Thermal Energy Storage Technologies: A Review of Current Landscape and Future Directions

1.1 Importance of energy storage in renewable energy systems

Global leaders endorse their commitment to limiting global warming to 1.5°C, and the UN urges accelerated innovation and technology sharing to reduce carbon emissions.¹⁹ By enabling low-carbon heating, thermal energy storage effectively mitigates the temporal mismatch between variable renewable energy generation and household demand. This capability enhances overall system efficiency, improves reliability, and supports the broader transition toward sustainable energy infrastructures.²⁰ TES has become key for ensuring reliable and uninterrupted energy supply across diverse areas, ranging from building systems to large-scale power generation, however, use of TES remains limited.^21,22

1.2 Role of TES in decarbonization and grid stability

Carbon dioxide emissions are a foremost contributor to global warming and represent a critical challenge that must be addressed by the current generation.²³ Transition from fossil fuel to renewable energy extremely a cornerstone strategy for reducing carbon emission and advancing sustainable electricity generation, at the same time it improve long-term energy security and global climate objectives.^24,25 Reducing carbon emissions in the power sector is essential for sustainable development, and while renewable sources provide cleaner alternatives to fossil fuels, their intermittency necessitates the use of long-duration energy storage systems to stabilize supply-demand fluctuations and ensure grid reliability.²⁶

2.1 Sensible Heat Storage (SHS)

SHS stores and releases thermal energy by increasing or decreasing the temperature of a material and relying on its specific heat capacity without undergoing a phase change. It is more cost-effective and easier to implement than latent heat energy storage and thermochemical energy Storage, though its lower energy density necessitates larger material volumes for equivalent energy storage.^13,30 Sensible heat energy storage commonly utilizes water, molten salts, and rocks as storage media (see Table 1). Each material provides unique benefits: water is low-cost and widely available, molten salts offer high thermal stability and suitability for elevated temperature ranges, while rocks enable scalability and robustness for large-scale applications.^30,31

Configuration of a TES is an essential element to optimize the over all performance of system. And configurations of Sensible Heat Storage can exist in different forms as follows:

2.2 Latent Heat Storage (LHS)

As shown in Table 2, LHS systems use materials like salt hydrates, ice, polyethelen glycol and paraffins that absorb and release heat during phase changes, offering high energy density and stable temperature operation,^35,36 making them effective for handling temperature and energy in thermal applications³⁷ and well-suited for compact and stable thermal energy storage, while maintaining nearly constant temperatures.^38,39 But their inherently low thermal conductivity limits heat exchange efficiency, and to address this, PCMs incorporating carbon-based 3D structures have emerged as promising solutions to improve thermal performance and system responsiveness.^40–42

Enhancing thermal conductivity, optimizing system design, and integrating sustainability are essential strategies to improve the performance and cost-efficiency of LHS storage systems.

Nano-enhanced PCMs (or Incorporating nanoparticles) such as carbon nanotubes, graphene, or metal oxides and biochar can improve their thermal conductivity and structural integrity during energy storage cycles.^43,44

Encapsulation is a technique employed to contain and safeguard PCMs within a protective shell or enclosure. This method prevents direct contact with the external environment and avoids leakage during the PCMs transition from solid to liquid.^45,46

Sustainable phase change material (PCM) selection is critical for identifying storage media that achieve an optimal balance among thermal performance, environmental sustainability, and cost-effectiveness. While, LHS system have a convincing solution for renewable energy storage, overcoming the thermal conductivity limitations of PCMs remains crucial.⁴⁷

2.3 Thermochemical Energy Storage (TCES)

TCES captures and releases heat through reversible chemical reactions, and it offering high energy density and long-duration storage potential.⁴⁸ As hown in Table 3, It is highly efficient for long-term energy storage because it stores heat in chemical bonds and recovers it through reversible reactions when needed.^49–51 TCES materials capture and discharge heat through reversible chemical or sorption reactions, providing high energy capacity and enabling durable storage for industrial and renewable energy applications.⁵² Unlike sensible or latent heat storage, TCES can preserve energy for long durations with minimal losses, making it suitable for seasonal and high-temperature applications.⁵¹

2.4 Hybrid TES

As shown in Figure 2, hybrid TES systems broadly adopted across sectors like buildings, industry, solar power, and district energy networks to improve energy efficiency, energy density, thermal efficiency, flexibility, responsiveness to changing operational demands, and renewable integration.^56,57

Figure 2. Hybrid TES configurations and applications.

Illustration of hybrid TES systems that integrate sensible, latent, and thermochemical mechanisms to enhance energy density, operational flexibility, and responsiveness across building, industrial, and solar power applications.

It integrates sensible, latent, and thermochemical mechanisms to enhance energy density, operational flexibility, and responsiveness to variable energy demands in multiple sectors.^58–60 TES selection depends on operating temperature, storage duration, and spatial limitations, and each selection influencing system design and performance (see Table 4). Selecting the right TES system requires aligning the technology with the specific thermal demands and the conditions in which it will operate.^15,62,64

3.1 TES in solar thermal systems (e.g., CSP)

Solar energy is an essential resource in daily life, and applied for home heating, hot water supply, and solar cooking purposes ( Figure 3). The inherent variability of solar energy, driven by weather conditions and diurnal cycles, necessitates reliable energy storage systems to guarantee the consistent and efficient operation of solar infrastructure. In regions with high Direct Normal Irradiance (DNI), CSP plants benefit significantly from TES systems by ensuring a stable and continuous power output, even after sunset, thereby improving the reliability and efficiency of solar energy generation.^65,66

Figure 3. Application areas of TES in solar thermal, building HVAC, and industrial systems.

Schematic representation of TES deployment in concentrated solar power plants, building heating/cooling systems, and industrial waste heat recovery, highlighting their role in improving efficiency and reliability.

3.2 TES in building HVAC and district heating

For heating and cooling application, TES typically operates at low temperatures—close to ambient conditions—and relies on sensible or latent heat storage methods and supports flexiblity and building efficiency and energy management,³⁷ reduces the need for multiple refrigeration units and alleviates pressure on the electrical grid. Incorporating thermal energy storage into energy infrastructures improves efficiency, mitigates greenhouse gas emissions, and accelerates the transition toward sustainable and resilient energy systems.

3.3 TES for industrial waste heat recovery

Waste heat recovery is an effective approach for improving the efficiency of thermal system and lowering overall energy use. By capturing heat energy released from industrial processe and power generation, TES operate more efficiently, reducing fuel demand and lowering operating cost of the industry, and this approach contributes to the reduction of greenhouse gas emission.^63,67,68

3.4 Hybrid systems: TES + batteries or hydrogen

TES with electrochemical (batteries) or chemical (hydrogen) storage technologies are gaining traction as advanced solutions for balancing renewable energy supply and demand. Batteries manage rapid fluctuation, while TES shifts thermal loads over longer duration, reducing electricity demand and enhancing system resilience. Hydrogen empowers long-duration, seasonal energy storage, and mantain decarbonization across heating and electricity sectors; and provides a practical solution for energy supply in off-grid or remote contexts. By integrating diverse storage technologies, these systems capitalize on the unique advantages of each type, thereby enhancing performance across varying timescale and application context.^69,70

4.1 Energy density, efficiency, thermal conductivity

Energy density, efficiency, and thermal conductivity are critical parameters in evaluating and selecting TES materials for various applications (see Table 5).

4.2 Environmental impact and recyclability

TES has lower environmental impact and higher recyclability compared to electrochemical batteries, especially when using natural or abundant materials like water, rocks, or molten salts.^73,74 TES used non-toxic, abundant materials such as water, sand, concrete, or molten salts (e.g., NaNO₃/KNO₃). Unlike lithium-ion batteries, thermal energy storage systems circumvent dependence on mining-intensive materials such as lithium, cobalt, and nickel. This distinction positions TES as a more sustainable and resource-efficient solution for large-scale energy storage, particularly in contexts where material scarcity and environmental impacts are critical concerns.⁷⁵ TES systems (especially sensible heat storage) require larger physical volumes but minimal water use and no hazardous waste.

5.1 Pilot projects in America, Europe, China, and Africa

America, Europe, China, and Africa have launched several pilot-scale CSP projects with TES, focusing on innovation, grid integration, and sustainable development as shown in Table 6.

5.2 TES in off-grid and rural applications

TES technologies are increasingly recognized as low-cost, low-tech alternatives to conventional energy systems in off-grid and rural settings. In rural communities, TES can be deployed across multiple sectors: for clean cooking and food preservation, solar-assisted crop drying and agro-processing, decentralized water purification, community-level heating and cooling, and small-scale industrial uses such as brick-making, dairy processing, or textile production. By bridging the gap between renewable generation and end-use needs, TES offers a pragmatic pathway for sustainable development in resource-constrained environments, particularly where conventional electrification remains economically or technically unfeasible.^60,92–94

5.3 Smart TES systems with AI-based control

Artificial intelligence in thermal energy storage system marks an important step forward in energy management. Smart thermal energy storage systems employ predictive control, real-time monitoring, and advanced optimization algorithms to enhance the efficiency of charging and discharging cycles. This intelligent management framework improves operational flexibility, reduces energy losses, and supports seamless integration with renewable energy sources. As shown in Figure 4, through dynamic response to demand variations and coordinated operation with photovoltaic systems, batteries, and grid signals, these technologies enhance operational flexibility, improve system efficiency, and strengthen overall grid resilience.^76,77

Figure 4. AI-controlled TES flow chart for smart energy management.

Flow chart showing predictive control, dynamic response, and fault detection mechanisms in AI-enhanced TES systems, demonstrating improved grid integration and operational efficiency.

5.4 Industrial and building applications

AI-enhanced TES systems in manufacturing and smart buildings improve grid responsiveness and energy efficiency.

6.1 Material degradation and thermal losses

TES systems experience material degradation and thermal losses over time, but these effects vary significantly by storage medium and operating conditions. A synergistic strategy that integrates meticulous material selection with optimized system design provides a robust framework for overcoming current limitations and significantly extending the operational lifespan of thermal energy storage systems. This holistic approach enhances performance, ensures long-term reliability, and strengthens the role of TES in sustainable energy infrastructures.^82,83

Molten salt systems, commonly used in CSP applications, face degradation through thermal decomposition, corrosion of containment materials, and nitrate breakdown above 550 °C; these issues can be mitigated by using corrosion-resistant alloys and chemical additives to stabilize salt composition, enabling a lifespan of 20–30 years with proper maintenance. Solid storage media—including concrete, rocks, and ceramics—are noted for their durability, especially when applied in low- to moderate-temperature thermal energy systems.^84,85

Heat losses mainly through conduction and convection across insulation materials and structural boundaries. At elevated operating temperatures, especially in concentrated solar power (CSP) applications, radiative losses also become a dominant factor, and can be effectively reduced through the application of reflective surface coatings or by employing vacuum-based insulation technologies. Well-insulated TES tanks generally maintain very low heat energy losse, often below 1% per day. In contrast, high-temperature CSP systems can increase losses upto 3% per day if insulation and system design are not adequately optimized.⁸⁴

6.2 Cost and scalability barriers

The limitations of thermal energy storage systems are frequently associated with material requirements, infrastructure demands, and integration complexities, which collectively constrain large-scale deployment and long-term reliability. These challenges, however, are highly context-specific and can be alleviated through modular design strategies and the deployment of hybrid energy systems.^76,82

TES systems encounter significant economic challenges that hinder large-scale adoption. Particularly for molten salt and phase-change technologies that demand specialized infrastructure combined with site-specific engineering needs substantial financial barriers.⁸⁶

TES systems encounter significant deployment barriers, primarily stemming from their extensive spatial footprint, the intricate requirements of coupling with diverse heat sources and end-use applications, and the absence of standardized components. These factors collectively constrain scalability, complicate system integration, and escalate engineering and capital costs, thereby limiting widespread adoption.

6.3 Integration with existing infrastructure

TES can be integrated into existing infrastructure effectively, especially in industrial, district heating, and solar thermal systems, but challenges remain in retrofitting complex, control requirements for interfacing with management systems, and thermal compatibility limitations that limit deployment in retrofitted or high-temperature industrial environments.⁸⁷

7.1 Emerging materials and long-duration storage

Emerging TES technologies using solid and liquid media offer HED and long-duration storage, supporting renewable integration and industrial decarbonization. And innovative systems like moving-particle solid storage use gravity-driven high-temperature particles in insulated silos can minimizing auxiliary power needs. Material innovation is a pivotal tool to advance future cost-effectiveness and performance in sustainable energy systems, positioning TES as a cornerstone technology in the global transition toward resilient, low-carbon infrastructures.^60,88 Some of the listed emerging materials in TES are discussed as follows:

7.2 Role in seasonal storage and climate adaptation

TES can be used in seasonal energy storage and climate adaptation by enabling long-duration heat retention, balancing renewable supply-demand mismatches, and enhancing resilience in heating and cooling systems.⁸⁹

7.3 TES in the water–food–energy nexus

The interdependence between water, food, and energy systems has become a central theme in sustainable development. TES technologies present a unique opportunity to reinforce the energy–water–food nexus by enabling an efficient capture, store, and reuse of thermal energy across multiple essential services ( Figure 5). In water systems, TES can be integrated with solar thermal desalination and purification units to provide clean drinking water in arid and semi-arid regions and supports continuous evaporation–condensation cycles even during non-sunlight hours, increasing overall freshwater production.^60,79,90 It also offer valuable applications in agriculture by regulating temperature and humidity in greenhouse to ensure optimal growing conditions while reducing reliance on continuous energy inputs, enabling efficient, low-cost, and sustainable crop drying processes that minimize post-harvest losses, and buffering soil against extreme temperature fluctuations to support root development and extend growing seasons in vulnerable climates.^86,91

Figure 5. TES for water, food, energy and sustainability.

In energy systems, it works synergistically with renewable sources such as solar and wind by providing dispatchable thermal power for heating, cooling, and industrial applications.^15,16

7.4 TES for Africa and developing regions

In rural and semi-urban African communities, access to reliable electricity and clean water remains limited,and this technology can presenting an opportunity for decentralized thermal energy solutions. TES can be constructed using low-cost, locally available materials such as stones, sand, clay bricks, paraffin wax, used engine oil, and agricultural byproducts, and these materials are applicable for both sensible and latent heat storage, thereby improving affordability and making TES technologies accessible to low-income communities while supporting sustainable energy solutions tailored to local contexts. The adoption of thermal energy storage systems reduces reliance on costly imported fuels, including kerosene and diesel, thereby promoting energy security and advancing the transition toward more sustainable energy infrastructures. This transition not only fosters economic empowerment by reducing energy costs but also advances environmental sustainability through lower greenhouse gas emissions and diminished reliance on fossil resources. This combined benefit positions TES as a practical approach for reducing energy poverty and carbon emissions, especially in regions that rely heavily on fuel imports. By highlighting TES within the continent’s unique energy and resource contexts, the study emphasizes its potential to drive resilience, affordability, and decarbonization across multiple sectors.⁹⁰ As shown in Table 7, TES road map is important to adopt this with in the continent.

Table 7. TES roadmap for Africa (2025-2050).

Near-term(2025 – 2030)	Mid-term (2030 – 2040)	Long-term (2040 – 2050)
Building-Scale TES	(Off-Grid/Rural TES)	(Climate-Resilient Hybrid TES)
− Residential TES − PCM in buildings − HVAC + thermal storage − Hot water storage tanks − Smart insulation (PCM walls)	− Community-scale TES − Solar-powered cooking − Water purification systems − Solar food drying − Agricultural TES (greenhouses)	− Regional climate-resilient TES − Disaster-resistant housing − Seasonal underground TES − AI-controlled TES networks − Hydrogen + TES hybrid integration
GOAL: Energy efficiency in buildings	GOAL: Energy access in rural areas	GOAL: Climate resilience and sustainability

7.5 TES as a climate adaptation and disaster-resilience tool

TES systems can play a significant role in climate adaptation and disaster resilience by enabling passive and active control of temperature in vulnerable regions. Thermal energy storage integrated with cooling systems offers a resilient strategy during heat waves by storing cooling capacity at night or during periods of abundant renewable generation, and discharging it during the day to maintain safe indoor temperatures in residential, healthcare, and emergency facilities. Integrating thermal energy storage into building energy systems improves operational efficiency, alleviates peak electricity demand, and safeguards occupants during extreme heat events. This integration not only strengthens resilience but also advances sustainability within the built environment, positioning TES as a critical enabler of climate-responsive and energy-efficient building design.^16,18 The implementation of thermal energy storage applications strengthens resilience, mitigates reliance on expensive fossil-based fuels, and fosters sustainable living in regions characterized by pronounced temperature variability. By buffering energy supply against climatic extremes, TES contributes to both environmental sustainability and socio-economic stability.^60,90 In disaster and refugee scenarios, portable TES units can support temporary shelters by maintaining stable indoor temperatures and enabling water purification and food preparation without reliance on grid electricity.⁷⁹ Combing with mobile solar systems, TES can form rapid-deployment and self-sustaining survival energy stations,^15,90 it can be recognized not only as an energy storage technique but also as a strategic climate resilience technology that strengthens community adaptation and survival capacity under extreme conditions.⁹¹

7.6 Framework for TES technology selection

To support practical deployment, this study introduces a decision-making framework for TES system selection, which transforms the review into an actionable engineering guide. The selection of TES type is based on the following key parameters⁹¹:

8.1 Conclusion

TES has emerged as a cornerstone technology for enabling sustainable energy transitions by bridging the gap between renewable generation and end-use demand. Its diverse mechanisms—sensible, latent, thermochemical, and hybrid—offer complementary strengths that can be tailored to specific applications ranging from building comfort and industrial heat recovery to long-duration and seasonal storage. TES not only enhances energy efficiency and grid stability but also contributes to climate resilience by supporting heating and cooling during extreme weather events and enabling decentralized resource management in vulnerable regions. Leveraging low-cost and locally sourced materials enhances the accessibility of thermal energy storage, offering practical pathways for deployment in developing regions where affordability and design simplicity are paramount. Looking ahead, advancing material durability, improving system scalability, and integrating TES into multi-sector frameworks such as the energy–water–food nexus will be crucial for unlocking its full potential. This review presents thermal energy storage not only as an energy storage option but as a broader enabling technology that supports sustainable development, enhances system resilience, reduces reliance on fossil fuels, and contributes to more equitable energy outcomes in both industrialized and emerging economies.

8.2 Recommendations

Based on the analysis presented in this review, the following recommendations are proposed: