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Frontiers in Energy

ISSN 2095-1701 (Print)
ISSN 2095-1698 (Online)
Formerly Known as Frontiers of Energy and Power Engineering in China
2017 Impact Factor: 0.753

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, Volume 12 Issue 4 Previous Issue   
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EDITORIAL
REVIEW ARTICLE
Energy internet in the Yangtze River Delta: opportunities, challenges, and suggestions
Zheng YAN, Jiayi HU
Front. Energy. 2018, 12 (4): 484-492.  https://doi.org/10.1007/s11708-018-0600-0
Abstract   HTML   PDF (243KB)

Energy internet is an Internet of Things (IoT) based network, which combines the multi-energy flows and the information flows. In this review, the opportunities and the challenges posed to developing energy internet in the Yangtze River Delta are analyzed concerning detailed analysis of its advantages in various aspects and problems of its energy systems. Then the framework of energy internet in the Yangtze River Delta is constructed, according to which specific suggestions are also provided. This review is dedicated to helping the policy makers to draw the roadmap of future-oriented energy internet.

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RESEARCH ARTICLE
Integrated energy in Germany–A critical look at the development and state of integrated energies in Germany
Saman AMANPOUR, Daniel HUCK, Mark KUPRAT, Harald SCHWARZ
Front. Energy. 2018, 12 (4): 493-500.  https://doi.org/10.1007/s11708-018-0570-2
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In the face of global warming and a scarcity of resources, future energy systems are urged to undergo a major and radical transformation. The recognition of the need to embrace renewable energy technologies and to move toward decarbonization has led to significant changes in the German energy generation, consumption and infrastructure. Ambitious German national plans to decrease carbon dioxide emissions on one side, and the unpredictable and volatile nature of renewable energy sources on the other side have elevated the importance of integrated energies in recent years. The deployment of integrated technologies as a solution to interlink various infrastructures creates opportunities for increasing the reliability of energy systems, minimizing environmental impacts and maximizing the share of renewable resources. This paper discusses the role of integrated energy systems in supporting of sustainable solutions for future energy transitions. Moreover, the reinforcement of this movement with the help of different technologies will be discussed and the development of integrated energy systems in Germany will be reviewed.

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A perspective on the promoting effect of Ir and Au on Pd toward the ethanol oxidation reaction in alkaline media
S. Y. SHEN, Y. G. GUO, G. H. WEI, L. X. LUO, F. LI, J. L. ZHANG
Front. Energy. 2018, 12 (4): 501-508.  https://doi.org/10.1007/s11708-018-0586-7
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There remain great challenges in developing highly efficient electrocatalysts with both high activity and good stability for the ethanol oxidation reaction in alkaline media. Herein, two architectures of tri-metallic PdIrAu/C electrocatalysts are designed and the promoting effect of Au and Ir on Pd toward the ethanol oxidation reaction (EOR) in alkaline media is investigated in detail. On the one hand, the tri-metallic Pd7Au7Ir/C electrocatalyst with a solid solution alloy architecture is less active relative to Pd7Ir/C and Pd/C while the stabilizing effect of Au leads to both a higher activity and a lower degradation percentage after 3000 cycles of the accelerated degradation test (ADT) on Pd7Au7Ir/C than those on Pd7Ir/C. On the other hand, the tri-metallic Pd7Ir@(1/3Au)/C electrocatalyst with a near surface alloy architecture delivers a much higher activity with an improvement up to 50.4% compared to Pd7Ir/C. It is speculated that for the tri-metallic Pd7Ir@(1/3Au)/C electrocatalyst, certain Au atoms are well designed on surfaces to introduce an electronic modification, thus leading to an anti-poisoning effect and improving the EOR activity.

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Technological development of multi-energy complementary system based on solar PVs and MGT
Xiaojing LV, Yu WENG, Xiaoyi DING, Shilie WENG, Yiwu WENG
Front. Energy. 2018, 12 (4): 509-517.  https://doi.org/10.1007/s11708-018-0598-3
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The complementary micro-energy network system consisting of solar photovoltaic power generation (solar PVs) and micro-gas turbine (MGT), which not only improves the absorption rate and reliability of photovoltaic power, but also has the advantages of low emission, high efficiency, and good fuel adaptability, has become one of the most promising distributed power systems in the field of micro grid. According to the development of current technology and the demand of actual work, this research described the domestic and foreign development of micro-energy network system based on solar PVs and MGT. Moreover, it analyzed the challenges and future development regarding the micro-energy network system in planning and design, energy utilization optimization and dispatching management, and system maintenance, respectively. Furthermore, it predicted the future development of the key technology of the multi-energy complementary system. These results will be beneficial for the progress of this field both in theory and practice.

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Multi-objective optimization of a hybrid distributed energy system using NSGA-II algorithm
Hongbo REN, Yinlong LU, Qiong WU, Xiu YANG, Aolin ZHOU
Front. Energy. 2018, 12 (4): 518-528.  https://doi.org/10.1007/s11708-018-0594-7
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In this paper, a multi-objective optimization model is established for the investment plan and operation management of a hybrid distributed energy system. Considering both economic and environmental benefits, the overall annual cost and emissions of CO2 equivalents are selected as the objective functions to be minimized. In addition, relevant constraints are included to guarantee that the optimized system is reliable to satisfy the energy demands. To solve the optimization model, the non-dominated sorting generic algorithm II (NSGA-II) is employed to derive a set of non-dominated Pareto solutions. The diversity of Pareto solutions is conserved by a crowding distance operator, and the best compromised Pareto solution is determined based on the fuzzy set theory. As an illustrative example, a hotel building is selected for study to verify the effectiveness of the optimization model and the solving algorithm. The results obtained from the numerical study indicate that the NSGA-II results in more diversified Pareto solutions and the fuzzy set theory picks out a better combination of device capacities with reasonable operating strategies.

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Optimisation for interconnected energy hub system with combined ground source heat pump and borehole thermal storage
Da HUO, Wei WEI, Simon Le BLOND
Front. Energy. 2018, 12 (4): 529-539.  https://doi.org/10.1007/s11708-018-0580-0
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Ground source heat pumps (GSHP) give zero-carbon emission heating at a residential level. However, as the heat is discharged, the temperature of the ground drops, leading to a poorer efficiency. Borehole inter-seasonal thermal storage coupled with GSHP maintains the efficiency at a high level. To adequately utilize the high performance of combined GSHP and the borehole system to further increase system efficiency and reduce cost, such a combined heating system is incorporated into the interconnected multi-carrier system to support the heat load of a community. The borehole finite element (FE) model and an equivalent borehole transfer function are proposed and respectively applied to the optimisation to analyze the variation of GSHP performance over the entire optimisation time horizon of 24 h. The results validate the borehole transfer function, and the optimisation computation time is reduced by 17 times compared with the optimisation using the FE model.

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Decoupling optimization of integrated energy system based on energy quality character
Shixi MA, Shengnan SUN, Hang WU, Dengji ZHOU, Huisheng ZHANG, Shilie WENG
Front. Energy. 2018, 12 (4): 540-549.  https://doi.org/10.1007/s11708-018-0597-4
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Connections among multi-energy systems become increasingly closer with the extensive application of various energy equipment such as gas-fired power plants and electricity-driven gas compressor. Therefore, the integrated energy system has attracted much attention. This paper establishes a gas-electricity joint operation model, proposes a system evaluation index based on the energy quality character after considering the grade difference of the energy loss of the subsystem, and finds an optimal scheduling method for integrated energy systems. Besides, according to the typical load characteristics of commercial and residential users, the optimal scheduling analysis is applied to the integrated energy system composed of an IEEE 39 nodes power system and a 10 nodes natural gas system. The results prove the feasibility and effectiveness of the proposed method.

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Smoothing ramp events in wind farm based on dynamic programming in energy internet
Jiang LI, Guodong LIU, Shuo ZHANG
Front. Energy. 2018, 12 (4): 550-559.  https://doi.org/10.1007/s11708-018-0593-8
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The concept of energy internet has been gradually accepted, which can optimize the consumption of fossil energy and renewable energy resources. When wind power is integrated into the main grid, ramp events caused by stochastic wind power fluctuation may threaten the security of power systems. This paper proposes a dynamic programming method in smoothing ramp events. First, the energy internet model of wind power, pumped storage power station, and gas power station is established. Then, the optimization problem in the energy internet is transformed into a multi-stage dynamic programming problem, and the dynamic programming method proposed is applied to solve the optimization problem. Finally, the evaluation functions are introduced to evaluate pollutant emissions. The results show that the dynamic programming method proposed is effective for smoothing wind power and reducing ramp events in energy internet.

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Power to gas: addressing renewable curtailment by converting to hydrogen
Xiaohe YAN, Xin ZHANG, Chenghong GU, Furong LI
Front. Energy. 2018, 12 (4): 560-568.  https://doi.org/10.1007/s11708-018-0588-5
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Renewable energy is the key to meeting increasing electricity demand and the decarburization targets in the generation mix. However, due to constrained power network capacity, a large volume of renewable generation is curtailed particularly from wind power, which is a huge waste of resources. There are typically three approaches to addressing excessive renewable: direct curtailment, the reinforcement of networks to expand transfer capacity, and the conversion of excessive renewable into other energy types, such as hydrogen, to transport. The costs and benefits of the three approaches could vary significantly across location, time, and penetration of renewable energy. This paper conducts a cost-benefit analysis and comparison of the three techniques to address wind curtailment. It uses a reduced 16-busbar UK transmission network to analyze the performance of the three approaches. The UK 2020 generation mix is used to quantify the saved renewable energy and incurred costs. The payback time and net present value of the two investment techniques are compared. From demonstration, it is reasonable to conclude that converting excessive wind power into hydrogen to transport is an environmentally friendly and cost-effective way to address wind curtailment.

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Optimal dispatch of multi energy system using power-to-gas technology considering flexible load on user side
Zi LING, Xiu YANG, Zilin LI
Front. Energy. 2018, 12 (4): 569-581.  https://doi.org/10.1007/s11708-018-0595-6
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The relation between power-to-gas technology (P2G) and energy interconnection becomes increasingly close. Meanwhile, the participation of flexible load on user side in system optimization has attracted much attention as an efficient approach to relieve the contradiction between energy supply and energy demand. Based on the concept of energy hub, according to its series characteristic, this paper established a generic multi-energy system model using the P2G technology. The characteristic of flexible load on user side was considered and optimal dispatch analysis was made, so as to reduce the cost, to reasonably dispatch the flexible load, to reduce the discharge, to enhance the new energy output, and to increase the power-to-gas conversion efficiency. Finally, a concrete analysis was made on the optimal dispatch result of the multi-energy system using the P2G technology considering flexible load on user side in the calculating example, and optimal dispatch of the system was verified via four different scenarios. The results indicate that cooperative dispatch of multi-energy system using the P2G technology considering flexible load on user side is the most economic, and can make a contribution to absorption of new energy and P2G conversion. In this way, environmental effects and safe and stable operation of the system can be guaranteed.

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A comprehensive energy solution for households employing a micro combined cooling, heating and power generation system
Huayi ZHANG, Can ZHANG, Fushuan WEN, Yan XU
Front. Energy. 2018, 12 (4): 582-590.  https://doi.org/10.1007/s11708-018-0592-9
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In recent years, micro combined cooling, heating and power generation (mCCHP) systems have attracted much attention in the energy demand side sector. The input energy of a mCCHP system is natural gas, while the outputs include heating, cooling and electricity energy. The mCCHP system is deemed as a possible solution for households with multiple energy demands. Given this background, a mCCHP based comprehensive energy solution for households is proposed in this paper. First, the mathematical model of a home energy hub (HEH) is presented to describe the inputs, outputs, conversion and consumption process of multiple energies in households. Then, electrical loads and thermal demands are classified and modeled in detail, and the coordination and complementation between electricity and natural gas are studied. Afterwards, the concept of thermal comfort is introduced and a robust optimization model for HEH is developed considering electricity price uncertainties. Finally, a household using a mCCHP as the energy conversion device is studied. The simulation results show that the comprehensive energy solution proposed in this work can realize multiple kinds of energy supplies for households with the minimized total energy cost.

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REVIEW ARTICLE
State-of-art review of the optimization methods to design the configuration of hybrid renewable energy systems (HRESs)
Maurizio FACCIO, Mauro GAMBERI, Marco BORTOLINI, Mojtaba NEDAEI
Front. Energy. 2018, 12 (4): 591-622.  https://doi.org/10.1007/s11708-018-0567-x
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The current research aims to present an inclusive review of latest research works performed with the aim of improving the efficiency of the hybrid renewable energy systems (HRESs) by employing diverse ranges of the optimization techniques, which aid the designers to achieve the minimum expected total cost, while satisfying the power demand and the reliability. For this purpose, a detailed analysis of the different classification drivers considering the design factors such as the optimization goals, utilized optimization methods, grid type as well as the investigated technology has been conducted. Initial results have indicated that among all optimization goals, load demand parameters including loss of power supply probability (LPSP) and loss of load probability (LLP), cost, sizing (configuration), energy production, and environmental emissions are the most frequent design variables which have been cited the most. Another result of this paper indicates that almost 70% of the research projects have been dedicated towards the optimization of the off-grid applications of the HRESs. Furthermore, it has been demonstrated that, integration of the PV, wind and battery is the most frequent configuration. In the next stage of the paper, a review concerning the sizing methods is also carried out to outline the most common techniques which are used to configure the components of the HRESs. In this regard, an analysis covering the optimized indicators such as the cost drivers, energy index parameters, load indicators, battery’s state of charge, PV generator area, design parameters such as the LPSP, and the wind power generation to load ratio, is also performed.

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COMMENTARY
Lessons from market reform for renewable integration in the European Union
Furong LI
Front. Energy. 2018, 12 (4): 623-629.  https://doi.org/10.1007/s11708-018-0575-x
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The European Union (EU) has the most advanced, mature, and liberal energy markets that gave rise to the most dramatic drop in wholesale energy prices, whose fallen, however, has not been translated into a reduction in retail energy prices. Instead, energy prices in Europe rose above inflation year-in-year-out, and are considerably higher compared with major economic partners. This paper highlights the key limitations in the EU market designs and network access toward renewable integration, and the wide range of reforms that the EU is currently undertaken across the Member States to achieve two goals: to make the market fit for renewable, and to set a practical example of how a competitive economy can be built on a sustainable and affordable energy system. This paper concludes with key recommendations to developing nations, particularly in addressing heavy renewable curtailment.

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