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Energies, Volume 11, Issue 6 (June 2018)

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Open AccessArticle The Future of Fossil Fired Power Plants in Germany—A Lifetime Analysis
Energies 2018, 11(6), 1616; https://doi.org/10.3390/en11061616
Received: 27 April 2018 / Revised: 6 June 2018 / Accepted: 11 June 2018 / Published: 20 June 2018
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Abstract
In many German energy projections, the assumption of power plant lifetimes plays a central role, since it is often used in projections for the existing fleet of power plants or as a criterion for decommissioning in model-based investigations. The result of these analyses
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In many German energy projections, the assumption of power plant lifetimes plays a central role, since it is often used in projections for the existing fleet of power plants or as a criterion for decommissioning in model-based investigations. The result of these analyses is a power plant capacity retirement graph, which is then used to determine the replacement demand. Especially in the context of the German Energy transition (“Energiewende”) the amount and dynamics of replacement play an important role. Against this background, a large number of studies have been evaluated and fleet developments compared. Many studies refer to empirical values for the assumption of lifetimes without specifying them in greater detail. This approach was used to conduct an ex post lifetime analysis—accurate to each number of units—of German power plants that have been decommissioned since 1990. The analysis is conducted with the aid of a power plant database, which has been continuously updated for each individual unit since 1985. In addition to the power plants currently in operation, the database includes also includes power plant units that have been successively decommissioned over the past decades. The ex post analysis presents the first lifetime analysis for decommissioned German plants, which can serve as a basis for future power plant fleet projections. The analyses show that the lifetime of fossil-fired power plants has extended considerably. For example, whereas the real lifetimes of coal-fired power plants were in a range of 30 to 35 years in the 1990s, today they amount to 40 to 45 years on average. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessReview Thermal Performance through Heat Retention in Integrated Collector-Storage Solar Water Heaters: A Review
Energies 2018, 11(6), 1615; https://doi.org/10.3390/en11061615
Received: 16 May 2018 / Revised: 7 June 2018 / Accepted: 19 June 2018 / Published: 20 June 2018
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Abstract
Solar thermal systems are a long-standing technology that is receiving increased attention, in terms of research and development, due to ambitious climate change targets and the need for renewable energy solutions. Integrated collector-storage solar water heaters (ICSSWHs) are a potential contributing solution and
[...] Read more.
Solar thermal systems are a long-standing technology that is receiving increased attention, in terms of research and development, due to ambitious climate change targets and the need for renewable energy solutions. Integrated collector-storage solar water heaters (ICSSWHs) are a potential contributing solution and numerous studies have focussed on the optimisation of their thermal performance and efficiency. A major drawback of these systems is the heavy heat losses experienced during non-collection periods. To combat this, various heat retention strategies have been proposed and evaluated, including baffles plates, additional insulation, multiple glazing layers, selective coatings, and phase change materials. This paper aims to bring together these studies through a systematic review of the existing literature surrounding the performance of ICSSWH systems, focusing on heat retention. This review provides a comprehensive and up-to-date point of reference on relevant research and developments for researchers in this field. Full article
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Open AccessArticle SnSb Alloy Blended with Hard Carbon as Anode for Na-Ion Batteries
Energies 2018, 11(6), 1614; https://doi.org/10.3390/en11061614
Received: 15 May 2018 / Revised: 9 June 2018 / Accepted: 15 June 2018 / Published: 20 June 2018
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Abstract
SnSb binary alloys blended with reduced graphene oxide (SnSb/RGO) or mixtures of SnSb/RGO with hard carbon (SnSb/RGO+HC) were tested as anode materials for sodium-ion batteries. The presence of hard carbon in the SnSb/RGO+HC blend improves its cycle efficiency and rate performance substantially. The
[...] Read more.
SnSb binary alloys blended with reduced graphene oxide (SnSb/RGO) or mixtures of SnSb/RGO with hard carbon (SnSb/RGO+HC) were tested as anode materials for sodium-ion batteries. The presence of hard carbon in the SnSb/RGO+HC blend improves its cycle efficiency and rate performance substantially. The synergy between the SnSb/RGO and the hard carbon phase is explained by the buffer action of the hard carbon, preventing SnSb interparticle agglomeration during the repeated recharge cycles. The feasibility of SnSb alloy anode for sodium-ion batteries was confirmed in full cell configuration vs. Na3V2(PO4)2F3 cathode. Full article
(This article belongs to the Special Issue Electrochemical Energy Conversion and Storage Technologies)
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Open AccessArticle Fully-distributed Load Frequency Control Strategy in an Islanded Microgrid Considering Plug-In Electric Vehicles
Energies 2018, 11(6), 1613; https://doi.org/10.3390/en11061613
Received: 22 May 2018 / Revised: 13 June 2018 / Accepted: 19 June 2018 / Published: 20 June 2018
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Abstract
With large-scale integration of electric vehicles, this paper investigates the load frequency control problem in an islanded microgrid with plug-in electric vehicles (PEVs), which can be regarded as mobile battery energy storages to provide a valuable contribution to frequency regulation. A novel fully-distributed
[...] Read more.
With large-scale integration of electric vehicles, this paper investigates the load frequency control problem in an islanded microgrid with plug-in electric vehicles (PEVs), which can be regarded as mobile battery energy storages to provide a valuable contribution to frequency regulation. A novel fully-distributed control strategy is proposed to achieve fast frequency regulation of islanded microgrids and effective coordination control of distributed energy sources. Firstly, distributed control based on an improved linear active disturbance rejection algorithm is realized through a multi-agent system, and it greatly enhances the anti-disturbance capability of the microgrid. Then, in order to guarantee the effectiveness of PEVs in frequency regulation, PEVs are controlled following the controllable power rate (CPR) calculated from the consensus-based multi-agent system. Furthermore, the system control construction in this paper is well designed to avoid the negative effects caused by system communication time delay. Finally, numerical simulations under different disturbances are carried out to demonstrate the effectiveness of the proposed control strategy in comparison with other previous control strategies. Full article
(This article belongs to the Special Issue Electric Power Systems Research 2018)
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Open AccessArticle Research on the Pressure Ratio Characteristics of a Swash Plate-Rotating Hydraulic Transformer
Energies 2018, 11(6), 1612; https://doi.org/10.3390/en11061612
Received: 16 May 2018 / Revised: 8 June 2018 / Accepted: 8 June 2018 / Published: 20 June 2018
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Abstract
This paper presents a theoretical model and its experimental validation for the pressure ratio of a swash plate-rotating hydraulic transformer. The structure and principle of the new type of transformer are described. The swash plate-rotating type can reduce the throttling loss caused by
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This paper presents a theoretical model and its experimental validation for the pressure ratio of a swash plate-rotating hydraulic transformer. The structure and principle of the new type of transformer are described. The swash plate-rotating type can reduce the throttling loss caused by the valve plate in traditional hydraulic transformers. The theoretical model of the pressure ratio was derived based on the displacements functioning as the pump and motor in the transformer, accounting for the friction losses. A specific experimental setup including the prototype was established to validate the principle and pressure ratio of the machine. The results show that the transformer has a wider pressure range. The increase in pressure at port A and the rotating speed of the cylinder can reduce the pressure ratio slightly due to the torque loss. The present work indicates the useful potential of the swash plate-rotating hydraulic transformer. Full article
(This article belongs to the Special Issue Energy Efficiency and Controllability of Fluid Power Systems 2018)
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Open AccessArticle 3-Leg Inverter Control for 2-Phase Outer Rotor Coreless Torque Actuator in Hybrid Multi-D.O.F System
Energies 2018, 11(6), 1611; https://doi.org/10.3390/en11061611
Received: 31 March 2018 / Revised: 6 June 2018 / Accepted: 19 June 2018 / Published: 20 June 2018
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Abstract
Since an existing 3-phase inner rotor torque actuator (TA) has severe torque ripples, it is not appropriate for a gimbal system that requires precise position control. Therefore, a coreless TA is considered to eliminate the core causing torque ripples. In order to compensate
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Since an existing 3-phase inner rotor torque actuator (TA) has severe torque ripples, it is not appropriate for a gimbal system that requires precise position control. Therefore, a coreless TA is considered to eliminate the core causing torque ripples. In order to compensate for several problems (e.g., problems of production structures and output degradation) when a coreless type is used, the final 2-phase outer rotor is proposed for the low vibration and high power TA in the gimbal system. To control the 2-phase TA applied to such the gimbal system, special inverter control methods, such as bi-directional drive for tilting control and control for output torque improvement, are required. The 2-phase 3-leg inverter is free of DC capacitor voltage unbalance compared to the 2-leg inverter, and is economical because it uses less power switches than the 4-leg inverter. Therefore, the 2-phase 3-leg inverter is applied to drive the 2-phase outer rotor coreless TA of a hybrid gimbal system, and it is verified through simulation. Full article
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Open AccessArticle Electro-Thermal Modeling of Metal-Oxide Arrester under Power Frequency Applied Voltages
Energies 2018, 11(6), 1610; https://doi.org/10.3390/en11061610
Received: 30 May 2018 / Revised: 11 June 2018 / Accepted: 14 June 2018 / Published: 20 June 2018
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Abstract
Metal-oxide arresters (MOAs) are used to absorb the electrical energy resulting from overvoltages in power systems. However, temperature rises caused by the absorbed energy can lead to the electrothermal failure of MOAs. Therefore, it is necessary to analyze the electric and thermal characteristics
[...] Read more.
Metal-oxide arresters (MOAs) are used to absorb the electrical energy resulting from overvoltages in power systems. However, temperature rises caused by the absorbed energy can lead to the electrothermal failure of MOAs. Therefore, it is necessary to analyze the electric and thermal characteristics of MOAs. In this paper, in order to study the electric and thermal characteristics of MOAs under power frequency voltage, an improved electrothermal model of an MOA is presented. The proposed electrothermal model can be divided into an electric model and a thermal model. In the electric model, based on the conventional MOA electric circuit, the effect of temperature on the voltage–current (V–I) characteristics of an MOA has been obtained. Using temperature and applied voltage as input data, the current flows through the MOA can be calculated using the artificial neural network (ANN) method. In the thermal model, the thermal circuit of a MOA has been built. The varistor power loss obtained from the electric model is used as input data, and the temperature of the zinc oxide varistors can be calculated. Therefore, compared with the existing MOA models, the interaction of leakage current and temperature can be considered in the proposed model. Finally, experimental validations have been done, and the electrothermal characteristics of an MOA have been studied by simulation and experimental methods. The electrothermal model proposed in this paper can assist with the prediction of the electric and thermal characteristics of MOAs. Full article
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Open AccessArticle Wind Farm Blockage and the Consequences of Neglecting Its Impact on Energy Production
Energies 2018, 11(6), 1609; https://doi.org/10.3390/en11061609
Received: 22 March 2018 / Revised: 14 June 2018 / Accepted: 15 June 2018 / Published: 20 June 2018
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Abstract
Measurements taken before and after the commissioning of three wind farms reveal that the wind speeds just upstream of each wind farm decrease relative to locations farther away after the turbines are turned on. At a distance of two rotor diameters upstream, the
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Measurements taken before and after the commissioning of three wind farms reveal that the wind speeds just upstream of each wind farm decrease relative to locations farther away after the turbines are turned on. At a distance of two rotor diameters upstream, the average derived relative slowdown is 3.4%; at seven to ten rotor diameters upstream, the average slowdown is 1.9%. Reynolds-Averaged Navier-Stokes (RANS) simulations point to wind-farm-scale blockage as the primary cause of these slowdowns. Blockage effects also cause front row turbines to produce less energy than they each would operating in isolation. Wind energy prediction procedures in use today ignore this effect, resulting in an overprediction bias that pervades the entire wind farm. Full article
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Open AccessArticle A Fully Coupled Numerical Model for Microwave Heating Enhanced Shale Gas Recovery
Energies 2018, 11(6), 1608; https://doi.org/10.3390/en11061608
Received: 18 May 2018 / Revised: 7 June 2018 / Accepted: 12 June 2018 / Published: 20 June 2018
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Abstract
Formation heat treatment (FHT) can be achieved by converting electromagnetic energy into heat energy (that is microwave heating or MWH). Experimental evidence shows that such FHT can significantly enhance oil and gas recovery. As relatively few research studies have been reported on microwave
[...] Read more.
Formation heat treatment (FHT) can be achieved by converting electromagnetic energy into heat energy (that is microwave heating or MWH). Experimental evidence shows that such FHT can significantly enhance oil and gas recovery. As relatively few research studies have been reported on microwave heating enhanced shale gas recovery (MWH-EGR), a fully coupled electromagnetic-thermo-hydro-mechanical (ETHM) model is developed for the MWH-EGR in the present study. In the ETHM model, a thermal-induced gas adsorption model is firstly proposed for shale gas adsorption and fitted by experimental data. This thermal-induced adsorption model considers the increase of matrix pore space due to the desorption of the adsorbed phase. Further, a thermal-induced fracture model in shale matrix is established and fitted by experimental data. Finally, this ETHM model is applied to a fractured shale gas reservoir to simulate gas production. Numerical results indicated that the thermal-induced fracturing and gas desorption make predominant contributions to the evolution of matrix porosity. The MWH can increase cumulative gas production by 44.9% after 31.7 years through promoting gas desorption and matrix diffusion. These outcomes can provide effective insights into shale gas recovery enhancement by microwave assistance. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle The Effect of a Vertical Electric Field on the Surface Flashover Characteristics of a Bushing Model
Energies 2018, 11(6), 1607; https://doi.org/10.3390/en11061607
Received: 27 May 2018 / Revised: 13 June 2018 / Accepted: 15 June 2018 / Published: 20 June 2018
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Abstract
High-voltage bushings play a crucial role in energy conveyance. Their specialized electric structure makes the bushing more vulnerable to surface discharge. However, the influence of a vertical electric field on the surface flashover of bushing structures remains unclear. To investigate this mechanism, four
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High-voltage bushings play a crucial role in energy conveyance. Their specialized electric structure makes the bushing more vulnerable to surface discharge. However, the influence of a vertical electric field on the surface flashover of bushing structures remains unclear. To investigate this mechanism, four simplified bushing samples were built and the influence of pollution, leakage length, and the electric field component vertical to the dielectric surface on flashover properties of the bushing samples were tested. It was found that the surface pollution level was the decisive factor that influenced flashover voltage. When the leakage length and form factor were the same, the pollution flashover of the bushing structure was lower than that of the post structure. It was also found that increasing the leakage length was not very effective in improving the flashover voltage of bushings when the equivalent salt deposit density (ESDD) was high. No obvious correlation was found between pollution flashover voltage and electric field stress. Furthermore, the uneven wetting flashover performance of the bushings was tested. Under this condition, the flashover voltage decreased with an increase of the electric field component vertical to the dielectric surface. In addition, the electric field distribution of the samples was calculated and the results were in accordance with the experimental results. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Reactive Power Planning for Regional Power Grids Based on Active and Reactive Power Adjustments of DGs
Energies 2018, 11(6), 1606; https://doi.org/10.3390/en11061606
Received: 19 May 2018 / Revised: 9 June 2018 / Accepted: 12 June 2018 / Published: 20 June 2018
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Abstract
To deal with extreme overvoltage scenarios with small probabilities in regional power grids, the traditional reactive power planning model requires a huge VAR compensator investment. Obviously, such a decision that makes a large investment to cope with a small probability event is not
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To deal with extreme overvoltage scenarios with small probabilities in regional power grids, the traditional reactive power planning model requires a huge VAR compensator investment. Obviously, such a decision that makes a large investment to cope with a small probability event is not economic. Therefore, based on the scenario analysis of power outputs of distributed generations and load consumption, a novel reactive power planning model considering the active and reactive power adjustments of distributed generations is proposed to derive the optimal allocation of VAR compensators and ensure bus voltages within an acceptable range under extreme overvoltage scenarios. The objective of the proposed reactive power planning model is to minimize the VAR compensator investment cost and active power adjustment cost of distributed generations. Moreover, since the proposed reactive power planning model is formulated as a mixed-integer nonlinear programming problem, a primal-dual interior point method-based particle swarm optimization algorithm is developed to effectively solve the proposed model. Simulation results were conducted with the modified IEEE 30-bus system to verify the effectiveness of the proposed reactive power planning model. Full article
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Open AccessArticle Short-Term Forecasting for Energy Consumption through Stacking Heterogeneous Ensemble Learning Model
Energies 2018, 11(6), 1605; https://doi.org/10.3390/en11061605
Received: 20 May 2018 / Revised: 8 June 2018 / Accepted: 13 June 2018 / Published: 19 June 2018
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Abstract
In the real-life, time-series data comprise a complicated pattern, hence it may be challenging to increase prediction accuracy rates by using machine learning and conventional statistical methods as single learners. This research outlines and investigates the Stacking Multi-Learning Ensemble (SMLE) model for time
[...] Read more.
In the real-life, time-series data comprise a complicated pattern, hence it may be challenging to increase prediction accuracy rates by using machine learning and conventional statistical methods as single learners. This research outlines and investigates the Stacking Multi-Learning Ensemble (SMLE) model for time series prediction problem over various horizons with a focus on the forecasts accuracy, directions hit-rate, and the average growth rate of total oil demand. This investigation presents a flexible ensemble framework in light of blend heterogeneous models for demonstrating and forecasting nonlinear time series. The proposed SMLE model combines support vector regression (SVR), backpropagation neural network (BPNN), and linear regression (LR) learners, the ensemble architecture consists of four phases: generation, pruning, integration, and ensemble prediction task. We have conducted an empirical study to evaluate and compare the performance of SMLE using Global Oil Consumption (GOC). Thus, the assessment of the proposed model was conducted at single and multistep horizon prediction using unique benchmark techniques. The final results reveal that the proposed SMLE model outperforms all the other benchmark methods listed in this study at various levels such as error rate, similarity, and directional accuracy by 0.74%, 0.020%, and 91.24%, respectively. Therefore, this study demonstrates that the ensemble model is an extremely encouraging methodology for complex time series forecasting. Full article
(This article belongs to the Special Issue Short-Term Load Forecasting by Artificial Intelligent Technologies)
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Open AccessArticle Improvement in Harmonic Compensation of a Smart Charger with a Constant DC-Capacitor Voltage-Control-Based Strategy for Electric Vehicles in Single-Phase Three-Wire Distribution Feeders
Energies 2018, 11(6), 1604; https://doi.org/10.3390/en11061604
Received: 19 April 2018 / Revised: 10 June 2018 / Accepted: 14 June 2018 / Published: 19 June 2018
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Abstract
This paper presents an improvement in harmonic compensation performance of a previously proposed smart charger (SC) with a constant dc-capacitor voltage-control (CDCVC) strategy for electric vehicles (EVs) in single-phase three-wire distribution feeders (SPTWDFs). A controller for 3rd harmonic currents in d-q
[...] Read more.
This paper presents an improvement in harmonic compensation performance of a previously proposed smart charger (SC) with a constant dc-capacitor voltage-control (CDCVC) strategy for electric vehicles (EVs) in single-phase three-wire distribution feeders (SPTWDFs). A controller for 3rd harmonic currents in d-q coordinates is added to the previously proposed SC. This addition improves harmonic compensation performance of the source currents. We briefly introduce harmonic current compensation using the previously proposed CDCVC-based algorithm for the SC. Then, the basic principles of the proposed controller for the 3rd harmonic currents in d-q coordinates are discussed in detail. It is shown that synchronization of the current controllers for both the fundamental and 3rd harmonic components is required. The switching frequency of a three-leg pulse-width modulated rectifier with a bidirectional dc–dc converter, which performs the SC, is determined considering the synchronization of the current controllers. Simulation and experimental results demonstrate that balanced and sinusoidal source currents with a unity power factor are achieved during both battery charging and discharging operations in EVs, improving the harmonic compensation performance of the previously proposed SC. Experimental results also demonstrate that the total harmonic distortion values of source currents are improved by 8.4% and 3.6% with the proposed controller for 3rd harmonic currents, when the SC is discharging, for example. Full article
(This article belongs to the Special Issue Power Electronics for Energy Storage)
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Open AccessArticle Investigation of Discharge Coefficients for Single Element Lean Direct Injection Modules
Energies 2018, 11(6), 1603; https://doi.org/10.3390/en11061603
Received: 11 May 2018 / Revised: 5 June 2018 / Accepted: 12 June 2018 / Published: 19 June 2018
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Abstract
Lean direct injection (LDI) combustion has a high potential as a low pollution combustion method for gas turbines. The present research aims to further investigate the discharge coefficient of an LDI module, axial swirler and convergent outlet under non-reaction and reaction conditions by
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Lean direct injection (LDI) combustion has a high potential as a low pollution combustion method for gas turbines. The present research aims to further investigate the discharge coefficient of an LDI module, axial swirler and convergent outlet under non-reaction and reaction conditions by theoretical, numerical and experimental methods. The functional relationship between the discharge coefficient of the LDI module, axial swirler and convergent outlet was established, and the effect of swirl angle (30°, 32°, 34°, 36°, 38°, 40°) and vane number (11, 12, 13, 14, 15, 16) on discharge coefficient was studied, and finally the differences in effective flow area of LDI combustor under different inlet conditions were analyzed. The results indicate that the flow separation on the suction side increases as the swirl angle increases, which leads to a decrease of the discharge coefficient of the axial swirler, however the discharge coefficient of the convergent outlet remains unchanged first and then decreases. As the vane number increases, the flow separation on the suction side decreases and the flow friction loss increases, so that the discharge coefficient of the axial swirler and convergent outlet will first increase with the increase of vane number and then decrease with further increases. The effective flow area of combustor changes as the conditions change, but it is approximately equal under high power conditions and normal temperature and pressure conditions. Full article
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Open AccessArticle Strategic Behavior of Retailers for Risk Reduction and Profit Increment via Distributed Generators and Demand Response Programs
Energies 2018, 11(6), 1602; https://doi.org/10.3390/en11061602
Received: 9 May 2018 / Revised: 5 June 2018 / Accepted: 8 June 2018 / Published: 19 June 2018
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Abstract
Following restructuring of power industry, electricity supply to end-use customers has undergone fundamental changes. In the restructured power system, some of the responsibilities of the vertically integrated distribution companies have been assigned to network managers and retailers. Under the new situation, retailers are
[...] Read more.
Following restructuring of power industry, electricity supply to end-use customers has undergone fundamental changes. In the restructured power system, some of the responsibilities of the vertically integrated distribution companies have been assigned to network managers and retailers. Under the new situation, retailers are in charge of providing electrical energy to electricity consumers who have already signed contract with them. Retailers usually provide the required energy at a variable price, from wholesale electricity markets, forward contracts with energy producers, or distributed energy generators, and sell it at a fixed retail price to its clients. Different strategies are implemented by retailers to reduce the potential financial losses and risks associated with the uncertain nature of wholesale spot electricity market prices and electrical load of the consumers. In this paper, the strategic behavior of retailers in implementing forward contracts, distributed energy sources, and demand-response programs with the aim of increasing their profit and reducing their risk, while keeping their retail prices as low as possible, is investigated. For this purpose, risk management problem of the retailer companies collaborating with wholesale electricity markets, is modeled through bi-level programming approach and a comprehensive framework for retail electricity pricing, considering customers’ constraints, is provided in this paper. In the first level of the proposed bi-level optimization problem, the retailer maximizes its expected profit for a given risk level of profit variability, while in the second level, the customers minimize their consumption costs. The proposed programming problem is modeled as Mixed Integer programming (MIP) problem and can be efficiently solved using available commercial solvers. The simulation results on a test case approve the effectiveness of the proposed demand-response program based on dynamic pricing approach on reducing the retailer’s risk and increasing its profit. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Influence of High-Speed Train Power Consumption and Arc Fault Resistances on a Novel Ground Fault Location Method for 2 × 25 kV Railway Power Supply Systems
Energies 2018, 11(6), 1601; https://doi.org/10.3390/en11061601
Received: 17 May 2018 / Revised: 5 June 2018 / Accepted: 15 June 2018 / Published: 19 June 2018
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Abstract
The 2 × 25 kV power supply system is the most frequently used traction rail system to provide the huge power needed by high-speed trains. However, locating the ground fault in this power supply system is more complicated than in other configurations of
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The 2 × 25 kV power supply system is the most frequently used traction rail system to provide the huge power needed by high-speed trains. However, locating the ground fault in this power supply system is more complicated than in other configurations of electrical railway power supply due to the installation of autotransformers throughout the line section. In previous papers, the authors have described a ground fault location method with an insignificant installation cost. The method and, moreover, the location discriminate between whether the ground fault is located between a positive conductor and ground or a negative conductor and ground. The current of the high-speed train influences the accuracy of the location of the ground fault. An additional factor which influences the location method is the existence of an arc resistance between the positive or negative conductor and ground. In this paper, the influence of high-speed train currents and arc resistances are analysed to evaluate the error in the location method. The major conclusion of the paper is that the location method has an acceptable precision even taking into consideration the high-speed train current and arc resistance. The validation of the method has been performed by laboratory tests and computer simulations with satisfactory results. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle A Frequency Control Strategy Considering Large Scale Wind Power Cluster Integration Based on Distributed Model Predictive Control
Energies 2018, 11(6), 1600; https://doi.org/10.3390/en11061600
Received: 7 May 2018 / Revised: 7 June 2018 / Accepted: 12 June 2018 / Published: 19 June 2018
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Abstract
With large scale wind integration and increasing wind penetration in power systems, relying solely on conventional generators for frequency control is not enough to satisfy system frequency stability requirements. It is imperative that wind power have certain capabilities to participate in frequency control
[...] Read more.
With large scale wind integration and increasing wind penetration in power systems, relying solely on conventional generators for frequency control is not enough to satisfy system frequency stability requirements. It is imperative that wind power have certain capabilities to participate in frequency control by cooperating with conventional power sources. Firstly, a multi-area interconnected power system frequency response model containing wind power clusters and conventional generators is established with consideration of several nonlinear constraints. Moreover, a distributed model predictive control (DMPC) strategy considering Laguerre functions is proposed, which implements online rolling optimization by using ultra-short-term wind power forecasting data in order to realize advanced frequency control. Finally, a decomposition-coordination control algorithm considering Nash equilibrium is presented, which realizes online fast optimization of multivariable systems with constraints. Simulation results demonstrate the feasibility and effectiveness of the proposed control strategy and algorithm. Full article
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Open AccessArticle A New Plugging Technology and Its Application for the Extensively Collapsed Ore Pass in the Non-Empty Condition
Energies 2018, 11(6), 1599; https://doi.org/10.3390/en11061599
Received: 25 April 2018 / Revised: 11 June 2018 / Accepted: 14 June 2018 / Published: 19 June 2018
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Abstract
Aiming at some long ore passes with severe damages and extensive collapses, we describe an optimal measure to plug a local area of ore pass in order to maintain the capacity of continued use. This paper, taking a new plug for the extensively
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Aiming at some long ore passes with severe damages and extensive collapses, we describe an optimal measure to plug a local area of ore pass in order to maintain the capacity of continued use. This paper, taking a new plug for the extensively collapsed long ore pass in the non-empty condition as a breakthrough, builds a structure-plugging system for ore pass based on plug effect, suspension effect, arch effect, and span-reducing effect. Meanwhile, a key plugging technology has been integrated which includes a stability evaluation method of plugging structure, controlled technology of drilling with casing in the composite rock mass, and controllable grouting for inhomogeneous loose rock mass. According to this structure-plugging system and technology, a case has been successful for the main ore pass in the Xingshan Iron Mine in China, which has created a precedent in the world. The practice results show that using this technology to plug the extensively collapsed long ore pass has a series of advantages including of scientific design, strong safety, high efficiency, and low cost. Full article
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Open AccessArticle Analysis and Optimization of the Electromagnetic Performance of a Novel Stator Modular Ring Drive Thruster Motor
Energies 2018, 11(6), 1598; https://doi.org/10.3390/en11061598
Received: 8 May 2018 / Revised: 7 June 2018 / Accepted: 13 June 2018 / Published: 19 June 2018
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Abstract
A rim driven thruster (RDT) is an integrated deep-sea motor thruster that has been widely studied. In order to improve the performance of RDT, a novel RDT motor with a modular stator is proposed in this paper. The electromagnetic performance of the new
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A rim driven thruster (RDT) is an integrated deep-sea motor thruster that has been widely studied. In order to improve the performance of RDT, a novel RDT motor with a modular stator is proposed in this paper. The electromagnetic performance of the new RDT motor is analyzed by the finite element method (FEM). The influence of structure parameters on the electromagnetic performance of the new RDT motor are analyzed in detail. It is shown that the effect of additional tooth width and pole arc coefficient on the electromagnetic performance of the stator modular RDT motor is significant. To obtain the optimal design with a maximum average electromagnetic torque and minimum torque fluctuation ratio, a multi-objective optimization design method combining the non-dominated sorting genetic algorithm II (NSGA-II), Kriging method and FEM is presented in this paper. A set of Pareto optimal solutions is obtained, and the optimal design point is selected from the Pareto fronts. Compared with the initial design, the average electromagnetic torque of the optimized model is improved by 16.591% and the fluctuation ratio is reduced to 3.18%. Full article
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Open AccessArticle The Influence of Operating Parameters on Adsorption/Desorption Characteristics and Performance of the Fluidised Desiccant Cooler
Energies 2018, 11(6), 1597; https://doi.org/10.3390/en11061597
Received: 21 May 2018 / Revised: 11 June 2018 / Accepted: 14 June 2018 / Published: 19 June 2018
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Abstract
This paper concerns the issue of the proper selection of the operating parameters of the fluidised desiccant cooler. Despite the fact that fluidised desiccant cooling technology is being reported in the literature as an efficient way to provide cooling for the purposes of
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This paper concerns the issue of the proper selection of the operating parameters of the fluidised desiccant cooler. Despite the fact that fluidised desiccant cooling technology is being reported in the literature as an efficient way to provide cooling for the purposes of air-conditioning, the improper control of its operation can lead to a significantly worse performance than expected. The objective of the presented theoretical study is to provide guidelines on the proper selection of such operating parameters of a fluidized desiccant cooler, such as superficial air velocity, desiccant particle diameter, bed switching time, and desiccant filling height. The influence of the chosen operating parameters on the performance of fluidised desiccant cooling technology is investigated based on their impact on electric and thermal coefficients of performance (COP) and specific cooling power (SCP). Moreover, the influence of the outlet air temperature, humidity, and desiccant water uptake on the adsorption/desorption characteristics was investigated, contributing to better understanding of sorption processes. Full article
(This article belongs to the Special Issue Energy Systems Engineering)
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Open AccessArticle Analysis of Carbon Storage and Its Contributing Factors—A Case Study in the Loess Plateau (China)
Energies 2018, 11(6), 1596; https://doi.org/10.3390/en11061596
Received: 14 May 2018 / Revised: 31 May 2018 / Accepted: 12 June 2018 / Published: 19 June 2018
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Abstract
The Chinese Loess Plateau is an ecologically fragile and sensitive area. The carbon storage dynamics in this region and the contributions from land use/land cover change (LUCC) and carbon density from 2000 to 2010 were analyzed in this paper. Normalized difference vegetation index
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The Chinese Loess Plateau is an ecologically fragile and sensitive area. The carbon storage dynamics in this region and the contributions from land use/land cover change (LUCC) and carbon density from 2000 to 2010 were analyzed in this paper. Normalized difference vegetation index (NDVI), biomass and soil carbon data in 2000 were used for regression analysis of biomass and soil carbon, and an inversion analysis was used to estimate biomass and soil carbon in 2005 and 2010. Quadrat data, including aboveground biomass and soil organic carbon, were used to calibrate the model output. Carbon storage and sequestration were calculated by the InVEST toolset with four carbon pools, including aboveground biomass, belowground biomass, dead wood and soil carbon. The results showed that carbon storage increased steadily from 2000 to 2010, increasing by 0.260 billion tons, and that woodland area increased and arable land decreased; the overall trend in land cover improved, but the improvement was not pronounced. Carbon storage in the Loess Plateau was correlated with geographical factors. We found that when assuming a constant carbon density, carbon storage decreased, accounting for −1% of the carbon storage dynamics. When assuming no land conversion, carbon storage increased, accounting for 101% of the carbon storage dynamics. Full article
(This article belongs to the Special Issue Carbon Capture and Storage)
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Open AccessArticle Volatility Spillovers between Energy and Agricultural Markets: A Critical Appraisal of Theory and Practice
Energies 2018, 11(6), 1595; https://doi.org/10.3390/en11061595
Received: 24 May 2018 / Revised: 11 June 2018 / Accepted: 12 June 2018 / Published: 19 June 2018
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Abstract
Energy and agricultural commodities and markets have been examined extensively, albeit separately, for a number of years. In the energy literature, the returns, volatility and volatility spillovers (namely, the delayed effect of a returns shock in one asset on the subsequent volatility or
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Energy and agricultural commodities and markets have been examined extensively, albeit separately, for a number of years. In the energy literature, the returns, volatility and volatility spillovers (namely, the delayed effect of a returns shock in one asset on the subsequent volatility or covolatility in another asset), among alternative energy commodities, such as oil, gasoline and ethanol across different markets, have been analysed using a variety of univariate and multivariate models, estimation techniques, data sets, and time frequencies. A similar comment applies to the separate theoretical and empirical analysis of a wide range of agricultural commodities and markets. Given the recent interest and emphasis in bio-fuels and green energy, especially bio-ethanol, which is derived from a range of agricultural products, it is not surprising that there is a topical and developing literature on the spillovers between energy and agricultural markets. Modelling and testing spillovers between the energy and agricultural markets has typically been based on estimating multivariate conditional volatility models, specifically the Baba, Engle, Kraft, and Kroner (BEKK) and dynamic conditional correlation (DCC) models. A serious technical deficiency is that the Quasi-Maximum Likelihood Estimates (QMLE) of a Full BEKK matrix, which is typically estimated in examining volatility spillover effects, has no asymptotic properties, except by assumption, so that no valid statistical test of volatility spillovers is possible. Some papers in the literature have used the DCC model to test for volatility spillovers. However, it is well known in the financial econometrics literature that the DCC model has no regularity conditions, and that the QMLE of the parameters of DCC has no asymptotic properties, so that there is no valid statistical testing of volatility spillovers. The purpose of the paper is to evaluate the theory and practice in testing for volatility spillovers between energy and agricultural markets using the multivariate Full BEKK and DCC models, and to make recommendations as to how such spillovers might be tested using valid statistical techniques. Three new definitions of volatility and covolatility spillovers are given, and the different models used in empirical applications are evaluated in terms of the new definitions and statistical criteria. Full article
(This article belongs to the Special Issue Multivariate Modelling of Fossil Fuel and Carbon Emission Prices)
Open AccessArticle Low-Frequency Oscillation Suppression of the Vehicle–Grid System in High-Speed Railways Based on H∞ Control
Energies 2018, 11(6), 1594; https://doi.org/10.3390/en11061594
Received: 29 April 2018 / Revised: 6 June 2018 / Accepted: 13 June 2018 / Published: 18 June 2018
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Abstract
Recently, a traction blockade in the depots of numerous electric multiple units (EMUs) of high-speed railways has occured and resulted in some accidents in train operation. The traction blockade is caused by the low-frequency oscillation (LFO) of the vehicle–grid (EMUs–traction network) system. To
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Recently, a traction blockade in the depots of numerous electric multiple units (EMUs) of high-speed railways has occured and resulted in some accidents in train operation. The traction blockade is caused by the low-frequency oscillation (LFO) of the vehicle–grid (EMUs–traction network) system. To suppress the LFO, a scheme of EMUs line-side converter based on the H∞ control is proposed in this paper. First, the mathematical model of the four-quadrant converter in EMUs is presented. Second, the state variables are determined and the weighting functions are selected. Then, an H∞ controller based on the dq coordinate is designed. Moreover, compared with the simulation results of traditional proportional integral (PI) control, auto-disturbance rejection control (ADRC) and multivariable control (MC) based on Matlab/Simulink and the RT-LAB platform, the simulation results of the proposed H∞ control confirm that the H∞ controller applied in EMUs of China Railway High-Speed 3 has better dynamic and static performances. Finally, a whole cascade system model of EMUs and a traction network is built, in which a reduced-order model of a traction network is adopted. The experimental results of multi-EMUs accessed in the traction network indicate that the H∞ controller has good suppression performance for the LFO of the vehicle–grid system. In addition, through the analysis of sensitivity of the H∞ controller and the traditional PI controller, it is indicated that the H∞ controller has better robustness. Full article
(This article belongs to the Special Issue Advanced Control Techniques for Power Converters)
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Open AccessArticle A Class of Control Strategies for Energy Internet Considering System Robustness and Operation Cost Optimization
Energies 2018, 11(6), 1593; https://doi.org/10.3390/en11061593
Received: 28 May 2018 / Revised: 12 June 2018 / Accepted: 14 June 2018 / Published: 18 June 2018
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Abstract
Aiming at restructuring the conventional energy delivery infrastructure, the concept of energy Internet (EI) has become popular in recent years. Outstanding benefits from an EI include openness, robustness and reliability. Most of the existing literatures focus on the conceptual design of EI and
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Aiming at restructuring the conventional energy delivery infrastructure, the concept of energy Internet (EI) has become popular in recent years. Outstanding benefits from an EI include openness, robustness and reliability. Most of the existing literatures focus on the conceptual design of EI and are lack of theoretical investigation on developing specific control strategies for the operation of EI. In this paper, a class of control strategies for EI considering system robustness and operation cost optimization is investigated. Focusing on the EI system robustness issue, system parameter uncertainty, external disturbance and tracking error are taken into consideration, and we formulate such robust control issue as a structure specified mixed H2/H control problem. When formulating the operation cost optimization problem, three aspects are considered: realizing the bottom-up energy management principle, reducing the cost involved by power delivery from power grid (PG) to microgrid (MG), and avoiding the situation of over-control. We highlight that this is the very first time that the above targets are considered simultaneously in the field of EI. The integrated control issue is considered in frequency domain and is solved by a particle swarm optimization (PSO) algorithm. Simulation results show that our proposed method achieves the targets. Full article
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Open AccessArticle A Dual-Function Instantaneous Power Theory for Operation of Three-Level Neutral-Point-Clamped Inverter-Based Shunt Active Power Filter
Energies 2018, 11(6), 1592; https://doi.org/10.3390/en11061592
Received: 10 May 2018 / Revised: 25 May 2018 / Accepted: 2 June 2018 / Published: 18 June 2018
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Abstract
This paper proposes a simple yet effective reference current generation algorithm based on instantaneous power pq theory to enhance mitigation performance of a three-phase three-level neutral-point-clamped (NPC) inverter-based shunt active power filter (SAPF). The proposed algorithm is developed for dual functionality: generate
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This paper proposes a simple yet effective reference current generation algorithm based on instantaneous power pq theory to enhance mitigation performance of a three-phase three-level neutral-point-clamped (NPC) inverter-based shunt active power filter (SAPF). The proposed algorithm is developed for dual functionality: generate reference current and synchronization phase to effectively govern operation of SAPF in mitigating harmonic current and compensating reactive power. Three key modifications are implemented: (1) replacement of numerical low-pass filter (LPF) with an average power detector to improve mitigation performance; (2) removal of needless reactive element to reduce algorithm complexity; and (3) integration of phase tracking feature to eliminate the needs of phase-locked loop (PLL). Simulation work of SAPF with the proposed algorithm was conducted and assessed in MATLAB–Simulink. In addition, to verify feasibility of the proposed algorithm, a laboratory prototype as constructed with TMS320F28335 digital signal processor (DSP) programmed as the controller. Performance of SAPF achieved by utilizing the proposed algorithm was thoroughly investigated and benchmarked with that demonstrated using the existing pq theory algorithm to evaluate the inherent advantages. Simulation and experimental results are obtained for different nonlinear loads and test conditions. Responses demonstrated by SAPF in both simulation and experimental works reveal superiority of the proposed algorithm over the existing algorithm. Full article
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Open AccessArticle The Integration of 3D Modeling and Simulation to Determine the Energy Potential of Low-Temperature Geothermal Systems in the Pisa (Italy) Sedimentary Plain
Energies 2018, 11(6), 1591; https://doi.org/10.3390/en11061591
Received: 15 May 2018 / Revised: 11 June 2018 / Accepted: 14 June 2018 / Published: 18 June 2018
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Abstract
Shallow, low-temperature geothermal resources can significantly reduce the environmental impact of heating and cooling. Based on a replicable standard workflow for three-dimensional (3D) geothermal modeling, an approach to the assessment of geothermal energy potential is proposed and applied to the young sedimentary basin
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Shallow, low-temperature geothermal resources can significantly reduce the environmental impact of heating and cooling. Based on a replicable standard workflow for three-dimensional (3D) geothermal modeling, an approach to the assessment of geothermal energy potential is proposed and applied to the young sedimentary basin of Pisa (north Tuscany, Italy), starting from the development of a geothermal geodatabase, with collated geological, stratigraphic, hydrogeological, geophysical and thermal data. The contents of the spatial database are integrated and processed using software for geological and geothermal modeling. The models are calibrated using borehole data. Model outputs are visualized as three-dimensional reconstructions of the subsoil units, their volumes and depths, the hydrogeological framework, and the distribution of subsoil temperatures and geothermal properties. The resulting deep knowledge of subsoil geology would facilitate the deployment of geothermal heat pump technology, site selection for well doublets (for open-loop systems), or vertical heat exchangers (for closed-loop systems). The reconstructed geological–hydrogeological models and the geothermal numerical simulations performed help to define the limits of sustainable utilization of an area’s geothermal potential. Full article
(This article belongs to the Special Issue Geothermal Energy: Utilization and Technology)
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Open AccessArticle One-Pot Hydrothermal Synthesis of Novel Cu-MnS with PVP Cabbage-Like Nanostructures for High-Performance Supercapacitors
Energies 2018, 11(6), 1590; https://doi.org/10.3390/en11061590
Received: 28 April 2018 / Revised: 6 June 2018 / Accepted: 13 June 2018 / Published: 17 June 2018
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Abstract
This paper reports the facile synthesis of a novel architecture of Cu-MnS with PVP, where the high theoretical capacitance of MnS, low-cost, and high electrical conductivity of Cu, as well as appreciable surface area with high thermal and mechanical conductivity of PVP, as
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This paper reports the facile synthesis of a novel architecture of Cu-MnS with PVP, where the high theoretical capacitance of MnS, low-cost, and high electrical conductivity of Cu, as well as appreciable surface area with high thermal and mechanical conductivity of PVP, as a single entity to fabricate a high-performance electrode for supercapacitor. Benefiting from their unique structures, the Cu-MnS with 2PVP electrode materials show a high specific capacitance of 833.58 F g−1 at 1 A g−1, reversibility for the charge/discharge process, which are much higher than that of the MnS-7 h, Cu-MnS, and Cu-MnS with 1 and 3PVP. The presence of an appropriate amount of PVP in Cu-MnS is favorable for improving the electrochemical performance of the electrode and the existence of Cu was inclined to enhance the electrical conductivity. The Cu-MnS with 2PVP electrode is a good reference for researchers to design and fabricate new electrode materials with enhanced capacitive performance. Full article
(This article belongs to the Special Issue Solar Energy Harvesting, Storage and Utilization)
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Open AccessArticle Approaches for Safety Analysis of Gas-Pipeline Functionality in Terms of Failure Occurrence: A Case Study
Energies 2018, 11(6), 1589; https://doi.org/10.3390/en11061589
Received: 24 May 2018 / Revised: 9 June 2018 / Accepted: 15 June 2018 / Published: 17 June 2018
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Abstract
The development of appropriate assessment methods of gas-pipeline functionality contributes to the reduction of failure consequences and helps engineers to make the right decisions as to the optimal solution choice for technical facilities, as well as provides procedures to protect their users and
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The development of appropriate assessment methods of gas-pipeline functionality contributes to the reduction of failure consequences and helps engineers to make the right decisions as to the optimal solution choice for technical facilities, as well as provides procedures to protect their users and the surrounding environment. This paper presents methods for the assessment of gas network operation. Pipe failure data were collected from a gas distribution network. A statistical analysis of the failure of gas networks was made. An attempt was made to isolate seasonal and accidental fluctuations in the tested failure stream. The Poisson distribution was proposed as a model of failure distribution of gas networks. The conducted analysis allowed us to propose the forecasting method of acceptable failure consequences using the homogeneous Markov chain. The obtained results are valuable for supporting the management of urban gas networks, mainly in terms of the strategic modernization plans and the rehabilitation techniques. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessArticle Electricity Price Forecasting with Dynamic Trees: A Benchmark Against the Random Forest Approach
Energies 2018, 11(6), 1588; https://doi.org/10.3390/en11061588
Received: 22 March 2018 / Revised: 25 May 2018 / Accepted: 14 June 2018 / Published: 17 June 2018
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Abstract
Dynamic Trees are a tree-based machine learning technique specially designed for online environments where data are to be analyzed sequentially as they arrive. Our purpose is to test this methodology for the very first time for Electricity Price Forecasting (EPF) by using data
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Dynamic Trees are a tree-based machine learning technique specially designed for online environments where data are to be analyzed sequentially as they arrive. Our purpose is to test this methodology for the very first time for Electricity Price Forecasting (EPF) by using data from the Iberian market. For benchmarking the results, we will compare them against another tree-based technique, Random Forest, a widely used method that has proven its good results in many fields. The benchmark includes several versions of the Dynamic Trees approach for a very short term EPF (one-hour ahead) and also a short term (one-day ahead) approach but only with the best versions. The numerical results show that Dynamic Trees are an adequate method, both for very short and short term EPF—even improving upon the performance of the Random Forest method. The comparison with other studies for the Iberian market suggests that Dynamic Trees is a proper and promising method for EPF. Full article
(This article belongs to the Special Issue Forecasting Models of Electricity Prices 2018)
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Open AccessArticle Life Cycle Analysis of Integrated Gasification Combined Cycle Power Generation in the Context of Southeast Asia
Energies 2018, 11(6), 1587; https://doi.org/10.3390/en11061587
Received: 24 May 2018 / Revised: 13 June 2018 / Accepted: 14 June 2018 / Published: 17 June 2018
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Abstract
Coal remains a major source of electricity production even under the current state of developments in climate policies due to national energy priorities. Coal remains the most attractive option, especially to the developing economies in Southeast Asia, due to its abundance and affordability
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Coal remains a major source of electricity production even under the current state of developments in climate policies due to national energy priorities. Coal remains the most attractive option, especially to the developing economies in Southeast Asia, due to its abundance and affordability in the region, despite the heavily polluting nature of this energy source. Gasification of coal running on an integration gasification combined cycle (IGCC) power generation with carbon capture and storage (CCS) represents an option to reduce the environmental impacts of power generation from coal, but the decarbonization potential and suitability of IGCC in the context of Southeast Asia remain unclear. Using Singapore as an example, this paper presents a study on the life cycle analysis (LCA) of IGCC power generation with and without CCS based on a generic process-driven analysis method. We further evaluate the suitability of IGCC with and without CCS as an option to address the energy and climate objectives for the developing economies in Southeast Asia. Findings suggest that the current IGCC technology is a much less attractive option in the context of Southeast Asia when compared to other available power generation technologies, such as solar photovoltaic systems, coal with CCS, and potentially nuclear power technologies. Full article
(This article belongs to the Section Electrical Power and Energy System)
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