thermal energy, significantly improving energy efficiency during the high-temperature clinker production process. This approach helps reduce the overall energy consumption and CO₂ emissions associated with cement manufacturing (Da et al., 2020; Hu et al., 2025). The chemical industry is also exploring the use of metal hydride-based TES systems. Metal hydrides absorb and release heat through reversible chemical reactions, making them suitable for chemical processes that require efficient heat management. These systems offer significant promise for improving heat storage and recovery, reducing energy demand and improving process sustainability (Chavan et al., 2022). These advancements demonstrate how TES technologies are improving the efficiency of industrial processes in multiple sectors, offering effective solutions for waste heat recovery and better energy utilization. Figure 18 depicts a thermal energy storage (TES) system for industrial processes, utilizing wind and solar energy, along with an optional heat source, to charge hot and cold storage tanks, which then discharge to power a turbine for electricity and optionally support district heating.

Smart grids are advanced electricity networks that use digital technology to monitor and manage the generation, distribution, and consumption of electricity. The integration of Thermal Energy Storage (TES) into smart grids is emerging as a promising strategy to enhance demand-side management (DSM) and facilitate renewable energy storage. This can help stabilize energy supply, reduce peak demand, and improve the flexibility of the grid to accommodate intermittent renewable energy sources like solar and wind (Tan et al., 2021). For instance, Denmark’s Marstal District Heating System uses a 75,000 m³ water tank for seasonal TES, storing solar heat at 90°C and reducing fossil fuel use by ∼30%. PCM-based TES in residential smart grids, like those in Germany’s E. ON pilot projects, shifts cooling loads, reducing peak demand by ∼20%. Figure 19 illustrates a thermal energy storage (TES) system for a smart grid, where a solar generator powers a low voltage AC bus, supported by hydrogen storage, a fuel cell, and a battery, all connected through AC/DC converters to manage load and grid interactions via a transformer.

Demand-side management (DSM) is a strategic approach to balancing electricity demand with supply, particularly during peak periods. Thermal Energy Storage (TES) systems play a crucial role in DSM by storing thermal energy during off-peak hours and releasing it when demand is high, thereby reducing the need for additional electricity generation and flattening demand curves for more efficient energy distribution. Phase Change Material (PCM)-based TES systems, for instance, can capture excess heat during low-demand periods such as at night or when solar energy production is high and release it during peak hours. This not only reduces the burden on the power grid but also optimizes energy use across sectors. In residential buildings, TES can be integrated through hot water tanks or thermally active building materials (e.g., walls and floors), which absorb and later release heat for space heating or cooling. This reduces dependence on grid electricity, contributes to energy conservation, and lowers utility costs. Moreover, TES significantly benefits consumers using heating, ventilation, and air conditioning (HVAC) systems by enabling load shifting. Systems like chilled water or ice storage can precool water at night when electricity is cheaper and demand is lower and use it for daytime cooling, thereby easing grid stress and enhancing cost efficiency (Groppi et al., 2021).

TES is also vital in supporting renewable energy penetration. When there is excess electricity generation (e.g., during peak solar hours), that energy can be converted into thermal form, stored as sensible or latent heat and used later when renewable generation is low. This strategy reduces curtailment and allows for better alignment between supply and demand (Kataray et al., 2023). Furthermore, in smart grid settings, TES systems are increasingly integrated with advanced energy management systems that use real-time grid data, dynamic pricing, and weather forecasts to optimize the timing and usage of stored thermal energy (Bakare et al., 2023).

Data centers, consuming approximately 1%–1.5% of global electricity, rely heavily on energy-intensive cooling systems to maintain optimal server temperatures amid rising global demand for data storage and processing. Thermal energy storage (TES) offers innovative solutions to enhance energy efficiency in data center cooling. For instance, Google’s Hamina data center in Finland employs chilled water TES to store cooling capacity at night, reducing daytime energy consumption by ∼15%. Similarly, the Green Mountain Data Center in Norway utilizes underground TES (UTES), leveraging stable ground temperatures to cut cooling costs by ∼20%. Recent advancements in TES, such as nano-enhanced phase change materials (PCMs) and hybrid systems, show promise for further improving thermal performance and scalability. However, research gaps persist, including challenges in scaling UTES for smaller data centers and enhancing PCM encapsulation for high-cycle durability.

Data centers require continuous cooling, traditionally achieved through energy-intensive air-conditioning systems, with cooling accounting for a substantial share of total energy consumption. To address this, Thermal Energy Storage (TES) systems such as Phase Change Material (PCM)-based units or chilled water storage tanks are increasingly being integrated into data center operations. These systems can store excess cooling capacity during periods of low demand (e.g., nighttime) and release it during peak operational hours, when computational loads and cooling needs spike. This load shifting not only alleviates pressure on cooling equipment but also enables the use of lower-cost electricity during off-peak times, improving overall energy efficiency. Innovative approaches, such as Underground Thermal Energy Storage (UTES), are being explored to further enhance cooling efficiency. UTES systems leverage the earth’s stable underground temperatures to store and retrieve thermal energy, offering a sustainable and resilient cooling solution for data centers (Winick et al., 2025). The integration of Thermal Energy Storage in data center cooling strategies presents a promising avenue for enhancing energy efficiency, reducing operational costs, and ensuring reliable performance. As data centers continue to grow in size and energy demand, the adoption of TES technologies will be instrumental in achieving sustainable and resilient operations. Figure 20 shows a thermal energy storage (TES) system for data centers, utilizing a cold energy storage system with a chiller, pump, and plate heat exchanger to manage cooling for racks through indirect contact type cooling, supported by a cold room and optional hot room integration.

TES enhances building energy efficiency. In Denmark’s Drake Landing Solar Community, a borehole TES system stores solar heat seasonally, achieving 97% solar fraction for space heating. PCM-integrated walls in retrofit projects, like those in Spain’s Cubelles pilot, reduce cooling energy by ∼25%. Thermal Energy Storage (TES) plays a crucial role in boosting energy efficiency and promoting sustainability in both residential and commercial buildings. By capturing and storing thermal energy during off peak periods such as at night or when renewable energy generation is high TES systems can release this energy when demand increases thereby optimizing heating cooling and hot water supply. In building applications TES commonly uses mediums like water tanks Phase Change Materials (PCMs) or thermally massive structures such as concrete slabs to store and later distribute thermal energy. This not only helps shift heating and cooling loads but also lowers overall energy consumption and operating costs. For instance, integrating TES into building envelopes can regulate indoor temperatures more effectively by absorbing excess heat during the day and releasing it at night (Pavlov and Olesen, 2011). In domestic hot water systems, solar energy can be harnessed during the day to heat water which is then stored in insulated tanks for later use particularly at night or during cloudy weather reducing dependence on conventional energy sources (Seddegh et al., 2015). Likewise, underfloor heating systems equipped with TES circulate warm water through embedded pipes or heat retaining materials radiating heat evenly across the space. These systems are more energy efficient than conventional heating methods and benefit greatly from the thermal buffering that TES provides (Nair et al., 2022). Overall the integration of TES into buildings for space heating and cooling domestic hot water and underfloor heating significantly enhances energy efficiency lowers energy bills and contributes to a more sustainable built environment. Figure 21 demonstrates a thermal energy storage (TES) system for buildings, where solar panels power a hydrogen-based energy cycle (H12-NEC) with NEC dehydrogenation and hydrogenation, storing energy in an H12-NEC/NEC tank to provide heat and electricity, supplemented by an electronic fuel cell and grid connection.

Thermal Energy Storage (TES) is becoming essential for improving the efficiency and sustainability of transportation, especially in electric vehicles (EVs) and refrigerated transport, with recent research highlighting its role in tackling energy management issues. TES improves thermal management in electric vehicles (EVs) and refrigerated transport. An example is Tesla’s Model S uses PCM-based battery thermal management systems (BTMS) to maintain battery temperatures, extending lifespan by ∼10%. In refrigerated trucks, PCM systems like those tested by Thermo King maintain 0°C–5°C, reducing energy use by ∼15%.

Effective thermal management systems (TMS), including air cooling, liquid cooling, and phase change material (PCM)-based cooling, are employed to maintain optimal battery temperatures, thereby enhancing efficiency and extending battery lifespan (Hwang et al., 2024). In electric vehicles, TES systems are being explored to optimize battery thermal management (Manisha et al., 2025). discusses the development of compact, lightweight, and high-performance Battery Thermal Management Systems (BTMS) achieved by constructing bi-functional heating-cooling plates, resulting in outstanding thermal control and energy storage density. Additionally, a novel synergetic cooling and charging strategy using a gallium-based liquid metal flexible charging connector has been developed to address the challenges of high-power direct current fast charging in EVs (Liu et al., 2025). Figure 22 describes a thermal energy storage (TES) system for electric vehicles, which includes a PCM heat exchanger combined with a dual-layer cabin heater. The system is regulated by an AC-powered PCM charger controller and is connected to the vehicle’s main system, featuring a PTC heater and a reservoir to maintain effective temperature management. In refrigerated transport systems, Thermal Energy Storage (TES) technologies, particularly those utilizing Phase Change Materials (PCMs), are instrumental in maintaining the required temperatures for perishable goods during transit. These systems absorb and release thermal energy to ensure temperature stability without continuous power supply, which is especially beneficial during power outages or transportation delays. TES systems enhance energy efficiency and thermal performance in cold chain logistics. For instance, a study by Calati et al. (2022) introduces a novel insulated wall concept for refrigerated trucks, integrating latent thermal energy storage with PCMs to improve temperature regulation. Furthermore, Selvnes et al. (2021) the application of cold thermal energy storage using PCMs in refrigeration systems, emphasizing their potential to reduce energy consumption and environmental impact. Recent research has focused on developing advanced TES materials, such as nano-encapsulated PCMs, which offer improved thermal conductivity and energy storage capacity. These materials enhance the performance of TES systems in transportation by providing more efficient thermal management and reducing the size and weight of storage systems. Such advancements are paving the way for more compact, lightweight, and efficient TES solutions, making them more viable for widespread adoption in various transportation applications.

Hydrogen is a versatile, clean energy carrier with high energy content per unit mass (120 MJ/kg), but its low volumetric density at ambient conditions poses significant storage challenges. Efficient storage is crucial for applications in transportation, stationary power, and industrial sectors (Usman, 2022). TES enhances hydrogen storage efficiency in metal hydride systems. The H2M project in Germany integrates PCMs with MgH₂, capturing heat at 300°C during hydrogen absorption and reusing it for desorption, improving efficiency by ∼25%. Challenges include slow kinetics and high material costs (∼$80–120/kWh) however research into complex hydrides like Na₂Mg₂NiH₆ is addressing these issues.

Metal hydrides offer a promising solution by chemically absorbing hydrogen, enabling storage at lower pressures and ambient temperatures. However, the hydrogen absorption (hydriding) and desorption (dehydriding) processes in metal hydrides are inherently exothermic and endothermic, respectively, necessitating efficient thermal management to optimize performance (Davis Cortina et al., 2024). Integrating TES with metal hydride systems addresses this need by capturing the heat released during hydrogen absorption and reusing it during desorption, thereby enhancing the overall energy efficiency of the storage system.

Metal hydrides typically store hydrogen via reversible chemical reactions that either absorb or release heat during the processes of hydrogen absorption and desorption. Thermal Energy Storage (TES) systems help regulate this heat flow, thereby enhancing the overall energy efficiency and economic viability of the storage system. For example, the heat generated during the exothermic hydrogen absorption process can be captured by TES systems using sensible, latent, or thermochemical storage materials and subsequently reused to provide the heat needed for the endothermic hydrogen release phase. A comprehensive review by Davis Cortina et al. (2024) explores the integration of Thermal Energy Storage (TES) within metal hydride systems, emphasizing the potential of such combined systems to enhance thermal management and system efficiency. The study examines various TES materials, including sensible, latent, and thermochemical storage options, and assesses their compatibility with different metal hydrides. The authors highlight that coupling TES with metal hydride storage can lead to more compact, efficient, and cost-effective hydrogen storage solutions, particularly beneficial for stationary energy applications and industries with significant waste heat. The review also discusses the thermophysical, thermodynamic, and kinetic properties of metal hydride materials, providing insights into their suitability for integration with TES systems. Additionally, it presents a detailed analysis of notable metal hydride–TES coupled systems from the literature and assesses potential future developments in the field, offering guidance for researchers and engineers in advancing innovative and efficient hydrogen energy systems. Additionally, research into complex hydrides, such as Na₂Mg₂NiH₆, has shown promise for dual applications in hydrogen and thermal energy storage (Humphries et al., 2018; Mohammadi et al., 2022) explores the thermal decomposition and hydrogen release characteristics of Na₂Mg₂NiH₆, highlighting its suitability for reversible hydrogen storage and thermal energy applications. Figure 23 illustrates a hydrogen storage system for a steam power plant, utilizing high-temperature (HT) and low-temperature (LT) metal hydrides to store and release hydrogen, powered by a solar concentration system during sun availability, and driving a steam generator and turbine for continuous 24/7 operation. The material efficiently desorbs hydrogen at 278°C–350°C and maintains stable capacity across multiple hydrogenation cycles. In summary, the integration of TES with metal hydride hydrogen storage systems offers a synergistic approach to address the thermal management challenges inherent in hydrogen storage.

Integrating advanced computational methods with thermal energy storage (TES) systems has significantly enhanced design precision, operational efficiency, and material innovation. Below is a technically detailed analysis supported by case studies and verification methodologies.

High-fidelity CFD and FEA enable precise prediction of thermal behavior in TES systems. For example, finite element models using COMSOL and MATLAB have been employed to simulate phase change material (PCM) melting dynamics, capturing interface movement and heat transfer rates in latent heat storage systems (Zeneli, et al., 2019). These models validate energy balance equations and ensure grid-independent solutions, critical for scaling simulations to real-world applications.

Machine learning algorithms optimize charge-discharge cycles by analyzing historical load data and weather patterns. For instance, AI controllers dynamically adjust HTF (heat transfer fluid) flow rates to balance supply-demand mismatches in hybrid TES systems, reducing energy waste by up to 20% (Guntreddi et al., 2024).

One of the major challenges in SHS systems is the low energy density of conventional materials such as water and concrete, which necessitate large storage volumes. To address this, researchers are focusing on the development of low-cost, high-specific-heat materials that can maintain thermal stability above 600°C. Additionally, improving thermal insulation and stratification in storage tanks is critical to minimizing heat loss. Promising alternatives such as recyclable basalt rock is being explored for industrial-scale energy storage applications (Li Y.-C. et al., 2022).

LHS systems, which use phase change materials (PCMs) such as paraffin wax and salt hydrates, are limited by low thermal conductivity and issues like supercooling and phase segregation. To improve their performance, nano-enhanced PCMs with thermal conductivities greater than 1 W/m·K and cycling stability exceeding 10,000 cycles are being developed. Furthermore, bio-based PCMs like erythritol offer sustainable alternatives, but their costs must fall below $30/kWh to be commercially viable (Saqib and Andrzejczyk, 2023).

TCES systems are capable of storing energy at very high densities, but their deployment is hampered by material degradation due to sintering and agglomeration, especially in carbonate-based cycles like CaCO₃/CaO and salt hydrates such as MgSO₄·7H₂O. Innovations in catalyst development and reactor design are necessary to improve reaction kinetics and cycling stability (targeting over 5,000 cycles), as well as to reduce decomposition temperatures (typically >800°C for CaCO₃). These improvements are central to the viability of TCES in concentrated solar power (CSP) systems (Raganati and Ammendola, 2023).