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Energies, Volume 13, Issue 3 (February-1 2020) – 266 articles

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Cover Story (view full-size image) Storage technology is one the main elements that supports the variable and intermittent energy [...] Read more.
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Open AccessArticle
Numerical Investigations of a Counter-Current Moving Bed Reactor for Thermochemical Energy Storage at High Temperatures
Energies 2020, 13(3), 772; https://doi.org/10.3390/en13030772 - 10 Feb 2020
Viewed by 285
Abstract
High temperature storage is a key factor for compensating the fluctuating energy supply of solar thermal power plants, and thus enables renewable base load power. In thermochemical energy storage, the thermal energy is stored as the reaction enthalpy of a chemically reversible gas-solid [...] Read more.
High temperature storage is a key factor for compensating the fluctuating energy supply of solar thermal power plants, and thus enables renewable base load power. In thermochemical energy storage, the thermal energy is stored as the reaction enthalpy of a chemically reversible gas-solid reaction. Metal oxides are suitable candidates for thermochemical energy storage for solar thermal power plants, due to their high reaction temperatures and use of oxygen as a gaseous reaction partner. However, it is crucial to extract both sensible and thermochemical energy at these elevated temperatures to boost the overall system efficiency. Therefore, this study focuses on the combined extraction of thermochemical and sensible energy from a metal oxide and its effects on thermal power and energy density during discharging. A counter-current moving bed, based on manganese-iron-oxide, was investigated with a transient, one-dimensional model using the finite element method. A nearly isothermal temperature distribution along the bed height was formed, as long as the gas flow did not exceed a tipping point. A maximal energy density of 933 kJ/kg was achieved, when ( Mn , Fe ) 3 O 4 was oxidized and cooled from 1050 ° C to 300 ° C . However, reaction kinetics can limit the thermal power and energy density. To avoid this drawback, a moving bed reactor based on the investigated manganese-iron oxide should combine direct and indirect heat transfer to overcome kinetic limitations. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessArticle
Coordinated Operation of Energy Storage Systems for Distributed Harmonic Compensation in Microgrids
Energies 2020, 13(3), 771; https://doi.org/10.3390/en13030771 - 10 Feb 2020
Viewed by 255
Abstract
Energy storage systems (ESSs) bring various opportunities for a more reliable and flexible operation of microgrids (MGs). Among them, energy arbitrage and ancillary services are the most investigated application of ESSs. Furthermore, it has been shown that some other services could also be [...] Read more.
Energy storage systems (ESSs) bring various opportunities for a more reliable and flexible operation of microgrids (MGs). Among them, energy arbitrage and ancillary services are the most investigated application of ESSs. Furthermore, it has been shown that some other services could also be provided by ESSs such as power quality (PQ) improvements. This issue could be more challenging in MGs with widespread nonlinear loads injecting harmonic currents to the MG. In this paper, the feasibility of ESSs to act as coordinated active harmonic filters (AHF) for distributed compensation was investigated. An optimization model was proposed for the coordination of the harmonic compensation activities of ESSs. The model takes into account the various technical and systematic constraints to economically determine the required reference currents of various AHFs. Simulation cases showed the performance of the proposed model for enhancing the harmonic filtering capability of the MG, reduction in the compensation cost, and more flexibility of the distributed harmonic compensation schemes. It was also shown that ESS activities in harmonic compensation do not have much of an effect on the ESSs revenue from energy arbitrage. Hence, it could make ESSs more justifiable for use in MGs. Full article
(This article belongs to the Special Issue Distributed Energy Storage Devices in Smart Grids)
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Open AccessArticle
Direct Voltage Control of a Doubly Fed Induction Generator by Means of Optimal Strategy
Energies 2020, 13(3), 770; https://doi.org/10.3390/en13030770 - 10 Feb 2020
Viewed by 242
Abstract
The major objective of the investigation reported in this article is to demonstrate the feasibility of controlling a Doubly Fed Induction Generator actuating directly on the rotor voltage produced by the Rotor Side Converter, as its reference value may be determined analytically, after [...] Read more.
The major objective of the investigation reported in this article is to demonstrate the feasibility of controlling a Doubly Fed Induction Generator actuating directly on the rotor voltage produced by the Rotor Side Converter, as its reference value may be determined analytically, after definition of the control objective. Two usual objectives are here considered: maximum power extraction from wind (MPPT) and stator reactive power equal to zero. This last objective defines the reference slip to be considered in the formulation of developed power that, jointly with the reactive power equation, forms the system to calculate the rotor reference voltages. The process is completed by specifying the desired dynamical response. Thus, the angular velocity of the rotor should quickly reach its reference value, which requires maximal power acceleration at the beginning, but respects the restriction that no overshoot should be allowed. This is achieved by means of a constrained optimization process solved in real time. Following recent trends, only measurements obtained from stator (voltages and currents) sensors are used. This way, angular velocity and rotor currents are estimated in real time. An algorithm for inductance estimation is also included, which prevents deviations of nominal values that could lead to false reference voltages. Full article
(This article belongs to the Special Issue Optimal Control and Nonlinear Dynamics in Electrical Power Systems)
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Open AccessArticle
Energy Footprint of Mechanized Agricultural Operations
Energies 2020, 13(3), 769; https://doi.org/10.3390/en13030769 - 10 Feb 2020
Viewed by 248
Abstract
The calculation of the energy cost of a cultivation is a determining factor in the overall assessment of agricultural sustainability. Most studies mainly examine the entire life cycle of the operation, considering reference values and reference databases for the determination of the machinery [...] Read more.
The calculation of the energy cost of a cultivation is a determining factor in the overall assessment of agricultural sustainability. Most studies mainly examine the entire life cycle of the operation, considering reference values and reference databases for the determination of the machinery contribution to the overall energy balance. This study presents a modelling methodology for the precise calculation of the energy cost of performing an agricultural operation. The model incorporates operational management into the calculation, while simultaneously considering the commercially available machinery (implements and tractors). As a case study, the operation of tillage was used considering both primary and secondary tillage (moldboard plow and field cultivator, respectively). The results show the importance of including specific operation parameters and the available machinery as part of determining the accurate total energy consumption, even though the field size and available time do not have a significant effect. Full article
(This article belongs to the Special Issue Supply Chain Management for Bioenergy and Bioresources)
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Open AccessArticle
Spatio-Temporal Assessment of Climate Change Impact on Wave Energy Resources Using Various Time Dependent Criteria
Energies 2020, 13(3), 768; https://doi.org/10.3390/en13030768 - 10 Feb 2020
Viewed by 318
Abstract
The wave energy resources in the Indian Ocean can be considered as a potential alternative to fossil fuels. However, the wave energy resources are subject to short-term fluctuations and long-term changes due to climate change. Hence, considering sustainable development goals, it is necessary [...] Read more.
The wave energy resources in the Indian Ocean can be considered as a potential alternative to fossil fuels. However, the wave energy resources are subject to short-term fluctuations and long-term changes due to climate change. Hence, considering sustainable development goals, it is necessary to assess both short-term (intra-annual) variation and long-term change. For this purpose, the simulated wave characteristics were utilized, and the wave power and its variation and change were analyzed in the whole domain and nearshore areas. The short-term fluctuation was investigated in terms of monthly and seasonal variations and the future change was discussed based on absolute and relative changes. Both analyses show that the Southern Indian Ocean, despite experiencing extreme events and having higher wave energy potential, is more stable in terms of both short and long-term variation and change. The assessment of the total and exploitable storages of wave energy and their future change revealed the higher potential and higher stability of the nearshores of the Southern Indian Ocean. It can be concluded that based on various factors, the south of Sri Lanka, Horn of Africa, southeast Africa, south of Madagascar and Reunion and Mauritius islands are the most suitable areas for wave energy extraction. Full article
(This article belongs to the Special Issue Wave and Tidal Energy 2020)
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Open AccessArticle
Accurate Location of Faults in Transmission Lines by Compensating for the Electrical Distance
Energies 2020, 13(3), 767; https://doi.org/10.3390/en13030767 - 10 Feb 2020
Viewed by 230
Abstract
Accurately locating faults is quite important, especially when the geographical environment is complicated. If the exact location of the fault is not given, wrong route would be chosen, which will greatly slow down repair. This paper proposes an improved traveling wave method by [...] Read more.
Accurately locating faults is quite important, especially when the geographical environment is complicated. If the exact location of the fault is not given, wrong route would be chosen, which will greatly slow down repair. This paper proposes an improved traveling wave method by compensating the electrical distance of transmission lines. The catenary model is constructed that considers parameters of the tower and the actual temperature. The actual line length is also derived by the catenary model. A 500 kV transmission line model is established by PSCAD/EMTDC. Various fault simulations are conducted and the results demonstrate that the presented method effectively reduces the error ratio of faulty segment positioning and locates faults with high accuracy. Full article
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Open AccessArticle
Experimental, Numerical and Application Analysis of Hydrokinetic Turbine Performance with Fixed Rotating Blades
Energies 2020, 13(3), 766; https://doi.org/10.3390/en13030766 - 09 Feb 2020
Viewed by 316
Abstract
In this study, a hydrokinetic turbine is designed for the high-altitude regions where local electricity network lines are difficult to reach. If there was a stream flow around, electricity production could be possible and necessary because of environmental reasons. The performance of the [...] Read more.
In this study, a hydrokinetic turbine is designed for the high-altitude regions where local electricity network lines are difficult to reach. If there was a stream flow around, electricity production could be possible and necessary because of environmental reasons. The performance of the hydrokinetic turbine was investigated experimentally and numerically. The numerical analyses of the turbine system were performed via MATLAB/Simulink version R2014a. Except power-based performance characteristics, efficiency of the system in terms of installation and necessary investment costs were also investigated. It is calculated that the system to be established on a river with a water flow rate of 30 m3/h will meet the investment cost in approximately 8 years. Full article
(This article belongs to the Section Energy and Environment)
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Open AccessArticle
Investigation of Start-Up Characteristics of Thermosyphons Modified with Different Hydrophilic and Hydrophobic Inner Surfaces
Energies 2020, 13(3), 765; https://doi.org/10.3390/en13030765 - 09 Feb 2020
Viewed by 274
Abstract
In this paper, the influence of wettability properties on the start-up characteristics of two-phase closed thermosyphons (TPCTs) is investigated. Chemical coating and etching techniques are performed to prepare the surfaces with different wettabilities that is quantified in the form of the contact angle [...] Read more.
In this paper, the influence of wettability properties on the start-up characteristics of two-phase closed thermosyphons (TPCTs) is investigated. Chemical coating and etching techniques are performed to prepare the surfaces with different wettabilities that is quantified in the form of the contact angle (CA). The 12 TPCTs are processed including the same CA and a different CA combination on the inner surfaces inside both the evaporator and the condenser sections. For TPCTs with the same wettability properties, the introduction of hydrophilic properties inside the evaporator section not only significantly reduces the start-up time but also decreases the start-up temperature. For example, the start-up time of a TPCT with CA = 28° at 40 W, 60 W and 80 W is 46%, 50% and 55% shorter than that of a TPCT with a smooth surface and the wall superheat degrees is 55%, 39% and 28% lower, respectively. For TPCTs with combined hydrophilic and hydrophobic properties, the start-up time spent on the evaporator section with hydrophilic properties is shorter than that of the hydrophobic evaporator section and the smaller CA on the condenser section shows better results. The start-up time of a TPCT with CA = 28° on the evaporator section and CA = 105° on the condenser section has the best start-up process at 40 W, 60 W and 80 W which is 14%, 22% and 26% shorter than that of a TPCT with smooth surface. Thus, the hydrophilic and hydrophobic modifications play a significant role in promoting the start-up process of a TPCT. Full article
(This article belongs to the Special Issue Heat Transfer in Energy Conversion Systems)
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Open AccessArticle
Effects of Input Voltage and Freestream Velocity on Active Flow Control of Passage Vortex in a Linear Turbine Cascade Using Dielectric Barrier Discharge Plasma Actuator
Energies 2020, 13(3), 764; https://doi.org/10.3390/en13030764 - 09 Feb 2020
Viewed by 304
Abstract
Passage vortex exists as one of the typical secondary flows in turbomachines and generates a significant total pressure loss and degrades the aerodynamic performance. Herein, a dielectric barrier discharge (DBD) plasma actuator was utilized for an active flow control of the passage vortex [...] Read more.
Passage vortex exists as one of the typical secondary flows in turbomachines and generates a significant total pressure loss and degrades the aerodynamic performance. Herein, a dielectric barrier discharge (DBD) plasma actuator was utilized for an active flow control of the passage vortex in a linear turbine cascade. The plasma actuator was installed on the endwall, 10 mm upstream from the leading edge of the turbine cascade. The freestream velocity at the outlet of the linear turbine cascade was set to range from UFS,out = 2.4 m/s to 25.2 m/s, which corresponded to the Reynolds number ranging from Reout = 1.0 × 104 to 9.9 × 104. The two-dimensional velocity field at the outlet of the linear turbine cascade was experimentally analyzed by particle image velocimetry (PIV). At lower freestream velocity conditions, the passage vortex was almost negligible as a result of the plasma actuator operation (UPA,max/UFS,out = 1.17). Although the effect of the jet induced by the plasma actuator weakened as the freestream velocity increased, the magnitude of the peak vorticity was reduced under all freestream velocity conditions. Even at the highest freestream velocity condition of UFS,out = 25.2 m/s, the peak value of the vorticity was reduced approximately 17% by the plasma actuator operation at VAC = 15 kVp-p (UPA,max/UFS,out = 0.18). Full article
(This article belongs to the Special Issue Control of Dynamic Flow Fields)
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Open AccessArticle
Enzymatic Saccharification of Laminaria japonica by Cellulase for the Production of Reducing Sugars
Energies 2020, 13(3), 763; https://doi.org/10.3390/en13030763 - 09 Feb 2020
Viewed by 243
Abstract
Enzymatic saccharification of Laminaria japonica seaweed biomass was optimized by four independent factors (enzyme dose, hydrolysis time, pH, and temperature) using response surface methodology (RSM). To confirm the significance of the quadratic model, an analysis of variance (ANOVA) was performed, and the F [...] Read more.
Enzymatic saccharification of Laminaria japonica seaweed biomass was optimized by four independent factors (enzyme dose, hydrolysis time, pH, and temperature) using response surface methodology (RSM). To confirm the significance of the quadratic model, an analysis of variance (ANOVA) was performed, and the F-value of 8.76 showed that the regression model was highly significant (≤0.1%). In the accuracy study, average recoveries were in the range of 97.00% to 98.32%. The optimum experimental conditions were an enzyme dose of 8.2%, a hydrolysis time of 26 h, a pH of 4.1, and a temperature of 43 °C. Temperature was the most important factor in the enzymatic saccharification. A relatively low temperature and short hydrolysis time were shown to improve the yield of reducing sugars. Full article
(This article belongs to the Section Bio-Energy)
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Open AccessArticle
Numerical Simulations on the Application of a Closed-Loop Lake Water Heat Pump System in the Lake Soyang, Korea
Energies 2020, 13(3), 762; https://doi.org/10.3390/en13030762 - 09 Feb 2020
Viewed by 249
Abstract
A lake is one of the geothermal energy sources to meet increasing demands for renewable energy use. In this study, a series of numerical modeling was performed to evaluate the applicability of a close-loop lake water heat pump (LWHP) system in Lake Soyang, [...] Read more.
A lake is one of the geothermal energy sources to meet increasing demands for renewable energy use. In this study, a series of numerical modeling was performed to evaluate the applicability of a close-loop lake water heat pump (LWHP) system in Lake Soyang, Korea. A non-isothermal pipe flow model was used to simulate the flow and heat transfer processes occurring in the LWHP system with the main pipe and several helical tubes for heat exchange. Based on the temperature data measured in the Lake Soyang for 4 years, the installation depth and the number of helical tubes were determined sequentially, and the sensitivities of additional installation and operation factors on the system performance were analyzed. Assuming a mild current in the lake, the installation and operation conditions for the efficient operation of the system were suggested as follows: The installation of 16 helical tubes at 50 m deep, the circulation rates of heat-carrier fluid of 189.3 L/min, the inner diameter of tubes of 32 mm, and the wall thickness and thermal conductivity of 2.9 mm and 0.4 W/mK, respectively. Considering many lakes and reservoirs in Korea, the closed-loop LWHP system would be a viable renewable energy application. Full article
(This article belongs to the Section Geo-Energy)
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Open AccessArticle
Triclosan Removal in Microbial Fuel Cell: The Contribution of Adsorption and Bioelectricity Generation
Energies 2020, 13(3), 761; https://doi.org/10.3390/en13030761 - 09 Feb 2020
Viewed by 272
Abstract
The occurrence of Triclosan (TCS) in natural aquatic systems has been drawing increasing attention due to its endocrine-disruption effects as well as for the development of antibiotic resistances. Wastewater discharge is the main source of water contamination by TCS. In this study, the [...] Read more.
The occurrence of Triclosan (TCS) in natural aquatic systems has been drawing increasing attention due to its endocrine-disruption effects as well as for the development of antibiotic resistances. Wastewater discharge is the main source of water contamination by TCS. In this study, the removal of TCS in microbial fuel cells (MFCs) was carefully investigated. A 94% removal of TCS was observed with 60 mV electricity generation as well as a slight drop in pH. In addition, we found that adsorption also contributed to the removal of TCS in aqueous solution and 21.73% and 19.92% of the total mass was adsorbed to the inner wall of the reactor and to the electrode, respectively. The results revealed that the attenuation of TCS depends on both biodegradation and physical adsorption in the anode chamber. Thus, the outcomes of our study provide a better understanding of the TCS removal mechanism in MFCs. Full article
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Open AccessArticle
Modified Slot Opening for Reducing Shaft-to-Frame Voltage of AC Motors
Energies 2020, 13(3), 760; https://doi.org/10.3390/en13030760 - 09 Feb 2020
Viewed by 194
Abstract
This paper presents a method to reduce the winding-to-rotor capacitance of electrical machines for the purpose of suppressing shaft-to-frame voltage, which causes reliability issues, such as electromagnetic interference (EMI) and bearing current. The proposed method is based on the modification of slot opening [...] Read more.
This paper presents a method to reduce the winding-to-rotor capacitance of electrical machines for the purpose of suppressing shaft-to-frame voltage, which causes reliability issues, such as electromagnetic interference (EMI) and bearing current. The proposed method is based on the modification of slot opening shape of the stator core, including the variation of slot opening width and the use of oblique slot opening. For the verification of the suggested method, six different slot opening shapes, including a reference design, are analyzed and compared using finite element analysis, and the results show that the proposed method can reduce the shaft-to-frame voltage by 98%, compared to the reference design. Full article
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Open AccessReview
Review of Design and Modeling of Regenerative Heat Exchangers
Energies 2020, 13(3), 759; https://doi.org/10.3390/en13030759 - 09 Feb 2020
Viewed by 249
Abstract
Heat regenerators are simple devices for heat transfer, but their proper design is rather difficult. Their design is based on differential equations that need to be solved. This is one of the reasons why these devices are not widely used. There are several [...] Read more.
Heat regenerators are simple devices for heat transfer, but their proper design is rather difficult. Their design is based on differential equations that need to be solved. This is one of the reasons why these devices are not widely used. There are several methods for solving them that were developed. However, due to the time demands of calculation, these models did not spread too much. With the development of computer technology, the situation changed, and these methods are now relatively easy to apply, as the calculation does not take a lot of time. Another problem arises when selecting a suitable method for calculating the heat transfer coefficient and pressure drop. Their choice depends on the type of packed bed material, and not all available computational equations also provide adequate accuracy. This paper describes the so-called open Willmott methods and provides a basic overview of equations for calculating the regenerative heat exchanger with a fixed bed. Based on the mentioned computational equations, it is possible to create a tailor-made calculation procedure of regenerative heat exchangers. Since no software was found on the market to design regenerative heat exchangers, it had to be created. An example of software implementation is described at the end of the article. The impulse to create this article was also to broaden the awareness of regenerative heat exchangers, to provide designers with an overview of suitable calculation methods and, thus, to extend the interest and use of this type of heat exchanger. Full article
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Open AccessArticle
Decarbonization of the Iron and Steel Industry with Direct Reduction of Iron Ore with Green Hydrogen
Energies 2020, 13(3), 758; https://doi.org/10.3390/en13030758 - 09 Feb 2020
Viewed by 386
Abstract
Production of iron and steel releases seven percent of the global greenhouse gas (GHG) emissions. Incremental changes in present primary steel production technologies would not be sufficient to meet the emission reduction targets. Replacing coke, used in the blast furnaces as a reducing [...] Read more.
Production of iron and steel releases seven percent of the global greenhouse gas (GHG) emissions. Incremental changes in present primary steel production technologies would not be sufficient to meet the emission reduction targets. Replacing coke, used in the blast furnaces as a reducing agent, with hydrogen produced from water electrolysis has the potential to reduce emissions from iron and steel production substantially. Mass and energy flow model based on an open-source software (Python) has been developed in this work to explore the feasibility of using hydrogen direct reduction of iron ore (HDRI) coupled with electric arc furnace (EAF) for carbon-free steel production. Modeling results show that HDRI-EAF technology could reduce specific emissions from steel production in the EU by more than 35 % , at present grid emission levels (295 kgCO2/MWh). The energy consumption for 1 ton of liquid steel (tls) production through the HDRI-EAF route was found to be 3.72 MWh, which is slightly more than the 3.48 MWh required for steel production through the blast furnace (BF) basic oxygen furnace route (BOF). Pellet making and steel finishing processes have not been considered. Sensitivity analysis revealed that electrolyzer efficiency is the most important factor affecting the system energy consumption, while the grid emission factor is strongly correlated with the overall system emissions. Full article
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Open AccessArticle
Real-Time Control Strategy for Aggregated Electric Vehicles to Smooth the Fluctuation of Wind-Power Output
Energies 2020, 13(3), 757; https://doi.org/10.3390/en13030757 - 09 Feb 2020
Viewed by 262
Abstract
Electric vehicles (EVs) are flexible demand-side response resources in a power distribution system. Reasonable and orderly control of charging/discharging processes of aggregated EVs can improve their coordination and interaction with the distribution system and ensure its efficient and stable operation. Aiming at the [...] Read more.
Electric vehicles (EVs) are flexible demand-side response resources in a power distribution system. Reasonable and orderly control of charging/discharging processes of aggregated EVs can improve their coordination and interaction with the distribution system and ensure its efficient and stable operation. Aiming at the problem that the fluctuation of wind power output may affect the stable operation of distribution system, a real-time control strategy for aggregated EVs to smooth the fluctuation of wind power is proposed. Firstly, considering the dispatchability of EVs, the charging/discharging energy boundary model is established to determine the charging/discharging margin of an EV at each moment. Then, first-order low-pass filtering is used to determine the total dispatching power of aggregated EVs. Finally, the total charging power of aggregated EVs is determined and power allocation is carried out. Simulation results show that the proposed strategy can achieve real-time smoothing for the fluctuation of wind power output while meeting the charging requirements of EVs, and the proposed strategy can not only reduce the fluctuation rate of total load, but also realize peak shaving and valley filling for the distribution system. Full article
(This article belongs to the Section Electric Vehicles)
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Open AccessArticle
Damage Evolution Mechanisms of Rock Induced by Blasting with the Aid of Empty-Hole Effect
Energies 2020, 13(3), 756; https://doi.org/10.3390/en13030756 - 09 Feb 2020
Viewed by 220
Abstract
Blasting has been widely used in coal mining as a method of reducing the integrity of rock mass. Its low controllability often leads to the unsatisfactory fragmentation effect of rock mass. The empty borehole effect has great significance in avoiding the excessive breakage [...] Read more.
Blasting has been widely used in coal mining as a method of reducing the integrity of rock mass. Its low controllability often leads to the unsatisfactory fragmentation effect of rock mass. The empty borehole effect has great significance in avoiding the excessive breakage of rock mass and guiding the directional propagation of blasting-induced fractures. Nevertheless, the rock mass damage type evolution induced by the empty borehole has been rarely studied. A tension–compression constitutive model of rock mass damage is established in this paper. The model is incorporated into the numerical modeling code LS-DYNA as a user-defined material model. Then, LS-DYNA is used to investigate the evolution mechanism of rock mass damage under the empty borehole effect. The damage types of rock mass caused by the empty borehole effect are also studied. The Fortran language is utilized to monitor the number variation of the tensile damaged elements and the compressive damaged elements in the rock mass around the empty borehole. The results indicate that existence of the empty borehole significantly enhances the tensile stress and the stress concentration factor in the rock mass nearby the empty borehole. Meanwhile, the rock mass nearby the empty borehole mainly damages in tension. Both the number of the tensile damaged elements and the tensile stresses in the elements increases as the empty borehole diameter increases. The number of the compressive damaged elements decreases with increasing empty borehole diameter. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle
A Hybrid PV-Battery System for ON-Grid and OFF-Grid Applications—Controller-In-Loop Simulation Validation
Energies 2020, 13(3), 755; https://doi.org/10.3390/en13030755 - 09 Feb 2020
Viewed by 253
Abstract
In remote locations such as villages, islands and hilly areas, there is a possibility of frequent power failures, voltage drops or power fluctuations due to grid-side faults. Grid-connected renewable energy systems or micro-grid systems are preferable for such remote locations to meet the [...] Read more.
In remote locations such as villages, islands and hilly areas, there is a possibility of frequent power failures, voltage drops or power fluctuations due to grid-side faults. Grid-connected renewable energy systems or micro-grid systems are preferable for such remote locations to meet the local critical load requirements during grid-side failures. In renewable energy systems, solar photovoltaic (PV) power systems are accessible and hybrid PV-battery systems or energy storage systems (ESS) are more capable of providing uninterruptible power to the local critical loads during grid-side faults. This energy storage system also improves the system dynamics during power fluctuations. In present work, a PV-battery hybrid system with DC-side coupling is considered, and a power balancing control (PBC) is proposed to transfer the power to grid/load and the battery. In this system, a solar power conditioning system (PCS) acts as an interface across PV source, battery and the load/central grid. With the proposed PBC technique, the system can operate in following operational modes: (a) PCS can be able to work in grid-connected mode during regular operation; (b) PCS can be able to charge the batteries and (c) PCS can be able to operate in standalone mode during grid side faults and deliver power to the local loads. The proposed controls are explained, and the system response during transient and steady-state conditions is described. With the help of controller-in-loop simulation results, the proposed power balancing controls are validated, for both off-grid and on-grid conditions. Full article
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Open AccessArticle
Simulation Analysis on the Heat Performance of Deep Borehole Heat Exchangers in Medium-Depth Geothermal Heat Pump Systems
Energies 2020, 13(3), 754; https://doi.org/10.3390/en13030754 - 08 Feb 2020
Viewed by 230
Abstract
Deep borehole heat exchangers (DBHEs) extract heat from the medium-depth geothermal energy with the depth of 2–3 km and provide high-temperature heat source for the medium-depth geothermal heat pump systems (MD-GHPs). This paper focuses on the heat transfer performance of DBHEs, where field [...] Read more.
Deep borehole heat exchangers (DBHEs) extract heat from the medium-depth geothermal energy with the depth of 2–3 km and provide high-temperature heat source for the medium-depth geothermal heat pump systems (MD-GHPs). This paper focuses on the heat transfer performance of DBHEs, where field tests and simulation are conducted to analyze the heat transfer process and the influence factors. Results identify that the heat transfer performance is greatly influenced by geothermal properties of the ground, thermal properties and depth of DBHEs and operation parameters, which could be classified into external factors, internal factors and synergic adjustment. In addition, the long-term operation effects are analyzed with the simulation, results show that with inlet water temperature setting at 20 °C and flow rate setting at 6.0 kg/s, the average outlet water temperature only drops 0.99 °C and the average heat extraction drops 9.5% after 20-years operation. Therefore, it demonstrates that the medium-depth geothermal energy can serve as the high-temperature heat source for heat pump systems stably and reliably. The results from this study can be potentially used to guide the system design and optimization of DBHEs. Full article
(This article belongs to the Section Energy and Buildings)
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Open AccessArticle
Optimal Placement, Sizing and Coordination of FACTS Devices in Transmission Network Using Whale Optimization Algorithm
Energies 2020, 13(3), 753; https://doi.org/10.3390/en13030753 - 08 Feb 2020
Viewed by 295
Abstract
Flexible AC Transmission Systems (FACTS) play an important role in minimizing power losses and voltage deviations while increasing the real power transfer capacity of transmission lines. The extent to which these devices can provide benefits to the transmission network depend on their optimal [...] Read more.
Flexible AC Transmission Systems (FACTS) play an important role in minimizing power losses and voltage deviations while increasing the real power transfer capacity of transmission lines. The extent to which these devices can provide benefits to the transmission network depend on their optimal location and sizing. However, finding appropriate locations and sizes of these devices in an electrical network is difficult since it is a nonlinear problem. This paper proposes a technique for the optimal placement and sizing of FACTS, namely the Thyristor-Controlled Series Compensators (TCSCs), Shunt VARs Compensators (SVCs), and Unified Power Flows Controllers (UPFCs). To find the optimal locations of these devices in a network, weak buses and lines are determined by constructing PV curves of load buses, and through the line stability index. Then, the whale optimization algorithm (WOA) is employed not only to find an ideal ratings for these devices but also the optimal coordination of SVC, TCSC, and UPFC with the reactive power sources already present in the network (tap settings of transformers and reactive power from generators). The objective here is the minimization of the operating cost of the system that consists of active power losses and FACTS devices cost. The proposed method is applied to the IEEE 14 and 30 bus systems. The presented technique is also compared with Genetic Algorithm (GA) and Particle Swarm Optimization (PSO). The findings showed that total system operating costs and transmission line losses were considerably reduced by WOA as compared to existing metaheuristic optimization techniques. Full article
(This article belongs to the Special Issue Electric Power Systems Research 2019)
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Open AccessArticle
A Data-Driven Method with Feature Enhancement and Adaptive Optimization for Lithium-Ion Battery Remaining Useful Life Prediction
Energies 2020, 13(3), 752; https://doi.org/10.3390/en13030752 - 08 Feb 2020
Viewed by 249
Abstract
Data-driven methods are widely applied to predict the remaining useful life (RUL) of lithium-ion batteries, but they generally suffer from two limitations: (i) the potentials of features are not fully exploited, and (ii) the parameters of the prediction model are difficult to determine. [...] Read more.
Data-driven methods are widely applied to predict the remaining useful life (RUL) of lithium-ion batteries, but they generally suffer from two limitations: (i) the potentials of features are not fully exploited, and (ii) the parameters of the prediction model are difficult to determine. To address this challenge, this paper proposes a new data-driven method using feature enhancement and adaptive optimization. First, the features of battery aging are extracted online. Then, the feature enhancement technologies, including the box-cox transformation and the time window processing, are used to fully exploit the potential of features. The box-cox transformation can improve the correlation between the features and the aging status of the battery, and the time window processing can effectively exploit the time information hidden in the historical features sequence. Based on this, gradient boosting decision trees are used to establish the RUL prediction model, and the particle swarm optimization is used to adaptively optimize the model parameters. This method was applied on actual lithium-ion battery degradation data, and the experimental results show that the proposed model is superior to traditional prediction methods in terms of accuracy. Full article
(This article belongs to the Special Issue Artificial Intelligence Applications to Energy Systems)
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Open AccessArticle
Coordinated Control of Aichi Microgrid for Efficient Power Management Using Novel Set Point Weighting Iterative Learning Controller
Energies 2020, 13(3), 751; https://doi.org/10.3390/en13030751 - 08 Feb 2020
Viewed by 257
Abstract
A novel Set Point Weighting Iterative Learning Controller (SPW-ILC) has been proposed for voltage stabilization at AC/DC bus, coordinated control among the distributed sources in the modeled hybrid microgrid (HMG) and synchronization of HMG with utility grid. The Aichi Micro grid test system [...] Read more.
A novel Set Point Weighting Iterative Learning Controller (SPW-ILC) has been proposed for voltage stabilization at AC/DC bus, coordinated control among the distributed sources in the modeled hybrid microgrid (HMG) and synchronization of HMG with utility grid. The Aichi Micro grid test system located at Aichi Institute of Technology, Japan has been considered for the simulation studies and modeled in MATLAB/Simulink environment. The Aichi microgrid can be operated in autonomous mode as AC system and DC system. When it is working as DC system, the dc bus voltage is maintained stable by incorporating dedicated fuzzy logic controllers (FLC) for DC-DC converters due to the variable distributed sources. Meanwhile, the bidirectional converter also called as Interlinking Converter (IC) located between ac bus and dc bus controlled by proposed SPW-ILC converts the DC voltage into AC voltage and meets AC loads. In AC system of autonomous mode, the inverters are controlled by proposed controller to meet the ac demands. The grid connected mode of Aichi microgrid system is performed by properly controlling the IC to meet ac and dc loads. The proposed SPW-ILC reduces the voltage deviation and maintains the power balance under variable source and load conditions. The results have been compared with the conventional proportional integral (PI) controller and FLC to validate the performance of the controller. The results show that the proposed SPW-ILC has efficiently control the voltage and maintain the power balance. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle
Exergetic Analysis and Exergy Loss Reduction in the Milk Pasteurization for Italian Cheese Production
Energies 2020, 13(3), 750; https://doi.org/10.3390/en13030750 - 08 Feb 2020
Viewed by 219
Abstract
The cheese industry has high energy consumption, and improvements to plant efficiency may lead to a reduction of its environmental impact. A survey on a sample of small-medium Italian cheese factories was carried out in order to assess the efficiency of heat recovery [...] Read more.
The cheese industry has high energy consumption, and improvements to plant efficiency may lead to a reduction of its environmental impact. A survey on a sample of small-medium Italian cheese factories was carried out in order to assess the efficiency of heat recovery of the milk pasteurization equipment for the cheese production. Then, an exergetic analysis to calculate the related exergy loss was carried out together with a cost-benefit analysis to identify the optimized value of the heat efficiency. The exergy loss reduction was determined throughout an exergy analysis that takes into account this last value and the comparison with the previous exergy losses. Finally, the feasibility and the consequent additional reduction of exergy losses were verified, if a cogeneration heat and power (CHP) combined to the pasteurization equipment is assumed. Results show a current heat recovery efficiency of 93.2% in the Italian cheese factories; a close connection between the exergetic losses and the efficiency of the heat recovery exchanger; the optimized recovery efficiency equal to 97.3% obtained from the cost-benefit analysis; a related important exergetic loss reduction of −45% in the heat exchangers, as a second result of the exergetic analysis; a similar reduction of the exergy loss (−42%) of the whole system, as a third result of the exergetic analysis; a total exergy loss reduction of 22.9 kJ kg−1milk, which corresponds to a lower environmental impact due to CO2 reduction; a further reduction of the exergy loss of −10% when the cogeneration heat and power CHP are used. Full article
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Open AccessArticle
Novel Soft-Switching Integrated Boost DC-DC Converter for PV Power System
Energies 2020, 13(3), 749; https://doi.org/10.3390/en13030749 - 08 Feb 2020
Viewed by 267
Abstract
This paper presents a novel soft-switching boost DC-DC converter, which uses an edge-resonant switch capacitor based on the pulse width modulation PWM technique. These converters have high gain voltage due to coupled inductors, which work as a transformer, while the boost converter works [...] Read more.
This paper presents a novel soft-switching boost DC-DC converter, which uses an edge-resonant switch capacitor based on the pulse width modulation PWM technique. These converters have high gain voltage due to coupled inductors, which work as a transformer, while the boost converter works as a resonant inductor. Upon turning on, the studied soft switching circuit works at zero-current soft switching (ZCS), and upon turning off, it works at zero-voltage soft switching (ZVS) while using active semiconductor switches. High efficiency and low losses are obtained while using soft switching and auxiliary edge resonance to get a high step-up voltage ratio. A prototype model is implemented in the Power Electronics Laboratory, Assiut University, Egypt. Seventy-two-panel PV modules of 250 W each were used to simulate and execute the setup to examine the proposed boost converter. Full article
(This article belongs to the Section Solar Energy and Photovoltaic Systems)
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Open AccessArticle
On Developing Techniques for Sharing Satellite Spectrum with Indoor Small Cells in 5G
Energies 2020, 13(3), 748; https://doi.org/10.3390/en13030748 - 08 Feb 2020
Viewed by 248
Abstract
In this paper, we present two spectrum sharing techniques for a multisystem, incorporating an integrated satellite-mobile system and an autonomous terrestrial-mobile system (iSMS/aTMS), namely orthogonal spectrum sharing (OSS) and non-orthogonal spectrum sharing (nOSS) techniques. aTMS consists of numerous small cells deployed in several [...] Read more.
In this paper, we present two spectrum sharing techniques for a multisystem, incorporating an integrated satellite-mobile system and an autonomous terrestrial-mobile system (iSMS/aTMS), namely orthogonal spectrum sharing (OSS) and non-orthogonal spectrum sharing (nOSS) techniques. aTMS consists of numerous small cells deployed in several buildings, and iSMS consists of a satellite station integrated with complementary ground component (CGC) stations deployed within buildings. By exploiting the high external wall penetration loss of a building, the iSMS spectrum is shared with small cells per building in OSS, and small cells per 3-dimensional (3D) cluster per building in nOSS. An interference management scheme, to avoid interference in apartments with collocated CGC stations and small cells, was developed and an optimal number of almost blank subframes (ABSs) per ABS pattern period (APP) was defined. System-level capacity, spectral efficiency, and energy efficiency performance metrics were derived. Furthermore, we present an algorithm for both OSS and nOSS techniques. With extensive simulation and numerical analysis, it is shown that the proposed nOSS significantly outperforms OSS in terms of spectral efficiency and energy efficiency, and both techniques can meet the expected spectral efficiency and energy efficiency requirements for the fifth-generation (5G) mobile networks. Full article
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Open AccessArticle
A Novel Control Scheme for Multi-Terminal Low-Frequency AC Electrical Energy Transmission Systems Using Modular Multilevel Matrix Converters and Virtual Synchronous Generator Concept
Energies 2020, 13(3), 747; https://doi.org/10.3390/en13030747 - 08 Feb 2020
Viewed by 247
Abstract
This paper proposes a new control scheme for the low frequency AC transmission (LFAC) system aiming at extending the point-to-point configuration to form a multi-terminal electrical energy network. The multi-terminal low frequency ac (MT-LFAC) system configuration is based on the use of modular [...] Read more.
This paper proposes a new control scheme for the low frequency AC transmission (LFAC) system aiming at extending the point-to-point configuration to form a multi-terminal electrical energy network. The multi-terminal low frequency ac (MT-LFAC) system configuration is based on the use of modular multilevel matrix converters (M3Cs) and virtual synchronous generator (VSG) control. The M3C is the next ac/ac converter generation, which is used as an interface with the conventional AC network and the LFAC electrical energy system. Application of VSG control is proposed to enable proper power sharing, to provide synchronization of each terminal, and frequency stabilization, thus, to offer multiterminal forming capability. Two different operation modes are applied in the system to damp the frequency deviation after a dynamic perturbation, which provides additional stabilization feature to the VSG. Frequency restoration mode and commanded mode of power sharing are applied as dynamic states to validate the robustness of the VSG control system. Besides, to solve the negative impact of low X/R ratio in the LFAC electrical energy system, we enhance the VSG control by proposing a virtual-impedance-based solution, which increases the output total impedance on the low frequency side and prevents the coupling between P and Q. The operation of the proposed system is examined by simulation results with a precise model of M3Cs in the PSCAD/ EMTDC software environment (version 4.2.1, Winnipeg, MB, Canada). Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle
A Genetic-Algorithm-Based DC Current Minimization Scheme for Transformless Grid-Connected Photovoltaic Inverters
Energies 2020, 13(3), 746; https://doi.org/10.3390/en13030746 - 08 Feb 2020
Viewed by 189
Abstract
Transformerless grid-connected inverters are of great industrial value in photovoltaic power generation. However, the direct current (DC) induced into the inverter’s output degrades the power quality of the grid. Recently, a back-propagation neural work proportional–integral–derivative (BP-PID) scheme has proven helpful in solving this [...] Read more.
Transformerless grid-connected inverters are of great industrial value in photovoltaic power generation. However, the direct current (DC) induced into the inverter’s output degrades the power quality of the grid. Recently, a back-propagation neural work proportional–integral–derivative (BP-PID) scheme has proven helpful in solving this problem. However, this scheme can be improved by reducing the suppressing time and overshoot. A genetic algorithm (GA)-based DC current minimization scheme, namely the genetic-algorithm-based BP-PID (GA-BP-PID) scheme, was established in this study. In this scheme, GA was used off-line to optimize the initial weights within the BP neural network. Subsequently, the optimal weight was applied to the online DC current suppression process. Compared with the BP-PID scheme, the proposed scheme can reduce the suppressing time by 59% and restrain the overshoot. A prototype of the proposed scheme was implemented and tested on experimental hardware as a proof of concept. The results of the scheme were verified using a three-phase inverter experiment. The novel GA-PB-PID scheme proposed in this study was proven efficient in reducing the suppressing time and overshoot. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle
Evaluation of Compressor Heat Pump for Root Zone Heating as an Alternative Heating Source for Leafy Vegetable Cultivation
Energies 2020, 13(3), 745; https://doi.org/10.3390/en13030745 - 08 Feb 2020
Viewed by 218
Abstract
Protected horticulture is a high energy-consuming sector in which the optimization of energy use and cost for heating facilities is strategic in achieving high environmental and economic sustainability of production. The main aim of the project was to evaluate the use of a [...] Read more.
Protected horticulture is a high energy-consuming sector in which the optimization of energy use and cost for heating facilities is strategic in achieving high environmental and economic sustainability of production. The main aim of the project was to evaluate the use of a heat pump for basal heating as an alternative technology to grow crops with reduced canopies, such as basil. During the test, an area of the greenhouse contained two systems of coaxial pipes circulating warm water from a heat pump and a condensing boiler. These pipes were placed above the growing media. At the same time, a separate area of the same greenhouse contained a traditional heating system consisting of an air heater, the solution commonly used to heat greenhouses. Microclimatic conditions and energy consumption were analyzed for the three heating technologies. The energy analysis of the three experimental heating options showed that all of them could ensure suitable thermal conditions for cultivation in the winter period. Overall, the results confirmed the energy saving resulting from the adoption of the heat pump, underlining the importance of this device in terms of the support that the energy-saving goal receives. Full article
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Ethanol Production from Hydrolyzed Kraft Pulp by Mono- and Co-Cultures of Yeasts: The Challenge of C6 and C5 Sugars Consumption
Energies 2020, 13(3), 744; https://doi.org/10.3390/en13030744 - 08 Feb 2020
Viewed by 263
Abstract
Second-generation bioethanol production’s main bottleneck is the need for a costly and technically difficult pretreatment due to the recalcitrance of lignocellulosic biomass (LCB). Chemical pulping can be considered as a LCB pretreatment since it removes lignin and targets hemicelluloses to some extent. Chemical [...] Read more.
Second-generation bioethanol production’s main bottleneck is the need for a costly and technically difficult pretreatment due to the recalcitrance of lignocellulosic biomass (LCB). Chemical pulping can be considered as a LCB pretreatment since it removes lignin and targets hemicelluloses to some extent. Chemical pulps could be used to produce ethanol. The present study aimed to investigate the batch ethanol production from unbleached Kraft pulp of Eucalyptus globulus by separate hydrolysis and fermentation (SHF). Enzymatic hydrolysis of the pulp resulted in a glucose yield of 96.1 ± 3.6% and a xylose yield of 94.0 ± 7.1%. In an Erlenmeyer flask, fermentation of the hydrolysate using Saccharomyces cerevisiae showed better results than Scheffersomyces stipitis. At both the Erlenmeyer flask and bioreactor scale, co-cultures of S. cerevisiae and S. stipitis did not show significant improvements in the fermentation performance. The best result was provided by S. cerevisiae alone in a bioreactor, which fermented the Kraft pulp hydrolysate with an ethanol yield of 0.433 g·g−1 and a volumetric ethanol productivity of 0.733 g·L−1·h−1, and a maximum ethanol concentration of 19.24 g·L−1 was attained. Bioethanol production using the SHF of unbleached Kraft pulp of E. globulus provides a high yield and productivity. Full article
(This article belongs to the Section Bio-Energy)
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Biogas from Anaerobic Digestion: Power Generation or Biomethane Production?
Energies 2020, 13(3), 743; https://doi.org/10.3390/en13030743 - 08 Feb 2020
Viewed by 246
Abstract
Biogas is a fuel obtained from organic waste fermentation and can be an interesting solution for producing electric energy, heat and fuel. Recently, many European countries have incentivized the production of biomethane to be injected into natural gas grids or compressed and used [...] Read more.
Biogas is a fuel obtained from organic waste fermentation and can be an interesting solution for producing electric energy, heat and fuel. Recently, many European countries have incentivized the production of biomethane to be injected into natural gas grids or compressed and used as biofuel in vehicles. The introduction of an upgrading unit into an existing anaerobic digestion plant to convert biogas to biomethane may have a strong impact on the overall energy balance of the systems. The amount of biomethane produced may be optimized from several points of view (i.e., energy, environmental and economic). In this paper, the mass and energy fluxes of an anaerobic digestion plant were analyzed as a function of the biogas percentage sent to the upgrading system and the amount of biomethane produced. A numerical model of an anaerobic digestion plant was developed by considering an existing case study. The mass and energy balance of the digesters, cogeneration unit, upgrading system and auxiliary boiler were estimated when the amount of produced biomethane was varied. An internal combustion engine was adopted as the cogeneration unit and a CO2 absorption system was assumed for biogas upgrading. Results demonstrated that the energy balance of the plant is strictly dependent on the biomethane production and that an excess of biomethane production makes the plant totally dependent on external energy sources. As for the environmental impact, an optimal level of biomethane production exists that minimizes the emissions of equivalent CO2. However, high biomethane subsides can encourage plant managers to increase biomethane production and thus reduce CO2 savings. Full article
(This article belongs to the Special Issue Production and Utilization of Biogas 2020)
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