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Energies, Volume 10, Issue 2 (February 2017)

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Cover Story The development of distributed energy resources increases the needs of higher grid capacity. It is [...] Read more.
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Editorial

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Open AccessEditorial Forecasting Models of Electricity Prices
Energies 2017, 10(2), 160; doi:10.3390/en10020160
Received: 14 January 2017 / Revised: 20 January 2017 / Accepted: 20 January 2017 / Published: 29 January 2017
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(This article belongs to the Special Issue Forecasting Models of Electricity Prices)

Research

Jump to: Editorial, Review

Open AccessArticle Integration of Electric Vehicles into the Power Distribution Network with a Modified Capacity Allocation Mechanism
Energies 2017, 10(2), 200; doi:10.3390/en10020200
Received: 10 November 2016 / Accepted: 6 February 2017 / Published: 10 February 2017
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Abstract
The growing penetration of electric vehicles (EVs) represents an operational challenge to system operators, mainly at the distribution level by introducing congestion and voltage drop problems. To solve these potential problems, a two-level coordination approach is proposed in this study. An aggregation entity,
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The growing penetration of electric vehicles (EVs) represents an operational challenge to system operators, mainly at the distribution level by introducing congestion and voltage drop problems. To solve these potential problems, a two-level coordination approach is proposed in this study. An aggregation entity, i.e., an EV virtual power plant (EV-VPP), is used to facilitate the interaction between the distribution system operator (DSO) and EV owners considering the decentralized electricity market structure. In level I, to prevent the line congestion and voltage drop problems, the EV-VPP internally respects the line and voltage constraints when making optimal charging schedules. In level II, to avoid power transformer congestion problems, this paper investigates three different coordination mechanisms, or power transformer capacity allocation mechanisms, between the DSO and the EV-VPPs, considering the case of EVs charging and discharging. The three mechanisms include: (1) a market-based approach; (2) a pro-rata approach; and (3) a newly-proposed constrained market-based approach. A case study considering a 37-bus distribution network and high penetration of electric vehicles is presented to demonstrate the effectiveness of the proposed coordination mechanism, comparing with the existing ones. Full article
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Open AccessArticle Efficiency Analysis of the Main Components of a Vertical Closed-Loop System in a Borehole Heat Exchanger
Energies 2017, 10(2), 201; doi:10.3390/en10020201
Received: 22 November 2016 / Revised: 30 January 2017 / Accepted: 3 February 2017 / Published: 10 February 2017
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Abstract
In vertical closed-loop systems, it is common to use single or double U-tube heat exchangers separated by longitudinal spacers. In addition, the helical-shaped pipe is another configuration that requires lower drilling lengths but it is less used. The aim of the present research
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In vertical closed-loop systems, it is common to use single or double U-tube heat exchangers separated by longitudinal spacers. In addition, the helical-shaped pipe is another configuration that requires lower drilling lengths but it is less used. The aim of the present research is to study the influence of these components on the total efficiency of a borehole heat exchanger (BHE). Thus, the differences between using single/double U-tubes (with or without spacers) and helical pipes are analysed in terms of efficiency. Through different laboratory tests, a small vertical closed-loop system was simulated in order to analyse all these possible configurations. The grouting materials and the temperatures of the ground were modified at the same time in these tests. Regarding the heat exchange process between the ground and the heat carrier fluid, it must be highlighted that the best results were obtained for the helical-shaped pipe configuration. Some of the improvements offered by this heat exchanger typology with respect to the vertical configuration is that a lower drilling depth is required even it requires a larger diameter. This leads to significant economic savings in the performing drilling process. Finally, it is also worth noting the importance of using spacers in vertical U-tubes and that no improvements have been found regarding the use of single or double configuration of U-tubes. Thanks to the laboratory results derived from this study it is possible to establish the optimum behaviour pattern for the entire vertical closed-loop systems. Full article
(This article belongs to the Special Issue Low Enthalpy Geothermal Energy)
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Open AccessArticle From Theory to Econometrics to Energy Policy: Cautionary Tales for Policymaking Using Aggregate Production Functions
Energies 2017, 10(2), 203; doi:10.3390/en10020203
Received: 18 November 2016 / Revised: 16 January 2017 / Accepted: 24 January 2017 / Published: 10 February 2017
Cited by 2 | PDF Full-text (1735 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Development of energy policy is often informed by economic considerations via aggregate production functions (APFs). We identify a theory-to-policy process involving APFs comprised of six steps: (1) selecting a theoretical energy-economy framework; (2) formulating modeling approaches; (3) econometrically fitting an APF to historical
[...] Read more.
Development of energy policy is often informed by economic considerations via aggregate production functions (APFs). We identify a theory-to-policy process involving APFs comprised of six steps: (1) selecting a theoretical energy-economy framework; (2) formulating modeling approaches; (3) econometrically fitting an APF to historical economic and energy data; (4) comparing and evaluating modeling approaches; (5) interpreting the economy; and (6) formulating energy and economic policy. We find that choices made in Steps 1–4 can lead to very different interpretations of the economy (Step 5) and policies (Step 6). To investigate these effects, we use empirical data (Portugal and UK) and the Constant Elasticity of Substitution (CES) APF to evaluate four modeling choices: (a) rejecting (or not) the cost-share principle; (b) including (or not) energy; (c) quality-adjusting (or not) factors of production; and (d) CES nesting structure. Thereafter, we discuss two revealing examples for which different upstream modeling choices lead to very different policies. In the first example, the (kl)e nesting structure implies significant investment in energy, while other nesting structures suggest otherwise. In the second example, unadjusted factors of production suggest balanced investment in labor and energy, while quality-adjusting suggests significant investment in labor over energy. Divergent outcomes provide cautionary tales for policymakers: greater understanding of upstream modeling choices and their downstream implications is needed. Full article
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Open AccessArticle Technical Feasibility Study of Thermal Energy Storage Integration into the Conventional Power Plant Cycle
Energies 2017, 10(2), 205; doi:10.3390/en10020205
Received: 7 December 2016 / Revised: 20 January 2017 / Accepted: 1 February 2017 / Published: 11 February 2017
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Abstract
The current load balance in the grid is managed mainly through peaking fossil-fuelled power plants that respond passively to the load changes. Intermittency, which comes from renewable energy sources, imposes additional requirements for even more flexible and faster responses from conventional power plants.
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The current load balance in the grid is managed mainly through peaking fossil-fuelled power plants that respond passively to the load changes. Intermittency, which comes from renewable energy sources, imposes additional requirements for even more flexible and faster responses from conventional power plants. A major challenge is to keep conventional generation running closest to the design condition with higher load factors and to avoid switching off periods if possible. Thermal energy storage (TES) integration into the power plant process cycle is considered as a possible solution for this issue. In this article, a technical feasibility study of TES integration into a 375-MW subcritical oil-fired conventional power plant is presented. Retrofitting is considered in order to avoid major changes in the power plant process cycle. The concept is tested based on the complete power plant model implemented in the ProTRAX software environment. Steam and water parameters are assessed for different TES integration scenarios as a function of the plant load level. The best candidate points for heat extraction in the TES charging and discharging processes are evaluated. The results demonstrate that the integration of TES with power plant cycle is feasible and provide a provisional guidance for the design of the TES system that will result in the minimal influence on the power plant cycle. Full article
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Open AccessArticle A Cell-to-Cell Equalizer Based on Three-Resonant-State Switched-Capacitor Converters for Series-Connected Battery Strings
Energies 2017, 10(2), 206; doi:10.3390/en10020206
Received: 23 December 2016 / Revised: 1 February 2017 / Accepted: 6 February 2017 / Published: 11 February 2017
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Abstract
Due to the low cost, small size, and ease of control, the switched-capacitor (SC) battery equalizers are promising among active balancing methods. However, it is difficult to achieve the full cell equalization for the SC equalizers due to the inevitable voltage drops across
[...] Read more.
Due to the low cost, small size, and ease of control, the switched-capacitor (SC) battery equalizers are promising among active balancing methods. However, it is difficult to achieve the full cell equalization for the SC equalizers due to the inevitable voltage drops across Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) switches. Moreover, when the voltage gap among cells is larger, the balancing efficiency is lower, while the balancing speed becomes slower as the voltage gap gets smaller. In order to soften these downsides, this paper proposes a cell-to-cell battery equalization topology with zero-current switching (ZCS) and zero-voltage gap (ZVG) among cells based on three-resonant-state SC converters. Based on the conventional inductor-capacitor (LC) converter, an additional resonant path is built to release the charge of the capacitor into the inductor in each switching cycle, which lays the foundations for obtaining ZVG among cells, improves the balancing efficiency at a large voltage gap, and increases the balancing speed at a small voltage gap. A four-lithium-ion-cell prototype is applied to validate the theoretical analysis. Experiment results demonstrate that the proposed topology has good equalization performances with fast equalization, ZCS, and ZVG among cells. Full article
(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))
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Open AccessArticle Linear Formulation for Short-Term Operational Scheduling of Energy Storage Systems in Power Grids
Energies 2017, 10(2), 207; doi:10.3390/en10020207
Received: 11 July 2016 / Revised: 2 January 2017 / Accepted: 7 February 2017 / Published: 12 February 2017
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Abstract
This paper presents linear programming (LP) formulations for short-term energy time-shift operational scheduling with energy storage systems (ESSs) in power grids. In particular, it is shown that the conventional nonlinear formulations for electric bill minimization, peak shaving, and load leveling can be formulated
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This paper presents linear programming (LP) formulations for short-term energy time-shift operational scheduling with energy storage systems (ESSs) in power grids. In particular, it is shown that the conventional nonlinear formulations for electric bill minimization, peak shaving, and load leveling can be formulated in the LP framework. New variables for the peak and off-peak values are introduced in peak shaving and load leveling model, and the historical peak value for demand charge are considered in the electric bill minimization model. The LP formulations simplify computation while maintaining the accuracy for including linear technical constraints of ESSs, such as the state-of-charge, charging/discharging efficiency, output power range, and energy limit considering the life cycle of ESS. Proposed LP formulations have been implemented and verified in practical power systems and a large-scale industrial customer using historical data. Full article
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Open AccessArticle Peaking China’s CO2 Emissions: Trends to 2030 and Mitigation Potential
Energies 2017, 10(2), 209; doi:10.3390/en10020209
Received: 21 November 2016 / Revised: 16 January 2017 / Accepted: 18 January 2017 / Published: 11 February 2017
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Abstract
China has submitted its nationally determined contribution to peak its energy-related emissions around 2030. To understand how China might develop its economy while controlling CO2 emissions, this study surveys a number of recent modeling scenarios that project the country’s economic growth, energy
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China has submitted its nationally determined contribution to peak its energy-related emissions around 2030. To understand how China might develop its economy while controlling CO2 emissions, this study surveys a number of recent modeling scenarios that project the country’s economic growth, energy mix, and associated emissions until 2050. Our analysis suggests that China’s CO2 emissions will continue to grow until 2040 or 2050 and will approximately double their 2010 level without additional policy intervention. The alternative scenario, however, suggests that peaking CO2 emissions around 2030 requires the emission growth rate to be reduced by 2% below the reference level. This step would result in a plateau in China’s emissions from 2020 to 2030. This paper also proposed a deep de-carbonization pathway for China that is consistent with China’s goal of peaking emissions by around 2030, which can best be achieved through a combination of improvements in energy and carbon intensities. Our analysis also indicated that the potential for energy intensity decline will be limited over time. Thus, the peaking will be largely dependent on the share of non-fossil fuel energy in primary energy consumption. Full article
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Open AccessArticle Recycling Possibility of the Salty Food Waste by Pyrolysis and Water Scrubbing
Energies 2017, 10(2), 210; doi:10.3390/en10020210
Received: 17 November 2016 / Revised: 19 January 2017 / Accepted: 4 February 2017 / Published: 13 February 2017
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Abstract
Salty food waste is difficult to manage with previous methods such as composting, anaerobic digestion, and incineration, due to the hindrance of salt and the additional burden to handle high concentrations of organic wastewater produced when raw materials are cleaned. This study presents
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Salty food waste is difficult to manage with previous methods such as composting, anaerobic digestion, and incineration, due to the hindrance of salt and the additional burden to handle high concentrations of organic wastewater produced when raw materials are cleaned. This study presents a possibility of recycling food waste as fuel without the burden of treatment washing with water by pyrolyzing and scrubbing. For this purpose, salty food waste with 3% NaCl was made using 10 materials and pyrolysis was conducted at temperature range between 200–400 °C. The result was drawn from elementary analysis (EA), X-ray photoelectron spectroscopy (XPS) analysis, atomic absorption spectrophotometry (AAS) analysis, water quality analysis and calorific value analysis of char, washed char, and washing water. The result of the EA showed that NaCl in food waste could be volatilized at a low pyrolysis temperature of 200–300 °C and it could be concentrated and fixed in char at a high pyrolysis temperature of 300–400 °C. The XPS analysis result showed that NaCl existed in form of chloride. Through the Na content result of the AAS analysis, NaCl remaining in char after water scrubbing was determined to be less than 2%. As the pyrolysis temperature increased, the chemical oxygen demand (COD) value of scrubbing water decreased rapidly, but the total phosphorus and nitrogen contents decreased gradually. The cleaned pyrolysis char showed an increase of higher heating value (HHV) approximately 3667–9920 J/g due to the removal of salt from the char and, especially at 300–400 °C, showed a similar HHV with normal fossil fuels. In conclusion, salty food waste, which is pyrolyzed at a temperature of 300–400 °C and cleaned by water, can be utilized as high-energy refuse derived fuel (RDF), without adverse effects, due to the volatilization of Cl and an additional process of contaminated water. Full article
(This article belongs to the Special Issue Pyrolysis of Biomass)
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Open AccessArticle Hydrothermal Carbonization of Waste Biomass: Process Design, Modeling, Energy Efficiency and Cost Analysis
Energies 2017, 10(2), 211; doi:10.3390/en10020211
Received: 23 December 2016 / Revised: 27 January 2017 / Accepted: 4 February 2017 / Published: 13 February 2017
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Abstract
In this paper, a hydrothermal carbonization (HTC) process is designed and modeled on the basis of experimental data previously obtained for two representative organic waste materials: off-specification compost and grape marc. The process accounts for all the steps and equipment necessary to convert
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In this paper, a hydrothermal carbonization (HTC) process is designed and modeled on the basis of experimental data previously obtained for two representative organic waste materials: off-specification compost and grape marc. The process accounts for all the steps and equipment necessary to convert raw moist biomass into dry and pelletized hydrochar. By means of mass and thermal balances and based on common equations specific to the various equipment, thermal energy and power consumption were calculated at variable process conditions: HTC reactor temperature T: 180, 220, 250 °C; reaction time θ: 1, 3, 8 h. When operating the HTC plant with grape marc (65% moisture content) at optimized process conditions (T = 220 °C; θ = 1 h; dry biomass to water ratio = 0.19), thermal energy and power consumption were equal to 1170 kWh and 160 kWh per ton of hydrochar produced, respectively. Correspondingly, plant efficiency was 78%. In addition, the techno-economical aspects of the HTC process were analyzed in detail, considering both investment and production costs. The production cost of pelletized hydrochar and its break-even point were determined to be 157 €/ton and 200 €/ton, respectively. Such values make the use of hydrochar as a CO2 neutral biofuel attractive. Full article
(This article belongs to the Special Issue Thermo-Chemical Conversion of Waste Biomass)
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Open AccessArticle Effect of Doubly Fed Induction GeneratorTidal Current Turbines on Stability of a Distribution Grid under Unbalanced Voltage Conditions
Energies 2017, 10(2), 212; doi:10.3390/en10020212
Received: 10 September 2016 / Revised: 30 January 2017 / Accepted: 1 February 2017 / Published: 13 February 2017
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Abstract
This paper analyses the effects of doubly fed induction generator (DFIG) tidal current turbines on a distribution grid under unbalanced voltage conditions of the grid. A dynamic model of an electrical power system under the unbalanced network is described in the paper, aiming
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This paper analyses the effects of doubly fed induction generator (DFIG) tidal current turbines on a distribution grid under unbalanced voltage conditions of the grid. A dynamic model of an electrical power system under the unbalanced network is described in the paper, aiming to compare the system performance when connected with and without DFIG at the same location in a distribution grid. Extensive simulations of investigating the effect of DFIG tidal current turbine on stability of the distribution grid are performed, taking into account factors such as the power rating, the connection distance of the turbine and the grid voltage dip. The dynamic responses of the distribution system are examined, especially its ability to ride through fault events under unbalanced grid voltage conditions. The research has shown that DFIG tidal current turbines can provide a good damping performance and that modern DFIG tidal current power plants, equipped with power electronics and low-voltage ride-through capability, can stay connected to weak electrical grids even under the unbalanced voltage conditions, whilst not reducing system stability. Full article
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Open AccessArticle Hybrid System Modeling and Full Cycle Operation Analysis of a Two-Stroke Free-Piston Linear Generator
Energies 2017, 10(2), 213; doi:10.3390/en10020213
Received: 16 December 2016 / Revised: 27 January 2017 / Accepted: 29 January 2017 / Published: 14 February 2017
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Abstract
Free-piston linear generators (FPLGs) have attractive application prospects for hybrid electric vehicles (HEVs) owing to their high-efficiency, low-emissions and multi-fuel flexibility. In order to achieve long-term stable operation, the hybrid system design and full-cycle operation strategy are essential factors that should be considered.
[...] Read more.
Free-piston linear generators (FPLGs) have attractive application prospects for hybrid electric vehicles (HEVs) owing to their high-efficiency, low-emissions and multi-fuel flexibility. In order to achieve long-term stable operation, the hybrid system design and full-cycle operation strategy are essential factors that should be considered. A 25 kW FPLG consisting of an internal combustion engine (ICE), a linear electric machine (LEM) and a gas spring (GS) is designed. To improve the power density and generating efficiency, the LEM is assembled with two modular flat-type double-sided PM LEM units, which sandwich a common moving-magnet plate supported by a middle keel beam and bilateral slide guide rails to enhance the stiffness of the moving plate. For the convenience of operation processes analysis, the coupling hybrid system is modeled mathematically and a full cycle simulation model is established. Top-level systemic control strategies including the starting, stable operating, fault recovering and stopping strategies are analyzed and discussed. The analysis results validate that the system can run stably and robustly with the proposed full cycle operation strategy. The effective electric output power can reach 26.36 kW with an overall system efficiency of 36.32%. Full article
(This article belongs to the collection Electric and Hybrid Vehicles Collection)
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Open AccessArticle Stochastic Optimal Control of Parallel Hybrid Electric Vehicles
Energies 2017, 10(2), 214; doi:10.3390/en10020214
Received: 8 September 2016 / Revised: 4 February 2017 / Accepted: 7 February 2017 / Published: 13 February 2017
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Abstract
Energy management strategies (EMSs) in hybrid electric vehicles (HEVs) are highly related to the fuel economy and emission performances. However, EMS constitutes a challenging problem due to the complex structure of a HEV and the unknown or partially known driving cycles. To meet
[...] Read more.
Energy management strategies (EMSs) in hybrid electric vehicles (HEVs) are highly related to the fuel economy and emission performances. However, EMS constitutes a challenging problem due to the complex structure of a HEV and the unknown or partially known driving cycles. To meet this problem, this paper adopts a stochastic dynamic programming (SDP) method for the EMS of a specially designed vehicle, a pre-transmission single-shaft torque-coupling parallel HEV. In this parallel HEV, the auto clutch output is connected to the transmission input through an electric motor, which benefits an efficient motor assist operation. In this EMS, demanded torque of driver is modeled as a one-state Markov process to represent the uncertainty of future driving situations. The obtained EMS has been evaluated with ADVISOR2002 over two standard government drive cycles and a self-defined one, and compared with a dynamic programming (DP) one and a rule-based one. Simulation results have shown the real-time performance of the proposed approach, and potential vehicle performance improvement relative to the rule-based one. Full article
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Open AccessArticle An Energy-Based Control Strategy for Battery Energy Storage Systems: A Case Study on Microgrid Applications
Energies 2017, 10(2), 215; doi:10.3390/en10020215
Received: 7 December 2016 / Accepted: 7 February 2017 / Published: 13 February 2017
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Abstract
Battery energy storage systems (BESSs) with proportional-integral (PI) control methods have been widely studied in microgrids (MGs). However, the performance of PI control methods might be unsatisfactory for BESSs due to the nonlinear characteristics of the system. To overcome this problem, an energy-based
[...] Read more.
Battery energy storage systems (BESSs) with proportional-integral (PI) control methods have been widely studied in microgrids (MGs). However, the performance of PI control methods might be unsatisfactory for BESSs due to the nonlinear characteristics of the system. To overcome this problem, an energy-based (EB) control method is applied to control the converter of a BESS in this study. The EB method is a robust nonlinear control method based on passivity theory with good performance in both transient and steady states. The detailed design process of the EB method in the BESS by adopting an interconnection and damping assignment (IDA) strategy is described. The design process comprises three steps: the construction of the port-controlled Hamiltonian model, the determination of the equilibrium point and the solution of the undetermined matrix. In addition, integral action is combined to eliminate the steady state error generated by the model mismatch. To establish the correctness and validity of the proposed method, we implement several case simulation studies based on a test MG system and compare the control performance of the EB and PI methods carefully. The case simulation results demonstrate that the EB method has better tracking and anti-disturbance performance compared with the classic PI method. Moreover, the proposed EB method shows stronger robustness to the uncertainty of system parameters. Full article
(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)
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Open AccessArticle A Novel Electric Vehicle Powertrain System Supporting Multi-Path Power Flows: Its Architecture, Parameter Determination and System Simulation
Energies 2017, 10(2), 216; doi:10.3390/en10020216
Received: 10 November 2016 / Accepted: 6 February 2017 / Published: 13 February 2017
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Abstract
In this paper, a novel electric vehicle powertrain system is proposed. In the system, a coaxial magnetic gear (CMG), an electromagnetic clutch, a lock, and two electric machines (EMs) are adopted to achieve the power-split by controlling the states of the clutch and
[...] Read more.
In this paper, a novel electric vehicle powertrain system is proposed. In the system, a coaxial magnetic gear (CMG), an electromagnetic clutch, a lock, and two electric machines (EMs) are adopted to achieve the power-split by controlling the states of the clutch and the lock, which enables electric vehicles (EVs) to work in four operation modes. The configuration, power flow paths and operation modes are depicted in detail. A dynamic model is established to help determine the parameters and build simulation models. The simple control strategy is adopted to achieve flexible power-splits. How to determine the relevant parameters to meet the drive requirements in the powertrain system is also elaborated. A dynamic simulation using MATLAB/Simulink is performed to take into account the control strategy and New European Drive Cycle. Finally, the simulation results demonstrate, in theory, the rationality of the determined parameters and the feasibility of the operation modes as well as the control strategy. Full article
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Open AccessArticle A Maximum Efficiency Point Tracking Control Scheme Based on Different Cross Coupling of Dual-Receiver Inductive Power Transfer System
Energies 2017, 10(2), 217; doi:10.3390/en10020217
Received: 15 October 2016 / Accepted: 7 February 2017 / Published: 13 February 2017
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Abstract
One of the most promising inductive power transfer applications is the wireless power supply for locomotives which may cancel the need for pantographs. In order to meet the dynamic and high power demands of wireless power supplies for locomotives, a relatively long transmitter
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One of the most promising inductive power transfer applications is the wireless power supply for locomotives which may cancel the need for pantographs. In order to meet the dynamic and high power demands of wireless power supplies for locomotives, a relatively long transmitter track and multiple receivers are usually adopted. However, during the dynamic charging, the mutual inductances between the transmitter and receivers vary and the load of the locomotives also changes randomly, which dramatically affects the system efficiency. A maximum efficiency point tracking control scheme is proposed to improve the system efficiency against the variation of the load and the mutual inductances between the transmitter and receivers while considering the cross coupling between receivers. Firstly, a detailed theoretical analysis on dual receivers is carried out. Then a control scheme with three control loops is proposed to regulate the receiver currents to be the same, to regulate the output voltage and to search for the maximum efficiency point. Finally, a 2 kW prototype is established to validate the performance of the proposed method. The overall system efficiency (DC-DC efficiency) reaches 90.6% at rated power and is improved by 5.8% with the proposed method under light load compared with the traditional constant output voltage control method. Full article
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Open AccessArticle Geospatial Analysis of Photovoltaic Mini-Grid System Performance
Energies 2017, 10(2), 218; doi:10.3390/en10020218
Received: 2 December 2016 / Revised: 20 January 2017 / Accepted: 2 February 2017 / Published: 15 February 2017
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Abstract
We present a geographic information system (GIS)-based tool for estimating the performance of photovoltaic (PV) mini-grid system over large geographical areas. The methodology consists of geospatial analysis and mapping of the energy output and reliability of PV mini-grid system. The algorithm uses a
[...] Read more.
We present a geographic information system (GIS)-based tool for estimating the performance of photovoltaic (PV) mini-grid system over large geographical areas. The methodology consists of geospatial analysis and mapping of the energy output and reliability of PV mini-grid system. The algorithm uses a combination of hourly solar radiation data from satellites combined with measured data on PV module and battery performance and estimated electricity consumption data. The methods also make it possible to optimize the PV array and battery storage size for a given location. Results are presented for an area covering Africa and most of Southern and Central Asia. We also investigate the effects of using Li-ion batteries instead of the traditional lead-acid batteries. The use of our spatial analysis as decision support tool could help governments, local authorities and non-governmental organizations to investigate the suitability of PV mini-grids for electrification of regions where access to electricity is lacking. In this way it is possible to identify areas where PV mini-grids are most suitable. Full article
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Open AccessArticle Thermal Analysis of a Thermal Energy Storage Unit to Enhance a Workshop Heating System Driven by Industrial Residual Water
Energies 2017, 10(2), 219; doi:10.3390/en10020219
Received: 17 December 2016 / Revised: 7 February 2017 / Accepted: 8 February 2017 / Published: 14 February 2017
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Abstract
Various energy sources can be used for room heating, among which waste heat utilization has significantly improved in recent years. However, the majority of applicable waste heat resources are high-grade or stable thermal energy, while the low-grade or unstable waste heat resources, especially
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Various energy sources can be used for room heating, among which waste heat utilization has significantly improved in recent years. However, the majority of applicable waste heat resources are high-grade or stable thermal energy, while the low-grade or unstable waste heat resources, especially low-temperature industrial residual water (IRW), are insufficiently used. A thermal energy storage (TES) unit with paraffin wax as a phase change material (PCM) is designed to solve this problem in a pharmaceutical plant. The mathematical models are developed to simulate the heat storage and release processes of the TES unit. The crucial parameters in the recurrence formulae are determined: the phase change temperature range of the paraffin wax used is 47 to 56 °C, and the latent heat is 171.4 kJ/kg. Several thermal behaviors, such as the changes of melting radius, solidification radius, and fluid temperature, are simulated. In addition, the amount of heat transferred, the heat transfer rate, and the heat storage efficiency are discussed. It is presented that the medicine production unit could save 10.25% of energy consumption in the investigated application. Full article
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Open AccessArticle Robust Clamping Force Control of an Electro-Mechanical Brake System for Application to Commercial City Buses
Energies 2017, 10(2), 220; doi:10.3390/en10020220
Received: 15 December 2016 / Revised: 1 February 2017 / Accepted: 7 February 2017 / Published: 14 February 2017
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Abstract
This paper proposes a sensor-less robust force control method for improving the control performance of an electro-mechanical brake (EMB) which is applicable to commercial city buses. The EMB generates the accurate clamping force commanded by a driver through an independent motor control at
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This paper proposes a sensor-less robust force control method for improving the control performance of an electro-mechanical brake (EMB) which is applicable to commercial city buses. The EMB generates the accurate clamping force commanded by a driver through an independent motor control at each wheel instead of using existing mechanical components. In general, an EMB undergoes parameter variation and a backdrivability problem. For this reason, the cascade control strategy (e.g., force-position cascade control structure) is proposed and the disturbance observer is employed to enhance control robustness against model variations. Additionally, this paper proposed the clamping force estimation method for a sensor-less control, i.e., the clamping force observer (CFO). Finally, in order to confirm the performance and effectiveness of a proposed robust control method, several experiments are performed and analyzed. Full article
(This article belongs to the Special Issue Methods to Improve Energy Use in Road Vehicles)
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Open AccessArticle Computational Study of the Noise Radiation in a Centrifugal Pump When Flow Rate Changes
Energies 2017, 10(2), 221; doi:10.3390/en10020221
Received: 1 December 2016 / Revised: 7 February 2017 / Accepted: 8 February 2017 / Published: 14 February 2017
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Abstract
Noise radiation is of importance for the performance of centrifugal pumps. Aiming at exploring noise radiation patterns of a typical centrifugal pump at different flow rates, a three-dimensional unsteady hydro/aero acoustic model with large eddy simulation (LES) closure is developed. Specifically, the Ffowcs
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Noise radiation is of importance for the performance of centrifugal pumps. Aiming at exploring noise radiation patterns of a typical centrifugal pump at different flow rates, a three-dimensional unsteady hydro/aero acoustic model with large eddy simulation (LES) closure is developed. Specifically, the Ffowcs Williams-Hawkings model (FW-H) is employed to predict noise generation by the impeller and volute. The simulated flow fields reveal that the interactions of the blades with the volute induce root mean square (RMS) pressure and further lead to noise radiation. Moreover, it is found that the profiles of total sound pressure level (TSPL) regarding the directivity field for the impeller-generated noise demonstrate a typical dipole characteristic behavior, whereas strictly the volute-generated noise exhibits an apparently asymmetric behavior. Additionally, the design operation (Here, 1 Q represents the design operation) generates the lowest TSPL vis-a-vis the off-design operations for all the flow rates studied. In general, as the flow rates decrease from 1 Q to 0.25 Q, TSPL initially increases significantly before 0.75 Q and then levels off afterwards. A similar trend appears for cases having the larger flow rates (1–1.25 Q). The TSPL deviates with the radiation directivity and the maximum is about 50%. It is also found that TSPL by the volute and the blades can reach ~87 dB and ~70 dB at most, respectively. The study may offer a priori guidance for the experimental set up and the actual design layout. Full article
(This article belongs to the Special Issue Engineering Fluid Dynamics)
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Open AccessArticle Economic and Environmental Study of Wineries Powered by Grid-Connected Photovoltaic Systems in Spain
Energies 2017, 10(2), 222; doi:10.3390/en10020222
Received: 1 October 2016 / Revised: 3 December 2016 / Accepted: 7 February 2017 / Published: 14 February 2017
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Abstract
This research developed a system that can make factories more independent from the grid. The system enhances efficiency since factory operation is powered by the renewable energy generated during the production process. Winemaking is a key sector that can profit from such a
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This research developed a system that can make factories more independent from the grid. The system enhances efficiency since factory operation is powered by the renewable energy generated during the production process. Winemaking is a key sector that can profit from such a system because wineries can recycle much of the waste from the raw materials employed in wine production. Moreover, the solar energy collected at winemaking facilities can also be used to reduce electricity consumption and thus increase energy efficiency. This study investigated the feasibility of using renewable energy sources, such as solar energy, in wineries in Spain, given the quantity of renewable energy produced in the country. For this purpose, cost-effectiveness, power generation, CO2 emissions and the renewable energy fraction were taken into account. The assumption was that the photovoltaic system was grid-connected. Research results showed a reduction in electrical power costs ranging from 4% to 36%. This reduction was accompanied by an increase in the use of renewable energy of up to 57%. The results obtained are based on self-consumption or net metering policy as well as the production capacity of the winery. Full article
(This article belongs to the collection Bioenergy and Biofuel)
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Open AccessFeature PaperArticle Alkaline Earth Element Adsorption onto PAA-Coated Magnetic Nanoparticles
Energies 2017, 10(2), 223; doi:10.3390/en10020223
Received: 3 January 2017 / Revised: 2 February 2017 / Accepted: 8 February 2017 / Published: 14 February 2017
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Abstract
In this paper, we present a study on the adsorption of calcium (Ca2+) onto polyacrylic acid-functionalized iron-oxide magnetic nanoparticles (PAA-MNPs) to gain an insight into the adsorption behavior of alkaline earth elements at conditions typical of produced water from hydraulic fracturing.
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In this paper, we present a study on the adsorption of calcium (Ca2+) onto polyacrylic acid-functionalized iron-oxide magnetic nanoparticles (PAA-MNPs) to gain an insight into the adsorption behavior of alkaline earth elements at conditions typical of produced water from hydraulic fracturing. An aqueous co-precipitation method was employed to fabricate iron oxide magnetic nanoparticles, whose surface was first coated with amine and then by PAA. To evaluate the Ca2+ adsorption capacity by PAA-MNPs, the Ca2+ adsorption isotherm was measured in batch as a function of pH and sodium chlorite (electrolyte) concentration. A surface complexation model accounting for the coulombic forces in the diffuse double layer was developed to describe the competitive adsorption of protons (H+) and Ca2+ onto the anionic carboxyl ligands of the PAA-MNPs. Measurements show that Ca2+ adsorption is significant above pH 5 and decreases with the electrolyte concentration. Upon adsorption, the nanoparticle suspension destabilizes and creates large clusters, which favor an efficient magnetic separation of the PAA-MNPs, therefore, helping their recovery and recycle. The model agrees well with the experiments and predicts that the maximum adsorption capacity can be achieved within the pH range of the produced water, although that maximum declines with the electrolyte concentration. Full article
(This article belongs to the Special Issue Nanotechnology for Oil and Gas Applications)
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Open AccessArticle Isolation and Characterization of Native Microalgae from the Peruvian Amazon with Potential for Biodiesel Production
Energies 2017, 10(2), 224; doi:10.3390/en10020224
Received: 10 December 2016 / Revised: 31 January 2017 / Accepted: 8 February 2017 / Published: 14 February 2017
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Abstract
Biodiesel production from microalgae triacylglycerols is growing, because this feedstock is a more sustainable and advantageous alternative. In this study, we isolated and identified fourteen strains of native microalgae from the Peruvian Amazon. These strains showed great heterogeneity in biomass productivity, lipid productivity
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Biodiesel production from microalgae triacylglycerols is growing, because this feedstock is a more sustainable and advantageous alternative. In this study, we isolated and identified fourteen strains of native microalgae from the Peruvian Amazon. These strains showed great heterogeneity in biomass productivity, lipid productivity and lipid content, and thus, three of them (Acutodesmus obliquus, Ankistrodesmus sp. and Chlorella lewinii) were selected for further evaluation under culture of nitrogen-sufficient (+N) and nitrogen-deficient (−N) Chu medium No. 10. These microalgae species showed modifications in biomolecule content (protein, lipid and carbohydrate) with a pronounced increase of lipids and carbohydrate and a decrease of protein content under stress culture. Furthermore, the fatty acid profile was peculiar for each species, and these patterns showed evident changes, particularly in the proportion of saturated and monounsaturated fatty acids. The results of this research suggest that the isolated native microalgae, from the Peruvian Amazon, could be suitable candidates for biodiesel production Full article
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Open AccessArticle One-Year Monitoring PV Power Plant Installed on Rooftop of Mineirão Fifa World Cup/Olympics Football Stadium
Energies 2017, 10(2), 225; doi:10.3390/en10020225
Received: 6 December 2016 / Accepted: 4 February 2017 / Published: 14 February 2017
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Abstract
This paper presents results of one-year monitoring of AC side electrical parameters and the characterization of local solar radiation at the biggest rooftop PV Power Plant, with an installed capacity of 1.42 MWp, mounted at Mineirão Football Stadium in Brazil. This stadium is
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This paper presents results of one-year monitoring of AC side electrical parameters and the characterization of local solar radiation at the biggest rooftop PV Power Plant, with an installed capacity of 1.42 MWp, mounted at Mineirão Football Stadium in Brazil. This stadium is one of the sport facilities that hosted 2014 FIFA World Cup and Rio 2016 Summer Olympics Games in the country. Results showed how it is important to study and characterize the solar resource in the region of interest, based on historic data, to provide the understanding of solar radiation and thus project PV power plants with better performance. Furthermore, AC electrical data show the behavior of active, reactive and apparent powers and the influence of the PV system on the power factor at the local grid utility connection point. Finally, PV power plant performance data (as annual final yield, performance ratio and capacity factor) are also presented and compared with data from PVsyst software simulations. The results over the monitoring period were good considering the specificities of the stadium Full article
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Open AccessArticle A Heuristic Diagnostic Method for a PV System: Triple-Layered Particle Swarm Optimization–Back-Propagation Neural Network
Energies 2017, 10(2), 226; doi:10.3390/en10020226
Received: 23 November 2016 / Revised: 5 January 2017 / Accepted: 9 February 2017 / Published: 15 February 2017
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Abstract
This paper proposes a heuristic triple layered particle swarm optimization–back-propagation (PSO-BP) neural network method for improving the convergence and prediction accuracy of the fault diagnosis system of the photovoltaic (PV) array. The parameters, open-circuit voltage (Voc), short-circuit current (Isc),
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This paper proposes a heuristic triple layered particle swarm optimization–back-propagation (PSO-BP) neural network method for improving the convergence and prediction accuracy of the fault diagnosis system of the photovoltaic (PV) array. The parameters, open-circuit voltage (Voc), short-circuit current (Isc), maximum power (Pm) and voltage at maximum power point (Vm) are extracted from the output curve of the PV array as identification parameters for the fault diagnosis system. This study compares performances of two methods, the back-propagation neural network method, which is widely used, and the heuristic method with MATLAB. In the training phase, the back-propagation method takes about 425 steps to convergence, while the heuristic method needs only 312 steps. In the fault diagnosis phase, the prediction accuracy of the heuristic method is 93.33%, while the back-propagation method scores 86.67%. It is concluded that the heuristic method can not only improve the convergence of the simulation but also significantly improve the prediction accuracy of the fault diagnosis system. Full article
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Open AccessArticle Effects of Increased Wind Power Generation on Mid-Norway’s Energy Balance under Climate Change: A Market Based Approach
Energies 2017, 10(2), 227; doi:10.3390/en10020227
Received: 25 November 2016 / Revised: 17 January 2017 / Accepted: 8 February 2017 / Published: 15 February 2017
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Abstract
Thanks to its huge water storage capacity, Norway has an excess of energy generation at annual scale, although significant regional disparity exists. On average, the Mid-Norway region has an energy deficit and needs to import more electricity than it exports. We show that
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Thanks to its huge water storage capacity, Norway has an excess of energy generation at annual scale, although significant regional disparity exists. On average, the Mid-Norway region has an energy deficit and needs to import more electricity than it exports. We show that this energy deficit can be reduced with an increase in wind generation and transmission line capacity, even in future climate scenarios where both mean annual temperature and precipitation are changed. For the considered scenarios, the deficit observed in winter disappears, i.e., when electricity consumption and prices are high. At the annual scale, the deficit behaviour depends more on future changes in precipitation. Another consequence of changes in wind production and transmission capacity is the modification of electricity exchanges with neighbouring regions which are also modified both in terms of average, variability and seasonality. Full article
(This article belongs to the Special Issue Applied Energy System Modeling 2016)
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Open AccessArticle Electric Vehicle Market Penetration and Impacts on Energy Consumption and CO2 Emission in the Future: Beijing Case
Energies 2017, 10(2), 228; doi:10.3390/en10020228
Received: 25 December 2016 / Revised: 9 February 2017 / Accepted: 9 February 2017 / Published: 15 February 2017
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Abstract
This study focuses on the development of electric vehicles (EV) in the private passenger vehicle fleet in Beijing (China), analyzes how EVs will penetrate in the market, and estimates the resulting impacts on energy consumption and CO2 emissions up to 2030. A
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This study focuses on the development of electric vehicles (EV) in the private passenger vehicle fleet in Beijing (China), analyzes how EVs will penetrate in the market, and estimates the resulting impacts on energy consumption and CO2 emissions up to 2030. A discrete choice model is adopted with consideration of variables including vehicle technical characteristics, fuel prices, charging conditions and support policies. Results show that by 2030, without technological breakthrough and support policies, the market share of EV will be less than 7%, with gasoline dominating the energy structure. With fast technological progress, charging facility establishment, subsidies and tax breaks, EVs will account for 70% of annual new vehicle sales and nearly half of the vehicle stock by 2030, resulting in the substitution of nearly 1 million tons of gasoline with 3.2 billion kWh electricity in 2030 and the reduction of 0.6 million tons of CO2 emission in 2030. Technological progress, charging conditions and fuel prices are the top three drivers. Subsidies play an important role in the early stage, while tax and supply-side policies can be good options as long-term incentives. Full article
(This article belongs to the Special Issue Methods to Improve Energy Use in Road Vehicles)
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Open AccessArticle Energy Contribution of OFMSW (Organic Fraction of Municipal Solid Waste) to Energy-Environmental Sustainability in Urban Areas at Small Scale
Energies 2017, 10(2), 229; doi:10.3390/en10020229
Received: 19 October 2016 / Revised: 3 February 2017 / Accepted: 9 February 2017 / Published: 15 February 2017
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Abstract
Urban waste management is one of the most challenging issues in energy planning of medium and large cities. In addition to the traditional landfill method, many studies are investigating energy harvesting from waste, not as a panacea but as a foreseeable solution. Thermo-chemical
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Urban waste management is one of the most challenging issues in energy planning of medium and large cities. In addition to the traditional landfill method, many studies are investigating energy harvesting from waste, not as a panacea but as a foreseeable solution. Thermo-chemical conversion to biogas, or even bio-methane under certain conditions, could be an option to address this challenge. This study focuses on municipal solid waste conversion to biogas as a local energy supply for the cities. Three urban models and their subdivision into urban areas were identified along with a typical Organic Fraction of Municipal Solid Waste (OFMSW) matrix for each urban area. Then, an energy analysis was carried out to provide an optimization map for an informed choice by urban policy-makers and stakeholders. The results highlighted how the urban context and its use could affect the opportunity to produce energy from waste or to convert it in fuel. So, in this case, sustainability means waste turning from a problem to a renewable resource. Full article
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Open AccessArticle Voltage-Based Hot-Spot Detection Method for Photovoltaic String Using a Projector
Energies 2017, 10(2), 230; doi:10.3390/en10020230
Received: 30 November 2016 / Revised: 12 January 2017 / Accepted: 1 February 2017 / Published: 15 February 2017
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Abstract
This paper proposes a voltage-based hot-spot detection method for photovoltaic (PV) string using the projector. Hot-spots form in solar cells at defects causing a high carrier recombination rate, it appears as a high reverse leakage current of p-n junctions when solar cells are
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This paper proposes a voltage-based hot-spot detection method for photovoltaic (PV) string using the projector. Hot-spots form in solar cells at defects causing a high carrier recombination rate, it appears as a high reverse leakage current of p-n junctions when solar cells are partially shadowed. Using this characteristic, authors previously developed a voltage-based hot-spot detection method to quickly identify and characterize the severity of a module hot-spot. However, previous experimental results were shown for just one module. In this paper, experiments are done on plural modules in the string. From the result, this method works effectively for PV string. Correlations among illuminance, load resistance, hot-spot temperature, and risk factor are also discussed. Full article
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Open AccessArticle Exploring the Environment/Energy Pareto Optimal Front of an Office Room Using Computational Fluid Dynamics-Based Interactive Optimization Method
Energies 2017, 10(2), 231; doi:10.3390/en10020231
Received: 21 December 2016 / Revised: 3 February 2017 / Accepted: 9 February 2017 / Published: 15 February 2017
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Abstract
This paper is concerned with the development of a high-resolution and control-friendly optimization framework in enclosed environments that helps improve thermal comfort, indoor air quality (IAQ), and energy costs of heating, ventilation and air conditioning (HVAC) system simultaneously. A computational fluid dynamics (CFD)-based
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This paper is concerned with the development of a high-resolution and control-friendly optimization framework in enclosed environments that helps improve thermal comfort, indoor air quality (IAQ), and energy costs of heating, ventilation and air conditioning (HVAC) system simultaneously. A computational fluid dynamics (CFD)-based optimization method which couples algorithms implemented in Matlab with CFD simulation is proposed. The key part of this method is a data interactive mechanism which efficiently passes parameters between CFD simulations and optimization functions. A two-person office room is modeled for the numerical optimization. The multi-objective evolutionary algorithm—non-dominated-and-crowding Sorting Genetic Algorithm II (NSGA-II)—is realized to explore the environment/energy Pareto front of the enclosed space. Performance analysis will demonstrate the effectiveness of the presented optimization method. Full article
(This article belongs to the Special Issue Zero-Carbon Buildings)
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Open AccessArticle Exploring Soot Particle Concentration and Emissivity by Transient Thermocouples Measurements in Laminar Partially Premixed Coflow Flames
Energies 2017, 10(2), 232; doi:10.3390/en10020232
Received: 15 December 2016 / Accepted: 8 February 2017 / Published: 15 February 2017
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Abstract
Soot formation in combustion represents a complex phenomenon that strongly depends on several factors such as pressure, temperature, fuel chemical composition, and the extent of premixing. The effect of partial premixing on soot formation is of relevance also for real combustion devices and
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Soot formation in combustion represents a complex phenomenon that strongly depends on several factors such as pressure, temperature, fuel chemical composition, and the extent of premixing. The effect of partial premixing on soot formation is of relevance also for real combustion devices and still needs to be fully understood. An improved version of the thermophoretic particle densitometry (TPD) method has been used in this work with the aim to obtain both quantitative and qualitative information of soot particles generated in a set of laminar partially-premixed coflow flames characterized by different equivalence ratios. To this aim, the transient thermocouple temperature response has been analyzed to infer particle concentration and emissivity. A variety of thermal emissivity values have been measured for flame-formed carbonaceous particles, ranging from 0.4 to 0.5 for the early nucleated soot particles up to the value of 0.95, representing the typical value commonly attributed to mature soot particles, indicating that the correct determination of the thermal emissivity is necessary to accurately evaluate the particle volume fraction. This is particularly true at the early stage of the soot formation, when particle concentration measurement is indeed particularly challenging as in the central region of the diffusion flames. With increasing premixing, an initial increase of particles is detected both in the maximum radial soot volume fraction region and in the central region of the flame, while the further addition of primary air determines the particle volume fraction drop. Finally, a modeling analysis based on a sectional approach has been performed to corroborate the experimental findings. Full article
(This article belongs to the Special Issue Combustion and Propulsion)
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Open AccessArticle Evaluation and Reliability Assessment of GaN-on-Si MIS-HEMT for Power Switching Applications
Energies 2017, 10(2), 233; doi:10.3390/en10020233
Received: 6 December 2016 / Revised: 20 January 2017 / Accepted: 8 February 2017 / Published: 16 February 2017
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Abstract
This paper reports an extensive analysis of the physical mechanisms responsible for the failure of GaN-based metal–insulator–semiconductor (MIS) high electron mobility transistors (HEMTs). When stressed under high applied electric fields, the traps at the dielectric/III-N barrier interface and inside the III-N barrier cause
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This paper reports an extensive analysis of the physical mechanisms responsible for the failure of GaN-based metal–insulator–semiconductor (MIS) high electron mobility transistors (HEMTs). When stressed under high applied electric fields, the traps at the dielectric/III-N barrier interface and inside the III-N barrier cause an increase in dynamic on-resistance and a shift of threshold voltage, which might affect the long term stability of these devices. More detailed investigations are needed to identify epitaxy- or process-related degradation mechanisms and to understand their impact on electrical properties. The present paper proposes a suitable methodology to characterize the degradation and failure mechanisms of GaN MIS-HEMTs subjected to stress under various off-state conditions. There are three major stress conditions that include: VDS = 0 V, off, and off (cascode-connection) states. Changes of direct current (DC) figures of merit in voltage step-stress experiments are measured, statistics are studied, and correlations are investigated. Hot electron stress produces permanent change which can be attributed to charge trapping phenomena and the generation of deep levels or interface states. The simultaneous generation of interface (and/or bulk) and buffer traps can account for the observed degradation modes and mechanisms. These findings provide several critical characteristics to evaluate the electrical reliability of GaN MIS-HEMTs which are borne out by step-stress experiments. Full article
(This article belongs to the Special Issue Semiconductor Power Devices)
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Open AccessFeature PaperArticle Computational Model of a Biomass Driven Absorption Refrigeration System
Energies 2017, 10(2), 234; doi:10.3390/en10020234
Received: 12 December 2016 / Revised: 7 February 2017 / Accepted: 9 February 2017 / Published: 16 February 2017
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Abstract
The impact of vapour compression refrigeration is the main push for scientists to find an alternative sustainable technology. Vapour absorption is an ideal technology which makes use of waste heat or renewable heat, such as biomass, to drive absorption chillers from medium to
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The impact of vapour compression refrigeration is the main push for scientists to find an alternative sustainable technology. Vapour absorption is an ideal technology which makes use of waste heat or renewable heat, such as biomass, to drive absorption chillers from medium to large applications. In this paper, the aim was to investigate the feasibility of a biomass driven aqua-ammonia absorption system. An estimation of the solid biomass fuel quantity required to provide heat for the operation of a vapour absorption refrigeration cycle (VARC) is presented; the quantity of biomass required depends on the fuel density and the efficiency of the combustion and heat transfer systems. A single-stage aqua-ammonia refrigeration system analysis routine was developed to evaluate the system performance and ascertain the rate of energy transfer required to operate the system, and hence, the biomass quantity needed. In conclusion, this study demonstrated the results of the performance of a computational model of an aqua-ammonia system under a range of parameters. The model showed good agreement with published experimental data. Full article
(This article belongs to the Special Issue Biomass for Energy Country Specific Show Case Studies)
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Open AccessArticle Distributed Economic Dispatch of Virtual Power Plant under a Non-Ideal Communication Network
Energies 2017, 10(2), 235; doi:10.3390/en10020235
Received: 25 October 2016 / Revised: 15 January 2017 / Accepted: 10 February 2017 / Published: 16 February 2017
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Abstract
A virtual power plant (VPP) is aimed to integrate distributed energy resources (DERs). To solve the VPP economic dispatch (VPED) problem, the power supply-demand balance, power transmission constraints, and power output constraints of each DER must be considered. Meanwhile, the impacts of communication
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A virtual power plant (VPP) is aimed to integrate distributed energy resources (DERs). To solve the VPP economic dispatch (VPED) problem, the power supply-demand balance, power transmission constraints, and power output constraints of each DER must be considered. Meanwhile, the impacts of communication time delays, channel noises, and the time-varying topology on the communication networks cannot be ignored. In this paper, a VPED model is established and a distributed primal-dual sub-gradient method (DPDSM) is employed to address the presented VPED model. Compared with the traditional centralized dispatch, the distributed dispatch has the advantages of lower communication costs and stronger system robustness, etc. Simulations are realized in the modified IEEE-34 and IEEE-123 bus test VPP systems and the results indicate that the VPED strategy via DPDSM has the superiority of better convergence, more economic profits, and stronger system stability. Full article
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Open AccessArticle Influence of Water Saturation on the Mechanical Behaviour of Low-Permeability Reservoir Rocks
Energies 2017, 10(2), 236; doi:10.3390/en10020236
Received: 5 October 2016 / Revised: 24 December 2016 / Accepted: 9 January 2017 / Published: 16 February 2017
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Abstract
The influence of water on the mechanical properties of rocks has been observed by many researchers in rock engineering and laboratory tests, especially for sedimentary rocks. In order to investigate the effect of water saturation on the mechanical properties of low-permeability rocks, uniaxial
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The influence of water on the mechanical properties of rocks has been observed by many researchers in rock engineering and laboratory tests, especially for sedimentary rocks. In order to investigate the effect of water saturation on the mechanical properties of low-permeability rocks, uniaxial compression tests were conducted on siltstone with different water contents. The effects of water on the strength, elastic moduli, crack initiation and damage thresholds were observed for different water saturation levels. It was found that 10% water saturation level caused more than half of the reductions in mechanical properties. A new approach is proposed to analyze the stress-strain relations at different stages of compression by dividing the axial and lateral stress-strain curves into five equal stress zones, where stress zones 1–5 refer to 0%–20%, 20%–40%, 40%–60%, 60%–80% and 80%–100% of the peak stress, respectively. Stress zone 2 represents the elastic range better than stress zone 3 which is at half of the peak stress. The normalized crack initiation and crack damage stress thresholds obtained from the stress-strain curves and acoustic emission activities averaged 31.5% and 83% of the peak strength respectively. Pore pressure is inferred to take part in the deformation of low-permeability siltstone samples, especially at full saturation levels. A change of failure pattern from multi-fracturing to single shear failure with the increase of water saturation level was also observed. Full article
(This article belongs to the Special Issue Unconventional Natural Gas (UNG) Recoveries)
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Open AccessArticle Correlation Characteristic Analysis for Wind Speed in Different Geographical Hierarchies
Energies 2017, 10(2), 237; doi:10.3390/en10020237
Received: 15 January 2017 / Revised: 11 February 2017 / Accepted: 13 February 2017 / Published: 16 February 2017
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Abstract
As the scale of wind power bases rises, it becomes significant in power system planning and operation to provide detailed correlation characteristic of wind speed in different geographical hierarchies, that is among wind turbines, within a wind farm and its regional wind turbines,
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As the scale of wind power bases rises, it becomes significant in power system planning and operation to provide detailed correlation characteristic of wind speed in different geographical hierarchies, that is among wind turbines, within a wind farm and its regional wind turbines, and among different wind farms. A new approach to analyze the correlation characteristics of wind speed in different geographical hierarchies is proposed in this paper. In the proposed approach, either linear or nonlinear correlation of wind speed in each geographical hierarchy is firstly identified. Then joint sectionalized wind speed probability distribution is modeled for linear correlation analysis while a Copula function is adopted in nonlinear correlation analysis. By this approach, temporal-geographical correlations of wind speed in different geographical hierarchies are properly revealed. Results of case studies based on Jiuquan Wind Power Base in China are analyzed in each geographical hierarchy, which illustrates the feasibility of the proposed approach. Full article
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Open AccessArticle Effect of Injection Flow Rate on Product Gas Quality in Underground Coal Gasification (UCG) Based on Laboratory Scale Experiment: Development of Co-Axial UCG System
Energies 2017, 10(2), 238; doi:10.3390/en10020238
Received: 7 January 2017 / Revised: 9 February 2017 / Accepted: 13 February 2017 / Published: 16 February 2017
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Abstract
Underground coal gasification (UCG) is a technique to recover coal energy without mining by converting coal into a valuable gas. Model UCG experiments on a laboratory scale were carried out under a low flow rate (6~12 L/min) and a high flow rate (15~30
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Underground coal gasification (UCG) is a technique to recover coal energy without mining by converting coal into a valuable gas. Model UCG experiments on a laboratory scale were carried out under a low flow rate (6~12 L/min) and a high flow rate (15~30 L/min) with a constant oxygen concentration. During the experiments, the coal temperature was higher and the fracturing events were more active under the high flow rate. Additionally, the gasification efficiency, which means the conversion efficiency of the gasified coal to the product gas, was 71.22% in the low flow rate and 82.42% in the high flow rate. These results suggest that the energy recovery rate with the UCG process can be improved by the increase of the reaction temperature and the promotion of the gasification area. Full article
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Open AccessArticle Greenhouse Gas Mitigation of Rural Household Biogas Systems in China: A Life Cycle Assessment
Energies 2017, 10(2), 239; doi:10.3390/en10020239
Received: 30 November 2016 / Accepted: 3 January 2017 / Published: 16 February 2017
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Abstract
Rural household biogas (RHB) systems are at a crossroads in China, yet there has been a lack of holistic evaluation of their energy and climate (greenhouse gas mitigation) efficiency under typical operating conditions. We combined data from monitoring projects and questionnaire surveys across
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Rural household biogas (RHB) systems are at a crossroads in China, yet there has been a lack of holistic evaluation of their energy and climate (greenhouse gas mitigation) efficiency under typical operating conditions. We combined data from monitoring projects and questionnaire surveys across hundreds of households from two typical Chinese villages within a consequential life cycle assessment (LCA) framework to assess net GHG (greenhouse gas) mitigation by RHB systems operated in different contexts. We modelled biogas production, measured biogas losses and used survey data from biogas and non-biogas households to derive empirical RHB system substitution rates for energy and fertilizers. Our results indicate that poorly designed and operated RHB systems in northern regions of China may in fact increase farm household GHG emissions by an average of 2668 kg CO2-eq· year−1, compared with a net mitigation effect of 6336 kg CO2-eq per household and year in southern regions. Manure treatment (104 and 8513 kg CO2-eq mitigation) and biogas leakage (-533 and -2489 kg CO2-eq emission) are the two most important factors affecting net GHG mitigation by RHB systems in northern and southern China, respectively. In contrast, construction (−173 and −305 kg CO2-eq emission), energy substitution (−522 emission and 653 kg·CO2-eq mitigation) and nutrient substitution (−1544 and −37 kg CO2-eq emission) made small contributions across the studied systems. In fact, survey data indicated that biogas households had higher energy and fertilizer use, implying no net substitution effect. Low biogas yields in the cold northern climate and poor maintenance services were cited as major reasons for RHB abandonment by farmers. We conclude that the design and management of RHB systems needs to be revised and better adapted to local climate (e.g., digester insulation) and household energy demand (biogas storage and micro power generators to avoid discharge of unburned biogas). More precise nutrient management planning could ensure that digestate nutrients are more effectively utilized to substitute synthetic fertilizers. Full article
(This article belongs to the Special Issue Economics of Bioenergy 2016)
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Open AccessArticle Investigation of a Diesel-Engined Vehicle’s Performance and Emissions during the WLTC Driving Cycle—Comparison with the NEDC
Energies 2017, 10(2), 240; doi:10.3390/en10020240
Received: 15 December 2016 / Accepted: 13 February 2017 / Published: 16 February 2017
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Abstract
The present work presents results from an experimentally validated simulation code, regarding a turbocharged diesel-powered vehicle running on the recently developed worldwide light-duty vehicles WLTC driving cycle. The simulation is based on an engine mapping approach, with correction coefficients applied vis-à-vis the transient
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The present work presents results from an experimentally validated simulation code, regarding a turbocharged diesel-powered vehicle running on the recently developed worldwide light-duty vehicles WLTC driving cycle. The simulation is based on an engine mapping approach, with correction coefficients applied vis-à-vis the transient discrepancies encountered. Both performance and engine-out emission results are presented and discussed. As regards the latter, the concerned pollutants are soot and nitrogen monoxide. Since the WLTC driving cycle is scheduled to replace the NEDC in Europe from September 2017 with regard to the certification of passenger cars and light-duty trucks, a comparative analysis between the two test schedules is also performed for the engine/vehicle under study. Full article
(This article belongs to the Special Issue Automotive Engines Emissions and Control)
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Open AccessArticle Optimization Models for Islanded Micro-Grids: A Comparative Analysis between Linear Programming and Mixed Integer Programming
Energies 2017, 10(2), 241; doi:10.3390/en10020241
Received: 23 December 2016 / Accepted: 10 February 2017 / Published: 16 February 2017
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Abstract
This paper presents a comparison of optimization methods applied to islanded micro-grids including renewable energy sources, diesel generators and battery energy storage systems. In particular, a comparative analysis between an optimization model based on linear programming and a model based on mixed integer
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This paper presents a comparison of optimization methods applied to islanded micro-grids including renewable energy sources, diesel generators and battery energy storage systems. In particular, a comparative analysis between an optimization model based on linear programming and a model based on mixed integer programming has been carried out. The general formulation of these models has been presented and applied to a real case study micro-grid installed in Somalia. The case study is an islanded micro-grid supplying the city of Garowe by means of a hybrid power plant, consisting of diesel generators, photovoltaic systems and batteries. In both models the optimization is based on load demand and renewable energy production forecast. The optimized control of the battery state of charge, of the spinning reserve and diesel generators allows harvesting as much renewable power as possible or to minimize the use of fossil fuels in energy production. Full article
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Open AccessArticle Effects of SiO2/Al2O3 Ratios on Sintering Characteristics of Synthetic Coal Ash
Energies 2017, 10(2), 242; doi:10.3390/en10020242
Received: 1 December 2016 / Accepted: 14 February 2017 / Published: 16 February 2017
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Abstract
This article explores the effects of SiO2/Al2O3 ratios (S/A) on sintering characteristics and provides guidance for alleviating ash depositions in a large-scale circulation fluidized bed. Five synthetic coal ash (SCA) samples with different S/As were treated in a muffle furnace for 12 h
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This article explores the effects of SiO2/Al2O3 ratios (S/A) on sintering characteristics and provides guidance for alleviating ash depositions in a large-scale circulation fluidized bed. Five synthetic coal ash (SCA) samples with different S/As were treated in a muffle furnace for 12 h at different temperatures (from 773 K to 1373 K, in 100 K intervals). The morphological and chemical results of the volume shrinkage ratio (VSR), thermal deformation analysis by dilatometer (DIL), scanning electron microscope (SEM), X-ray photoelectron spectrometer (XPS), and X-ray diffraction (XRD) were combined to describe the sintering characteristics of different samples. The results showed that the sintering procedure mainly occurred in the third sintering stage when the temperature was over 1273 K, accompanied with significant decreases in the VSR curve. Excess SiO2 (S/A = 4.5) resulted in a porous structure while excess Al2O3 (S/A = 0.5) brought out large aggregations. The other three samples (S/A = 1.5, 2.5, 3.5) are made up of an amorphous compacted structure and are composed of low fusion temperature materials (e.g., augite and wadsleysite.). Sintering temperatures first dramatically decrease to a low level and then gradually rise to a high level as S/A increases, suggesting that Al2O3-enriched additives are more effective than SiO2enriched additives in alleviating depositions. Full article
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Open AccessArticle An Optimized Energy Management Strategy for Preheating Vehicle-Mounted Li-ion Batteries at Subzero Temperatures
Energies 2017, 10(2), 243; doi:10.3390/en10020243
Received: 5 December 2016 / Revised: 14 February 2017 / Accepted: 15 February 2017 / Published: 17 February 2017
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Abstract
This paper presents an optimized energy management strategy for Li-ion power batteries used on electric vehicles (EVs) at low temperatures. In low-temperature environments, EVs suffer a sharp driving range loss resulting from the energy and power capability reduction of the battery. Simultaneously, because
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This paper presents an optimized energy management strategy for Li-ion power batteries used on electric vehicles (EVs) at low temperatures. In low-temperature environments, EVs suffer a sharp driving range loss resulting from the energy and power capability reduction of the battery. Simultaneously, because of Li plating, battery degradation becomes an increasing concern as the temperature drops. All these factors could greatly increase the total vehicle operation cost. Prior to battery charging and vehicle operating, preheating the battery to a battery-friendly temperature is an approach to promote energy utilization and reduce total cost. Based on the proposed LiFePO4 battery model, the total vehicle operation cost under certain driving cycles is quantified in the present paper. Then, given a certain ambient temperature, a target preheating temperature is optimized under the principle of minimizing total cost. As for the preheating method, a liquid heating system is also implemented on an electric bus. Simulation results show that the preheating process becomes increasingly necessary with decreasing ambient temperature, however, the preheating demand declines as driving range grows. Vehicle tests verify that the preheating management strategy proposed in this paper is able to save on total vehicle operation costs. Full article
(This article belongs to the collection Electric and Hybrid Vehicles Collection)
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Open AccessArticle Maximum Safety Regenerative Power Tracking for DC Traction Power Systems
Energies 2017, 10(2), 244; doi:10.3390/en10020244
Received: 25 December 2016 / Revised: 11 February 2017 / Accepted: 12 February 2017 / Published: 17 February 2017
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Abstract
Direct current (DC) traction power systems are widely used in metro transport systems, with running rails usually being used as return conductors. When traction current flows through the running rails, a potential voltage known as “rail potential” is generated between the rails and
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Direct current (DC) traction power systems are widely used in metro transport systems, with running rails usually being used as return conductors. When traction current flows through the running rails, a potential voltage known as “rail potential” is generated between the rails and ground. Currently, abnormal rises of rail potential exist in many railway lines during the operation of railway systems. Excessively high rail potentials pose a threat to human life and to devices connected to the rails. In this paper, the effect of regenerative power distribution on rail potential is analyzed. Maximum safety regenerative power tracking is proposed for the control of maximum absolute rail potential and energy consumption during the operation of DC traction power systems. The dwell time of multiple trains at each station and the trigger voltage of the regenerative energy absorbing device (READ) are optimized based on an improved particle swarm optimization (PSO) algorithm to manage the distribution of regenerative power. In this way, the maximum absolute rail potential and energy consumption of DC traction power systems can be reduced. The operation data of Guangzhou Metro Line 2 are used in the simulations, and the results show that the scheme can reduce the maximum absolute rail potential and energy consumption effectively and guarantee the safety in energy saving of DC traction power systems. Full article
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Open AccessArticle Multi-Objective Optimization for Energy Performance Improvement of Residential Buildings: A Comparative Study
Energies 2017, 10(2), 245; doi:10.3390/en10020245
Received: 1 January 2017 / Revised: 30 January 2017 / Accepted: 14 February 2017 / Published: 17 February 2017
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Abstract
Numerous conflicting criteria exist in building design optimization, such as energy consumption, greenhouse gas emission and indoor thermal performance. Different simulation-based optimization strategies and various optimization algorithms have been developed. A few of them are analyzed and compared in solving building design problems.
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Numerous conflicting criteria exist in building design optimization, such as energy consumption, greenhouse gas emission and indoor thermal performance. Different simulation-based optimization strategies and various optimization algorithms have been developed. A few of them are analyzed and compared in solving building design problems. This paper presents an efficient optimization framework to facilitate optimization designs with the aid of commercial simulation software and MATLAB. The performances of three optimization strategies, including the proposed approach, GenOpt method and artificial neural network (ANN) method, are investigated using a case study of a simple building energy model. Results show that the proposed optimization framework has competitive performances compared with the GenOpt method. Further, in another practical case, four popular multi-objective algorithms, e.g., the non-dominated sorting genetic algorithm (NSGA-II), multi-objective particle swarm optimization (MOPSO), the multi-objective genetic algorithm (MOGA) and multi-objective differential evolution (MODE), are realized using the propose optimization framework and compared with three criteria. Results indicate that MODE achieves close-to-optimal solutions with the best diversity and execution time. An uncompetitive result is achieved by the MOPSO in this case study. Full article
(This article belongs to the Special Issue Zero-Carbon Buildings)
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Open AccessArticle Development of Shale Gas Supply Chain Network under Market Uncertainties
Energies 2017, 10(2), 246; doi:10.3390/en10020246
Received: 21 July 2016 / Revised: 7 November 2016 / Accepted: 7 November 2016 / Published: 18 February 2017
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Abstract
The increasing demand of energy has turned the shale gas and shale oil into one of the most promising sources of energy in the United States. In this article, a model is proposed to address the long-term planning problem of the shale gas
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The increasing demand of energy has turned the shale gas and shale oil into one of the most promising sources of energy in the United States. In this article, a model is proposed to address the long-term planning problem of the shale gas supply chain under uncertain conditions. A two-stage stochastic programming model is proposed to describe and optimize the shale gas supply chain network. Inherent uncertainty in final products’ prices, such as natural gas and natural gas liquids (NGL), is treated through the utilization of a scenario-based method. A binomial option pricing model is utilized to approximate the stochastic process through the generation of scenario trees. The aim of the proposed model is to generate an appropriate and realistic supply chain network configuration as well as scheduling of different operations throughout the planning horizon of a shale gas development project. Full article
(This article belongs to the Special Issue Energy Production Systems)
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Open AccessArticle Decentralized Electric Vehicle Charging Strategies for Reduced Load Variation and Guaranteed Charge Completion in Regional Distribution Grids
Energies 2017, 10(2), 147; doi:10.3390/en10020147
Received: 10 November 2016 / Revised: 10 January 2017 / Accepted: 18 January 2017 / Published: 24 January 2017
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Abstract
A novel, fully decentralized strategy to coordinate charge operation of electric vehicles is proposed in this paper. Based on stochastic switching control of on-board chargers, this strategy ensures high-efficiency charging, reduces load variations to the grid during charging periods, achieves charge completion with
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A novel, fully decentralized strategy to coordinate charge operation of electric vehicles is proposed in this paper. Based on stochastic switching control of on-board chargers, this strategy ensures high-efficiency charging, reduces load variations to the grid during charging periods, achieves charge completion with high probability, and accomplishes approximate “valley-filling”. Further improvements on the core strategy, including individualized power management, adaptive strategies, and battery support systems, are introduced to further reduce power fluctuation variances and to guarantee charge completion. Stochastic analysis is performed to establish the main properties of the strategies and to quantitatively show the performance improvements. Compared with the existing decentralized charging strategies, the strategies proposed in this paper can be implemented without any information exchange between grid operators and electric vehicles (EVs), resulting in a communications cost reduction. Additionally, it is shown that by using stochastic charging rules, a grid-supporting battery system with a very small energy capacity can achieve substantial reduction of EV load fluctuations with high confidence. An extensive set of simulations and case studies with real-world data are used to demonstrate the benefits of the proposed strategies. Full article
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Open AccessArticle Environmental Assessment of Possible Future Waste Management Scenarios
Energies 2017, 10(2), 247; doi:10.3390/en10020247
Received: 14 December 2016 / Revised: 5 February 2017 / Accepted: 7 February 2017 / Published: 19 February 2017
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Abstract
Waste management has developed in many countries and will continue to do so. Changes towards increased recovery of resources in order to meet climate targets and for society to transition to a circular economy are important driving forces. Scenarios are important tools for
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Waste management has developed in many countries and will continue to do so. Changes towards increased recovery of resources in order to meet climate targets and for society to transition to a circular economy are important driving forces. Scenarios are important tools for planning and assessing possible future developments and policies. This paper presents a comprehensive life cycle assessment (LCA) model for environmental assessments of scenarios and waste management policy instruments. It is unique by including almost all waste flows in a country and also allow for including waste prevention. The results show that the environmental impacts from future waste management scenarios in Sweden can differ a lot. Waste management will continue to contribute with environmental benefits, but less so in the more sustainable future scenarios, since the surrounding energy and transportation systems will be less polluting and also because less waste will be produced. Valuation results indicate that climate change, human toxicity and resource depletion are the most important environmental impact categories for the Swedish waste management system. Emissions of fossil CO2 from waste incineration will continue to be a major source of environmental impacts in these scenarios. The model is used for analyzing environmental impacts of several policy instruments including weight based collection fee, incineration tax, a resource tax and inclusion of waste in a green electricity certification system. The effect of the studied policy instruments in isolation are in most cases limited, suggesting that stronger policy instruments as well as combinations are necessary to reach policy goals as set out in for example the EU action plan on circular economy. Full article
(This article belongs to the Special Issue Energy and Waste Management)
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Open AccessArticle Influence of Tip Clearance on Pressure Fluctuation in Low Specific Speed Mixed-Flow Pump Passage
Energies 2017, 10(2), 148; doi:10.3390/en10020148
Received: 17 November 2016 / Revised: 16 January 2017 / Accepted: 18 January 2017 / Published: 24 January 2017
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Abstract
To explore the influence of tip clearance on pressure fluctuation in a low specific speed mixed-flow pump, tip clearances δ of 0.25 mm, 0.75 mm and 1.00 mm, along with no tip clearance, were selected. The reliability of the simulation was verified by
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To explore the influence of tip clearance on pressure fluctuation in a low specific speed mixed-flow pump, tip clearances δ of 0.25 mm, 0.75 mm and 1.00 mm, along with no tip clearance, were selected. The reliability of the simulation was verified by comparison with the experimental data of external characteristics and fluctuation in the guide vane passage. Through ANSYS-CFX, MATLAB code and fast Fourier transform (FFT) algorithm, pressure fluctuation characteristics in this pump were obtained. The results show that pressure fluctuation exists in all conditions due to the rotor-stator interaction. Under the no tip clearance and tip clearance conditions, the maximum fluctuation value was located near the guide inlet and impeller outlet, respectively. Clearance leakage had less influence on pressure fluctuation at the impeller inlet and central regions within a certain range of the clearance; beyond this range, fluctuations in the whole flow passage increased significantly, while the clearance variation had less effect on fluctuation in the guide vane. When the tip clearance value was 1.00 mm, pressure fluctuation of the shroud at the impeller inlet section suddenly increases, which was closely related to the obvious leakage vortexes and a larger low pressure area. Full article
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Open AccessArticle A New Model for Estimating the Diffuse Fraction of Solar Irradiance for Photovoltaic System Simulations
Energies 2017, 10(2), 248; doi:10.3390/en10020248
Received: 21 December 2016 / Revised: 6 February 2017 / Accepted: 13 February 2017 / Published: 18 February 2017
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Abstract
We present a new model for the calculation of the diffuse fraction of the global solar irradiance for solar system simulations. The importance of an accurate estimation of the horizontal diffuse irradiance is highlighted by findings that an inaccurately calculated diffuse irradiance can
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We present a new model for the calculation of the diffuse fraction of the global solar irradiance for solar system simulations. The importance of an accurate estimation of the horizontal diffuse irradiance is highlighted by findings that an inaccurately calculated diffuse irradiance can lead to significant over- or underestimations in the annual energy yield of a photovoltaic (PV) system by as much as 8%. Our model utilizes a time series of global irradiance in one-minute resolution and geographical information as input. The model is validated by measurement data of 28 geographically and climatologically diverse locations worldwide with one year of one-minute data each, taken from the Baseline Surface Radiation Network (BSRN). We show that on average the mean absolute deviation of the modelled and the measured diffuse irradiance is reduced from about 12% to about 6% compared to three reference models. The maximum deviation is less than 20%. In more than 80% of the test cases, the deviation is smaller 10%. The root mean squared error (RMSE) of the calculated diffuse fractions is reduced by about 18%. Full article
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Open AccessArticle Fault Tolerant and Optimal Control of Wind Turbines with Distributed High-Speed Generators
Energies 2017, 10(2), 149; doi:10.3390/en10020149
Received: 3 October 2016 / Revised: 10 January 2017 / Accepted: 11 January 2017 / Published: 24 January 2017
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Abstract
In this paper, the control scheme of a distributed high-speed generator system with a total amount of 12 generators and nominal generator speed of 7000 min1 is studied. Specifically, a fault tolerant control (FTC) scheme is proposed to keep the turbine
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In this paper, the control scheme of a distributed high-speed generator system with a total amount of 12 generators and nominal generator speed of 7000 min 1 is studied. Specifically, a fault tolerant control (FTC) scheme is proposed to keep the turbine in operation in the presence of up to four simultaneous generator faults. The proposed controller structure consists of two layers: The upper layer is the baseline controller, which is separated into a partial load region with the generator torque as an actuating signal and the full-load operation region with the collective pitch angle as the other actuating signal. In addition, the lower layer is responsible for the fault diagnosis and FTC characteristics of the distributed generator drive train. The fault reconstruction and fault tolerant control strategy are tested in simulations with several actuator faults of different types. Full article
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Open AccessArticle Sectoral Electricity Consumption and Economic Growth: The Time Difference Case of China, 2006–2015
Energies 2017, 10(2), 249; doi:10.3390/en10020249
Received: 17 November 2016 / Revised: 16 January 2017 / Accepted: 15 February 2017 / Published: 18 February 2017
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Abstract
Unlike existing studies focused on the causal relationship between electricity consumption and economic growth at the macro level, this paper uses monthly data from January 2006 to December 2015 and applies the correlation coefficient, as well as Kullback-Leibler (KL) divergence, to study the
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Unlike existing studies focused on the causal relationship between electricity consumption and economic growth at the macro level, this paper uses monthly data from January 2006 to December 2015 and applies the correlation coefficient, as well as Kullback-Leibler (KL) divergence, to study the time difference relationship between sectoral electricity consumption and economic growth. The empirical results draw some main findings as follows: First, the time difference relationships show diversity at the sector level but will form a kind of overall characteristic between economic growth and total electricity consumption. Secondly, not all sectors have a remarkable correlation between sectoral electricity consumption and economic growth as only part of them have reasonable values to describe the time difference relationship. Thirdly, the results present both diversity and aggregation at the industry level, while lagging sectors mainly concentrate in the manufacturing industry. The relationship between sectoral electricity consumption and economic growth can be further explored and described from a new perspective based on the results. Further, the trend of economic development and sectoral electricity consumption can be predicted to help policy-makers formulate proper policies. Full article
(This article belongs to the Special Issue Energy Economics 2016)
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Open AccessArticle Application of Meta-Heuristic Techniques for Optimal Load Shedding in Islanded Distribution Network with High Penetration of Solar PV Generation
Energies 2017, 10(2), 150; doi:10.3390/en10020150
Received: 27 September 2016 / Revised: 5 December 2016 / Accepted: 17 January 2017 / Published: 24 January 2017
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Abstract
Recently, several environmental problems are beginning to affect all aspects of life. For this reason, many governments and international agencies have expressed great interest in using more renewable energy sources (RESs). However, integrating more RESs with distribution networks resulted in several critical problems
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Recently, several environmental problems are beginning to affect all aspects of life. For this reason, many governments and international agencies have expressed great interest in using more renewable energy sources (RESs). However, integrating more RESs with distribution networks resulted in several critical problems vis-à-vis the frequency stability, which might lead to a complete blackout if not properly treated. Therefore, this paper proposed a new Under Frequency Load Shedding (UFLS) scheme for islanding distribution network. This scheme uses three meta-heuristics techniques, binary evolutionary programming (BEP), Binary genetic algorithm (BGA), and Binary particle swarm optimization (BPSO), to determine the optimal combination of loads that needs to be shed from the islanded distribution network. Compared with existing UFLS schemes using fixed priority loads, the proposed scheme has the ability to restore the network frequency without any overshooting. Furthermore, in terms of execution time, the simulation results show that the BEP technique is fast enough to shed the optimal combination of loads compared with BGA and BPSO techniques. Full article
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Open AccessArticle Production Characteristics with Different Superimposed Modes Using Variogram: A Case Study of a Super-Giant Carbonate Reservoir in the Middle East
Energies 2017, 10(2), 250; doi:10.3390/en10020250
Received: 30 August 2016 / Revised: 15 January 2017 / Accepted: 6 February 2017 / Published: 18 February 2017
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Abstract
Heterogeneity of permeability is an important factor affecting the production of a carbonate reservoir. How to correctly characterize the heterogeneity of permeability has become a key issue for carbonate reservoir development. In this study, the reservoirs were categorized into four superimposed modes based
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Heterogeneity of permeability is an important factor affecting the production of a carbonate reservoir. How to correctly characterize the heterogeneity of permeability has become a key issue for carbonate reservoir development. In this study, the reservoirs were categorized into four superimposed modes based on the actual logging data from a super-giant heterogeneous carbonate reservoir in the Middle East. A modified permeability formula in terms of the variogram method was presented to reflect the heterogeneity of the reservoirs. Furthermore, the models of oil production and water cut were established and the analytical solutions were obtained. The calculation results show that the present model can predict the productivity of wells with different heterogeneous layers more accurately and rapidly. The larger the varigoram value, the stronger the heterogeneity of the reservoirs, and the faster the decline of production owing to a quicker reduction of formation pressure. With the increase in variogram value, the relative permeability of the oil phase is smaller and the water phase larger, and the water cut becomes larger. This study has provided a quick and reasonable prediction model for heterogeneous reservoir. Full article
(This article belongs to the Special Issue Oil and Gas Engineering)
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Open AccessArticle Implementation and Assessment of a Decentralized Load Frequency Control: Application to Power Systems with High Wind Energy Penetration
Energies 2017, 10(2), 151; doi:10.3390/en10020151
Received: 12 October 2016 / Revised: 29 November 2016 / Accepted: 13 December 2016 / Published: 24 January 2017
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Abstract
This paper describes and assesses a decentralized solution based on a wireless sensor-actuator network to provide primary frequency control from demand response in power systems with high wind energy penetration and, subsequently, with relevant frequency excursions. The proposed system is able to modify
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This paper describes and assesses a decentralized solution based on a wireless sensor-actuator network to provide primary frequency control from demand response in power systems with high wind energy penetration and, subsequently, with relevant frequency excursions. The proposed system is able to modify the electrical power demand of a variety of thermostatically-controlled loads, maintaining minimum comfort levels and minimizing both infrastructure requirements and primary reserves from the supply side. This low-cost hardware solution avoids any additional wiring, extending the wireless sensor-actuator network technology towards small customers, which account for over a 30% share of the current power demand. Frequency excursions are collected by each individual load controller, considering not only the magnitude of the frequency deviation, but also their evolution over time. Based on these time-frequency excursion characteristics, controllers are capable of modifying the power consumption of thermostatically-controlled loads by switching them off and on, thus contributing to primary frequency control in power systems with higher generation unit oscillations as a consequence of relevant wind power integration. Field tests have been carried out in a laboratory environment to assess the load controller performance, as well as to evaluate the electrical and thermal response of individual loads under frequency deviations. These frequency deviations are estimated from power systems with a high penetration of wind energy, which are more sensitive to frequency oscillations and where demand response can significantly contribute to mitigate these frequency excursions. The results, also included in the paper, evaluate the suitability of the proposed load controllers and their suitability to decrease frequency excursions from the demand side in a decentralized manner. Full article
(This article belongs to the collection Smart Grid)
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Open AccessArticle The Efficiency Improvement by Combining HHO Gas, Coal and Oil in Boiler for Electricity Generation
Energies 2017, 10(2), 251; doi:10.3390/en10020251
Received: 29 October 2016 / Revised: 9 February 2017 / Accepted: 10 February 2017 / Published: 20 February 2017
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Abstract
Electricity is an essential energy that can benefit our daily lives. There are many sources available for electricity generation, such as coal, natural gas and nuclear. Among these sources, coal has been widely used in thermal power plants that account for about 41%
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Electricity is an essential energy that can benefit our daily lives. There are many sources available for electricity generation, such as coal, natural gas and nuclear. Among these sources, coal has been widely used in thermal power plants that account for about 41% of the worldwide electricity supply. However, these thermal power plants are also found to be a big pollution source to our environment. There is a need to explore alternative electricity sources and improve the efficiency of electricity generation. This research focuses on improving the efficiency of electricity generation through the use of hydrogen and oxygen mixture (HHO) gas. In this research, experiments have been conducted to investigate the combined effects of HHO gas with other fuels, including coal and oil. The results show that the combinations of HHO with coal and oil can improve the efficiency of electricity generation while reducing the pollution to our environment. Full article
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Open AccessArticle Spatial and Temporal Wind Power Forecasting by Case-Based Reasoning Using Big-Data
Energies 2017, 10(2), 252; doi:10.3390/en10020252
Received: 12 January 2017 / Accepted: 13 February 2017 / Published: 20 February 2017
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Abstract
The massive penetration of wind generators in electrical power systems asks for effective wind power forecasting tools, which should be high reliable, in order to mitigate the effects of the uncertain generation profiles, and fast enough to enhance power system operation. To address
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The massive penetration of wind generators in electrical power systems asks for effective wind power forecasting tools, which should be high reliable, in order to mitigate the effects of the uncertain generation profiles, and fast enough to enhance power system operation. To address these two conflicting objectives, this paper advocates the role of knowledge discovery from big-data, by proposing the integration of adaptive Case Based Reasoning models, and cardinality reduction techniques based on Partial Least Squares Regression, and Principal Component Analysis. The main idea is to learn from a large database of historical climatic observations, how to solve the windforecasting problem, avoiding complex and time-consuming computations. To assess the benefits derived by the application of the proposed methodology in complex application scenarios, the experimental results obtained in a real case study will be presented and discussed. Full article
(This article belongs to the Special Issue Advances in Power System Operations and Planning)
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Open AccessArticle Phase Change Material Based Accumulation Panels in Combination with Renewable Energy Sources and Thermoelectric Cooling
Energies 2017, 10(2), 152; doi:10.3390/en10020152
Received: 28 September 2016 / Revised: 3 January 2017 / Accepted: 17 January 2017 / Published: 24 January 2017
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Abstract
The article deals with the use of modern materials and technologies that can improve the thermal comfort in buildings. The article describes the design and usage of a special accumulation device, which is composed of thermal panels based on phase change materials (PCMs).
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The article deals with the use of modern materials and technologies that can improve the thermal comfort in buildings. The article describes the design and usage of a special accumulation device, which is composed of thermal panels based on phase change materials (PCMs). The thermal panels have an integrated tube heat exchanger and heating foils. The technology can be used as a passive or active system for heating and cooling. It is designed as a “green technology”, so it is able to use renewable energy sources, e.g., photovoltaic (PV) panels, solar thermal collectors and heat pumps. Moreover, an interesting possibility is the ability to use thermoelectric coolers. In the research, measurements of the different operating modes were made, and the results are presented in the text. The measurement approves that the technology improves the thermal capacity of the building, and it is possible to use it for active heating and cooling. Full article
(This article belongs to the Special Issue Advanced Heating and Cooling Techniques)
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Open AccessArticle A Parameter Selection Method for Wind Turbine Health Management through SCADA Data
Energies 2017, 10(2), 253; doi:10.3390/en10020253
Received: 14 January 2017 / Revised: 9 February 2017 / Accepted: 14 February 2017 / Published: 20 February 2017
Cited by 1 | PDF Full-text (4276 KB) | HTML Full-text | XML Full-text
Abstract
Wind turbine anomaly or failure detection using machine learning techniques through supervisory control and data acquisition (SCADA) system is drawing wide attention from academic and industry While parameter selection is important for modelling a wind turbine’s condition, only a few papers have been
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Wind turbine anomaly or failure detection using machine learning techniques through supervisory control and data acquisition (SCADA) system is drawing wide attention from academic and industry While parameter selection is important for modelling a wind turbine’s condition, only a few papers have been published focusing on this issue and in those papers interconnections among sub-components in a wind turbine are used to address this problem. However, merely the interconnections for decision making sometimes is too general to provide a parameter list considering the differences of each SCADA dataset. In this paper, a method is proposed to provide more detailed suggestions on parameter selection based on mutual information. First, the copula is proven to be capable of simplifying the estimation of mutual information. Then an empirical copulabased mutual information estimation method (ECMI) is introduced for application. After that, a real SCADA dataset is adopted to test the method, and the results show the effectiveness of the ECMI in providing parameter selection suggestions when physical knowledge is not accurate enough. Full article
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Open AccessFeature PaperArticle Technology and Reliability of Normally-Off GaN HEMTs with p-Type Gate
Energies 2017, 10(2), 153; doi:10.3390/en10020153
Received: 28 November 2016 / Revised: 16 January 2017 / Accepted: 17 January 2017 / Published: 25 January 2017
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Abstract
GaN-based transistors with p-GaN gate are commonly accepted as promising devices for application in power converters, thanks to the positive and stable threshold voltage, the low on-resistance and the high breakdown field. This paper reviews the most recent results on the technology and
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GaN-based transistors with p-GaN gate are commonly accepted as promising devices for application in power converters, thanks to the positive and stable threshold voltage, the low on-resistance and the high breakdown field. This paper reviews the most recent results on the technology and reliability of these devices by presenting original data. The first part of the paper describes the technological issues related to the development of a p-GaN gate, and the most promising solutions for minimizing the gate leakage current. In the second part of the paper, we describe the most relevant mechanisms that limit the dynamic performance and the reliability of GaN-based normally-off transistors. More specifically, we discuss the following aspects: (i) the trapping effects specific for the p-GaN gate; (ii) the time-dependent breakdown of the p-GaN gate during positive gate stress and the related physics of failure; (iii) the stability of the electrical parameters during operation at high drain voltages. The results presented within this paper provide information on the current status of the performance and reliability of GaN-based E-mode transistors, and on the related technological issues. Full article
(This article belongs to the Special Issue Semiconductor Power Devices)
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Open AccessArticle A System Dynamics Analysis of Investment, Technology and Policy that Affect Natural Gas Exploration and Exploitation in China
Energies 2017, 10(2), 154; doi:10.3390/en10020154
Received: 24 September 2016 / Revised: 22 December 2016 / Accepted: 3 January 2017 / Published: 25 January 2017
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Abstract
Natural gas has an increasing role in Chinese energy transformation. We present a system dynamics model of the natural gas industry in China. A new system dynamics model for natural gas companies based on reserve exploration and well construction as well as investment
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Natural gas has an increasing role in Chinese energy transformation. We present a system dynamics model of the natural gas industry in China. A new system dynamics model for natural gas companies based on reserve exploration and well construction as well as investment dynamics is proposed. The contribution of the paper is to analyze the influence of technology, investment and policy factors on the natural gas industry. We found that the dynamics of the main variables, including gas policy, cost of investment, accounting depreciation and exploitation technology, are sensitive to the sustainable development of resources. The simulations and results presented here will be helpful for government to reform policies, and for upstream companies to make decisions. Full article
(This article belongs to the Special Issue Applied Energy System Modeling 2016)
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Open AccessArticle Power Consumption Efficiency Evaluation of Multi-User Full-Duplex Visible Light Communication Systems for Smart Home Technologies
Energies 2017, 10(2), 254; doi:10.3390/en10020254
Received: 29 November 2016 / Revised: 8 February 2017 / Accepted: 14 February 2017 / Published: 20 February 2017
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Abstract
Visible light communication (VLC) has recently gained significant academic and industrial attention. VLC has great potential to supplement the functioning of the upcoming radio-frequency (RF)-based 5G networks. It is best suited for home, office, and commercial indoor environments as it provides a high
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Visible light communication (VLC) has recently gained significant academic and industrial attention. VLC has great potential to supplement the functioning of the upcoming radio-frequency (RF)-based 5G networks. It is best suited for home, office, and commercial indoor environments as it provides a high bandwidth and high data rate, and the visible light spectrum is free to use. This paper proposes a multi-user full-duplex VLC system using red-green-blue (RGB), and white emitting diodes (LEDs) for smart home technologies. It utilizes red, green, and blue LEDs for downlink transmission and a simple phosphor white LED for uplink transmission. The red and green color bands are used for user data and smart devices, respectively, while the blue color band is used with the white LED for uplink transmission. The simulation was carried out to verify the performance of the proposed multi-user full-duplex VLC system. In addition to the performance evaluation, a cost-power consumption analysis was performed by comparing the power consumption and the resulting cost of the proposed VLC system to the power consumed and resulting cost of traditional Wi-Fi based systems and hybrid systems that utilized both VLC and Wi-Fi. Our findings showed that the proposed system improved the data rate and bit-error rate performance, while minimizing the power consumption and the associated costs. These results have demonstrated that a full-duplex VLC system is a feasible solution suitable for indoor environments as it provides greater cost savings and energy efficiency when compared to traditional Wi-Fi-based systems and hybrid systems that utilize both VLC and Wi-Fi. Full article
(This article belongs to the Special Issue Smart Home Energy Management)
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Open AccessArticle A Methodological Approach to Assess the Impact of Smarting Action on Electricity Transmission and Distribution Networks Related to Europe 2020 Targets
Energies 2017, 10(2), 155; doi:10.3390/en10020155
Received: 14 December 2016 / Revised: 13 January 2017 / Accepted: 19 January 2017 / Published: 26 January 2017
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Abstract
The achievement of the so-called 2020 targets requested by the European Union (EU) has determined a significant growth of proposals of solutions and of technical projects aiming at reducing the CO2 emissions and increasing the energy efficiency, as well as the penetration
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The achievement of the so-called 2020 targets requested by the European Union (EU) has determined a significant growth of proposals of solutions and of technical projects aiming at reducing the CO2 emissions and increasing the energy efficiency, as well as the penetration of Renewable Energy Sources (RES) in the electric network. As many of them ask for funding from the EU itself, there is the necessity to define a methodology to rank them and decide which projects should be sponsored to obtain the maximum effect on the EU 2020 targets. The present paper aims at (i) defining a set of Key Performance Indicators (KPIs) to compare different proposals, (ii) proposing an analytical methodology to evaluate the defined KPIs and (iii) evaluating the maximum impact that the considered action is capable of producing. The proposed methodology is applied to a set of possible interventions performed on a benchmark transmission network test case, in order to show that the defined indicators can be either calculated or measured and that they are useful to rank different “smarting actions”. Full article
(This article belongs to the Special Issue Electric Power Systems Research 2017)
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Open AccessArticle Research on the Combustion Characteristics and Kinetic Analysis of the Recycling Dust for a COREX Furnace
Energies 2017, 10(2), 255; doi:10.3390/en10020255
Received: 9 August 2016 / Revised: 17 November 2016 / Accepted: 22 January 2017 / Published: 20 February 2017
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Abstract
Thermogravimetric analysis of recycling dust (RD) from the melter gasifier of COREX, coke1 (C-1), coke2 (C-2) and coal char (CC) under 70% oxygen atmosphere was carried out using thermal balance. The chemical composition and physical structure of the samples were investigated. The characteristic
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Thermogravimetric analysis of recycling dust (RD) from the melter gasifier of COREX, coke1 (C-1), coke2 (C-2) and coal char (CC) under 70% oxygen atmosphere was carried out using thermal balance. The chemical composition and physical structure of the samples were investigated. The characteristic temperatures and comprehensive combustion characteristic indexes were calculated and kinetic parameters during the combustion process were calculated as well using a distributed activation energy model (DAEM). The results show that the carbon in the recycling dust originates from unconsumed CC and coke fines, and the average stacking height of carbon in RD is larger than that of C-1, C-2 and CC. The conversion curves of RD are different from those of C-1, C-2 and CC, and there are two peaks in the RD conversion rate curves. The combustion profiles of RD moves to a higher temperature zone with increasing heating rates. The average activation energies of their combustion process for RD, C-1, C-2 and CC range from 191.84 kJ/mol to 128.31 kJ/mol. The activation energy for recycling dust increases as the fractional conversion increases, but the value for C-1, C-2 and CC decreases with increasing conversion, indicating different combustion mechanisms. Full article
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Open AccessArticle A New Vertical JFET Power Device for Harsh Radiation Environments
Energies 2017, 10(2), 256; doi:10.3390/en10020256
Received: 15 December 2016 / Revised: 4 February 2017 / Accepted: 15 February 2017 / Published: 20 February 2017
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Abstract
An increasing demand for power electronic devices able to be operative in harsh radiation environments is now taking place. Specifically, in High Energy Physics experiments the required power devices are expected to withstand very high radiation levels which are normally too hard for
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An increasing demand for power electronic devices able to be operative in harsh radiation environments is now taking place. Specifically, in High Energy Physics experiments the required power devices are expected to withstand very high radiation levels which are normally too hard for most of the available commercial solutions. In this context, a new vertical junction field effect transistor (JFET) has been designed and fabricated at the Instituto de Microelectrónica de Barcelona, Centro Nacional de Microelectrónica (IMB-CNM, CSIC). The new silicon V-JFET devices draw upon a deep-trenched technology to achieve volume conduction and low switch-off voltage, together with a moderately high voltage capability. The first batches of V-JFET prototypes have been already fabricated at the IMB-CNM clean room, and several aspects of their design, fabrication and the outcome of their characterization are summarized and discussed in this paper. Radiation hardness of the fabricated transistors have been tested both with gamma and neutron irradiations, and the results are also included in the contribution. Full article
(This article belongs to the Special Issue Semiconductor Power Devices)
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Open AccessArticle Impact of Distributed Generation Grid Code Requirements on Islanding Detection in LV Networks
Energies 2017, 10(2), 156; doi:10.3390/en10020156
Received: 8 November 2016 / Revised: 20 December 2016 / Accepted: 19 January 2017 / Published: 26 January 2017
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Abstract
The recent growing diffusion of dispersed generation in low voltage (LV) distribution networks is entailing new rules to make local generators participate in network stability. Consequently, national and international grid codes, which define the connection rules for stability and safety of electrical power
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The recent growing diffusion of dispersed generation in low voltage (LV) distribution networks is entailing new rules to make local generators participate in network stability. Consequently, national and international grid codes, which define the connection rules for stability and safety of electrical power systems, have been updated requiring distributed generators and electrical storage systems to supply stabilizing contributions. In this scenario, specific attention to the uncontrolled islanding issue has to be addressed since currently required anti-islanding protection systems, based on relays locally measuring voltage and frequency, could no longer be suitable. In this paper, the effects on the interface protection performance of different LV generators’ stabilizing functions are analysed. The study takes into account existing requirements, such as the generators’ active power regulation (according to the measured frequency) and reactive power regulation (depending on the local measured voltage). In addition, the paper focuses on other stabilizing features under discussion, derived from the medium voltage (MV) distribution network grid codes or proposed in the literature, such as fast voltage support (FVS) and inertia emulation. Stabilizing functions have been reproduced in the DIgSILENT PowerFactory 2016 software environment, making use of its native programming language. Later, they are tested both alone and together, aiming to obtain a comprehensive analysis on their impact on the anti-islanding protection effectiveness. Through dynamic simulations in several network scenarios the paper demonstrates the detrimental impact that such stabilizing regulations may have on loss-of-main protection effectiveness, leading to an increased risk of unintentional islanding. Full article
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Open AccessArticle Improvement of Wind Energy Production through HVDC Systems
Energies 2017, 10(2), 157; doi:10.3390/en10020157
Received: 26 October 2016 / Revised: 19 December 2016 / Accepted: 10 January 2017 / Published: 27 January 2017
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Abstract
Variable and non-programmable resources, such as solar and wind, have undergone a stunning growth in recent years and are likely to gain even more importance in the future. Their strong presence in the national electricity mix has created issues in many countries regarding
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Variable and non-programmable resources, such as solar and wind, have undergone a stunning growth in recent years and are likely to gain even more importance in the future. Their strong presence in the national electricity mix has created issues in many countries regarding the secure operation of the power system. In order to guarantee the stability of the system, several TSOs have resorted to wind energy curtailment, which represents a waste of clean energy and an economic loss. In order to analyze this issue, a model of the Italian power system was developed, a program able to simulate the electricity dispatching mechanism. The model was, then, used to evaluate possible solutions to reduce wind curtailment. In particular, a proposal for the construction of an HVDC line linking Southern and Northern Italy was studied. Full article
(This article belongs to the Special Issue Innovative Methods for Smart Grids Planning and Management)
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Open AccessFeature PaperArticle A Cluster Design on the Influence of Energy Taxation in Shaping the New EU-28 Economic Paradigm
Energies 2017, 10(2), 257; doi:10.3390/en10020257
Received: 4 December 2016 / Revised: 3 February 2017 / Accepted: 15 February 2017 / Published: 21 February 2017
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Abstract
Environmental and energy taxation are essential components for designing global economic policies and they often contribute to achieving the sustainable economic development goals in contemporary economies. Starting from the analysis of certain elements such as the share of environmental, energy, transport and pollution
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Environmental and energy taxation are essential components for designing global economic policies and they often contribute to achieving the sustainable economic development goals in contemporary economies. Starting from the analysis of certain elements such as the share of environmental, energy, transport and pollution taxation in GDP and using the Hierarchical Clustering methodology, the paper aims to identify economic models of behaviour and to understand the influence of energy taxation in designing an economic paradigm. In addition, another objective of the paper is to deepen the relationships that energy taxation has in designing certain economic models of behaviour and to group the EU-28 Member States based on the specified criteria. The research results confirm that at the EU-28 level could exist elements for achieving energy taxation convergence and that the states should promote a more accurate fiscal policy in order to improve the loss of competitivity caused by an inaccurate energy taxation. Full article
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Open AccessArticle The Impact of Shale Gas on the Cost and Feasibility of Meeting Climate Targets—A Global Energy System Model Analysis and an Exploration of Uncertainties
Energies 2017, 10(2), 158; doi:10.3390/en10020158
Received: 5 October 2016 / Revised: 13 January 2017 / Accepted: 17 January 2017 / Published: 27 January 2017
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Abstract
There exists considerable uncertainty over both shale and conventional gas resource availability and extraction costs, as well as the fugitive methane emissions associated with shale gas extraction and its possible role in mitigating climate change. This study uses a multi-region energy system model,
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There exists considerable uncertainty over both shale and conventional gas resource availability and extraction costs, as well as the fugitive methane emissions associated with shale gas extraction and its possible role in mitigating climate change. This study uses a multi-region energy system model, TIAM (TIMES integrated assessment model), to consider the impact of a range of conventional and shale gas cost and availability assessments on mitigation scenarios aimed at achieving a limit to global warming of below 2 °C in 2100, with a 50% likelihood. When adding shale gas to the global energy mix, the reduction to the global energy system cost is relatively small (up to 0.4%), and the mitigation cost increases by 1%–3% under all cost assumptions. The impact of a “dash for shale gas”, of unavailability of carbon capture and storage, of increased barriers to investment in low carbon technologies, and of higher than expected leakage rates, are also considered; and are each found to have the potential to increase the cost and reduce feasibility of meeting global temperature goals. We conclude that the extraction of shale gas is not likely to significantly reduce the effort required to mitigate climate change under globally coordinated action, but could increase required mitigation effort if not handled sufficiently carefully. Full article
(This article belongs to the Special Issue Low Carbon Economy)
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Open AccessArticle The Influence of Micro-Oxygen Addition on Desulfurization Performance and Microbial Communities during Waste-Activated Sludge Digestion in a Rusty Scrap Iron-Loaded Anaerobic Digester
Energies 2017, 10(2), 258; doi:10.3390/en10020258
Received: 23 November 2016 / Revised: 14 February 2017 / Accepted: 16 February 2017 / Published: 21 February 2017
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Abstract
In this study, micro-oxygen was integrated into a rusty scrap iron (RSI)-loaded anaerobic digester. Under an optimal RSI dosage of 20 g/L, increasing O2 levels were added stepwise in seven stages in a semi-continuous experiment. Results showed the average methane yield was
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In this study, micro-oxygen was integrated into a rusty scrap iron (RSI)-loaded anaerobic digester. Under an optimal RSI dosage of 20 g/L, increasing O2 levels were added stepwise in seven stages in a semi-continuous experiment. Results showed the average methane yield was 306 mL/g COD (chemical oxygen demand), and the hydrogen sulphide (H2S) concentration was 1933 ppmv with RSI addition. O2 addition induced the microbial oxidation of sulphide by stimulating sulfur-oxidizing bacteria and chemical corrosion of iron, which promoted the generation of FeS and Fe2S3. In the 6th phase of the semi-continuous test, deep desulfurization was achieved without negatively impacting system performance. Average methane yield was 301.1 mL/g COD, and H2S concentration was 75 ppmv. Sulfur mass balance was described, with 84.0%, 11.90% and 0.21% of sulfur present in solid, liquid and gaseous phases, respectively. The Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) analysis revealed that RSI addition could enrich the diversity of hydrogenotrophic methanogens and iron-reducing bacteria to benefit methanogenesis and organic mineralization, and impoverish the methanotroph (Methylocella silvestris) to reduce the consumption of methane. Micro-oxygen supplementation could enhance the diversity of iron-oxidizing bacteria arising from the improvement of Fe(II) release rate and enrich the sulphur-oxidising bacteria to achieved desulfurization. These results demonstrated that RSI addition in combination with micro-oxygenation represents a promising method for simultaneously controlling biogas H2S concentration and improving digestion performance. Full article
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Open AccessFeature PaperArticle A Nafion-Ceria Composite Membrane Electrolyte for Reduced Methanol Crossover in Direct Methanol Fuel Cells
Energies 2017, 10(2), 259; doi:10.3390/en10020259
Received: 7 January 2017 / Revised: 5 February 2017 / Accepted: 10 February 2017 / Published: 21 February 2017
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Abstract
An alternative Nafion composite membrane was prepared by incorporating various loadings of CeO2 nanoparticles into the Nafion matrix and evaluated its potential application in direct methanol fuel cells (DMFCs). The effects of CeO2 in the Nafion matrix were systematically studied in
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An alternative Nafion composite membrane was prepared by incorporating various loadings of CeO2 nanoparticles into the Nafion matrix and evaluated its potential application in direct methanol fuel cells (DMFCs). The effects of CeO2 in the Nafion matrix were systematically studied in terms of surface morphology, thermal and mechanical stability, proton conductivity and methanol permeability. The composite membrane with optimum filler content (1 wt. % CeO2) exhibits a proton conductivity of 176 mS·cm−1 at 70 °C, which is about 30% higher than that of the unmodified membrane. Moreover, all the composite membranes possess a much lower methanol crossover compared to pristine Nafion membrane. In a single cell DMFC test, MEA fabricated with the optimized composite membrane delivered a peak power density of 120 mW·cm−2 at 70 °C, which is about two times higher in comparison with the pristine Nafion membrane under identical operating conditions. Full article
(This article belongs to the Special Issue Direct Alcohol Fuel Cells)
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Open AccessArticle Effect of the Dendrimer Generation Used in the Synthesis of Pt-Ru Nanoparticles Supported on Carbon Nanofibers on the Catalytic Activity towards Methanol Oxidation
Energies 2017, 10(2), 159; doi:10.3390/en10020159
Received: 30 November 2016 / Revised: 12 January 2017 / Accepted: 19 January 2017 / Published: 28 January 2017
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Abstract
Pt-Ru nanoparticles supported on carbon nanofibers (CNF) were synthesized by the sodium borohydride reduction method, using different generation dendrimers (zero, one, two and three generations). After the synthesis process, these materials were submitted to a heat treatment at 350 °C, in order to
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Pt-Ru nanoparticles supported on carbon nanofibers (CNF) were synthesized by the sodium borohydride reduction method, using different generation dendrimers (zero, one, two and three generations). After the synthesis process, these materials were submitted to a heat treatment at 350 °C, in order to clean the nanoparticle surface of organic residues. TEM characterization showed that the Pt-Ru nanoparticles size ranged between 1.9 and 5.5 nm. The use of dendrimers did not totally avoid the formation of aggregates, although monodisperse sizes were observed. The heat treatment produces the desired surface cleaning, although promoted the formation of agglomerates and crystalline Ru oxides. The study of the electrochemical activity towards the methanol oxidation displayed some clues about the influence of both the dendrimer generation and the presence of Ru oxides. Moreover, the apparent activation energy Eap for this reaction was determined. The results showed a beneficial effect of the heat treatment on the methanol oxidation current densities for the materials synthesized with the biggest dendrimers, being the methanol deprotonation and COad diffusion the predominant rate determining steps (rds). Full article
(This article belongs to the Special Issue Direct Alcohol Fuel Cells)
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Open AccessArticle Switchgrass-Based Bioethanol Productivity and Potential Environmental Impact from Marginal Lands in China
Energies 2017, 10(2), 260; doi:10.3390/en10020260
Received: 29 December 2016 / Revised: 9 February 2017 / Accepted: 17 February 2017 / Published: 21 February 2017
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Abstract
Switchgrass displays an excellent potential to serve as a non-food bioenergy feedstock for bioethanol production in China due to its high potential yield on marginal lands. However, few studies have been conducted on the spatial distribution of switchgrass-based bioethanol production potential in China.
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Switchgrass displays an excellent potential to serve as a non-food bioenergy feedstock for bioethanol production in China due to its high potential yield on marginal lands. However, few studies have been conducted on the spatial distribution of switchgrass-based bioethanol production potential in China. This study created a land surface process model (Environmental Policy Integrated Climate GIS (Geographic Information System)-based (GEPIC) model) coupled with a life cycle analysis (LCA) to explore the spatial distribution of potential bioethanol production and present a comprehensive analysis of energy efficiency and environmental impacts throughout its whole life cycle. It provides a new approach to study the bioethanol productivity and potential environmental impact from marginal lands based on the high spatial resolution GIS data, and this applies not only to China, but also to other regions and to other types of energy plant. The results indicate that approximately 59 million ha of marginal land in China are suitable for planting switchgrass, and 22 million tons of ethanol can be produced from this land. Additionally, a potential net energy gain (NEG) of 1.75 x 106 million MJ will be achieved if all of the marginal land can be used in China, and Yunnan Province offers the most significant one that accounts for 35% of the total. Finally, this study obtained that the total environmental effect index of switchgrass-based bioethanol is the equivalent of a population of approximately 20,300, and a reduction in the global warming potential (GWP) is the most significant environmental impact. Full article
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Open AccessArticle Numerical Investigation of the Production Behavior of Methane Hydrates under Depressurization Conditions Combined with Well-Wall Heating
Energies 2017, 10(2), 161; doi:10.3390/en10020161
Received: 2 December 2016 / Accepted: 19 January 2017 / Published: 30 January 2017
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Abstract
In this study, a 2D hydrate dissociation simulator has been improved and verified to be valid in numerical simulations of the gas production behavior using depressurization combined with a well-wall heating method. A series of numerical simulations were performed and the results showed
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In this study, a 2D hydrate dissociation simulator has been improved and verified to be valid in numerical simulations of the gas production behavior using depressurization combined with a well-wall heating method. A series of numerical simulations were performed and the results showed that well-wall heating had an influence enhancing the depressurization-induced gas production, but the influence was limited, and it was even gradually weakened with the increase of well-wall heating temperature. Meanwhile, the results of the sensitivity analysis demonstrated the gas production depended on the initial hydrate saturation, initial pressure and the thermal boundary conditions. The supply of heat for hydrate dissociation mainly originates from the thermal boundaries,whichcontrolthehydratedissociationandgasproductionbydepressurizationcombined with well-wall heating. However, the effect of initial temperature on the gas production could be nearly negligible under depressurization conditions combined with well-wall heating. Full article
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Open AccessArticle MACsec Layer 2 Security in HSR Rings in Substation Automation Systems
Energies 2017, 10(2), 162; doi:10.3390/en10020162
Received: 9 November 2016 / Accepted: 12 January 2017 / Published: 31 January 2017
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Abstract
The smart-grid concept takes the communications from the enclosed and protected environment of a substation to the wider city or nationwide area. In this environment, cyber security takes a key role in order to secure the communications. The challenge is to be able
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The smart-grid concept takes the communications from the enclosed and protected environment of a substation to the wider city or nationwide area. In this environment, cyber security takes a key role in order to secure the communications. The challenge is to be able to secure the grid without impacting the latency while, at the same time, maintaining compatibility with older devices and non secure services. At the lower level, added security must not interfere with the redundancy and the latency required for the real-time substation automation communications. This paper studies how to integrate IEEE MAC Security standard (MACsec) in the substation environment, especially when used in substation system communications Full article
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Open AccessArticle Parallel Multi-Objective Genetic Algorithm for Short-Term Economic Environmental Hydrothermal Scheduling
Energies 2017, 10(2), 163; doi:10.3390/en10020163
Received: 15 November 2016 / Accepted: 13 January 2017 / Published: 31 January 2017
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Abstract
With the increasingly serious energy crisis and environmental pollution, the short-term economic environmental hydrothermal scheduling (SEEHTS) problem is becoming more and more important in modern electrical power systems. In order to handle the SEEHTS problem efficiently, the parallel multi-objective genetic algorithm (PMOGA) is
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With the increasingly serious energy crisis and environmental pollution, the short-term economic environmental hydrothermal scheduling (SEEHTS) prob