Based on the time-of-use electricity price and the cost of wind-PV-energy storage system, technical and economic research of source-grid-load-storage system is studied. Firstly, a microgrid system model integrating renewable energy and energy storage system is proposed, which includes PV, wind power, energy storage system, grid, and load. Then, under the premise of ensuring reliable power supply to the load, an optimization model of the source-grid-load-storage system is established with the goal of optimizing the system economy based on load data, irradiation data, wind speed data, time-of-use electricity price data, and the costs of each unit of the system. Finally, the optimal capacity and economic feasibility of configuring a wind-PV-storage system in a certain region are analyzed in detail through a numerical example. The analysis results indicate that, the energy storage systems store energy at low electricity prices and release energy at high electricity prices, thereby avoiding users from purchasing electricity from the grid at high electricity prices and reducing the cost of purchasing electricity from the grid. The configuration of a wind-PV-energy storage system can effectively reduce the annual cost of purchasing electricity from the grid.

Compressed air energy storage (CAES) technologies have garnered widespread attention due to their large scale, high efficiency, and environmental friendliness. Among them, the non-combustion compressed air energy storage technology is mature, and produces no carbon emissions during operation. There are already several adiabatic non-combustion compressed air energy storage power stations in operation, under construction, and in planning in China. However, the design parameters of the CAES system lack a unified standardization system, which poses many challenges in system design and performance optimization of CAES. To solve this problem, the design of medium-temperature and high-temperature thermal energy storage system schemes for a 200 MW class CAES system is presented, the key equipment parameters and system boundary conditions are determined. Moreover, the performance and technical economy of the medium- and high-temperature thermal energy storage system schemes is compared. The results show that, the high-temperature thermal energy storage system is superior to the medium-temperature thermal energy storage system in performance indicators, but it has a higher investment cost, indicating that when choosing the thermal energy storage technology route for large-capacity CAES systems, it is necessary to consider comprehensively based on specific application scenarios and economic budgets.

Under deep peak shaving and variable operating conditions of thermal power units, significant changes in steam temperature have caused a significant increase in thermal stress in some structures of the units, which accelerated structural damage, and resulted in frequent safety accidents. To solve these problems, by taking the regulating stage rotor of a 300 MW steam turbine as the object, and Ansys software is used to analyze the thermal stress, aerodynamic force, and centrifugal force of the blades. Firstly, structural optimization is carried out on root of the blade to significantly eliminate the unreasonable local stress concentration phenomenon commonly found in conventional calculations. Then, the distribution laws of temperature and stress fields in the regulating stage under different conditions such as steady-state and transient during the deep peak shaving process of thermal power units are revealed. Moreover, the effects of the temperature and stress fields on safety performance of the unit are also investigated. The results indicate that, the maximum equivalent stress increases by about 24% under steady-state conditions with temperature difference of different nozzle groups of 50 ℃. The transient load increase rate of 5% THA/min is about three times higher than that of 2% THA/min, causing low cycle fatigue damage to the rotor. Compared with steady-state operating conditions, increasing the load once a day at a rate of 2% THA/min from half load to full load increases the overall damage by about 38%.

To improve steam parameters for better power generation efficiency and economy and meet the development needs of nuclear power plants, a duct-type steam generator is proposed, which is suitable for high-temperature gas-cooled reactors with ultra-supercritical parameters. The main features of the duct-type steam generator’s structure are introduced, and the advantages of this structure in terms of heat transfer performance, operation safety, and production cost are analyzed. Through the establishment of a theoretical calculation model, thermal engineering analysis and heat transfer performance study of axial, radial, and quasi-three-dimensional temperature distributions and other parameters of the steam generator with direct countercurrent heat transfer mode are carried out. The calculation results show that, the duct-type steam generator is mainly based on convection heat transfer mode, with obvious temperature distribution segments and excellent heat transfer performance, which meets the relevant heat transfer requirements. This study can provide a reference for design and development of steam generators in nuclear power plants.

A new type of liquid air energy storage (LAES) system coupled with solar energy is proposed to address the issue of low round-trip efficiency (RTE) in current LAES systems. The discharging process of the new system is equipped with series-connected two-stage air heaters, which improves the RTE while allowing the system to operate in conventional ways under low solar radiation conditions. Sensitivity analysis of main parameters and exergy analysis are conducted on the new system, and the results show that, within the allowable range, the lower the liquefaction temperature, the lower the charging pressure and the higher the discharging pressure, resulting in higher RTE of the system. The optimal RTE of the system can reach 72.4%, and the system can still operate at an RTE of 53.6% when solar radiation is insufficient. The exergy efficiency of the new system is 38.0%, among which the solar collector field has the highest exergy destruction, accounting for 52.4% of the total exergy destruction, followed by the throttle valve and thermoelectric generator. In heat exchangers, there is significant exergy destruction in cold boxes and evaporators.

“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 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.

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.

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.

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.