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Energies, Volume 10, Issue 5 (May 2017)

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Cover Story Energy-optimal kinematic redundancy resolution is required for future robotic closed-loop [...] Read more.
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Open AccessArticle China Building Energy Consumption: Definitions and Measures from an Operational Perspective
Energies 2017, 10(5), 582; doi:10.3390/en10050582
Received: 18 February 2017 / Revised: 12 March 2017 / Accepted: 17 April 2017 / Published: 25 April 2017
Cited by 2 | PDF Full-text (962 KB) | HTML Full-text | XML Full-text
Abstract
China building energy consumption (BEC) has been gradually derived and also sparked attention. However, something worth discussing is estimating the BEC based on the definition of life cycle or building operation. In addition, there exists discrepancy in the previous studies and the real
[...] Read more.
China building energy consumption (BEC) has been gradually derived and also sparked attention. However, something worth discussing is estimating the BEC based on the definition of life cycle or building operation. In addition, there exists discrepancy in the previous studies and the real status of BEC has not been known well. In order to settle the disputes over the calculation of BEC, this paper establishes an appropriate accounting method of building energy to present the BEC situation in China and lays the foundation for policymakers to develop appropriate energy saving policies. Meanwhile, this study attempts to clarify the BEC to help policymakers assess the effect of environmental policies. Using the method in this document, we find that the energy consumption of buildings just accounts for 15%–16% of the final total energy consumption in China; by contrast, the previous studies usually have double accounting through a top-down approach if central heat supply of buildings was taken into additional consideration. Full article
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Open AccessArticle A Cost Optimized Fully Sustainable Power System for Southeast Asia and the Pacific Rim
Energies 2017, 10(5), 583; doi:10.3390/en10050583
Received: 2 March 2017 / Revised: 14 April 2017 / Accepted: 19 April 2017 / Published: 25 April 2017
Cited by 2 | PDF Full-text (5085 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this paper, a cost optimal 100% renewable energy based system is obtained for Southeast Asia and the Pacific Rim region for the year 2030 on an hourly resolution for the whole year. For the optimization, the region was divided into 15 sub-regions
[...] Read more.
In this paper, a cost optimal 100% renewable energy based system is obtained for Southeast Asia and the Pacific Rim region for the year 2030 on an hourly resolution for the whole year. For the optimization, the region was divided into 15 sub-regions and three different scenarios were set up based on the level of high voltage direct current grid connections. The results obtained for a total system levelized cost of electricity showed a decrease from 66.7 €/MWh in a decentralized scenario to 63.5 €/MWh for a centralized grid connected scenario. An integrated scenario was simulated to show the benefit of integrating additional demand of industrial gas and desalinated water which provided the system the required flexibility and increased the efficiency of the usage of storage technologies. This was reflected in the decrease of system cost by 9.5% and the total electricity generation by 5.1%. According to the results, grid integration on a larger scale decreases the total system cost and levelized cost of electricity by reducing the need for storage technologies due to seasonal variations in weather and demand profiles. The intermittency of renewable technologies can be effectively stabilized to satisfy hourly demand at a low cost level. A 100% renewable energy based system could be a reality economically and technically in Southeast Asia and the Pacific Rim with the cost assumptions used in this research and it may be more cost competitive than the nuclear and fossil carbon capture and storage (CCS) alternatives. Full article
(This article belongs to the Special Issue Sustainable Energy Technologies)
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Open AccessArticle A Short-Current Control Method for Constant Frequency Current-Fed Wireless Power Transfer Systems
Energies 2017, 10(5), 585; doi:10.3390/en10050585
Received: 24 February 2017 / Revised: 15 April 2017 / Accepted: 20 April 2017 / Published: 25 April 2017
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Abstract
Frequency drift is a serious problem in Current-Fed Wireless Power Transfer (WPT) systems. When the operating frequency is drifting from the inherent Zero Voltage Switching (ZVS) frequency of resonant network, large short currents will appear and damage the switches. In this paper, an
[...] Read more.
Frequency drift is a serious problem in Current-Fed Wireless Power Transfer (WPT) systems. When the operating frequency is drifting from the inherent Zero Voltage Switching (ZVS) frequency of resonant network, large short currents will appear and damage the switches. In this paper, an inductance-dampening method is proposed to inhibit short currents and achieve constant-frequency operation. By adding a small auxiliary series inductance in the primary resonant network, short currents are greatly attenuated to a safe level. The operation principle and steady-state analysis of the system are provided. An overlapping time self-regulating circuit is designed to guarantee ZVS running. The range of auxiliary inductances is discussed and its critical value is calculated exactly. The design methodology is described and a design example is presented. Finally, a prototype is built and the experimental results verify the proposed method. Full article
(This article belongs to the Special Issue Wireless Power Transfer and Energy Harvesting Technologies)
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Open AccessArticle H∞ Repetitive Control Based on Active Damping with Reduced Computation Delay for LCL-Type Grid-Connected Inverters
Energies 2017, 10(5), 586; doi:10.3390/en10050586
Received: 21 February 2017 / Revised: 20 April 2017 / Accepted: 20 April 2017 / Published: 25 April 2017
Cited by 2 | PDF Full-text (9340 KB) | HTML Full-text | XML Full-text
Abstract
In the paper, the H∞ repetitive current control scheme based on active damping along with the design method is proposed for three-phase grid-connected inverters with inductor-capacitor-inductor (LCL) filters. The control scheme aims to reduce the harmonic distortion of the output currents and achieve
[...] Read more.
In the paper, the H∞ repetitive current control scheme based on active damping along with the design method is proposed for three-phase grid-connected inverters with inductor-capacitor-inductor (LCL) filters. The control scheme aims to reduce the harmonic distortion of the output currents and achieve better efficiency. The design method introduces capacitor-current-feedback active damping into the H∞ controller design process by proposing an equivalent controlled plant. Additionally, based on the discrete model of the controlled plant with variable computation delay, the algebraic expression of the stable region for the feedback coefficient and the computation delay is obtained to avoid system instability caused by the digital control delay. Finally, the stability criterion is proposed to evaluate the stability of the discrete control system with the H∞ repetitive current control scheme. The theoretical analysis and experimental results prove that the control scheme presented in this paper not only can reject the harmonics of output currents, but is robust under the variation of the grid-impedance. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Space Vector Modulation for an Indirect Matrix Converter with Improved Input Power Factor
Energies 2017, 10(5), 588; doi:10.3390/en10050588
Received: 16 February 2017 / Revised: 17 April 2017 / Accepted: 19 April 2017 / Published: 25 April 2017
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Abstract
Pulse width modulation strategies have been developed for indirect matrix converters (IMCs) in order to improve their performance. In indirect matrix converters, the LC input filter is used to remove input current harmonics and electromagnetic interference problems. Unfortunately, due to the existence of
[...] Read more.
Pulse width modulation strategies have been developed for indirect matrix converters (IMCs) in order to improve their performance. In indirect matrix converters, the LC input filter is used to remove input current harmonics and electromagnetic interference problems. Unfortunately, due to the existence of the input filter, the input power factor is diminished, especially during operation at low voltage outputs. In this paper, a new space vector modulation (SVM) is proposed to compensate for the input power factor of the indirect matrix converter. Both computer simulation and experimental studies through hardware implementation were performed to verify the effectiveness of the proposed modulation strategy. Full article
(This article belongs to the Special Issue Power Electronics and Power Quality)
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Open AccessArticle Evaluation of Interface Defects in Inaccessible Reactor Shrink Fit Nozzle Welds Using Ultrasonic Waves
Energies 2017, 10(5), 589; doi:10.3390/en10050589
Received: 11 January 2017 / Revised: 3 April 2017 / Accepted: 20 April 2017 / Published: 25 April 2017
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Abstract
This study proposes an effective method to inspect inaccessible nuclear power reactor head nozzles using interface waves that propagate along the shrink fit boundary of a reactor head. The reactor head is relatively thick, which makes it difficult to inspect from the outside
[...] Read more.
This study proposes an effective method to inspect inaccessible nuclear power reactor head nozzles using interface waves that propagate along the shrink fit boundary of a reactor head. The reactor head is relatively thick, which makes it difficult to inspect from the outside by conventional ultrasonic testing. However, interface waves can propagate a long distance from a fixed transducer position. The inside of the nuclear reactor has limited access due to the high radiation, so the transducers are located outside the nuclear reactor head, and interface waves propagate into the nuclear reactor to detect defects. A numerical simulation and experiments were carried out to validate the method. Various defect cases that simulate field failures are also presented, and the proposed technique shows satisfactory defect classification. Full article
(This article belongs to the Special Issue Next Generation Reactors and Materials for Advanced Fuel Cycles)
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Open AccessArticle Probabilistic Power Flow Method Considering Continuous and Discrete Variables
Energies 2017, 10(5), 590; doi:10.3390/en10050590
Received: 26 March 2017 / Revised: 12 April 2017 / Accepted: 19 April 2017 / Published: 26 April 2017
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Abstract
This paper proposes a probabilistic power flow (PPF) method considering continuous and discrete variables (continuous and discrete power flow, CDPF) for power systems. The proposed method—based on the cumulant method (CM) and multiple deterministic power flow (MDPF) calculations—can deal with continuous variables such
[...] Read more.
This paper proposes a probabilistic power flow (PPF) method considering continuous and discrete variables (continuous and discrete power flow, CDPF) for power systems. The proposed method—based on the cumulant method (CM) and multiple deterministic power flow (MDPF) calculations—can deal with continuous variables such as wind power generation (WPG) and loads, and discrete variables such as fuel cell generation (FCG). In this paper, continuous variables follow a normal distribution (loads) or a non-normal distribution (WPG), and discrete variables follow a binomial distribution (FCG). Through testing on IEEE 14-bus and IEEE 118-bus power systems, the proposed method (CDPF) has better accuracy compared with the CM, and higher efficiency compared with the Monte Carlo simulation method (MCSM). Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Control Strategy of Single-Phase Three Level Neutral Point Clamped Cascaded Rectifier
Energies 2017, 10(5), 592; doi:10.3390/en10050592
Received: 20 March 2017 / Revised: 21 April 2017 / Accepted: 22 April 2017 / Published: 28 April 2017
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Abstract
Single-phase 3-level neutral point clamped cascaded rectifier (3LNPC-CR) has been successfully made its way into traction drive system as a high-voltage traction converter. In this passage, the control issue of the 3LNPC-CR is considered. A transient current control strategy, combined with proportional integral
[...] Read more.
Single-phase 3-level neutral point clamped cascaded rectifier (3LNPC-CR) has been successfully made its way into traction drive system as a high-voltage traction converter. In this passage, the control issue of the 3LNPC-CR is considered. A transient current control strategy, combined with proportional integral (PI) controllers, is adopted to achieve unity power factor, satisfactory sinusoidal grid current, regulated overall dc voltage, and even efficient voltage balance between each module. Besides, with regard to the instinct voltage fluctuation problem among dc-link capacitors in one 3-level neutral point clamped (3LNPC) rectifier module, a phase shift carrier space vector pulse width modulation (PSC-SVPWM) worked along with a reasonable redundancy selection scheme is addressed. In addition, two auxiliary balancing circuits for a single-phase 3LNPC rectifier is proposed. The voltage balancing capacity of these internal-module balancing schemes are analyzed and compared. Finally, the control performance of these proposed strategies are verified by simulations and experiments. Full article
(This article belongs to the Special Issue Power Electronics in Power Quality)
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Open AccessArticle Research on Partial Discharge Source Localization Based on an Ultrasonic Array and a Step-by-Step Over-Complete Dictionary
Energies 2017, 10(5), 593; doi:10.3390/en10050593
Received: 15 March 2017 / Revised: 17 April 2017 / Accepted: 20 April 2017 / Published: 29 April 2017
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Abstract
Partial discharge (PD) in electrical equipment is one of the major causes of electrical insulation failures. Fast and accurate positioning of PD sources allows timely elimination of insulation faults. In order to improve the accuracy of PD detection, this paper mainly studies the
[...] Read more.
Partial discharge (PD) in electrical equipment is one of the major causes of electrical insulation failures. Fast and accurate positioning of PD sources allows timely elimination of insulation faults. In order to improve the accuracy of PD detection, this paper mainly studies the direction of arrival (DOA) estimation of PD ultrasonic signals based on a step-by-step over-complete dictionary. The simulation results show that the step by step dictionary can improve the operation speed and save signal processing time. Firstly, a step-by-step over-complete dictionary covering all the angles of space is established according to the expression of the steering vector for a matching pursuit direction finding algorithm, which can save computation time. Then, the step-by-step complete dictionary is set up according to the direction vector, and the atomic precision is respectively set to 10°, 1° and 0.1°. The matching pursuit algorithm is used to carry out the sparse representation of the received data X and select the optimal atom from the step-by-step complete dictionary, and the angle information contained in atoms is DOA of the PD sources. According to the direction finding results, combined with the installation location of the ultrasonic array sensor, the spatial position of a partial discharge source can be obtained using the three platform array location method. Finally, a square ultrasonic array sensor is developed, and an experimental platform for the ultrasonic array detection of partial discharges is set up and used to carry out an experimental study. The results show that the DOA estimation method based on a step-by-step over-complete dictionary can improve the direction finding precision, thereby increasing the subsequent positioning accuracy, and the spatial position estimation error of the PD source obtained under laboratory conditions is about 5 cm, making this a feasible method. Full article
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Open AccessArticle Comparison of Solar Radiation Models to Estimate Direct Normal Irradiance for Korea
Energies 2017, 10(5), 594; doi:10.3390/en10050594
Received: 10 February 2017 / Revised: 17 April 2017 / Accepted: 20 April 2017 / Published: 30 April 2017
Cited by 2 | PDF Full-text (3027 KB) | HTML Full-text | XML Full-text
Abstract
Reliable solar radiation data are important for energy simulations in buildings and solar energy systems. Although direct normal irradiance (DNI) is required for simulations, in addition to global horizontal irradiance (GHI), a lack of DNI measurement data is quite often due to high
[...] Read more.
Reliable solar radiation data are important for energy simulations in buildings and solar energy systems. Although direct normal irradiance (DNI) is required for simulations, in addition to global horizontal irradiance (GHI), a lack of DNI measurement data is quite often due to high cost and maintenance. Solar radiation models are widely used in order to overcome the limitation, but only a few studies have been devoted to solar radiation data and modeling in Korea. This study investigates the most suitable solar radiation model that converts GHI into DNI for Korea, using measurement data of the city of Daejeon from 2007 to 2009. After ten existing models were evaluated, the Reindl-2 model was selected as the best. A new model was developed for further improvement, and it substantially decreased estimation errors compared to the ten investigated models. The new model was also evaluated for nine major cities other than Daejeon from the standpoint of typical meteorological year (TMY) data, and consistent evaluation results confirmed that the new model is reliably applicable across Korea. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle High-Gain Disturbance Observer-Based Robust Load Frequency Control of Power Systems with Multiple Areas
Energies 2017, 10(5), 595; doi:10.3390/en10050595
Received: 28 February 2017 / Revised: 21 April 2017 / Accepted: 22 April 2017 / Published: 29 April 2017
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Abstract
This paper proposes a high-gain disturbance observer (HDOB)-based controller for load frequency control (LFC) of power systems with multiple areas. The main goal of LFC problem is to maintain the frequency to its nominal value. The objective of this paper is to reject
[...] Read more.
This paper proposes a high-gain disturbance observer (HDOB)-based controller for load frequency control (LFC) of power systems with multiple areas. The main goal of LFC problem is to maintain the frequency to its nominal value. The objective of this paper is to reject frequency variations due to abrupt load changes and diverse uncertainties (e.g., inertia and damping parameters, and interconnection topology, etc.) by employing the HDOB for the LFC. The simulation results demonstrate the effectiveness of the proposed HDOB-based LFC by showing that it successfully rejects frequency variations owing to load changes and frequency variations occurring in various locations in interconnected power systems. Besides, it is shown that the proposed LFC can eliminate frequency deviations although there are delays in transmission among the power systems with multiple areas. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Electricity Production by the Application of a Low Voltage DC-DC Boost Converter to a Continuously Operating Flat-Plate Microbial Fuel Cell
Energies 2017, 10(5), 596; doi:10.3390/en10050596
Received: 16 February 2017 / Revised: 25 March 2017 / Accepted: 24 April 2017 / Published: 29 April 2017
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Abstract
An ultra-low voltage customized DC-DC booster circuit was developed using a LTC3108 converter, and used continuously on a flat-plate microbial fuel cell (FPM) system. The boost converter successfully stepped up the microbial fuel cell (MFC) voltage from ~0.5 V to 3.3 and 5.0
[...] Read more.
An ultra-low voltage customized DC-DC booster circuit was developed using a LTC3108 converter, and used continuously on a flat-plate microbial fuel cell (FPM) system. The boost converter successfully stepped up the microbial fuel cell (MFC) voltage from ~0.5 V to 3.3 and 5.0 V of outputs. The designed circuit and system displayed the dynamic variations of the source FPM as well as the output voltage through the designed three connection points within the booster circuit. The source MFC voltage was interrelated with the booster circuit and its performance, and it adapted to the set points of the booster dynamically. The maximum output power density of the MFC with the DC-DC booster circuit was 8.16 W/m3 compared to the maximum source FPM input power of 14.27 W/m3 at 100 Ω, showing a conversion efficiency of 26–57%, but with a 10-fold higher output than that of the source voltage. The combined LTC3108 with FPM supplied power for electronic devices using synthetic and real domestic wastewater. This report presents a promising strategy for utilizing the electrical energy produced from MFCs, and expands the applicability of bioelectrochemical systems with an improved energy efficiency of the present wastewater treatment system. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle A Data-Driven Learning-Based Continuous-Time Estimation and Simulation Method for Energy Efficiency and Coulombic Efficiency of Lithium Ion Batteries
Energies 2017, 10(5), 597; doi:10.3390/en10050597
Received: 17 March 2017 / Revised: 21 April 2017 / Accepted: 25 April 2017 / Published: 29 April 2017
PDF Full-text (5431 KB) | HTML Full-text | XML Full-text
Abstract
Lithium ion (Li-ion) batteries work as the basic energy storage components in modern railway systems, hence estimating and improving battery efficiency is a critical issue in optimizing the energy usage strategy. However, it is difficult to estimate the efficiency of lithium ion batteries
[...] Read more.
Lithium ion (Li-ion) batteries work as the basic energy storage components in modern railway systems, hence estimating and improving battery efficiency is a critical issue in optimizing the energy usage strategy. However, it is difficult to estimate the efficiency of lithium ion batteries accurately since it varies continuously under working conditions and is unmeasurable via experiments. This paper offers a learning-based simulation method that employs experimental data to estimate the continuous-time energy efficiency and coulombic efficiency of lithium ion batteries, taking lithium titanate batteries as an example. The state of charge (SOC) regions and discharge current rates are considered as the main variables that may affect the efficiencies. Over eight million empirical datasets are collected during a series of experiments performed to investigate the efficiency variation. A back propagation (BP) neural network efficiency estimation and simulation model is proposed to estimate the continuous-time energy efficiency and coulombic efficiency. The empirical data collected in the experiments are used to train the BP network model, which reveals a test error of 10−4. With the input of continuous SOC regions and discharge currents, continuous-time efficiency can be estimated by the trained BP network model. The estimated and simulated result is proven to be consistent with the experimental results. Full article
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Open AccessArticle Experimental and Theoretical Study of the Interactions between Fe2O3/Al2O3 and CO
Energies 2017, 10(5), 598; doi:10.3390/en10050598
Received: 5 December 2016 / Revised: 24 April 2017 / Accepted: 25 April 2017 / Published: 29 April 2017
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Abstract
The behavior of Fe2O3/Al2O3 particles as oxygen carriers (OCs) for CO chemical looping combustion (CLC) under different reaction temperatures (700 °C, 800 °C, 900 °C, and 1000 °C) were tested in a lab-scale fluidized bed and
[...] Read more.
The behavior of Fe2O3/Al2O3 particles as oxygen carriers (OCs) for CO chemical looping combustion (CLC) under different reaction temperatures (700 °C, 800 °C, 900 °C, and 1000 °C) were tested in a lab-scale fluidized bed and a thermogravimetric analysis (TGA) unit. The results show that the oxygen carrier presents the highest reactivity at 800 °C, even after 30 cycles of redox reaction in a fluidized bed, while more obvious carbon deposition occurred for the case at 700 °C, and agglomeration for the case at 1000 °C. Moreover, the detailed behavior of the prepared Fe2O3/Al2O3 particle was detected in the TGA apparatus at different reaction temperatures. Furthermore, temperature-programming TGA experiments were performed to investigate the influence of different CO concentrations and CO/CO2 concentrations on the reaction between CO and OC during the chemical looping combustion processes. Based on these experimental behaviors of the prepared Fe2O3/Al2O3 during the CLC of CO, the detailed models and electronic properties of the pure and reduced Fe2O3/Al2O3 supported the slabs, CO adsorption, and oxidation, and the decomposition reactions on these surfaces were revealed using density functional theory (DFT) calculations which went deep into the nature of the synergetic effect of the support of Al2O3 on the activity of Fe2O3 for the CLC of CO. Full article
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Open AccessArticle The Effect of Solvents on the Performance of CH3NH3PbI3 Perovskite Solar Cells
Energies 2017, 10(5), 599; doi:10.3390/en10050599
Received: 15 March 2017 / Revised: 24 April 2017 / Accepted: 25 April 2017 / Published: 29 April 2017
Cited by 1 | PDF Full-text (17852 KB) | HTML Full-text | XML Full-text
Abstract
The properties of perovskite solar cells (PSCs) fabricated using various solvents was studied. The devices had an indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)/CH3NH3PbI3 (fabricated by using various solvents)/fullerene (C60)/bathocuproine (BCP)/silver (Ag) structure. The solvents used were
[...] Read more.
The properties of perovskite solar cells (PSCs) fabricated using various solvents was studied. The devices had an indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)/CH3NH3PbI3 (fabricated by using various solvents)/fullerene (C60)/bathocuproine (BCP)/silver (Ag) structure. The solvents used were dimethylformamide (DMF), γ-butyrolactone (GBL), dimethyl sulfoxide (DMSO), a mixture of DMSO and DMF (1:1 v/v), and a mixture of DMSO and GBL (DMSO: GBL, 1:1 v/v), respectively. The power conversion efficiency (PCE) of the device fabricated using DMF is zero, which is attributed to the poor coverage of CH3NH3PbI3 film on the substrate. In addition, the PCE of the device made using GBL is only 1.74% due to the low solubility of PbI2 and CH3NH3I. In contrast, the PCE of the device fabricated using the solvents containing DMSO showed better performance. This is ascribed to the high solubilization properties and strong coordination of DMSO. As a result, a PCE of 9.77% was obtained using a mixed DMSO:GBL solvent due to the smooth surface, uniform film coverage on the substrate and the high crystallization of the perovskite structure. Finally, a mixed DMSO: DMF:GBL (5:2:3 v/v/v) solvent that combined the advantages of each solvent was used to fabricate a device, leading to a further improvement of the PCE of the resulting PSC to 10.84%. Full article
(This article belongs to the Special Issue Solid State Lighting)
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Open AccessArticle China’s Energy Transition in the Power and Transport Sectors from a Substitution Perspective
Energies 2017, 10(5), 600; doi:10.3390/en10050600
Received: 20 February 2017 / Revised: 24 April 2017 / Accepted: 25 April 2017 / Published: 29 April 2017
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Abstract
Facing heavy air pollution, China needs to transition to a clean and sustainable energy system, especially in the power and transport sectors, which contribute the highest greenhouse gas (GHG) emissions. The core of an energy transition is energy substitution and energy technology improvement.
[...] Read more.
Facing heavy air pollution, China needs to transition to a clean and sustainable energy system, especially in the power and transport sectors, which contribute the highest greenhouse gas (GHG) emissions. The core of an energy transition is energy substitution and energy technology improvement. In this paper, we forecast the levelized cost of electricity (LCOE) for power generation in 2030 in China. Cost-emission effectiveness of the substitution between new energy vehicles and conventional vehicles is also calculated in this study. The results indicate that solar photovoltaic (PV) and wind power will be cost comparative in the future. New energy vehicles are more expensive than conventional vehicles due to their higher manufacturer suggested retail price (MSRP). The cost-emission effectiveness of the substitution between new energy vehicles and conventional vehicles would be $96.7/ton or $114.8/ton. Gasoline prices, taxes, and vehicle insurance will be good directions for policy implementation after the ending of subsidies. Full article
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Open AccessArticle Investigating the Effect of Rainfall Parameters on the Self-Cleaning of Polluted Suspension Insulators: Insight from Southern China
Energies 2017, 10(5), 601; doi:10.3390/en10050601
Received: 31 October 2016 / Revised: 21 April 2017 / Accepted: 21 April 2017 / Published: 1 May 2017
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Abstract
The cleaning effect of heavy rain (the rainfall reaches 5 mm every day) on surface contamination of insulators is more effective than dew, fog, mist, and other light rain conditions which can initiate leakage currents and increase the likelihood of flashover. It is
[...] Read more.
The cleaning effect of heavy rain (the rainfall reaches 5 mm every day) on surface contamination of insulators is more effective than dew, fog, mist, and other light rain conditions which can initiate leakage currents and increase the likelihood of flashover. It is well understood that heavy rain can wash away contamination from the surface of high voltage (HV) insulators and thereby reduce the risk of pollution flashover. This study examines the cleaning effect of natural wetting conditions on HV insulators on four 500 kV transmission lines in Hunan Province, China. Historical meteorological data, monthly equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD) measurements taken over a period of five years were analyzed to investigate the relationship between rainfall intensity and insulator cleaning. The measured data show that the ESDD/NSDD changes with the seasonal variation, which accumulates in dry season (January–April, about 117–122 days) and is washed off in the wet season (June–October, about 118–127 days). According to the measured data, the ESDD and NSDD on the surface of insulators were affected by the rainfall intensity (in the dry season it is about 1 mm/day and in the wet season it is about 5 mm/day). Based on a comparison of the four study sites, we propose a mathematical model to show the functional relationship between rainfall intensity and insulator self-cleaning capability. The mathematical model’s coefficient of determination (R2) is greater than 0.9 and the effective rate of self-cleaning capability reaches 80%. Full article
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Open AccessArticle The Contribution of Non-CO2 Greenhouse Gas Mitigation to Achieving Long-Term Temperature Goals
Energies 2017, 10(5), 602; doi:10.3390/en10050602
Received: 28 February 2017 / Revised: 11 April 2017 / Accepted: 14 April 2017 / Published: 1 May 2017
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Abstract
This paper analyses the emissions and cost impacts of mitigation of non-CO2 greenhouse gases (GHGs) at a global level, in scenarios aimed at meeting a range of long-term temperature goals (LTTGs). The study combines an integrated assessment model (TIAM-Grantham) representing CO2
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This paper analyses the emissions and cost impacts of mitigation of non-CO2 greenhouse gases (GHGs) at a global level, in scenarios aimed at meeting a range of long-term temperature goals (LTTGs). The study combines an integrated assessment model (TIAM-Grantham) representing CO2 emissions (and their mitigation) from the fossil fuel combustion and industrial sectors, coupled with a model covering non-CO2 emissions (GAINS), using the latest global warming potentials from the Intergovernmental Panel on Climate Change’s Fifth Assessment Report. We illustrate that in general non-CO2 mitigation measures are less costly than CO2 mitigation measures, with the majority of their abatement potential achievable at US2005$100/tCO2e or less throughout the 21st century (compared to a marginal CO2 mitigation cost which is already greater than this by 2030 in the most stringent mitigation scenario). As a result, the total cumulative discounted cost over the period 2010–2100 (at a 5% discount rate) of limiting global average temperature change to 2.5 °C by 2100 is $48 trillion (about 1.6% of cumulative discounted GDP over the period 2010–2100) if only CO2 from the fossil fuel and industrial sectors is targeted, whereas the cost falls to $17 trillion (0.6% of GDP) by including non-CO2 GHG mitigation in the portfolio of options—a cost reduction of about 65%. The criticality of non-CO2 mitigation recommends further research, given its relatively less well-explored nature when compared to CO2 mitigation. Full article
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Open AccessArticle Volume and Mass Measurement of a Burning Wood Pellet by Image Processing
Energies 2017, 10(5), 603; doi:10.3390/en10050603
Received: 2 March 2017 / Revised: 5 April 2017 / Accepted: 12 April 2017 / Published: 1 May 2017
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Abstract
Wood pellets are a form of solid biomass energy and a renewable energy source. In 2015, the new and renewable energy (NRE) portion of wood pellets was 4.6% of the total primary energy in Korea. Wood pellets account for 6.2% of renewable energy
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Wood pellets are a form of solid biomass energy and a renewable energy source. In 2015, the new and renewable energy (NRE) portion of wood pellets was 4.6% of the total primary energy in Korea. Wood pellets account for 6.2% of renewable energy consumption in Korea, the equivalent of 824,000 TOE (ton of oil equivalent, 10 million kcal). The burning phases of a wood pellet can be classified into three modes: (1) gasification; (2) flame burning and (3) charcoal burning. At each wood pellet burning mode, the volume and weight of the burning wood pellet can drastically change; these parameters are important to understand the wood pellet burning mechanism. We developed a new method for measuring the volume of a burning wood pellet that involves no contact. To measure the volume of a wood pellet, we take pictures of the wood pellet in each burning mode. The volume of a burning wood pellet can then be calculated by image processing. The difference between the calculation method using image processing and the direct measurement of a burning wood pellet in gasification mode is less than 8.8%. In gasification mode in this research, mass reduction of the wood pellet is 37% and volume reduction of the wood pellet is 7%. Whereas in charcoal burning mode, mass reduction of the wood pellet is 10% and volume reduction of the wood pellet is 41%. By measuring volume using image processing, continuous and non-interruptive volume measurements for various solid fuels are possible and can provide more detailed information for CFD (computational fluid dynamics) analysis. Full article
(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications)
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Open AccessArticle Sliding Mode Control of a Variable- Speed Wind Energy Conversion System Using a Squirrel Cage Induction Generator
Energies 2017, 10(5), 604; doi:10.3390/en10050604
Received: 25 January 2017 / Revised: 19 April 2017 / Accepted: 19 April 2017 / Published: 1 May 2017
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Abstract
This paper deals with the control of a variable-speed wind energy conversion (WEC) system using a squirrel cage induction generator (SCIG) connected to the grid through a back-to-back three phase (AC-DC-AC) power converter. The sliding mode control technique is used to control the
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This paper deals with the control of a variable-speed wind energy conversion (WEC) system using a squirrel cage induction generator (SCIG) connected to the grid through a back-to-back three phase (AC-DC-AC) power converter. The sliding mode control technique is used to control the WEC system. The objective of the controllers is to force the states of the system to track their desired states. One controller is used to regulate the generator speed and the flux so that maximum power is extracted from the wind. Another controller is used to control the grid side converter, which controls the DC bus voltage and the active and reactive powers injected into the grid. The performance of the controlled wind energy conversion system is verified through MATLAB simulations, which show that the controlled system performs well. Full article
(This article belongs to the collection Wind Turbines)
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Open AccessArticle Management System for Large Li-Ion Battery Packs with a New Adaptive Multistage Charging Method
Energies 2017, 10(5), 605; doi:10.3390/en10050605
Received: 14 February 2017 / Revised: 28 March 2017 / Accepted: 21 April 2017 / Published: 1 May 2017
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Abstract
Among the wide diversity of existing technologically mature batteries, lithium-ion (Li-ion) batteries have become popular because of their longevity, high energy density, high efficiency and lack of memory effect. Differential charging of cells with age has turned balancing management systems into an important
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Among the wide diversity of existing technologically mature batteries, lithium-ion (Li-ion) batteries have become popular because of their longevity, high energy density, high efficiency and lack of memory effect. Differential charging of cells with age has turned balancing management systems into an important research subject. This paper proposes a new battery management system (BMS) to improve the capacity usage and lifespan of large Li-ion battery packs and a new charging algorithm based on the traditional multistage method. The main advantages of the proposed system are its versatility and ability to implement different charging and balancing methods in a very accessible way. The combination of charging methods with balancing methods represents an evolution when compared with other works in the literature. Full article
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Open AccessArticle Optimization of Hybrid Energy Storage Systems at the Building Level with Combined Heat and Power Generation
Energies 2017, 10(5), 606; doi:10.3390/en10050606
Received: 20 March 2017 / Revised: 24 April 2017 / Accepted: 25 April 2017 / Published: 1 May 2017
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Abstract
The average daily benefit to cost ratio of a building energy storage system is mainly constrained by the battery lifetime. This paper aims to minimize the average daily cost of a hybrid energy storage system (HESS) (comprised of a battery and supercapacitor) by
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The average daily benefit to cost ratio of a building energy storage system is mainly constrained by the battery lifetime. This paper aims to minimize the average daily cost of a hybrid energy storage system (HESS) (comprised of a battery and supercapacitor) by optimizing the battery capacity. A novel optimization model is proposed with the objective to find the minimum average daily investment cost of the HESS. The objective function has two parts: (1) the investment cost formula for the battery is derived as a function of the battery capacity, which has an interdependence with the minimum state of charge (SOC) and the maximum discharge current; (2) the investment cost formula for the supercapacitor is also established as a function of battery capacity by matching the maximum battery power with that of the supercapacitor. Case studies demonstrate several ways to increase the average daily benefit to cost ratio: (1) adopting a suitable control strategy to avoid capacity saturation; (2) reducing the battery SOC to increase the threshold for the maximum discharge current (MDC) saturation; and (3) increasing MDC to raise the threshold for the SOC saturation. Results show that the average daily benefit to cost ratio is doubled compared to previous work. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessArticle Harvesting-Aware Energy Management for Environmental Monitoring WSN
Energies 2017, 10(5), 607; doi:10.3390/en10050607
Received: 14 February 2017 / Revised: 20 April 2017 / Accepted: 21 April 2017 / Published: 1 May 2017
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Abstract
Wireless sensor networks can be used to collect data in remote locations, especially when energy harvesting is used to extend the lifetime of individual nodes. However, in order to use the collected energy most effectively, its consumption must be managed. In this work,
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Wireless sensor networks can be used to collect data in remote locations, especially when energy harvesting is used to extend the lifetime of individual nodes. However, in order to use the collected energy most effectively, its consumption must be managed. In this work, forecasts of diurnal solar energies were made based on measurements of atmospheric pressure. These forecasts were used as part of an adaptive duty cycling scheme for node level energy management. This management was realized with a fuzzy logic controller that has been tuned using differential evolution. Controllers were created using one and two days of energy forecasts, then simulated in software. These controllers outperformed a human-created reference controller by taking more measurements while using less reserve energy during the simulated period. The energy forecasts were comparable to other available methods, while the method of tuning the fuzzy controller improved overall node performance. The combination of the two is a promising method of energy management. Full article
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Open AccessArticle A Data-Driven Method for Energy Consumption Prediction and Energy-Efficient Routing of Electric Vehicles in Real-World Conditions
Energies 2017, 10(5), 608; doi:10.3390/en10050608
Received: 11 March 2017 / Revised: 19 April 2017 / Accepted: 21 April 2017 / Published: 1 May 2017
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Abstract
Limited driving range remains one of the barriers for widespread adoption of electric vehicles (EVs). To address the problem of range anxiety, this paper presents an energy consumption prediction method for EVs, designed for energy-efficient routing. This data-driven methodology combines real-world measured driving
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Limited driving range remains one of the barriers for widespread adoption of electric vehicles (EVs). To address the problem of range anxiety, this paper presents an energy consumption prediction method for EVs, designed for energy-efficient routing. This data-driven methodology combines real-world measured driving data with geographical and weather data to predict the consumption over any given road in a road network. The driving data are linked to the road network using geographic information system software that allows to separate trips into segments with similar road characteristics. The energy consumption over road segments is estimated using a multiple linear regression (MLR) model that links the energy consumption with microscopic driving parameters (such as speed and acceleration) and external parameters (such as temperature). A neural network (NN) is used to predict the unknown microscopic driving parameters over a segment prior to departure, given the road segment characteristics and weather conditions. The complete proposed model predicts the energy consumption with a mean absolute error (MAE) of 12–14% of the average trip consumption, of which 7–9% is caused by the energy consumption estimation of the MLR model. This method allows for prediction of energy consumption over any route in the road network prior to departure, and enables cost-optimization algorithms to calculate energy efficient routes. The data-driven approach has the advantage that the model can easily be updated over time with changing conditions. Full article
(This article belongs to the Special Issue Advances in Electric Vehicles and Plug-in Hybrid Vehicles 2017)
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Open AccessArticle An Energy Aware Unified Ant Colony System for Dynamic Virtual Machine Placement in Cloud Computing
Energies 2017, 10(5), 609; doi:10.3390/en10050609
Received: 31 December 2016 / Revised: 16 February 2017 / Accepted: 17 February 2017 / Published: 1 May 2017
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Abstract
Energy efficiency is a significant topic in cloud computing. Dynamic consolidation of virtual machines (VMs) with live migration is an important method to reduce energy consumption. However, frequent VM live migration may cause a downtime of service. Therefore, the energy save and VM
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Energy efficiency is a significant topic in cloud computing. Dynamic consolidation of virtual machines (VMs) with live migration is an important method to reduce energy consumption. However, frequent VM live migration may cause a downtime of service. Therefore, the energy save and VM migration are two conflict objectives. In order to efficiently solve the dynamic VM consolidation, the dynamic VM placement (DVMP) problem is formed as a multiobjective problem in this paper. The goal of DVMP is to find a placement solution that uses the fewest servers to host the VMs, including two typical dynamic conditions of the assignment of new coming VMs and the re-allocation of existing VMs. Therefore, we propose a unified algorithm based on an ant colony system (ACS), termed the unified ACS (UACS), that works on both conditions. The UACS firstly uses sufficient servers to host the VMs and then gradually reduces the number of servers. With each especial number of servers, the UACS tries to find feasible solutions with the fewest VM migrations. Herein, a dynamic pheromone deposition method and a special heuristic information strategy are also designed to reduce the number of VM migrations. Therefore, the feasible solutions under different numbers of servers cover the Pareto front of the multiobjective space. Experiments with large-scale random workloads and real workload traces are conducted to evaluate the performance of the UACS. Compared with traditional heuristic, probabilistic, and other ACS based algorithms, the proposed UACS presents competitive performance in terms of energy consumption, the number of VM migrations, and maintaining quality of services (QoS) requirements. Full article
(This article belongs to the Special Issue Smart Design, Smart Manufacturing and Industry 4.0)
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Open AccessArticle Statistical Feature Extraction for Fault Locations in Nonintrusive Fault Detection of Low Voltage Distribution Systems
Energies 2017, 10(5), 611; doi:10.3390/en10050611
Received: 25 February 2017 / Revised: 21 April 2017 / Accepted: 25 April 2017 / Published: 29 April 2017
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Abstract
This paper proposes statistical feature extraction methods combined with artificial intelligence (AI) approaches for fault locations in non-intrusive single-line-to-ground fault (SLGF) detection of low voltage distribution systems. The input features of the AI algorithms are extracted using statistical moment transformation for reducing the
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This paper proposes statistical feature extraction methods combined with artificial intelligence (AI) approaches for fault locations in non-intrusive single-line-to-ground fault (SLGF) detection of low voltage distribution systems. The input features of the AI algorithms are extracted using statistical moment transformation for reducing the dimensions of the power signature inputs measured by using non-intrusive fault monitoring (NIFM) techniques. The data required to develop the network are generated by simulating SLGF using the Electromagnetic Transient Program (EMTP) in a test system. To enhance the identification accuracy, these features after normalization are given to AI algorithms for presenting and evaluating in this paper. Different AI techniques are then utilized to compare which identification algorithms are suitable to diagnose the SLGF for various power signatures in a NIFM system. The simulation results show that the proposed method is effective and can identify the fault locations by using non-intrusive monitoring techniques for low voltage distribution systems. Full article
(This article belongs to the Special Issue Electric Power Systems Research 2017)
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Open AccessArticle Grain Size Distribution Effect on the Hydraulic Properties of Disintegrated Coal Mixtures
Energies 2017, 10(5), 612; doi:10.3390/en10050612
Received: 6 April 2017 / Revised: 25 April 2017 / Accepted: 27 April 2017 / Published: 29 April 2017
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Abstract
In order to better understand groundwater influx and protection in coal mining extraction works, an in-house water flow apparatus coupled with an industrial rock testing system, known as MTS 815.02, were used to study the effects of grain size mixtures on the compaction
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In order to better understand groundwater influx and protection in coal mining extraction works, an in-house water flow apparatus coupled with an industrial rock testing system, known as MTS 815.02, were used to study the effects of grain size mixtures on the compaction and flow properties of disintegrated, or non-cemented, coal samples. From the Reynolds number evaluation of the samples with different grain mixtures, and the relationship between the water flow velocity and pore pressure gradient differences, it was found that seepage through the mixtures are of non-Darcy flow type. The porosity of coal specimens was found to be highly affected by compaction, and the variations of the porosity were also influenced by the samples’ grain size distribution. It was found that the sample porosity decreases with increasing compaction and decreasing grain sizes. Grain crushing during compaction was observed to be the main cause of the appearance of fine grains, and the washing away of fine grains was consequently the main contributing factor for the weight loss due to water seepage. It was observed that during the tests and with the progression of compaction, permeability k decreases and non-Darcy factor β increases with decreasing porosity φ. The k-φ and β-φ plots show that as the sizes of disintegrated coal samples are getting smaller, there are more fluctuations between the porosity values with their corresponding values of k and β. The permeability value of the sample with smallest grains was observed to be considerably lower than that of the sample with largest grains. Non-Darcy behavior could reduce the hydraulic conductivity. It was found that the porosity, grain breakage and hydraulic properties of coal samples are related to grain sizes and compaction levels, as well as to the arrangement of the grains. At high compaction levels, the porosity of disintegrated coal samples decreased strongly, resulting in a significant decrease of the permeability at its full compression state; Non-Darcy flow behavior has the slightest effect in uniform samples, therefore, indicating that disintegrated coal in uniform grain size mixtures could be treated as an aquicluding (water-resisting) stratum. Full article
(This article belongs to the Special Issue Mathematical and Computational Modeling in Geothermal Engineering)
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Open AccessArticle A Comparison Study between Two MPPT Control Methods for a Large Variable-Speed Wind Turbine under Different Wind Speed Characteristics
Energies 2017, 10(5), 613; doi:10.3390/en10050613
Received: 5 April 2017 / Revised: 26 April 2017 / Accepted: 27 April 2017 / Published: 1 May 2017
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Abstract
Variable speed wind turbines (VSWTs) usually adopt a maximum power point tracking (MPPT) method to optimize energy capture performance. Nevertheless, obtained performance offered by different MPPT methods may be affected by the impact of wind turbine (WT)’s inertia and wind speed characteristics and
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Variable speed wind turbines (VSWTs) usually adopt a maximum power point tracking (MPPT) method to optimize energy capture performance. Nevertheless, obtained performance offered by different MPPT methods may be affected by the impact of wind turbine (WT)’s inertia and wind speed characteristics and it needs to be clarified. In this paper, the tip speed ratio (TSR) and optimal torque (OT) methods are investigated in terms of their performance under different wind speed characteristics on a 1.5 MW wind turbine model. To this end, the TSR control method based on an effective wind speed estimator and the OT control method are firstly presented. Then, their performance is investigated and compared through simulation test results under different wind speeds using Bladed software. Comparison results show that the TSR control method can capture slightly more wind energy at the cost of high component loads than the other one under all wind conditions. Furthermore, it is found that both control methods present similar trends of power reduction that is relevant to mean wind speed and turbulence intensity. From the obtained results, we demonstrate that, to further improve MPPT capability of large VSWTs, other advanced control methods using wind speed prediction information need to be addressed. Full article
(This article belongs to the Special Issue Wind Turbine 2017)
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Open AccessArticle Energy Return on Investment of Canadian Oil Sands Extraction from 2009 to 2015
Energies 2017, 10(5), 614; doi:10.3390/en10050614
Received: 24 January 2017 / Revised: 24 April 2017 / Accepted: 24 April 2017 / Published: 2 May 2017
PDF Full-text (2450 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Oil sands, as unconventional oil, are so essential to both Canada and the world that special attention should be paid to their extraction status, especially their energy efficiency. One of the most commonly used methods to evaluate energy efficiency is the Energy Return
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Oil sands, as unconventional oil, are so essential to both Canada and the world that special attention should be paid to their extraction status, especially their energy efficiency. One of the most commonly used methods to evaluate energy efficiency is the Energy Return on Investment (EROI) analysis. This paper focuses on EROI analysis for both in situ oil sands and mining oil sands over the period of 2009 to 2015. This time period represents an extension to periods previously considered by other analyses. An extended Input-Output model is used to quantify indirect energy input, which has been ignored by previous analyses of oil sands extraction. Results of this paper show that EROI of both mining oil sands (range of value: 3.9–8) and in situ oil sands (range of value: 3.2–5.4) display an upward trend over the past 7 years; EROI of mining oil sands is generally higher, but is more fluctuating than the EROI of in situ oil sands. Compared with EROI of other hydrocarbons, the EROI of oil sands is still quite low, despite the fact that it is increasing gradually. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle Surfactant-Assisted Perovskite Nanofillers Incorporated in Quaternized Poly (Vinyl Alcohol) Composite Membrane as an Effective Hydroxide-Conducting Electrolyte
Energies 2017, 10(5), 615; doi:10.3390/en10050615
Received: 2 March 2017 / Revised: 24 April 2017 / Accepted: 28 April 2017 / Published: 2 May 2017
Cited by 3 | PDF Full-text (4038 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Perovskite LaFeO3 nanofillers (0.1%) are incorporated into a quaternized poly(vinyl alcohol) (QPVA) matrix for use as hydroxide-conducting membranes in direct alkaline methanol fuel cells (DAMFCs). The as-synthesized LaFeO3 nanofillers are amorphous and functionalized with cetyltrimethylammonium bromide (CTAB) surfactant. The annealed LaFeO
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Perovskite LaFeO3 nanofillers (0.1%) are incorporated into a quaternized poly(vinyl alcohol) (QPVA) matrix for use as hydroxide-conducting membranes in direct alkaline methanol fuel cells (DAMFCs). The as-synthesized LaFeO3 nanofillers are amorphous and functionalized with cetyltrimethylammonium bromide (CTAB) surfactant. The annealed LaFeO3 nanofillers are crystalline without CTAB. The QPVA/CTAB-coated LaFeO3 composite membrane shows a defect-free structure while the QPVA/annealed LaFeO3 film has voids at the interfaces between the soft polymer and rigid nanofillers. The QPVA/CTAB-coated LaFeO3 composite has lower methanol permeability and higher ionic conductivity than the pure QPVA and QPVA/annealed LaFeO3 films. We suggest that the CTAB-coated LaFeO3 provides three functions to the polymeric composite: increasing polymer free volume, ammonium group contributor, and plasticizer to enhance the interfacial compatibility. The composite containing CTAB-coated LaFeO3 results in superior cell performance. A maximum power density of 272 mW cm−2 is achieved, which is among the highest power outputs reported for DAMFCs in the literature. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle Research on Control Strategies of an Open-End Winding Permanent Magnet Synchronous Driving Motor (OW-PMSM)-Equipped Dual Inverter with a Switchable Winding Mode for Electric Vehicles
Energies 2017, 10(5), 616; doi:10.3390/en10050616
Received: 1 March 2017 / Revised: 11 April 2017 / Accepted: 27 April 2017 / Published: 2 May 2017
Cited by 2 | PDF Full-text (5707 KB) | HTML Full-text | XML Full-text
Abstract
An open-end winding permanent magnet synchronous motor (PMSM) has a larger range of speed regulation than normal PMSM with the same DC voltage, and the control method is more flexible. It can also manage energy distribution between two power sources without a DC/DC
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An open-end winding permanent magnet synchronous motor (PMSM) has a larger range of speed regulation than normal PMSM with the same DC voltage, and the control method is more flexible. It can also manage energy distribution between two power sources without a DC/DC converter. This paper aims at an electric vehicle equipped with OW-PMSM drive system with dual power sources and dual inverters; based on analyzing the external characteristics of each winding mode, we propose a winding mode switching strategy whose torque saturation judgmental algorithm, which is insensitive to motor’s parameters, could automatically realize upswitching of the winding mode. The proposed multi-level current hysteresis modulation algorithm could set the major power source and switch it at any time in independent mode, which accomplishes energy distribution between two power sources; its two control methods, low switching frequency method and high power difference method, could achieve different energy distribution effects. Simulation results confirm the validity and effectiveness of the winding mode switching strategy and current modulation method. They also show that an electric vehicle under the proposed control methods has better efficiency than one equipped with a traditional OW-PMSM drive system under traditional control. Full article
(This article belongs to the Special Issue Advanced Electrification for Transportation and Built Environment)
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Open AccessArticle An Investigation of the Restitution Coefficient Impact on Simulating Sand-Char Mixing in a Bubbling Fluidized Bed
Energies 2017, 10(5), 617; doi:10.3390/en10050617
Received: 17 March 2017 / Revised: 19 April 2017 / Accepted: 27 April 2017 / Published: 3 May 2017
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Abstract
In the present work, the effect of the restitution coefficient on the numerical results for a binary mixture system of sand particles and char particles in a bubbling fluidized bed with a huge difference between the particles in terms of density and volume
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In the present work, the effect of the restitution coefficient on the numerical results for a binary mixture system of sand particles and char particles in a bubbling fluidized bed with a huge difference between the particles in terms of density and volume fraction has been studied based on two-fluid model along with the kinetic theory of granular flow. Results show that the effect of restitution coefficient on the flow characteristics varies in different regions of the bed, which is more evident for the top region of the bed. The restitution coefficient can be categorized into two classes. The restitution coefficients of 0.7 and 0.8 can be included into one class, whereas the restitution coefficient of 0.9 and 0.95 can be included into another class. Moreover, four vortices can be found in the time-averaged flow pattern distribution, which is very different from the result obtained for the binary system with the similar values between particles in density and volume fraction. Full article
(This article belongs to the Special Issue Engineering Fluid Dynamics)
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Open AccessArticle A Network Reconfiguration Method Considering Data Uncertainties in Smart Distribution Networks
Energies 2017, 10(5), 618; doi:10.3390/en10050618
Received: 29 January 2017 / Revised: 25 April 2017 / Accepted: 26 April 2017 / Published: 2 May 2017
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Abstract
This work presents a method for distribution network reconfiguration with the simultaneous consideration of distributed generation (DG) allocation. The uncertainties of load fluctuation before the network reconfiguration are also considered. Three optimal objectives, including minimal line loss cost, minimum Expected Energy Not Supplied,
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This work presents a method for distribution network reconfiguration with the simultaneous consideration of distributed generation (DG) allocation. The uncertainties of load fluctuation before the network reconfiguration are also considered. Three optimal objectives, including minimal line loss cost, minimum Expected Energy Not Supplied, and minimum switch operation cost, are investigated. The multi-objective optimization problem is further transformed into a single-objective optimization problem by utilizing weighting factors. The proposed network reconfiguration method includes two periods. The first period is to create a feasible topology network by using binary particle swarm optimization (BPSO). Then the DG allocation problem is solved by utilizing sensitivity analysis and a Harmony Search algorithm (HSA). In the meanwhile, interval analysis is applied to deal with the uncertainties of load and devices parameters. Test cases are studied using the standard IEEE 33-bus and PG&E 69-bus systems. Different scenarios and comparisons are analyzed in the experiments. The results show the applicability of the proposed method. The performance analysis of the proposed method is also investigated. The computational results indicate that the proposed network reconfiguration algorithm is feasible. Full article
(This article belongs to the Special Issue Electric Power Systems Research 2017)
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Open AccessArticle Experimental Assessment of a Helical Coil Heat Exchanger Operating at Subcritical and Supercritical Conditions in a Small-Scale Solar Organic Rankine Cycle
Energies 2017, 10(5), 619; doi:10.3390/en10050619
Received: 8 March 2017 / Revised: 14 April 2017 / Accepted: 19 April 2017 / Published: 4 May 2017
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Abstract
In this study, the performance of a helical coil heat exchanger operating at subcritical and supercritical conditions is analysed. The counter-current heat exchanger was specially designed to operate at a maximal pressure and temperature of 42 bar and 200 °C, respectively. The small-scale
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In this study, the performance of a helical coil heat exchanger operating at subcritical and supercritical conditions is analysed. The counter-current heat exchanger was specially designed to operate at a maximal pressure and temperature of 42 bar and 200 °C, respectively. The small-scale solar organic Rankine cycle (ORC) installation has a net power output of 3 kWe. The first tests were done in a laboratory where an electrical heater was used instead of the concentrated photovoltaic/thermal (CPV/T) collectors. The inlet heating fluid temperature of the water was 95 °C. The effects of different parameters on the heat transfer rate in the heat exchanger were investigated. Particularly, the performance analysis was elaborated considering the changes of the mass flow rate of the working fluid (R-404A) in the range of 0.20–0.33 kg/s and the inlet pressure varying from 18 bar up to 41 bar. Hence, the variation of the heat flux was in the range of 5–9 kW/m2. The results show that the working fluid’s mass flow rate has significant influence on the heat transfer rate rather than the operational pressure. Furthermore, from the comparison between the experimental results with the heat transfer correlations from the literature, the experimental results fall within the uncertainty range for the supercritical analysis but there is a deviation of the investigated subcritical correlations. Full article
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Open AccessArticle Networked Control of Electric Vehicles for Power System Frequency Regulation with Random Communication Time Delay
Energies 2017, 10(5), 621; doi:10.3390/en10050621
Received: 4 February 2017 / Revised: 7 April 2017 / Accepted: 13 April 2017 / Published: 3 May 2017
Cited by 1 | PDF Full-text (3197 KB) | HTML Full-text | XML Full-text
Abstract
Electric vehicles (EVs) can have noteworthy impact on power system dynamic performance. This paper develops two novel controllers which can take into account the random time delay in the communication channel of the control system. With the designed robust controller, the system can
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Electric vehicles (EVs) can have noteworthy impact on power system dynamic performance. This paper develops two novel controllers which can take into account the random time delay in the communication channel of the control system. With the designed robust controller, the system can utilize EVs to participate in automatic generation control (AGC) processes so as to assist conventional thermal power units to respond rapidly and accurately to load fluctuations, as well as to enhance the capability of a power system to accommodate renewable energy forms such as wind power. Owing to the distributed nature of EVs, a networked control scheme for EVs’ participation in frequency regulation is first proposed in the paper. A closed-loop block diagram, which incorporates EVs and wind power, is then developed. Two controllers are then designed based on rigorous linear matrix inequalities (LMI) theory to ensure the robustness and stability of the system. Finally, comprehensive case studies based on a two-area equivalent of the IEEE 39-bus test system are performed to demonstrate the effectiveness of the proposed methods. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Development of a Leader-End Reclosing Algorithm Considering Turbine-Generator Shaft Torque
Energies 2017, 10(5), 622; doi:10.3390/en10050622
Received: 8 March 2017 / Revised: 21 April 2017 / Accepted: 28 April 2017 / Published: 3 May 2017
PDF Full-text (3729 KB) | HTML Full-text | XML Full-text
Abstract
High-speed auto-reclosing is used in power system protection schemes to ensure the stability and reliability of the transmission system; leader-follower auto-reclosing is one scheme type that is widely used. However, when a leader-follower reclosing scheme responds to a permanent fault that affects a
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High-speed auto-reclosing is used in power system protection schemes to ensure the stability and reliability of the transmission system; leader-follower auto-reclosing is one scheme type that is widely used. However, when a leader-follower reclosing scheme responds to a permanent fault that affects a transmission line in the proximity of a generation plant, the reclosing directly impacts the turbine-generator shaft; furthermore, the nature of this impact is dependent upon the selection of the leader reclosing terminal. We therefore analyzed the transient torque of the turbine-generator shaft according to the selection of the leader-follower reclosing end between both ends of the transmission line. We used this analysis to propose an adaptive leader-end reclosing algorithm that removes the stress potential of the transient torque to prevent it from damaging the turbine-generator shaft. We conducted a simulation in actual Korean power systems based on the ElectroMagnetic Transients Program (EMTP) and the Dynamic Link Library (DLL) function in EMTP-RV (Restructured Version) to realize the proposed algorithm. Full article
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Open AccessArticle Theoretical and Experimental Evaluation of the Temperature Distribution in a Dry Type Air Core Smoothing Reactor of HVDC Station
Energies 2017, 10(5), 623; doi:10.3390/en10050623
Received: 17 March 2017 / Revised: 19 April 2017 / Accepted: 26 April 2017 / Published: 3 May 2017
PDF Full-text (3599 KB) | HTML Full-text | XML Full-text
Abstract
The outdoor ultra-high voltage (UHV) dry-type air-core smoothing reactors (DASR) of High Voltage Direct Current systems are equipped with a rain cover and an acoustic enclosure. To study the convective heat transfer between the DASR and the surrounding air, this paper presents a
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The outdoor ultra-high voltage (UHV) dry-type air-core smoothing reactors (DASR) of High Voltage Direct Current systems are equipped with a rain cover and an acoustic enclosure. To study the convective heat transfer between the DASR and the surrounding air, this paper presents a coupled model of the temperature and fluid field based on the structural features and cooling manner. The resistive losses of encapsulations calculated by finite element method (FEM) were used as heat sources in the thermal analysis. The steady fluid and thermal field of the 3-D reactor model were solved by the finite volume method (FVM), and the temperature distribution characteristics of the reactor were obtained. Subsequently, the axial and radial temperature distributions of encapsulation were investigated separately. Finally, an optical fiber temperature measurement scheme was used for an UHV DASR under natural convection conditions. Comparative analysis showed that the simulation results are in good agreement with the experimental data, which verifies the rationality and accuracy of the numerical calculation. These results can serve as a reference for the optimal design and maintenance of UHV DASRs. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Multi-Objective Dynamic Economic Dispatch with Demand Side Management of Residential Loads and Electric Vehicles
Energies 2017, 10(5), 624; doi:10.3390/en10050624
Received: 22 January 2017 / Revised: 26 April 2017 / Accepted: 27 April 2017 / Published: 3 May 2017
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Abstract
In this paper, a multi-objective optimization method based on the normal boundary intersection is proposed to solve the dynamic economic dispatch with demand side management of individual residential loads and electric vehicles. The proposed approach specifically addresses consumer comfort through acceptable appliance deferral
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In this paper, a multi-objective optimization method based on the normal boundary intersection is proposed to solve the dynamic economic dispatch with demand side management of individual residential loads and electric vehicles. The proposed approach specifically addresses consumer comfort through acceptable appliance deferral times and electric vehicle charging requirements. The multi-objectives of minimizing generation costs, emissions, and energy loss in the system are balanced in a Pareto front approach in which a fuzzy decision making method has been implemented to find the best compromise solution based on desired system operating conditions. The normal boundary intersection method is described and validated. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Optimal Allocation of Energy Storage System Considering Multi-Correlated Wind Farms
Energies 2017, 10(5), 625; doi:10.3390/en10050625
Received: 19 January 2017 / Revised: 13 April 2017 / Accepted: 27 April 2017 / Published: 4 May 2017
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Abstract
With the increasing penetration of wind power, not only the uncertainties but also the correlation among the wind farms should be considered in the power system analysis. In this paper, Clayton-Copula method is developed to model the multiple correlated wind distribution and a
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With the increasing penetration of wind power, not only the uncertainties but also the correlation among the wind farms should be considered in the power system analysis. In this paper, Clayton-Copula method is developed to model the multiple correlated wind distribution and a new point estimation method (PEM) is proposed to discretize the multi-correlated wind distribution. Furthermore, combining the proposed modeling and discretizing method with Hybrid Multi-Objective Particle Swarm Optimization (HMOPSO), a comprehensive algorithm is explored to minimize the power system cost and the emissions by searching the best placements and sizes of energy storage system (ESS) considering wind power uncertainties in multi-correlated wind farms. In addition, the variations of load are also taken into account. The IEEE 57-bus system is adopted to perform case studies using the proposed approach. The results clearly demonstrate the effectiveness of the proposed algorithm in determining the optimal storage allocations considering multi-correlated wind farms. Full article
(This article belongs to the Special Issue Sustainable and Renewable Energy Systems)
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Open AccessArticle Methane Adsorption Rate and Diffusion Characteristics in Marine Shale Samples from Yangtze Platform, South China
Energies 2017, 10(5), 626; doi:10.3390/en10050626
Received: 6 January 2017 / Revised: 13 April 2017 / Accepted: 21 April 2017 / Published: 4 May 2017
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Abstract
Knowledge of the gas adsorption rate and diffusion characteristics in shale are very important to evaluate the gas transport properties. However, research on methane adsorption rate characteristics and diffusion behavior in shale is not well established. In this study, high-pressure methane adsorption isotherms
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Knowledge of the gas adsorption rate and diffusion characteristics in shale are very important to evaluate the gas transport properties. However, research on methane adsorption rate characteristics and diffusion behavior in shale is not well established. In this study, high-pressure methane adsorption isotherms and methane adsorption rate data from four marine shale samples were obtained by recording the pressure changes against time at 1-s intervals for 12 pressure steps. Seven pressure steps were selected for modelling, and three pressure steps of low (~0.4 MPa), medium (~4.0 MPa), and high (~7.0 MPa) were selected for display. According to the results of study, the methane adsorption under low pressure attained equilibrium much more quickly than that under medium and high pressure, and the adsorption rate behavior varied between different pressure steps. By fitting the diffusion models to the methane adsorption rate data, the unipore diffusion model based upon unimodal pore size distribution failed to describe the methane adsorption rate, while the bidisperse diffusion model could reasonably describe most of the experimental adsorption rate data, with the exception of sample YY2-1 at high pressure steps. This phenomenon may be related to the restricted assumption on pore size distribution and linear adsorption isotherm. The diffusion parameters α and β/α obtained from the bidisperse model indicated that both macro- and micropore diffusion controlled the methane adsorption rate in shale samples, as well as the relative importance and influence of micropore diffusion and adsorption to adsorption rate and total adsorption increased with increasing pressure. This made the inflection points, or two-stage process, at higher pressure steps not as evident as at low pressure steps, and the adsorption rate curves became less steep with increasing pressure. This conclusion was also supported by the decreasing difference values with increasing pressures between macro- and micropore diffusivities obtained using the bidisperse model, which is roughly from 10−3 to 100, and 10−3 to 10−1, respectively. Additionally, an evident negative correlation between macropore diffusivities and pressure lower than 3–4 MPa was observed, while the micropore diffusivities only showed a gentle decreasing trend with pressure. A mirror image relationship between the variation in the value of macropore diffusivity and adsorption isotherms was observed, indicating the negative correlation between surface coverage and gas diffusivity. The negative correlation of methane diffusivity with pressure and surface coverage may be related to the increasing degree of pore blockage and the decreasing concentration gradient of methane adsorption. Finally, due to the significant deviation between the unipore model and experimental adsorption rate data, a new estimation method based upon the bidisperse model is proposed here. Full article
(This article belongs to the Special Issue Unconventional Natural Gas (UNG) Recoveries)
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Open AccessArticle A Game Theoretical Approach Based Bidding Strategy Optimization for Power Producers in Power Markets with Renewable Electricity
Energies 2017, 10(5), 627; doi:10.3390/en10050627
Received: 26 February 2017 / Revised: 18 April 2017 / Accepted: 2 May 2017 / Published: 4 May 2017
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Abstract
In a competitive electricity market with substantial involvement of renewable electricity, maximizing profits by optimizing bidding strategies is crucial to different power producers including conventional power plants and renewable ones. This paper proposes a game-theoretic bidding optimization method based on bi-level programming, where
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In a competitive electricity market with substantial involvement of renewable electricity, maximizing profits by optimizing bidding strategies is crucial to different power producers including conventional power plants and renewable ones. This paper proposes a game-theoretic bidding optimization method based on bi-level programming, where power producers are at the upper level and utility companies are at the lower level. The competition among the multiple power producers is formulated as a non-cooperative game in which bidding curves are their strategies, while uniform clearing pricing is considered for utility companies represented by an independent system operator. Consequently, based on the formulated game model, the bidding strategies for power producers are optimized for the day-ahead market and the intraday market with considering the properties of renewable energy; and the clearing pricing for the utility companies, with respect to the power quantity from different power producers, is optimized simultaneously. Furthermore, a distributed algorithm is provided to search the solution of the generalized Nash equilibrium. Finally, simulation results were performed and discussed to verify the feasibility and effectiveness of the proposed non-cooperative game-based bi-level optimization approach. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Effects of Building Occupancy on Indicators of Energy Efficiency
Energies 2017, 10(5), 628; doi:10.3390/en10050628
Received: 3 March 2017 / Revised: 18 April 2017 / Accepted: 27 April 2017 / Published: 4 May 2017
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Abstract
The potential to reduce energy consumption in buildings is high. The design phase of the building is very important. In addition, it is vital to understand how to measure the energy efficiency in the building operation phase in order to encourage the right
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The potential to reduce energy consumption in buildings is high. The design phase of the building is very important. In addition, it is vital to understand how to measure the energy efficiency in the building operation phase in order to encourage the right efficiency efforts. In understanding the building energy efficiency, it is important to comprehend the interplay of building occupancy, space efficiency, and energy efficiency. Recent studies found in the literature concerning energy efficiency in office buildings have concentrated heavily on the technical characteristics of the buildings or technical systems. The most commonly used engineering indicator for building energy efficiency is the specific energy consumption (SEC), commonly measured in kWh/m2 per annum. While the SEC is a sound way to measure the technical properties of a building and to guide its design, it obviously omits the issues of building occupancy and space efficiency. This paper studies existing energy efficiency indicators and introduces a new indicator for building energy efficiency which takes into account both space and occupancy efficiency. Full article
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Open AccessArticle Understanding and Modelling the Effect of Dissolved Metals on Solvent Degradation in Post Combustion CO2 Capture Based on Pilot Plant Experience
Energies 2017, 10(5), 629; doi:10.3390/en10050629
Received: 16 February 2017 / Revised: 24 April 2017 / Accepted: 26 April 2017 / Published: 4 May 2017
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Abstract
Oxidative degradation is a serious concern for upscaling of amine-based carbon capture technology. Different kinetic models have been proposed based on laboratory experiments, however the kinetic parameters included are limited to those relevant for a lab-scale system and not a capture plant. Besides,
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Oxidative degradation is a serious concern for upscaling of amine-based carbon capture technology. Different kinetic models have been proposed based on laboratory experiments, however the kinetic parameters included are limited to those relevant for a lab-scale system and not a capture plant. Besides, most of the models fail to recognize the catalytic effect of metals. The objective of this work is to develop a representative kinetic model based on an apparent auto-catalytic reaction mechanism between solvent degradation, corrosion and ammonia emissions. Measurements from four different pilot plants: (i) EnBW’s plant at Heilbronn, Germany (ii) TNO’s plant at Maasvlakte, The Netherlands; (iii) CSIRO’s plants at Loy Yang and Tarong, Australia and (iv) DONG Energy’s plant at Esbjerg, Denmark are utilized to propose a degradation kinetic model for 30 wt % ethanolamine (MEA) as the capture solvent. The kinetic parameters of the model were regressed based on the pilot plant campaign at EnBW. The kinetic model was validated by comparing it with the measurements at the remaining pilot campaigns. The model predicted the trends of ammonia emissions and metal concentration within the same order of magnitude. This study provides a methodology to establish a quantitative approach for predicting the onset of unacceptable degradation levels which can be further used to devise counter-measure strategies such as reclaiming and metal removal. Full article
(This article belongs to the Special Issue CO2 Capture)
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Open AccessArticle Design and Implementation of a Data Acquisition System for Combustion Tests
Energies 2017, 10(5), 630; doi:10.3390/en10050630
Received: 30 March 2017 / Revised: 25 April 2017 / Accepted: 27 April 2017 / Published: 4 May 2017
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Abstract
In recent years, the biomass market has constantly increased. The pellet manufacture industry has started looking for new products, such as wastes from forest, agriculture, and agroindustrial residues, among others, with the potential to be used as biofuels. However, some of these wastes
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In recent years, the biomass market has constantly increased. The pellet manufacture industry has started looking for new products, such as wastes from forest, agriculture, and agroindustrial residues, among others, with the potential to be used as biofuels. However, some of these wastes have some characteristics that make both the combustion process and operating and maintenance conditions of thermal equipment difficult. Thus, further research to optimize the performance and ensure the compliance of the maximum atmospheric levels is needed. In order to carry out these studies, the design and implementation of a supervision, control, and data acquisition system for a domestic pellet boiler was carried out, which makes obtaining further information about the performance of non-conventional biofuels possible. Thus, these biofuels, coming from different sources, underwent different working regimes, facilitating the understanding of the results and the correction of limiting elements. The results from initial tests were reliable and precise, coinciding with the check readings that were done with a thermometer and a combustion gas analyser. Under these conditions, the system designed constitutes a fundamental tool to examine thermal processes with alternative biofuels, with the objective of making the most of different biomass wastes as renewable energy sources. Full article
(This article belongs to the Special Issue Thermo-Chemical Conversion of Waste Biomass)
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Open AccessArticle Quality Assessment of Biodiesel Blends Proposed by the New Mexican Policy Framework
Energies 2017, 10(5), 631; doi:10.3390/en10050631
Received: 26 January 2017 / Revised: 28 March 2017 / Accepted: 27 April 2017 / Published: 4 May 2017
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Abstract
Nowadays, biodiesel is being promoted worldwide as a sustainable and alternative to diesel fuel. However, there is still a lack of a biodiesel market in Mexico. Hence, a new initiative to reform the Mexican biofuels framework by decree includes the production and use
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Nowadays, biodiesel is being promoted worldwide as a sustainable and alternative to diesel fuel. However, there is still a lack of a biodiesel market in Mexico. Hence, a new initiative to reform the Mexican biofuels framework by decree includes the production and use of biodiesel. This regulation can ensure and contribute to the development of the biodiesel market in Mexico. The initiative proposes to start from the B5.8 blend by the end of 2017 and reach the B10 by 2020. Therefore, the objective of the present work was the quality assessment of biodiesel blends proposed by the new Mexican policy framework. The techniques applied were Fourier transform infrared (FT-IR) spectroscopy, X-ray fluorescence analysis, scanning electron microscopy analysis, viscosity, higher heating value, thermogravimetric analysis, refractive index, acid number, specific gravity, flash point, and copper strip corrosion based on ASTM standards. The results indicate that the biodiesel and its blends B5.8 and B10 fulfilled relevant quality specifications established in the ASTM D6751 and EN14214 standards for fuels. However, the fuel blends presented a higher heating value (HHV) diminution. The experimental HHV percentages decrease for the mandatory mixtures compared to diesel were 2.29% (B10), and 0.29% (B5.8). Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle Case Study on the Socio-Economic Benefit of Allowing Active Power Curtailment to Postpone Grid Upgrades
Energies 2017, 10(5), 632; doi:10.3390/en10050632
Received: 22 December 2016 / Revised: 22 March 2017 / Accepted: 28 April 2017 / Published: 5 May 2017
PDF Full-text (2640 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The penetration of distributed generation is rapidly increasing in the power system. Traditionally, a fit-and-forget approach has been applied for grid integration of distributed generation, by investing in a grid capacity that can deal with worst-case situations. However, there is now increasing interest
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The penetration of distributed generation is rapidly increasing in the power system. Traditionally, a fit-and-forget approach has been applied for grid integration of distributed generation, by investing in a grid capacity that can deal with worst-case situations. However, there is now increasing interest for the possible cost savings that can be achieved through more active network management. This paper presents a case study on the possible socio-economic benefit of postponing a grid upgrade in an area of surplus generation. Two alternatives for grid integration of an 8 MW run-on-river hydro power plant in the southern part of Norway are investigated: (i) grid upgrade; and (ii) active power curtailment whenever needed to avoid network congestion. This study shows that cost savings corresponding to 13% of the investment cost for the grid upgrade is possible through active power curtailment. Full article
(This article belongs to the Special Issue Sustainable and Renewable Energy Systems)
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Open AccessArticle Wide Area Information-Based Transmission System Centralized Out-of-Step Protection Scheme
Energies 2017, 10(5), 633; doi:10.3390/en10050633
Received: 15 February 2017 / Revised: 26 April 2017 / Accepted: 28 April 2017 / Published: 5 May 2017
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Abstract
A wide area monitoring system (WAMS) with reliable telecommunication infrastructure can be expanded and enhanced with additional protection and control functionalities using synchronized phasor data measurements. With that aim, we have developed a multifunctional line protection (MFLP) model with both system and back-up
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A wide area monitoring system (WAMS) with reliable telecommunication infrastructure can be expanded and enhanced with additional protection and control functionalities using synchronized phasor data measurements. With that aim, we have developed a multifunctional line protection (MFLP) model with both system and back-up protection functions. Theoretical premises based on transmission and relay protection system knowledge, together with the experience gathered from the operation of existing wide area systems, were used to develop the proposed model. Four main groups of simulation scenarios were defined in order to test the newly implemented functions. The results of the simulation process confirm the assumptions underlying the design of our MFLP module. Simulation results are then used for definition of the protection criteria required for implementation of the wide area protection algorithm in a control center. Conclusions drawn from the protection responses of the proposed algorithm that strengthen the algorithm design process are elaborated in the paper. The main contribution of the paper is the design and development of a centralized MFLP algorithm based on synchronized phasor data that is able to issue a trip command to a circuit breaker before an out-of-step condition occurs. Full article
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Open AccessArticle Numerical Study of Pressure Fluctuation in a Gas- Liquid Two-Phase Mixed-Flow Pump
Energies 2017, 10(5), 634; doi:10.3390/en10050634
Received: 29 March 2017 / Revised: 27 April 2017 / Accepted: 2 May 2017 / Published: 5 May 2017
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Abstract
To explore the pressure fluctuation characteristics in a mixed-flow pump handling a gas-liquid two-phase flow, an unsteady simulation was carried out with ANSYS CFX for the whole flow passage when the inlet gas void fraction (IGVF) was 0%, 5%, and 10%,
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To explore the pressure fluctuation characteristics in a mixed-flow pump handling a gas-liquid two-phase flow, an unsteady simulation was carried out with ANSYS CFX for the whole flow passage when the inlet gas void fraction (IGVF) was 0%, 5%, and 10%, respectively. Under pure water conditions (IGVF = 0%), the reliability of the simulation was verified by comparing with the experiment in both aspects of external characteristics and fluctuation. Through the implementation of the fast Fourier transform (FFT) algorithm, the characteristics of the pressure fluctuation in the impeller and the guide vane were obtained at different IGVF conditions. The results demonstrate that pressure fluctuations exist under different IGVF conditions due to the rotor-stator interaction and the gas-liquid phase interaction, and the intensity of the fluctuation is firstly enhanced, and then weakened, along the streamwise direction with the maximum located near the impeller outlet. The relationship between the gas content and the pressure fluctuation was analyzed, and it is shown that the regional pressure fluctuation will be intensified only if the gas content therein reaches a certain level and the local phase interaction is strong. In addition, the pressure fluctuation in both the rotor-stator interaction region and the guide vane may be effectively inhibited under small IGVF conditions. Full article
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Open AccessArticle The Impact of Shading Type and Azimuth Orientation on the Daylighting in a Classroom–Focusing on Effectiveness of Façade Shading, Comparing the Results of DA and UDI
Energies 2017, 10(5), 635; doi:10.3390/en10050635
Received: 7 February 2017 / Revised: 4 April 2017 / Accepted: 25 April 2017 / Published: 10 May 2017
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Abstract
There are many kinds of façade shading designs which provide optimal indoor daylighting conditions. Thus, considering combinations of different types of façade shading systems is an essential aspect in the optimization of daylighting in the building design process. This study explores (1) how
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There are many kinds of façade shading designs which provide optimal indoor daylighting conditions. Thus, considering combinations of different types of façade shading systems is an essential aspect in the optimization of daylighting in the building design process. This study explores (1) how the pattern and different characteristics are evaluated by varying façade shading types and considering their impact on daylighting metrics; and (2) the relative relationships between Daylight Autonomy (DA) and Useful Daylight Illuminance (UDI) with changes of the façade shading types, input parameters, and azimuth orientations. A typical high-school classroom has been chosen as a base model, and seven different façade shading types: vertical louver, horizontal louver, eggcrate louver, overhang, vertical slat, horizontal slat, and light shelf have been applied to eight azimuth orientations for the building. As tools for parametric design and indoor lighting analysis, Design Iterate Validate Adapt (DIVA)-for-Grasshopper has been used to obtain DA and UDI for comparison. Based on the simulation, (1) the effectiveness of the installation of façade shading compared to a non-shading case; and (2) design considerations for façade shading are presented. The result shows that there are some meaningful differences in DA and UDI metrics with the variation of orientation and façade shading types, although all cases of façade shading show some degree of decrease in DA and increase in UDI values. The types of shading devices which produce a dramatic decrease in DA values are the light shelf, horizontal slats, horizontal louvers, and eggcrate louvers. On the contrary, the types of shading devices which produce a dramatic increase in UDI values are the light shelf, horizontal slats, horizontal louvers, and eggcrate louvers. In the case of the vertical and vertical slat shading, the improvements of UDI values are significant in the east and west orientations. This demonstrates that the application and design of shading devices in certain façade orientations should be carefully considered for daylight control. Also, the results show that UDI explains relatively well the daylight performance in the case of the installation of a shading device. Full article
(This article belongs to the Special Issue Solar Energy Application in Buildings)
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Open AccessArticle Bacteria Foraging Reinforcement Learning for Risk-Based Economic Dispatch via Knowledge Transfer
Energies 2017, 10(5), 638; doi:10.3390/en10050638
Received: 18 January 2017 / Revised: 9 April 2017 / Accepted: 24 April 2017 / Published: 6 May 2017
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Abstract
This paper proposes a novel bacteria foraging reinforcement learning with knowledge transfer method for risk-based economic dispatch, in which the economic dispatch is integrated with risk assessment theory to represent the uncertainties of active power demand and contingencies during power system operations. Moreover,
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This paper proposes a novel bacteria foraging reinforcement learning with knowledge transfer method for risk-based economic dispatch, in which the economic dispatch is integrated with risk assessment theory to represent the uncertainties of active power demand and contingencies during power system operations. Moreover, a multi-agent collaboration is employed to accelerate the convergence of knowledge matrix, which is decomposed into several lower dimension sub-matrices via a knowledge extension, thus the curse of dimension can be effectively avoided. Besides, the convergence rate of bacteria foraging reinforcement learning is increased dramatically through a knowledge transfer after obtaining the optimal knowledge matrices of source tasks in pre-learning. The performance of bacteria foraging reinforcement learning has been thoroughly evaluated on IEEE RTS-79 system. Simulation results demonstrate that it can outperform conventional artificial intelligence algorithms in terms of global convergence and convergence rate. Full article
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Open AccessArticle Design Optimization of a High Power LED Matrix Luminaire
Energies 2017, 10(5), 639; doi:10.3390/en10050639
Received: 16 February 2017 / Revised: 5 April 2017 / Accepted: 6 April 2017 / Published: 5 May 2017
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Abstract
This work presents a methodology for optimizing the layout and geometry of an m×n high power (HP) light emitting diode (LED) luminaire. Two simulators are used to analyze an LED luminaire model. The first simulator uses the finite element method (FEM)
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This work presents a methodology for optimizing the layout and geometry of an m × n high power (HP) light emitting diode (LED) luminaire. Two simulators are used to analyze an LED luminaire model. The first simulator uses the finite element method (FEM) to analyze the thermal dissipation, and the second simulator uses the ray tracing method for lighting analysis. The thermal and lighting analysis of the luminaire model is validated with an error of less than 10%. The goal of the optimization process is to find a solution that satisfies both thermal dissipation and light efficiency. The optimization goal is to keep the LED temperature at an acceptable level while still obtaining uniform illumination on a target plane. Even though no optical accessories or active cooling systems are used in the model, the results demonstrate that it is possible to obtain satisfactory results even with a limited number of parameters. The optimization results show that it is possible to design luminaires with 4, 6 and up to 8 HP-LEDs, keeping the LED temperature at about 100 C. However, the best uniformity on a target plane was found by the heuristic algorithm. Full article
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Open AccessArticle Study on the Characteristic Decomposition Components of DC SF6-Insulated Equipment under Positive DC Partial Discharge
Energies 2017, 10(5), 640; doi:10.3390/en10050640
Received: 15 March 2017 / Revised: 24 April 2017 / Accepted: 28 April 2017 / Published: 5 May 2017
Cited by 1 | PDF Full-text (1034 KB) | HTML Full-text | XML Full-text
Abstract
Pulses with different amplitudes occur when an inner partial discharge fault exists in SF6-gas-insulated DC high-voltage electrical equipment. SF6 decomposes following complex physical and chemical processes. Discussing and quantifying the mathematical relationship of pulse discharge quantities to SF6 decomposition
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Pulses with different amplitudes occur when an inner partial discharge fault exists in SF6-gas-insulated DC high-voltage electrical equipment. SF6 decomposes following complex physical and chemical processes. Discussing and quantifying the mathematical relationship of pulse discharge quantities to SF6 decomposition component characteristics is helpful to evaluate and predict the insulation fault severity and development trends in SF6-insulated DC equipment. Numerous simulation experiments on SF6 decomposition under positive DC partial discharge were performed on a needle-plane model. The DC partial discharge quantities of pulses are obtained, and decomposition characteristics based on the mechanism of SF6 decomposition are analyzed. Results show that generation, effective generation rate and concentration ratio c(SO2F2 + SOF4)/c(SOF2 + SO2) of components increase with partial discharge severity, and the first two act in the following order: SOF4 > SOF2 > SO2F2 > SO2 > CF4 when the discharge quantity level is higher than 238,957 pC. Finally, a coefficient matrix illustrates the mathematical effects of pulses with different discharge quantities on different SF6 decomposition components. The pulses whose discharge quantity is higher than 50 pC have obvious promotion effects on the formation of decomposition components, whereas the pulses whose discharge quantity lower than 50 pC decrease the positive promotion effects that large discharge pulses have on decomposition components. The higher the effective generation rates are, the greater the partial discharge severity is, and their change laws provide a new method to evaluate and predict insulation fault severity and development trends in DC SF6-insulated equipment with high reliability and detection stability. Full article
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Open AccessArticle Watching the Smoke Rise Up: Thermal Efficiency, Pollutant Emissions and Global Warming Impact of Three Biomass Cookstoves in Ghana
Energies 2017, 10(5), 641; doi:10.3390/en10050641
Received: 3 December 2016 / Revised: 28 April 2017 / Accepted: 2 May 2017 / Published: 6 May 2017
Cited by 1 | PDF Full-text (2620 KB) | HTML Full-text | XML Full-text
Abstract
In Ghana, about 73% of households rely on solid fuels for cooking. Over 13,000 annual deaths are attributed to exposure to indoor air pollution from inefficient combustion. In this study, assessment of thermal efficiency, emissions, and total global warming impact of three cookstoves
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In Ghana, about 73% of households rely on solid fuels for cooking. Over 13,000 annual deaths are attributed to exposure to indoor air pollution from inefficient combustion. In this study, assessment of thermal efficiency, emissions, and total global warming impact of three cookstoves commonly used in Ghana was completed using the International Workshop Agreement (IWA) Water Boiling Test (WBT) protocol. Statistical averages of three replicate tests for each cookstove were computed. Thermal efficiency results were: wood-burning cookstove: 12.2 ± 5.00% (Tier 0); coalpot charcoal stove: 23.3 ± 0.73% (Tier 1–2); and Gyapa charcoal cookstove: 30.00 ± 4.63% (Tier 2–3). The wood-burning cookstove emitted more CO, CO2, and PM2.5 than the coalpot charcoal stove and Gyapa charcoal cookstove. The emission factor (EF) for PM2.5 and the emission rate for the wood-burning cookstove were over four times higher than the coalpot charcoal stove and Gyapa charcoal cookstove. To complete the WBT, the study results showed that, by using the Gyapa charcoal cookstove instead of the wood-burning cookstove, the global warming impact could be potentially reduced by approximately 75% and using the Gyapa charcoal cookstove instead of the coalpot charcoal cookstove by 50%. We conclude that there is the need for awareness, policy, and incentives to enable end-users to switch to, and adopt, Gyapa charcoal cookstoves for increased efficiency and reduced emissions/global warming impact. Full article
(This article belongs to the collection Bioenergy and Biofuel)
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Open AccessArticle Determination of the Most Suitable Technology Transfer Strategy for Wind Turbines Using an Integrated AHP-TOPSIS Decision Model
Energies 2017, 10(5), 642; doi:10.3390/en10050642
Received: 12 February 2017 / Revised: 30 April 2017 / Accepted: 2 May 2017 / Published: 6 May 2017
Cited by 1 | PDF Full-text (1031 KB) | HTML Full-text | XML Full-text
Abstract
The high-speed development of industrial products and goods in the world has caused “technology” to be considered as a crucial competitive advantage for most large organizations. In recent years, developing countries have considerably tended to promote their technological and innovative capabilities through importing
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The high-speed development of industrial products and goods in the world has caused “technology” to be considered as a crucial competitive advantage for most large organizations. In recent years, developing countries have considerably tended to promote their technological and innovative capabilities through importing high-tech equipment owned and operated by developed countries. There are currently a variety of solutions to transfer a particular technology from a developed country. The selection of the most profitable technology transfer strategy is a very complex decision-making problem for technology importers as it involves different technical, environmental, social, and economic aspects. In this study, a hybrid multiple-criteria decision making (MCDM) model based on the analytic hierarchy process (AHP) and the technique for order of preference by similarity to ideal solution (TOPSIS) is proposed to evaluate and prioritise various technology transfer strategies for wind turbine systems. For this purpose, a number of criteria and sub-criteria are defined from the viewpoint of wind energy investors, wind turbine manufacturers, and wind farm operators. The relative importance of criteria and sub-criteria with respect to the ultimate goal are computed using the eigenvalue method and then, the technology transfer alternatives are ranked based on their relative closeness to the ideal solution. The model is finally applied to determine the most suitable wind turbine technology transfer strategy among four options of reverse engineering, technology skills training, turn-key contracts, and technology licensing for the renewable energy sector of Iran, and the results are compared with those obtained by classical decision-making models. Full article
(This article belongs to the Special Issue Wind Turbine 2017)
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Open AccessArticle Optimal Control Based on Maximum Power Point Tracking (MPPT) of an Autonomous Hybrid Photovoltaic/Storage System in Micro Grid Applications
Energies 2017, 10(5), 643; doi:10.3390/en10050643
Received: 3 March 2017 / Revised: 7 April 2017 / Accepted: 16 April 2017 / Published: 7 May 2017
Cited by 1 | PDF Full-text (1494 KB) | HTML Full-text | XML Full-text
Abstract
This paper investigates how to increase the efficiency of a photovoltaic/energy storage generation unit supplying dynamic loads by regulating and managing both the photovoltaic generator and the storage battery charge-discharge modes. The proposed photovoltaic/energy storage unit is proposed to supply an induction motor
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This paper investigates how to increase the efficiency of a photovoltaic/energy storage generation unit supplying dynamic loads by regulating and managing both the photovoltaic generator and the storage battery charge-discharge modes. The proposed photovoltaic/energy storage unit is proposed to supply an induction motor driven industrial pump with controlled speed and/or a DC motor driven water pump. An optimal proportional-integral-derivative control based on an Artificial Bee Colony Optimization algorithm is used to regulate the photovoltaic generator in case of normal operation or in case of maximum power point tracking (MPPT) and to also control the battery storage charge discharge modes. A vector control based on the proposed optimal control is used to regulate the induction motor rotor speed at its low reference values needed by the industrial pump. First, a total model of the entire system is obtained. The controller performance with the proposed system is studied with both a DC motor and/or induction motor loads. Simulation results show that the proposed photovoltaic/storage generator is able to supply the suggested dynamic loads under different conditions and with good performance. Also, it is noticed that operating the photovoltaic base on maximum power point tracking condition will give about 43% extra generation power than the normal operation case. Full article
(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)
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Open AccessArticle Effect of Carbon Nanoadditives on Lithium Hydroxide Monohydrate-Based Composite Materials for Low Temperature Chemical Heat Storage
Energies 2017, 10(5), 644; doi:10.3390/en10050644
Received: 5 April 2017 / Revised: 2 May 2017 / Accepted: 3 May 2017 / Published: 6 May 2017
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Abstract
Carbon nanospheres (CNSs) and multi-walled carbon nanotubes (MWCNTs) as nanoadditives were used to modify lithium hydroxide monohydrate for low temperature chemical heat storage application. The lithium hydroxide monohydrate particles were well dispersed on the nanoscale level, and the diameter of nanoparticles was about
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Carbon nanospheres (CNSs) and multi-walled carbon nanotubes (MWCNTs) as nanoadditives were used to modify lithium hydroxide monohydrate for low temperature chemical heat storage application. The lithium hydroxide monohydrate particles were well dispersed on the nanoscale level, and the diameter of nanoparticles was about 20–30 nm in the case of the carbon nanospheres and 50–100 nm the case of the MWCNTs, as shown by transmission electron microscopy characterization results. X-ray diffraction results indicated that the LiOH·H2O-carbon nano thermochemical composite materials were successfully synthesized. The thermochemical composite materials LiOH·H2O/CNSs (2020 kJ/kg), LiOH·H2O/MWCNTs (1804 kJ/kg), and LiOH·H2O/AC (1236 kJ/kg) exhibited obviously improved heat storage density and higher hydration rate than pure LiOH·H2O (661 kJ/kg), which was shown by thermogravimetric and differential scanning calorimetric (TG-DSC) analysis. It appears that nanocarbon-modified lithium hydroxide monohydrate thermochemical composite materials have a huge potential for the application of low temperature chemical heat storage. Full article
(This article belongs to the Special Issue Thermal Energy Storage and Thermal Management (TESM2017))
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Open AccessArticle Active Vibration Control of Swash Plate-Type Axial Piston Machines with Two-Weight Notch Least Mean Square/Filtered-x Least Mean Square (LMS/FxLMS) Filters
Energies 2017, 10(5), 645; doi:10.3390/en10050645
Received: 30 March 2017 / Revised: 21 April 2017 / Accepted: 2 May 2017 / Published: 6 May 2017
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Abstract
In this paper, swash plate active vibration control techniques were investigated utilizing the weight-limited multi-frequency two-weight notch Least Mean Square (LMS) filter with unit delay compensation and multi-frequency two-weight notch Filtered-x Least Mean Sqaure (FxLMS) filter with offline modeling to achieve adjustable swash
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In this paper, swash plate active vibration control techniques were investigated utilizing the weight-limited multi-frequency two-weight notch Least Mean Square (LMS) filter with unit delay compensation and multi-frequency two-weight notch Filtered-x Least Mean Sqaure (FxLMS) filter with offline modeling to achieve adjustable swash plate vibration reduction at the desired frequency. Simulation studies of the high fidelity pump control system model including realistic swash plate moments are presented to demonstrate the feasibility of the swash plate active vibration control. A 75-cm3/rev swash plate type axial piston pump was modified to implement a high bandwidth pump control system which is required for canceling the swash plate vibration. High speed real-time controllers were proposed and realized using an National Instrument LabVIEW Field Programmable Gate Array (FPGA). Vibration measurements using a tri-axial swash plate acceleration sensor were conducted to show the influence and effectiveness of the proposed swash plate active vibration control system and algorithms. Full article
(This article belongs to the Special Issue Energy Efficiency and Controllability of Fluid Power Systems)
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Open AccessArticle Energy Harvesting Based on a Novel Piezoelectric 0.7PbZn0.3Ti0.7O3-0.3Na2TiO3 Nanogenerator
Energies 2017, 10(5), 646; doi:10.3390/en10050646
Received: 21 January 2017 / Revised: 27 April 2017 / Accepted: 2 May 2017 / Published: 6 May 2017
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Abstract
Recently, piezoelectric materials have achieved remarkable attention for charging wireless sensor nodes. Among piezoelectric materials, non-ferroelectric materials are more cost effective because they can be prepared without a polarization process. In this study, a non-ferroelectric nanogenerator was manufactured from 0.7PbZn0.3Ti0.7
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Recently, piezoelectric materials have achieved remarkable attention for charging wireless sensor nodes. Among piezoelectric materials, non-ferroelectric materials are more cost effective because they can be prepared without a polarization process. In this study, a non-ferroelectric nanogenerator was manufactured from 0.7PbZn0.3Ti0.7O3-0.3Na2TiO3 (PZnT-NT). It was demonstrated that the increment of conductivity via adding the Na2TiO3 plays an essential role in increasing the permittivity of the non-ferroelectric nanogenerator and hence improved the generated power density. The dielectric measurements of this material demonstrated high conductivity that quenched the polarization phase. The performance of the device was studied experimentally over a cantilever test rig; the vibrating cantilever (0.4 ms−2) was excited by a motor operated at 30 Hz. The generated power successfully illuminated a light emitting diode (LED). The PZnT-NT nanogenerator produced a volume power density of 0.10 μw/mm3 and a surface power density of 10 μw/cm2. The performance of the proposed device with a size of (20 × 15 × 1 mm3) was higher in terms of power output than that of the commercial microfiber composite (MFC) (80 × 57 × 0.335 mm3) and piezoelectric bimorph device (70 × 50 × 0.7 mm3). Compared to other existing ferroelectric and non-ferroelectric nanogenerators, the proposed device demonstrated great performance in harvesting the energy at low acceleration and in a low frequency environment Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Global Energy-Optimal Redundancy Resolution of Hydraulic Manipulators: Experimental Results for a Forestry Manipulator
Energies 2017, 10(5), 647; doi:10.3390/en10050647
Received: 15 March 2017 / Revised: 13 April 2017 / Accepted: 3 May 2017 / Published: 6 May 2017
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Abstract
This paper addresses the energy-inefficiency problem of four-degrees-of-freedom (4-DOF) hydraulic manipulators through redundancy resolution in robotic closed-loop controlled applications. Because conventional methods typically are local and have poor performance for resolving redundancy with respect to minimum hydraulic energy consumption, global energy-optimal redundancy resolution
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This paper addresses the energy-inefficiency problem of four-degrees-of-freedom (4-DOF) hydraulic manipulators through redundancy resolution in robotic closed-loop controlled applications. Because conventional methods typically are local and have poor performance for resolving redundancy with respect to minimum hydraulic energy consumption, global energy-optimal redundancy resolution is proposed at the valve-controlled actuator and hydraulic power system interaction level. The energy consumption of the widely popular valve-controlled load-sensing (LS) and constant-pressure (CP) systems is effectively minimised through cost functions formulated in a discrete-time dynamic programming (DP) approach with minimum state representation. A prescribed end-effector path and important actuator constraints at the position, velocity and acceleration levels are also satisfied in the solution. Extensive field experiments performed on a forestry hydraulic manipulator demonstrate the performance of the proposed solution. Approximately 15–30% greater hydraulic energy consumption was observed with the conventional methods in the LS and CP systems. These results encourage energy-optimal redundancy resolution in future robotic applications of hydraulic manipulators. Full article
(This article belongs to the Special Issue Energy Efficiency and Controllability of Fluid Power Systems)
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Open AccessArticle Investigation of Methane Oxy-Fuel Combustion in a Swirl-Stabilised Gas Turbine Model Combustor
Energies 2017, 10(5), 648; doi:10.3390/en10050648
Received: 27 March 2017 / Revised: 27 April 2017 / Accepted: 28 April 2017 / Published: 8 May 2017
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Abstract
CO2 has a strong impact on both operability and emission behaviours in gas turbine combustors. In the present study, an atmospheric, preheated, swirl-stabilised optical gas turbine model combustor rig was employed. The primary objectives were to analyse the influence of CO2
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CO2 has a strong impact on both operability and emission behaviours in gas turbine combustors. In the present study, an atmospheric, preheated, swirl-stabilised optical gas turbine model combustor rig was employed. The primary objectives were to analyse the influence of CO2 on the fundamental characteristics of combustion, lean blowout (LBO) limits, CO emission and flame structures. CO2 dilution effects were examined with three preheating temperatures (396.15, 431.15, and 466.15 K). The fundamental combustion characteristics were studied utilising chemical kinetic simulations. To study the influence of CO2 on the operational range of the combustor, equivalence ratio (Ф) was varied from stoichiometric conditions to the LBO limits. CO emissions were measured at the exit of the combustor using a water-cooled probe over the entire operational range. The flame structures and locations were characterised by performing CH chemiluminescence imaging. The inverse Abel transformation was used to analyse the CH distribution on the axisymmetric plane of the combustor. Chemical kinetic modelling indicated that the CO2 resulted in a lower reaction rate compared with the CH4/air flame. Fundamental combustion properties such as laminar flame speed, ignition delay time and blowout residence time were found to be affected by CO2. The experimental results revealed that CO2 dilution resulted in a narrower operational range for the equivalence ratio. It was also found that CO2 had a strong inhibiting effect on CO burnout, which led to a higher concentration of CO in the combustion exhaust. CH chemiluminescence showed that the CO2 dilution did not have a significant impact on the flame structure. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Case Study of an Organic Rankine Cycle (ORC) for Waste Heat Recovery from an Electric Arc Furnace (EAF)
Energies 2017, 10(5), 649; doi:10.3390/en10050649
Received: 20 March 2017 / Revised: 26 April 2017 / Accepted: 4 May 2017 / Published: 7 May 2017
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Abstract
The organic Rankine cycle (ORC) is a mature technology for the conversion of waste heat to electricity. Although many energy intensive industries could benefit significantly from the integration of ORC technology, its current adoption rate is limited. One important reason for this arises
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The organic Rankine cycle (ORC) is a mature technology for the conversion of waste heat to electricity. Although many energy intensive industries could benefit significantly from the integration of ORC technology, its current adoption rate is limited. One important reason for this arises from the difficulty of prospective investors and end-users to recognize and, ultimately, realise the potential energy savings from such deployment. In recent years, electric arc furnaces (EAF) have been identified as particularly interesting candidates for the implementation of waste heat recovery projects. Therefore, in this work, the integration of an ORC system into a 100 MWe EAF is investigated. The effect of evaluations based on averaged heat profiles, a steam buffer and optimized ORC architectures is investigated. The results show that it is crucial to take into account the heat profile variations for the typical batch process of an EAF. An optimized subcritical ORC system is found capable of generating a net electrical output of 752 kWe with a steam buffer working at 25 bar. If combined heating is considered, the ORC system can be optimized to generate 521 kWe of electricity, while also delivering 4.52 MW of heat. Finally, an increased power output (by 26% with combined heating, and by 39% without combined heating) can be achieved by using high temperature thermal oil for buffering instead of a steam loop; however, the use of thermal oil in these applications has been until now typically discouraged due to flammability concerns. Full article
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Open AccessArticle A Battery Power Bank with Series-Connected Buck–Boost-Type Battery Power Modules
Energies 2017, 10(5), 650; doi:10.3390/en10050650
Received: 14 March 2017 / Revised: 18 April 2017 / Accepted: 2 May 2017 / Published: 8 May 2017
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Abstract
The operation of a battery power bank with series-connected buck–boost-type battery power modules (BPMs) was investigated in this study. Each BPM consisted of a battery pack with an associated buck–boost converter for individually controlling battery currents. With a proposed discharging scenario, load voltage
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The operation of a battery power bank with series-connected buck–boost-type battery power modules (BPMs) was investigated in this study. Each BPM consisted of a battery pack with an associated buck–boost converter for individually controlling battery currents. With a proposed discharging scenario, load voltage regulation with charge equalization among batteries was performed by controlling the battery currents in accordance with their state-of-charges (SOCs) estimated by real-time battery-loaded voltages detected under the same operating condition. In addition, the fault tolerance was executed to isolate exhausted or faulty batteries from the battery power bank without interrupting the system operation. Experiments were conducted to verify the effectiveness of the discharging scenario for a laboratory battery power bank with four series buck–boost BPMs. Full article
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Open AccessArticle 2D Numerical Simulation of Improving Wellbore Stability in Shale Using Nanoparticles Based Drilling Fluid
Energies 2017, 10(5), 651; doi:10.3390/en10050651
Received: 13 January 2017 / Revised: 13 April 2017 / Accepted: 2 May 2017 / Published: 9 May 2017
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Abstract
The past decade has seen increased focus on nanoparticle (NP) based drilling fluid to promote wellbore stability in shales. With the plugging of NP into shale pores, the fluid pressure transmission can be retarded and wellbore stability can be improved. For better understanding
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The past decade has seen increased focus on nanoparticle (NP) based drilling fluid to promote wellbore stability in shales. With the plugging of NP into shale pores, the fluid pressure transmission can be retarded and wellbore stability can be improved. For better understanding of the interaction between shale and NP based drilling fluid based on previous pressure transmission tests (PTTs) on Atoka shale samples, this paper reports the numerical simulation findings of wellbore stability in the presence of NP based drilling fluid, using the 2D fluid-solid coupling model in FLAC3D™ software. The results of previous PTT are discussed first, where the steps of numerical simulation, the simulation on pore fluid pressure transmission, the distribution of stress and the deformation of surrounding rock are presented. The mechanisms of NP in reducing permeability and stabilizing shale are also discussed. Results showed that fluid filtrate from water-based drilling fluid had a strong tendency to invade the shale matrix and increase the likelihood of wellbore instability in shales. However, the pore fluid pressure near wellbore areas could be minimized by plugging silica NP into the nanoscale pores of shales, which is consistent with previous PTT. Pore pressure transmission boundaries could also be restricted with silica NP. Furthermore, the stress differential and shear stress of surrounding rock near the wellbore was reduced in the presence of NP. The plastic yield zone was minimized to improve wellbore stability. The plugging mechanism of NP may be attributed to the electrostatic and electrodynamic interactions between NP and shale surfaces that are governed by Derjaguin-Landau-Verwey-Overbeek (DLVO) forces, which allowed NP to approach shale surfaces and adhere to them. We also found that discretization of the simulation model was beneficial in distinguishing the yield zone distribution of the surrounding rock in shales. The combination of PTT and the 2D numerical simulation offers a better understanding of how NP-based drilling fluid can be developed to address wellbore stability issues in shales. Full article
(This article belongs to the Special Issue Nanotechnology for Oil and Gas Applications)
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Open AccessArticle Tidal Current Power Resources and Influence of Sea-Level Rise in the Coastal Waters of Kinmen Island, Taiwan
Energies 2017, 10(5), 652; doi:10.3390/en10050652
Received: 2 March 2017 / Revised: 31 March 2017 / Accepted: 4 May 2017 / Published: 9 May 2017
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Abstract
The tidal current power (TCP) resource, the impact of TCP extraction on hydrodynamics and the influence of sea-level rise (SLR) on TCP output in the coastal waters of Kinmen Island (Taiwan) are investigated using a state-of-the-art unstructured-grid depth-integrated numerical model. The model was
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The tidal current power (TCP) resource, the impact of TCP extraction on hydrodynamics and the influence of sea-level rise (SLR) on TCP output in the coastal waters of Kinmen Island (Taiwan) are investigated using a state-of-the-art unstructured-grid depth-integrated numerical model. The model was driven by eight tidal constituents extracted from a global tidal prediction model and verified with time series of measured data for tide level and depth-averaged current. The simulations showed reasonable agreement with the observations; the skill index was in the excellent (0.71–0.93) range with regard to simulating tide level and currents. Model predictions indicated that the channel between Kinmen and Lieyu serves as an appropriate site for deploying the tidal turbines because of its higher tidal current and deeper water depth. The bottom friction approach was utilized to compute the average TCP over a spring-neap cycle (i.e., 15 days). Mean TCP reached its maximum to 45.51 kW for a coverage area of 0.036 km2 when an additional turbine friction coefficient (Ct) increased to 0.08, and a cut-in speed of 0.5 m/s was used. The annual TCP output was estimated to be 1.08 MW. The impact of TCP extraction on the change in current is significant, with a maximum reduction rate of instant current exceeding 60%, and the extent of influence for the average current is 1.26 km in length and 0.30 km in width for the −0.05 m/s contour line. However, the impact of TCP extraction on the change in tide level is insignificant; the maximum change in amplitude is only 0.73 cm for the K2 tide. The influence of SLR on the TCP output in Kinmen waters was also estimated. Modeling assessments showed that due to SLR produces faster tidal current, the annual TCP output increased to 1.52 MW, 2.01 MW, 2.48 MW and 2.97 MW under the same cut-in speed and coverage area conditions when SLR 0.25 m, SLR 0.5 m, SLR 0.75 m and SLR 1.0 m were imposed on the model. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle A Hybrid Dynamic System Assessment Methodology for Multi-Modal Transportation-Electrification
Energies 2017, 10(5), 653; doi:10.3390/en10050653
Received: 15 February 2017 / Revised: 16 April 2017 / Accepted: 4 May 2017 / Published: 9 May 2017
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Abstract
In recent years, electrified transportation, be it in the form of buses, trains, or cars have become an emerging form of mobility. Electric vehicles (EVs), especially, are set to expand the amount of electric miles driven and energy consumed. Nevertheless, the question remains
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In recent years, electrified transportation, be it in the form of buses, trains, or cars have become an emerging form of mobility. Electric vehicles (EVs), especially, are set to expand the amount of electric miles driven and energy consumed. Nevertheless, the question remains as to whether EVs will be technically feasible within infrastructure systems. Fundamentally, EVs interact with three interconnected systems: the (physical) transportation system, the electric power grid, and their supporting information systems. Coupling of the two physical systems essentially forms a nexus, the transportation-electricity nexus (TEN). This paper presents a hybrid dynamic system assessment methodology for multi-modal transportation-electrification. At its core, it utilizes a mathematical model which consists of a marked Petri-net model superimposed on the continuous time microscopic traffic dynamics and the electrical state evolution. The methodology consists of four steps: (1) establish the TEN structure; (2) establish the TEN behavior; (3) establish the TEN Intelligent Transportation-Energy System (ITES) decision-making; and (4) assess the TEN performance. In the presentation of the methodology, the Symmetrica test case is used throughout as an illustrative example. Consequently, values for several measures of performance are provided. This methodology is presented generically and may be used to assess the effects of transportation-electrification in any city or area; opening up possibilities for many future studies. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Study on the Propagation Laws of Hydrofractures Meeting a Faulted Structure in the Coal Seam
Energies 2017, 10(5), 654; doi:10.3390/en10050654
Received: 21 February 2017 / Revised: 2 April 2017 / Accepted: 5 May 2017 / Published: 10 May 2017
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Abstract
Hydraulic fracturing is an important technique for increasing coal seam permeability and productivity of CBM (coalbed methane). As a common type of faulted structure in the coal seam, the fault has a direct impact on the direction and scope of hydrofracture propagation, weakening
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Hydraulic fracturing is an important technique for increasing coal seam permeability and productivity of CBM (coalbed methane). As a common type of faulted structure in the coal seam, the fault has a direct impact on the direction and scope of hydrofracture propagation, weakening fracturing effects. To study the propagation laws of a hydrofracture meeting a fault in the coal seam, based on a two-dimensional model of a hydrofracture meeting a fault, the combined elastic mechanics and fracture mechanics, the propagation mode, critical internal water pressure, and influencing factors were analyzed. A numerical simulation on the propagation laws of hydrofracture meeting a fault was conducted by using the coupling system of flow and solid in the rock failure process analysis (RFPA2D-Flow). The results show that the horizontal crustal stress difference, the intersection angle between hydrofracture and fault plane, and the physical mechanics characteristics of coal-rock bed are the main factors influencing fracture propagation. With a decrease of horizontal crustal stress differences, intersection angle and an increase of roof elasticity modulus, it is easier for the footwall hydrofracture to enter the hanging wall along the bedding plane, forming an effective fracture. When the stress difference is large and the dip angle of fault plane surpasses 45°, the hydrofracture is easy to propagate towards the coal roof and floor by going through the fault plane. At this time, the coal seams of the footwall and the hanging wall should be fractured respectively to ensure fracturing effects, and the support of the roof and floor should be strengthened. The field experiment, theoretical analysis and numerical simulation were consistent in their results, which will contribute to the optimization of hydraulic fracturing and the prediction of hydrofracture in the coal seams containing faults. Full article
(This article belongs to the Special Issue Mathematical and Computational Modeling in Geothermal Engineering)
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Open AccessArticle Identification of Non-Stationary Magnetic Field Sources Using the Matching Pursuit Method
Energies 2017, 10(5), 655; doi:10.3390/en10050655
Received: 16 February 2017 / Revised: 23 April 2017 / Accepted: 4 May 2017 / Published: 9 May 2017
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Abstract
The measurements of electromagnetic field emissions, performed on board a vessel have showed that, in this specific environment, a high level of non-stationary magnetic fields (MFs) is observed. The adaptive time-frequency method can be used successfully to analyze this type of measured signal.
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The measurements of electromagnetic field emissions, performed on board a vessel have showed that, in this specific environment, a high level of non-stationary magnetic fields (MFs) is observed. The adaptive time-frequency method can be used successfully to analyze this type of measured signal. It allows one to specify the time interval in which the individual frequency components of the signal occur. In this paper, the method of identification of non-stationary MF sources based on the matching pursuit (MP) algorithm is presented. It consists of the decomposition of an examined time-waveform into the linear expansion of chirplet atoms and the analysis of the matrix of their parameters. The main feature of the proposed method is the modification of the chirplet’s matrix in a way that atoms, whose normalized energies are lower than a certain threshold, will be rejected. On the time-frequency planes of the spectrograms, obtained separately for each remaining chirlpet, it can clearly identify the time-frequency structures appearing in the examined signal. The choice of a threshold defines the computing speed and precision of the performed analysis. The method was implemented in the virtual application and used for processing real data, obtained from measurements of time-vary MF emissions onboard a ship. Full article
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Open AccessArticle Analysis of the Relative Price in China’s Energy Market for Reducing the Emissions from Consumption
Energies 2017, 10(5), 656; doi:10.3390/en10050656
Received: 2 March 2017 / Revised: 27 April 2017 / Accepted: 4 May 2017 / Published: 9 May 2017
Cited by 2 | PDF Full-text (784 KB) | HTML Full-text | XML Full-text
Abstract
As a developing country, extensive carbon and sulfur emissions are associated with China’s rapid social and economic development. Chief among them are the emissions from coal and oil consumption. This paper focuses on the demand side, attempting to regulate the range of relative
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As a developing country, extensive carbon and sulfur emissions are associated with China’s rapid social and economic development. Chief among them are the emissions from coal and oil consumption. This paper focuses on the demand side, attempting to regulate the range of relative price of oil to coal at the consumption level. Through the adjustment of the relative price, the goal of reducing the emissions of carbon and sulfur could be achieved in the market of energy consumption. Data regression is applied to investigate the functional relationship between emissions and energy prices. The results indicate that when the coal price is less than 300, the higher relative price leads to less carbon and sulfur emissions; when the coal price is more than 300 and less than 500, there exists an optimal relative price which has the least carbon emissions, and this value is not more than 11.5; when the coal price is more than 500, the smaller relative price is beneficial to decline carbon and sulfur emissions. The changed trend of relative price-sulfur emissions is very similar to relative price-carbon emissions. Compared to the present energy situation in China, the relative price of oil to coal still need to be reduced especially when coal price is more than 500. Full article
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Open AccessArticle A Low-Order System Frequency Response Model for DFIG Distributed Wind Power Generation Systems Based on Small Signal Analysis
Energies 2017, 10(5), 657; doi:10.3390/en10050657
Received: 26 March 2017 / Revised: 1 May 2017 / Accepted: 2 May 2017 / Published: 9 May 2017
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Abstract
Integrating large amounts of wind power into power systems brings a large influence on the dynamic frequency response characteristic (DFRC). The traditional low-order system frequency response (SFR) model is no longer applicable at the current time. Based on the small signal analysis theory,
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Integrating large amounts of wind power into power systems brings a large influence on the dynamic frequency response characteristic (DFRC). The traditional low-order system frequency response (SFR) model is no longer applicable at the current time. Based on the small signal analysis theory, a set of novel low-order SFR models for doubly-fed induction generator (DFIG) distributed wind power generation systems (DWPGS) are derived under low, medium, and high wind speed conditions, respectively. Time-domain simulations have been conducted on PSCAD/EMTDC, and the novel SFR model is tested and evaluated on a real system. The simulation results from the novel model agree with those from the detailed model. The novel SFR model can also directly show the impact of the initial wind speed and auxiliary frequency controller (AFC) parameters on DFRC, but not on the detailed model. Full article
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Open AccessArticle Economic and Thermal Evaluation of Different Uses of an Existing Structure in a Warm Climate
Energies 2017, 10(5), 658; doi:10.3390/en10050658
Received: 2 March 2017 / Revised: 27 April 2017 / Accepted: 2 May 2017 / Published: 9 May 2017
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Abstract
Accounting for nearly 40% of final energy consumption, buildings are central to European energy policy. The Directive on Energy Performance of Buildings establishes a benchmarking system known as cost-optimality to set minimum energy performance requirements in new and existing buildings. This paper applies
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Accounting for nearly 40% of final energy consumption, buildings are central to European energy policy. The Directive on Energy Performance of Buildings establishes a benchmarking system known as cost-optimality to set minimum energy performance requirements in new and existing buildings. This paper applies the cost-optimal methodology to an existing structure located in the Mediterranean area (Southern Italy). The building is composed of two units that have been considered for different uses: hotel and multi-residential. Several energy efficiency and renewable measures have been implemented both individually and as part of packages of measures. The cost-optimal solution has been identified as able to optimize energy consumption and costs from financial and macroeconomic perspectives. The first reference building (hotel use) shows a maximum reduction of primary energy and CO2 emission of about 42%, falling within the CasaClima energy class D, while the second reference building (residential use) achieves a value of 88% for primary energy and 85% for CO2 emissions, falling into class B. Thermal dispersions through the envelope can be limited using a suitable combination of insulating materials while a variety of technical variants are selected, such as VRF (variant refrigerant flow) systems, heat pumps with fan coils associated with controlled mechanical ventilation, solar thermal and photovoltaic. This paper illustrates the development of energy retrofit projects, in order to reach a balance between efficiency measures and costs for a building having two different uses, providing guidance to similar case studies related to a warm climate. Full article
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Open AccessArticle A Method for Thermal Dimensioning and for Energy Behavior Evaluation of a Building Envelope PCM Layer by Using the Characteristic Days
Energies 2017, 10(5), 659; doi:10.3390/en10050659
Received: 30 March 2017 / Revised: 25 April 2017 / Accepted: 5 May 2017 / Published: 9 May 2017
Cited by 4 | PDF Full-text (5300 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Net zero energy buildings (nZEB) require the development of innovative technologies such as the use of phase change materials (PCMs) in walls for the energy requalification of low inertia buildings. The presence of a PCM layer in the external building wall, due to
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Net zero energy buildings (nZEB) require the development of innovative technologies such as the use of phase change materials (PCMs) in walls for the energy requalification of low inertia buildings. The presence of a PCM layer in the external building wall, due to the effect of storage and release of latent energy phenomena, modifies the energy behavior, both during the summer and winter periods. This paper addresses the problem of the definition of the energetic behavior of a layer subject to phase change with periodic non-sinusoidal boundary conditions, characterizing the external walls of air-conditioned buildings. In such conditions, the layer is the site of the formation of one or more bi-phase interfaces, which originate on the boundary surfaces, or are always present and fluctuate within the layer. It is also possible that the layer does not undergo any phase change. The study has been developed by a finite difference numeric calculation model which explicitly determines the number and the position of the bi-phase interfaces that originate in the layer and the temperature and the heat flux fields. The surface heat fluxes are used to evaluate the PCM layer energetic behavior in terms of energy transferred through the boundary surfaces and of stored energy in sensible and latent form. The proposed method employs the characteristic day that it is periodically repeated for all the days of the considered month. The use of the characteristic days drastically reduces the computational burden of the numerical calculation and it allows to obtain guidance on the behaviour of the PCM throughout the year, in accordance with the variability of external climatic conditions, in order to select the PCM with the most suitable thermophysical properties. The methodology developed is applied to PCM layers with different melting temperatures and subject to climatic conditions of two locations, one with a continental climate and the second one with a Mediterranean climate. The results obtained allowed us to identify which PCM is more suitable in improving the energetic performances of building walls in the heating or cooling period during the year. In particular, the energy analysis highlighted that, in both localities, during the winter period: the lowest energy exiting from the indoor environment is ensured by a PCM with a melting temperature of 15 °C; the highest contribution of energy entering the indoor environment, mainly due to solar radiation, is recorded for a PCM with a melting temperature of 26 °C. During the summer period: the lowest value of energy entering the indoor environment is obtained by a PCM with melting temperature of 26 °C; the highest value of energy exiting from the indoor environment is ensured by a melting temperature equal to 20 °C. In both locations, a PCM with a melting temperature intermediate between those of the winter and summer set points of the indoor environment is the best compromise between winter and summer energy needs for an air-conditioned environment, as it allows obtainment of the highest values of the yearly total stored energy. Full article
(This article belongs to the Section Energy Storage and Application)
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