Energy Storage: From Fundamental Principles to Industrial Applications

Abstract

The increasing global energy demand and the transition toward sustainable energy systems have highlighted the importance of energy storage technologies by ensuring efficiency, reliability, and decarbonization. This study reviews chemical and thermal energy storage technologies, focusing on how they integrate with renewable energy sources, industrial applications, and emerging challenges. Chemical Energy Storage systems, including hydrogen storage and power-to-fuel strategies, enable long-term energy retention and efficient use, while thermal energy storage technologies facilitate waste heat recovery and grid stability. Key contributions to this work are the exploration of emerging technologies, challenges in large-scale implementation, and the role of artificial intelligence in optimizing Energy Storage Systems through predictive analytics, real-time monitoring, and advanced control strategies. This study also addresses regulatory and economic barriers that hinder widespread adoption, emphasizing the need for policy incentives and interdisciplinary collaboration. The findings suggest that energy storage will be a fundamental pillar of the sustainable energy transition. Future research should focus on improving material stability, enhancing operational efficiency, and integrating intelligent management systems to maximize the benefits of these technologies for a resilient and low-carbon energy infrastructure.

1. Introduction

Energy consumption has had a growth of about 2.6% annually over the past decade within developing economies and in emerging markets. These economies and markets account for approximately 85% of the global population. This growth is being driven by key factors such as a population increase of over 720 million people, a 40% rise in industrial activity, and a 50% economic expansion [1]. The resulting surge in energy demand has intensified global warming, prompting cities and governments to collaborate in achieving the Paris Agreement objectives of limiting the rise of global temperatures below 2 °C, with an aspirational goal of 1.5 °C [2]. In order to meet these targets without hindering economic growth, energy efficiency has become a cornerstone of global sustainability policies [3]. Decarbonizing the energy sector is essential, with the Energy Storage Systems (ESS) being of great importance in the achievement of this goal. These technologies enhance the integration of renewable sources, improving supply stability and efficiency, thus facilitating the transition to a more sustainable energy model [4].

From the start of the 21st century, the study of renewable energy systems has received significant attention [5] due to its sustainability advantages and its importance in ESS, enabling its controlled use across various sectors through diverse techniques. However, natural resources employed to generate energy have faced intermittent challenges due to seasonal and climatic factors. In response, researchers worldwide have made substantial contributions to the advancement of ESS to enhance efficiency, meet rising energy demand, and adapt to evolving requirements [6]. Moreover, efforts that have focused on large-scale implementation, addressing the gap between small-scale advancements and industrial applications, have, in some cases, hindered their practical deployment [7].

The conversion of electricity into energy carriers or chemical products, which can be stored and used when and where required, began to be developed in Germany in the early 2010s. This strategy is known as “Power-to-X” (PtX or P2X) [8]. PtX or P2X is a process that transforms electrical energy into other forms of chemical substances (X) [9]. This process is crucial for medium- and long-term energy storage, as it enables surplus renewable electricity to be converted into usable energy forms, facilitating its integration into the global energy system. In general terms, P2X systems can be classified into Power-to-Gas (PtG), Power-to-Heat (PtH), Power-to-Liquid (PtL), and Power-to-Chemicals (PtCs). Each P2X system is responsible for converting surplus renewable electricity into different energy carriers or products [10]. PtG, for example, utilizes electricity to produce either hydrogen or synthetic natural gas through electrolysis or CO₂ methanation. PtH converts electricity into heat (thermal energy). This process typically utilizes heat pumps combined with thermal storage. PtL and PtCs systems use electricity to synthesize liquid fuels such as ammonia, methanol, synthetic hydrocarbons, and other valuable chemical products [11,12].

The heat generated in PtH strategies is not only applied in district heating networks or used to power heat pumps and resistive heating but it can also be used in many other applications. PtH-generated heat can be coupled with ESS, specifically Thermal Energy Storage (TES) systems, and used in a controlled manner either to enhance energy efficiency or to integrate renewable resources [13]. This heat can be stored in molten salts, hot water, or rocks [14]. ESS, as an energy efficiency device, can also be paired with Chemical Energy Storage (CES) systems to enable long-term energy retention through the modification of chemical bonds in various materials. Throughout these reactions, the stored energy is released, causing changes in their chemical structures as bonds break and reform. Among the most widely used CES technologies are hydrogen, synthetic natural gas, solar fuels, and batteries, offering efficient solutions for various energy applications [15]. ESS is crucial in the transition toward a renewable-based energy system by managing the intermittency of these technologies and by ensuring a stable and reliable supply. Their large-scale integration is essential in order to reduce dependence on fossil fuels and to decarbonize the energy sector [4].

In recent years, Artificial Intelligence (AI) and Machine Learning (ML) have progressed from theoretical approaches to practical tools implemented in energy storage systems. Pilot-scale and industrial applications, particularly in lithium-ion batteries, already employ ML models for predictive maintenance, efficiency optimization, and system health monitoring. These early-stage implementations demonstrate the growing role of AI and ML in enhancing performance and reliability across existing ESS infrastructures, beyond their prospective value.

This study examines ESS and its applications in the context of renewable energy sources, with a particular focus on thermal (TES) and chemical (CES) storage, both essential in the management of the growing energy demand and supply variability. While some of these systems have fully developed, others remain well under development. Challenges related to large-scale implementation and research perspectives for optimizing performance and sustainability are addressed here. This study aims to guide researchers, government agencies, and the energy sector in developing safe and efficient ESS with the purpose of integrating renewable energy.

2. Methodology

This review is based on the analysis of 148 scientific and technical sources published between 2004 and 2025. The documents were collected from a combination of peer-reviewed journals, official institutional reports (e.g., IEA), patents, doctoral theses, and reputable online repositories. Searches were conducted using the Scopus, Web of Science, Google Scholar, and ScienceDirect platforms, complemented by a manual selection from institutional and governmental websites relevant to energy systems and storage technologies.

The search strategy employed combinations of the following keywords: “Chemical Energy Storage,” “Thermal Energy Storage,” “Power-to-X,” “Hydrogen Storage,” “Electrochemical Batteries,” “Molten Salt Storage,” “MGTES,” “District Heating,” and “Industrial Waste Heat Recovery.” Articles were included if they met at least one of the following criteria: (1) addressed the operating principles, technological development, or industrial deployment of CES or TES systems; (2) presented techno-economic assessments, integration pathways, or environmental impacts of energy storage; or (3) offered sector-specific applications in heavy industry or district energy systems.

After collection, the selected sources were categorized into four thematic clusters: (i) foundational concepts and classifications of CES and TES technologies, (ii) technological mechanisms and performance parameters, (iii) industrial-scale and cross-sectoral applications, and (iv) challenges, limitations, and future research directions. These thematic groups comprise approximately 32 sources for foundational concepts and classifications, 46 for technological mechanisms and performance parameters, 38 for industrial-scale and cross-sectoral applications, and 32 for challenges, limitations, and future research directions. This classification enabled a critical synthesis of state-of-the-art knowledge, combining academic advances with applied insights to support future innovations in sustainable energy storage and decarbonization strategies.

3. Chemical Energy Storage: Concepts and Classification

3.1. Definition and Working Principles of Chemical Energy Storage

When it comes to energy supply, some resources, such as fossil fuels, are able to be utilized in a deterministic way as their consumption can be planned based on consumer demand, while the non-required fuel can be stored in its base form [16]. On the other hand, the problem with other renewable resources is their management [17]. When wind generators, for example, are used, there may be fluctuations in the wind turbine output, and during rapid discharge periods, the power system must be able to provide a quick response in order to stabilize the energy supply. This stabilization can be achieved with ESS [18]. In addition, solar generators do not always generate energy, such as on cloudy days or at nighttime; thus, it is essential to have a storage system capable of storing large amounts of energy to be slowly discharged throughout long demand periods [19].

It is for these reasons that ESS has become highly relevant in the present, as they enable improved energy security and allow for the expansion of the installation of these renewable energy systems [20]. ESS offers various options. Within this section, CES systems, among the most widely used technologies in the world due to their high energy density, their versatility, and their long-term storage capacity are addressed.

In the literature, the concept of CES refers to the process of storing energy in the form of chemicals. Electrical energy is used to produce chemicals that can be stored and used at a later date depending on their demand [21]. When the stored energy is set to be used, the chemical substance undergoes combustion. This combustion can be either an electrochemical or a chemical transformation reaction depending on the storage method that was used. The stored energy is then commonly released in electricity or in heat form [22].

The working principles of CES can be mostly described as follows:

• Energy Conversion. Depending on the storage system, electrical energy is converted into chemical energy through processes such as electrochemical reactions or chemical syntheses of products with high energy potential. This process can be observed in batteries or fuel cells [23].
• Energy Storage. Chemical energy is stored in chemical substances such as electrolytes or metals, or gaseous fuels such as hydrogen. Taking into account the batteries, this process can be conducted through the movement of ions between an anode and a cathode in an electrolyte [24]. In other systems, energy storage is used to generate fuels such as ammonia, hydrogen, or synthetic methane [25].
• Energy Retrieval. When the stored energy is required, it is released by reversing the process. In batteries, the process involves connecting the power system to a reduction-oxidation reaction (REDOX), where the ions flow back, and the stored energy is discharged in the form of electrical energy useful for powering any electrical device [24]. In fuel cells, the storage system or chemical substance is subjected to a combustion reaction from which electricity, heat, and water are obtained [26].

CES can be defined as the conversion of electrical energy into a chemical form that is then stored, transported, and converted back into electrical energy or some other form of energy. There are various technologies in this category, one of the most common being electrochemical CES in batteries, which has driven the automotive industry to new horizons thanks to the use of lithium-ion (Li-ion) batteries in emission-free electric vehicles [27]. Another technology in this category is the method of storing residual energy in high-density chemical substances. This technology has been classified in the literature as Power-to-X Technologies, consisting of the production of synthetic fuels such as hydrogen, ammonia, and methanol, among others [28]. Figure 1 describes the role of renewable energy in supplying local demand while also managing surplus energy through two main storage pathways: electrochemical storage in batteries and CES via Power-to-X technologies [29]. This approach is particularly useful in addressing the variability in collecting renewable energy, such as the diurnal nature of solar energy [30]. Figure 2 is an example of the Power-to-X strategy for the conversion of different forms of energy (solar, excess process heat, etc.) to energy carriers that can be stored and dispatched. In this example, electric and thermal energy are collected through photovoltaic cells and thermal collectors. The thermal energy from solar collectors and from excess processing heat can be used or converted to electric energy, which is used to electrolyze water. Both hydrogen and oxygen are used directly or stored and dispatched as needed. Oxygen is used for the partial oxidation of natural gas. The produced synthesis gas (syngas) is processed into energy carriers (e.g., hydrogen, methanol, ammonia), which can be connected to the vast infrastructure and supply chains of such chemicals. Such chemical storage of energy has the advantages of overcoming the unsteady rate of collecting solar energy, the losses associated with excess process heat, and the difficulty in storing and dispatching energy.

3.2. Categorization of Chemical Energy Storage Systems

3.2.1. Electrochemical Storage: Batteries

The current market is mainly dominated by lithium-ion batteries that can power everything from small electrical devices to a wide range of electric vehicles [31]. Their operating principles rely on the properties of the electrolyte itself, with the electrolyte components and the positive and negative electrodes serving as the active elements of each cell. When the battery is being discharged or is providing energy, the positive electrode is known as the cathode, and the negative electrode is known as the anode [32]. The cell voltage is determined by the electrode material selection, and the cell capacity is determined by the quantity of the materials used [25]. Lithium-ion batteries’ main advantages are their long lifecycles, allowing the batteries to run for thousands of cycles without showing significant degradation. The batteries’ high efficiency, around 90% in charging and discharging, is also another one of their advantages [33]. However, lithium-ion batteries lack large-scale applications due to the large number of individual units required to assemble them. Nevertheless, lithium-ion batteries’ main problem in large-scale applications is associated with the overheating of batteries when they are damaged [34]. With the city of New York banning the use of lithium-ion batteries for indoor storage, flow batteries have made progress. Flow batteries use a storage system based on liquid electrolytes. These batteries are stored in external tanks that are pumped through an electrochemical cell to generate electricity [35]. Clearly, their operating principle implies the use of a larger battery size compared to that of lithium-ion batteries; however, flow batteries have proven to be especially useful in large-scale energy storage for renewable energy integration and in backup power for critical infrastructure. Flow batteries are also favored for having a lower risk of thermal runaway problems [36].

Among the most common types of Flow batteries are Vanadium Redox Flow Batteries (VRFB). VRFBs store ions in a vanadium sulfate solution and use vanadium redox couples at the electrodes. Known primarily for their long lifecycles, over 10,000 cycles [37], these batteries offer high efficiency (approximately 90% at light loads), moderate energy, and power densities. Compared to Zinc-bromine (ZnBr) batteries, VRFBs are undoubtedly worth their value. ZnBr batteries use zinc as the negative electrode and bromine as the positive electrode, with a zinc bromide solution as the electrolyte. ZnBr batteries have moderate energy densities, and long lifecycles (10 to 20 years), but offer a lower efficiency rate (65 to 80%) and are prone to corrosion and toxicity [38]. Despite their advantages, VRFB face notable challenges that hinder their widespread adoption. One of the main technical issues is membrane fouling, which can degrade performance over time by reducing ion selectivity and increasing resistance. Economically, the cost of vanadium (key component) can be highly volatile, significantly impacting the overall cost-effectiveness of the technology and limiting its scalability in some markets.

The alternative of replacing the conventional liquid electrolyte in lithium-ion batteries with a solid electrolyte has been explored. This change would translate into a higher energy density capable of storing practically twice as much energy as a conventional lithium battery [39]. However, problems related to the difficulty in its production and its high cost would make lithium-ion batteries a battery limited only to specific uses, such as in Aerospace, in specialized applications requiring high safety and energy density, and in Next-generation electric vehicles [40].

A fairly new alternative, still in development, is sodium-ion batteries. Sodium-ion batteries replace the use of lithium with sodium. The production of these types of batteries would imply a lower cost in their production as sodium is an abundant element. Sodium-ion batteries also have a lower risk of thermal runaway when compared to lithium batteries, however, it is important to note that when damage occurs, sodium batteries are more prone to severe thermal runaway effects [41]. Moreover, its lower energy efficiency makes it an inferior battery to be applied in the use of electric vehicles. It is worth noting that sodium-ion batteries are still in development, and over the coming years, their performance and economic viability will improve.

Solid-state batteries, which utilize solid electrolytes instead of liquid ones, offer promising advantages in terms of energy density and safety. One of the primary scientific challenges lies in achieving high ionic conductivity in solid electrolytes comparable to their liquid counterparts. Interface stability between the solid electrolyte and electrodes is another critical concern, often leading to increased resistance or mechanical degradation. Additionally, dendrite formation of metallic lithium growth that can pierce the electrolyte and cause short circuits is a major safety risk. To mitigate this, researchers are exploring electrolyte formulations and interface engineering strategies aimed at suppressing dendrite growth and enhancing overall cell stability. It is expected that future research will increase the energy density of sodium batteries, improve the safety of lithium-ion batteries, and reduce the production costs of solid-state batteries. Figure 3 and

Table 1. Parameter comparison of battery technologies [5,7,24,27,31].

Battery Type	Materials	Cost	Efficiency	Limits/Risk	Operating Conditions	Lifecycle (Cycles)	Applications
Flow	Vanadium or iron redox	Medium–High	65–80%	Low energy density; low thermal risk	~20–40 °C, atmospheric pressure	>10,000	Grid storage, renewables
Na-ion	Sodium-based	Low	80–90%	Lower density than Li-ion; low fire risk	−20 to 60 °C, atmospheric pressure	2000–4000	Stationary, backup
Li-ion	Lithium-based	Medium	90–95%	Temp-sensitive; high thermal risk	0–45 °C, atmospheric pressure	1000–3000	EVs, electronics
Solid-state	Li metal + solid electrolyte	High	90–98%	High cost; interface stability	~20–80 °C, moderate pressure	>5000	Future EVs, aerospace

show a comparative analysis of different battery technologies based on cost, efficiency, and safety aspects.

3.2.2. Power-to-X Technologies: Power-to-Gas and Power-to-Liquid

P2X technologies allow the conversion of surplus renewable energy into different forms of energy carriers. The literature usually classifies them according to the phase in which the product is produced: Power-to-Gas (P2G), and Power-to-Liquid (P2L), which produces hydrogen (P2H), synthetic methane, ammonia, methanol, and other e-fuels.

P2G primarily produces hydrogen or methane through processes such as electrolysis and methanation. Electrolysis separates hydrogen from oxygen in water molecules. The hydrogen produced in this process is usually used in fuel cells or it is injected directly into natural gas grids [42]. The production of green hydrogen is expected to be of great importance in the decarbonization of steel production [43] and in transportation thanks to automotive brands such as Toyota [44] committing to this fuel. The production of methane through methanation is based on the Sabatier reaction, which consists of combining hydrogen with CO₂ to produce methane. This methane can be easily used as a substitute for natural gas without needing to invest in new infrastructure [45].

Unlike P2G processes, P2L processes produce liquid fuels such as ammonia, methanol, and synthetic e-fuels. Ammonia (NH₃) is commonly produced by the Haber-Bosch process using nitrogen and hydrogen produced by electrolysis as raw materials [46]. This product can be used as fuel directly through combustion, it can be used in fuel cells or in the production of fertilizers [47].

Methanol, on the other hand, can be obtained by combining green hydrogen with CO₂ using a catalyst composed of copper, zinc, or aluminum. Methanol can be used as a raw material to produce products with a high economic potential such as Olefins (Ethylene and Propylene) [48], Dimethyl Carbonate (DMC) [49], and others.

The production of e-fuels, known as synthetic hydrocarbons, offers an alternative to traditional fossil fuels. Synthetic hydrocarbons’ main advantage lies in their compatibility with the existing infrastructure. If these hydrocarbons are produced from green H₂ and CO₂ captured from some other industrial process, then they are considered neutral emissions fuels [50].

All of these P2X processes require large amounts of energy and CO₂ capture systems. Since there are currently no high efficiencies in these processes, their production directly affects the production costs. However, these technologies have a great strategic value in applications (see

Table 2. Overview of P2X technologies [1,4,5,6,7,13,14,19,20,23].

Technology	Main Output Products	Main Process	Operating Conditions	Applications
P2H	Hydrogen (H2)	Electrolysis	50–80 °C (Alkaline), 60–80 °C, 30–60 bar	Fuel cells, industry (steel), transport
P2G	Synthetic methane	Methanation (Sabatier reaction)	250–400 °C, 10–30 bar	Injection into gas grid, heating
P2L	Ammonia, Methanol, E-fuels	Haber-Bosch, catalytic synthesis	400–500 °C, 100–200 bar (ammonia); 200–300 °C, 50–100 bar (methanol)	Fuel, chemicals, fertilizers, energy storage

) where obtaining electrical energy from renewable resources is not the objective [51].

3.2.3. Hydrogen Storage Technologies

Hydrogen storage could be of great importance in the adoption of renewable energy on a large scale, with research currently being directed towards the development of metal hydrides and Liquid Organic Hydrogen Carriers (LOHCs). The production of metal hydrides enables the storage of hydrogen in a solid compound along with metals or metal alloys. This process allows for a high volumetric density of hydrogen storage as well as significantly facilitating its treatment and transportation [52]. Although it is necessary to consider the high thermal requirements associated with this technology’s hydrogen desorption process [53], the dependence on high-value metals or even rare metals such as titanium or lanthanum has shown to improve, in recent studies, the performance of the hydrogen storage technique [54,55]. There are also other current technologies that facilitate the handling of hydrogen as a conventional fuel using LOHC through different hydrogenation or dehydrogenation processes. However, these processes lack high efficiency and require constant maintenance due to the degradation of the catalysts responsible for the charging and discharging of hydrogen; this degradation can affect both the purity of the fuel and the performance of the fuel cell [56].

Thanks to the development of these technologies, there are now alternatives for hydrogen storage apart from the most common technology based on high-pressure hydrogen storage, which can present risks in its large-scale adoption [57]. The technical and economic limitations of these technologies restrict their acceptance; however, their unique advantages make them attractive technologies to be used in specific applications, and ongoing research is constantly improving their viability in large-scale implementations.

One of the main challenges in hydrogen storage and distribution is the inherent trade-off between its high gravimetric energy density and low volumetric energy density. Although hydrogen contains more energy per kilogram than most fuels, its energy per unit volume is significantly lower under standard conditions. This implies that for applications such as long-distance transportation or storage in retrofitted natural gas pipelines, compression or liquefaction is required to increase its volumetric density, processes that result both energy-intensive and costly. Moreover, while high-pressure gas cylinders and cryogenic liquid hydrogen increase volumetric density, they raise safety and infrastructure concerns. These limitations underscore the importance of alternative storage solutions like metal hydrides and LOHCs, which offer greater volumetric storage potential and more manageable conditions for transportation and storage, although at higher material or operational costs. Understanding and optimizing this balance remains a critical area of ongoing research for large-scale hydrogen deployment.

4. Power-to-Heat and Thermal Energy Storage

The transition towards a sustainable and decarbonized energy system requires the development of flexible technologies that not only integrate renewable energy sources but also reduce reliance on fossil fuels [58,59]. P2H, among other technologies, has emerged as a key solution, enabling the direct conversion of electricity into thermal energy. This energy can either be used immediately or stored for later applications [28,60]. This approach is of great importance as it balances the intermittency of renewable power generation, optimizes grid stability, and decarbonizes the industrial heat demand and the district heating networks [61].

The fundamental principle behind P2H is the conversion of electrical energy into heat, a process that can be achieved through two primary mechanisms [62]. The first mechanism is resistive heating, where electrical energy is converted into heat via resistive elements [13,63]. This method has an efficiency rate of almost 100%, making it an effective solution for high-temperature industrial applications such as metal processing, chemical manufacturing, and glass production [64,65]. The second mechanism is the electro-thermal heat pump, which utilizes thermodynamic cycles to transfer heat from a lower temperature source into a higher temperature process, thus achieving a coefficient of performance (COP) between 3 and 5 [66]. This mechanism makes electrical energy highly efficient to be used in applications such as waste heat recovery, district heating, and low-temperature industrial heating [67].

P2H solutions are particularly relevant in industries where direct electrification of thermal processes is difficult [68]. By converting excess renewable electricity into stored thermal energy, these technologies provide grid flexibility, reduce renewable curtailment, and ensure a stable energy supply [69]. Furthermore, heat pumps and cogeneration systems can provide an effective approach to upgrading the quality of excess process heat, addressing the variable nature of renewable energy collection, and utilizing energy from flaring systems [70,71].

P2H technologies contribute significantly to decarbonization efforts by integrating renewable energy sources, reducing industrial carbon emissions, and enhancing energy system flexibility [72]. By utilizing excess wind and solar power, P2H mitigates the variability of renewable energy, ensuring its effective use [60]. Electrified heating replaces fossil fuel combustion as it lowers CO₂ emissions in energy-intensive sectors. The ability to store and dispatch heat allows for better grid management, preventing overloads and enhancing system resilience. However, one of the main challenges of P2H is the intermittency of renewable electricity [73]. To address this issue, TES and Electro-Thermal Energy Storage (ETES) technologies are used to allow surplus heat to be stored and used when needed.

4.1. Thermal Energy Storage and Electro-Thermal Energy Storage

TES is an essential component of P2H systems as it enables excess heat to be retained for later use, thus optimizing energy efficiency [13]. TES solutions are classified based on the methods used to store thermal energy.

One widely utilized TES technology is molten salt storage. This technology is used particularly in Concentrated Solar Power (CSP) plants [74,75]. The molten salt storage employs a mixture of sodium nitrate (NaNO₃) and potassium nitrate (KNO₃) to store heat at temperatures between 290 °C and 566 °C [76]. The highly specific heat capacity and thermal stability of molten salts make them a well-suited method in which to store heat for long periods [77,78]. The molten salt storage is commonly used in power generation as it stores solar heat to generate electricity during cloudy days or at nighttime. It is also used in industrial heat supply, where it provides continuous high-temperature heat for cement and metallurgy to be manufactured [78]. Despite its efficiency, the molten salt storage system presents challenges such as corrosion, material degradation over long-term operation periods, and freezing risks below 240 °C, thus the need for advances in salt formulations and containment materials [79].

Another promising method is solid-state thermal storage, also known as Magaldi Green Thermal Energy Storage (MGTES). This method utilizes fluidized sand beds as the heat storage medium [80,81]. Sand is an excellent TES material due to its high thermal stability, low cost, and environmental sustainability. This technology is particularly useful for industrial waste heat recovery, high-temperature industrial heating applications exceeding 1000 °C, and district heating networks, thus reducing fossil fuel dependency [81]. Unlike molten salts, MGTES does not suffer from phase transition limitations, making it an attractive alternative for industries that require reliable and long-duration heat storage with minimal maintenance requirements [82].

Phase-Change Materials (PCMs) offer an advanced TES solution by utilizing latent heat during phase transitions, such as in the solid-to-liquid phase [83,84]. PCMs provide higher energy density and allow for a more compact storage solution compared to sensible heat storage solutions [85]. These materials are used to regulate temperature in industrial drying processes, thermal food buffering, pharmaceutical storage, the enhancement of energy efficiency in HVAC, and building energy management [86]. Despite their advantages, PCMs often exhibit low thermal conductivity and phase separation issues requiring technological improvements such as nano-enhanced PCMs and encapsulation techniques to enhance their long-term reliability and performance [87]. Moreover, the lack of detailed analysis of their thermal dynamics and long-term stability limits the validity of certain evaluations. For industrial implementation, it is essential to characterize not only their static thermal properties but also their cyclic performance and thermal response capability under real operating conditions [88,89].

A more traditional method is high-temperature rock thermal storage, where natural rock materials such as basalt and granite store and release heat [14,90]. These systems provide stable, high-efficiency energy storage solutions with minimal environmental impact [90]. Industries rely on them for large-scale heat storage in industrial plants and renewable energy integration for high-temperature applications. The key advantages of rock-based storage include low cost, long-term durability, and compatibility with high-temperature processes [91]. However, the effectiveness of rock thermal storage depends on factors such as thermal conductivity, porosity, and heat transfer efficiency, influencing system scalability and energy dispatch capabilities [14].

Liquid Air Energy Storage (LAES) is a cryogenic storage solution that uses the liquefaction of air at −196 °C to store energy [92]. Although it is primarily used for electricity storage, LAES is also utilized in the industrial cooling processes [93]. LAES provides long-duration storage capabilities, making it suitable to be applied where extended energy retention is required [94]. However, the energy-intensive process of liquefaction and low round-trip efficiency (~50–60%) create barriers to large-scale deployment [95]. Ongoing research is focused on enhancing the thermal integration of LAES with waste heat recovery to improve the overall system efficiency (see

Table 3. Core characteristics and applications of TES technologies [14,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95].

TES Technology	Main Material	Temperature/Efficiency	Limitations/Risks	Key Advantages	Applications
Molten Salt Storage	NaNO3 and KNO3	290–566 °C; high thermal capacity	Corrosion, degradation, freezing below 240 °C	Long-duration, efficient heat storage	CSP plants, cement and metallurgy industries
Solid-State (MGTES)	Sand	>1000 °C; high thermal stability	No phase transition (advantage)	Low cost, sustainable, reliable, low maintenance	Industrial heating, district heating, waste heat recovery
Phase Change Materials (PCM)	Materials with solid-liquid transition	High energy density; compact solution	Low thermal conductivity, phase separation	Efficiency in HVAC, compact thermal regulation	Drying, food and pharmaceutical storage, HVAC, buildings
High-Temperature Rock Storage	Basalt, granite	High temperature; stable efficiency	Dependent on conductivity, porosity	Low cost; durable; low environmental impact	Large-scale heat storage; renewable integration
Liquid Air Energy Storage (LAES)	Liquefied air (−196 °C)	50–60% efficiency	High energy consumption	Long-duration storage	Industrial refrigeration; electricity storage

).

Overall, TES and ETES technologies are of great importance in order to ensure that P2H applications operate efficiently and reliably. By leveraging a combination of molten salts, solid-state materials, phase-changing systems, and cryogenic storage, industries can achieve enhanced energy security, reduced operational costs, and improved sustainability. The continuous improvement of these technologies, including better thermal insulation materials, advanced heat exchangers, and optimized control systems will further amplify their role in the global energy transition.

4.2. MGTES Technology (Fluidized Sand Bed): Principles to Industrial Applications

MGTES represents a breakthrough in high-temperature solid-state thermal storage, leveraging fluidized sand bed technology to store and release heat efficiently [81]. Unlike traditional TES methods, MGTES operates with a non-corrosive, stable, and low-maintenance method, making it a preferred choice for industries requiring high-temperature stability and long-duration thermal retention [80]. The system heats fine sand particles, which have exceptional heat retention properties only to subsequently use stored thermal energy for various industrial applications.

One of the key advantages of MGTES is its ability to sustain temperatures above 1000 °C, a capability that surpasses molten salt storage [81]. This makes MGTES ideal to be applied in high-temperature heat processes such as metallurgy, cement manufacturing, and chemical industries. The fluidized sand bed design ensures a uniform heat distribution, preventing thermal hotspots and enabling efficient heat transfer with minimal energy losses [81].

Another one of MGTES’ benefits is its low operational risk compared to other TES technologies. Unlike molten salts, which present challenges such as corrosion, freezing, and degradation over time, MGTES offers a robust and stable alternative that requires minimal maintenance and ensures extended operational lifecycles [80]. Its modular scalability allows industries to tailor storage capacities based on their specific heat demand profiles.

Industries are progressively adopting MGTES for its energy flexibility and sustainability advantages. MGTES is being integrated into district heating networks, where it enables the provision of carbon-free heat while reducing peak energy demand [80]. Furthermore, in waste heat recovery, MGTES is demonstrated to be a game-changer by capturing and repurposing excess industrial heat, thus enhancing energy efficiency and reducing overall emissions.

Regarding the future, advancements in thermal management techniques, improved material science for sand-based storage, and hybrid integration with renewable energy systems are expected to further enhance the performance of MGTES [81]. As industries shift towards electrification and sustainable energy solutions, MGTES stands out as a crucial innovation in the transition to a low-carbon, highly efficient energy landscape.

5. Industrial Applications of Chemical and Thermal Energy Storage

5.1. Decarbonization of Industrial Processes Using CES and TES

CES and TES are key technologies used in industrial decarbonization, as they enable the integration of renewable energy, improve process efficiency, and reduce fossil fuel dependency [96,97].

Solar heat, for example, can be utilized in most industrial processes as a sustainable alternative to fossil fuels. The integration of TES systems is essential in order to maximize efficiency and ensure availability. These systems use solar thermal energy or industrial waste heat as their energy source.

These energy sources are mainly employed in heating, drying, and cooling applications [98]. Applications are currently focusing on low-temperature processes (<150 °C) with a particular emphasis on the food and beverage industry, where more than half of the projects use TES to supply hot water (up to 95 °C) for pasteurization, cleaning, and preheating processes [99].

CES emerges as a key solution for the management and optimization of energy supply by using secondary energy carriers such as hydrocarbons, hydrogen, ammonia, and synthetic natural gas. This system enables efficient energy storage and release by facilitating its integration into various industrial and mobility applications. Among its main applications, CES supports the stability of the electrical grid, improves the efficiency of land, maritime, and air transportation, and contributes to the decarbonization of sectors with high energy demands. CES is an enabling technology that will aid in the expansion of renewable and hybrid energy systems, ensuring a more sustainable and flexible transition into clean energy sources [100].

5.2. Sector-Specific Applications:

Global energy consumption has increased due to economic growth, industrialization, and technological advancements within developing countries [6]. The global demand for electricity is expected to grow at a faster pace than in previous years, with an annual increase of close to 4% over the next two years. This rise in consumption is driven by a greater use of electricity in industrial production, the electrification of transportation, the growing demand for air conditioning, and the rapid expansion of data centers [101]. However, most of the energy consumed is still being produced from fossil fuels causing a detrimental effect on the environment. And although alternative and eco-friendly energy sources are being looked upon these sources present challenges, such as resource intermittency and the need to meet specific site requirements [102]. In this context, ESS has emerged as an important technology with a wide range of applications, including demand peak reduction, renewable energy integration, energy system optimization, and advanced transportation development solutions. These systems can be classified according to their specific use and their field of application. As energy needs grow, storage applications continue to expand driving the design of more versatile systems [20]. In this regard, the economic footprint of the TES field covers various areas, such as thermal energy generation, textile manufacture, construction, transportation, agriculture, and healthcare, among others [97]. On the other hand, general application areas of CES technology include the fueling of transportation systems, and the efficient management of the electrical grid [5,103].

5.2.1. Heavy Industry (Steel, Cement, Glass)

A great potential has been identified in the industrial processes of Waste Heat Recovery (WHR). Since most heat is being lost and released without usage, the main challenges have now become the technical and economic approaches needed to recover this lost heat. The glass, steel, and cement industries, all energy-intensive industries, are the ones that primarily waste and release heat directly into the environment [104].

The steel industry, with its high energy consumption and rising energy costs, faces the most pressure to reduce its emissions [105]. Most of the energy or heat that is lost in the steel industry is caused by the electric arc furnaces and by the hot steel slags. If this energy were to be recovered, it would not only improve the efficiency of the production process but would also reduce operational costs and increase plant productivity. To value this waste heat is a key strategy to strengthen the sector’s competitiveness as it would push the industry toward more sustainable operations by reducing its emissions. ArcelorMittal, for example, recovers heat from exhaust gases in Poland, reducing CO₂ emissions by 56,000 tons per year [106]. Tenaris uses Consteel^® technology in Argentina to preheat the charge with process gases [107], and Thyssenkrupp applies heat exchangers to reuse residual energy [108]. In this context, TES emerges as an innovative and effective alternative to harness this wasted resource [109,110].

Methods have also been developed to produce cement with lower carbon emissions by integrating renewable energy sources. By doing so, the integration of these renewable energy sources will gradually replace fossil fuels in the traditional kiln. Renewable energy is converted into heat and stored providing the thermal energy required to decompose CaCO₃. High-temperature CO₂ is used as a carrier to transfer heat between the storage system and the kiln [111]. The SolCement project, presented as an innovative initiative aimed at the cement industry [112], developed two advanced experimental technologies: the first one being a solar kiln that uses solar energy in the limestone calcination process, and the second one being a solar TES reactor that allows solar energy to be stored throughout the day in order to be used throughout the nighttime [113]. In addition, integrated CSP-TES systems (Concentrated Solar Power and Thermal Energy Storage) combine two key technologies for power generation. The first uses mirrors or lenses to concentrate sunlight and heat a thermal fluid, while the second allows the captured heat to be stored for later use, even in the absence of solar radiation. These systems have been applied in cement plants, particularly because this industry requires very high temperatures, making solar concentration an especially attractive thermal source. Several projects have demonstrated the potential of integrating CSP-TES systems in the cement industry. The European project SOLPART validated the feasibility of using solar energy for the calcination of cement particles at temperatures up to 950 °C, operating continuously for 24 h [114]. Meanwhile, CEMEX and Synhelion succeeded in producing clinker using only solar heat, marking a key step toward the decarbonization of cement production [115].

The decarbonization of the steel industry depends on efficient energy storage solutions. Hydrogen, in this context, stands out as a key resource as it can be used as an energy source in the combustion processes of various industrial reactions. The management and storage of oxygen, nitrogen, propane, and gas by-products allow for production to be optimized, thus ensuring operational stability, regulated pressure, and the generation of energy [116].

The glass industry is a high energy-intensive industry with heat being generated from the combustion of fossil fuels, from electric heating methods, or from a combination of both processes. These processes are key when it comes to evaluating the environmental impact and the energy efficiency that takes place during the glass melting process [117]. The proposed systems for waste heat recovery within the glass industry include thermochemical recovery, natural gas preheating, batch or glass preheating, the production of steam or hot water, and the generation of electricity [118].

5.2.2. Industrial Manufacturing

The industry is currently working on the development of energy storage technologies. The potential of industrial facilities to reduce energy and demand costs through these technologies is one of the industry’s advantages. This creates a balance between production and consumption while also improving the reliability and financial performance of the electrical grid [119].

The ability to integrate the capabilities of storage technologies to the specific requirements of each industrial process is one of the main challenges of energy storage, with the selection of the optimal storage system depending on the needs of the industrial process. Key factors driving the development and adoption of large-scale energy storage in the manufacturing industry include engineering, technological, and investment innovations as well as regulatory and energy policy factors based on market dynamics [120]. The progress made in TES has been remarkable, leading to numerous innovative applications. These developments have attracted the attention of various industries as these solutions could help reduce electricity consumption peaks in their operations, as well as the costs associated with energy demand [121].

TES and CES systems are currently being implemented in cement, glass, steel, and metal production as well as in the chemical and petrochemical industries focusing on waste heat recovery [122]. TES and CES systems are also of great importance to the textile, food, automotive, and assembly industries, with TES technologies being utilized to reduce fossil fuel emissions and optimize energy efficiency [123]. Likewise, data centers and electronic devices are using energy storage to enhance both efficiency and sustainability [124]. The integration of renewable energy strengthens the flexibility and sustainability of energy systems through TES and CES technologies, which are also applied specifically to improve energy management in various industries [125,126] (see

Table 4. Integration of TES and CES in industrial facilities.

Sector	Main Use	Applications	References
Cement	Waste heat recovery	Optimization of energy consumption in the kiln and other process stages	[111,112]
Glass	Waste heat recovery	Thermochemical recovery, natural gas preheating, batch or glass preheating, as well as electricity generation and steam or hot water production	[118]
Steel and metals	Waste heat recovery	Energy recovery from electric arc furnace and hot steel slag.	[109,110]
Chemical and petrochemical industry	Waste heat recovery	Heat utilization in distillation, cracking, and chemical synthesis processes	[122]
Textile, food, automotive and assembly industries	Emission reduction and energy efficiency	Store and manage energy more efficiently in drying, dyeing, washing, pasteurization, refrigeration, and thermal management processes such as welding and painting.	[123]
Data centers and electronic devices	Efficiency and sustainability improvement	Reduction of energy consumption in cooling systems and backup energy management	[124]
General in various industries	Energy system flexibility and sustainability	Integration with renewable energy sources and energy management optimization through TES and CES	[125,126]

).

5.2.3. District Heating and CHP Plants

District heating systems are an efficient and cost-effective alternative method for the distribution of heat throughout multiple buildings within a closed circuit. This method minimizes environmental impact by controlling the interior climate of the building and by providing it with hot water [127]. The waste heat that is released into the environment by many energy-intensive industries can be utilized in the district heating systems since its use has proven to significantly decarbonize this sector. However, most of the heat must come from renewable energy sources [128]. It is important for utility companies to minimize their CO₂ emissions rather than merely increase the proportion of their renewable energy. To achieve this, they can implement solutions such as TES to improve demand management, optimize grid operations, and directly replace fossil fuels, thus facilitating a more efficient transition to a low-carbon energy system [129]. Electrification, in this context, emerges as a promising strategy to effectively reduce emissions in district heating systems. However, electrification exposes systems to a greater volatility in electricity prices, affecting their economic viability. In this scenario, TES and its engagement within the energy reserve market are of great importance, as they not only help mitigate costs associated with electrification but also reduce investment risks and strengthen the stability of the energy system [61,130].

Small- and medium-scale energy systems are gradually integrating renewable energy sources into their designs. These sources are characterized by providing low-temperature electricity and by meeting heat requirements. Conversely, the large-scale industrial sector continues not only to depend on a significant amount of medium- and high-temperature heat, typically in the form of steam but it also consumes high amounts of electricity. In this scenario, Combined Heat and Power (CHP) plants emerge as a promising energy solution, as they enable the simultaneous production of electricity and heat, optimizing the supply for various end-users [131]. Due to their importance, high-temperature latent heat TES systems have been designed and integrated into CHP plants [132].

5.2.4. Impact and Challenges

Demand-Side Management (DSM) in industrial facilities presents a significant opportunity to reduce energy costs as it is one of the largest energy consumers worldwide [133]. This industry has great potential for waste heat recovery, but its use remains limited. This limited use is due to technical and economic challenges as well as the temporal or geographical mismatch between heat generation and heat demand. TES solves this problem as it recovers and stores waste heat for later use [134].

Even though ESS, together with TES and CES, have experienced rapid growth, further research is still needed to reduce their production costs. Research advancements will help lower the costs of these emerging technologies, they will accelerate their market adoption and will improve their competitiveness [135]. Despite the fact that capacity, lifespan, safety, and environmental impact are still some of the biggest technological challenges limiting the practical implementation of ESS, this matter is further complicated by the challenge of industrial acceptance, as the uncertainty and unpredictable performance of these systems can present key barriers to their commercialization in industrial applications [136]. In this context, the combination of chemical and thermal energy is essential for industrial decarbonization. While chemical energy enables the substitution of fossil fuels and energy storage, thermal energy optimizes energy consumption and reduces heat losses. The integration of technologies such as heat recovery and renewable energy in industrial processes can accelerate the transition to a more sustainable and lower-carbon sector (see Figure 4).

6. Comparative Assessment of Storage Technologies

The diversity of energy storage systems, particularly in the domains of CES and TES, reflects the range of technological strategies being pursued to address the intermittency and decarbonization challenges of modern energy systems. However, their performance characteristics, economic feasibility, and scalability vary considerably across applications. This section provides a comparative synthesis of the reviewed technologies, emphasizing their operating conditions, efficiencies, and limitations, thereby responding to the need for deeper quantitative insight into their technical maturity and deployment potential.

Electrochemical storage systems, notably lithium-ion batteries, have demonstrated round-trip efficiencies as high as 90% and energy densities of approximately 150–250 Wh/kg [31,33]. Despite these advantages, their scalability is constrained by safety risks such as thermal runaway and by the reliance on critical raw materials like cobalt and lithium [34,129]. In contrast, VRFBs offer over 10,000 life cycles and comparable efficiencies (75–90%) under moderate load conditions, making them particularly attractive for stationary grid applications [37]. However, VRFBs face challenges in energy density and cost due to the need for large electrolyte volumes and expensive vanadium compounds.

Zinc–bromine batteries, while similarly designed for stationary applications, exhibit lower efficiencies (typically 65–80%) and are prone to corrosion and toxicity issues [38]. Recent advances in solid-state lithium batteries suggest the possibility of doubling energy density relative to conventional lithium-ion cells, but high costs and fabrication complexities currently limit their industrial adoption [39,40]. Emerging sodium-ion batteries, though promising due to sodium’s abundance and reduced thermal risks, still face significant performance gaps in terms of energy efficiency and volumetric density compared to lithium-based systems [41].

In the realm of CES via P2X technologies, PtG processes such as hydrogen production via electrolysis have demonstrated conversion efficiencies ranging from 65% to 75% [42,43]. Hydrogen’s high gravimetric energy density (120 MJ/kg) and compatibility with fuel cells and industrial combustion make it a key vector in decarbonization pathways for the steel and transport sectors [44,46]. However, compression, liquefaction, and storage still impose considerable energy and cost penalties [52]. Recent developments in metal hydride and LOHC systems enable higher volumetric storage and safer handling, but they suffer from catalyst degradation and limited reversibility in real-world cycling conditions [54,56].

In PtL pathways, the synthesis of methanol and ammonia from green hydrogen and CO₂ enables the production of drop-in fuels and chemical intermediates. Methanol synthesis can reach efficiencies of around 60%, but its viability depends heavily on carbon capture infrastructure and catalyst optimization [47,48,49]. The strategic advantage of PtL technologies lies in their compatibility with existing logistics and combustion systems, offering a path to low-carbon fuels without radical infrastructure overhaul [50].

Thermal energy storage systems reveal even greater diversity in terms of temperature range, material costs, and industrial compatibility. Molten salt systems, primarily used in CSP plants, operate at 290–566 °C with thermal efficiencies exceeding 90%, yet they are limited by freezing risks below 240 °C and material degradation over time [74,75,76,77,78]. Their high thermal capacity makes them suitable for electricity generation and continuous heat supply in cement and metallurgy.

On the other hand, MGTES systems using fluidized sand beds can operate above 1000 °C with minimal thermal losses and low material costs [80,81,82]. Their non-corrosive nature and absence of phase-change limitations grant them an edge over molten salts in high-temperature industrial applications, particularly in sectors such as glass and metal processing.

PCMs offer latent heat storage with energy densities up to 200 kJ/kg and operational temperatures tailored through material selection [83,84,85,86,87]. However, low thermal conductivity and phase separation remain technical barriers, currently addressed through nano-enhanced additives and encapsulation methods. Rock-based storage, employing materials like basalt or granite, provides robust and low-cost heat storage at high temperatures but exhibits relatively low energy densities (~100 kWh/m³) compared to PCMs or salts [90,91].

LAES introduces a cryogenic alternative, offering long-duration storage with integration potential into industrial cooling chains. However, its round-trip efficiency (~50–60%) and energy-intensive liquefaction process pose economic hurdles that are yet to be fully mitigated [92,93,94,95].

While round-trip efficiencies and energy densities are reported for various energy storage technologies, it is important to clarify that these values are derived from individual studies and do not always reflect standardized operating conditions. Frequently, the reported figures correspond to ideal or laboratory settings and do not explicitly account for factors such as system scale, load profiles, or specific environmental conditions. Nevertheless, due to the wide diversity of sources and technologies considered, detailing the operational conditions for each case falls beyond the scope of this work. Instead, a relative comparison is presented, highlighting typical performance ranges and the most common technical challenges. Despite this limitation, the reported efficiency and energy density values remain useful for identifying general trends and guiding preliminary technology selection according to the application type (mobility, power grids, industrial thermal processes, etc.).

From a systems-level perspective, TES technologies have been more extensively adopted in industrial waste heat recovery and district heating applications due to their simplicity, low-cost materials, and compatibility with thermal networks [109,110,111,127,128,129,130]. Conversely, CES technologies, while still advancing in maturity and cost-effectiveness, are gaining momentum in transportation decarbonization, grid balancing, and chemical process electrification [103,122,123].

Overall, while no single storage solution dominates across all dimensions, the literature clearly indicates that the most promising technologies are those with high modularity, long cycle life, and integration flexibility with renewable sources (see

Table 5. Comparative assessment of emerging and established energy storage technologies [4,5,6,7,13,14,19,20].

Technology	Type	TRL	CAPEX	OPEX	Utilization Potential	Energy Efficiency (%)	Emission Reduction Potential	Current Limitation for Adoption
Li-ion batteries	CES	9	Medium–High (€300–500/kWh)	Medium	EVs, small-scale grid, industry backup	90–95%	High (transportation, mobile loads)	Fire risk, resource dependency (Li, Co), recycling barriers
VRFBs	CES	7–8	High (€500–800/kWh)	Low	Stationary storage for grids/industry	75–90%	High (stationary decarbonization)	Low energy density, vanadium cost
Na-ion batteries	CES	6–7	Low–Medium (€100–300/kWh)	Low	Emerging grid & industrial applications	80–90%	Moderate–High	Immature market, lower density than Li-ion
Solid-state batteries	CES	5–6	Very High (>€800/kWh)	Medium–High	Future high-energy EVs, aerospace	90–98%	High (long-term)	High fabrication complexity, interfacial issues
Zinc–bromine batteries	CES	6–7	Medium	Medium	Stationary storage	65–80%	Moderate	Corrosion, toxicity, low round-trip efficiency
Hydrogen	CES	7–8	High	High	Steel, ammonia, fuel, H2 turbines	65–75%	Very High (hard-to-abate sectors)	Costly infrastructure, compression/liquefaction challenges
LOHCs/Metal hydrides	CES	5–6	High	Medium	Portable/mid-scale storage	40–60% (system-level)	Moderate	Catalyst degradation, reversibility limitations
Methanol	CES	6–7	High	Medium–High	Drop-in fuel, chemicals	~60%	High	Dependent on CCU, catalyst optimization
Molten salts	TES	8–9	Medium (€30–80/kWh)	Low	CSP, cement, metallurgy	>90%	High	Freezing below 240 °C, material degradation
MGTES	TES	6–7	Low (€10–30/kWh)	Very Low	High-temp industries (metal, glass)	~90–95%	High	Scaling and heat exchanger integration
PCMs	TES	6–7	Medium (€50–150/kWh)	Medium	HVAC, food, low-medium temp industries	75–85%	Moderate	Phase stability, low thermal conductivity
Rock thermal storage	TES	7–8	Low	Very Low	District heating, high-temp storage	60–80%	Moderate	Low energy density
LAES (Cryogenic storage)	CES/TES	6–7	High (€100–300/kWh)	Medium	Long-duration storage, industrial cooling	50–60%	Moderate	Energy-intensive liquefaction, low RTE

). As shown in comparative studies [96,97,133,134,135,136], hybrid approaches that combine TES for heat-intensive operations with CES for long-duration or mobile applications are increasingly regarded as essential for achieving industrial decarbonization and energy resilience. The convergence of efficiency, safety, lifecycle, and system compatibility will be the decisive factors in technology selection as storage solutions continue to evolve toward large-scale implementation.

7. Challenges and Future Prospects

The use of energy storage is subject to various challenges that need to be addressed in order to achieve a sustainable energy transition.

Economic Competitiveness: One of the main challenges in the large-scale implementation of thermal and chemical ESS is their high costs, restricting companies with economic limitations. However, technological advances and the rise of AI have improved this detail since Machine Learning (ML) and real-time monitoring systems can optimize energy storage management by improving efficiency and profitability [137,138].

One illustrative example of the real-world application of ML in energy storage is the use of predictive maintenance models for lithium-ion battery systems. For instance, researchers have developed ML algorithms capable of estimating battery remaining useful life and predicting thermal runaway conditions based on real-time monitoring data, including voltage, temperature, and current [139,140]. These models have been deployed in pilot-scale energy storage installations to reduce unplanned outages, optimize charging cycles, and extend battery lifespan, demonstrating the tangible benefits of ML-based maintenance strategies.

Figure 5 illustrates a general architecture showing how AI, particularly ML, can be integrated into energy storage systems. The framework includes real-time data acquisition from sensors (e.g., voltage, temperature, current), followed by data preprocessing and analysis using trained ML models. These models enable functions such as state-of-health estimation, thermal risk prediction, and remaining useful life forecasting. The insights derived feed into control loops that adjust system parameters dynamically and support predictive maintenance and operational planning. This integration enhances the reliability, safety, and efficiency of storage systems.

On the other hand, promising chemical and TES technologies, such as sodium batteries, P2X technologies, and molten salts, may see their economic viability compromised due to their low efficiency in energy conversion or in the degradation of materials present in these systems. Factors such as the use of short-life catalysts and corrosive processes can limit their adoption. Research on new materials, such as advanced PCMs, metal hydrides, and nanomaterials, improves the efficiency, thermal stability, and durability of these technologies [141,142].

Infrastructure: The integration of ESS into existing industrial infrastructures constitutes a great challenge due to the difficulty of adapting industrial plants, to safety risks associated with chemical storage systems, and to strict environmental regulations that do not promote the use of these systems. Industrial plants that need to be upgraded in order to incorporate energy storage into their facilities will most likely be required to modify their existing processes with the exception of P2X technologies that generate fuels such as methane or e-fuels. Another example is the need to develop the necessary infrastructure for energy carriers such as hydrogen. New distribution systems will have to be developed and integrated with existing infrastructures.

Simultaneous process and molecular design: Advances in the simultaneous design of molecules (involved in energy storage and energy-system processing) with process design can offer unique opportunities for innovating new systems and chemicals. In this context, approaches such as property integration and data-driven structure-property models can be highly effective [143,144,145].

Safety and resilience: Chemical storage systems, especially those that utilize hydrogen and synthetic fuels, are flammable and can leak or cause reactivity. These shortcomings will most likely cause strict regulations to be implemented on emissions and industrial waste disposals, affecting the implementation of these technologies. To mitigate these risks, enhanced safety protocols, such as advanced containment systems and automated monitoring, are being developed and implemented. The exploration of batteries, for example, with water-saturated cellulosic sponges has been proposed as an alternative to reduce the risk of fires associated with conventional lithium-ion batteries [146,147]. Another safety issue deals with the operational aspects of emerging infrastructures for integrating renewable energy with existing energy systems [148,149]. Furthermore, resilience considerations must be taken into consideration during the development of energy transformation, storage, and dispatch systems, especially in light of the vulnerabilities because by natural disasters [150].

Decarbonization: Investing in the improvement of current CO₂ capture systems can be of great importance in the use of these technologies [151,152]. Emerging technologies offer promising alternatives for the simultaneous production of energy carriers while significantly reducing the carbon footprint [153,154]. Furthermore, the development of decarbonization infrastructure will have to be integrated with the establishment of energy storage and dispatch infrastructure [155].

Regulations and Policies: Regulatory challenges will significantly impact the adoption of energy storage. Active collaboration with regulators to establish clear and consistent regulations will only ease the complex regulatory landscape. The coordination of state and federal policies is critical to streamline regulatory compliance and to foster the adoption of energy storage technologies [156,157].

8. Conclusions

The rapid transformation of the global energy sector underscores the importance of ESS in ensuring a sustainable, resilient, and decarbonized future. This study has explored the diverse technological advancements in CES and TES, highlighting their important contributions to the integration of renewable energy, the implementation of energy efficiency, and their effort to decarbonize the industry. However, beyond the conventional discourse on technical and economic challenges, the integration of AI and ML emerges as a transformative pathway that will optimize energy storage management, enhance efficiency, and accelerate its adoption.

Technological Outlook

▪

The advancement of ESS technologies is essential in order to mitigate the intermittency of renewable energy sources.

▪

CES solutions, such as hydrogen storage and P2X strategies, offer long-term energy retention options allowing surplus renewable energy to be converted into valuable fuels and chemicals.

▪

TES, on the other hand, provides immediate solutions for heat management, improving industrial efficiency and enabling waste heat recovery.

▪

However, challenges remain in terms of material degradation, thermal stability, and large-scale implementation with the need for continued research into novel materials and system designs.

AI Integration

▪

AI and ML have demonstrated their potential in overcoming key limitations associated with ESS, particularly in predictive maintenance, real-time system monitoring, and energy demand forecasting.

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Advanced analytics enable dynamic optimization of energy storage operations by identifying inefficiencies, predicting material degradation, and recommending adaptive control strategies.

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These capabilities significantly improve the reliability and cost-effectiveness of CES and TES, addressing major barriers such as system lifespan, safety, and performance variability.

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Beyond operational enhancements, AI-driven modeling and digital twins provide a framework to simulate large-scale deployment scenarios, assess the economic viability of emerging technologies, and guide strategic decision-making.

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Reinforcement learning algorithms can dynamically adjust storage dispatch strategies based on fluctuating electricity prices, grid conditions, and renewable energy availability, thereby maximizing economic returns and minimizing emissions.

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AI-enabled automation enhances safety measures in chemical storage systems and mitigates risks related to fires, leakage, and reactivity.

Policy Recommendations and Future Directions

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Despite technological advancements, regulatory and economic barriers still hinder the widespread adoption of ESS.

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Policy incentives, investment in research, development, and industry collaborations are crucial to accelerate the transition into a decarbonized energy system.

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The development of standardized frameworks for energy storage deployment, safety, and grid integration will also be essential in ensuring the long-term viability of these solutions.

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The rising demand for sustainable energy solutions calls for interdisciplinary methods that merge advances in materials science, chemical engineering, and digital technologies to optimize ESS performance.

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The convergence of AI, ML, and ESS constitutes a paradigm shift in energy management, transcending traditional storage limitations and paving the way for a more adaptive, efficient, and low-carbon energy landscape.

▪

Future research should focus on refining AI-based control strategies, advancing hybrid storage architectures, and fostering interdisciplinary collaborations to bridge the gap between theoretical advancements and real-world deployment.

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Moreover, efforts to enhance the economic feasibility, safety, and regulatory acceptance of ESS technologies will be instrumental in achieving a cleaner and more resilient global energy infrastructure.