What is compressed air energy storage?
Compressed air energy storage is an energy‑storage method that uses electrical energy to compress air during periods of low grid demand and releases the compressed air to drive a steam turbine and generate electricity during peak demand. The main configurations include conventional compressed air energy storage systems, compressed air energy storage systems with thermal‑energy storage, and liquid‑gas compression energy storage systems.

Composition of a Compressed Air Energy Storage System
Compressed air energy storage systems typically comprise six major components:
The compressor is typically a multi-stage unit equipped with interstage cooling.

An expander is typically a multi-stage turboexpander equipped with interstage reheating equipment.

The combustion chamber and heat exchanger are used for fuel combustion and waste heat recovery, among other applications.

Gas storage facilities, such as underground or aboveground caverns or pressure vessels;

The electric motor and the generator are connected, respectively, to the clutch, the compressor, and the expander.

Control systems and auxiliary equipment, including the control system, fuel tanks, mechanical transmission system, piping, and fittings.

Compressed air system

The working principle of compressed air energy storage
Compressed air energy storage systems use the potential energy of high-pressure air as the energy storage medium and generate electricity by expanding the high-pressure air to perform work when needed. The system’s operation can be divided into two stages: energy storage and energy release.

Energy storage stage: Compressed air energy storage systems use wind or solar power, or off-peak electricity, to drive a compressor, converting electrical energy into pneumatic potential energy. The high-pressure air is then sealed and stored in decommissioned mines, rock caverns, abandoned oil wells, or man-made gas storage facilities.

Energy‑release phase: High‑pressure air is expanded to drive a turbine, converting the stored pneumatic energy back into mechanical or electrical energy. In conventional compressed‑air energy storage systems, the energy‑release stage requires burning fossil fuels in a combustion chamber to heat the air, thereby enabling electricity generation.
Compressed air system
Storage configurations of compressed air energy storage
Compressed air energy storage is primarily implemented in two forms: compressed-air energy-storage tanks and underground gas storage facilities.

Compressed air energy storage tank

Compressed air energy storage tanks store compressed air in large gas vessels. This storage method requires careful consideration of tank size and pressure to ensure that the air inside can efficiently drive a generator.

Compressed air storage tanks are generally classified into two types: steel‑walled tanks and concrete‑walled tanks. Steel tanks can withstand higher pressures and are better suited for high‑intensity storage, though they are more expensive. Concrete tanks, by contrast, are less costly but require a larger footprint to store the same volume of compressed air.

Underground gas storage facility

Underground gas storage involves storing compressed natural gas in subsurface caverns or salt domes. This storage method offers high storage capacity and enhanced safety, but it requires careful consideration of the geological characteristics of the storage cavities or salt formations, as well as potential environmental impacts.

Underground gas storage facilities come in two types: injection‑type and withdrawal‑type. Injection‑type storage involves pumping compressed air into caverns or salt domes via pipelines, while withdrawal‑type storage entails extracting compressed air from storage formations through wells or pipelines.

Classification of Compressed Air Energy Storage

In general, compressed air energy storage can be classified into the following types:

Mechanical compression-based energy storage system: This system compresses and stores air using mechanical equipment, then converts the stored energy into electricity via a generator.

Thermal Compression Energy Storage System: This system generates high-temperature gas by utilizing geothermal or solar energy sources, compresses and stores the hot gas, and then converts the stored thermal energy into electricity.

Liquid Air Energy Storage System: This system compresses air into a liquid state and stores it in tanks. When needed, the liquid air is heated to convert it back into a gaseous state, and the stored energy is then converted into electricity via a turbine‑generator.

Adsorption-based compressed air energy storage system: This system compresses and stores air by utilizing physical or chemical adsorbent materials, and releases the stored energy when needed through thermal processes or pressure reduction.

Technical pathways for compressed air energy storage

At present, the most prominent next-generation compressed air energy storage systems primarily follow three new technological pathways: thermal‑storage compressed air energy storage (TS‑CAES), liquid‑air compressed energy storage (LAES), and supercritical compressed air energy storage (SC‑CAES).

Thermal‑storage compressed air energy storage (TS‑CAES): During the air compression process, compression heat is generated. In conventional compressed air energy storage, this heat is typically removed by cooling water and ultimately dissipated. By contrast, TS‑CAES captures and stores this waste heat during the storage phase, then uses it to preheat the inlet air of the expander during discharge, thereby recovering and reusing the energy and enhancing system efficiency. Moreover, with the compression heat serving as a preheating source for the expander, the combustion chamber can be eliminated, enabling the system to operate independently of fossil fuels.
Compressed air system

Liquid‑air energy storage (LAES) systems leverage air‑cooling and liquefaction technologies to store compressed air in liquid form. During charging, high‑pressure air from the compressor is routed through a regenerator to cool and depressurize it, after which it is liquefied and stored as low‑temperature, ambient‑pressure liquid air in a storage tank. During discharge, the liquid air is pressurized by a cryogenic pump, heated in a regenerator, and then fed into a combustion chamber, where it is mixed with fuel and combusted before entering an expander to expand and generate work.
Compressed air system
Supercritical Compressed Air Energy Storage (SC‑CAES) system: Leveraging the supercritical properties of air, it achieves highly efficient heat and cold transfer during thermal storage and release, while storing air in liquid form. This approach delivers both high system efficiency and high energy density. The system combines the advantages of thermal‑storage and liquid‑compressed‑air energy storage, while eliminating reliance on large underground caverns and fossil fuels.

Compressed air system

What are the advantages of compressed air energy storage?

Compressed air energy storage boasts advantages such as large capacity, long storage duration, and relatively high safety, as follows:

In terms of scale, it ranks second only to pumped-storage hydropower and is well suited for large-scale energy storage. Compressed-air energy storage systems can operate continuously for several hours or even days.

Project site selection faces few constraints. While storing compressed air in suitable underground mines or rock caverns is the most cost-effective approach, ground‑based high‑pressure storage tanks can also be used as an alternative to underground caverns.

The system boasts a long service life. With proper maintenance, it can operate for 40 to 50 years, approaching the 50-year lifespan of pumped-storage hydropower plants. Moreover, its efficiency can exceed 60%, comparable to that of pumped-storage power stations.

It boasts high safety. Compressed air energy storage utilizes air as its primary resource, which is non-combustible and does not produce any toxic or harmful gases.

Of course, compressed air energy storage also has some notable drawbacks, particularly when compared with electrochemical energy storage:
At present, the efficiency of compressed air energy storage can exceed 60%, which is relatively lower compared to high-efficiency batteries (over 90%).

The response speed is not as fast as that of electrochemical energy storage; the typical response time for load changes from 0% to 100% is on the order of minutes, whereas electrochemical energy storage achieves response times in the range of seconds to milliseconds.

In general, it is not suitable for very small-scale use cases; when the scale is too small, system efficiency declines and unit costs rise.

Characteristics of Compressed Air Energy Storage Technology

Compressed air is the core energy carrier for compressed-air energy storage power generation, while long‑term, large‑scale storage of compressed air relies on dedicated air‑storage facilities. To enable compressed‑air energy storage systems to operate safely and efficiently at large capacities and over extended time scales, these storage facilities must possess specific technical characteristics:

High-pressure resistant, suitable for storing compressed air at working pressures of 6 to 15 MPa, and equipped with protection against overpressure, leakage, permeation, and corrosion; impact-resistant, designed for cyclic pressurization and depressurization operations on a daily basis, with excellent resistance to alternating pressure and temperature cycles.

Easy to implement, with mature technology and well-established production and processing methods; convenient operation and maintenance, and low decommissioning and disposal costs; large capacity, offering an effective usable volume ranging from several thousand cubic meters to hundreds of thousands of cubic meters.

High flow rates, capable of delivering gas filling and venting flows ranging from several thousand to hundreds of thousands of standard cubic meters per hour;

It exhibits low pressure loss, with the pressure drop per charge–discharge cycle kept within a few kilograms of pressure; it also requires minimal space, occupying a small footprint on the ground.

Low cost, with an economically reasonable construction cost per unit cubic storage volume.

Key Design Considerations for Compressed Air Energy Storage
When designing a compressed air energy storage system, it is necessary to conduct a thorough assessment of all hazardous areas throughout the system and provide appropriate safety signage, including but not limited to grounding signs, escape route indicators, “No Smoking or Open Flames” warnings, and “Caution: Electric Shock” labels. In addition, all equipment should be designed to resist dust, moisture, and salt spray to ensure reliable and stable operation.

The gas storage facility of a compressed air energy storage system shall be designed in accordance with the characteristics of the gas supply, the gas consumption profile, the material of the storage tanks, and the safety considerations in the vicinity of the storage installation. For underground high-pressure gas storage facilities, geological investigations must be conducted, and a regional tectonic stability assessment should be performed based on the engineering rock mass classification. Following comprehensive analysis and a techno-economic comparison, the final process scheme shall be determined.

Compressed air energy storage systems shall take into account information on hazardous areas and provide safety signage in accordance with area classification. Such signage shall include, but not be limited to, grounding signs, escape‑route indicators, “No Smoking or Open Flames,” “Caution: Electric Shock,” “Do Not Operate Under Voltage,” as well as warnings for pressure vessels and high‑temperature, high‑speed equipment. In the event of an emergency, these signs shall enable operators to promptly and correctly evacuate the hazardous area.

The design of production workshops, work areas, auxiliary buildings, ancillary structures, residential buildings, flammable and explosive hazardous areas, and underground structures for compressed air energy storage systems shall comply with the relevant provisions of GB 50016.

Supplementary‑combustion compressed air energy storage systems shall be equipped with fire‑protection measures in accordance with GB 50016, and flanges in the piping system shall be fitted with bonding conductors to prevent static electricity.

All equipment in the compressed air energy storage system shall be protected against dust, moisture, and salt spray, and shall be sealed to prevent the ingress of insects and animals, thereby avoiding short circuits and equipment damage.
Pipe insulation materials, cable materials, and wall sealing materials shall be made of flame-retardant materials.

Pipes and vessels with internal temperatures exceeding 100°C should be designed to prevent direct human contact in the event of a leak.
Gas storage facilities shall be equipped with safety warning signs and an alarm system.

Pressure vessels and pressurized systems shall be equipped with safety valves and safety barriers.

Gas storage facilities shall be equipped with hazard signage indicating the presence of a high-pressure gas supply, and pressure relief and venting systems should be installed at the highest point to ensure safe pressure release.

Development History of Compressed Air Energy Storage Technology

The technological evolution of compressed air energy storage is advancing toward higher efficiency and more flexible application scenarios:

I. The Initial Exploration Phase (1940s–1970s) — During this period, the fundamental principles and concepts of compressed air energy storage were validated. The idea was first proposed in 1949, suggesting the use of underground caverns to store compressed air as a means of energy storage.

II. Commercialization Phase (1980s–1990s) — During this period, compressed air energy storage technology continued to advance and expand its applications. Key developments included: 1) refinements in the use of underground caverns or mines as storage facilities, ensuring their safety and structural stability; and 2) the development of high-efficiency turbines, which significantly improved the system’s energy conversion efficiency.

III. The Rapid Development Phase (2000s to Present) — During this phase, significant advances have been made in both efficiency and application scenarios. The key advancements include:
1) Advanced thermal management systems: These include adiabatic compression technology, which enhances overall efficiency through an efficient heat recovery and reuse system. A notable example is the German ADELE project, which features a 90 MW capacity, approximately 500,000 cubic meters of gas storage in an underground salt cavern, and an efficiency of 70%.

2) Diversification of energy storage media: Various energy storage technologies have been researched and deployed, including liquid air energy storage (LAES), enhancing system flexibility and adaptability. A notable example is the Highview Power project in the United Kingdom, currently in the demonstration phase. The project boasts a 5 MW capacity with an adjustable storage duration ranging from several hours to several days, and is expected to achieve an efficiency of 50%–60%.

3) Intelligent Control System: An advanced control and monitoring system has been implemented, enhancing operational efficiency and safety while improving compatibility with modern power grids.

Compressed Air Energy Storage Industry Chain

Upstream—Equipment and Resource Supply: Core equipment includes air compressors, turboexpanders, and heat‑storage heat‑exchanger systems, among others; additionally, gas‑storage cavern resources are required.

Midstream—Technology Provision and Project Development: At present, China has achieved a globally leading position in both technological R&D and project implementation for compressed air energy storage. The primary technology providers include Zhongchu Guoneng, a subsidiary of the Institute of Thermophysics, Chinese Academy of Sciences, as well as universities such as Tsinghua University.

Downstream—Power Grid System: Compressed air energy storage plants are integrated into the power grid, serving industrial, commercial, and residential electricity consumers, and playing critical roles such as peak shaving, valley filling, frequency regulation, phase adjustment, energy storage, and emergency backup.
Compressed air system

Applications of Compressed Air Energy Storage

Compressed air energy storage technology, owing to its high efficiency and flexibility, is widely employed across multiple sectors, primarily including:

Power side:
Compressed air energy storage systems, when integrated with renewable generation sources such as wind and solar power, effectively enhance the power quality and controllability of these renewables. By establishing wind–storage or solar–storage hybrid systems, the stability and efficiency of renewable power generation can be further improved.

Grid side:
It can be directly connected to the transmission or distribution grid and is subject to unified dispatch by the power dispatching authority. By providing technical services such as peak shaving, frequency regulation, phase adjustment, reserve capacity, and black-start support, it helps alleviate transmission and distribution congestion and enhances power supply reliability.

Load side:
Coupled with solar thermal, geothermal, and industrial waste heat, it is applied in industrial parks, public buildings, and other settings, enhancing the flexibility of system deployment and improving utilization efficiency.

Revenue model for compressed air energy storage
The first approach is renewable energy plus energy storage, integrating wind, solar, and storage into a single system.

The second approach is grid‑side energy storage, similar to pumped hydro storage, which responds to grid dispatch and relies on both capacity‑based and energy‑based tariffs. This model is feasible as a demonstration project. The grid has a critical need for long‑duration storage; although many pumped‑hydro projects have been initiated, they typically do not enter service until seven years or more after construction begins.

The third model is the user‑side approach. A particularly successful example is Shandong’s shared‑storage scheme, where users can lease or purchase services. Shared energy storage has proven to be a viable business model; in Shandong, revenue from this segment accounts for the bulk of earnings, while capacity‑based tariffs remain relatively low.

Fourth, power generation companies or end-users can install their own systems to capitalize on peak‑valley price differentials and reduce costs, ensure high‑quality power supply, provide backup power in extreme situations, and enhance the reliability of electricity provision.

Compressed air system

Prospects for Compressed Air Energy Storage

Compressed air energy storage technology holds strategic significance in the context of integrating high‑proportion, intermittent renewable energy into the grid. An adiabatic compressed air energy storage system with thermal storage not only achieves a combined storage efficiency as high as 70% but also eliminates the need for an external heat source. Compared with non‑adiabatic compressed air energy storage systems that rely on a heat source, this thermally stored‑air system does not require fuel combustion to provide heat, making it easier to achieve carbon dioxide emission reductions.

In summary, against the backdrop of the “dual carbon” goals and the gradual increase in the share of renewable energy, adiabatic compressed air energy storage systems coupled with thermal‑storage technologies hold significant potential for future development.

Disclaimer: The content is sourced from publicly available online platforms, including PowerChina Beijing Institute, Baidu Baike, Xin’andao, Baidu Wenku, Yongcheng Electric Power Observation, Dangfeng Lai Shi, the Power Knowledge Graph, Tianfeng Securities, Compressor Magazine, Baidu, WeChat official accounts, Zhihu, and others. It is provided solely for readers’ educational purposes. Reposting or sharing is permitted; copyright belongs to the original authors. If your copyright has been infringed, please notify us, and we will address the issue promptly. Thank you for your support!