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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’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.
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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 The Optimal Road Grade Design for Minimizing Ground Vehicle Energy Consumption
Energies 2017, 10(5), 700; doi:10.3390/en10050700
Received: 7 April 2017 / Revised: 9 May 2017 / Accepted: 10 May 2017 / Published: 16 May 2017
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Abstract
Reducing energy consumption of ground vehicles is a paramount pursuit in academia and industry. Even though the road infrastructural has a significant influence on vehicular fuel consumption, the majority of the R&D efforts are dedicated to improving vehicles. Little investigation has been made
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Reducing energy consumption of ground vehicles is a paramount pursuit in academia and industry. Even though the road infrastructural has a significant influence on vehicular fuel consumption, the majority of the R&D efforts are dedicated to improving vehicles. Little investigation has been made in the optimal design of the road infrastructure to minimize the total fuel consumption of all vehicles running on it. This paper focuses on this overlooked design problem and the design parameters of the optimal road infrastructure is the profile of road grade angle between two fixed points. We assume that all vehicles on the road follow a given acceleration profile between the two given points. The mean value of the energy consumptions of all vehicles running on the road is defined as the objective function. The optimization problem is solved both analytically by Pontryagin’s minimum principle and numerically by dynamic programming. The two solutions agree well. A large number of Monte Carlo simulations show that the vehicles driving on the road with the optimal road grade consume up to 31.7% less energy than on a flat road. Finally, a rough cost analysis justifies the economic advantage of building the optimal road profile. Full article
(This article belongs to the Special Issue Methods to Improve Energy Use in Road Vehicles)
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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
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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 Dynamic Charging of Electric Vehicle with Negligible Power Transfer Fluctuation
Energies 2017, 10(5), 701; doi:10.3390/en10050701
Received: 9 March 2017 / Revised: 29 April 2017 / Accepted: 3 May 2017 / Published: 16 May 2017
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Abstract
High-efficiency inductive power transfer (IPT) with low misalignment effects is a key issue in the dynamic charging of electric vehicle (EV) systems. In this study, an advanced concept of analysis and design of transmitter and receiver coils with a special coil assembly is
[...] Read more.
High-efficiency inductive power transfer (IPT) with low misalignment effects is a key issue in the dynamic charging of electric vehicle (EV) systems. In this study, an advanced concept of analysis and design of transmitter and receiver coils with a special coil assembly is proposed for the dynamic charging of EVs. In each transmitter coil, large rectangular section is series connected with two zigzag-shaped small rectangular sections. These small sections are back-to-back series connected and located inside the large rectangular section. An adjacent pair of proposed transmitter coils with back-to-back series connection named extended double D (DD)-shaped transmitter is used throughout this paper. The major contribution in the case of the extended DD transmitter is negligible power transfer fluctuation, regardless of any horizontal misalignment of the receiver coil. Justification of the coil design is performed based on its load independent voltage gain and power transfer fluctuation characteristics. Experimental results prove that the power transfer fluctuation with load independent voltage gain is within ±6%, and the efficiency is approximately 93% under horizontal misalignment of receiver coil with an air gap of 140 mm. Finally, a new coil design set with a special arrangement has been proposed to maintain nearly uniform coupling factor and negligible power transfer fluctuation. 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 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 Scale-Model Experiments for the Surface Wave Influence on a Submerged Floating Ocean-Current Turbine
Energies 2017, 10(5), 702; doi:10.3390/en10050702
Received: 24 February 2017 / Revised: 11 May 2017 / Accepted: 12 May 2017 / Published: 16 May 2017
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Abstract
In order to harness the kinetic energy of marine currents, we propose a novel ocean-current turbine with a horizontal axis. The turbine can be moored to the seabed and function similarly to kites in a water flow. To operate such turbines in a
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In order to harness the kinetic energy of marine currents, we propose a novel ocean-current turbine with a horizontal axis. The turbine can be moored to the seabed and function similarly to kites in a water flow. To operate such turbines in a marine current, the resulting rotor torque needs to be canceled. Therefore, the proposed turbine is designed with a float at its top and a counterweight at its bottom. Thus far, we have verified the turbine stability and blade performance through towing experiments. As the next step, we constructed a scale-model turbine to confirm the mooring system. This experiment was performed at a circulating water channel with wave-making facilities. The influence of waves on the floating body was also investigated. In this paper, we report the behavior of the scale-model turbine moored to the tank bottom and discuss the influence of surface waves. Full article
(This article belongs to the Special Issue Marine Energy)
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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
[...] Read more.
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 A Numerical Study on the Impact of Grouting Material on Borehole Heat Exchangers Performance in Aquifers
Energies 2017, 10(5), 703; doi:10.3390/en10050703
Received: 24 March 2017 / Revised: 11 May 2017 / Accepted: 12 May 2017 / Published: 17 May 2017
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Abstract
U-pipes for ground source heat pump (GSHP) installations are generally inserted in vertical boreholes back-filled with pumpable grouts. Grout thermal conductivity is a crucial parameter, dominating the borehole thermal resistance and impacting the heat exchanger efficiency. In order to seal the borehole and
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U-pipes for ground source heat pump (GSHP) installations are generally inserted in vertical boreholes back-filled with pumpable grouts. Grout thermal conductivity is a crucial parameter, dominating the borehole thermal resistance and impacting the heat exchanger efficiency. In order to seal the borehole and prevent leakages of the heat carrier fluid, grouting materials are also hydraulically impermeable, so that groundwater flow inside the borehole is inhibited. The influence of groundwater flow on the borehole heat exchangers (BHE) performance has recently been highlighted by several authors. However groundwater impact and grouting materials influence are usually evaluated separately, disregarding any combined effect. Therefore simulation is used to investigate the role of the thermal and hydraulic conductivities of the grout when the BHE operates in an aquifer with a relevant groundwater flow. Here 3 main cases for a single U-pipe in a sandy aquifer are compared. In Case 1 the borehole is back-filled with the surrounding soil formation, while a thermally enhanced grout and a low thermal conductivity grout are considered in Case 2 and Case 3 respectively. Simulations are carried out maintaining the inlet temperature constant in order to reproduce the yearly operation of the GSHP system. For each of the 3 cases three different groundwater flow velocities are considered. The results show that a high thermal conductivity grout further enhances the effects of a significant groundwater flow. The conditions when neglecting the grout material in the numerical model does not lead to relevant errors are also identified. Full article
(This article belongs to the Special Issue Low Enthalpy Geothermal Energy)
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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 A Failure Probability Calculation Method for Power Equipment Based on Multi-Characteristic Parameters
Energies 2017, 10(5), 704; doi:10.3390/en10050704
Received: 30 March 2017 / Revised: 9 May 2017 / Accepted: 11 May 2017 / Published: 17 May 2017
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Abstract
Although traditional fault diagnosis methods can qualitatively identify the failure modes for power equipment, it is difficult to evaluate the failure probability quantitatively. In this paper, a failure probability calculation method for power equipment based on multi-characteristic parameters is proposed. After collecting the
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Although traditional fault diagnosis methods can qualitatively identify the failure modes for power equipment, it is difficult to evaluate the failure probability quantitatively. In this paper, a failure probability calculation method for power equipment based on multi-characteristic parameters is proposed. After collecting the historical data of different fault characteristic parameters, the distribution functions and the cumulative distribution functions of each parameter, which are applied to dispersing the parameters and calculating the differential warning values, are calculated by using the two-parameter Weibull model. To calculate the membership functions of parameters for each failure mode, the Apriori algorithm is chosen to mine the association rules between parameters and failure modes. After that, the failure probability of each failure mode is obtained by integrating the membership functions of different parameters by a weighted method, and the important weight of each parameter is calculated by the differential warning values. According to the failure probability calculation result, the series model is established to estimate the failure probability of the equipment. Finally, an application example for two 220 kV transformers is presented to show the detailed process of the method. Compared with traditional fault diagnosis methods, the calculation results not only identify the failure modes correctly, but also reflect the failure probability changing trend of the equipment accurately. Full article
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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
[...] Read more.
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 Design of a Bearingless Outer Rotor Induction Motor
Energies 2017, 10(5), 705; doi:10.3390/en10050705
Received: 16 December 2016 / Revised: 10 May 2017 / Accepted: 11 May 2017 / Published: 17 May 2017
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Abstract
A bearingless induction (BI) motor with an outer rotor for flywheel energy storage systems is proposed due to the perceived advantages of simple rotor structure, non-contact support and high speed operation. Firstly, the configuration and operation principle of the proposed motor are described.
[...] Read more.
A bearingless induction (BI) motor with an outer rotor for flywheel energy storage systems is proposed due to the perceived advantages of simple rotor structure, non-contact support and high speed operation. Firstly, the configuration and operation principle of the proposed motor are described. Then several leading dimensional parameters are optimally calculated for achieving the maximum average values and the minimum ripples of torque output and suspension force. Finally, by using the finite element method, the characteristics and performance of the proposed machine are analyzed and verified. 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 Performance Analysis of a Four-Switch Three-Phase Grid-Side Converter with Modulation Simplification in a Doubly-Fed Induction Generator-Based Wind Turbine (DFIG-WT) with Different External Disturbances
Energies 2017, 10(5), 706; doi:10.3390/en10050706
Received: 9 March 2017 / Revised: 12 May 2017 / Accepted: 14 May 2017 / Published: 18 May 2017
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Abstract
This paper investigates the performance of a fault-tolerant four-switch three-phase (FSTP) grid-side converter (GSC) in a doubly-fed induction generator-based wind turbine (DFIG-WT). The space vector pulse width modulation (SVPWM) technique is simplified and unified duty ratios are used for controlling the FSTP GSC.
[...] Read more.
This paper investigates the performance of a fault-tolerant four-switch three-phase (FSTP) grid-side converter (GSC) in a doubly-fed induction generator-based wind turbine (DFIG-WT). The space vector pulse width modulation (SVPWM) technique is simplified and unified duty ratios are used for controlling the FSTP GSC. Steady DC-bus voltage, sinusoidal three-phase grid currents and unity power factor are obtained. In addition, the balance of capacitor voltages is accomplished based on the analysis of current flows at the midpoint of DC bus in different operational modes. Besides, external disturbances such as fluctuating wind speed and grid voltage sag are considered to test its fault-tolerant ability. Furthermore, the effects of fluctuating wind speed on the performance of DFIG-WT system are explained according to an approximate expression of the turbine torque. The performance of the proposed FSTP GSC is simulated in Matlab/Simulink 2016a based on a detailed 1.5 MW DFIG-WT Simulink model. Experiments are carried out on a 2 kW platform by using a discrete signal processor (DSP) TMS320F28335 controller to validate the reliability of DFIG-WT for the cases with step change of the stator active power and grid voltage sag, respectively. Full article
(This article belongs to the Section Electrical Power and Energy System)
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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,
[...] Read more.
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 ITO-Free Transparent Organic Solar Cell with Distributed Bragg Reflector for Solar Harvesting Windows
Energies 2017, 10(5), 707; doi:10.3390/en10050707
Received: 30 March 2017 / Revised: 8 May 2017 / Accepted: 11 May 2017 / Published: 17 May 2017
Cited by 1 | PDF Full-text (5288 KB) | HTML Full-text | XML Full-text
Abstract
We demonstrated an indium tin oxide (ITO)-free, highly transparent organic solar cell with the potential to be integrated into window panes for energy harvesting purposes. A transparent, conductive ZnO/Ag/ZnO multilayer electrode and a Ag:Ca thin film electrode were used in this transparent device
[...] Read more.
We demonstrated an indium tin oxide (ITO)-free, highly transparent organic solar cell with the potential to be integrated into window panes for energy harvesting purposes. A transparent, conductive ZnO/Ag/ZnO multilayer electrode and a Ag:Ca thin film electrode were used in this transparent device as the bottom and top electrode, respectively. To further improve the transmittance of the solar cell, the thickness of the top ZnO layer was investigated both experimentally and with simulations. An average visible transmittance of >60% was reached, with a maximum transmittance of 73% at 556 nm. Both top and bottom illumination of the solar cell generated comparable power conversion efficiencies, which indicates the wide application of this solar cell structure. In addition, we fabricated distributed Bragg reflector mirrors with sputtered SiO2 and TiO2, which efficiently increased the power conversion efficiency over 20% for the solar cells on glass and poly(ethylene terephthalate) (PET) substrates. Full article
(This article belongs to the Special Issue Solar Energy Application in Buildings)
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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
[...] Read more.
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 Bifurcation Phenomena Studies of a Voltage Controlled Buck-Inverter Cascade System
Energies 2017, 10(5), 708; doi:10.3390/en10050708
Received: 5 April 2017 / Revised: 9 May 2017 / Accepted: 14 May 2017 / Published: 18 May 2017
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Abstract
This paper studies the complex bifurcation phenomena of a voltage-controlled Buck-inverter cascade system. A state-flow chart is drawn to illustrate the complex relations among the linear operating modes. Combined with the state transition function of each mode, the time response of the system
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This paper studies the complex bifurcation phenomena of a voltage-controlled Buck-inverter cascade system. A state-flow chart is drawn to illustrate the complex relations among the linear operating modes. Combined with the state transition function of each mode, the time response of the system can be obtained. For period-one steady state, the periodic mapping function and its fixed point are further derived, on the basis of which the Jacobi matrix is developed and its maximum eigenvalue is analyzed to understand the bifurcation diagram. By globally analyzing the state space using this cell mapping method, the coexistence of attractors is revealed in the Buck-inverter system. All theoretical results have been verified experimentally on a prototype system. The results obtained can be used for guiding the design and analysis of the Buck-inverter system. The analyzing method can be helpful for studying other power electronics systems with compound topologies. Full article
(This article belongs to the Section Electrical Power and Energy System)
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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 Research on the Optimal Charging Strategy for Li-Ion Batteries Based on Multi-Objective Optimization
Energies 2017, 10(5), 709; doi:10.3390/en10050709
Received: 6 March 2017 / Revised: 21 April 2017 / Accepted: 12 May 2017 / Published: 17 May 2017
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Abstract
Charging performance affects the commercial application of electric vehicles (EVs) significantly. This paper presents an optimal charging strategy for Li-ion batteries based on the voltage-based multistage constant current (VMCC) charging strategy. In order to satisfy the different charging demands of the EV users
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Charging performance affects the commercial application of electric vehicles (EVs) significantly. This paper presents an optimal charging strategy for Li-ion batteries based on the voltage-based multistage constant current (VMCC) charging strategy. In order to satisfy the different charging demands of the EV users for charging time, charged capacity and energy loss, the multi-objective particle swarm optimization (MOPSO) algorithm is employed and the influences of charging stage number, charging cut-off voltage and weight factors of different charging goals are analyzed. Comparison experiments of the proposed charging strategy and the traditional normal and fast charging strategies are carried out. The experimental results demonstrate that the traditional normal and fast charging strategies can only satisfy a small range of EV users’ charging demand well while the proposed charging strategy can satisfy the whole range of the charging demand well. The relative increase in charging performance of the proposed charging strategy can reach more than 80% when compared to the normal and fast charging dependently. Full article
(This article belongs to the collection Electric and Hybrid Vehicles Collection)
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Open AccessArticle The Potential of Thermal Plasma Gasification of Olive Pomace Charcoal
Energies 2017, 10(5), 710; doi:10.3390/en10050710
Received: 15 March 2017 / Revised: 19 April 2017 / Accepted: 9 May 2017 / Published: 17 May 2017
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Abstract
Annually, the olive oil industry generates a significant amount of by-products, such as olive pomace, olive husks, tree prunings, leaves, pits, and branches. Therefore, the recovery of these residues has become a major challenge in Mediterranean countries. The utilization of olive industry residues
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Annually, the olive oil industry generates a significant amount of by-products, such as olive pomace, olive husks, tree prunings, leaves, pits, and branches. Therefore, the recovery of these residues has become a major challenge in Mediterranean countries. The utilization of olive industry residues has received much attention in recent years, especially for energy purposes. Accordingly, this primary experimental study aims at investigating the potential of olive biomass waste for energy recovery in terms of synthesis gas (or syngas) production using the thermal arc plasma gasification method. The olive charcoal made from the exhausted olive solid waste (olive pomace) was chosen as a reference material for primary experiments with known composition from the performed proximate and ultimate analysis. The experiments were carried out at various operational parameters: raw biomass and water vapour flow rates and the plasma generator power. The producer gas involved principally CO, H2, and CO2 with the highest concentrations of 41.17%, 13.06%, and 13.48%, respectively. The produced synthesis gas has a lower heating value of 6.09 MJ/nm3 at the H2O/C ratio of 3.15 and the plasma torch had a power of 52.2 kW. Full article
(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications)
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Open AccessArticle Economic Assessment of Network-Constrained Transactive Energy for Managing Flexible Demand in Distribution Systems
Energies 2017, 10(5), 711; doi:10.3390/en10050711
Received: 8 April 2017 / Revised: 10 May 2017 / Accepted: 15 May 2017 / Published: 18 May 2017
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Abstract
The increasing number of distributed energy resources such as electric vehicles and heat pumps connected to power systems raises operational challenges to the network operator, for example, introducing grid congestion and voltage deviations in the distribution network level if their operations are not
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The increasing number of distributed energy resources such as electric vehicles and heat pumps connected to power systems raises operational challenges to the network operator, for example, introducing grid congestion and voltage deviations in the distribution network level if their operations are not properly coordinated. Coordination and control of a large number of distributed energy resources requires innovative approaches. In this paper, we follow up on a recently proposed network-constrained transactive energy (NCTE) method for scheduling of electric vehicles and heat pumps within a retailer’s aggregation at distribution system level. We extend this method with: (1) a new modeling technique that allows the resulting congestion price to be directly interpreted as a locational marginal pricing in the system; (2) an explicit analysis of the benefits and costs of different actors when using the NCTE method in the system, given the high penetration of distributed energy resources. This paper firstly describes the NCTE-based distribution system that introduces a new interacting scheme for actors at the distribution system level. Then, technical modeling and economic interpretation of the NCTE-based distribution system are described. Finally, we show the benefits and costs of different actors within the NCTE-based distribution system. Full article
(This article belongs to the Section Electrical Power and Energy System)
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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 Hydrodynamic Investigation of an Oscillating Buoy Wave Energy Converter Integrated into a Pile-Restrained Floating Breakwater
Energies 2017, 10(5), 712; doi:10.3390/en10050712
Received: 27 March 2017 / Revised: 9 May 2017 / Accepted: 10 May 2017 / Published: 18 May 2017
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Abstract
An analytical model is developed based on linear potential flow theory and matching eigenfunction expansion technique to investigate the hydrodynamics of a two-dimensional floating structure. This structure is an integration system consisting of a breakwater and an oscillating buoy wave energy converter (WEC).
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An analytical model is developed based on linear potential flow theory and matching eigenfunction expansion technique to investigate the hydrodynamics of a two-dimensional floating structure. This structure is an integration system consisting of a breakwater and an oscillating buoy wave energy converter (WEC). It is constrained to heave motion, and linear power take-off (PTO) damping is used to calculate the absorbed power. The proposed model is verified against the published results. The proposed integrated structure is compared with the fixed structure and free heave-motion structure, respectively. The hydrodynamic properties of the integrated structure with the optimal PTO damping i.e., the transmission coefficient, reflection coefficient, capture width ratio (CWR), and heave response amplitude operator (RAO), are investigated. The effect of the PTO damping on the performance of the integrated system is also evaluated. Results indicate that with the proper adjustment of the PTO damping, the proposed integrated system can produce power efficiently. Meanwhile, the function of coastal protection can be compared with that of the fixed structure. Full article
(This article belongs to the Section Energy Sources)
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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 Improved Capacitor Voltage Feedforward for Three-Phase LCL-Type Grid-Connected Converter to Suppress Start-Up Inrush Current
Energies 2017, 10(5), 713; doi:10.3390/en10050713
Received: 5 April 2017 / Revised: 11 May 2017 / Accepted: 12 May 2017 / Published: 18 May 2017
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Abstract
Three-phase active damping LCL-type grid-connected converters are usually used in distributed power generation systems. However, serious inrush current will be aroused when the grid-connected converter starts, especially in rectifier mode, if no effective control method is taken. The point of common coupling (PCC)
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Three-phase active damping LCL-type grid-connected converters are usually used in distributed power generation systems. However, serious inrush current will be aroused when the grid-connected converter starts, especially in rectifier mode, if no effective control method is taken. The point of common coupling (PCC) voltage feedforward is usually used to suppress start-up inrush current. Unfortunately, it will introduce a positive feedback loop related to the grid current and grid impedance under weak grid conditions, and therefore, the grid current will be distorted and the system stability margin will be significantly reduced. To solve the above problems, this paper proposes a simple method based on a d-axis fundamental positive-sequence component of filter capacitor voltage feedforward, without extra sensors and software resources. With the proposed method, it is possible to suppress the start-up inrush current and maintain the grid current quality and system stability under weak grid conditions. The mechanism of start-up inrush current and the effectiveness of the method for inrush current suppression are analyzed in detail. Then, the influences of different feedforward methods on system stability are analyzed under weak grid conditions by the impedance model of grid-connected converter. Finally, experimental results verify the validity of the proposed method. Full article
(This article belongs to the Section Electrical Power and Energy System)
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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
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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 Insulation Resistance Monitoring Algorithm for Battery Pack in Electric Vehicle Based on Extended Kalman Filtering
Energies 2017, 10(5), 714; doi:10.3390/en10050714
Received: 16 March 2017 / Revised: 1 May 2017 / Accepted: 12 May 2017 / Published: 18 May 2017
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Abstract
To improve the accuracy of insulation monitoring between the battery pack and chassis of electric vehicles, we established a serial battery pack model composed of first-order resistor-capacitor (RC) circuit battery cells. We then designed a low-voltage, low-frequency insulation monitoring model based on this
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To improve the accuracy of insulation monitoring between the battery pack and chassis of electric vehicles, we established a serial battery pack model composed of first-order resistor-capacitor (RC) circuit battery cells. We then designed a low-voltage, low-frequency insulation monitoring model based on this serial battery pack model. An extended Kalman filter (EKF) was designed for this non-linear system to filter the measured results, thus mitigating the influence of noise. Experimental and simulation results show that the proposed monitoring model and extended Kalman filtering algorithm for insulation resistance monitoring present satisfactory estimation accuracy and robustness. Full article
(This article belongs to the Section Electrical Power and Energy System)
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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 2 | 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 A SVPWM to Eliminate Common-Mode Voltage for Multilevel Inverters
Energies 2017, 10(5), 715; doi:10.3390/en10050715
Received: 5 April 2017 / Revised: 25 April 2017 / Accepted: 2 May 2017 / Published: 18 May 2017
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Abstract
This paper presents a new space vector pulse width modulation (SVPWM) to eliminate common-mode voltage (CMV) for multilevel inverters. The proposed SVPWM is performed in a new coordinate system, in which the converter voltage vectors have only integer entries and the absolute coordinate
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This paper presents a new space vector pulse width modulation (SVPWM) to eliminate common-mode voltage (CMV) for multilevel inverters. The proposed SVPWM is performed in a new coordinate system, in which the converter voltage vectors have only integer entries and the absolute coordinate increment between adjacent vectors is equal to 1. The location of the reference vector, detection of the nearest three CMV vectors, and duty cycles of the nearest three CMV vectors are all obtained by simple calculations, no lookup table is needed and the SVPWM is computationally fast. Compared with earlier pulse width modulations (PWMs), the realization of the CMV vectors is very simple, and the CMV of multilevel inverters are limited to zero with any modulation index. Because the SVPWM is independent of the level number of the inverter, the proposed SVPWM is suitable for any level of inverter. This paper also thoroughly compares the proposed SVPWM with prior PWMs. Experimental results are also given in the paper. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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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
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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 The Investigation of High Quality PEDOT:PSS Film by Multilayer-Processing and Acid Treatment
Energies 2017, 10(5), 716; doi:10.3390/en10050716
Received: 29 March 2017 / Revised: 27 April 2017 / Accepted: 15 May 2017 / Published: 18 May 2017
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Abstract
In this study, we have investigated the performance of multilayer films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) treated with one of the perfluorinated carboxylic acids, named trifluoroacetic acid (TFA). According to the increased density of the PEDOT chain under unit area conditions, the sheet resistance (R
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In this study, we have investigated the performance of multilayer films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) treated with one of the perfluorinated carboxylic acids, named trifluoroacetic acid (TFA). According to the increased density of the PEDOT chain under unit area conditions, the sheet resistance (Rsq) has improved from 300 to 65 Ω/sq through additional processing of PEDOT:PSS from single layer to multilayer. After the further treatment with TFA, however, the Rsq of the multilayer PEDOT:PSS was enhanced to 45 Ω/sq, leading to the decline of film thickness from 400 to 270 nm. Both conductivity and work function based on X-ray photoelectron spectroscopy results have built a breakthrough by double-processing because of the higher density of conductive PEDOT chains and the increase of 0.4 eV alternatives to typical indium tin oxide substrate, respectively. This improvement is contributed to the development of more effective transparent electrodes. Full article
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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 Determination of Equivalent Thermal Conductivity of Window Spacers in Consideration of Condensation Prevention and Energy Saving Performance
Energies 2017, 10(5), 717; doi:10.3390/en10050717
Received: 18 April 2017 / Revised: 15 May 2017 / Accepted: 17 May 2017 / Published: 18 May 2017
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Abstract
This study investigated the impact of thermally improved spacers (TISs) on the condensation prevention and energy saving performances of residential windows. The temperature factor and total U-value were analyzed with the two-box model, by which the TISs are represented with the equivalent thermal
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This study investigated the impact of thermally improved spacers (TISs) on the condensation prevention and energy saving performances of residential windows. The temperature factor and total U-value were analyzed with the two-box model, by which the TISs are represented with the equivalent thermal conductivity. The results showed that the TISs could increase the temperature factor by up to 12%, and this significantly improved the condensation prevention performance. In addition, it was proved that the TIS enables the prevention of the condensation at an outdoor temperature that is 4.2 °C to 15.7 °C lower compared with the conventional spacer. Also, it was shown that the TISs reduce the total U-value by an amount from 0.07 W/m2K to 0.12 W/m2K, implying that the heat loss through the window is reduced by a rate from 2.8% to 8.2%. In addition, the results of the whole building energy simulation proved that the TISs can reduce the annual heating-energy consumption by a rate from 3.0% to 6.3%. The results were then used for the development of monographs to determine the equivalent thermal conductivity of a window spacer that can meet the performance criteria in terms of condensation prevention and energy saving. Full article
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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 Waste Heat Recovery from Marine Gas Turbines and Diesel Engines
Energies 2017, 10(5), 718; doi:10.3390/en10050718
Received: 14 February 2017 / Revised: 8 May 2017 / Accepted: 12 May 2017 / Published: 18 May 2017
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Abstract
The paper presents the main results of a research project directed to the development of mathematical models for the design and simulation of combined Gas Turbine-Steam or Diesel-Steam plants for marine applications. The goal is to increase the energy conversion efficiency of both
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The paper presents the main results of a research project directed to the development of mathematical models for the design and simulation of combined Gas Turbine-Steam or Diesel-Steam plants for marine applications. The goal is to increase the energy conversion efficiency of both gas turbines and diesel engines, adopted in ship propulsion systems, by recovering part of the thermal energy contained in the exhaust gases through Waste Heat Recovery (WHR) dedicated installations. The developed models are used to identify the best configuration of the combined plants in order to optimize, for the different applications, the steam plant layout and the performance of WHR plant components. This research activity has allowed to obtain significant improvements in terms of energy conversion efficiency, but also on other important issues: dimensions and weights of the installations, ship load capacity, environmental compatibility, investment and operating costs. In particular, the main results of the present study can be summarized as follows: (a) the quantitative assessment of the advantages (and limits) deriving by the application of a Combined Gas And Steam (COGAS) propulsion system to a large container ship, in substitution of the traditional two-stroke diesel engine; (b) the proposal of optimized WHR propulsion and power systems for an oil tanker, for which a quantitative evaluation is given of the attainable advantages, in terms of fuel consumption and emissions reduction, in comparison with more traditional solutions. Full article
(This article belongs to the Special Issue Waste Heat Recovery)
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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 A Multistage DC-DC Step-Up Self-Balanced and Magnetic Component-Free Converter for Photovoltaic Applications: Hardware Implementation
Energies 2017, 10(5), 719; doi:10.3390/en10050719
Received: 24 December 2016 / Revised: 15 May 2017 / Accepted: 15 May 2017 / Published: 18 May 2017
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Abstract
This article presents a self-balanced multistage DC-DC step-up converter for photovoltaic applications. The proposed converter topology is designed for unidirectional power transfer and provides a doable solution for photovoltaic applications where voltage is required to be stepped up without magnetic components (transformer-less and
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This article presents a self-balanced multistage DC-DC step-up converter for photovoltaic applications. The proposed converter topology is designed for unidirectional power transfer and provides a doable solution for photovoltaic applications where voltage is required to be stepped up without magnetic components (transformer-less and inductor-less). The output voltage obtained from renewable sources will be low and must be stepped up by using a DC-DC converter for photovoltaic applications. 2 K diodes and 2 K capacitors along with two semiconductor control switch are used in the K-stage proposed converter to obtain an output voltage which is (K + 1) times the input voltage. The conspicuous features of proposed topology are: (i) magnetic component free (transformer-less and inductor-less); (ii) continuous input current; (iii) low voltage rating semiconductor devices and capacitors; (iv) modularity; (v) easy to add a higher number of levels to increase voltage gain; (vi) only two control switches with alternating operation and simple control. The proposed converter is compared with recently described existing transformer-less and inductor-less power converters in term of voltage gain, number of devices and cost. The application of the proposed circuit is discussed in detail. The proposed converter has been designed with a rated power of 60 W, input voltage is 24 V, output voltage is 100 V and switching frequency is 100 kHz. The performance of the converter is verified through experimental and simulation results. Full article
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Open AccessArticle Mapping Urban Heat Demand with the Use of GIS-Based Tools
Energies 2017, 10(5), 720; doi:10.3390/en10050720
Received: 21 March 2017 / Revised: 8 May 2017 / Accepted: 10 May 2017 / Published: 19 May 2017
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Abstract
This article presents a bottom-up approach for calculation of the useful heat demand for space heating and hot water preparation using geo-referenced datasets for buildings at the city level. This geographic information system (GIS) based approach was applied in the case study for
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This article presents a bottom-up approach for calculation of the useful heat demand for space heating and hot water preparation using geo-referenced datasets for buildings at the city level. This geographic information system (GIS) based approach was applied in the case study for the city of Krakow, where on the one hand the district heat network is well developed, while on the other hand there are still substantial number of buildings burning solid fuels in individual boilers and stoves, causing air pollution. The calculated heat demand was aggregated in the grid with 100 m × 100 m spatial resolution to deliver the heat map depicting the current situation for 21 buildings types. The results show that the residential buildings, in particular one- and multi-family buildings, have the highest share in overall demand for heat. By combining the results with location of the district heat (DH) network, the potential areas in its close vicinity that have sufficient heat demand density for developing the net were pointed out. Future evolution in heat demand for space heating in one-family houses was evaluated with the use of deterministic method employing building stock model. The study lays a foundation for planning the development of the heating system at the city level. Full article
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Open AccessArticle The Role of Shearing Energy and Interfacial Gibbs Free Energy in the Emulsification Mechanism of Waxy Crude Oil
Energies 2017, 10(5), 721; doi:10.3390/en10050721
Received: 28 March 2017 / Revised: 6 May 2017 / Accepted: 16 May 2017 / Published: 19 May 2017
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Abstract
Crude oil is generally produced with water, and the water cut produced by oil wells is increasingly common over their lifetime, so it is inevitable to create emulsions during oil production. However, the formation of emulsions presents a costly problem in surface process
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Crude oil is generally produced with water, and the water cut produced by oil wells is increasingly common over their lifetime, so it is inevitable to create emulsions during oil production. However, the formation of emulsions presents a costly problem in surface process particularly, both in terms of transportation energy consumption and separation efficiency. To deal with the production and operational problems which are related to crude oil emulsions, especially to ensure the separation and transportation of crude oil-water systems, it is necessary to better understand the emulsification mechanism of crude oil under different conditions from the aspects of bulk and interfacial properties. The concept of shearing energy was introduced in this study to reveal the driving force for emulsification. The relationship between shearing stress in the flow field and interfacial tension (IFT) was established, and the correlation between shearing energy and interfacial Gibbs free energy was developed. The potential of the developed correlation model was validated using the experimental and field data on emulsification behavior. It was also shown how droplet deformation could be predicted from a random deformation degree and orientation angle. The results indicated that shearing energy as the energy produced by shearing stress working in the flow field is the driving force activating the emulsification behavior. The deformation degree and orientation angle of dispersed phase droplet are associated with the interfacial properties, rheological properties and the experienced turbulence degree. The correlation between shearing stress and IFT can be quantified if droplet deformation degree vs. droplet orientation angle data is available. When the water cut is close to the inversion point of waxy crude oil emulsion, the interfacial Gibbs free energy change decreased and the shearing energy increased. This feature is also presented in the special regions where the suddenly changed flow field can be formed. Hence, the shearing energy is an effective form that can show the contribution of kinetic energy for the oil-water mixtures to interfacial Gibbs free energy in emulsification process, and the emulsification mechanism of waxy crude oil-water emulsions was further explained from the theoretical level. Full article
(This article belongs to the Special Issue Oil and Gas Engineering)
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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
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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 An Innovative Adaptive Control System to Regulate Microclimatic Conditions in a Greenhouse
Energies 2017, 10(5), 722; doi:10.3390/en10050722
Received: 13 March 2017 / Revised: 1 May 2017 / Accepted: 15 May 2017 / Published: 19 May 2017
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Abstract
In the recent past home automation has been expanding its objectives towards new solutions both inside the smart home and in its outdoor spaces, where several new technologies are available. This work has developed an approach to integrate intelligent microclimatic greenhouse control into
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In the recent past home automation has been expanding its objectives towards new solutions both inside the smart home and in its outdoor spaces, where several new technologies are available. This work has developed an approach to integrate intelligent microclimatic greenhouse control into integrated home automation. Microclimatic control of greenhouses is a critical issue in agricultural practices, due to often common sudden daily variation of climatic conditions, and to its potentially detrimental effect on plant growth. A greenhouse is a complex thermodynamic system where indoor temperature and relative humidity have to be closely monitored to facilitate plant growth and production. This work shows an adaptive control system tailored to regulate microclimatic conditions in a greenhouse, by using an innovative combination of soft computing applications. In particular, a neural network solution has been proposed in order to forecast the climatic behavior of greenhouse, while a parallel fuzzy scheme approach is carried out in order to adjust the air speed of fan-coil and its temperature. The proposed combined approach provides a better control of greenhouse climatic conditions due to the system’s capability to base instantaneous solutions both on real measured variables and on forecasted climatic change. Several simulation campaigns were carried out to perform accurate neural network and fuzzy schemes, aimed at obtaining respectively a minimum forecasted error value and a more appropriate fuzzification and de-fuzzification process. A Matlab/Simulink solution implemented with a combined approach and its relevant obtained performance is also shown in present study, demonstrating that through controlled parameters it will be possible to maintain a better level of indoor climatic conditions. In the present work we prove how with a forecast of outside temperature at the next time-instant and rule-based controller monitoring of cooling or heating air temperatures and air velocities of devices that regulate the indoor micro-climate inside, a better adjustment of the conditions of comfort for crops is achievable. Full article
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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
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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 A Study on the Conduction Mechanism and Evaluation of the Comprehensive Efficiency of Photovoltaic Power Generation in China
Energies 2017, 10(5), 723; doi:10.3390/en10050723
Received: 25 February 2017 / Revised: 26 March 2017 / Accepted: 20 April 2017 / Published: 19 May 2017
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Abstract
In the context of the global potential energy crisis and aggravating regional environmental pollution, Chinese photovoltaic power generation still faces the key problems of sustainable development, even given its favorable background in large-scale exploitation. Scientific evaluation of the comprehensive efficiency of photovoltaic power
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In the context of the global potential energy crisis and aggravating regional environmental pollution, Chinese photovoltaic power generation still faces the key problems of sustainable development, even given its favorable background in large-scale exploitation. Scientific evaluation of the comprehensive efficiency of photovoltaic power generation is of great significance because it will improve investment decision-making and enhance management level, evaluate the development conditions of photovoltaic power generation and then promote sustainable development capability. The concept of “comprehensive efficiency” is proposed in this paper on the basis of the resource development of solar energy and exploitation of photovoltaic power generation. A system dynamics model is used to study the conduction mechanism of the comprehensive efficiency of photovoltaic power generation. This paper collects data from 2005 to 2015 as research models, establishes the evaluation model of the comprehensive efficiency of photovoltaic power generation and conducts empirical analysis based on a super-efficient data envelopment analysis (SE-DEA) model. With the evaluation results, this paper puts forward political suggestions as to the optimization of the comprehensive efficiency of photovoltaic power generation. The research results may provide policy-oriented references on the sustainable development of photovoltaic power generation and give theoretical guidance on the scientific evaluation and diagnosis of photovoltaic power generation efficiency. Full article
(This article belongs to the Section Energy Sources)
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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
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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 Anomaly Detection in Gas Turbine Fuel Systems Using a Sequential Symbolic Method
Energies 2017, 10(5), 724; doi:10.3390/en10050724
Received: 12 April 2017 / Revised: 12 May 2017 / Accepted: 14 May 2017 / Published: 20 May 2017
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Abstract
Anomaly detection plays a significant role in helping gas turbines run reliably and economically. Considering the collective anomalous data and both sensitivity and robustness of the anomaly detection model, a sequential symbolic anomaly detection method is proposed and applied to the gas turbine
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Anomaly detection plays a significant role in helping gas turbines run reliably and economically. Considering the collective anomalous data and both sensitivity and robustness of the anomaly detection model, a sequential symbolic anomaly detection method is proposed and applied to the gas turbine fuel system. A structural Finite State Machine is used to evaluate posterior probabilities of observing symbolic sequences and the most probable state sequences they may locate. Hence an estimation-based model and a decoding-based model are used to identify anomalies in two different ways. Experimental results indicate that both models have both ideal performance overall, but the estimation-based model has a strong robustness ability, whereas the decoding-based model has a strong accuracy ability, particularly in a certain range of sequence lengths. Therefore, the proposed method can facilitate well existing symbolic dynamic analysis- based anomaly detection methods, especially in the gas turbine domain. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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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 A Switching Frequency Optimized Space Vector Pulse Width Modulation (SVPWM) Scheme for Cascaded Multilevel Inverters
Energies 2017, 10(5), 725; doi:10.3390/en10050725
Received: 21 March 2017 / Revised: 3 May 2017 / Accepted: 12 May 2017 / Published: 21 May 2017
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Abstract
This paper presents a novel switching frequency optimized space vector pulse width modulation (SVPWM) scheme for cascaded multilevel inverters. The proposed SVPWM is developed in a α′β′ coordinate system, in which the voltage vectors have only integer entries and the absolute increment of
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This paper presents a novel switching frequency optimized space vector pulse width modulation (SVPWM) scheme for cascaded multilevel inverters. The proposed SVPWM is developed in a α′β′ coordinate system, in which the voltage vectors have only integer entries and the absolute increment of coordinate values between adjacent vectors is equal to dc-bus voltage of power cells (1 pu). The new SVPWM scheme is built with three categories of switching paths. During each switching path, the change of one phase voltage is limited in 1 pu. This contributes to decrease the number of commutations of switches. The proposed SVPWM scheme is validated on a 7-level cascaded inverter and the results show that it significantly outperforms traditional SVPWM schemes in terms of decreasing the number of switch commutations. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Effects of Support Structures in an LES Actuator Line Model of a Tidal Turbine with Contra-Rotating Rotors
Energies 2017, 10(5), 726; doi:10.3390/en10050726
Received: 30 March 2017 / Revised: 11 May 2017 / Accepted: 12 May 2017 / Published: 19 May 2017
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Abstract
Computational fluid dynamics is used to study the impact of the support structure of a tidal turbine on performance and the downstream wake characteristics. A high-fidelity computational model of a dual rotor, contra-rotating tidal turbine in a large channel domain is presented, with
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Computational fluid dynamics is used to study the impact of the support structure of a tidal turbine on performance and the downstream wake characteristics. A high-fidelity computational model of a dual rotor, contra-rotating tidal turbine in a large channel domain is presented, with turbulence modelled using large eddy simulation. Actuator lines represent the turbine blades, permitting the analysis of transient flow features and turbine diagnostics. The following four cases are considered: the flow in an unexploited, empty channel; flow in a channel containing the rotors; flow in a channel containing the support structure; and flow in a channel with both rotors and support structure. The results indicate that the support structure contributes significantly to the behaviour of the turbine and to turbulence levels downstream, even when the rotors are upstream. This implies that inclusion of the turbine structure, or some parametrisation thereof, is a prerequisite for the realistic prediction of turbine performance and reliability, particularly for array layouts where wake effects become significant. Full article
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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 Simulation Modeling Method and Experimental Investigation on the Uniflow Scavenging System of an Opposed-Piston Folded-Cranktrain Diesel Engine
Energies 2017, 10(5), 727; doi:10.3390/en10050727
Received: 20 December 2016 / Revised: 3 May 2017 / Accepted: 18 May 2017 / Published: 20 May 2017
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Abstract
The scavenging process for opposed-piston folded-cranktrain (OPFC) diesel engines can be described by the time evolution of the in-cylinder and exhaust chamber residual gas rates. The relation curve of in-cylinder and exhaust chamber residual gas rate is called scavenging profile, which is calculated
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The scavenging process for opposed-piston folded-cranktrain (OPFC) diesel engines can be described by the time evolution of the in-cylinder and exhaust chamber residual gas rates. The relation curve of in-cylinder and exhaust chamber residual gas rate is called scavenging profile, which is calculated through the changes of in-cylinder and exhaust chamber gas compositions determined by computational fluid dynamics (CFD) simulation. The scavenging profile is used to calculate the scavenging process by mono-dimensional (1D) simulation. The tracer gas method (TGM) is employed to validate the accuracy of the scavenging profile. At the same time, the gas exchange performance under different intake and exhaust state parameters was examined based on the TGM. The results show that the scavenging process from 1D simulation and experiment match well, which means the scavenging model obtained by CFD simulation performs well and validation of its effectiveness by TGM is possible. The difference between intake and exhaust pressure has a significant positive effect on the gas exchange performance and trapped gas mass, but the pressure difference has little effect on the scavenging efficiency and the trapped air mass if the delivery ratio exceeds 1.4. Full article
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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 A Feasibility Study on Hydrate-Based Technology for Transporting CO2 from Industrial to Agricultural Areas
Energies 2017, 10(5), 728; doi:10.3390/en10050728
Received: 15 April 2017 / Revised: 16 May 2017 / Accepted: 17 May 2017 / Published: 20 May 2017
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Abstract
Climate change caused by global warming has become a serious issue in recent years. The main purpose of this study was to evaluate the effectiveness of the above system to quantitatively supply CO2 or CO2 hydrate from industrial to agricultural areas.
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Climate change caused by global warming has become a serious issue in recent years. The main purpose of this study was to evaluate the effectiveness of the above system to quantitatively supply CO2 or CO2 hydrate from industrial to agricultural areas. In this analysis, several transportation methods, namely, truck, hydrate tank lorry, and pipeline, were considered. According to this analysis, the total CO2 supply costs including transportation ranged from 15 to 25 yen/kg-CO2 when the transportation distance was 50 km or less. The cost of the hydrate-based method increased with the transport distance in contrast to the liquefied CO2 approach. However, the technology of supplying CO2 hydrate had merit by using a local cooling technique for cooling specific parts of agricultural products. Full article
(This article belongs to the Special Issue Methane Hydrate Research and Development)
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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 Incorporating Charging/Discharging Strategy of Electric Vehicles into Security-Constrained Optimal Power Flow to Support High Renewable Penetration
Energies 2017, 10(5), 729; doi:10.3390/en10050729
Received: 18 January 2017 / Revised: 27 April 2017 / Accepted: 28 April 2017 / Published: 20 May 2017
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Abstract
This research aims to improve the operational efficiency and security of electric power systems at high renewable penetration by exploiting the envisioned controllability or flexibility of electric vehicles (EVs); EVs interact with the grid through grid-to-vehicle (G2V) and vehicle-to-grid (V2G) services to ensure
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This research aims to improve the operational efficiency and security of electric power systems at high renewable penetration by exploiting the envisioned controllability or flexibility of electric vehicles (EVs); EVs interact with the grid through grid-to-vehicle (G2V) and vehicle-to-grid (V2G) services to ensure reliable and cost-effective grid operation. This research provides a computational framework for this decision-making process. Charging and discharging strategies of EV aggregators are incorporated into a security-constrained optimal power flow (SCOPF) problem such that overall energy cost is minimized and operation within acceptable reliability criteria is ensured. Particularly, this SCOPF problem has been formulated for Jeju Island in South Korea, in order to lower carbon emissions toward a zero-carbon island by, for example, integrating large-scale renewable energy and EVs. On top of conventional constraints on the generators and line flows, a unique constraint on the system inertia constant, interpreted as the minimum synchronous generation, is considered to ensure grid security at high renewable penetration. The available energy constraint of the participating EV associated with the state-of-charge (SOC) of the battery and market price-responsive behavior of the EV aggregators are also explored. Case studies for the Jeju electric power system in 2030 under various operational scenarios demonstrate the effectiveness of the proposed method and improved operational flexibility via controllable EVs. Full article
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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 A New Methodology for Building-Up a Robust Model for Heliostat Field Flux Characterization
Energies 2017, 10(5), 730; doi:10.3390/en10050730
Received: 2 March 2017 / Revised: 9 May 2017 / Accepted: 17 May 2017 / Published: 20 May 2017
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Abstract
The heliostat field of solar central receiver systems (SCRS) is formed by hundreds, even thousands, of working heliostats. Their adequate configuration and control define a currently active research line. For instance, automatic aiming methodologies of existing heliostat fields are being widely studied. In
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The heliostat field of solar central receiver systems (SCRS) is formed by hundreds, even thousands, of working heliostats. Their adequate configuration and control define a currently active research line. For instance, automatic aiming methodologies of existing heliostat fields are being widely studied. In general, control techniques require a model of the system to be controlled in order to obtain an estimation of its states. However, this kind of information may not be available or may be hard to obtain for every plant to be studied. In this work, an innovative methodology for data-based analytical heliostat field characterization is proposed and described. It formalizes the way in which the behavior of a whole field can be derived from the study of its more descriptive parts. By successfully applying this procedure, the instantaneous behavior of a field could be expressed by a reduced set of expressions that can be seen as a field descriptor. It is not intended to replace real experimentation but to enhance researchers’ autonomy to build their own reliable and portable synthetic datasets at preliminary stages of their work. The methodology proposed in this paper is successfully applied to a virtual field. Only 30 heliostats out of 541 were studied to characterize the whole field. For the validation set, the average difference in power between the flux maps directly fitted from the measured information and the estimated ones is only of 0.67% (just 0.10946 kW/m2 of root-mean-square error, on average, between them). According to these results, a consistent field descriptor can be built by applying the proposed methodology, which is hence ready for use. Full article
(This article belongs to the Section Electrical Power and Energy System)
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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
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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 Fast Calculation Model and Theoretical Analysis of Rotor Unbalanced Magnetic Pull for Inter-Turn Short Circuit of Field Windings of Non-Salient Pole Generators
Energies 2017, 10(5), 732; doi:10.3390/en10050732
Received: 27 March 2017 / Revised: 14 May 2017 / Accepted: 16 May 2017 / Published: 20 May 2017
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Abstract
Inter-turn short circuit of field windings (ISCFW) may cause the field current of a generator to increase, output reactive power to decrease, and unit vibration to intensify, seriously affecting its safe and stable operation. Full integration of mechanical and electrical characteristics can improve
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Inter-turn short circuit of field windings (ISCFW) may cause the field current of a generator to increase, output reactive power to decrease, and unit vibration to intensify, seriously affecting its safe and stable operation. Full integration of mechanical and electrical characteristics can improve the sensitivity of online monitoring, and detect the early embryonic period fault of small turns. This paper studies the calculations and variations of unbalanced magnetic pull (UMP), of which the excitation source of rotor vibration is the basis and key to online fault monitoring. In grid load operation, ISCFW are first calculated with the multi-loop method, so as to obtain the numerical solutions of the stator and the rotor currents during the fault. Next, the air-gap magnetic field of the ISCFW is analyzed according to the actual composition modes of the motor loops in the fault, so as to obtain the analytic expressions of the air-gap magnetic motive force (MMF) and magnetic density. The UMP of the rotor is obtained by solving the integral of the Maxwell stress. The correctness of the electric quantity calculation is verified by the ISCFW experiment, conducted in a one pair-pole non-salient pole model machine. On this basis, comparing the simulation analysis with the calculation results of the model in this paper not only verifies the accuracy of the electromagnetic force calculation, but also proves that the latter has the advantages of a short time consumption and high efficiency. Finally, the influencing factors and variation law of UMP are analyzed by means of an analytic model. This develops a base for the online monitoring of ISCFW with the integration of mechanical and electrical information. Full article
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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 Modeling and Optimization of a CoolingTower-Assisted Heat Pump System
Energies 2017, 10(5), 733; doi:10.3390/en10050733
Received: 15 April 2017 / Revised: 16 May 2017 / Accepted: 17 May 2017 / Published: 20 May 2017
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Abstract
To minimize the total energy consumption of a cooling tower-assisted heat pump (CTAHP) system in cooling mode, a model-based control strategy with hybrid optimization algorithm for the system is presented in this paper. An existing experimental device, which mainly contains a closed wet
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To minimize the total energy consumption of a cooling tower-assisted heat pump (CTAHP) system in cooling mode, a model-based control strategy with hybrid optimization algorithm for the system is presented in this paper. An existing experimental device, which mainly contains a closed wet cooling tower with counter flow construction, a condenser water loop and a water-to-water heat pump unit, is selected as the study object. Theoretical and empirical models of the related components and their interactions are developed. The four variables, viz. desired cooling load, ambient wet-bulb temperature, temperature and flow rate of chilled water at the inlet of evaporator, are set to independent variables. The system power consumption can be minimized by optimizing input powers of cooling tower fan, spray water pump, condenser water pump and compressor. The optimal input power of spray water pump is determined experimentally. Implemented on MATLAB, a hybrid optimization algorithm, which combines the Limited memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm with the greedy diffusion search (GDS) algorithm, is incorporated to solve the minimization problem of energy consumption and predict the system’s optimal set-points under quasi-steady-state conditions. The integrated simulation tool is validated against experimental data. The results obtained demonstrate the proposed operation strategy is reliable, and can save energy by 20.8% as compared to an uncontrolled system under certain testing conditions. Full article
(This article belongs to the Special Issue Solar Energy Application in Buildings)
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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 Analysis of Development Pattern of a Water-Flowing Fissure Zone in Shortwall Block Mining
Energies 2017, 10(5), 734; doi:10.3390/en10050734
Received: 19 April 2017 / Revised: 8 May 2017 / Accepted: 17 May 2017 / Published: 20 May 2017
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Abstract
In order to effectively recover the residual coal resources, such as coal pillars and irregular coal blocks induced by large-scale extensive mining, in this study, we proposed a shortwall block mining (SBM) technology and examined the development pattern of the water-flowing fissure zone
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In order to effectively recover the residual coal resources, such as coal pillars and irregular coal blocks induced by large-scale extensive mining, in this study, we proposed a shortwall block mining (SBM) technology and examined the development pattern of the water-flowing fissure zone (WFZ) in the overlying strata during the SBM process. By analyzing the overlying rocks’ movement rules in SBM, the main controlling factors affecting the development of the height of the water-flowing fissure zone (HWFZ) determined are as follows: mining height, block length, and the width of the protective coal pillar among the blocks. Moreover, based on the elastic foundation beam theory, the mechanical model for the calculation of HWFZ in SBM was established. Based on the first strength theory, the calculation formula of the development HWFZ was derived. Using this model, the calculated HWFZ after SBM was 50.3 m, whereas the measured heights of the leakage of drilling washing fluid were 47.98 and 50.06 m, respectively. The calculated values almost fit well with the field-measured data, verifying the reliability of the proposed mechanical model. The results of this study can provide a significant reference for enhancing the recovery ratio of coal resources and optimizing water protection mining theory. 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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