The compressed air energy storage is a large-scale physical energy storage technology and a highly promising new type of energy storage technology. This paper summarizes the basic principles of isothermal compressed air energy storage, and introduces the principles and current development status of key equipment and related technologies. It provides an analysis and summary of liquid pistons, pumps and turbines. Moreover, it reviews the basic principles of isothermal compressed air energy storage, and analyzes the existing research progress on isothermal compressed air energy storage technology. An analysis and summary are presented for liquid piston technology, as well as pump and turbine technology in the system. The data of existing compressed air energy storage power stations are summarized and analyzed. The data of existing compressed air energy storage power stations are summarized and analyzed. On this basis, the future development direction of isothermal compressed air energy storage technology is prospected, which provides a certain data reference for the selection of power equipment in isothermal compressed air energy storage system and the promotion of demonstration projects.

“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.

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.

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 reduce the fluctuation of renewable energy power generation output and improve the utilization rate of renewable energy, this paper designs an on/off grid wind solar hybrid hydrogen synthesis ammonia system. Taking the maximum annual revenue of the system as the objective function, considering the operation constraints such as power balance, hydrogen balance and grid interaction, a capacity allocation scheduling optimization model is established. Taking the real output of the wind and solar energy in a certain area of Inner Mongolia as the input, through the analysis on wind and solar energy capacity ratio, this paper explores the technical and economic effect of the wind and solar energy capacity ratio on the system. The results show that, after the capacity configuration and scheduling optimization of the on/off grid wind solar complementary hydrogen and ammonia system, the system can reasonably switch the working state under different wind and solar output conditions, stabilize the wind and solar fluctuations, and realize the stable and efficient operation of ammonia equipment. The grid connected system is better than the off grid system. Through the analysis of the ratio of wind and solar capacity, in the case area, with the increase of wind capacity, the capacity of electrolyzer and hydrogen storage tank to be configured in the system shows a trend of first decreasing and then increasing. When the capacity of wind power generation and photovoltaic power generation is close to or equal, the economic efficiency of the system is high.

Hydrogen storage by physical adsorption offers significant advantages, including high safety, high hydrogen storage density, and fast hydrogen charging and discharging rates, making it a highly promising method for hydrogen storage. Among the various materials, metal-organic frameworks (MOFs) have emerged as ideal hydrogen storage materials due to their highly ordered porous structures and tunable characteristics. To investigate the influence of thermal effects during the hydrogen adsorption process on storage performance, a numerical model of hydrogen storage by adsorption is established and validated. Subsequently, the hydrogen storage properties of Cu-BTC and activated carbon AX-21 tanks are analyzed and compared. Furthermore, the hydrogen storage capacity of Cu-BTC tank at different temperatures is explored. The results indicate that, compared with AX-21, the hydrogen storage capacity at room temperature increases by 12.8% when using Cu-BTC as adsorbent. When the storage temperature is reduced to 77 K, the maximum pressure in the Cu-BTC tank decreases to 0.97 MPa, and the hydrogen storage capacity increases by 174% compared with room temperature (300 K). These findings provide valuable insights for further research on the hydrogen storage capabilities of Cu-BTC materials.

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.

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.