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  • REVIEW ARTICLE
    Zerong XING, Junheng FU, Sen CHEN, Jianye GAO, Ruiqi ZHAO, Jing LIU
    Frontiers in Energy, 2022, 16(1): 23-48. https://doi.org/10.1007/s11708-022-0815-y

    Recent years have witnessed a rapid development of deformable devices and epidermal electronics that are in urgent request for flexible batteries. The intrinsically soft and ductile conductive electrode materials can offer pivotal hints in extending the lifespan of devices under frequent deformation. Featuring inherent liquidity, metallicity, and biocompatibility, Ga-based room-temperature liquid metals (GBRTLMs) are potential candidates to fulfill the requirement of soft batteries. Herein, to illustrate the glamour of liquid components, high-temperature liquid metal batteries (HTLMBs) are briefly summarized from the aspects of principle, application, advantages, and drawbacks. Then, Ga-based liquid metals as main working electrodes in primary and secondary batteries are reviewed in terms of battery configurations, working mechanisms, and functions. Next, Ga-based liquid metals as auxiliary working electrodes in lithium and nonlithium batteries are also discussed, which work as functional self-healing additives to alleviate the degradation and enhance the durability and capacity of the battery system. After that, Ga-based liquid metals as interconnecting electrodes in multi-scenarios including photovoltaics solar cells, generators, and supercapacitors (SCs) are interpreted, respectively. The summary and perspective of Ga-based liquid metals as diverse battery materials are also focused on. Finally, it was suggested that tremendous endeavors are yet to be made in exploring the innovative battery chemistry, inherent reaction mechanism, and multifunctional integration of Ga-based liquid metal battery systems in the coming future.

  • RESEARCH ARTICLE
    Chuanke LIU, Zhizhu HE
    Frontiers in Energy, 2022, 16(3): 460-470. https://doi.org/10.1007/s11708-022-0825-9

    In this paper, a novel liquid metal-based minichannel heat dissipation method was developed for cooling electric devices with high heat flux. A high-performance electromagnetic induction pump driven by rotating permanent magnets is designed to achieve a pressure head of 160 kPa and a flow rate of 3.24 L/min, which could enable the liquid metal to remove the waste heat quickly. The liquid metal-based minichannel thermal management system was established and tested experimentally to investigate the pumping capacity and cooling performance. The results show that the liquid metal cooling system can dissipate heat flux up to 242 W/cm2 with keeping the temperature rise of the heat source below 50°C. It could remarkably enhance the cooling performance by increasing the rotating speed of permanent magnets. Moreover, thermal contact resistance has a critical importance for the heat dissipation capacity. The liquid metal thermal grease is introduced to efficiently reduce the thermal contact resistance (a decrease of about 7.77 × 10−3 °C/W). This paper provides a powerful cooling strategy for thermal management of electric devices with large heat power and high heat flux.

  • NEWS & HIGHLIGHTS
    Wenzhong SHEN, Yixin ZHAO, Feng LIU
    Frontiers in Energy, 2022, 16(1): 1-8. https://doi.org/10.1007/s11708-022-0816-x
  • RESEARCH ARTICLE
    Lin LI, Cehuang FU, Shuiyun SHEN, Fangling JIANG, Guanghua WEI, Junliang ZHANG
    Frontiers in Energy, 2022, 16(5): 812-821. https://doi.org/10.1007/s11708-020-0669-0

    The development of highly active nitrogen-doped carbon-based transition metal (M-N-C) compounds for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) greatly helps reduce fuel cell cost, thus rapidly promoting their commercial applications. Among different M-N-C electrocatalysts, the series of Fe-N-C materials are highly favored because of their high ORR activity. However, there remains a debate on the effect of Fe, and rare investigations focus on the influence of Fe addition in the second heat treatment usually performed after acid leaching in the catalyst synthesis. It is thus very critical to explore the influences of Fe on the ORR electrocatalytic activity, which will, in turn, guide the design of Fe-N-C materials with enhanced performance. Herein, a series of Fe-N-C electrocatalysts are synthesize and the influence of Fe on the ORR activity are speculated both experimentally and theoretically. It is deduced that the active site lies in the structure of Fe-N4, accompanied with the addition of appropriate Fe, and the number of active sites increases without the occurrence of agglomeration particles. Moreover, it is speculated that Fe plays an important role in stabilizing N as well as constituting active sites in the second pyrolyzing process.

  • PERSPECTIVE
    Zhen HUANG, Lei ZHU, Ang LI, Zhan GAO
    Frontiers in Energy, 2022, 16(2): 145-149. https://doi.org/10.1007/s11708-022-0828-6
  • REVIEW ARTICLE
    Pardeep SINGLA, Manoj DUHAN, Sumit SAROHA
    Frontiers in Energy, 2022, 16(2): 187-223. https://doi.org/10.1007/s11708-021-0722-7

    In the last two decades, renewable energy has been paid immeasurable attention to toward the attainment of electricity requirements for domestic, industrial, and agriculture sectors. Solar forecasting plays a vital role in smooth operation, scheduling, and balancing of electricity production by standalone PV plants as well as grid interconnected solar PV plants. Numerous models and techniques have been developed in short, mid and long-term solar forecasting. This paper analyzes some of the potential solar forecasting models based on various methodologies discussed in literature, by mainly focusing on investigating the influence of meteorological variables, time horizon, climatic zone, pre-processing techniques, air pollution, and sample size on the complexity and accuracy of the model. To make the paper reader-friendly, it presents all-important parameters and findings of the models revealed from different studies in a tabular mode having the year of publication, time resolution, input parameters, forecasted parameters, error metrics, and performance. The literature studied showed that ANN-based models outperform the others due to their nonlinear complex problem-solving capabilities. Their accuracy can be further improved by hybridization of the two models or by performing pre-processing on the input data. Besides, it also discusses the diverse key constituents that affect the accuracy of a model. It has been observed that the proper selection of training and testing period along with the correlated dependent variables also enhances the accuracy of the model.

  • REVIEW ARTICLE
    Jibao ZHANG, Shujun CHEN, Ning MAO, Tianbiao HE
    Frontiers in Energy, 2022, 16(3): 445-459. https://doi.org/10.1007/s11708-021-0740-5

    With the continuous growth of the population and the improvement of production, the shortage of freshwater has plagued many countries. The use of novel technologies such as desalination to produce fresh water on a large scale has become inevitable in the world. Hydrate-based desalination (HBD) technology has drawn an increasing amount of attention due to its mild operation condition and environmental friendliness. In this paper, literature on hydrate-based desalination is comprehensively analyzed and critically evaluated, focuses on experimental progress in different hydrate formers that have an impact on thermodynamics and dynamics in hydrate formation. Besides, various porous media promotion is investigated. Besides, the hydrate formation morphology and hydrate crystal structure with different hydrate formers are analyzed and compared. Moreover, molecular dynamic simulation is discussed to further understand microscopic information of hydrate formation. Furthermore, simulations of the HBD process by considering the energy consumption are also investigated. In conclusion, the hydrated based desalination is a potential technology to get fresh water in a sustainable way.

  • REVIEW ARTICLE
    Zhi JIANG, Zhen YE, Wenfeng SHANGGUAN
    Frontiers in Energy, 2022, 16(1): 49-63. https://doi.org/10.1007/s11708-022-0817-9

    Solar energy-driven photocatalytic water splitting has been investigated for decades to produce clean and renewable green hydrogen. In this paper, the cutting-edge research within the overall water splitting system is summarized from the one-step photocatalytic overall water splitting (POWS) system to the two-step system and the cocatalysts research in this field. In addition, the photocatalytic reaction engineering study is also reviewed which is crucial for future scale-up. This mini-review provides a picture of survey of recent progress of relevant overall water splitting system, with particular attention paid to material system and mechanistic breakthroughs, and highlights the challenge and opportunity of the current system.

  • REVIEW ARTICLE
    Shu LI, Yonglin JU
    Frontiers in Energy, 2022, 16(3): 429-444. https://doi.org/10.1007/s11708-021-0747-y

    The intermediate fluid vaporizer (IFV), different from other liquefied natural gas (LNG) vaporizers, has many advantages and has shown a great potential for future applications. In this present paper, studies of IFV and its heat transfer characteristics in the LNG vaporization unit E2 are systematically reviewed. The research methods involved include theoretical analysis, experimental investigation, numerical simulation, and process simulation. First, relevant studies on the overall calculation and system design of IFV are summarized, including the structural innovation design, the thermal calculation model, and the selection of different intermediate fluids. Moreover, studies on the fluid flow and heat transfer behaviors of the supercritical LNG inside the tubes and the condensation heat transfer of the intermediate fluid outside the tubes are summarized. In the thermal calculations of the IFV, the selections of the existing heat transfer correlations about the intermediate fluids are inconsistent in different studies, and there lacks the accuracy evaluation of those correlations or comparison with experimental data. Furthermore, corresponding experiments or numerical simulations on the cryogenic condensation heat transfer outside the tubes in the IFV need to be further improved, compared to those in the refrigeration and air-conditioning temperature range. Therefore, suggestions for further studies of IFV are provided as well.

  • RESEARCH ARTICLE
    Xiaojun XUE, Yuting WANG, Heng CHEN, Gang XU
    Frontiers in Energy, 2022, 16(2): 307-320. https://doi.org/10.1007/s11708-021-0790-8

    A promising scheme for coal-fired power plants in which biomass co-firing and carbon dioxide capture technologies are adopted and the low-temperature waste heat from the CO2 capture process is recycled to heat the condensed water to achieve zero carbon emission is proposed in this paper. Based on a 660 MW supercritical coal-fired power plant, the thermal performance, emission performance, and economic performance of the proposed scheme are evaluated. In addition, a sensitivity analysis is conducted to show the effects of several key parameters on the performance of the proposed system. The results show that when the biomass mass mixing ratio is 15.40% and the CO2 capture rate is 90%, the CO2 emission of the coal-fired power plant can reach zero, indicating that the technical route proposed in this paper can indeed achieve zero carbon emission in coal-fired power plants. The net thermal efficiency decreases by 10.31%, due to the huge energy consumption of the CO2 capture unit. Besides, the cost of electricity (COE) and the cost of CO2 avoided (COA) of the proposed system are 80.37 $/MWh and 41.63 $/tCO2, respectively. The sensitivity analysis demonstrates that with the energy consumption of the reboiler decreasing from 3.22 GJ/tCO2 to 2.40 GJ/ tCO2, the efficiency penalty is reduced to 8.67%. This paper may provide reference for promoting the early realization of carbon neutrality in the power generation industry.

  • PERSPECTIVE
    Sijie CHEN, Jian PING, Zheng YAN, Jinjin LI, Zhen HUANG
    Frontiers in Energy, 2022, 16(1): 9-18. https://doi.org/10.1007/s11708-022-0818-8

    The structure of a power energy system is becoming more distributed than before. It becomes challenging to manage such a system in a centralized way, because a central authority may not exist or may not be trusted by all parties. Blockchain is a promising tool to address this challenge, by enabling trusted collaboration in the absence of a trusted central authority. Its use in the energy sector has been pioneered by several pilot projects. However, to date the energy sector has not seen large-scale deployment of blockchain, partly because the founders of those pilot projects, the public, and utilities have not reached consensus on the values and limitations of blockchain in energy. This perspective aims to bridge this gap. First, the philosophy and unique values of blockchain are discussed. Second, some promising blockchain-based applications in energy systems are presented. Third, some common misunderstandings of blockchain in energy are discussed. Last, some frequently-asked questions from utilities are discussed. Hopefully this perspective can help advance large-scale deployment of blockchain in energy systems.

  • RESEARCH ARTICLE
    Zhuohuan HU, Dongcheng WANG, Wei LU, Jian CHEN, Yuwen ZHANG
    Frontiers in Energy, 2022, 16(4): 683-696. https://doi.org/10.1007/s11708-020-0689-9

    A series of inline pico hydropower systems, which could be used in confined space, especially for water distribution networks (WDNs), was designed and investigated. The turbine with an eye-shaped vertical water baffle was developed to evaluate the hydraulic performance. A three-dimensional dynamic mesh was employed and the inlet velocity was considered as the inlet boundary condition, whereas the outlet boundary was set as the outflow. Then, numerical simulations were conducted and the standard k-ε turbulence model was found to be the best capable of predicting flow features through the comparison with the experimental results. The effects of the opening diameter of the water baffle and installation angle of the rotor on the flow field in the turbine were investigated. The results suggested that the water baffle opening at d = 30 mm and the rotor at a 52° angle could achieve the highest efficiency of 5.93%. The proper eye-shaped baffle not only accelerates the fluid flow and generates positive hydrodynamic torque, but also eliminates the flow separation. The scheme proposed in this paper can be exploited for practical applications in the water pipelines at various conditions and power requirements.

  • RESEARCH ARTICLE
    Chenyi HU, Aiming WU, Fengjuan ZHU, Liuxuan LUO, Fan YANG, Guofeng XIA, Guanghua WEI, Shuiyun SHEN, Junliang ZHANG
    Frontiers in Energy, 2022, 16(3): 502-508. https://doi.org/10.1007/s11708-021-0750-3

    An environment-friendly, water-soluble, and cellulose based binder (lithium carboxymethyl cellulose, CMC-Li) was successfully synthesized by using Li+ to replace Na+ in the commercial sodium carboxymethyl cellulose (CMC-Na). Li-O2 batteries based on the CMC-Li binder present enhanced discharge specific capacities (11151 mA·h/g at 100 mA/g) and a superior cycling stability (100 cycles at 200 mA/g) compared with those based on the CMC-Na binder. The enhanced performance may originate from the electrochemical stability of the CMC-Li binder and the ion-conductive nature of CMC-Li, which promotes the diffusion of Li+ in the cathode and consequently retards the increase of charge transfer resistance of the cathode during cycling. The results show that the water-soluble CMC-Li binder can be a green substitute for poly(vinylidene fluoride) (PVDF) binder based on organic solvent in the lithium oxygen batteries (LOBs).

  • VIEWPOINT
    Yueguang DENG, Jing LI, Ertai E
    Frontiers in Energy, 2022, 16(3): 393-396. https://doi.org/10.1007/s11708-022-0829-5
  • REVIEW ARTICLE
    Kai GONG, Jianlin YANG, Xu WANG, Chuanwen JIANG, Zhan XIONG, Ming ZHANG, Mingxing GUO, Ran LV, Su WANG, Shenxi ZHANG
    Frontiers in Energy, 2022, 16(1): 74-94. https://doi.org/10.1007/s11708-021-0792-6

    Smart buildings have been proven to be a kind of flexible demand response resources in the power system. To maximize the utilization of the demand response resources, such as the heating, ventilating and air-conditioning (HVAC), the energy storage systems (ESSs), the plug-in electric vehicles (PEVs), and the photovoltaic systems (PVs), their controlling, operation and information communication technologies have been widely studied. Involving human behaviors and cyber space, a traditional power system evolves into a cyber-physical-social system (CPSS). Lots of new operation frameworks, controlling methods and potential resources integration techniques will be introduced. Conversely, these new techniques urge the reforming requirement of the techniques on the modeling, structure, and integration techniques of smart buildings. In this paper, a brief comprehensive survey of the modeling, controlling, and operation of smart buildings is provided. Besides, a novel CPSS-based smart building operation structure is proposed, and the integration techniques for the group of smart buildings are discussed. Moreover, available business models for aggregating the smart buildings are discussed. Furthermore, the required advanced technologies for well-developed smart buildings are outlined.

  • RESEARCH ARTICLE
    Puzhe LAN, Dong HAN, Ruimin ZHANG, Xiaoyuan XU, Zheng YAN
    Frontiers in Energy, 2022, 16(1): 95-104. https://doi.org/10.1007/s11708-021-0788-2

    With the continuous development of the spot market, in the multi-stage power market environment with the day-ahead market and right market, the study associated with the portfolio of energy storage devices requires that attention should be paid to transmission congestion and power congestion. To maximize the profit of energy storage and avoid the imbalance of power supply and consumption and the risk of node price fluctuation caused by transmission congestion, this paper presents a portfolio strategy of energy storage devices with financial/physical contracts. First, the concepts of financial/physical transmission rights and financial/physical storage rights are proposed. Then, the portfolio models of financial contract and physical contract are established with the conditional value-at-risk to measure the risks. Finally, the portfolio models are verified through the test data of the Pennsylvania-New Jersey-Maryland (PJM) electric power spot market, and the comparison between the risk aversion of portfolios based on financial/physical contract with the portfolio of the market without rights. The simulation results show that the portfolio models proposed in this paper can effectively avoid the risk of market price fluctuations.

  • REVIEW ARTICLE
    Meng SONG, Wei SUN
    Frontiers in Energy, 2022, 16(1): 64-73. https://doi.org/10.1007/s11708-021-0732-5

    More flexibility is desirable with the proliferation of variable renewable resources for balancing supply and demand in power systems.Thermostatically controlled loads (TCLs) attract tremendous attentions because of their specific thermal inertia capability in demand response (DR) programs. To effectively manage numerous and distributed TCLs, intermediate coordinators, e.g., aggregators, as a bridge between end users and dispatch operators are required to model and control TCLs for serving the grid. Specifically, intermediate coordinators get the access to fundamental models and response modes of TCLs, make control strategies, and distribute control signals to TCLs according the requirements of dispatch operators. On the other hand, intermediate coordinators also provide dispatch models that characterize the external characteristics of TCLs to dispatch operators for scheduling different resources. In this paper, the bottom-up key technologies of TCLs in DR programs based on the current research have been reviewed and compared, including fundamental models, response modes, control strategies, dispatch models and dispatch strategies of TCLs, as well as challenges and opportunities in future work.

  • REVIEW ARTICLE
    Maria Carolina ANDRADE, Caio de Oliveira GORGULHO SILVA, Leonora Rios de SOUZA MOREIRA, Edivaldo Ximenes FERREIRA FILHO
    Frontiers in Energy, 2022, 16(2): 224-245. https://doi.org/10.1007/s11708-021-0730-7

    Interest in lignocellulosic biomass conversion technologies has increased recently because of their potential to reduce the dependency on non-renewable feedstocks. Residues from a variety of crops are the major source of lignocellulose, which is being produced in increasingly large quantities worldwide. The commercial exploitation of crop residues as feedstocks for biorefineries which could be used to produce a variety of goods such as biofuels, biochemicals, bioplastics, and enzymes is an attractive approach not only for adding value to residues but also for providing renewable products required by the expanding bioeconomy market. Moreover, the implementation of biorefineries in different regions has the potential to add value to the specific crop residues produced in the region. In this review, several aspects of crop residue application in biorefineries are discussed, including the role of crop residues in the bioeconomy and circular economy concepts, the main technical aspects of crop residue conversion in biorefineries, the main crop residues generated in different regions of the world and their availability, the potential value-added bioproducts that can be extracted or produced from each crop residue, and the major advantages and challenges associated with crop residue utilization in biorefineries. Despite their potential, most biomass refining technologies are not sufficiently advanced or financially viable. Several technical obstacles, especially with regard to crop residue collection, handling, and pre-treatment, prevent the implementation of biorefineries on a commercial scale. Further research is needed to resolve these scale-up-related challenges. Increased governmental incentives and bioeconomic strategies are expected to boost the biorefinery market and the cost competitiveness of biorefinery products.

  • REVIEW ARTICLE
    Sumit NAGAR, Kamal SHARMA, A. K. PANDEY, V. V. TYAGI
    Frontiers in Energy, 2022, 16(2): 150-186. https://doi.org/10.1007/s11708-021-0795-3

    Phase change materials (PCMs) play a leading role in overcoming the growing need of advanced thermal management for the storage and release of thermal energy which is to be used for different solar applications. However, the effectiveness of PCMs is greatly affected by their poor thermal conductivity. Therefore, in the present review the progress made in deploying the graphene (Gr) in PCMs in the last decade for providing the solution to the aforementioned inadequacy is presented and discussed in detail. Gr and its derivatives ((Gr oxide (GO), Gr aerogel (GA) and Gr nanoplatelets (GNPs)) based PCMs can improve the thermal conductivity and shape stability, which may be attributed to the extra ordinary thermo-physical properties of Gr. Moreover, it is expected from this review that the advantages and disadvantages of using Gr nanoparticles provide a deep insight and help the researchers in finding out the exact basic properties and finally the applications of Gr can be enhanced.

    In this work, Gr and its derivatives based PCMs was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction spectroscopy (XRD), and scanning electron microscopy (SEM) by which crystal structure was known, phase was identified along with the knowledge of surface structure respectively. The increase in the mass fraction (%) of the filler (Gr and its derivatives) led to even better thermo-physical properties and thermal stability. The thermal characterization was also done by differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and thermal conductivity tests. The enthalpy of freezing and melting showed that Gr and its derivatives based PCMs had a very high energy storage capability as reflected in its various applications.

  • RESEARCH ARTICLE
    Lijie ZHANG, Kaixuan YANG, Rui ZHAO, Mingfei CHEN, Yaoyao YING, Dong LIU
    Frontiers in Energy, 2022, 16(2): 292-306. https://doi.org/10.1007/s11708-020-0658-3

    This paper investigated the nanostructure and oxidation reactivity of soot generated from biofuel 2,5-dimethylfuran pyrolysis with different CO2 additions and different temperatures in a quartz tube flow reactor. The morphology and nanostructure of soot samples were characterized by a low and a high resolution transmission electron spectroscopy (TEM and HRTEM) and an X-ray diffraction (XRD). The oxidation reactivity of these samples was explored by a thermogravimetric analyzer (TGA). Different soot samples were collected in the tail of the tube. With the increase of temperature, the soot showed a smaller mean particle diameter, a longer fringe length, and a lower fringe tortuosity, as well as a higher degree of graphization. However, the variation of soot nanostructures resulting from different CO2 additions was not linear. Compared with 0%, 50%, and 100% CO2 additions at one fixed temperature, the soot collected from the 10% CO2 addition has the highest degree of graphization and crystallization. At three temperatures of 1173 K, 1223 K, and 1273 K, the mean values of fringe length distribution displayed a ranking of 10% CO2>100% CO2>50% CO2 while the mean particle diameters showed the same order. Furthermore, the oxidation reactivity of different soot samples decreased in the ranking of 50% CO2 addition>100% CO2 addition>10% CO2 addition, which was equal to the ranking of mean values of fringe tortuosity distribution. The result further confirmed the close relationship between soot nanostructure and oxidation reactivity.

  • REVIEW ARTICLE
    Muni Raj MAURYA, John-John CABIBIHAN, Kishor Kumar SADASIVUNI, Kalim DESHMUKH
    Frontiers in Energy, 2022, 16(4): 548-580. https://doi.org/10.1007/s11708-022-0826-8

    The introduction of a practical solar cell by Bell Laboratory, which had an efficiency of approximately 6%, signified photovoltaic technology as a potentially viable energy source. Continuous efforts have been made to increase power conversion efficiency (PCE). In the present review, the advances made in solar cells (SCs) are summarized. Material and device engineering are described for achieving enhanced light absorption, electrical properties, stability and higher PCE in SCs. The strategies in materials and coating techniques for large area deposition are further elaborated, which is expected to be helpful for realizing high-efficiency SCs. The methods of light-harvesting in SCs via anti-reflecting coatings, surface texturing, patterned growth of nanostructure, and plasmonics are discussed. Moreover, progress in mechanical methods that are used for sun tracking are elaborated. The assistance of the above two protocols in maximizing the power output of SCs are discussed in detail. Finally, further research efforts needed to overcome roadblocks in commercialization were highlighted and perspectives on the future development of this rapidly advancing field are offered.

  • VIEWPOINT
    Xiaoshi QIAN
    Frontiers in Energy, 2022, 16(1): 19-22. https://doi.org/10.1007/s11708-022-0820-1
  • REVIEW ARTICLE
    Shahriar AHMED, KH. Nazmul AHSHAN, Md. Nur Alam MONDAL, Shorab HOSSAIN
    Frontiers in Energy, 2022, 16(3): 397-428. https://doi.org/10.1007/s11708-021-0758-8

    Having the wide application of metal oxides in energy technologies, in recent years, many researchers tried to increase the performance of the PV/T system by using metal oxide-based nanofluids (NFs) as coolants or optical filters or both at the same time. This paper summarizes recent research activities on various metal oxides (Al2O3, TiO2, SiO2, Fe3O4, CuO, ZnO, MgO)-based NFs performance in the PV/T system regarding different significant parameters, e.g., thermal conductivity, volume fraction, mass flowrate, electrical, thermal and overall efficiency, etc. By conducting a comparative study among the metal oxide-based NFs, Al2O3/SiO2-water NFs are mostly used to achieve maximum performance. The Al2O3-water NF has a prominent heat transfer feature with a maximum electrical efficiency of 17%, and a maximum temperature reduction of PV module of up to 36.9°C can be achieved by using the Al2O3-water NF as a coolant. Additionally, studies suggest that the PV cell’s efficiency of up to 30% can be enhanced by using a solar tracking system. Besides, TiO2-water NFs have been proved to have the highest thermal efficiency of 86% in the PV/T system, but TiO2 nanoparticles could be hazardous for human health. As a spectral filter, SiO2-water NF at a size of 5 nm and a volume fraction of 2% seems to be very favorable for PV/T systems. Studies show that the combined use of NFs as coolants and spectral filters in the PV/T system could provide a higher overall efficiency at a cheaper rate. Finally, the opportunities and challenges of using NFs in PV/T systems are also discussed.

  • REVIEW ARTICLE
    Zhouyu ZHANG, Hao CHEN, Zhenglin HU, Shoubin ZHOU, Lan ZHANG, Jiayan LUO
    Frontiers in Energy, 2022, 16(5): 706-733. https://doi.org/10.1007/s11708-022-0833-9

    Solid-state electrolytes (SSEs) can address the safety issue of organic electrolyte in rechargeable lithium batteries. Unfortunately, neither polymer nor ceramic SSEs used alone can meet the demand although great progress has been made in the past few years. Composite solid electrolytes (CSEs) composed of flexible polymers and brittle but more conducting ceramics can take advantage of the individual system for solid-state lithium metal batteries (SSLMBs). CSEs can be largely divided into two categories by the mass fraction of the components: “polymer rich” (PR) and “ceramic rich” (CR) systems with different internal structures and electrochemical properties. This review provides a comprehensive and in-depth understanding of recent advances and limitations of both PR and CR electrolytes, with a special focus on the ion conduction path based on polymer-ceramic interaction mechanisms and structural designs of ceramic fillers/frameworks. In addition, it highlights the PR and CR which bring the leverage between the electrochemical property and the mechanical property. Moreover, it further prospects the possible route for future development of CSEs according to their rational design, which is expected to accelerate the practical application of SSLMBs.

  • REVIEW ARTICLE
    Yujing BI, Yonglin JU
    Frontiers in Energy, 2022, 16(5): 793-811. https://doi.org/10.1007/s11708-022-0821-0

    CO2 in natural gas (NG) is prone to condense directly from gas to solid or solidify from liquid to solid at low temperatures due to its high triple point and boiling temperature, which can cause a block of equipment. Meanwhile, CO2 will also affect the calorific value of NG. Based on the above reasons, CO2 must be removed during the NG liquefaction process. Compared with conventional methods, cryogenic technologies for CO2 removal from NG have attracted wide attention due to their non-polluting and low-cost advantages. Its integration with NG liquefaction can make rational use of the cold energy and realize the purification of NG and the production of by-product liquid CO2. In this paper, the phase behavior of the CH4-CO2 binary mixture is summarized, which provides a basis for the process design of cryogenic CO2 removal from NG. Then, the detailed techniques of design and optimization for cryogenic CO2 removal in recent years are summarized, including the gas-liquid phase change technique and the gas-solid phase change technique. Finally, several improvements for further development of the cryogenic CO2 removal process are proposed. The removal process in combination with the phase change and the traditional techniques with renewable energy will be the broad prospect for future development.

  • RESEARCH ARTICLE
    Lifu YAN, Lingling ZHAO, Guiting YANG, Shichao LIU, Yang LIU, Shangchao LIN
    Frontiers in Energy, 2022, 16(4): 581-594. https://doi.org/10.1007/s11708-022-0831-y

    Solid-state thermoelectric energy conversion devices attract broad research interests because of their great promises in waste heat recycling, space power generation, deep water power generation, and temperature control, but the search for essential thermoelectric materials with high performance still remains a great challenge. As an emerging low cost, solution-processed thermoelectric material, inorganic metal halide perovskites CsPb(I1–xBrx)3 under mechanical deformation is systematically investigated using the first-principle calculations and the Boltzmann transport theory. It is demonstrated that halogen mixing and mechanical deformation are efficient methods to tailor electronic structures and charge transport properties in CsPb(I1–xBrx)3 synergistically. Halogen mixing leads to band splitting and anisotropic charge transport due to symmetry-breaking-induced intrinsic strains. Such band splitting reconstructs the band edge and can decrease the charge carrier effective mass, leading to excellent charge transport properties. Mechanical deformation can further push the orbital energies apart from each other in a more controllable manner, surpassing the impact from intrinsic strains. Both anisotropic charge transport properties andZT values are sensitive to the direction and magnitude of strain, showing a wide range of variation from 20% to 400% (with a ZT value of up to 1.85) compared with unstrained cases. The power generation efficiency of the thermoelectric device can reach as high as approximately 12% using mixed halide perovskites under tailored mechanical deformation when the heat-source is at 500 K and the cold side is maintained at 300 K, surpassing the performance of many existing bulk thermoelectric materials.

  • RESEARCH ARTICLE
    Xingchao WANG, Chunjian PAN, Carlos E. ROMERO, Zongliang QIAO, Arindam BANERJEE, Carlos RUBIO-MAYA, Lehua PAN
    Frontiers in Energy, 2022, 16(2): 246-262. https://doi.org/10.1007/s11708-021-0749-9

    A comprehensive thermo-economic model combining a geothermal heat mining system and a direct supercritical CO2 turbine expansion electric power generation system was proposed in this paper. Assisted by this integrated model, thermo-economic and optimization analyses for the key design parameters of the whole system including the geothermal well pattern and operational conditions were performed to obtain a minimal levelized cost of electricity (LCOE). Specifically, in geothermal heat extraction simulation, an integrated wellbore-reservoir system model (T2Well/ECO2N) was used to generate a database for creating a fast, predictive, and compatible geothermal heat mining model by employing a response surface methodology. A parametric study was conducted to demonstrate the impact of turbine discharge pressure, injection and production well distance, CO2 injection flowrate, CO2 injection temperature, and monitored production well bottom pressure on LCOE, system thermal efficiency, and capital cost. It was found that for a 100 MWe power plant, a minimal LCOE of $0.177/kWh was achieved for a 20-year steady operation without considering CO2 sequestration credit. In addition, when CO2 sequestration credit is $1.00/t, an LCOE breakeven point compared to a conventional geothermal power plant is achieved and a breakpoint for generating electric power generation at no cost was achieved for a sequestration credit of $2.05/t.

  • RESEARCH ARTICLE
    Dorota RZETELSKA, Madeleine COMBRINCK
    Frontiers in Energy, 2022, 16(2): 336-356. https://doi.org/10.1007/s11708-021-0748-x

    Fuel poverty is most prevalent in North East England with 14.4% of fuel poor households in Newcastle upon Tyne. The aim of this paper was to identify a grid connected renewable energy system coupled with natural gas reciprocating combined heat and power unit, that is cost-effective and technically feasible with a potential to generate a profit from selling energy excess to the grid to help alleviate fuel poverty. The system was also aimed at low carbon emissions. Fourteen models were designed and optimized with the aid of the HOMER Pro software. Models were compared with respect to their economic, technical, and environmental performance. A solution was proposed where restrictions were placed on the size of renewable energy components. This configuration consists of 150 kW CHP, 300 kW PV cells, and 30 kW wind turbines. The renewable fraction is 5.10% and the system yields a carbon saving of 7.9% in comparison with conventional systems. The initial capital investment is $1.24 million which enables the system to have grid sales of 582689 kWh/a. A conservative calculation determined that 40% of the sales can be used to reduce the energy cost of fuel poor households by $706 per annum. This solution has the potential to eliminate fuel poverty at the site analyzed.

  • RESEARCH ARTICLE
    Jialiang CHEN, Xiaoyuan XU, Zheng YAN, Han WANG
    Frontiers in Energy, 2022, 16(1): 121-129. https://doi.org/10.1007/s11708-021-0780-x

    This paper proposes a data-driven topology identification method for distribution systems with distributed energy resources (DERs). First, a neural network is trained to depict the relationship between nodal power injections and voltage magnitude measurements, and then it is used to generate synthetic measurements under independent nodal power injections, thus eliminating the influence of correlated nodal power injections on topology identification. Second, a maximal information coefficient-based maximum spanning tree algorithm is developed to obtain the network topology by evaluating the dependence among the synthetic measurements. The proposed method is tested on different distribution networks and the simulation results are compared with those of other methods to validate the effectiveness of the proposed method.

  • RESEARCH ARTICLE
    Islam HASHEM, Aida A. HAFIZ, Mohamed H. MOHAMED
    Frontiers in Energy, 2022, 16(4): 661-682. https://doi.org/10.1007/s11708-020-0713-0

    Wind-lens turbines (WLTs) exhibit the prospect of a higher output power and more suitability for urban areas in comparison to bare wind turbines. The wind-lens typically comprises a diffuser shroud coupled with a flange appended to the exit periphery of the shroud. Wind-lenses can boost the velocity of the incoming wind through the turbine rotor owing to the creation of a low-pressure zone downstream the flanged diffuser. In this paper, the aerodynamic performance of the wind-lens is computationally assessed using high-fidelity transient CFD simulations for shrouds with different profiles, aiming to assess the effect of change of some design parameters such as length, area ratio and flange height of the diffuser shroud on the power augmentation. The power coefficient (Cp) is calculated by solving the URANS equations with the aid of the SST k–ω model. Furthermore, comparisons with experimental data for validation are accomplished to prove that the proposed methodology could be able to precisely predict the aerodynamic behavior of the wind-lens turbine. The results affirm that wind-lens with cycloidal profile yield an augmentation of about 58% increase in power coefficient compared to bare wind turbine of the same rotor swept-area. It is also emphasized that diffusers (cycloid type) of small length could achieve a twice increase in power coefficient while maintaining large flange heights.