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[Display omitted] • PCM energy storage and PV/T coupled multi-source heat pump systems were combined. • The thermal performance, energy efficiency, and economy of the system were analyzed. • The performance of paraffin C17 and water as energy storage materials were compared. • The performance of six low-temperature PCMs applied to the system were analyzed. • Compared to the existing system, it saves 56 % of energy and 27.7 % of operating costs. To improve the application of renewable energy in the heating zone, as well as to address the limitations of air and water source heat pump. The study presents a PV/T (photovoltaic/thermal) coupled air–water source heat pump system integrated with phase change energy storage. A theoretical analytical model and TRNSYS simulation model of the system were developed to evaluate the thermal performance, energy efficiency and economics of the system. The performance of phase change energy storage was compared with that of water storage, and the effect of different phase change materials on the system characteristics. The results show that the coupled system achieves a seasonal performance factor of 2.3, a 56 % reduction in energy consumption, and a 27.7 % reduction in operating costs compared to a conventional gas boiler system. Comparative analysis with the water storage system showed that the system equipped with phase change materials performed well in terms of energy consumption, operating costs and heating stability. In addition, the density of the phase change material has a biased effect on the overall performance of the system. This paper can provide a reference value for the study of renewable energy heating systems in cold zone. [ABSTRACT FROM AUTHOR]

• Battery transport and logistics to increase renewable use and system flexibility. • Full train transport and carpooling to improve the economics of battery use. • Levelized cost of energy of battery transport & logistics is $0.045/kWh averagely. High share of variable renewable energy is challenging to the traditional power system technically and economically. This calls for a significant increase to the system flexibility, which might result in the costs associated with energy storage and costly upgrades to the traditional transmission and distribution system. This paper presents a multi-stage battery transportation and logistics optimization method to increase the renewable energy consumptions, economics, and mobilities of the battery utilization. A new approach is proposed in which the batteries are charged in the renewable power plants and transported back and forth by railways between the renewable power plants and cities. Based on the forecasts of battery supplies/demands, multiple optimization stages (full train transport and carpooling) are designed by the branch-and-bound algorithm and genetic algorithm respectively. The proposed battery transportation and logistics concept and model are performed using the Beijing-Tianjin-Hebei region in China as an example. The results show that the levelized cost of energy of the battery transportation and logistics model is $0.045/kWh averagely. Also, by the use of mobilized batteries, the proposed battery transportation and logistics model increases the system flexibilities and renewable energy deliveries to the end users without the reinforcement of transmission and distribution system and any constraint from a highly penetrated power system. [ABSTRACT FROM AUTHOR]

• Province-level grid parity potential of wind and solar PV power plants in China. • Techno-economic feasibility of baseload supply in hybrid renewable energy system. • Correlation analysis of system cost and resource potential and complementarity. • Projected Grid parity potential of renewable energy system for baseload supply. To promote the large-scale deployment and grid integration of renewable-based power system, this paper investigates the province-level techno-economic feasibility of wind-photovoltaic-battery hybrid renewable energy system (HRES) for baseload supply application around China. Firstly, the power generation cost and grid parity potential of province-level standalone wind and photovoltaic power plants are assessed. Then, the optimal sizing of province-level HRESs aims to minimize the net present cost and meet the reliability constraint for baseload supply, which is solved by teaching and learning-based optimization. Finally, the techno-economic comparison between different system configurations, the correlation between HRES cost-effectiveness and resource potential as well as resources complementarity, and the grid parity potential of HRES for baseload supply are quantitatively analyzed. The results reveal that: (i) 84.4% of regions in China can achieve solar photovoltaic plant-side grid parity in 2022, while only 15.6% of regions can achieve wind power plant-side grid parity; (ii) HRESs in all regions are technically feasible but not cost-effective for baseload supply; (iii) wind-photovoltaic-battery HRES is the optimal configuration for most regions, indicating that the wind-solar hybridization is more reliable and cost-effective than standalone power plants; (iv) the economic performance of HRES depends mainly on the wind-solar joint resource potentials and the supply-demand relative deviation; (v) investment cost reduction and utilization of energy curtailment are promising to help HRES achieve plant-side grid parity for baseload supply. The findings of this paper can help policy-makers and investors optimally determine the national pathway of renewable energy transition. [ABSTRACT FROM AUTHOR]

• A solar assisted ground source heat pump system with graded thermal energy storage (SAGSHP-GTES) was proposed. • Performance for two SAGSHP systems were simulated and compared in depth. • The SAGSHP system showed a poor η SC of around 19.4%, while the SAGSHP-GTES system showed excellent performance, with a high η SC of around 42.7%, and the problem of soil temperature reduction was solved. • The SAGSHP-GTES system was a feasible and efficient technology for hot water supply in all climate zones of China. The solar assisted ground source heat pump system (SAGSHP) is recognized as an efficient, clean and economical renewable energy technology for hot water supply. However, in SAGSHP systems with an all-day hot water supply, the solar collectors can only heat the water tank with intense solar radiation, which wastes moderate and weak solar resources. In addition, as the SAGSHP system draws heat from the soil for a long time, the soil temperature around the borehole decreases, causing the performance of the GSHP to deteriorate. To solve the above problems, a SAGSHP system with graded thermal energy storage (SAGSHP-GTES) was proposed. This paper investigated the performance and feasibility of the SAGSHP-GTES system, using a case study of hot water supply in a campus dormitory in Changsha, China. Firstly, the drawbacks of solar energy utilization in the conventional SAGSHP system were analyzed. Then, the SAGSHP-GTES system was modeled by TRNSYS, and its operational performance was evaluated and compared with the conventional SAGSHP system. Finally, the feasibility and performance of the SAGSHP-GTES system in different climate zones of China were analyzed. The results showed that the conventional SAGSHP system had a poor solar energy utilization efficiency, with an average thermal efficiency of the SC (η SC) of only around 19.4%. The long period of operation caused the soil temperature to drop from 18.1 °C to 2.78 °C, which led to a decrease in system efficiency and an increase in electricity consumption. By controlling the heat collection of the SC and the graded utilization of solar energy in the SAGSHP-GTES system, a high η SC of around 42.7% was obtained, which improved the system efficiency while eliminating the problem of soil temperature drop. After 15 years of operation, the soil temperature increased from 18.1 °C to 19.9 °C, which led to an increase in the coefficient of performance of the system (COP sys) from 3.77 kW/kW to 3.84 kW/kW and COP GSHP from 3.45 kW/kW to 3.5 kW/kW, and a reduction in electricity consumption from 51,746 kWh to 50,735 kWh. In addition, the conventional SAGSHP system was not feasible in severe cold zones (Harbin) and cold zones (Beijing) of China, where soil temperatures fell below 0 °C and freezing of the circulating fluid occurred, while the SAGSHP-GTES system showed excellent performance in all climatic zones of China and is a feasible and efficient technology for hot water supply. [ABSTRACT FROM AUTHOR]

Currently, the conventional Fushun-type retorting process is the most main way of shale oil production in China. However, it has many disadvantages, such as low resource utilization efficiency and severe environmental pollution inevitably. In this paper, the framework of exergetic life cycle assessment (ELCA) is applied to the shale oil production process, and the indicator of resource utilization efficiency ( γ ) and the indicator of environmental sustainability ( ζ ) were defined to evaluate the performance of the resource utilization efficiency and environmental sustainability. The results indicate that the Aspen Plus simulation results are reasonably consistent with industrial data. The yield of shale oil is 4.52 kg/s by the pyrolysis of 100 kg/s oil shale. The framework of ELCA is applicable for the Fushun-type shale oil production process. During the whole life cycle, the cumulative exergy consumption (CExC) and the Abatement exergy (AbatEx) of pollutants (per kg shale oil produced) are 225.65 MJ and 61.69 MJ, respectively. The retorting stage has the lowest exergy efficiency, 62.49%, followed by the semi-coke gasification stage 63.15%. The γ and ζ values in shale oil production stage are very poor, 42.64% and 32.64%, respectively. When the retorting temperature is set to 500 °C and the saturation of feeding air is controlled to 80 °C, the γ and ζ values of the whole life cycle achieve the greatest potential, 35.85% and 28.05%, respectively. [ABSTRACT FROM AUTHOR]

• The system engineering based on photovoltaic thermal heat pump was constructed. • A new idea for the energy-saving reconstruction of district heating was introduced. • The prediction model of system heating performance was established and optimized. • The equivalent electricity consumption of heating was defined. • The economic performance of energy-saving reconstruction was studied. Actively promoting the reconstruction of clean heating is the key direction of the "Planning for clean heating in winter in northern China (2017–2021)". The photovoltaic thermal heat pump system was introduced in this paper to improve the comprehensive energy efficiency and reduce the operation energy consumption of the heat source system, which provided a new idea for the energy saving reconstruction of clean district heating. In order to verify the feasibility of the energy saving reconstruction by photovoltaic thermal heat pump, following studies were carried out in this paper: First, the integrated energy system engineering based on photovoltaic thermal heat pump was constructed to study the heating performance of the system in winter. Subsequently, the prediction model of heating performance based on back propagation neural network was established and optimized to simulate the heating performance throughout the year. Then, the calculation model of district heating system was established and the evaluation method of system operation energy efficiency and economic performance based on "equivalent electricity consumption of heating" was introduced. Finally, a residential area of Dalian was taking as an example to study the economic performance of energy saving reconstruction of district heating system based on three conventional heat sources by photovoltaic thermal heat pump. The results showed that after the capacity expansion and energy saving reconstruction based on photovoltaic thermal heat pump were conducted, the payback period of energy saving reconstruction investment was 5 years. Besides, with the increase of the configuration ratio of photovoltaic in the system from 1 to 2, the payback period was further shortened to 3 years. [ABSTRACT FROM AUTHOR]

• A higher accuracy engine performance simulation model is developed and calibrated. • A GT-Simulink coupling simulation platform with NSGA II is established. • The SVM model is established and calibrated by the experimental data. • Integrated platform for simulation-optimization and verification is developed. • Maximum fuel consumption and NOx reduction rates reach 5.0% and 70% respectively. This paper is pioneered in developing digital twins by GT-Power software and multi-objective evolutionary optimization (MOEO) using NSGA II algorithm for an Atkinson cycle gasoline engine under China VI emissions standards. Firstly, an experimental investigation is conducted and relevant experimental data is obtained. Based on this, the corresponding 1D GT-Power simulation model is established and calibrated according to the obtained test data. Secondly, the four decision variables including the spark advance angle (SA), exhaust gas recirculation (EGR) rate, exhaust variable valve timing (VVT-E) and intake variable valve timing (VVT-I) are input into the simulation model, the optimal values of the decision variables will be determined via MOEO to minimize NOx emissions and the brake specific fuel consumption (BSFC). Thirdly, based on the data obtained from the scanning test, a machine learning method is used to build an engine performance prediction model through the support vector machine (SVM) regression algorithm. The inputs (control parameters obtained from the optimization process) including SA, EGR, VVT-I and VVT-E are imported to predict the performance output of the engine. The results show that under the engine control parameters obtained by the NSGA II algorithm, the simulation values of engine performance parameters have been greatly optimized, the decreasing extent of fuel consumption is about 5.0%, besides, the decreasing extent of NOx is about 70%. What is more, the increased EER and EEE is up to 6.21% and 2.26%, respectively. And then most of the predicted values obtained by machine learning have been optimized. For BSFC, in general, the simulation value and the predicted value are in good agreement at the smaller value, indicating that the simulation model and the regression prediction model basically achieve the same value at the lower BSFC of the engine. For NOx, the simulated and predicted values have all been optimized. Furthermore, the method and platform developed in this paper will help to carry out a series of related work in the field of vehicle energy flow distribution and optimization when changing different control strategies and optimization methods in the future. Besides, the above work provides a reliable theoretical basis and digital model support for the development of energy-saving and efficient Atkinson cycle engines, which further drives the application of Atkinson cycle engines in new energy vehicles. [ABSTRACT FROM AUTHOR]

• A practical coordination mode of wind, photovoltaic and hydropower is proposed. • A successive mixed integer linear programming model is developed. • Multiple uncertainties of wind and photovoltaic power are considered. • Coordinated operation increases the generation profits and power output stability. Integrating abundant wind and photovoltaic power into large-capacity hydropower plants is an important way for China to promote the consumption of renewable energy on a large scale. This paper establishes a novel coordination mode for a large-scale hybrid energy system including wind, photovoltaic and cascade hydropower plants. Scenario analysis based on Latin hypercube sampling and k-means is used to model the total forecast errors of power output for wind and photovoltaic plants. In order to deal with the imbalanced cost caused by the deviation between the actual power output and the submitted schedule and increase the expected profit, a wind-photovoltaic-cascade hydropower plants coordinated operation model is established. Ecological flow demand for cascade hydropower plants operation is also considered to meet the comprehensive utilization demand of reservoirs. Through several linearization methods and successive approximation technique, the original model is transformed into a successive mixed integer linear programming model. The real-world case studies show that the coordinated operation of the hybrid system can smooth the power output fluctuation and improve the controllability of wind and PV power output. Moreover, compared with the uncoordinated operation, the total expected profit from the coordinated operation increases by 4.66%. Through sensitivity analysis, the influences of penalty factors, electricity price mechanism and ecological flow on the overall performance of the hybrid system are evaluated. [ABSTRACT FROM AUTHOR]

• Comprehensive analyses of six CO 2 booster refrigeration solutions are conducted. • The energy efficiency level of the solutions is revealed, and application feasibility in China is evaluated. • The CO 2 refrigeration system combined with flooded evaporation and parallel compression is optimal. • These CO 2 solutions are recommended for use in northern China, while it is not suitable for hot climate regions. The cold chain industry related to people's livelihood in China is developing rapidly today. The energy efficiency level and environmentally-friendly characteristics of cold chain equipment need to be enhanced and improved urgently. The CO 2 booster refrigeration systems (BRS) are widely used and developed in European supermarkets due to outstanding environmental benefits. The two objectives of this paper are to reveal the energy efficiency level of six CO 2 BRS solutions under five typical Chinese climate conditions, as well as to objectively evaluate the application feasibility in Chinese supermarkets to inform manufacturers. Comprehensive analyses consist of energy efficiency, economy, and environment are conducted. The results show that the CO 2 BRS assisted with flooded evaporation and parallel compression has the best performance. For most cities, its annual energy efficiency ratio improved by 3.9 ~ 23.2%, the payback period is averaging less than 5.5 years, and the total equivalent warming impact reduced by 11.9 ~ 52.9% compared to the reference systems. The CO 2 BRS solutions are proved to be good alternatives and recommended for use in northern China, while it is not suitable for hot climate cities, such as Guangzhou, and further modifications are required. For the reference systems, the R134a/CO 2 cascade refrigeration system can be considered a short-term transition solution in southern China, considering its relatively decent performance. [ABSTRACT FROM AUTHOR]

• Renewable energy integrated cross-regional hydrogen supply route is proposed. • Economic, energy and environmental performance, focusing on hydrogen production and provision. • A methodology for analyzing hydrogen supply routes in production, delivery and refueling stage. To decarbonize transportation sector, one of the most promising solution is using green hydrogen as an alternative transport fuel to gasoline and diesel. For countries with uneven distribution of renewable energy, it is necessary to evaluate both cross-regional and on-site green hydrogen supply pathways. The goal of this paper is to identify the economic, energy and environmental aspects of potential solar energy integrated green hydrogen supply routes including cross-regional and on-site options for hydrogen refueling stations in China. Four green hydrogen supply routes are proposed in our study: 1) northwest solar power integrated methanol production as hydrogen carrier coupled with cross-regional delivery to hydrogen refueling station for onsite hydrogen production pathway (Route I), 2) northwest solar power integrated hydrogen production coupled with gas H 2 cross-regional delivery pathway (Route II), 3) northwest solar power integrated hydrogen production coupled with liquid H 2 cross-regional delivery pathway (Route III) and 4) on-site solar energy -powered hydrogen refueling station (Route IV). The results indicate that solar energy integrated hydrogen supply pathways have remarkable CO 2 emission reduction effect. Route I, Route II, Route III and Route IV can reduce CO 2 emission by 83%, 59%, 96%, and more than 99% respectively, compared with the conventional coal gasification for hydrogen production coupled with gas H 2 delivery to nearby fueling station pathway (coal-H 2 delivery). In term of energy consumption, Route III and Route IV show advantage in energy efficiency, which consumes 27% and 38% less energy compared with coal-H 2 delivery, respectively. In economic aspect, the four routes are not competitive with conventional coal-H 2 delivery, but from the perspective of green hydrogen supply, Route I and Route III are economically competitive compared with on-site solar energy-powered hydrogen refueling station (Route IV). If considering carbon tax in 2030 reported by World Bank, Route I will have potential to be economically competitive with coal-H 2 delivery. Route III is also expected to be economically feasible as the solar energy electricity price and liquefaction cost further decline. [ABSTRACT FROM AUTHOR]

• Three different flexibility measures in a distributed energy system were modeled. • A dynamic economic dispatch model considering multi flexibility measures was proposed. • The effects of price-driven demand response program on consumer and power grid were analyzed. • The different ancillary services for power grid provided by the distributed energy system were discussed. Distributed energy systems are a promising integrated energy technology due to their energy efficiency and environment benefits. However, the increasing complexity of distributed energy systems, integrated with variable renewable energy, requires more intelligent operational methods to achieve economic efficiency, and reduce negative effects on the power grid. In this study, multi-flexibility measures are used to facilitate interaction between a distributed energy system and the power grid. First, a mixed-integer and linear programming model is proposed for optimizing the dispatch of a distributed energy system with minimum operational costs. Then, the price-driven demand response is performed by coordinating flexibility measures optimally in the operation of a distributed energy system in Guangdong province, China. A detailed case study is conducted in which three types of flexibility measures are modeled, and their effects on end-users and power grid are discussed. The optimal results show that each flexibility measure can well response to the time-of-use price. The distributed energy system's operating costs were reduced by 1.7–12.9% when individual flexibility measures were applied and 19.6% when all the flexibility measures were implemented. However, the price-driven demand response program significantly decreases the tie-line's (i.e. the power line connecting the distributed energy system to the main power grid) power stability. Three types of ancillary services based on multi-flexibility measures in a distributed energy system are proposed in this paper and optimized based on the ε - constraint method to facilitate smooth interaction between the power grid and a distributed energy system. The Pareto frontiers indicate that all the operational costs decrease along with the ancillary service. The technical and economic boundaries of each ancillary service are further determined, which can help distributed energy system operators make more informed operational decisions. [ABSTRACT FROM AUTHOR]

• A comprehensive performance of R134a-TCS, R744-TCS and R744-PC-TCS is compared. • Five typical representative cities are selective to represent five major climate zones in China. • The seasonal performance of three systems in different climates is analyzed. • The proposed R744-PC-TCS has a great potential for the supermarket refrigeration application. In this paper, a R744 Partial Cascaded Two-stage Compression Refrigeration System (R744-PC-TCS) was proposed and evaluated in terms of coefficient of performance (COP) and seasonal energy efficiency ratio (SEER) when it operated in five typical climate representative cities in China. R134a and CO 2 are used as refrigerants in this study. The results show that the SEER of the supermarket refrigeration system in the severe cold zone and the mild zone is higher than that of the other climate zones. The performance of the R134a Two-stage Compression Refrigeration System (R134a-TCS) performs better than the R744 Two-stage Compression Refrigeration System (R744-TCS). However, both COP and SEER of the CO 2 system can be improved significantly by adding a parallel compressor, as well as using the single-stage vapor compression partial cascade cycle for subcooling under the practical working conditions (such as R744-PC-TCS). The greatest improvement of R744-PC-TCS can be achieved in the areas with poor climatic conditions, in which COP increases by 48.9% at an ambient temperature of 39 °C, and SEER increases by the maximum of 21.5% in hot summer and warm winter zones, compared with that of R744-TCS. Compared with R134a system, the R744-PC-TCS basically achieves the comparable or even higher energy efficiency. It can be concluded that the proposed R744-PC-TCS has a great potential to replace the existing R134a refrigeration system for the supermarket refrigeration application. [ABSTRACT FROM AUTHOR]

• Three CO 2 two-stage compression based refrigeration systems are compared. • Demonstrated the feasibility of CTRS + PC + PCRS. • Five typical climate representative cities in China are considered. • The new concepts of SEER and ESS were proposed. To discuss the application feasibility of CO 2 two-stage compression refrigeration system with parallel compression and solar absorption partial cascade refrigeration system (CTRS + PC + PCRS), a CO 2 two-stage compression refrigeration system was proposed for the purpose of commercial supermarket application. Some important parameters, including coefficient of performance (COP), energy saving share (ESS), and partial seasonal energy efficiency ratio (PSEER) are taken as the objective functions to make comparisions among basic CO 2 two-stage compression refrigeration system (BCTRS), CO 2 two-stage compression refrigeration system with parallel compression (CTRS + PC) and CTRS + PC + PCRS. China's five typical climate representative cities (Beijing, Harbin, Wuhan, Guangzhou, Chengdu) are considered in this study. The results indicated that the COP of CTRS + PC + PCRS increased by 47.28% and 14.28% in Harbin area, compared with BCTRS and CTRS + PC, respectively. When operating under subcritical and transcritical conditions, the maximum COP of CTRS + PC + PCRS increased by 31.71% (Wuhan) and 47.28% (Harbin) respectively compared with the BCTRS, and increased by 12.27% (Harbin) and 7.78% (Wuhan) respectively compared with the CTRS + PC. The ESS and PSEER were introduced to evaluate the energy-saving effect of the solar partial cascade system (PCRS) and the performance of the composite system, and the maximum ESS is 0.19 (Beijing). Compared with the BCTRS and the CTRS + PC, the PSEER is increased by 22.54% and 2.81%, respectively. The research results in this paper provide a theoretical basis for the application of CO 2 two-stage compression refrigeration system in the application of commercial supermarket. [ABSTRACT FROM AUTHOR]