Advancements in Energy-Storage Technologies: A Review of Current Developments and Applications

Abstract

Energy-storage technologies have rapidly developed under the impetus of carbon-neutrality goals, gradually becoming a crucial support for driving the energy transition. This paper systematically reviews the basic principles and research progress of current mainstream energy-storage technologies, providing an in-depth analysis of the characteristics and differences of various technologies. Additionally, a comprehensive summary of the economic characteristics of energy-storage technologies is presented. By evaluating the advantages and limitations of different energy-storage technologies, the potential value and application prospects of each in future energy systems are revealed, providing a scientific basis for the selection and promotion of energy-storage technologies. Furthermore, the paper summarizes the current applications of energy-storage technologies in power systems and the transportation sector, presenting typical case studies of energy-storage engineering demonstrations in China. These case studies offer valuable references for the development of related research in the field of energy storage.

1. Introduction

Against the backdrop of the global energy transition, escalating energy crises, and urgent environmental challenges, the rapid advancement and widespread adoption of renewable energy technologies have become indispensable. Constructing resilient power systems and establishing sustainable energy frameworks represent crucial foundations for achieving global carbon-neutrality targets. International initiatives such as the Paris Agreement [1] and comprehensive reports published by organizations like the International Renewable Energy Agency (IRENA) [2] underscore the urgency and significance of accelerating renewable energy integration through effective energy-storage systems.

Recognizing these imperatives, governments worldwide have introduced targeted policies and regulatory frameworks to foster the adoption of energy-storage solutions. For instance, in April 2024, the National Energy Administration of China issued the “Notice on Promoting the Grid Connection and Dispatch of New Energy Storage” [3], which provides a solid institutional foundation for the effective grid integration and optimized dispatch of advanced energy-storage technologies. This policy not only accelerates China’s energy transition but also contributes significantly to achieving sustainable development goals.

Energy-storage technologies play a pivotal role in enabling the effective integration and utilization of intermittent renewable energy resources, particularly solar and wind power, by stabilizing supply–demand fluctuations and ensuring grid reliability [4]. These technologies are widely deployed throughout various stages of power systems, including generation, transmission, distribution, substations, and consumption. Their applications extend to critical functions such as Automatic Generation Control, frequency regulation, peak-shaving, and demand response programs [5]. The integration of robust energy-storage systems significantly enhances power grid stability, increases renewable energy penetration, and promotes energy efficiency and conservation.

Despite substantial advancements, key challenges persist, including high costs, technological maturity limitations, safety concerns, environmental impacts, and the scalability of specific storage technologies. These challenges necessitate a systematic examination of current technologies, their operational characteristics, economic feasibility, and appropriate deployment contexts.

A growing body of research has been conducted by scholars both in China and abroad to examine the classification, development status, and key characteristics of existing energy-storage technologies. Wang, Wei et al. [6] provided a comprehensive overview of various energy-storage applications, evaluating their effectiveness in mitigating the intermittency and uncertainty of renewable energy sources, while also analyzing their core techno-economic attributes. Yixue Liu et al. [7], in the context of China’s power sector reform, reviewed the evolution of energy-storage business models in China. Their study systematically examined the development of the Chinese energy-storage sector, its roles across different segments of the power system, and presented an in-depth discussion of prevailing business models. Erdemir, Dogan et al. [8] offered a broad survey of current energy-storage technologies, their practical applications, and the future challenges and opportunities facing the sector. The study investigated the technological outlook of storage methods and discussed trending topics related to emerging application domains. Moreover, it emphasized key research directions and technological advancements that are likely to reshape the energy-storage landscape in the coming years. Aghmadi, Ahmed et al. [9] reviewed recent developments in high-power energy-storage systems, highlighting the deployment of hybrid storage technologies in microgrid environments and scenarios involving critical or pulsed loads. Their analysis further explored the comparative performance metrics of storage technologies, including power density, energy capacity, cost, and operational lifetime. In addition to these reviews, a significant body of literature has also focused on emerging topics such as the integration of new storage technologies in demonstration projects, critical enabling technologies, performance evaluation methods, and the development of technical standards.

This paper aims to provide a comprehensive review of diverse energy-storage technologies, analyzing and comparing their technical specifications, economic viability, and sector-specific application scenarios. By thoroughly examining the principles, strengths, and limitations of different storage methods, the review elucidates the potential and practical implications of these technologies in driving the global energy transition. The remainder of this paper is organized as follows. Section 2 introduces fundamental definitions and characteristics of various energy-storage technologies. Section 3 provides a horizontal comparison of technical characteristics across different energy-storage types. Section 4 discusses the economic feasibility of energy-storage technologies, while Section 5 focuses on the benefit analysis of these technologies and highlights several typical application scenarios of energy-storage technologies. Finally, Section 6 summarizes the key findings and insights of this review.

2. Types of Energy-Storage Technologies

Energy-storage technologies encompass diverse mechanisms and principles, and their classification typically depends on the form in which energy is stored, converted, and retrieved. Generally, these technologies can be systematically categorized into mechanical, electromagnetic, electrochemical, thermal, and chemical energy-storage methods, as illustrated in Figure 1. Mechanical energy-storage technologies store energy through physical mechanisms such as gravitational potential, kinetic motion, or compressed gases. Electromagnetic energy-storage systems leverage electric or magnetic fields for rapid charging and discharging capabilities. Electrochemical energy storage involves chemical reactions within batteries or cells, enabling efficient conversion and storage of electrical energy. Thermal energy-storage methods rely on heat capacity, latent heat, or thermochemical processes, allowing the temporary storage of thermal energy at varying temperatures. Chemical energy storage utilizes chemical bonds, with hydrogen being a notable example, enabling energy storage through chemical synthesis and decomposition processes. Each category of these technologies offers distinct technical characteristics, efficiency ranges, operational flexibility, scalability, and economic implications. Understanding these attributes facilitates selecting optimal energy-storage solutions tailored to specific application scenarios and requirements.

2.1. Mechanical Energy Storage

Mechanical energy-storage technologies represent one of the earliest and most established categories of energy-storage systems. By converting electrical energy into mechanical forms such as potential or kinetic energy, these systems offer robust solutions for large-scale and long-duration applications. This category primarily includes three representative technologies: pumped hydro storage (PHS), compressed air energy storage (CAES), and flywheel energy storage (FES). Each of these systems utilizes distinct physical principles—gravitational potential, air compression, and rotational inertia—to store and release energy with varying response times, efficiencies, and power characteristics. Mechanical storage systems are particularly well suited for grid-level load balancing, frequency regulation, and backup power due to their high reliability, long lifespan, and scalability.

2.1.1. Pumped Hydro Storage

Mechanical energy storage mainly includes pumped storage, compressed air energy storage, and flywheel energy storage. Pumped hydro storage (PHS) stores electrical energy in the form of potential energy in water. It is a large-scale energy-storage technology widely applied in power systems, playing a key role in peak-shaving, valley-filling, emergency backup, and improving power quality. The basic principle of pumped hydro storage is to use surplus electricity during periods of low demand to drive a pump that transfers water from a lower reservoir to an upper reservoir for storage. During peak demand periods, the water is released back to the lower reservoir, driving a turbine to generate electricity, thereby enabling effective energy scheduling and utilization. Pumped hydro storage systems require specific geographical conditions, such as abundant water resources and significant elevation differences. When these conditions are met, pumped hydro storage is a suitable choice for renewable energy storage and grid energy storage. The fundamental operating principle of pumped hydro energy storage is illustrated in Figure 2.

Current research trends in PHS technology primarily focus on optimizing system performance, enhancing operational flexibility, and improving integration with renewable energy sources and power grids. Significant efforts are directed toward advanced fault detection methods, operational reliability, and precise modeling techniques. For instance, recent studies have developed advanced diagnostic methods for rotor winding faults and excitation system malfunctions in doubly-fed induction pumped-storage units, enabling rapid fault identification and improved system reliability [10]. Additionally, in scenarios characterized by significant integration of wind and solar power, researchers have introduced probabilistic modeling approaches, such as Gaussian mixture models, to accurately quantify cumulative forecast errors and establish robust operational boundaries for pumped hydro storage dispatching strategies [11]. Moreover, recent advancements in environmental-economic dispatching strategies have demonstrated the integration benefits of wind power combined with pumped hydro storage and thermal generation, significantly enhancing renewable energy absorption, reducing operational fluctuations, and minimizing dispatching costs [12]. These research outcomes underscore the critical role of PHS in contemporary power system management and the ongoing pursuit of innovation for enhanced sustainability and reliability.

2.1.2. Compressed Air Energy Storage

Compressed Air Energy Storage (CAES) is a promising large-scale energy-storage technology that converts electrical energy into pressurized potential energy by compressing air and storing it in suitable underground structures, such as salt caverns or aquifers. During off-peak periods, surplus electricity drives compressors that store compressed air; during peak demand, the stored air is released, reheated, and expanded through turbines to regenerate electricity. The round-trip efficiency of traditional CAES systems typically ranges from 40% to 55%, but can be significantly improved in Adiabatic CAES (A-CAES) configurations, where heat from the compression stage is captured and reused during expansion via integrated thermal storage systems. The fundamental operating principle of compressed air energy storage is illustrated in Figure 3.

Key components of CAES systems include compressors, expanders, thermal energy-storage units, heat exchangers, and advanced control systems. Compared with other mechanical storage technologies, CAES offers the advantages of high scalability, long-duration energy discharge, and effective coupling with intermittent renewable energy sources. However, CAES deployment requires suitable geological conditions and faces challenges related to system integration, thermal management, and equipment efficiency.

Recent research efforts have addressed several technical challenges in CAES systems. For example, cavern structural reliability is a critical concern in large-scale deployments. A study modeled non-Darcy flow behavior in porous formations by conducting high-speed injection and extraction experiments on rock cores with different permeability levels, establishing optimal design parameters for subsurface air storage [14]. In the field of compressor optimization, surrogate models based on Latin hypercube sampling and radial basis function neural networks have been coupled with multi-objective genetic algorithms to refine the aerodynamic design of axial-flow compressors [15]. Additionally, a multi-stage optimization framework for A-CAES systems has been developed, addressing planning scenarios such as peak-shaving, emergency backup, ramping services, and inertia provision. This approach enhances the operational flexibility and planning accuracy of grid-integrated CAES installations [16].

2.1.3. Flywheel Energy Storage

Flywheel Energy-Storage (FES) systems utilize the rotational kinetic energy of a high-speed rotor to store and release electrical energy. A typical FES system comprises a flywheel rotor, a bearing system (often magnetic), a power conversion unit including a motor-generator set and power electronic converters, and auxiliary systems such as vacuum chambers to minimize aerodynamic losses. During the charging phase, electrical energy powers the motor to accelerate the rotor, thereby storing energy in the form of angular momentum. During discharge, the stored rotational energy is converted back into electricity by operating the motor in generator mode. The kinetic energy stored in a flywheel can be expressed as:

$$E_F={\displaystyle \frac{1}{2}}J{\omega }^2$$

(1)

where J is the moment of inertia of the rotor, and $\omega$ is its angular velocity. Since energy-storage capacity is directly proportional to J and to the square of $\omega$, modern FES systems prioritize high-speed operation and lightweight, high-strength materials (e.g., carbon fiber composites) to maximize energy density while maintaining structural integrity. Typical systems operate at speeds exceeding 10,000 rpm and can achieve round-trip efficiencies above 90%. The fundamental operating principle of flywheel energy storage is illustrated in Figure 4.

FES systems are characterized by high power density, rapid charge/discharge capability, long life cycle, and low maintenance requirements. However, due to inherent self-discharge and limited energy retention duration, they are generally unsuitable for long-term energy storage and are often employed in hybrid configurations with other storage technologies.

Recent research in FES technology has focused on system integration, hybrid energy-storage configurations, and advanced control strategies for grid and microgrid applications. For instance, one study proposed enhancing the frequency regulation capability of pumped hydro storage systems by integrating FES. A mathematical model was developed to analyze system stability and determine the required flywheel capacity to suppress frequency deviations effectively [17]. In another study, a two-layer distributed cooperative control strategy was introduced for FES clusters in DC microgrids [18]. The primary control layer combines field-oriented control (FOC) with space vector pulse width modulation (SVPWM), while the secondary layer utilizes a consensus-based mechanism for adaptive droop control through inter-unit communication. This approach mitigates voltage deviation and addresses the single-point failure and scalability limitations associated with centralized control architectures.

These developments underscore the potential of FES as a fast-response, high-efficiency storage option in modern power systems, particularly for ancillary services, grid stability enhancement, and distributed coordination.

2.2. Electrochemical Energy Storage

Electrochemical energy-storage systems (EESS) store and release electrical energy through reversible electrochemical reactions, typically in the form of redox reactions at the electrodes. These systems convert electrical energy into chemical energy during charging and reconvert it into electricity during discharging. Owing to their compactness, high energy density, rapid response, and modular design flexibility, EESS are widely adopted in various domains, including grid-scale storage, renewable energy integration, electric vehicles, and distributed power systems. EESS can be broadly classified into solid-state batteries (e.g., lithium-ion, lead-acid, sodium-ion, sodium-sulfur) and flow batteries (e.g., all-vanadium redox, zinc-bromine). Among current electrochemical energy-storage technologies, lithium-ion batteries, flow batteries, and sodium-sulfur batteries are the three most representative types. Each embodies distinct technical advantages—namely high energy density, system flexibility, and long-duration storage—making them widely applicable across various energy scenarios.

2.2.1. Lithium-Ion Batteries

Lithium-ion batteries are among the most mature and extensively researched electrochemical energy-storage technologies. In a typical lithium-ion battery, the anode is composed of carbon or graphite, while the cathode consists of metal oxides such as lithium cobalt oxide, nickel oxide, manganese oxide, or their composites. The electrodes are separated by a porous membrane soaked in a lithium salt electrolyte. The electrolyte may take the form of a liquid, gel, or solid-state conductive polymer. The structural principle is illustrated in Figure 5 [19]. Compared with other types of batteries, lithium-ion batteries offer several advantages, including fast response time, compact size and lightweight, high energy efficiency, high nominal voltage, and ease of modular integration. As a result, lithium-ion batteries have been widely deployed in electric vehicles and grid-side energy-storage systems. They have become the dominant technology in both commercial and residential energy-storage applications and are gradually expanding toward larger-scale deployment scenarios.

2.2.2. Flow Batteries

Flow batteries are high-performance energy-storage systems in which the positive and negative electrolytes are stored separately and circulate independently during operation. Vanadium redox flow batteries represent the most widely adopted type, utilizing liquid electrolytes as energy carriers. A key structural advantage of flow batteries lies in their decoupled design of power and energy capacities, allowing for flexible system scaling based on specific application requirements.

Although the energy density of flow batteries is relatively low compared to other technologies, they exhibit excellent safety characteristics and an exceptionally long life cycle. They support deep charge/discharge operations and high-frequency cycling, with relatively low system maintenance costs. Flow batteries also operate over a broad temperature range, making them suitable for reliable performance in various climatic conditions.

Owing to these attributes, flow batteries are particularly well suited for large-scale, long-duration energy-storage applications, including renewable energy integration, grid peak-shaving and frequency regulation, and microgrid systems. The structural schematic of a flow battery is illustrated in Figure 6.

2.2.3. Sodium-Sulfur Batteries

Sodium-sulfur (Na–S) batteries consist of molten electrodes and a solid electrolyte. The active material at the anode is molten metallic sodium, while the cathode comprises liquid sulfur and polysulfide molten salts. The structural schematic of a sodium-sulfur battery is shown in Figure 7. These batteries offer relatively high energy density and efficiency, making them especially suitable for long-duration and high-capacity energy-storage applications. They utilize abundant and low-cost sodium and sulfur as raw materials, which provides a strong cost advantage and favorable environmental adaptability. However, due to their high operating temperature, they require advanced thermal management systems to ensure safe and stable operation. As a result, their use is generally limited to large-scale power system applications. Sodium-sulfur battery technology has already reached pilot and commercial deployment stages in several countries, emerging as a viable option for utility-scale storage projects. Current research efforts are primarily focused on improving battery performance and reducing the cost associated with high-temperature operation.

Except for sodium-sulfur batteries, many emerging battery technologies have the potential to improve energy density, safety, and cost-effectiveness, but still face challenges such as material and interface stability.

Solid-state batteries are considered promising due to their higher energy density and better safety. Research is focused on the development of solid electrolytes and electrode materials. However, their long-term cycle life and output power density still need to be improved to achieve commercial applications. Zinc-air batteries have been widely studied due to their high energy density and cost-effectiveness. Current challenges include lower power density, shorter lifespan, and air electrode corrosion, which leads to performance degradation. Future research will focus on optimizing electrode materials and electrolytes to improve the battery’s cycle life and performance. Nickel-zinc batteries offer higher voltage and power density, making them suitable for high-power applications. However, zinc’s self-corrosion and the battery’s cycle life are significant challenges. Magnesium-ion batteries are considered a potential alternative to lithium-ion batteries due to their high volumetric energy density and safety. However, the lower migration rate of magnesium ions and the lack of suitable electrolytes limit their performance.

Recent research in electrochemical energy storage focuses on enhancing battery performance in terms of energy and power density, thermal stability, cycle life, safety, and cost-efficiency. Advanced electrode materials (e.g., silicon anodes, lithium metal), solid-state electrolytes, and innovative cell architectures are under extensive investigation. Moreover, system-level concerns such as thermal management and battery degradation under real-world operating conditions are gaining increasing attention. For instance, Liu et al. [20] conducted a comprehensive experimental study on the thermal behavior and capacity fade mechanisms of large-format lithium-ion batteries. They demonstrated that temperature distribution during high-rate operation is nonuniform, which leads to accelerated degradation and performance inconsistency. Their findings emphasize the need for precise thermal management strategies in large-scale battery installations. In another study, Zhang et al. [21] compared a range of electrochemical storage technologies from the perspective of materials, cost, and electrochemical characteristics, with a particular focus on aluminum-ion batteries. They also discussed the role of power conversion systems and emerging wide-bandgap semiconductors (e.g., SiC, GaN) in improving overall system efficiency, and evaluated the performance and integration challenges of electrochemical storage in renewable energy applications.

Despite their maturity, EESS technologies face ongoing challenges related to resource availability (e.g., lithium, cobalt), recyclability, safety under abuse conditions, and the development of sustainable battery supply chains. Addressing these issues is essential to support the long-term deployment of electrochemical storage in decarbonized energy systems.

2.3. Thermal Energy Storage

Thermal energy-storage (TES) systems store energy in the form of heat using various thermal media and release it when needed to meet fluctuating thermal or electrical demand. TES plays a critical role in improving energy utilization efficiency, particularly when integrated with renewable energy systems, such as solar thermal power, or in capturing industrial waste heat. The stored heat can be used directly for heating or converted into electricity using thermodynamic cycles.

TES technologies are generally classified into three categories based on the underlying storage mechanism: (1) Sensible Heat Storage (SHS): Stores thermal energy by raising the temperature of a solid or liquid medium without changing its phase. Common materials include water, molten salts, and rocks. (2) Latent Heat Storage (LHS): Utilizes the phase change (typically solid–liquid) of a material to store and release heat at nearly constant temperature. Phase change materials (PCMs) such as paraffin waxes and salt hydrates are commonly used. (3) Thermochemical Energy Storage (TCES): Involves reversible chemical reactions to absorb and release thermal energy. TCES offers high energy density and long-duration storage potential. Common reactions include hydration–dehydration and redox reactions.

Each TES type offers distinct advantages. SHS systems are cost-effective and simple but have lower energy density. LHS systems enable higher storage density and operate at nearly constant temperature, while TCES systems provide very high-energy-density and lossless long-duration storage, albeit with higher technical complexity. Recent research in TES focuses on improving the thermal conductivity of PCMs using composite materials, developing corrosion-resistant high-temperature storage materials for molten salt systems, and enhancing the reversibility and cyclability of thermochemical storage media. Additionally, integrated systems combining TES with solar thermal power plants, district heating, and industrial waste heat recovery are attracting increasing attention for decarbonization strategies.

2.3.1. Sensible Heat Storage

Sensible heat storage is a form of thermal energy storage that utilizes the inherent heat capacity of materials. It stores and releases thermal energy through temperature changes during the heating or cooling process, typically using water, brine, or other heat transfer media. The performance of sensible heat storage media depends on factors such as specific heat capacity, thermal conductivity, density, operating temperature range, and cost. Ground heat storage is the most common form of sensible heat storage and represents a large-scale thermal energy-storage technology that uses underground soil, rock, or aquifers as the heat storage medium. It is mainly applied for seasonal heat storage and regional energy systems. Molten salt storage is one of the commonly used sensible heat storage methods. Due to the high heat capacity and thermal conductivity of molten salts, this technology is often employed in high-temperature heat storage applications, such as solar thermal energy storage. Chunhao Zhao et al. [22] proposed a coupled dual-tank storage system based on binary molten salts for a 660 MW supercritical coal-fired unit. The study simulated the heat storage and release performance of the molten salt storage system, examining the steady-state operational characteristics with respect to molten salt flow and the temperature difference at the molten salt heat exchanger. They analyzed the flexibility improvement potential of the power plant, calculating changes in the plant’s ramp-up/ramp-down rates and load enhancement capabilities after integrating the storage system.

2.3.2. Latent Heat Storage

Latent heat storage technology utilizes the latent heat released or absorbed during phase changes in materials, such as solid–liquid or liquid–gas transitions, to store and release energy. Phase change materials (PCMs) generally possess higher thermal energy-storage capacity than non-phase change materials. These storage media exhibit high energy density and maintain nearly constant temperatures during the phase transition, making them suitable for applications requiring a stable temperature heat supply. Research on latent heat storage primarily focuses on the development and introduction of new storage media as well as the enhancement of the thermodynamic properties of existing materials. Sikiru, S. et al. [23] reviewed the applications of phase change materials, heat transfer enhancement techniques, selection criteria, and photovoltaic performance indicators. Their study examined storage configuration methods, the performance of phase change materials and their mixtures, heat and mass transfer fluids, and storage mechanisms, summarizing the research trends and shortcomings of phase change materials in photovoltaic energy utilization.

2.3.3. Thermochemical Energy Storage

Thermochemical energy storage stores and releases energy through endothermic and exothermic reactions of the storage medium, enabling the conversion between thermal energy and chemical energy. This technology requires suitable materials or material combinations that meet criteria such as high storage efficiency, low thermal loss, and reversible stability, allowing energy to be released on demand. The process primarily involves three stages: endothermic dissociation, storage of reaction products, and exothermic recombination of the dissociated products. Figure 8 represents the working principles of a thermochemical energy-storage systems.

Because thermochemical storage exhibits lower energy loss during storage compared to sensible or latent heat storage, it holds great potential for long-term energy-storage applications. However, challenges remain regarding material stability and system integration. Yan, T. et al. [24] analyzed the thermodynamic properties and reaction kinetics of salt hydrates to evaluate the potential of salt hydrate adsorption-based thermochemical heat storage. The study summarized typical principles of thermochemical adsorption heat storage, selection criteria for adsorbent materials, thermophysical properties of salt hydrates, and reaction kinetics. It further detailed thermodynamic data of salt hydrates as well as desorption/adsorption reaction rate models and dehydration/hydration behaviors.

2.4. Electromagnetic Energy Storage

Electromagnetic energy storage refers to a class of advanced technologies that store energy in the form of electric or magnetic fields. These systems are particularly suitable for applications requiring rapid dynamic regulation and high-frequency charge–discharge cycles. Currently, the main types of electromagnetic storage technologies include supercapacitor energy storage and superconducting magnetic energy storage (SMES). Although their large-scale deployment is currently limited by high costs and technical complexity, electromagnetic energy storage has demonstrated significant engineering value in specific critical scenarios. The following sections provide a systematic overview of the fundamental principles, core components, and development potential of these two technologies.

2.4.1. Supercapacitors

Supercapacitors, also known as electrochemical capacitors or electric double-layer capacitors, combine the high-current rapid charge–discharge characteristics of capacitors with the energy-storage capabilities of batteries. They store energy through the formation of an electric double layer at the interface between the electrode and the electrolyte, as well as through fast Faradaic reactions on the electrode surface. Supercapacitors exhibit high charge density and extremely high power output, enabling them to respond to power demand changes within tens to hundreds of milliseconds. Therefore, they are well suited for applications requiring instantaneous high power output. The structure of a supercapacitor is illustrated in Figure 9.

Key technologies that require further breakthroughs and innovation in supercapacitors include the preparation techniques for key materials, fabrication processes, and structures of individual cells, as well as system integration and applications. Dry electrode technology has demonstrated significant potential in both supercapacitors and lithium-ion batteries. Guolei Zhang et al. [25] systematically elaborated on the preparation processes and characteristics of dry electrodes, focusing on their application progress in supercapacitors and lithium-ion batteries. This includes critical research outcomes such as electrode load optimization and enhancement of electrochemical performance. Furthermore, they discussed future development directions in light of current technical bottlenecks. The use of low-cost and environmentally friendly biochar as an electrode material for supercapacitors is currently a major research focus. Yuhui Liang et al. [26] reviewed the adaptability of biochar as an electrode raw material in relation to its preparation methods, and analyzed how properties such as specific surface area, pore structure, and surface functional groups affect the performance of biochar-based supercapacitors. Additionally, the study explored the performance improvements brought by activation and modification treatments and compared the suitability of different biomass feedstocks.

2.4.2. Superconducting Magnetic Energy Storage

Superconducting magnetic energy storage (SMES) stores electrical energy using superconducting coils. Its core principle relies on the zero-resistance property of superconducting materials below their critical temperature, allowing direct current to flow continuously with negligible loss in a closed loop, thereby storing electrical energy in the form of a magnetic field over extended periods. The system consists of superconducting coil assemblies, a cryogenic cooling unit, and a power conditioning system. The superconducting coils store energy by generating a magnetic field through direct current excitation. The cryogenic cooling system uses liquid helium or liquid nitrogen to maintain the superconducting materials below their critical temperature. The power conditioning system manages the conversion and output of electrical energy between direct current and alternating current during charging and discharging processes. The schematic diagram of a SMES is shown in Figure 10.

Current research on superconducting magnetic energy-storage (SMES) systems primarily focuses on medium- to large-scale power-level storage solutions. Key challenges to be addressed include advancements in high-temperature superconducting materials, cryogenic cooling technologies, low-temperature high-voltage insulation, superconducting current limiting techniques, power conversion systems, and dynamic monitoring systems. Li Chao et al. [27] proposed a large-capacity high-temperature superconducting spring energy-storage system capable of efficiently storing and releasing electromagnetic energy without the need for power electronic converters. The system exploits the interaction between multiple high-temperature superconducting coils and permanent magnets, and its operating principles and performance were validated through simulations and experiments. This system holds broad application prospects in fields such as railway transportation, electromagnetic launchers, and superconducting magnetic energy storage. Li WX et al. [28] introduced a novel configuration of superconducting energy-storage converters consisting of two permanent magnets and two superconducting coils, which significantly improves power distribution uniformity and increases energy-storage capacity. Through theoretical analysis and numerical derivation, the study provided a mathematical description of the new configuration’s parameters and verified the key parameters against experimental prototype results. The research further explored critical factors influencing power distribution, demonstrating that an optimal magnetic moment ratio can be achieved at specific distances, thereby optimizing power performance.

2.5. Chemical Energy Storage

Hydrogen is a storable, transportable, efficient, and clean energy carrier with a high energy density. Hydrogen energy-storage technology primarily consists of three components: electrolyzers, hydrogen storage devices, and fuel cell systems. Electrolyzers convert electrical energy into hydrogen through water electrolysis. Hydrogen storage devices, such as high-pressure tanks or liquid hydrogen storage systems, store the generated hydrogen. Fuel cell systems then reconvert the chemical energy of hydrogen back into electrical energy through electrochemical reactions, forming a complete hydrogen energy conversion and storage chain. Compared to other energy-storage technologies, hydrogen technology generally involves lower costs but exhibits relatively low energy-storage efficiency.

As illustrated in Figure 11, the Proton Exchange Membrane (PEM) electrolyzer facilitates this process by splitting water into hydrogen and oxygen under an applied electric current. At the anode, water molecules are oxidized to produce oxygen, protons, and electrons. The protons migrate through the membrane to the cathode, where they combine with electrons to form hydrogen gas. This zero-emission process is highly compatible with renewable energy integration, offering a promising pathway for long-duration and large-scale energy storage.

Research on hydrogen energy storage primarily focuses on innovations in hydrogen production and storage technologies, comprehensive performance evaluation, and current application status. Integrated hydrogen energy systems offer an effective solution to address fossil fuel depletion and climate change. To enhance system stability and operational efficiency, Dongyang Wu et al. [30] proposed an optimized scheduling method based on the deep deterministic policy gradient algorithm. By modeling the scheduling problem as a Markov decision process and employing policy gradient and neural networks to train an actor-critic network, they developed an optimal energy scheduling approach that adaptively optimizes according to system dynamic responses. Jamil, H. et al. [31] investigated a multi-objective optimization method to balance hydrogen production-consumption dynamics, storage capacity, and operational cost reduction. Their approach integrates key indicators such as hydrogen production, solar, and wind energy conversion efficiencies. Utilizing a novel mathematical optimization model, the study explored the interaction between efficient hydrogen synthesis and renewable energy, and conducted sensitivity analysis to assess the impact of efficiency parameters on system performance.

3. Current Development Status of Technical Characteristics of Energy-Storage Technology

3.1. Characterization of Energy-Storage Technologies

To meet the demands of large-scale applications, energy-storage technologies must be developed into engineering-compatible devices that ensure high safety, reliability, and favorable techno-economic performance. These attributes are essential to satisfy power system requirements and facilitate widespread practical deployment. Key performance indicators for energy-storage technologies include capacity, power, efficiency, and response time. Among these, response time reflects the speed at which the storage system reacts to external changes such as grid load variations or fluctuations in power demand. Cycle life and cycle efficiency are closely related to the cost of energy storage, indicating the number of charge–discharge cycles the device can undergo and the efficiency of energy conversion, respectively. Power density refers to the amount of energy that a storage device can deliver or absorb per unit mass or volume within a unit time, representing the technology’s capability for rapid charging and discharging. Volumetric energy density relates to the required footprint and spatial constraints, while gravimetric energy density reflects the requirements for the equipment carrier.

This paper compares various energy-storage technologies in terms of response time, cycle life, cycle efficiency, energy density, and power density.

Table 1. Comparison of Various Energy-Storage Technologies [13,32].

Energy Storage Type	Energy Storage Type	Response Time	Cycle Life (Times)	Power Density (kW/m3)
Mechanical Energy Storage	Pumped Hydro Storage	Minute-level	≥50 years	0.5–1.5
	Compressed Air Energy Storage	Minute-level	30–50 years	0.5–2
	Flywheel Energy Storage	10 ms range	≥20 years	1000–2000
Electrical Storage	Superconducting Magnetic	Millisecond-level	10,000–100,000	300–4000
	Supercapacitor	Millisecond-level	≥50,000	>100,000
Electrochemical Energy Storage	Lead-Acid Battery	100 ms range	500–2000	200–500
	Nickel-Cadmium Battery	100 ms range	1000–4500	250–1000
	Lithium-Ion Battery	100 ms range	1000–5000	100–3500
	Sodium-Sulfur Battery	100 ms range	2500–4500	150–230
	Flow Battery	100 ms range	>1000	0.5–2
Thermal Energy Storage	Sensible Heat Storage	Minutes to Hours	Thousands–Tens of Thousands	Hundreds–Thousands
	Latent Heat Storage	Minutes to Hours	≥Tens of Thousands	Hundreds
	Thermochemical Energy Storage	Hours to Days	Millions	100–1000
Chemical Energy Storage	Hydrogen Energy Storage	Minute-level	500–2000	>500

Note: Response time units—ms: milliseconds, s: seconds.

summarizes the technical characteristics of each energy-storage technology.

Energy-storage technologies exhibit distinct advantages across key performance metrics, including response time, energy density, power density, efficiency, and cycle life.

In terms of response time, electromagnetic energy-storage technologies demonstrate the most outstanding performance. Superconducting magnetic energy storage (SMES) and supercapacitors both achieve millisecond-level responses, while flywheel energy storage operates within the 10 ms range, making them highly suitable for scenarios requiring fast and dynamic response. Electrochemical storage systems exhibit response times in the range of 100 milliseconds, making them appropriate for short- to mid-term regulation. In contrast, mechanical energy-storage systems—such as pumped hydro and compressed air energy storage—and thermal energy storage typically exhibit response times from minutes to hours, rendering them suitable for long-duration energy-storage applications.

Regarding cycle life, thermal energy-storage technologies offer significant advantages. Thermochemical energy storage can reach up to one million cycles, while sensible and latent heat storage systems typically achieve several thousand to tens of thousands of cycles. Supercapacitors also stand out with a cycle life of up to 50,000 times, significantly exceeding conventional electrochemical storage systems. Among electrochemical options, flow batteries exceed 1000 cycles, while lithium-ion and sodium-sulfur batteries generally achieve between 1000 and 5000 cycles. Mechanical systems such as pumped hydro storage are measured in years and can operate for 30 to 50 years.

In terms of power density, supercapacitors lead by a wide margin, reaching up to 100,000 kW/m³, followed by flywheel energy storage at 1000–2000 kW/m³, which makes them highly effective for applications requiring short-duration, high-power output. Lithium-ion and sodium-sulfur batteries also offer relatively high power densities, whereas technologies like pumped hydro, compressed air energy storage, and flow batteries exhibit lower power densities (typically <2 kW/m³), making them more suitable for energy capacity-focused applications.

Overall, technologies such as supercapacitors, flywheels, and lithium-ion batteries offer significant advantages in terms of response time and power density, while thermochemical energy storage and pumped hydro excel in terms of cycle life and operational stability. Each technology should be selected and deployed based on specific application scenarios and system requirements.

The energy density comparison among various energy-storage technologies is illustrated in Figure 12.

The bar chart distinctly illustrates the variation in energy densities across different energy-storage technologies, highlighting the disparities in their storage capabilities. Chemical energy storage, represented by hydrogen storage, demonstrates a clear advantage with an exceptionally high energy density ranging from 800 to 10,000 Wh/kg, indicating its strong potential for large-scale, long-duration, and seasonal energy applications. Superconducting magnetic energy storage also exhibits excellent performance, with energy densities between 300 and 3000 Wh/kg, making it a leading option within electromagnetic storage systems. Thermochemical storage shows considerable capacity as well, achieving energy densities between 120 and 1000 Wh/kg.

Among electrochemical storage technologies, lithium-ion batteries offer the highest energy density (200–350 Wh/kg), while also featuring fast response times and technological maturity. These attributes contribute to their widespread adoption across various energy systems. In contrast, conventional mechanical storage technologies and supercapacitors display significantly lower energy densities, limiting their suitability to specific use cases such as grid-scale load leveling or high-frequency short-duration applications.

Overall, the data clearly underscore the superior energy density characteristics of hydrogen storage, superconducting magnetic storage, thermochemical storage, and lithium-ion batteries. These technologies are poised to become the primary focus of future development in high-energy-density storage systems.

The cycle efficiency comparison among various energy-storage technologies is illustrated in Figure 13.

The comparison of cycle efficiency shown in the bar chart clearly reveals significant differences among various energy-storage technologies in terms of energy conversion performance. Among thermal energy-storage technologies, sensible heat storage and latent heat storage demonstrate excellent performance, with cycle efficiencies reaching 85–95% and 80–90%, respectively. These technologies show broad application prospects in multi-energy systems and thermal-electric coupling scenarios. Flywheel energy storage (85–90%) and superconducting magnetic energy storage (80–99%) also exhibit outstanding efficiency, making them well suited for high-frequency charge–discharge operations and dynamic regulation applications. In the electrochemical storage category, lithium-ion batteries achieve a cycle efficiency of 80–86%, striking a good balance between performance stability and conversion efficiency. In contrast, mechanical storage technologies such as compressed air energy storage (≥70%) and pumped hydro storage (70–85%), as well as flow batteries (60–70%) and hydrogen storage (30–50%), present relatively lower efficiencies. Nonetheless, they remain critical for large-scale, long-duration storage and renewable energy integration.

Overall, the chart highlights the superior cycle efficiency of sensible heat storage, flywheel storage, and superconducting magnetic storage, indicating their strong potential in high-efficiency energy-storage systems.

Various energy-storage technologies play a crucial role in driving the transition to sustainable energy, but they still face certain environmental challenges in terms of resource extraction, carbon emissions, ecological impacts, and lifecycle management, which need to be comprehensively considered during technological development and implementation.

The environmental impact of mechanical energy-storage technologies is relatively small, but it is necessary to consider their environmental impact comprehensively during site selection, resource utilization, and system construction. Pumped hydro storage, as the most mature mechanical energy-storage technology, typically requires specific geographical conditions, and its construction process may involve large land use and ecological disruption [33]. Compressed Air Energy Storage relies on underground caverns or storage vessels for energy storage, with lower resource scarcity, but still requires specific geographical conditions, such as suitable underground storage space. Flywheel energy storage uses rotating mechanical devices to store energy, with relatively low resource requirements, though its energy density is lower compared to other technologies, resulting in larger system volumes.

The overall environmental impact of electrochemical energy-storage technologies primarily involves resource extraction, ecological damage, carbon emissions, and recycling. For example, in lithium-ion batteries, the extraction of rare metals such as lithium, cobalt, and nickel has some impact on resources and the environment. Although lithium-ion batteries have minimal emissions during use, their production process involves high resource consumption. Sodium-sulfur batteries still face environmental challenges related to high-temperature operation and the demand for sodium and sulfur resources.

Electromagnetic energy-storage technologies have relatively low environmental impact, but there are still some potential environmental issues. Superconducting Magnetic Energy Storage (SMES) relies on superconducting materials, and the need to maintain low-temperature environments for cooling can result in some carbon emissions. Additionally, the scarcity and extraction of superconducting materials may have an impact on resources. Compared to lithium-ion batteries and other energy-storage technologies, supercapacitors have lower resource requirements and carbon emissions. Their recycling rate is relatively high, and due to their simple structure and materials, the environmental burden of the recycling process is also minimal.

The environmental impact of thermal energy-storage technologies is smaller compared to other energy-storage technologies, mainly concentrated in material production, system construction, and recycling processes. The extraction and use of materials for sensible heat storage have a relatively low environmental burden, with the main environmental impact coming from the construction and maintenance of the storage systems. Many phase change materials used in latent heat storage technologies may involve the use of chemicals and the emission of waste during production, which can have an environmental impact. Additionally, the recycling and reuse technologies for these materials are still underdeveloped, which may lead to resource waste. Thermochemical storage involves chemical reactions and the production of materials, which can require significant energy and generate emissions, particularly during the synthesis and processing of reaction materials.

In hydrogen energy storage, energy losses and high emissions still occur during the production, storage, and transportation of hydrogen, especially in the process of water electrolysis using fossil fuels. Overall, various energy-storage technologies still face certain challenges in promoting sustainable development, particularly in the management of resource scarcity, environmental burdens, and lifecycle emissions.

3.2. Comparison of Application Characteristics of Energy-Storage Technologies

With the acceleration of the global energy transition, policy support, regulatory frameworks, and the continuously evolving market have played a crucial role in driving the innovation, application, and deployment of energy-storage system technologies. Many countries and regions have begun to develop policies and incentive measures to support energy-storage technologies and promote their commercialization. By providing financial subsidies, tax incentives, green finance, and other means, energy-storage project construction and operation can be facilitated. Additionally, mechanisms such as carbon markets and capacity markets have been established to encourage energy-storage technologies as key components for enhancing grid stability, thus facilitating the large-scale integration of renewable energy.

In terms of regulatory frameworks, the application of energy-storage systems often faces regulations related to grid operations, market access, and service fees. Effective policies and regulatory frameworks reduce industry uncertainties by clarifying market positioning, compensation mechanisms, and participation standards for energy-storage systems, thereby promoting innovation and investment in energy-storage technologies. Meanwhile, the market space for energy-storage systems continues to expand. As the cost of energy-storage technologies gradually decreases and their efficiency improves, it provides support for the maturity and diversification of the energy-storage market. Through market-oriented reforms, energy-storage systems are gradually transforming from being a “cost center” to a “profit center,” becoming an important part of the flexible resources in the electricity market, thus driving innovation and development in the electricity market [34].

In order to further promote the widespread application of energy-storage technologies and optimize the flexibility of the power system, in addition to policy and market support, the specific applications of various energy-storage technologies are also continuously developing and improving. Among various energy-storage technologies, pumped hydro storage is currently the most mature and widely deployed, with the largest installed capacity. Due to its advanced and mature technology, pumped hydro storage has been widely implemented in China. According to the latest resource survey results from the National Energy Administration, there are 1529 potential sites for pumped-storage plants in China, with a total capacity of approximately 160.4 million kilowatts. By the end of 2024, the installed pumped hydro storage capacity in China is expected to reach 58.46 million kilowatts, with an additional 205 million kilowatts under construction. Some regions in China have already started cluster development practices for pumped-storage resources, and the high proportion of pumped hydro storage has become a significant feature of the new power system [35]. Meanwhile, with the research and promotion of various new compressed air energy-storage technologies, the efficiency of compressed air energy storage has significantly improved, and its cost still has considerable potential for reduction. It has reached initial conditions for large-scale commercialization and is expected to become an important complement to pumped hydro storage.

However, the construction of pumped hydro storage projects requires favorable terrain, geological conditions, and water sources, making site selection more limited. In addition to pumped hydro storage, electrochemical energy storage, particularly lithium-ion battery storage, has become one of the fastest-growing energy storage technologies in recent years. Although electrochemical energy storage still cannot compete with pumped hydro storage in terms of cost-effectiveness and technical costs, it holds an irreplaceable position in applications such as frequency regulation and emergency backup power. This is due to its advantages of fast response, flexible site selection, and high energy density. It plays a crucial role, especially in scenarios that require highly flexible frequency regulation services and rapid-response power demands.

In the current context of carbon neutrality, hydrogen energy storage is developing favorably, with broad commercialization prospects. It provides a new approach for large-scale energy storage and is expected to become an essential part of driving the energy strategy transformation.

Table 2. Development Status of Various Energy-Storage Technologies [13,36].

Energy Storage Type	Energy Storage Type	Application Phase	Market Development Stage	Advantages	Disadvantages
Mechanical Energy Storage	Pumped Hydro Storage	Integration of renewable energy, grid-scale energy storage, peaking, load balancing	maturity	High capacity, long service life, low maintenance	Requires specific terrain, geological, and water conditions, limited site selection
	Compressed Air Energy Storage	Grid peaking, system backup power	Research phase	Long service life, fast response speed, environmentally friendly, high capacity and low cost	Efficiency fluctuations, potential safety hazards, and high requirements for geographical environment
	Flywheel Energy Storage	Peaking, frequency control, UPS, power quality regulation, transmission and distribution system stabilization	Demonstration phase	High power density, fast charging speed, long service life and high cycle efficiency	Low energy density, high self-discharge, high unit energy storage cost
Electromagnetic Energy Storage	Superconducting Magnetic Energy Storage	UPS, power quality regulation, transmission and distribution system stability	Experimental research and early application phase	Fast response, high energy-storage capacity, high reliability	High cost, cooling issues, loss of super, large magnetic field requirement
	Supercapacitors	Power quality regulation, transmission and distribution system stability	Demonstration application phase	High energy density	Interdependence of battery component characteristics, safety issues, environmental impacts
Electrochemical Energy Storage	Lead-acid Battery	UPS, Renewable Energy Systems, Power Backups, Emergency Power Supplies	maturity	Fast reaction speed, low self-discharge rate, high cycle efficiency, low capital cost	Low energy density, high environmental impact
	Lead-carbon Battery	Power quality, frequency control, plant standby, renewable energy storage	Early stage of industrialization	Cost-effective and low consistency	Low energy density, short cycle life, environmental issues
	Lithium-ion Batteries	Integrated renewable energy, grid-scale energy storage, electric vehicles	Commercial scale phase	High energy density, fast response, low self-discharge rate, long service life, high reliability	Lifecycle depends on discharge level, high cost, need for operating temperature and overcharge protection
	Sodium-Sulfur Battery	Power quality, backup power, peak-to-valley, energy management, renewable energy storage	Demonstration application phase	High energy density, low self-discharge rate, fast response time, non-toxic materials	High internal resistance, sodium corrosion, for additional systems requiring high-temperature heating
	Flow Battery	Backup power systems, grid-scale energy storage, renewable energy integration	Demonstration application phase	Fast response time and high energy-storage capacity	Complex structure, low energy and power density, environmental concerns
Thermal Energy Storage	Sensible Heat Storage	Solar thermal systems, industrial waste heat recovery, centralized heat supply	maturity	No need to use toxic or expensive materials, wide range of available materials, low cost	Low energy density, high cycle efficiency, energy density is affected by the material selected
	Latent Heat Storage	Solar thermal power, building thermoregulation, cold chain transportation	Demonstration application phase	High energy density, small temperature shift range	Differentiation of PCM volume per cycle, high demand for PCMs
	Thermochemical Energy Storage	High-temperature thermal energy storage, thermal energy management in industrial processes, energy conversion and storage	Research and development phase	High efficiency, high energy density, long-term stability during storage, low energy loss	High manufacturing cost, low efficiency, poor heat transfer performance
Chemical Storage	Hydrogen Energy Storage	Balanced dispatch of renewable energy, enhanced power system stability, clean energy drive in transportation	demonstration application phase	High energy density, long discharge time, better environmental compatibility	Overall low energy conversion efficiency and high investment costs

lists the development status of various energy-storage technologies.

The table presents a summary of the development status, application directions, and key advantages and disadvantages of various energy-storage technologies. Overall, mechanical energy storage, particularly pumped hydro storage, is the most mature technology. Its advantages include high efficiency, long service life, and low operational and maintenance costs, which make it widely used for grid peak-shaving and frequency regulation. However, pumped hydro storage is limited by specific geographical conditions, and its relatively low energy density also restricts its broader application. Compressed air energy storage and flywheel energy storage are still in the research and demonstration stages. CAES offers relatively fast response times and long-duration storage capability, but its development is primarily limited by the thermal losses during the compression and expansion processes, as well as the high requirements for specific geographical conditions. FES, characterized by high power density and fast response, is suitable for applications such as frequency regulation that require short-duration high power. However, its energy density is lower compared to electrochemical and thermal energy-storage technologies, which limits its application in large-scale energy storage.

Electromagnetic storage technologies like superconducting magnetic energy storage and supercapacitors excel in response speed and are suitable for high-frequency regulation scenarios, though they face challenges including high costs and technical complexity. Superconducting Magnetic Energy Storage is primarily applied in high-end fields for short-duration, high-power energy storage, while supercapacitors are widely used in short-duration, high-power demand scenarios such as electric transportation, though their application in large-scale energy storage is still limited by energy density.

In electrochemical storage, lithium-ion batteries have entered large-scale commercial applications, offering high energy density and fast response times, making them the dominant technology at present. Despite facing challenges such as raw material supply bottlenecks, environmental impacts, and rising costs, the market share of lithium-ion batteries continues to grow robustly, driven by advancements in production technologies and material innovations. Another electrochemical storage technology, flow batteries, is currently at the demonstration stage. They offer significant advantages in terms of safety, lifespan, and scalability, with fast response times and high storage capacity. Flow batteries can independently scale energy and power modules, making them ideal for large-scale storage systems. However, their lower energy density, complex structure, and high costs still require further technological advancements to improve their economic viability.

In thermal energy-storage technologies, sensible heat storage is mature and cost-effective, making it suitable for industrial waste heat recovery and combined heat and power systems. Latent heat storage offers higher energy density, making it ideal for compact energy-storage systems, although its material costs are higher and its commercialization is still slow. Thermochemical storage, however, stands out for its ability to convert thermal energy into chemical energy for long-term storage, making it highly suitable for seasonal and long-duration energy-storage applications. While most of these thermal energy-storage technologies remain in the research or demonstration phase, they offer promising solutions for addressing the needs of large-scale and long-term energy storage, as well as optimizing energy usage.

Hydrogen energy storage, as a chemical energy-storage technology, offers extremely high energy density and long-duration storage capabilities, with significant potential for future development. Hydrogen can play a role in sectors such as transportation and electricity, particularly as a solution for long-duration energy storage. However, its challenges are primarily focused on low efficiency, energy losses during conversion and storage, and high costs. Nevertheless, with technological advancements and the gradual reduction of costs, hydrogen energy storage is still regarded as a crucial component of future energy systems, particularly in supporting long-duration storage and large-scale renewable energy integration.

In summary, each energy-storage technology has its own suitable application scenarios. Future deployment should focus on selecting appropriate storage solutions based on specific system requirements, thereby enabling coordinated and diversified development across technologies.

4. Economic Feasibility of Energy-Storage Technologies

The economic performance of energy-storage technologies is typically evaluated from two complementary perspectives: lifecycle costs and associated benefits. The lifecycle cost perspective encompasses all expenditures incurred over the entire lifespan of an energy-storage system, while the benefit perspective focuses on the economic value and system-level advantages enabled by its deployment. In the following sections, each of these aspects is examined in detail to provide a comprehensive understanding of the economic feasibility of different energy-storage technologies.

4.1. Lifecycle Cost

The lifecycle cost of energy-storage technologies includes capital expenditure, operation and maintenance cost, replacement cost, charging cost, and subsequent recycling cost [37].

4.1.1. Capital Expenditure

The capital expenditure (CAPEX) refers to the upfront construction cost associated with different types of energy-storage technologies. It typically includes expenses related to equipment procurement, installation, commissioning, site preparation, and engineering construction. The CAPEX is commonly divided into two main components: capacity cost and power cost.

Capacity cost is directly related to the energy-storage capacity and includes the equipment and construction expenses associated with the quantity of energy that can be stored. This mainly covers storage media such as battery cells, hydrogen tanks, and thermal storage materials, as well as auxiliary infrastructure such as storage tanks, reservoirs, insulated containers, and land use associated with large-scale energy-storage systems.

Power cost refers to the portion of CAPEX associated with the charging and discharging power of the system—that is, the system’s ability to absorb and release energy over time. It primarily includes power conversion components such as inverters, transformers, and grid interface equipment; as well as thermal management systems, protection devices, and other power electronics needed to support dynamic operation.

$$C_{\mathrm{Inv}}=C_P·W_P+C_E·Q_E$$

(2)

where $C_P$ is the investment cost per unit of power capacity, $W_P$ is the rated power capacity, $C_E$ is the investment cost per unit of energy capacity, and $Q_E$ is the rated energy capacity. For specific energy-storage projects, the total investment amount may also be estimated based on actual capital costs from comparable existing systems or pilot demonstrations.

4.1.2. Operation and Maintenance Cost

Operation and maintenance (O&M) cost refers to the recurring expenditures incurred during the operational phase of an energy-storage system to maintain its performance, reliability, and availability. It includes regular maintenance, system inspections, performance diagnostics, and component repairs or replacements.

O&M costs are typically categorized into three components: energy-related maintenance cost $C_{E,\mathrm{OM}}$, power-related maintenance cost $C_{P,\mathrm{OM}}$, and labor and operational expenses $C_{\mathrm{labor}}$. These components can be aggregated as follows:

$$C_{\mathrm{OM}}=C_{E,\mathrm{OM}}+C_{P,\mathrm{OM}}+C_{\mathrm{labor}}$$

(3)

In practice, the magnitude of O&M costs varies across energy-storage technologies. Electrochemical systems such as lithium-ion batteries require periodic battery management system updates, thermal regulation, and cell health monitoring, whereas mechanical systems like pumped hydro or CAES may incur higher structural maintenance but lower electronic servicing costs.

4.1.3. Replacement Cost

Certain components of energy-storage systems, particularly in electrochemical technologies, experience degradation over time due to cycling fatigue, thermal stress, and calendar aging, and must be replaced at predefined intervals based on their service life. Replacement cost refers to the expenditure incurred for substituting such components during the operational phase of the system.

The replacement cost is typically calculated based on the unit replacement cost per unit of energy capacity $U_R$ (CNY/(MW·h)) and the rated energy capacity $Q_E$ (MW·h), as follows:

$$C_{\mathrm{R}}=U_R·Q_E$$

(4)

In practice, replacement costs primarily apply to battery modules, but may also involve power conversion systems, thermal management components, or control units, depending on the system configuration and lifespan of subsystems.

4.1.4. Charging Cost

Charging cost refers to the expenditure incurred when an energy-storage system absorbs electricity from the grid or another energy source to store energy for later use. This cost is typically affected by the prevailing electricity price structure, which may include flat rates, time-of-use (TOU) tariffs, or real-time pricing schemes.

It can be calculated using the unit electricity price during charging $U_C$ (CNY/(MW·h)), the energy input per charging cycle $Q_C$ (MW·h), and the number of charging cycles per year $N_y$, as shown below:

$$C_{\mathrm{C}}=U_C·Q_C·N_y$$

(5)

In practical scenarios, the actual charging cost may vary depending on whether the system is charged from the grid or co-located renewable sources such as photovoltaic or wind generation. Furthermore, charging cost constitutes a significant portion of the lifecycle operating cost, particularly for systems deployed in markets with high electricity prices or limited time-of-use flexibility.

4.1.5. Recycling Cost

Recycling cost refers to the expenditure incurred when an energy-storage system reaches the end of its operational life. This includes costs associated with system disassembly, equipment recovery, material processing, reuse, and environmentally compliant disposal. Such costs are particularly significant for electrochemical storage systems, where batteries may contain hazardous substances such as heavy metals or flammable electrolytes, posing environmental and safety risks if not properly managed.

The recycling cost typically comprises three components: battery or module recovery and processing, system-level disassembly, and environmental restoration or remediation expenses. Depending on the storage technology and material composition, recycling costs may be positive (a net cost) or negative (a net revenue), as valuable materials such as lithium, cobalt, and nickel may be recovered and sold.

A widely used metric is the scrap cost ratio, which represents the ratio of the recycling cost to the initial capital investment. The total recycling cost can be estimated as:

$$C_{\mathrm{Rec}}=C_{\mathrm{inv}}·F_{EOL}$$

(6)

where $F_{EOL}$ is the scrap cost ratio and $C_{\mathrm{inv}}$ is the capital expenditure.

For example, lithium-ion battery recycling processes may involve pyrometallurgical, hydrometallurgical, or direct recycling techniques, each with different cost implications. Recycling policies and regulatory frameworks also significantly influence end-of-life economics.

4.1.6. Net Present Value of Total Lifecycle Cost

The total lifecycle cost of an energy-storage system can be evaluated using a net present value (NPV) framework, where all future expenditures are discounted to the time of system commissioning. The initial capital expenditure is incurred at year 0, while other cost components, such as operation and maintenance, charging, and component replacement, occur annually or at specific intervals. End-of-life recycling cost typically occurs in the final year.

The total lifecycle cost $C_{\mathrm{total}}$ is given by:

$$C_{\mathrm{total}}=C_{\mathrm{inv}}+\sum _{n=1}^N{\displaystyle \frac{C_{\mathrm{OM}}^{\left(n\right)}+C_{\mathrm{C}}^{\left(n\right)}+C_{\mathrm{R}}^{\left(n\right)}}{{(1+r)}^n}}+{\displaystyle \frac{C_{\mathrm{Rec}}}{{(1+r)}^N}}$$

(7)

where r is the annual discount rate and N is the project lifetime (years).

4.1.7. Net Present Value of Total Discharged Energy

The total discharged energy over the lifecycle of the energy-storage system determines the economic output against which costs are evaluated. The net discharged energy in year n, denoted as $E_n$, depends on the rated energy capacity $Q_E$, annual cycle count $N_y$, depth of discharge ${\theta }_{\mathrm{DoD}}$, round-trip efficiency ${\eta }_{\mathrm{rt}}$, and degradation rate ${\eta }_{\mathrm{deg}}$.

The annual discharged energy can be estimated by:

$$E_n=Q_E·N_y·{(1-{\eta }_{\mathrm{deg}})}^{n-1}·{\theta }_{\mathrm{DoD}}·{\eta }_{\mathrm{rt}}$$

(8)

Accordingly, the net present value of the total discharged energy over the system’s lifecycle is:

$$E_{\mathrm{total}}=\sum _{n=1}^N{\displaystyle \frac{E_n}{{(1+r)}^n}}$$

(9)

4.1.8. Levelized Cost of Electricity (LCOE)

The levelized cost of electricity (LCOE) over the entire lifecycle is the average cost of delivering one kilowatt-hour (kWh) of electricity from the energy-storage system over its full service life. It represents the unit electricity cost and serves as a key metric for assessing the economic performance of energy-storage technologies. The LCOE can be compared with peak-valley electricity price differentials to evaluate the economic viability of storage investments. This is crucial for evaluating the economic feasibility of energy-storage technologies in capacity-oriented or time-shifting applications.

The LCOE incorporates various factors, including capital expenditure, operation and maintenance cost, round-trip efficiency, and cycle life, and is expressed as the ratio of the total lifecycle cost to the total discharged energy over the lifecycle. Figure 14 illustrates the calculation process of the levelized cost of electricity over the entire lifecycle.

4.2. Benefit Analysis of Energy-Storage Technologies

The main economic benefits of energy-storage systems can be broadly classified into three categories: (i) time-of-use (TOU) peak-valley arbitrage on the user side, (ii) revenue from participation in ancillary services markets, and (iii) capacity-based compensation mechanisms.

Each of these benefit streams can be evaluated separately or jointly, depending on market structure, regulatory policies, and technological configuration. The following subsections provide a detailed analysis of each benefit category.

4.2.1. User-Side Time-of-Use Peak-Valley Arbitrage

The main source of revenue for energy-storage systems on the user side is the price differential between peak and off-peak electricity rates. The peak-valley arbitrage model refers to a revenue strategy whereby the energy-storage system charges during periods of low electricity prices and discharges during high-price periods, thereby generating profit by capturing the time-varying price spread in the electricity market.

This revenue is primarily determined by the magnitude of the peak-valley price gap, the system’s charge/discharge efficiency, and the frequency of daily operation. There are two main participants in this model: large industrial and commercial users that deploy behind-the-meter energy-storage systems, and independent energy-storage operators or aggregators that collaborate with electricity-consuming enterprises.

The economic benefit from time-of-use arbitrage can be estimated by:

$$R_p=(C_h-C_l)·E$$

(10)

where $C_h$ is the peak electricity price (CNY/kWh), $C_l$ is the off-peak electricity price (CNY/kWh), and E is the amount of energy discharged per day (kWh).

This formulation assumes ideal charge–discharge efficiency and does not account for degradation cost; refinements may include system efficiency and replacement cost amortization for more accurate economic assessment [38].

4.2.2. Auxiliary Services Market Revenues

Electricity auxiliary services refer to the power system support and regulation services provided synchronously during electricity transmission to ensure the safe and stable operation of the power grid and to meet electricity quality standards. These services are coordinated and dispatched by the scheduling organization, which allocates various flexible regulating resources. The compensation paid to participating energy-storage systems should cover both the capacity provision and energy loss incurred by these flexible assets [39].

Based on the duration and response characteristics of regulation, energy-storage applications in ancillary services can be broadly classified into four timescales: ultra-short-term regulation, short-term regulation, medium-term regulation, and long-term regulation. Ultra-short-term regulation typically involves instantaneous response services such as primary frequency regulation. Short-term regulation mainly supports dynamic balancing through services like Automatic Generation Control (AGC). Medium-term regulation includes system reserves, peak-shaving, and black-start support. Long-term regulation is used to mitigate seasonal renewable output volatility and support grid resilience under extreme weather conditions [40].

The revenue generated from energy-storage systems participating in ancillary services mainly includes compensation for primary and secondary frequency regulation, peak-shaving, voltage and reactive power support, and black-start capability. In recent years, the scope of compensated services has expanded significantly, reflecting the increasing value of storage in grid operations.

In China, the auxiliary services compensation and trading mechanism currently operates under a “dual-track” system, where both policy-based fixed compensation and market-based pricing mechanisms coexist.

4.2.3. Energy-Storage Capacity Revenue

Through unified coordination and dispatch by the power grid, energy-storage systems can integrate distributed storage resources from the grid side, generation side, and user side, achieving optimal allocation across the entire system and fully unlocking storage potential throughout generation, transmission, and consumption stages.

Capacity pricing is a mechanism designed to incentivize investment by providing direct compensation to power generation or energy-storage operators based on their installed or available capacity. The capacity revenue is determined by the unit compensation standard and the certified compensable capacity, typically verified by government agencies. This revenue stream is intended to supplement operational earnings and ensure a reasonable return on investment.

Currently, regions such as Sichuan, Zhejiang, Guangdong, Beijing, and Chongqing have introduced regional capacity compensation schemes, offering one or more rounds of incentive payments for new energy-storage projects to promote industry growth [41].

In addition, a capacity leasing model has recently gained traction. Under this model, independent energy-storage stations lease capacity to renewable energy projects in exchange for compensation. This approach allows renewable generators to meet regulatory requirements for minimum storage capacity—without incurring the upfront capital costs of building dedicated storage facilities. As a result, capacity leasing revenue has become one of the most promising and scalable profit mechanisms for energy-storage operators.

5. Application of Energy-Storage Technologies

Energy-storage technologies play an increasingly vital role in modern energy systems, serving as critical enablers for flexibility, reliability, and efficiency. With the rapid growth of renewable energy generation, the deepening of electrification across sectors, and the emergence of smart grid technologies, energy storage has become an indispensable component of the evolving energy landscape.

Broadly speaking, the application scenarios of energy-storage technologies can be categorized into three major domains: enhancing power system stability, improving the integration of renewable energy sources, and supporting the decarbonization of transportation systems. Each domain presents unique technical challenges and performance requirements, leading to the adoption of different storage technologies and deployment strategies.

The following sections explore the specific roles and functions of energy storage across these domains, highlighting representative technologies, key implementation strategies, and recent advancements supported by case studies and empirical research.

5.1. Enhancing Power System Stability

Energy-storage technologies play a pivotal role in enhancing the stability, flexibility, and reliability of modern power systems. As electricity systems become increasingly complex—due to the integration of intermittent renewable energy, dynamic load behaviors, and aging infrastructure—maintaining real-time supply–demand balance and ensuring high power quality have become central challenges. Energy-storage systems (ESS) address these challenges by providing rapid-response capabilities for frequency and voltage regulation, load leveling, peak-shaving, and emergency support. These functions significantly improve a system’s ability to withstand disturbances and recover from faults. In practical deployments, the stabilizing role of ESS can be examined from three distinct perspectives: the generation side, where ESS smooths power output and enhances dispatchability; the grid side, where ESS contributes to frequency stability, voltage control, and inertia support; and the user side, where ESS ensures supply reliability, facilitates demand-side management, and improves power resilience.

Figure 15 illustrates the multi-type energy storage for wind power fluctuation smoothing, demonstrating the collaborative operation of heterogeneous energy-storage systems to mitigate renewable output variability across different layers of the power system.

5.1.1. Generation Side

On the power generation side, energy-storage technologies contribute significantly to balancing supply and demand by enabling load shifting, particularly through peak-shaving and valley-filling. By charging during off-peak hours and discharging during peak demand periods, ESS helps alleviate grid stress, improve generation dispatchability, and prevent energy curtailment. These systems dynamically adjust charge–discharge schedules in response to load fluctuations, thereby supporting a stable and continuous energy supply to the grid. Liu Xing et al. [43] developed a frequency–power relationship model and proposed a coordinated scheduling strategy for battery energy storage to optimize combined peak-shaving and frequency regulation. Zhao, K., et al. [44] analyzed the thermal storage and release strategies for single and multiple steam-source heating configurations in combined heat and power (CHP) units. In addition, energy-storage technologies are effective in mitigating the variability and intermittency of renewable energy sources such as wind and solar. By smoothing power output, ESS reduces renewable energy curtailment and enhances generation reliability and utilization. Lin, L., et al. [45] proposed a dual-objective model predictive control strategy with a weighted moving average mechanism for hybrid energy-storage systems (HESS), targeting output smoothing. The study incorporated a battery degradation model accounting for calendar aging, which was integrated into the HESS cost framework to optimize energy-storage configuration.

5.1.2. Generation Side

On the generation side, energy-storage technologies can participate in system frequency regulation by rapidly responding to frequency changes, helping balance the grid frequency and maintain the stable operation of the power grid. Li, C., et al. [46] proposed a joint optimization strategy for thermal power frequency regulation based on an energy-storage life model, with multiple constraints. The paper developed a multidimensional energy-storage life loss model and a simplified wear model for thermal power units, optimizing the loss resistance coefficient between energy storage and thermal power frequency regulation. Considering the frequency regulation cost and charging state planning, the paper proposed a two-layer model to optimize power distribution between thermal power and energy storage, with storage power constrained by the SOC deviation coefficient.

On the generation side, while meeting the expected load demand, energy-storage systems can store active power capacity, smoothing the fluctuations of renewable energy sources such as wind and solar power, reducing the frequency of startup and shutdown of conventional units, and enhancing the flexibility and resilience of the grid. When load fluctuations or unexpected events occur, energy-storage systems can quickly release energy, provide backup capacity, and improve the stability and efficiency of the power generation system. By optimizing energy-storage scheduling, it also significantly reduces the frequent start-stop cycles and excessive wear of power generation units, thereby extending the lifespan of the equipment.

5.1.3. Grid Side

On the grid side, energy-storage technologies serve as critical assets for enhancing system stability, particularly in frequency regulation, voltage control, and inertia compensation. Their ability to respond within milliseconds makes them ideal for maintaining real-time balance between supply and demand in the face of sudden load or generation fluctuations. In practice, large-capacity storage technologies such as flywheels, supercapacitors, and battery energy-storage systems (BESS) are increasingly deployed for grid-side services due to their high responsiveness and scalability. These systems participate in ancillary services such as primary frequency control, load-following, and contingency reserves, thereby reducing the burden on conventional generators and improving grid flexibility.

In addition, the integration of energy-storage systems with smart grid technology enables more intelligent and efficient grid dispatch, allowing real-time monitoring and optimization of the grid’s operational status. The smart grid, through its interaction with energy-storage systems, achieves more precise load regulation and energy distribution, especially in cases of large fluctuations in renewable energy generation and load variations, enabling rapid response and balancing of grid demand. Furthermore, energy-storage systems participate in demand response mechanisms, automatically adjusting based on grid load changes and electricity price fluctuations, providing the grid with more flexible regulation capabilities and emergency response.

Moreover, energy-storage systems provide backup power and can be rapidly dispatched during system disturbances, enhancing the grid’s fault recovery capability. Energy-storage systems effectively regulate voltage, suppress harmonics, and provide reactive power support, ensuring the safety and quality of the power supply. Furthermore, by optimizing the allocation of energy-storage capacity, the costs and aging effects of the storage system can be reduced without compromising the performance of the grid.

5.1.4. User Side

On the user side, energy-storage technologies are increasingly applied to support electricity self-consumption, time-of-use price arbitrage, and power supply continuity. These systems charge during off-peak periods when electricity is cheap and discharge during peak hours to reduce costs, thereby enhancing economic efficiency. In addition, user-side storage serves as backup power during outages, helping to prevent production interruptions and equipment failures, thus improving power supply reliability and service continuity. During extreme weather events or natural disasters, user-deployed energy-storage units act as distributed emergency power sources, safeguarding critical loads and enhancing the resilience and disaster response capability of local power systems.

Wang, HB, et al. [30] proposed an optimal configuration method for user-side energy storage based on multi-timescale demand sensing. By analyzing the electricity consumption patterns of large-scale industrial and commercial users, they developed a set of indicators to guide tailored energy-storage capacity planning. The resulting optimization model enables comparison and evaluation of allocation strategies across diverse user profiles, supporting more efficient and commercially viable deployment of user-side energy-storage systems.

5.2. Improving the Reliability of Renewable Energy Integration

As renewable energy becomes a central pillar in the global energy transition, its large-scale integration into power systems introduces several operational challenges. Due to the spatial-temporal mismatch between generation and demand, as well as the intermittent and stochastic nature of wind and solar resources, maintaining grid reliability and balancing supply–demand becomes increasingly complex [47]. In particular, issues such as reverse peak-shaving, reduced system inertia, and forecasting uncertainty hinder the stable and flexible operation of power systems.

Energy-storage systems, with their fast response, bidirectional controllability, and multi-timescale dispatch capabilities, offer an effective solution to these challenges. They support grid operations by smoothing renewable generation profiles, enabling frequency regulation, shifting load in time, and providing reserve capacity, thereby enhancing the overall integration efficiency of renewable energy and promoting system-level stability.

To address the operational decision-making problem for renewable-side energy storage participating in electricity markets, Li, Q. et al. [48] proposed a residual-capacity-based scheduling model that enables energy-storage systems to concurrently engage in energy trading and frequency regulation. Their model incorporates day-ahead planning and real-time rolling optimization, accounting for uncertainties in market demand and the effects of regulation overshoot on profitability. Liu X. et al. [49] examined the deployment of hybrid energy-storage systems in wind farms to mitigate output fluctuations. They proposed a two-layer planning model—adaptive RSSD-ICEEMDAN smoothing and configuration optimization—which utilizes advanced signal decomposition techniques to improve smoothing accuracy and adaptively allocates storage capacity, thereby enhancing grid compliance and prolonging battery life. These studies collectively demonstrate that integrating intelligent control strategies and hybrid storage configurations can significantly enhance the reliability and economic value of renewable energy systems.

5.3. Transportation

5.3.1. Electric Vehicles

The new energy vehicle (NEV) industry is experiencing rapid development, driven by technological advancements and supportive policies. Electric vehicles rely on batteries with high specific energy, high power density, extended cycle life, and excellent thermal stability to meet demanding operational requirements. Commonly used rechargeable battery types include nickel-based batteries, lithium-ion batteries, and sodium-sulfur batteries. These battery technologies not only power EVs but also offer the potential to participate in broader power system services as distributed energy-storage units.

As shown in Figure 16, energy storage enables efficient power management between renewable generation, hydrogen systems, and EV fast-charging infrastructure under both AC and DC grid environments.

Electrochemical energy storage in EVs can facilitate peak-shaving and valley-filling, improve the load curve of the power grid, and serve as a mobile backup power source. This dual functionality positions EVs as key contributors to smart grid development. Habib, AKMA, et al. [50] analyzed the architecture of battery management systems (BMS), focusing on multi-physical field monitoring of voltage, current, and temperature; dynamic charge–discharge control; balancing mechanisms; and data acquisition systems. Through comparative evaluation of circuit designs, efficiency-cost trade-offs, and stress distributions, the study revealed the suitability boundaries of active and passive balancing topologies across EVs and stationary energy-storage systems.

Battery aging, a critical concern in electric vehicles, directly impacts energy efficiency, safety, and vehicle lifecycle. However, existing hybrid battery–supercapacitor systems often overlook the need for coordinated energy distribution and degradation mitigation. To bridge this gap, Xu, B., et al. [51] proposed an energy management strategy based on simulated Q-learning, which adaptively adjusts power allocation between battery and supercapacitor subsystems. This approach enhances overall energy efficiency while effectively mitigating battery degradation, thereby extending system lifespan and reliability.

5.3.2. Urban Rail Transit

Urban rail transit is characterized by short station intervals and frequent acceleration–braking cycles, resulting in substantial regenerative braking energy, rapid power fluctuations, and high-frequency charge–discharge operations. Therefore, energy-storage systems in this domain must exhibit high power density, extended cycle life, fast dynamic response, and high round-trip efficiency. Commonly adopted technologies include supercapacitors, flywheel energy storage, electrochemical batteries, and hybrid energy-storage systems (HESS) [52].

Flywheel energy storage, as a mechanical storage solution, offers fast response, high instantaneous power output, long service life, and robust charge–discharge capability. These properties make it particularly well suited for capturing and utilizing regenerative braking energy (RBE) in rail systems. In addition, flywheel systems can mitigate stray currents by redistributing return currents, balancing power flow, and enhancing rail potential control. Effective flywheel control is essential for operational stability. Zhang Jianwei et al. [53] proposed an improved active disturbance rejection control (ADRC) strategy using a cascaded nonlinear extended state observer. This was combined with sliding mode control to enhance disturbance rejection. Furthermore, particle swarm optimization was applied to fine-tune SM-ADRC parameters, significantly improving system robustness and efficiency.

Supercapacitor-based energy storage continues to evolve with innovations in electrode materials, electrolytes, and modular design [54]. These systems effectively absorb RBE during braking and release it during subsequent acceleration, improving energy utilization. The performance of stationary supercapacitor systems is highly dependent on the design of their Energy Management System (EMS). Zhao YJ et al. [55] proposed a multi-layer EMS structure.

5.3.3. Ships

The shipboard power grid system has distinct characteristics compared to land-based grids, such as smaller total capacity, larger individual unit capacity, and exposure to harsh marine environments. These features, combined with complex and rapidly varying load conditions, pose unique challenges to maintaining grid stability, power quality, and operational safety.

Energy-storage systems, with their fast dynamic response and multi-timescale power regulation capabilities, offer critical solutions for ensuring stable and efficient shipboard power management. Existing marine energy-storage technologies are generally classified into two categories: high-energy and high-power types. High-energy systems, primarily based on electrochemical batteries, function as onboard “energy reservoirs” supporting propulsion and auxiliary systems. High-power systems—including supercapacitors, flywheel energy storage, and superconducting magnetic energy storage (SMES)—are designed to handle transient high-power events such as pulse loads and stochastic disturbances.

To optimize the configuration of hybrid energy-storage systems for all-electric ships operating under diverse conditions, Wang Yufan et al. [56] proposed a collaborative optimization strategy based on adaptive second-order filtering. Their approach formulates a multi-objective model incorporating power fluctuation suppression, investment cost minimization, and battery lifetime extension. An improved particle swarm optimization (PSO) algorithm was employed to derive the optimal capacity distribution and operating strategy for the hybrid system. The results demonstrate enhanced performance adaptability and extended service life under varying maritime operating scenarios.

Looking ahead, shipboard energy-storage systems are expected to play a vital role in realizing zero-emission shipping and integrated energy management with onshore infrastructure, driving the decarbonization of the maritime industry.

5.4. Domestic Energy-Storage Projects in China

The strong support from national policies and the continuous growth in market demand have driven the rapid development of domestic energy-storage projects. Demonstrations and promotions of energy-storage projects in key industries such as power, transportation, and manufacturing have gradually been realized, showcasing significant market potential and application prospects. The northwest region, with its unique geographical resource advantages and abundant wind and solar resources, has become a key location for the deployment of new energy-storage projects in China. Among them, the development scale of renewable energy storage in Gansu and Xinjiang, as well as grid-side independent energy storage in Ningxia, ranks among the top in the country, with total installed capacity exceeding 1 GW in all cases [57].

5.5. Domestic Energy-Storage Projects in China

With China emerging as one of the global leaders in the deployment of energy-storage systems, a wide range of projects have been implemented across various sectors and regions. Backed by strong policy incentives and accelerating demand for renewable integration, the landscape of domestic energy storage is evolving rapidly. Demonstrations and promotions of energy-storage projects in key industries such as power, transportation, and manufacturing have gradually been realized, showcasing significant market potential and application prospects. The northwest region, with its unique geographical resource advantages and abundant wind and solar resources, has become a key location for the deployment of new energy-storage projects in China. Among them, the development scale of renewable energy storage in Gansu and Xinjiang, as well as grid-side independent energy storage in Ningxia, ranks among the top in the country, with total installed capacity exceeding 1 GW in all cases [57].

Table 3. Typical Domestic Energy Storage Projects in China [58,59,60,61].

Energy Storage Type	Project Location/Name	Installed Capacity	Function	Time
Pumped Hydro Storage	Fujian–Zhouning	4 × 300 MW	Peak-shaving and valley-filling, emergency backup, and improvement of the operating conditions of regional nuclear power units	2022
Compressed Air Energy Storage	Hebei–Zhangjiakou	100 MW	Peaking, frequency and phase control, rotating standby, black start	2022
	Hubei Yingcheng compressed air energy storage power station	300 MW	Peaking, frequency regulation, standby	2024
Flywheel Energy Storage	Ningxia–Lingwu	22 MW	Frequency regulation to promote new energy consumption	Construction to begin in 2021
Flywheel Energy Storage	Shuozhou Cogeneration Flywheel Energy Storage Complex FM Project	8 MW	frequency regulation	2023
Supercapacitors	Shanxi Intelligent Energy Internet Demonstration Project	—	Energy Time Shift, Power Smoothing, Voltage Support and System FM	2023
	Huaneng Luoyuan Power Plant Hybrid Super Capacitor + Lithium Battery Energy Storage and FM System	20 MW	Frequency regulation to improve grid frequency and voltage stability and promote renewable energy consumption	2023
Lithium-ion Battery	CNNC Concentric Quanye 100 MW/200 MWh Energy Storage Power Station	30 sets of 3.45 MW/ 6.7 MWh lithium iron phosphate battery energy storage systems	Shaving peaks and filling valleys, promoting new energy consumption and improving grid stability	2022
Lead-carbon Battery	Zhejiang Huzhou, Jidian’s first lead-carbon “100 MWh” customer-side energy storage project	Phase I; 10 MW/97.312 MWh	Peak-shaving and valley-filling, promotion of new energy consumption, backup power supply	Construction to begin in 2022
Flow Battery	Liaoning-Dalian	200 MW; Phase I: 100 MW/400 MW-h	Peaking to promote new energy consumption	Commissioning in 2022
Hydrogen Energy Storage	Anhui-Liuan	1 MW	valley-filling and peak-shaving	2021
Thermal Energy Storage	Jiangsu Jingjiang Power Plant Molten Salt Storage and Peaking Heat Supply Project	75 MW·h	Peak-shaving and frequency regulation, Safe Steam Supply, New Energy Consumption	2023
	Huayuan Jining Thermal Power Molten Salt Energy Storage FM Project	50 MW (using “10 MW steam + 40 MW electricity” combined heating of molten salt)	Peak-shaving and frequency regulation, Safe Steam Supply, New Energy Consumption	2024

lists some typical demonstration projects of energy-storage systems that have been commissioned or are under construction in China. These representative projects reflect the diversity and rapid development of energy-storage technologies across China. Mechanical storage (e.g., pumped hydro and compressed air) dominates large-scale, long-duration applications; electrochemical storage is widely deployed on the grid and user sides due to its flexibility and modularity; while supercapacitor and flywheel systems offer promising solutions for frequency regulation and power smoothing.

From these cases, we observe that pilot and demonstration projects are not only concentrated in resource-rich regions such as the northwest, but are also increasingly deployed in densely populated and industrially advanced areas like the Yangtze River Delta and Beijing-Tianjin-Hebei. The emergence of hybrid systems and integrated energy-storage configurations further highlights the trend toward multi-functional and scenario-specific solutions.

The demonstration projects listed in the table highlight China’s advancements in various energy storage technologies. The Fujian Zhouning Pumped Hydro Energy Storage Station, with an installed capacity of 4 × 300 MW, stands out as the largest roller-compacted concrete dam in China and operates under an advanced “one-button dispatch” mode. Officially commissioned in 2022, the project serves multiple functions, including peak-shaving, frequency regulation, and emergency backup, playing a crucial role in enhancing grid reliability and operational flexibility. Since the commissioning of the unit, the station has generated over 3.026 billion kilowatt-hours, significantly enhancing the flexibility and reliability of the Fujian power grid, especially playing a crucial role in increasing the integration capacity of renewable energy. The project fully applied digital technology during its design and construction, ensuring that the dam’s seepage rate was far below the design standard. In addition, the project achieved several domestic innovations during the construction process, including the precision of the water intake shaft and the technology for the oversized flue gas vertical shaft. The Fujian Zhou Ning pumped-storage power station has played an important supporting role in promoting the absorption of new energy and ensuring power supply for key activities, becoming an important demonstration project for China in energy transition and energy storage technology application.

In the field of electrochemical energy storage, the Dalian Vanadium Flow Battery Project in Liaoning is a representative benchmark. With a total planned capacity of 200 MW, the project is being developed in two phases. The first phase—100 MW/400 MWh—marks China’s first 100 MW-scale national demonstration of flow battery technology and is currently the world’s largest vanadium flow battery system in both power and energy capacity. During the project implementation, the self-developed all-vanadium flow battery technology was adopted, utilizing vanadium ions in different oxidation states as the active material to achieve reversible energy storage and release. The advantages of this technology include high safety, long lifespan, and relatively low environmental impact, making it particularly suitable for large-scale energy storage systems. The project not only provided a stable power supply to the grid, enhancing the efficiency and reliability of grid operations, but also provided valuable experience for the commercialization of vanadium flow battery technology.

In the domain of thermal energy storage, the Jiangsu Jingjiang Thermal Storage Peak Regulation and Heating Project holds considerable demonstration significance. With a capacity of 75 MWh, it is China’s first large-scale project that couples electric frequency regulation with heating using molten salt storage technology. After the project was implemented, the unit’s peak-shaving capacity reached 75% of its rated load, increasing the annual renewable energy consumption by 300 million kWh, and reducing coal consumption by 100,000 tons and carbon dioxide emissions by 240,000 tons annually. By enhancing the unit’s frequency regulation, peak-shaving capabilities, and heat supply stability, the project effectively promoted the integration and consumption of renewable energy, reduced reliance on traditional energy sources, and lowered carbon emissions. Additionally, the project’s implementation provided valuable demonstration experience for the flexible transformation of coal-fired power units, with significant potential for replication. Officially commissioned in 2023, the system enhances energy system flexibility and overall efficiency through coordinated regulation of renewable energy output and thermal energy utilization, signaling a practical breakthrough in multi-energy integrated storage applications.

Collectively, these three projects represent China’s key technological progress and large-scale implementation in mechanical, electrochemical, and thermal energy storage. They demonstrate the coordinated development pathways of diversified energy storage technologies within modern power systems.

6. Conclusions

Energy storage technology, as a key technology to address energy transition and promote sustainable development, is increasingly becoming an important part of the global energy structure transformation. Due to the different characteristics of various energy storage technologies, different technologies have broad application potential in power systems, transportation, and other related industries. Although energy storage technologies still face certain challenges in terms of cost, efficiency, and large-scale application, with ongoing research and development and increased policy support, the future development prospects of energy storage technologies are vast. To achieve the “dual carbon” goals and promote a green and low-carbon transformation, energy storage technologies are an indispensable driving force.

In future developments, innovations in energy storage technologies will further enhance their role in the energy transition. For instance, improving the energy density of battery containers is an important direction in the development of current battery technologies. In recent years, significant progress has been made in the research of new battery technologies such as solid-state batteries and lithium-sulfur batteries, which are expected to improve energy density while maintaining safety and long lifespan, thereby enhancing the capacity of large-scale energy storage systems. Through continuous optimization of materials and structures, the energy density of supercapacitors is gradually increasing, and they are expected to provide stronger support for large-scale energy storage and the efficient integration of renewable energy. At the same time, with advancements in superconducting materials and breakthroughs in low-temperature technologies, the cost and technical complexity of SMES are gradually decreasing, and it is expected to be widely applied in global power grids in the future.

Overall, the continuous innovation and development of energy storage technologies will provide solid technical support for the global transition to a green and low-carbon energy system. Future research should continue to focus on optimizing and applying energy storage technologies to promote the development of intelligent, efficient, and sustainable energy systems.