Accelerating the transformation of energy structure and promoting the grid connection of renewable energy power generation is an important initiative to address climate change and the development of renewable energy. Energy storage technology can improve the stability of power grid and enhance the utilization rate of renewable energy. Among the energy storage technologies, compressed air energy storage has been widely studied for its high efficiency, low investment cost and environmental friendliness. Compared with the conventional constant-capacity compressed air energy storage technology, isobaric compressed air energy storage avoids the unavoidable buffer air in the constant-capacity compressed air energy storage system, enables the compressor and expander to operate efficiently at constant discharge pressure, and eliminates the throttling loss in front of the expander unit. The advantages of isobaric compressed air energy storage technologies are introduced, and the isobaric compressed air energy storage technologies are classified into underwater compressed air energy storage, pumping-compensated compressed air energy storage, solid-compensated compressed air energy storage, and gas-phase-change-compensated compressed air energy storage. Moreover, the basic principles, research progress and challenges of the above four types of isobaric compressed air energy storage technologies are discussed. Finally, the development of the isobaric compressed air energy storage technologies is prospected.

In order to explore the type of underground cavern with compressed air energy storage from the perspective of thermodynamics, a numerical model of the first inflation and pressurization process of the cavern considering turbulence, heat transfer and real air characteristics is established, by using the computational fluid dynamics (CFD) method. The effects of different length-diameter ratios and inlet diameters of inflatable pipes on temperature rise of gas and lining materials in the cavern and the temperature distribution in the cavern are studied, and the control measures are put forward for the local high temperature phenomenon in the cavern. The main conclusions are as follows. When the length-diameter ratio is small (large tank gas storage), the temperature distribution in the cavern is relatively uniform. With the increase of the ratio of length to diameter (tunnel-type gas storage), the temperature distribution in the cavern appears stratification phenomenon, and the extremely high temperature zone appears at the end of the cavern (stuffy top effect). The temperature rise of the steel plate sealing layer is the largest in the process of inflation and pressurization of the cavern, the temperature change of the concrete lining is small, and the surrounding rock is almost not affected by temperature change in the cavern. Reducing the inlet diameter of the inflatable pipe can reduce the temperature in the cavern to a certain extent and promote the outward heat transfer. For the annular tunnel type cavern, the proposed improved inflation method can make the temperature distribution in the cavern uniform, avoid the stuffy roof effect, and provide a useful reference for engineering design.

The arrangement of micro adiabatic compressed air energy storage (A-CAES) system is flexible and suitable for typical distributed energy systems. By accurately modelling a typical device of the miniature A-CAES system based on pneumatic motors, a thermodynamic model that can reflect its system performance is constructed. The experimental bench of the A-CAES system is built, and the average error rate between the simulation model and the experiment is around 5.38%, which verifies the reliability of the model. The round-trip efficiency and comprehensive efficiency of the system are 4.81% and 27.23%, respectively, verifying the necessity of the existence of thermal energy storage devices in the A-CAES system. The effects of compression level and compression ratio on the system performance are analyzed by using this model. The results show that, as the compression level increases, the round-trip efficiency and comprehensive efficiency of the system both increase, and the optimal efficiency of the system can reach 6.10% and 35.81%, respectively. Taking the combination of compression ratios of 2, 3, and 5 as an example, reasonable distribution of compression ratios can improve the round-trip efficiency and overall efficiency of the system by 1.27% and 4.38%, respectively.

At present, the construction technology of salt cavern gas storage has been mature, and it is developing in the direction of intelligence. Based on the technical status of salt cavern gas storage, the current construction technologies of salt cavern gas storage are analyzed. From the perspective of whole life cycle management, the intelligent construction of salt cavern gas storage is divided into four stages: intelligent location, intelligent design, intelligent construction and intelligent operation and maintenance, and the key technologies involved in each stage are studied. The technical framework of intelligent construction technology of salt cavern gas storage and its specific content is put forward. Moreover, the future research focus of intelligent construction of salt cavern gas storage is proposed and summarized from four aspects: system, technology, theory and model. The relevant technologies have been effectively applied in Yingcheng 300 MW compressed air energy storage demonstration project.

A wind-drove compressed air energy storage (W-CAES) system is proposed, its main advantage is that it can reduce the waste of wind energy caused by the fluctuation and randomness of wind energy. The direct-driven compressor of wind turbine gets rid of the dependence of compressor on the input electricity, which is more suitable for off-grid power generation system. The model of the W-CAES system is established, the parameters of the wind turbine direct-drive compressed air energy storage system are designed, and the effects of wind speed, ambient temperature, and air humidity on efficiency of the system are analyzed. The results show that, the filling time increases with the decrease of wind speed with the same storage volume, and the filling times are 0.71 h and 1.64 h when the wind speeds are 14 m/s and 6 m/s, respectively. The system efficiency decreases slightly with the increase of ambient temperature and air humidity. When the ambient temperatures are -30 ℃ and 40 ℃, the corresponding system efficiencies are 52.97% and 52.08%, respectively. When the relative humidity of the air is 0 and 1, the corresponding system efficiencies are 52.27% and 52.14%, respectively.

Liquid air energy storage (LAES) is a promising technology for large-scale energy storage due to its geographical flexibility and high energy storage density. To further improve the round-trip efficiency and economic benefits of LAES, a novel integrated system combining liquid natural gas (LNG) cold energy utilization and organic Rankine cycle (ORC) with LAES is proposed. Thermodynamic and economic analysis methods for the integrated system are established, and the effects of key parameters on the system’s thermal performance are investigated based on simulations. An economic analysis of the system is also conducted. The results show that, as the system’s expansion pressure increases, both efficiency and power output rise, but at a decreasing rate. The system’s round-trip efficiency increases with more expansion stages up to a point, then decreases. With four-stage expansion, the system efficiency reaches 62.26%, which is 7%~12% higher than that of the conventional LAES system. When the difference between peak and valley electricity prices is 0.848 yuan/(kW·h), the net present value, dynamic payback period, and levelized cost of electricity are 119 058 500 yuan, 4.48 years, and 0.893 yuan/(kW·h), respectively. The results of this study can provide a reference for engineering application and efficiency improvement of LAES systems.

Liquid air energy storage (LAES) technology stands out as a large-scale energy storage technology due to its superior energy storage density and adaptability to external energy sources. An LAES system that recovers waste cold of liquid ethylene and introduces an external low-temperature heat source is proposed. Moreover, thermodynamical and economic analysis on key parameters, including isentropic efficiency of the compressor and expander, and temperature of the heat source, are conducted. The results reveal that, when the ethylene flow rate is 34 t/h, the energy storage capacity can reach up to 5 MW/40 (MW·h). At isentropic efficiency of the compressor and expander of 90%, the round-trip efficiency can achieve 77.45% by solely relying on an ambient heat source of 25 ℃ for air heating. When the heat source temperature is increased to 125 °C, the system’s optimal round-trip efficiency, net present value, and dynamic payback period reaches 106.99%, 144.73 million yuan, and 3.56 years, respectively. These findings provide reference for research on the coupling of LAES systems with external cold energy.

The intermittency and volatility of renewable energy poses significant challenges to stable operation of power grids. Energy storage technology can address these issues effectively. Liquid air energy storage technology offers significant advantages of high energy storage density, being unconstrained by geographical conditions and atmospheric pressure storage. However, its round-trip efficiency is relatively low. To solve this problem, a liquid nitrogen and liquid air hybrid energy storage system (N-LAES) is proposed. By charging liquid nitrogen during energy release process, the gas flow in the expander increases, and gas pressure in front of the expander rises as well, thus the system’s round-trip efficiency increases. A thermodynamic model is developed, and the analysis results indicate that, for a typical scale N-LAES, the round-trip efficiency is increased to 66.47% compared with 56.90% for a standalone LAES. The net present value at the 30th year increases to 120 213 500 yuan, compared with 58 077 400 yuan for a standalone LAES, and the levelized cost of storage decreases to 0.809 4 yuan/(kW·h) from 0.897 2 yuan/(kW·h) for a standalone LAES. These findings demonstrate that both the thermodynamic and economic performance of the N-LAES is superior to that of the standalone LAES, offering a new approach for development of the liquid air energy storage technology.

“Power entropy” can quantitatively reflect the characteristic difference of multi-time scale energy storage configuration. The power curve synthesized by two sinusoidal power curves is used to study the entropy difference and characteristics of main scenarios of energy storage applications such as frequency regulation, peak regulation and cross-season energy regulation. The results show that, power entropy can effectively reflect the difference of characteristics of energy storage for different time scales. For the scenarios of frequency regulation and peak regulation, using two sets of energy storage is better. For the scenarios that the difference between frequency and amplitude is less than 2 times, it is appropriate to apply a single set of energy storage. The research theoretically explores the methods and basis of multi-time scale energy storage configuration, reveals the essential differences of multi-time scale problems, it is helpful to form a scientific and optimal energy storage configuration scheme, scheduling scheme and optimization scheme.

To explore the heat and mass transfer process in a solid-state hydrogen storage reactor, a two-dimensional numerical calculation model for the reactor is developed. The radial reaction rate distribution characteristics of the solid-state hydrogen storage material within the reactor is investigated, and the influence laws of bed thickness of the hydrogen storage material and diameter of the heat exchange tube on saturation radius are also studied. Based on this, the arrangement of the heat exchange tube bundle is optimized. The results show that, the heat exchange tube has the corresponding maximum saturation radius, and it increases with the tube radius. When the tube radius is 1.00~6.00 mm with single-tube arrangement, the maximum saturation radius is 2.60, 3.30, 3.50, 3.70, 3.80 and 3.90 mm, respectively. The volume fraction of heat exchange tubes with radius of 1.00, 2.00 and 3.00 mm is relatively small, which is 7.72%, 14.24% and 21.30%. The optimal bed thickness between tubes is 4.86, 6.09 and 6.38 mm when arranging the above three types of tubes in a tube bundle. Moreover, adding heat exchange tube bundles can effectively improve the hydrogen storage performance of reaction dead zone in the reactor. In the reactor equipped with heat exchange tube bundles with radius of 2.00 mm, adding 12 heat exchange tubes with radius of 2.00 mm in the reaction deadzone can reduce the hydrogen storage time to 267 s (by 40.00%), while the volume fraction of tube bundle only increases by 1.92%, and the hydrogen storage capacity just decreases by 2.17%. The research findings can establish a fundamental basis for the optimal design of solid-state hydrogen storage reactors and offer valuable guidance for subsequent engineering applications.