Dynamic Payback Period Research Articles

Green hydrogen production and liquefaction using offshore wind power, liquid air, and LNG cold energy

Coastal regions have abundant off-shore wind energy resources, and surrounding areas have large-scale liquefied natural gas (LNG) receiving stations. From the engineering perspectives, there are limitations in unstable off-shore wind energy and fluctuating LNG loads. This article offers a new energy scheme to combine these 2 energy units, which uses surplus wind energy to produce hydrogen, and use LNG cold energy to liquefy and store hydrogen. In addition, in order to improve the efficiency of utilizing LNG cold energy, and reduce electricity consumption for liquid hydrogen (LH2) production at coastal regions, this article introduces the liquid air energy storage (LAES) technology as the intermediate stage, which can stably store the cold energy from LNG gasification. A new scheme for LNG-LAES-LH2 hybrid LH2 production is built. The case study is based on a real LNG receiving station at Hainan province, China, and this article presents the design of hydrogen production/liquefaction process, and carries out the optimizations at key nodes, and proves the feasibility using specific energy consumption and exergy analysis. In a 100 MW system, the liquid air storage round-trip efficiency is 71.0% and the specific energy consumption is 0.189 kWh/kg, and the liquid hydrogen specific energy consumption is 7.87 kWh/kg and the exergy efficiency is 46.44%. Meanwhile, the corresponding techno-economic model is built, and for a LNG-LAES-LH2 system with LH2 daily production 140.4 tons, the shortest dynamic payback period is 9.56 years. Overall, this novel hybrid energy scheme can produce green hydrogen using a more efficient and economical method, and also can make full use of surplus off-shore wind energy and coastal LNG cold energy.

Multi-criteria thermo-economic analysis of solar-driven tri-generation systems equipped with organic Rankine cycle and bottoming absorption refrigeration and Kalina cycles

Optimal thermo-economic integration of renewable energy sources with multi-generation energy systems is a prime research topic today. The present study proposes a multi-criteria evaluation method of such integration, based on combined heating and power (CHP), and combined cooling and power (CCP) scenarios, for three different solar intensities. Three novel solar-driven tri-generation systems are selected. They include different organic Rankine cycle (ORC) architectures and a Kalina cycle system (KCS) and a double-effect absorption refrigeration cycle as bottoming cycles. Evaluation of the tri-generation systems, both with and without the KCS system, indicates a performance improvement of up to 23% in various thermoeconomic characteristics when the KCS system is present. Selection of the suitable tri-generation system for each condition and optimization of the working fluid are carried out based on a multi-attribute decision-making method. P-xylene is found as the optimal organic working fluid for ORC and ORC (ORC integrated with internal heat exchanger) based systems, and benzene for the regenerative ORC-based system in both CHP and CCP scenarios. Multi-criteria analysis shows that ORC-based system outperforms other systems with net outranking flow of 0.44 (0.39) for CHP (CCP) application. The optimal configuration gives 95.6 M$ and 1.99 years for net present value and dynamic payback period, and 83.03% and 34.55% for energy and exergy efficiencies, respectively.

Economic feasibility assessment of a solar aided liquid air energy storage system with different operation strategies

In response to severe environmental problems, the proportion of new energy consumption worldwide is on an unprecedented upward trend, bringing energy storage technologies into focus. Among various energy storage systems, the solar aided liquid air energy storage (SALAES) system shows great prospects for development due to its cleanliness and high efficiency. This paper develops a basic operation strategy based on the idea of peak and valley reduction, considering the temporal fluctuation characteristics of solar energy. Further, operation modes for replacing the oil-air heat exchangers are proposed and an optimized strategy is developed accordingly. Real weather data of Beijing are used to estimate the annual power output of each system, and economic analyses are carried out on this basis using the levelized cost of storage (LCOS) method. The results show that the introduction of solar energy can reduce the LCOS of the liquid air energy storage system by 4.1 %–13.67 % and the proposed optimized operation strategy can increase the annual power output, resulting in a 0.2 %–0.4 % reduction in LCOS compared to the basic operation strategy. In addition, the impact of the molten salt tank capacity on the investment and return of the SALAES system is investigated. The optimal molten salt tank capacity obtained in this paper is 5 h, with the lowest LCOS of 0.1477 $/kWh and the shortest dynamic payback period of 10.29 years when operating with the optimized strategy.

Tech-economic analysis of liquid air energy storage - A promising role for carbon neutrality in China

Liquid air energy storage (LAES), a green novel large-scale energy storage technology, is getting popular under the promotion of carbon neutrality in China. However, the low round trip efficiency of LAES (~50 %) has curtailed its commercialization prospects. Limited research is conducted about the economic analysis, especially on the end-user side, as some national electricity policies may be friendly to the development of LAES. Therefore, a practical LAES system with 100 MW peak electricity output and a 501 MW heating supply is proposed. A typical example system built in Huitong District, Hebei Province, is given. The simple payback period and dynamic payback period are respectively 10.4 years and 6.5 years, while the levelized cost of storage is 0.11 $/kWh and the levelized cost of energy is 0.32 $/kWh. The subsequent economic analyses show that the payback period of the LAES system at the end-user side can be reduced by half compared to the LAES system at the power grid dispatching side, owing to its diversified incomes. There is an optimal peak regulation depth of 20 % in the thermal/renewable power plants integrated with LAES under the effects of the national electricity price policies. Finally, the potential carbon-emission economy of LAES should be taken seriously, particularly in the likely event that the carbon trading market is established. Among the four typical provinces in China, Hubei Province stands out with possible earnings of 0.07–0.074 $M/year, attributed to the sound carbon-emission basis and policies. Overall, the study provides a profound understanding of the application forms of LAES with the assistance of Chinese government policies, which will be vital for the development of energy storage technologies in the future.

Thermodynamic and Economic Analysis of a Liquid Air Energy Storage System with Carbon Capture and Storage for Gas Power Plants

Liquid air energy storage (LAES) technology is helpful for large-scale electrical energy storage (EES), but faces the challenge of insufficient peak power output. To address this issue, this study proposed an efficient and green system integrating LAES, a natural gas power plant (NGPP), and carbon capture. The research explores whether the integration design is theoretically feasible for future adoption in operating the LAES system and NGPP. The effect of the charging pressure, the number of air expansion stages, and electricity prices on the overall thermodynamic and economic characteristics are investigated. The round-trip efficiency and the exergy round-trip efficiency of the proposed system are 47.72% and 69.74%, respectively. The calculations show that the minimum dynamic payback period for such a project is 3.72 years, and the lowest levelized cost of electricity is 0.0802 USD·kWh−1. This work provides a reference for peak-shaving power stations with energy storage and carbon capture.

Heating Performance and Economic Analysis of Solar-Assisted Cold-Water Phase-Change-Energy Heat Pump System in Series and Parallel Connections

To study the heating performance of a solar-assisted cold-water phase-change-energy heat pump system, its heating performance under series and parallel connections is simulated for a community in Harbin, the influence of ice thickness on the different operation modes is analyzed, and the economy of the system is calculated for series and parallel connections in this paper. The results show that the water supply temperature is higher and more uniform in the parallel operation, and more terminal heat is supplied; the ice thickness has more of an influence on the series connection compared to the parallel connection; and the dynamic payback period is 6.72 years for the series connection and 7.28 years for the parallel connection. This case study can serve as a guide for practical engineering application projects and act as a reference for heating and economic data for the promotion of this heat pump system.

Comparative study on flexibility enhancement of combined heat and power for wind power accommodation

Flexibility enhancement of coal-fired combined heat and power units is an essential approach for improving the wind power accommodation and a significant low-carbon way to achieve clean urban heating. To consume excess wind power, this paper proposed a novel combined heat and power system integrated with the various flexible technologies. The EBSILON software was applied for modeling the proposed thermal systems and analyzing the thermal performance under different operating conditions. On this basis, the mechanism of their heating compensation and wind power consumption was revealed and the indicator, the heating compensation capacity, was presented considering from both peak shaving and coal-savings perspectives. Compared with the conventional system, the wind power accommodation rate of the novel system had a maximum increment of 31.7% and the standard coal consumption had a maximum reduction of 14.3%. Meanwhile, by adding dynamic payback period and internal rate of return, the techno-economic performances were more reasonable and precise. The results showed that the heating compensation capacities of absorption heat pumps, low-pressure cylinder of turbine removal and thermal energy storage with extracted steam from turbine are 0.29 t/MWh, 0.26 t/MWh, and 0.25 t/MWh, respectively, which are better than that of other technologies. The net annual revenue of thermal energy storage system could reach 3.87 M$, 0.57 and 0.37 M$ higher than that of low-pressure cylinder of turbine removal and absorption heat pumps, respectively. It can be concluded that thermal energy storage can be the best to balance the peak shaving demand and techno-economic performance. In all, the proposed systems provided a promising method for the flexibilization of coal-fired combined heat and power units alongside new renewable systems.

Thermodynamic and economic analysis of a novel design combining waste tire pyrolysis with silicon production waste heat recovery and organic Rankine cycle

In this study, a novel design highly integrated with waste tire pyrolysis, silicon production waste heat recovery, and organic Rankine cycle has been developed. In the hybrid configuration, waste tires are converted into useful pyrolysis oil and carbon through pyrolysis. At the same time, the waste heat generated by silicon production is recovered to generate additional electricity, and provides electricity and heat for tire pyrolysis, allowing the subsystems to be closely coupled and achieving self-sustain the energy consumption of the entire system. And a thermodynamic and techno-economic of the hybrid system is investigated based on the simulation results. The thermodynamic results show that the energy efficiency and exergy efficiency of the proposal can achieve 64.14% and 72.13%. The techno-economic results indicate that the proposal has a short dynamic payback period of 3.79 years and a high net present value of 26,231.40 k$. The results confirmed that the novel design is advantageous from the perspectives of both thermodynamics and economics.

Economic analysis of whole-county PV projects in China considering environmental benefits

Distributed photovoltaic generation is an important measure to address climate change and boost rural revitalization. In the context of new energy grid parity, driving rooftop distributed photovoltaics to participate in the green power trading market is an inevitable necessity for energy and market development. Thus, based on the cost-benefit theory, this paper considers both the green power trading market and the carbon trading market in an integrated manner and develops an economic efficiency model that takes taxation into account. The net present value (NPV), dynamic payback period (DPP) and internal rate of return (IRR) were chosen for the economic feasibility analysis, comparing green power trading with whole power carbon trading, and sensitivity analysis. An analysis of a whole-county rooftop DPVG pilot in Northeast China as an example shows that the whole-county rooftop DPVG project is economically viable. After participating in green power trading, the NPV reaches $5956.083 thousand, IRR is 13.629 % and DPP is shortened from 21.517 years to 14.248 years, fully reflecting the value of the environmental attributes of green power. In addition, sensitivity analysis shows that the green power trading price and the self-consumption contract tariff are non-negligible factors, and it is proposed that the green power trading price awaits enhancement. Finally, relevant policy recommendations to promote the development of whole-county DPVG are put forward. The findings of the study provide new directions for the scaled development of new energy sources, as well as effective references for investment decision-makers.

Thermodynamic and economic evaluation on a novel cogeneration system based on energy sectionalized closed utilization method

Based on the characteristics of temperature evolution during steam energy release, the idea of energy sectionalized conversion is proposed, and a dual-stage organic Rankine cycle (DORC) that can be respectively matched with varying temperature process and constant temperature process of the steam is constructed to enhance effective energy input from the energy input end. Besides, an absorption heat pump (AHP) is considered as the bottom cycle to recycle all exhaust vapor waste heat of DORC to achieve closed utilization of heat energy. The coupling of DORC and AHP to form a DORC-AHP cogeneration system can simultaneously improve the energy conversion efficiency of medium–low temperature steam from both the energy quality and quantity perspectives. Energy, exergy and economic assessments are carried out to disclose the superiority of the new energy utilization method. Compared with the singular-stage organic Rankine cycle (SORC) and DORC, the thermal efficiency of DORC-AHP is enhanced by 84.74% and 84.15%, the exergy efficiency is enhanced by 10.48% and 8.36%, and the exergy loss is decreased by 912.15 kW and 687.25 kW as the saturation temperature of the steam, superheat degree and mass fraction of R600 are 132℃, 40℃ and 0.10. Furthermore, there is an optimal saturation temperature and superheat degree of the steam to make the exergy efficiency of new cogeneration system the highest. Meanwhile, there is an optimal steam saturation temperature that enables AHP to assimilate all the exhaust vapor waste heat of DORC with the lowest driving heat source flow rate ratio between AHP and DORC. In addition, compared with the SORC and DORC, the exergy cost of new cogeneration system is decreased by 0.0007 $/kWh and 0.0006 $/kWh, multiple of investment cost (MOIC) is increased by 5.02 and 5.35, and dynamic payback period (DPP) is shortened by 2.46 years and 3.00 years. The DPP and MOIC of DORC-AHP system are both gradually close to those of SORC and DORC with the rise of electricity price. The results indicate that the new energy sectionalized closed conversion pattern demonstrates distinct superiority in the thermal and economic performance. The study achievement can lay a theoretical foundation for improving medium–low temperature steam energy utilization degree.

Implementing a one-dimensional quick model for dynamic simulation and economic analysis of a forced circulation crystallizer

Forced circulation crystallizer is one of the main contributors in Zero Liquid Discharge wastewater treatment processes. This technology enables the extraction of pure water from wastewater and separates impurities in the form of crystals. In the present study, a fast one-dimensional (nodal) model with high accuracy is introduced to predict the dynamic performance of the crystallization process in an FC crystallizer. Besides, to design and optimize a crystallizer, the parameters affecting the system performance should be evaluated from thermodynamic and economic perspectives. For this purpose, the developed model is used to investigate the crystallizer thermo-economic performance. Results show that the performance of the crystallizer system has the most significant sensitivity to varying the inlet feed concentration, suspension concentration, and rotational speed of the circulation pump. Increasing the suspension concentration reduces the mean diameter of output crystals. Also, increasing the pump rotational speed by about two times decreases the mean size of output crystals by approximately 41.39 %. From an economic point of view, increasing the heat input has a significant effect on the reduction of the dynamic payback period. Also, increasing the inlet feed concentration by 36 % leads to a 7.84 % increase in the internal rate of return.

Capacity and operation optimization of a low-temperature nuclear heating system considering heat storage

Integrating heat storage devices with the pool-type low-temperature heating reactor (PLTHR) can improve the flexibility of PLTHR for load following. A novel low-temperature nuclear heating system (HST-NHS) is proposed, which combines the DHR-400 heating reactor system, a heat storage tank (HST), and a gas boiler (GB) to achieve real-time matching between heating supply and demand. A mixed integer nonlinear programming (MINLP) optimization model with the annual cost (AC) as the optimization objective is established. An operation strategy that considers the device priority is proposed. The capacity and operation of HST-NHS are simultaneously optimized using the CPLEX solver. The optimization results indicate that an HST with a rated capacity of 1324.14 MWh and a GB with a rated capacity of 201.69 MW can provide the operational flexibility needed for the HST-NHS throughout the heating period. When compared with comparison schemes 1 (DHR-400 and HST), 2 (DHR-400 and GB), and 3 (pure gas boiler heating system), HST-NHS achieves significant annual cost savings. Finally, a sensitivity analysis of device price and fuel price is conducted, revealing that the unit price of the DHR-400 heating reactor system and natural gas price are the main factors affecting the AC and dynamic payback period (DPP) of HST-NHS. This work offers theoretical guidance for the subsequent engineering application of the DHR-400 heating reactor system.

A novel LH2/GH2/battery multi-energy vehicle supply station using 100% local wind energy: Technical, economic and environmental perspectives

With the gradual maturity of wind power technology, China's wind power generation has grown rapidly over the recent years. However, due to the on-site inconsumable electricity, the phenomenon of large-scale “wind curtailment” occurs in some areas. In this paper, a novel hybrid hydrogen/electricity refueling station is built near a wind farm, and a part of the surplus wind power is used to charge electric trucks, and the other part of the surplus power is used to produce “green hydrogen”. According to real-time load changes, different amounts of liquid hydrogen and gas hydrogen can be properly coordinated to provide timely energy supply for hydrogen trucks. For a 400 MW wind farm in the western Inner Mongolia, China, the feasibility of the proposed system has been carried out based on the sensitivity and reliability analysis, the static and dynamic economic modeling, with an entire life cycle analysis. Compared to the conventional technology, the initial investment of the proposed scheme (700.07 M$) decreases by 13.97%, and the dynamic payback period (10.93 years) decreases by 25.87%. During the life cycle of the proposed system, the accumulative NPV reaches 184.63 M$, which increases by 3.14 times compared to the case by conventional wind technology.

Capacity optimization of hybrid renewable energy system considering part-load ratio and resource endowment

To help decarbonize the energy sector, a hybrid renewable energy system consisting of wind, solar, and biogas-fueled combined cooling, heating, and power components was investigated. In such systems, thermal and electrical energy are inextricably linked, the local resource endowment is critical, and the main components can be run at part-load. Taken together, these factors make it difficult to optimize a hybrid renewable energy system. To address this issue, we propose a novel method which combines orthogonal design and intelligent algorithms to optimize the capacity of each unit within the system. The optimization results show that the initial investment cost and the dynamic payback period can be reduced by 24.8% and 23.5% compared with optimal orthogonal capacity, and the emission reduction rate increases by 2.3%. In addition, by considering part-load operation and the local resource endowment, it is possible to achieve a 52.2% increase in comprehensive value of the whole system and a 40.4% reduction in investment cost as compared to a simplified model. Importantly, a regional analysis justifies that the proposed evaluation method provides a versatile assessment tool for system optimization.

Thermo-economic analysis of a waste-to-energy assisted carbon capture system for a coal-fired power plant

An advanced energy system was proposed that hybridizes a waste-to-energy plant and a coal-fired power plant accompanied by a carbon capture and storage system. Compared with previous similar systems, the innovations of this system include: (1) a new approach to municipal solid waste energy use was proposed: energy supply for carbon capture and storage systems; (2) the heat integration design of the novel system was conducted based on the principle of energy cascade utilization, and high energy efficiency was achieved; (3) the equipment of the waste-to-energy plant is streamlined due to system integration, reducing investment costs. The main parameters of several existing reference systems were collected, and the benefits of the proposed systems were analyzed, compared and evaluated in terms of energy, exergy and economy. The results show that the net electric efficiency of the integrated system is improved by 1.75%, the electricity generation is increased by 14.37 MW, and at a discount rate of 5%, the dynamic payback period of the waste-to-energy system can be advanced by about 2.34 years. These indicators demonstrate the engineering potential of the proposed system and can be used as a reference for similar investment projects.

Optimization of combined heat and power cogeneration via modification of low-pressure regenerative system with absorption heat exchanger

The large exergy loss during heat transfer is a key problem for the combined heat and power cogeneration. Instead of the traditional heat source coming from high-grade extracted steam at the outlet of the intermediate-pressure turbine, a novel combined heat and power configuration is proposed for large heat demand by modifying the low-pressure regenerative system. By adding a new LP unit with sufficient extracted flow and heat exchange, a part of the heat source from high-grade extracted steam at the outlet of the intermediate-pressure turbine is replaced by low-grade extracted steam within the LP turbine, avoiding the off-design operation of the LP turbine in the traditional combined heat and power configuration. In addition, the new combined heat and power configuration is optimized by introducing an absorption heat exchanger. The absorption heat exchanger lowers the return temperature of the PHS, which further reduces the energy grade of the heat source. The thermodynamic results show that the electric efficiency of the novel combined heat and power configuration is increased by 4.24% in total at a given heat demand of 241.37 MW. Exergetic results reveal that the exergy loss of two heat exchange links is drastically reduced from 30.47 MW and 26.04 MW to 8.80 MW and 11.81 MW respectively. An economic analysis of the new CHP configuration indicates that the dynamic payback period counteracting the investment increment is only 2.15 years, and the net present value increment over a 25-year period can reach $55.818 million.

Analysis of modified CO2 based combined power and ejector-expansion refrigeration cycle with dual evaporators activated by engine exhaust

ABSTRACT In this research, a combined system consisting of a supercritical CO2 Brayton cycle and an ejector-expansion refrigeration cycle with dual evaporators is presented with the aim to harness the engine exhaust heat effectively. Cascade ejectors are adopted to further reduce the destruction caused by the isenthalpic expansion process, which also can be considered as pressure recovery process. Comparative analysis in terms of thermodynamic and economic is performed between the previously reported system and the modified system under the combined power, refrigeration, and freezing mode (mode 1) and combined refrigeration and freezing mode (mode 2). It is found that improvements of 0.57% and 10.22% in exergy efficiency under mode 1 and mode 2 were achieved by the modified system, respectively, and the sum unit cost of product is reduced by 7.72% compared to the basic system. In the optimized condition, cooling capacities of 18.79 kW and 33.80 kW can be provided for refrigerated zone and freezing zone, respectively. And the exergy efficiency and sum unit cost of product of the system are 16.95% and 108.64 $/GJ, respectively, with a dynamic payback period of 4.994 years.

Design and Performance Evaluation of Integrating the Waste Heat Recovery System (WHRS) for a Silicon Arc Furnace with Plasma Gasification for Medical Waste.

A hybrid scheme integrating the current waste heat recovery system (WHRS) for a silicon arc furnace with plasma gasification for medical waste is proposed. Combustible syngas converted from medical waste is used to drive the gas turbine for power generation, and waste heat is recovered from the raw syngas and exhaust gas from the gas turbine for auxiliary heating of steam and feed water in the WHRS. Meanwhile, the plasma gasifier can also achieve a harmless disposal of the hazardous fine silica particles generated in polysilicon production. The performance of the proposed design is investigated by energy, exergy, and economic analysis. The results indicate that after the integration, medical waste gave rise to 4.17 MW net power at an efficiency of up to 33.99%. Meanwhile, 4320 t of the silica powder can be disposed conveniently by the plasma gasifier every year, as well as 23,040 t of medical waste. The proposed design of upgrading the current WHRS to the hybrid system requires an initial investment of 18,843.65 K$ and has a short dynamic payback period of 3.94 years. Therefore, the hybrid scheme is feasible and promising for commercial application.

Thermodynamics, flexibility and techno-economics assessment of a novel integration of coal-fired combined heating and power generation unit and compressed air energy storage

The new power system with increasingly high renewable energy proportion necessitates the combined heating and power (CHP) generation units to provide more flexibility. With full consideration of operation characteristics, this paper firstly proposes an advanced coal-fired CHP-CAES system consisting of a 350 MW coal-fired CHP unit and a 30 MW CAES system, which realizes more efficient energy utilization and enhances the system adjusting flexibility through thermal cycles integration and energy comprehensive utilization. The thermodynamic models and multi-dimensional performance analysis models are separately established. Based on that, the comparative study is conducted for two CHP-CAES configurations and the stand-alone CHP unit. With 80% heating load, the minimum power ratio is lowered by 11.69% rated power and the maximum power output is increased by 6.35% rated power, and 27.26 tons of coal can be saved for a single cycle compared with the stand-alone CHP unit. The results also demonstrate that the system still has superiority when the load ratio changes. Techno-economic evaluations for a typical application scene show that the dynamic payback period of the proposed system is shortened by 10.41 years compared with the reference separate CHP-CAES system. These results show that the proposed system presents better performance in energy utilization, enhancing flexibility, realizing clean and low-carbon heating as well as techno-economics. In addition, parametric analysis is implemented to find the influence of CAES parameters on the system. It is found that increasing the expander inlet temperature and air storage pressure can further enhance the system round-trip performance. Yet, the investment cost increases greatly for higher storage pressure and the payback period will be lengthened. Furthermore, the system advantages are strengthened with a CAES system of greater capacity. Nevertheless, we find that the deep coupling in the thermodynamic cycle of the two systems results in an upper capacity for the integrated CAES system, and it is nearly 35 MW for the studied system. These regularities and conclusions can provide theoretical guides and directions for the customized CAES system design with the purpose to integrate with a coal-fired CHP unit.

Performance of a CO2-mixture cycled energy storage system: Thermodynamic and economic analysis

Liquid state storage is one of the most features for CO2 energy storage. How to effectively liquefy the gaseous CO2 after generating the power severely restricts its further development. In this paper, the refrigerants are employed as the additives to the CO2 working fluid and utilizing the temperature glide of zeotropic mixtures the two-tank cold energy storage can be designed to complete the condensation and evaporation processes of the gaseous working fluid. The numerical simulations for the system are completed by using an in-house code with the built mathematical models. The round trip efficiency and the economic indicators including levelized cost of storage, net present value, dynamic payback period and savings to investment ratio are analyzed in detail. The results demonstrate that increasing the mass fraction of refrigerants is negative to the system efficiency. The efficiency of the system with working fluid CO2/R32 is obviously insensitive to the additive mass fraction, with just a 3.5% change ratio when mass fraction of R32 is varied from 0.05 to 0.5. There is always an optimized mass fraction to reach the best economic performance for each additive. The mixtures CO2/R32 and CO2/R161 are firstly recommended as the working fluid pairs of the designed system with the suggested mass compositions of about 0.65/0.35 and 0.85/0.15, respectively. The charge pressure is advocated at 15 MPa and the discharge pressure is suggested at 13–16 MPa. Furthermore, the proposed energy storage system is favorable to adapt the surrounding temperatures.