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• Introduces a novel optimization model for integrating network and battery storage expansions to enhance system strength at minimal costs. • Addresses the overlooked impact of system investment planning on system strength. • Utilizes logistic regression analysis trained on dynamic simulations to capture probability of instabilities within investment planning optimization models. • Demonstrates the critical role of system strength considerations in system planning with significant penetration of converter interfaced generation. The increased penetration of renewables through converter interfaced generation (CIG) and the associated displacement of synchronous generators (SGs) can significantly reduce system strength. Although some network enhancements, such as the installation of battery energy storage systems (BESS), can partially counterbalance the reduction in strength, current network planning methodologies overlook system strength effects. In this context, this work proposes a new optimization model for co-optimizing investments in network expansions and battery systems to meet, at minimum cost, system strength requirements quantified through short circuit levels (SCL). Recognizing that SCL needs vary on a case-by-case basis, this model incorporates a logistic regression analysis trained on offline time-domain dynamic simulations; this approach effectively correlates SCL with system stability, providing a tailored strategy for each power system. To solve the optimization, we also propose an algorithm to iteratively find the optimal solution for the co-optimized portfolio of new transmission and energy storage investments. Through various case studies, we demonstrate the importance of considering system strength requirements in planning studies with significant penetration of CIG. [ABSTRACT FROM AUTHOR]

In this study, some locations with different climates, off-grid zero energy buildings with hydrogen energy storage systems are designed, and transient analysis is conducted. These considered buildings supply their electricity consumption without using the electrical grid and PV panels or wind turbines. Also, they supply thermal comfort to occupants by using a vapor compression chiller and humidifier. Domestic hot water of occupants is supplied using solar collectors. For analyzing building's performance and objectives achievement, TRNSYS software is used. Also, for evaluating occupant thermal comfort, the Fanger model is used. The considered building is a one-story building with a 150 m2 area. Four occupants are considered. Both of them are seated at rest, and another is seated with light working such as typing. Using the Fanger model equation and MATLAB software, the thermal comfort of occupants is determined. For domestic hot water consumption, verified profiles that vary during 24 h of the day are considered. Achieved results show that for humid and cold cities, PV panels with an area of 73 and 76 m2 can be supplied the required electricity of considered building with four occupants and battery state of charge is higher than 50% and 10%, respectively. Moreover, with a suitable air conditioner system, the predicted percentage of dissatisfied (PPD) can be lower than 12% and 8% for humid and cold cities. Therefore, the building can be converted to a zero-energy building using its rooftop area. • Analyzing wind and PV panels as renewable energy suppliers for supplying energy. • Storing hydrogen energy system as for off-grid zero energy buildings. • Transient analysis and design of off-grid zero energy buildings. • Evaluating thermal comfort of occupant in zero energy buildings. • Using Fanger model and PPD and PMV parameters. [ABSTRACT FROM AUTHOR]

In this article, the solar hydrogen storage is modeled and hourly investigated with TRNSYS software. The Photovoltaic (PV) panel is employed for green power generation that is consumed in the electrolyzer subsystem and produced hydrogen. Additionally, the required electricity at the lack of enough solar irradiation is supplied from the grid. The performance of the system is comparatively analyzed for three main cities. Results show that the maximum power generation by PV panel is about 1670 kW in June which approximately is the same for two cities. The energy and Faraday efficiency of electrolyzer changes between 0.85-0.89 and 0.89–0.92 respectively. The amount of hydrogen production reaches 1235 m3/h for one of them in May. The total amount of hydrogen production is 13,181 m3/year in Yazd, 13,143 m3/year in hot city, and 13,141 m3/year in most populated city. • Transient simulation of power to hydrogen system using TRNSYS. • Influence of various places on hydrogen production rate. • Designing a hydrogen storage system with a solar energy source. • Analyzing the performance of the electrolyzer from an energy viewpoint. [ABSTRACT FROM AUTHOR]

Solar energy systems are an effective way to meet the needs of zone heating, cooling, electricity, and domestic hot water. However, to reach sustainability, and energy storage unit should be considered for installation. In this study, two combined cooling, heating and power (CCHP) systems are simulated and studied using TRNSYS software; both using natural gas engine generators and photovoltaics as prime movers and a hydrogen fuel cell/electrolyzer storage unit, one with absorption chiller and another with compression chiller cooling. For the study, a residential building is modeled for three major populated climate zones of the United States of America, namely, Hot-humid, mixed-humid and cold using DesignBuilder and EnergyPlus software. The energy demand for its HVAC operation and domestic electricity is obtained and used for system simulation in TRNSYS software. Due to choosing actual equipment for the CCHP arrangement, precise economic and environmental models are designed to further evaluate the possibility of execution of the system. The results show that absorption chiller-equipped CCHP has better performance both environmentally and economically. In addition, the outcome shows that the suggested systems show less favorability to be utilized in hot humid climate zones. • Design a multi objective optimization system with TRNSYS simulator. • Various geographical location is considered for study the proposed system. • Designed system with chiller in colder climates has less Carbon-dioxide emission. • Hot climate leads to a higher energy consumption in the designed unit. [ABSTRACT FROM AUTHOR]

Remote energy systems are applicable, especially in critical circumstances like earthquakes, floods, etc. Besides, renewable energy systems are suitable energy sources in remote areas. Therefore, Due to high solar and wind potential and its location as an earthquake-prone, a solar-wind energy system for a remote application on a Conex is presented in this study. Considered wind turbines have power production of 1 kW and 3 kW. PV panels have an efficiency of about 20%. This Conex has 12 m2 of the area and resides three to five people and supplies 520 W power consumption of equipment except for the HVAC unit. A considered lifetime of the Conex is 20 years. The considered capacity of batteries is about 100–200 Ah. Six cities are selected as representatives of the six major climate types in Iran. The studied system is optimized for each city. The heating and cooling demand of Conex in cities are specified using TRNSYS software. The heat pump's electricity requirement as a cooling and heating unit with COP of four, lighting (20 W), laptops (140 W), and refrigerators (360 W) is calculated for Conex in each city. Mixed-integer linear programming is employed to optimize an off-grid renewable energy system to supply this electricity demand. The system's total cost, which includes the initial and O&M cost of PV panels and wind turbines, and the capital and replacement cost of the batteries together with the loss of power supply probability during a year, are considered two objective functions. The interest rate is assumed to be 15%. Achieved results show that Iran's solar and wind potential can balance the required load of the Conex with a probability of power outage as low as 1% of a year. However, there is a variance in the cost of the required renewable energy system for supplying Conex power consumption for different climate zones: in the Mediterranean region, the system costs 500–5000 $ as the most expensive one, and in the hot coastal dry region, it costs 900 $-2000 $ as the most cost-efficient region. Finally, results show that wind turbines can be cost-effective energy suppliers for most considered climates, especially considering O&M costs. This study can fill the gap of requiring off-grid temporary portable residences in different climates after disasters, which destroy buildings. Therefore, the lack of these temporary residences can be supplied without adding greenhouse gases to the environment, which reduces greenhouse emissions and electrical grid dependence of the building sector. • A solar-wind energy system for an off-grid residential Conex is presented. • Proposal of a new off-grid system for location with high risk of an earthquake. • Six critical cities are selected as major climates in Iran. • A mixed-integer linear program determining the optimum system is implemented. • Optimization results are brought using pareto frontiers. [ABSTRACT FROM AUTHOR]

In order to further research the dynamic characteristics of liquid air energy storage (LAES) system under typical operating conditions, a dynamic simulation model of energy release process of the 10 MW LAES system is established in this paper. The characteristic curves of expander are considered during modeling and simulation process. The dynamic changes of key parameters, such as temperature, pressure, mass flow rate, and so on, of energy storage system over time under the startup and grid connection are simulated. The sensitivity analyses of rotor speed rising rate and frequency disturbance on the key parameters are carried out. The results show that the outlet temperature and outlet pressure of 1st expander stabilized at 395.96K and 5.37 MPa, respectively, at 602s when the rotor starts up with a rising rate of 360 rpm/min. The actual rotor speed reaches the maximum value of 3010r/min at 504s, the overspeed ratio is 100.3%. During the grid connection, the outlet temperature and outlet pressure of 1st expander stabilized at 345.6K and 3.0 MPa, respectively, at 910s, and the mass flow rate of air rises from 11.25 kg/s of the no-load operation to 23.60 kg/s. In addition, the rotor speed rising rate and frequency disturbance have great influence on the key parameters of expander. The new startup scheme of changing rotor speed rising rate have been put forward to balance the relationship between maximum rotor speed and startup time. The fluctuation amplitudes of outlet temperature, outlet pressure, power and rotor speed increase with the frequency disturbance amplitude increasing. The analysis results of dynamic simulation can provide data reference for learning the dynamic characteristics of LAES system. [ABSTRACT FROM AUTHOR]

Pumped thermal energy storage (PTES) technology offers numerous advantages as a novel form of physical energy storage. However, there needs to be a more dynamic analysis of PTES systems. This paper proposes a dynamic simulation model of the PTES system using a multi-physics domain modeling method to investigate the dynamic response of key system parameters during the system's start-up and variable operating conditions. Additionally, the impact of equipment parameters on system characteristics was analyzed. Furthermore, a comparative analysis was conducted to assess the variation in system characteristics when considering the different working medium properties. The results show that the system cavity volume should be selected as 5 m3, and the initial pressure of the system during the charge/discharge period should be selected as 2.1 MPa and 3.8 MPa, respectively. The system runs to the design operating conditions during the start-up process in about 1400 s. In the process of variable operation conditions, the power load in the charge/discharge period can be increased or reduced from the rated value by gas filling or venting, and the system characteristics change accordingly. The simulation model and research findings will offer theoretical insights for optimizing the design of the PTES system. • A dynamic simulation physical model of the PTES system was proposed. • The dynamic changes in system characteristics were analyzed. • The TES tank's thermal inertia and heat management of the PTES system were analyzed. • The effects of main equipment parameters on system characteristics were analyzed. • System characteristics were compared when using different gas properties. [ABSTRACT FROM AUTHOR]

A dynamic model of a compressed gas energy storage system is constructed in this paper to discover the system's non-equilibrium nature. Meanwhile, the dynamic characteristics of the CO 2 binary mixture (i.e., CO 2 /propane, CO 2 /propylene, CO 2 /R161, CO 2 /R32, and CO 2 /DME) based system are first studied through energy and exergy analyses. Performance indicators are considered, including round trip efficiency, exergy efficiency, energy density, discharge time, and average power output. The effects of tank volume and ambient temperature on the system performance are analyzed. According to the results, although the round trip efficiency of the CO 2 mixture system is reduced by about 0.68%–11.97% compared to pure CO 2 , the compressor performance and the system pressure stability are improved. When the tank volume increases from 10,000 m3 to 15,000 m3, the system round trip efficiency increases by 0.16%–0.33%. A further improvement of round trip efficiency for the CO 2 mixture is found compared to pure CO 2 at higher ambient temperature. This paper demonstrates the dynamic operational characteristics of the compressed gas energy storage system when using different CO 2 binary mixtures, providing a reference for optimizing related systems. Potential scenarios and applications for the CO 2 binary mixture are discussed for future research. • A dynamic model of Compressed CO 2 binary mixture Energy Storage is constructed. • The effects of different CO 2 binary mixtures on dynamic performance are compared. • The effects of storage pressure and ambient temperature on performance are analyzed. • The RTE of CO 2 mixture system is reduced by 0.68%–11.97% compared to pure CO 2. • A 1 K increase in ambient temperature results in a 5% increase in storage density. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2D dynamic models for rSOC and methanol synthesis are developed in COMSOL. • Dynamic models are run jointly by MATLAB call with fluctuating PV power supply. • Multi-physics analysis and operation optimization on full PMPS are conducted. • Techno-economic comparison of PMPS and PHPS is conducted. • The roundtrip efficiency and levelized cost are 78% and 0.49 $/t CH 3 OH, respectively. Power-to-Methanol-to-Power System (PMPS) has a great potential for fluctuating renewable power storage and flexible power generation. In this study, a dynamic-cycle model of PMPS is developed by coupling reversible solid oxide cells with methanol synthesis process. The system stores energy from fluctuating photovoltaic power in the form of methanol during the day and generates electricity at night using the methanol fuel generated in the daytime. It is found that reducing the CO 2 ratio in co-electrolysis from 60% to 30% increases CH 3 OH production by 64% and doubles electricity efficiency due to the increased H 2 supply to methanol synthesis section. While in the fuel cell, reducing methanol supply rate from 500 to 200 SCCM increases power generation capacity by 110% with longer generating duration, and the electricity efficiency is improved from 30% to 61%. Besides, the optimized PMPS presents a round-trip efficiency of 78%, along with high conversion rates of carbon (97%) and hydrogen (84%), significantly exceeding that of the Power-to-Hydrogen-to-Power System (PHPS, the round-trip efficiency of 45%) under similar cell's inputs. Furthermore, our techno-economic analysis shows that the levelized fuel cost (0.49 $ t−1 CH 3 OH) and levelized generating capacity cost (0.22 $ /kWh) of PMPS are about 10% (4.8 $ t−1 H 2) and 74% of the PHPS, mainly due to the 16% lower capital expenditure of PMPS. [ABSTRACT FROM AUTHOR]

Intelligent design and operation optimization allow energy systems to take advantage of the flexibility that multi-generation provides. This study proposes a basic solar-driven system integrated with thermal energy storage for round-the-clock energy harvesting. A modified configuration is then designed incorporating innovative multi-heat recovery approaches to increase the capacity and product diversity of the basic system. The modified system is able to cover vital urban utilities such as electricity, fresh water, cooling, and hydrogen throughout the day. To overcome the time-consuming procedure of dynamic techno-economic simulation as well as the limitation of commercial engineering equation solvers for tri-objective optimization, a deep learning approach is developed to reduce the computational complexity and improve the analysis accuracy. In this regard, the trained neural networks play an intermediary role in coupling the developed code with the MATLAB optimization toolbox. A comparison between the modified and conventional configurations indicates that implementing the multi-heat recovery approach results in a 29% increase in power generation while only increasing the overall system cost by 1.97%. From an economic perspective, the Sankey diagram depicts that the storage unit with a cost rate of 12.25 $/h accounts for 6.77% of the plant's cost rate, which enables the system to operate continuously. According to the sensitivity analysis and contour plots, the number of collectors significantly affects the total cost rate and fresh water production capacity while it has no tangible effect on the exergy efficiency. • A novel multigeneration system with thermal energy storage is designed. • A modified configuration with heat recovery is introduced to boost the capacity. • The comparative study indicates a 17.6% improvement in the power generation. • A dynamic simulation code is developed based on meteorological data. • A deep learning techno-economic optimization is applied to the system. [ABSTRACT FROM AUTHOR]

• An innovative slim decentralised plug-and-play tank is proposed for DHW production. • Model calibration is performed by experimental data in charge/discharge process. • Retrofit solution cuts required annual energy in half of which 82% is RES quota. • Optimised charging scheme reduces the total annual electrical energy by 5.2 %. • A degree increment in draw-off temperature increases annual CO 2 emission by 103 kg. The present study deals with a multi-objective analysis of an innovative decentralised system to produce and store domestic hot water (DHW), emphasising on the combined effects of the technological aspect, control strategy and user's behaviour. The proposed system, by relying on thermal energy storage, decouples energy production and demand while shaves peaks in the energy demand and, at the same time, provides more autonomy to users through local storages. To identify subtle interactions in components of DHW system, dynamic simulations are carried out by establishing a coupled TRNSYS-MATLAB code, calibrated and validated by experimental measurements. The energy analysis implies that the proposed system cuts the required annual electrical energy in half, of which up to 82% of needed primary energy is supplied from renewable sources, compared to previous electrical-decentralised system. The optimisation of the results through applying control strategies indicates that adopting a three-time charging scheme is advantageous in terms of providing a more stable temperature profile as well as a higher hot water temperature. Compared to an available-by-demand operation, this scheme reduces the required total annual electricity by 5.2 % and enhances total thermal loss from components up to 4.0%. Furthermore, a sensitivity analysis on the results emphasises the striking role of the user behaviour in electrical energy consumption either via draw-off temperature or adjusting the pre-defined temperature for activation of the built-in auxiliary heater. [ABSTRACT FROM AUTHOR]

The aim of the paper is to simulate multi-tank storage with the thermocline moving from tank to tank and compare the results against single tank storage. No analysis of this nature has previously been performed. The results lend added impetus to developing this new type of thermal energy storage, especially as heat losses through insulation have already been reduced a minimum. Dividing a seasonal thermal energy storage tank into smaller tanks reduces the negative effect of heat transfer through the thermocline. The work is a continuation of the concept already proposed in available literature of using multiple solar energy stores, but we focus mainly on developing a dynamic model of a system of this type and presenting the results of a time and thermocline dependent simulation. The study also encompassed examination of the thickness of thermal insulation of the storage tanks, with definitions of its critical size. Our study revealed that the use of multi-tank thermal energy storage reduces heat loss through the thermocline. This is illustrated mainly by changes in water temperature in the upper part of the tank, which fluctuates across a much smaller range than for a single tank. In the single tank system, the temperature drops below 60 °C, whereas for the multi-tank system it always remains above 64 °C. In addition, in the multi-tank solution the loss caused by the thermocline occurs in only one tank, leaving 3/4 of the storage system unaffected by thermocline loss. • The concept of multi tank seasonal thermal energy storage is examined. • The examination is based on the dynamic modeling. • Results are compared with the single tank thermal energy storage systems. • The examined system is more efficient due thermocline losses limitation. [ABSTRACT FROM AUTHOR]

Reversible solid oxide cell (rSOC) can flexibly switch between the electrolysis mode and the fuel cell mode for electrical energy storage and power generation. For practical application, sweeping gas is needed to bring in the reactants and take out the products timely. In this study, we use steam as anode sweeping gas in electrolysis to decrease the overpotential loss and collect pure O 2 , which is then used as the fuel cell cathode oxidant. The real fluctuating power generated from solar photovoltaic is used as the power supply, which allows rSOC to generate H 2 from 6:45 a.m. to 5:45 p.m. and produce electricity in the night. Compared with the conventional strategy, the proposed system can utilize more than 35% electricity in electrolysis, and its efficiency and total H 2 production can be increased by 8% and 50%, respectively. The total power generation and the power density are also increased by 290% and 160%, respectively. Overall, this new strategy results in a doubled round-trip voltage efficiency due to the much-decreased overpotential losses in the electrochemical processes. This study provides a guidance for the optimization of practical rSOC application with dynamic operating conditions. • 2D dynamic models for tubular SOEC and SOFC are developed. • Parametric studies on SOECs are conducted with fluctuating PV power supply. • H 2 O is used as sweeping gas in SOEC and pure O 2 is used as reactant in SOFC. • The production efficiency and rate of H 2 are increased by 8% and 50%, respectively. • Power generation and power density are increased by 2.9 and 1.6 times, respectively. [ABSTRACT FROM AUTHOR]

This study presents the optimal design of a multi-source renewable energy combined cooling, heating, and power (M−RCCHP) system integrated with energy storage units for an apartment community from techno-economic perspectives using response surface methodology (RSM) and dynamic evaluation. The proposed M−RCCHP system is consisted of photovoltaic/thermal (PV/T) collectors, wind turbines (WTs), fuel cell subsystem, heat pump (HP), while the battery banks and hydrogen storage tank are the energy storage subsystems. The behavior of the system is examined by a dynamic approach using the TRNSYS simulation platform. Besides, the main design variables of the M−RCCHP system are selected to find the foremost combination of them using the design of experiments (DOE) technique. The number of PV/T panels, number of WT, fuel cell power, HP cooling capacity and HP heating capacity were considered as decision variables. Overall electricity consumption (OEC) and boiler fuel consumption (BFC) as indicators of primary energy consumption of the system and predicted average vote (PMV) as an index of thermal comfort of the system and life cycle cost (LCC) as economic criteria as 4 objective functions were selected for optimization. The optimization results showed that the M−RCCHP system with 225 PV/T collectors, 15 wt, fuel cells with a power of 74.96 kW, HP cooling capacity of 50.25 kW and HP heating capacity of 20 kW achieved the best techno-economic performance during the period. The results of the system modeling showed that the fuel cell subsystem, PV/T collectors and WTs with the maximum power of 75 kW, 52 kW and 24 kW have the largest contribution in electricity production. The optimization results showed that the system cycle cost (LCC) is 323,004.96 $ per year, the system comfort coefficient (PMV) is 0.115 per year, the boiler fuel consumption is 41,067.88 cubic meters per year, and the total electricity consumption is −317,194.94 kWh per year, as well as the amount The optimal cooling and heating capacities of HP were calculated as 50.25 and 20 kW, respectively. And finally, the error percentage of the optimization method was reported as 6.53 %. [ABSTRACT FROM AUTHOR]

In this work, a novel re-compressed adiabatic compressed air energy storage (RA-CAES) system is proposed to raise the operating pressure of the expansion train. In the discharging process, a compressor is employed to enhance the low-pressure air from storage vessels to the operating pressure. Off-design models for components have been established and experimental data available in the open literature are adopted for validation. Potential induced degradation (PID) control technology is employed to control the outlet temperature of the air in inter-cooling and after-cooling heat exchangers. The calculation results for the components have been presented and discussed. Meanwhile, the system performances of the proposed RA-CAES are compared with that of conventional A-CAES. The comparison results show the round trip efficiency (RTE) of RA-CAES is 69.89%, while it is only 65.23% for A-CAES, and the increment of RTE between A-CAES and RA-CAES is 4.66%. The influence of isentropic efficiencies of turbine and compressor is also investigated, the RTE of RA-CAES is always higher than that of A-CAES, and the minimum increment of RTE is near 4%. Overall, this study presents valuable insights into the design of A-CAES, the proposed RA-CAES is more efficient than the conventional A-CAES. • A novel re-compressed adiabatic compressed air energy storage system is proposed. • The discharge pressure can be raised up by an additional compressor. • Off-design models have been established and validated for the components. • The round trip efficiency of the proposed system is 4.66% higher than that of the conventional system. [ABSTRACT FROM AUTHOR]

The necessary integration of renewable based technologies in the current energy systems is leading to a faster development of energy storage technologies. As widely known, renewables suffer for unpredictability, and their massive utilization is significantly affecting grid stability and management. In this framework, the development of efficient and large electrical storage systems is becoming a pivotal point to achieve a stable electrical network based on renewables. This paper proposes a novel approach to reduce the energy excesses exported to the grid by a residential user equipped with a100 kW solar photovoltaic field. In particular, the electricity is stored as hydrogen by means of a 50 kW reversible solid oxide fuel cell. A comprehensive energy and economic simulation model of the system is proposed. In particular, a model of the reversible solid oxide fuel cell is developed in MatLab® and then integrated in TRNSYS17 for dynamic simulation purpose. Results showed that using the plant waste heat is crucial for improving fuel cell efficiency and plant energy performance. The proposed system achieves a reduction of the primary energy consumption by 74%. However, the proposed plant exhibits a poor economic profitability, with a payback period of 15 years. • Novel paradigm for residential electric energy storage based on hydrogen technology. • Hydrogen as electric energy storage system is able to shave the peak of power demand and production. • Very profitable energy and environmental results are achieved. • The high capital cost of hydrogen related technologies limits the economic profitably of such plants. [ABSTRACT FROM AUTHOR]

In the current study, an innovative smart energy system based on hybrid solar-GT energies is proposed. Transient performance assessment and techno-economic analyses are conducted to evaluate the dynamic performance of the system. The system has three main parts: solar panels, a Hydrogen production and storage system and gas turbine system, a chiller, and several heat exchangers and auxiliary components. The goal is to set a stand-alone system to generate the need of the building, including heating, power, and cooling. The system is an off-grid system due to its energy storage system. The system is analyzed comprehensively from 3E standpoints. A parametric study of key design variables is performed, and optimization is carried out to find the best solution point. Results indicate that at the optimized point, the system reaches the effectiveness of 39.5%, the emission of 0.85 kg/kWh and the Levelized product cost of 0.051 $/kWh. Furthermore, increasing the pressure of the (absorption chiller) AC in the (gas turbine) GT cycle from 1.5 to 7.5 results in a sharp decline in net output work. • Dynamic simulation and optimization of a novel energy system is conducted. • Objective optimization is carried out to seek the best solution point. • The system reaches efficiency of 39.5%, the emission of 0.85 kg/kWh. • At the best point system has the LCOP 0.051 $/kWh. [ABSTRACT FROM AUTHOR]

In order to solve the safety problem caused by the abnormal load shedding of the liquefied air energy storage (LAES) system during expansion process, the dynamic simulation model of the 500 kW expansion unit was established. The model is used to simulate normal shutdown and emergency shutdown of the unit, and the changes of parameters such as unit load, valve opening, and rotor speed during the expansion process are analyzed. By studying the influence of valve closing time and rotor time constant on rotor speed and rotor downtime when the unit is shut down due to accident, the value range of valve closing time and rotor time constant which can meet the safety requirements of the unit was proposed. The simulation results show that during the process of shutdown, the highest rotor speed increases first and then decreases with the increase of valve closing time when the rotor time constant remains unchanged, and the valve closing time when the highest speed reaches the maximum value is related to the rotor time constant. When the valve closing time remains unchanged, the highest rotor speed decreases gradually with the increase of the rotor time constant, but the downtime increases. The rotor time constant should be set not less than 7s, and the closing time of the control valve should not exceed 1.5s to ensure the safe operation of the expansion process of the liquefied air energy storage system. • A dynamic model of liquefied air energy storage expansion unit was established. • The influence of valve and rotor parameters when unit break down were obtained. • The range of valve and rotor parameters meeting safety requirements were proposed. [ABSTRACT FROM AUTHOR]