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Energies, Volume 15, Issue 8 (April-2 2022) – 260 articles

Cover Story (view full-size image): Six carbonates commonly used in Li-ion battery electrolyte solutions were unambiguously identified using two-dimensional gas chromatography with electron ionization time of flight mass spectrometry (GC×GC/EI TOF MS; shown in graphic) and two-dimensional gas chromatography with flame ionization detection (GC×GC/FID). Unlike in previous analytical methods, analysis was performed without prior removal of the lithium hexafluorophosphate (LiPF6) salt. Both methods were found to be precise (uncertainty < 5%), accurate (error < 5%), and sensitive (limit of detection <0.12 ppm for FID and <2.7 ppm for MS). View this paper
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Article
Distributed Secondary Control in Microgrids Using Synchronous Condenser for Voltage and Frequency Support
Energies 2022, 15(8), 2968; https://doi.org/10.3390/en15082968 - 18 Apr 2022
Cited by 1 | Viewed by 783
Abstract
A high share of distributed energy resources (DERs) in power distribution grids has posed many challenges for system operation and control. Microgrid (MG) application with different distributed control approaches for DERs has been drawn a lot of attention from the research community to [...] Read more.
A high share of distributed energy resources (DERs) in power distribution grids has posed many challenges for system operation and control. Microgrid (MG) application with different distributed control approaches for DERs has been drawn a lot of attention from the research community to provide more flexibility, reliability and resilience for the system. This paper develops a distributed secondary control for DERs in MGs and on top of that using synchronous condenser (SC) participating in the secondary control for voltage support. The proposed distributed secondary control framework of MGs is designed to obtain four objectives as follows: (i) frequency restoration, (ii) average voltage restoration, (iii) arbitrary active power sharing among SGs and BESSs and (iv) arbitrary reactive power sharing among all SGs, BESSs and SCs. The comparison results under different scenarios show that with SC participating in the distributed secondary control in MGs, the system frequency and voltage response are much improved and quickly recovered to the nominal values thanks to the natural inertia response and fast reactive power control of SC sharing with other DERs in the MGs. Additionally, a multi-agent system is implemented to realize the proposed control method in hardware environment. Full article
(This article belongs to the Special Issue Control of Power Electronic Converters for Future Power Systems)
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Article
A Compendium of Formulae for Natural Frequencies of Offshore Wind Turbine Structures
Energies 2022, 15(8), 2967; https://doi.org/10.3390/en15082967 - 18 Apr 2022
Cited by 1 | Viewed by 1241
Abstract
The design of an offshore wind turbine system varies with the turbine capacity, water depth, and environmental loads. The natural frequency of the structure, considering foundation flexibility, forms an important factor in structural design, lifetime performance estimates, and cost estimates. Although nonlinear numerical [...] Read more.
The design of an offshore wind turbine system varies with the turbine capacity, water depth, and environmental loads. The natural frequency of the structure, considering foundation flexibility, forms an important factor in structural design, lifetime performance estimates, and cost estimates. Although nonlinear numerical analysis in the time domain is widely used in the offshore industry for detailed design, it becomes necessary for project planners to estimate the natural frequency at an earlier stage and rapidly within reasonable accuracy. This paper presents a compendium of mathematical expressions to compute the natural frequencies of offshore wind turbine (OWT) structures on various foundation types by assimilating analytical solutions for each type of OWT, obtained by a range of authors over the past decade. The calculations presented can be easily made using spreadsheets. Example calculations are also presented where the compiled solutions are compared against publicly available sources. Full article
(This article belongs to the Special Issue Marine Renewable Energy Technology)
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Article
An Accurate Switching Transient Analytical Model for GaN HEMT under the Influence of Nonlinear Parameters
Energies 2022, 15(8), 2966; https://doi.org/10.3390/en15082966 - 18 Apr 2022
Cited by 1 | Viewed by 533
Abstract
The Gallium Nitride high electron mobility transistor (GaN HEMT) has been considered as a potential power semiconductor device for high switching speed and high power density application since its commercialization. Compared with the traditional Si transistors, GaN HEMT has faster switching speed and [...] Read more.
The Gallium Nitride high electron mobility transistor (GaN HEMT) has been considered as a potential power semiconductor device for high switching speed and high power density application since its commercialization. Compared with the traditional Si transistors, GaN HEMT has faster switching speed and lower on-off loss. As a result, it is more sensitive to the nonlinear parameters due to the fast switching speed. The subsequent voltage and current overshooting will affect the efficiency and safety of the GaN HEMT and power electronic systems. In this paper, an accurate switching transient analytical model for GaN HEMT is proposed, which considers the effects of parasitic inductances, nonlinear junction capacitances and nonlinear transconductance. The model characteristic of turn-ON process and turn-OFF process is illustrated in detail, and the equivalent circuits are derived for each switching transition. The accuracy of the proposed model can be verified by comparing the predicted switching waveform and switching loss with that of the experimental results based on the double pulse test (DPT) circuit. Compared with the conventional model, the proposed model is more accurate and matches better with the experimental results than the conventional model. Finally, this model can be used for analyzing the influences of gate resistance, nonlinear junction capacitances, and parasitic inductances on switching transient waveform and refining calculation switching loss. Full article
(This article belongs to the Topic Application of Innovative Power Electronic Technologies)
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Article
Oscillation of Cavitating Vortices in Draft Tubes of a Simplified Model Turbine and a Model Pump–Turbine
Energies 2022, 15(8), 2965; https://doi.org/10.3390/en15082965 - 18 Apr 2022
Viewed by 463
Abstract
The self-oscillation of the cavitating vortices is one of the dangerous phenomena of hydraulic turbine operation near full-load conditions. This work is an attempt to generalize data and expand insight on the phenomenon of self-excited oscillations by comparing the experimental results obtained on [...] Read more.
The self-oscillation of the cavitating vortices is one of the dangerous phenomena of hydraulic turbine operation near full-load conditions. This work is an attempt to generalize data and expand insight on the phenomenon of self-excited oscillations by comparing the experimental results obtained on a simplified turbine and scaled-down pump–turbine models. In both cases, a series of high-speed imaging was carried out, which made it possible to study these phenomena with high temporal resolution. The high-speed imaging data was subjected to additional processing such as binarization, cropping, and scaling. For a simplified turbine model, the volume of the vapor cavity was calculated based on the assumption of the axial symmetry of the cavity, after which fast Fourier transform (FFT) analysis was carried out. A proper orthogonal decomposition (POD) analysis was also performed to examine individual modes in the original digital imaging data. For the pump–turbine, visualization data on the cavitation cavity oscillations were supplemented by pressure measurements in the draft tube cone to determine the frequency characteristics. Based on obtained experimental data, an improved one-dimensional model describing the oscillations of the cavitation cavity arising behind the hydraulic turbine runner is proposed. Full article
(This article belongs to the Special Issue Advances in Pumped Storage Hydraulic System)
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Article
Kron Reduction Based on Node Ordering Optimization for Distribution Network Dispatching with Flexible Loads
Energies 2022, 15(8), 2964; https://doi.org/10.3390/en15082964 - 18 Apr 2022
Cited by 2 | Viewed by 532
Abstract
Kron reduction is a general tool of network simplification for flow calculation. With a growing number of flexible loads appearing in distribution networks, traditional Kron reduction cannot be widely used in control and scheduling due to the elimination of controllable and variable load [...] Read more.
Kron reduction is a general tool of network simplification for flow calculation. With a growing number of flexible loads appearing in distribution networks, traditional Kron reduction cannot be widely used in control and scheduling due to the elimination of controllable and variable load buses. Therefore, this paper proposes an improved Kron reduction based on node ordering optimization whose principles guarantee that all the boundary nodes are retained eventually after eliminating the first row and the first column in every step according to the order, thereby making it possible to take full advantage of their potential to meet different requirements in power system calculation and dispatching. The proposed method is verified via simulation models of IEEE 5-bus and 30-bus systems through illustrating the dynamic consistency of the output active power of the generator nodes and the power flow data of preserved nodes before and after reduction. Full article
(This article belongs to the Special Issue Smart Grids and Renewables)
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Article
Efficiency Analytical Characterization for Brushless Electric Drives
Energies 2022, 15(8), 2963; https://doi.org/10.3390/en15082963 - 18 Apr 2022
Viewed by 422
Abstract
The paper is focused on the formalization of an experimental procedure aimed to characterize the efficiency behaviour of a Permanent Magnet Synchronous Motor-based drive. The characterization is intended to expose the analytical behaviour of the system efficiency by the actual operating condition assigned [...] Read more.
The paper is focused on the formalization of an experimental procedure aimed to characterize the efficiency behaviour of a Permanent Magnet Synchronous Motor-based drive. The characterization is intended to expose the analytical behaviour of the system efficiency by the actual operating condition assigned through torque/speed value. The availability of such a relation in a simple analytical form would allow for real-time adjustment by advanced power management strategies to maximize the whole system efficiency. The proposed method is based on a defined set of measures corresponding to several drive operating conditions. A straightforward elaboration procedure is then formulated with the aim to quantify the different parameters, which intervene in the efficiency characterization. The method has been applied on a 155 kW drive. The results show that good accuracy is achieved while keeping the analytical approach relatively simple. Full article
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Article
Energy System Development Scenarios: Case of Poland
Energies 2022, 15(8), 2962; https://doi.org/10.3390/en15082962 - 18 Apr 2022
Cited by 3 | Viewed by 501
Abstract
Europe’s ambition to be the first climate-neutral continent and to achieve net-zero greenhouse gas emissions by 2050 will result in changes to the energy systems of many countries. This overlaps with the principles of circular economy, energy independence, and the continuity of operations [...] Read more.
Europe’s ambition to be the first climate-neutral continent and to achieve net-zero greenhouse gas emissions by 2050 will result in changes to the energy systems of many countries. This overlaps with the principles of circular economy, energy independence, and the continuity of operations enshrined in many national and regional documents. From the above, a scenario based on renewable resources emerges. However, in a country such as Poland, with conventional energy sources and large state participation in the sector, is this feasible? The authors assumed that the urgent need for a turbulence-sensitive analysis of energy sector changes can be met by using a new view, defined by the authors as a matrix of four oceans scenarios. Black, Grey, Red and Green scenarios are determined by the proportion of the state and the local-community sector. Then, assuming the possibility of introducing two of them by 2050—Green (radical) and Red (competitive)—empirical research was carried out on a purposively selected group of experts. The business model of the sector was analyzed in terms of six links that create economic and social value: energy sources, energy producers, transmission networks with infrastructure, energy storage, energy system management and energy consumers. According to experts, development of business model links will be based on the Red scenario. Thus, we get a picture of a model that should be considered by politicians, scientists, as well as a wide audience that absorbs the effects of environmental pollution. Full article
(This article belongs to the Special Issue Green Energy Economies)
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Article
Modeling, Analysis, Design, and Simulation of a Bidirectional DC-DC Converter with Integrated Snow Removal Functionality for Solar PV Electric Vehicle Charger Applications
Energies 2022, 15(8), 2961; https://doi.org/10.3390/en15082961 - 18 Apr 2022
Viewed by 602
Abstract
Different factors affect solar photovoltaic (PV) systems by decreasing input energy and reducing the conversion efficiency of the system. One of these factors is the effect of snow cover on PV panels, a subject lacking sufficient academic research. This paper reviews and compares [...] Read more.
Different factors affect solar photovoltaic (PV) systems by decreasing input energy and reducing the conversion efficiency of the system. One of these factors is the effect of snow cover on PV panels, a subject lacking sufficient academic research. This paper reviews and compares current research for snow removal in solar PV modules. Additionally, this paper presents the design, analysis and modelling of a smart heating system for solar PV Electric Vehicle (EV) charging applications. The system is based on a bidirectional DC-DC converter that redirects the grid/EV-battery power into heating of the solar PV modules, thus removing snow cover, as well as providing the function of MPPT when required to charge the EV battery pack. A control scheme for each mode of operation was designed. Subsequently, a performance evaluation by simulating the system under various conditions is presented validating the usefulness of the proposed converter to be used in solar PV systems under extreme winter conditions. Full article
(This article belongs to the Special Issue Recent Advances in Renewable Energy)
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Article
Shapelets to Classify Energy Demand Time Series
Energies 2022, 15(8), 2960; https://doi.org/10.3390/en15082960 - 18 Apr 2022
Viewed by 549
Abstract
Data are an important asset that the electric power industry have available today to support management decisions, excel in operational efficiency, and be more competitive. The advent of smart grids has increased power grid sensorization and so, too, the data availability. However, the [...] Read more.
Data are an important asset that the electric power industry have available today to support management decisions, excel in operational efficiency, and be more competitive. The advent of smart grids has increased power grid sensorization and so, too, the data availability. However, the inability to recognize the value of data beyond the siloed application in which data are collected is seen as a barrier. Power load time series are one of the most important types of data collected by utilities, because of the inherent information in them (e.g., power load time series comprehend human behavior, economic momentum, and other trends). The area of time series analysis in the energy domain is attracting considerable interest because of growing available data as more sensorization is deployed in power grids. This study considers the shapelet technique to create interpretable classifiers for four use cases. The study systematically applied the shapelet technique to data from different hierarchical power levels (national, primary power substations, and secondary power substations). The study has experimentally shown shapelets as a technique that embraces the interpretability and accuracy of the learning models, the ability to extract interpretable patterns and knowledge, and the ability to recognize and monetize the value of the data, important subjects to reinforce the importance of data-driven services within the energy sector. Full article
(This article belongs to the Special Issue Energy Digitalisation and Data)
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Article
Petrology, Physical Properties and Geochemical Characteristics of Alkaline Lake Shale—Fengcheng Formation in Mahu Sag, Junggar Basin
Energies 2022, 15(8), 2959; https://doi.org/10.3390/en15082959 - 18 Apr 2022
Viewed by 467
Abstract
There are rare comparative studies on the geological characteristics of shale in different members of Permian Fengcheng Formation in Mahu Sag, Junggar basin, China. In order to compare the mineral composition, physical properties, and geochemical characteristics of shale in three members of Fengcheng [...] Read more.
There are rare comparative studies on the geological characteristics of shale in different members of Permian Fengcheng Formation in Mahu Sag, Junggar basin, China. In order to compare the mineral composition, physical properties, and geochemical characteristics of shale in three members of Fengcheng Formation in Mahu Sag, a large number of test data such as X-ray diffraction, high-pressure mercury injection, organic carbon, rock pyrolysis, and vitrinite reflectance were collected and analyzed. Results showed that the content of clay minerals in the shale of the third member of Fengcheng Formation (P1f3) is the highest. The content of carbonate minerals is the highest and the content of clay minerals is the lowest in the shale of the second member of Fengcheng Formation (P1f2). The content of felsic minerals is the highest and the content of carbonate minerals is the lowest in the shale of the first member of Fengcheng Formation (P1f1). The physical properties of the shale of P1f3 are the best, and the porosity of the shale of P1f2 is the smallest, but its permeability is relatively large, and the permeability of shale of P1f1 is the lowest. The organic matter abundance of shale of P1f2 is the highest, while that of P1f1 is relatively the lowest. Most of the organic matter types of shale of P1f3 are type I–II, those of P1f2 are mainly type II, and those of P1f1 section are distributed from type I–III. On the whole, the shale of Fengcheng Formation in the peripheral fault zone and slope area of Mahu Sag has reached the low mature to mature stage, and the shale in the central area of the sag has reached the mature stage. More than half of the shale samples of Fengcheng Formation belong to fair to good source rocks, especially the samples of P1f2. A few samples from P1f3 and P1f1 belong to non-source rocks. This study indicates that the shale of Fengcheng Formation in Mahu Sag has good hydrocarbon generation potential, especially the shale of P1f2, and can become the target of shale oil exploration. Full article
(This article belongs to the Special Issue Shale Oil and Gas Accumulation Mechanism)
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Editorial
Bioeconomy for Resilient Post-COVID Economies
Energies 2022, 15(8), 2958; https://doi.org/10.3390/en15082958 - 18 Apr 2022
Viewed by 450
Abstract
In the creation of this Special Issue, the editors identified circular bioeconomy, i [...] Full article
(This article belongs to the Special Issue Bioeconomy for Resilient Post-COVID Economies)
Review
Silicon–Germanium: The Legacy Lives On
Energies 2022, 15(8), 2957; https://doi.org/10.3390/en15082957 - 18 Apr 2022
Viewed by 477
Abstract
Alloy systems comprised of silicon with germanium, lead with tellurium, and bismuth with antimony have constituted a majority of thermoelectric applications during the last half-century. These legacy materials are primarily covalently bonded with a maximum ZT near one. Silicon–germanium alloys have provided the [...] Read more.
Alloy systems comprised of silicon with germanium, lead with tellurium, and bismuth with antimony have constituted a majority of thermoelectric applications during the last half-century. These legacy materials are primarily covalently bonded with a maximum ZT near one. Silicon–germanium alloys have provided the thermal to electrical conversion for many of NASA’s radioisotope thermoelectric generator (RTG) configurations and for nearly all of its deep space and outer planetary flights, such as Pioneer I and II, Voyager I and 11, Ulysses, Galileo, and Cassini. The remarkable success of these materials and their respective devices is evidenced by the fact that there has never been a failure of the RTG systems even after over 1 billion cumulative mission-hours. The history of this alloy system as a thermoelectric conversion material spans over six decades and research to further improve its performance continues to this day. Si-Ge alloys have long been a mainstay of thermoelectric research because of a fortuitous combination of a sufficiently high melting temperature, reasonable energy band gap, high solubility for both n- and p-type dopants, and the fact that this alloy system exhibits complete miscibility in the solid state, which enable tuning of both electrical and thermal properties. This article reviews the history of silicon–germanium as a thermoelectric material and its use in NASA’s RTG programs. Since the device technology is also a critical operational consideration, a brief review of some of the unique challenges imposed by the use in an RTG is also discussed. Full article
(This article belongs to the Special Issue Advanced Thermoelectric Generation Technologies 2022)
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Article
Pore Characteristics and Gas Preservation of the Lower Cambrian Shale in a Strongly Deformed Zone, Northern Chongqing, China
Energies 2022, 15(8), 2956; https://doi.org/10.3390/en15082956 - 18 Apr 2022
Cited by 1 | Viewed by 518
Abstract
The Lower Paleozoic marine shale in southern China has undergone several strong tectonic transformations in an extensive region outside the Sichuan Basin. Although some shale strata underwent strong deformation, they still contain a significant amount of shale gas. The gas preservation mechanism in [...] Read more.
The Lower Paleozoic marine shale in southern China has undergone several strong tectonic transformations in an extensive region outside the Sichuan Basin. Although some shale strata underwent strong deformation, they still contain a significant amount of shale gas. The gas preservation mechanism in the strongly deformed shale has become the focus of attention. In this paper, the Lower Cambrian gas-bearing shale samples with a strong deformation taken from an exploration well in northern Chongqing, China, were investigated on their pore types and structure, with the aim to reveal the reason for the gas preservation. The pore types of the Lower Cambrian shale are dominated by microfractures and interparticle (interP) pores occurring mainly between clay minerals and between organic matter (OM) and clay minerals, while pores within OM that can be observed by FE-SEM (field emission-scanning electron microscopy) are rare. The shale has a low porosity, with an average of 1.56%, which is mainly controlled by the clay mineral content. The adsorption experiments of low pressure N2 (LPNA) and CO2 (LPCA) indicate that the shale is rich in micropores and small mesopores (<2–3 nm) provided mainly by OM, but mesopores with a size range of 3–50 nm are underdeveloped. The shale, as revealed by LPNA data, has dominant slit-like or plate-like pores and an obvious low-pressure hysteresis (LPH), indicating a low gas diffusion. The deformed shale samples with a removal of OM by oxidation and their isolated kerogen further indicate that the LPH is completely related to OM, without any relationship with minerals, while an undeformed shale sample, taken from another well for a comparison, has no obvious LPH for both of its OM-removed sample and kerogen. Based on a comprehensive analysis of the relative data, it is suggested that the nanopores related to OM and clay minerals in the shale were significantly altered owing to the deformation, with a result of the pores being squeezed into the slit-like shape and converted into micropores. This extraordinary pore structure of the shale formed during the deformation process should be the main preservation mechanism of shale gas. Full article
(This article belongs to the Special Issue New Challenges in Shale Gas and Oil)
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Article
Analysis and Operation of a High DC-AC Gain 3-ϕ Capacitor Clamped Boost Inverter
Energies 2022, 15(8), 2955; https://doi.org/10.3390/en15082955 - 18 Apr 2022
Viewed by 450
Abstract
This article introduces a three-phase capacitor clamped inverter with inherent boost capability by relocating the filter components from the AC side to the configuration’s midpoint. This topology has several distinguishing characteristics, including: (a) low component count; (b) high DC-AC gain; (c) decreased capacitor [...] Read more.
This article introduces a three-phase capacitor clamped inverter with inherent boost capability by relocating the filter components from the AC side to the configuration’s midpoint. This topology has several distinguishing characteristics, including: (a) low component count; (b) high DC-AC gain; (c) decreased capacitor voltage stresses; (d) improved power quality (extremely low voltage and current THDs) without the use of an AC-side filter; and (e) decreased voltage stresses on power semiconductor devices. Simulations were carried out on the MATLAB Simulink platform, and results under steady-state conditions, load and reference change conditions, and phase sequence change conditions, along with THD profiles, are presented. This inverter’s performance was compared to that of similar converters with intrinsic gain. A 1200 W experimental prototype was built to demonstrate the system’s feasibility and benefits. When compared to existing topologies, simulation and experimental results indicate that the proposed inverter provides superior high gain, smooth control, low stress, and a long life time. Full article
(This article belongs to the Topic Application of Innovative Power Electronic Technologies)
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Review
Recent Advances in Low-Carbon and Sustainable, Efficient Technology: Strategies and Applications
Energies 2022, 15(8), 2954; https://doi.org/10.3390/en15082954 - 18 Apr 2022
Cited by 3 | Viewed by 695
Abstract
The COVID-19 pandemic has had a significant impact on the supply chains of traditional fossil fuels. According to a report by the International Energy Agency (IEA) from 2020, oil-refining activity fell by more than the IEA had anticipated. It was also assumed that [...] Read more.
The COVID-19 pandemic has had a significant impact on the supply chains of traditional fossil fuels. According to a report by the International Energy Agency (IEA) from 2020, oil-refining activity fell by more than the IEA had anticipated. It was also assumed that the demand in 2021 would likely be 2.6 million bpd below the 2019 levels. However, renewable markets have shown strong resilience during the crisis. It was determined that renewables are on track to meet 80% of the growth in electricity demand over the next 10 years and that sustainable energy will act as the primary source of electricity production instead of coal. On the other hand, the report also emphasized that measures for reducing environmental pollution and CO2 emissions are still insufficient and that significant current investments should be further expanded. The Sustainable Development of Energy, Water and Environment Systems (SDEWES) conference series is dedicated to the advancement and dissemination of knowledge on methods, policies and technologies for improving the sustainability of development by decoupling growth from the use of natural resources. The 15th SDEWES conference was held online from 1–5 September 2020; more than 300 reports with 7 special sections were organized on the virtual conference platform. This paper presents the major achievements of the recommended papers in the Special Issue of Energies. Additionally, related studies connected to the above papers published in the SDEWES series are also introduced, including the four main research fields of energy saving and emission reduction, renewable energy applications, the development of district heating systems, and the economic assessment of sustainable energy. Full article
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Article
Sieving and Covering of Wood Chips Improves Storability
Energies 2022, 15(8), 2953; https://doi.org/10.3390/en15082953 - 18 Apr 2022
Viewed by 397
Abstract
Minimising dry matter losses during storage of comminuted forest fuels is desirable from both an economic and a sustainability perspective. This study examined fuel quality and amount of recovered energy during the storage of forest wood chips stored at full industrial scale at [...] Read more.
Minimising dry matter losses during storage of comminuted forest fuels is desirable from both an economic and a sustainability perspective. This study examined fuel quality and amount of recovered energy during the storage of forest wood chips stored at full industrial scale at three locations, and the effect of sieving and covering piles with a water-resistant, vapour-permeable fabric. Sieving wood chips before storage, that is, reducing the number of fines smaller than 8 mm, reduced the cumulative dry matter losses to <2%, while cumulative dry matter losses after storage for 4–6 months using current practices, that is, unsieved and uncovered, reached 10.6%. The combined effect of storage management led to a value loss of 11.5%, while both covering and sieving led to lower losses, with the combination of sieving and covering giving a 1.3% value increase, and thus, increased storability. Full article
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Article
Demagnetization Fault Detection and Location in PMSM Based on Correlation Coefficient of Branch Current Signals
Energies 2022, 15(8), 2952; https://doi.org/10.3390/en15082952 - 18 Apr 2022
Viewed by 450
Abstract
To address such challenges as an uncertain number of demagnetization poles of the permanent magnet synchronous motor (PMSM) and cases in which the fault cannot be located, this paper proposes a fault identification and location methodology based on the analysis of the motor [...] Read more.
To address such challenges as an uncertain number of demagnetization poles of the permanent magnet synchronous motor (PMSM) and cases in which the fault cannot be located, this paper proposes a fault identification and location methodology based on the analysis of the motor stator current. First, the influence of the irreversible demagnetization of permanent magnets on the analytical model of the back electromotive force (Back-EMF) of the rotor in a single motor stator slot is analyzed. Moreover, considering the topology of the motor, the influence of the demagnetization fault on the stator phase current and branch current is analyzed. Since the stator phase currents cannot diagnose the partial demagnetization faults of PMSM with some topological structures, the stator branch current is selected as the signal for the identification and localization of the demagnetization fault. Secondly, the demagnetization fault diagnosis and mode recognition of the motor are carried out through the amplitude of the real-time branch current and the harmonic components of the PMSM. A sample database of demagnetization faults is established through calculation and normalization of the residual value of the stator branch current and the branch current of the healthy motor after demagnetization in one pole order. The fault threshold is obtained by analyzing the residual of the branch current of uniform demagnetization and the Pearson correlation coefficient of the fault sample database. Then, the correlation coefficient between the real-time branch current residual value of PMSM and the fault sample database is analyzed, and the number of demagnetization poles and the fault location are determined by the number and location of the calculated correlation coefficient exceeding the threshold. Finally, the feasibility and effectiveness of the proposed method are verified by the finite element analysis (FEA) results. Full article
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Article
Condensation Flow and Heat Transfer Characteristics of R410A in Micro-Fin Tubes and Three-Dimensional Surface Enhanced Tubes
Energies 2022, 15(8), 2951; https://doi.org/10.3390/en15082951 - 18 Apr 2022
Viewed by 479
Abstract
Condensation heat transfer characteristics (using R410A as the working fluid) were studied experimentally to evaluate the heat transfer performance in copper and stainless-steel heat transfer tubes (smooth and enhanced). Experiments were carried out for a mass flux that varied from 250 to 450 [...] Read more.
Condensation heat transfer characteristics (using R410A as the working fluid) were studied experimentally to evaluate the heat transfer performance in copper and stainless-steel heat transfer tubes (smooth and enhanced). Experiments were carried out for a mass flux that varied from 250 to 450 kg m−2 s−1, at a saturation temperature of 318 K. Single-phase heat balance verification found that the heat loss is less than 6%, and the deviation between single-phase experimental results and various prediction correlations is less than 15%. Additionally, tube side condensation flow patterns were observed and recorded. Experimental results found that the enhancement ratio of the condensation heat transfer coefficient (enhanced tube/smooth tube) of the three-dimensional surface (1EHT) tube is in the range of 1.15~1.90, while the ratio of the micro-fin (HX) tube is in the range of 1.18~1.80. Heat transfer performance is affected by material conductivity, with the thermal conductivity of the smooth tube slightly affecting the heat transfer performance; larger heat transfer enhancements are produced in the enhanced tubes. At a low mass flow rates and vapor qualities, the flow pattern is a stratified wavy flow, while at higher mass flow rates and vapor qualities, the flow pattern is an annular flow (with the area in the enhanced tube being larger than the area of a smooth tube). Flow patterns in the smooth tube are consistent with the predicted values shown in previously reported flow pattern maps. A flow pattern diagram for condensation heat transfer in enhanced tubes is presented as part of this study. The condensation heat transfer coefficient increases with an increase in mass flow. When the mass flow rate increases, the turbulence of the liquid flow increases and the liquid film becomes thinner; thermal resistance is reduced and the heat transfer coefficient increases. Heat transfer values at lower mass velocities increase slightly with increasing mass flux values; however, at higher mass flux rates the heat transfer increase is larger than that at low mass flux values. Finally, tubes produced from high thermal conductivity materials produce larger heat transfer performance gains than the gains found in smooth tubes; small diameter tubes produce larger gains than larger diameter tubes. Full article
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Article
Effect of Varying AgNO3 and CS(NH2)2 Concentrations on Performance of Ag2S/ZnO NRs/ITO Photoanode
Energies 2022, 15(8), 2950; https://doi.org/10.3390/en15082950 - 18 Apr 2022
Cited by 1 | Viewed by 632
Abstract
This research focuses on improving the photoelectrochemical performance of binary heterostructure Ag2S/ZnO NRs/ITO by manipulating synthesis conditions, particularly the concentrations of sliver nitrate AgNO3 and thiourea CS(NH2)2. The photoelectrochemical performance of Ag2S/ZnO nanorods on [...] Read more.
This research focuses on improving the photoelectrochemical performance of binary heterostructure Ag2S/ZnO NRs/ITO by manipulating synthesis conditions, particularly the concentrations of sliver nitrate AgNO3 and thiourea CS(NH2)2. The photoelectrochemical performance of Ag2S/ZnO nanorods on indium tin oxide (ITO) nanocomposite was compared to pristine ZnO NRs/ITO photoanode. The hydrothermal technique, an eco-friendly, low-cost method, was used to successfully produce Ag2S/ZnO NRs at different concentrations of AgNO3 and CS(NH2)2. The obtained thin films were characterized using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis), and photoelectrochemical studies (PECs). We observed that there was an enhancement in absorbance in the visible region and effective photoelectron transfer between the Ag2S/ZnO NRs/ITO photoelectrode and the electrolyte Red-Ox when illuminated with 100 mW cm−2. Increasing the concentration of AgNO3 caused a remarkable decrease in the optical bandgap energy (Eg) values. However, we noticed that there was an unstable trend in Eg when the concentration of CS(NH2)2 was adjusted. The photoelectrochemical studies revealed that at a bias of 1.0 V, and 0.005 M of AgNO3 and 0.03 M of CS(NH2)2, the maximum photocurrent of the Ag2S/ZnO NRs/ITO photoanode was 3.97 mA/cm2, which is almost 11 times that of plain ZnO nanorods. Based on the outcomes of this investigating, the Ag2S/ZnO NRs/ITO photoanode is proposed as a viable alternative photoanode in photoelectrochemical applications. Full article
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Editorial
Monitoring and Automation of Complex Power Systems
Energies 2022, 15(8), 2949; https://doi.org/10.3390/en15082949 - 18 Apr 2022
Viewed by 466
Abstract
This Special Issue aims at collecting new research contributions and perspectives on the topic of the monitoring and automation of modern power systems [...] Full article
(This article belongs to the Special Issue Monitoring and Automation of Complex Power Systems)
Article
Sedimentary Environment and Model for Organic Matter Enrichment: Chang 7 Shale of Late Triassic Yanchang Formation, Southern Margin of Ordos Basin, China
Energies 2022, 15(8), 2948; https://doi.org/10.3390/en15082948 - 17 Apr 2022
Viewed by 526
Abstract
Shale oil is an unconventional oil resource that needs to be developed and utilized urgently. However, the Chang 7 shale in the Ordos Basin, as the most typical continental source rock in China, is limited by the study of organic matter (OM) enrichment [...] Read more.
Shale oil is an unconventional oil resource that needs to be developed and utilized urgently. However, the Chang 7 shale in the Ordos Basin, as the most typical continental source rock in China, is limited by the study of organic matter (OM) enrichment factors in continental lacustrine facies, and there are still controversies about the controlling factors, which limit the progress of oil and gas exploration. This paper aims to reconstruct the paleoenvironment of Chang 7 shale in the southern margin of Ordos Basin and reveal the controlling factors of organic rich shale by organic and elemental analysis, X-ray diffraction (XRD) analysis, thin section observation, and scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) analysis. The results show that during the deposition period of Chang 7 shale, the climate was warm and humid, the lake water has strong reducing, low salinity and rapid depth changes. Total organic carbon (TOC) is positively correlated with salinity and hydrothermal action and inversely proportional to terrigenous input. The high productivity, low consumption and low dilution result in high enrichment of shale OM in the southern margin of Ordos Basin. Full article
(This article belongs to the Special Issue Shale Oil and Gas Accumulation Mechanism)
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Article
Collaborative Robust Optimization Strategy of Electric Vehicles and Other Distributed Energy Considering Load Flexibility
Energies 2022, 15(8), 2947; https://doi.org/10.3390/en15082947 - 17 Apr 2022
Cited by 1 | Viewed by 543
Abstract
Aggregated electric vehicles (EVs) integrated to the grid and intermittent wind and solar energy increased the complexity of the economic dispatch of the power grid. Aggregated EVs have a great potential to reduce system operating costs because of their dual attributes of load [...] Read more.
Aggregated electric vehicles (EVs) integrated to the grid and intermittent wind and solar energy increased the complexity of the economic dispatch of the power grid. Aggregated EVs have a great potential to reduce system operating costs because of their dual attributes of load and energy storage. In this paper, plugged-in EV is refined into three categories: rated power charging, adjustable charging, and flexible charging–discharging, and then control models are established separately; the concept of temporal flexibility for EV clusters is proposed for the adjustable charging and flexible charging–discharging of EV sets; then, the schedule boundary of EV clusters is determined under the flexibility constraints. The interval is used to describe the intermittent nature of renewable energy, and the minimum operating cost of the system is taken as the goal to construct a distributed energy robust optimization model. By decoupling the model, a two-stage efficient solution is achieved. An example analysis verifies the effectiveness and superiority of the proposed strategy. The proposed strategy can minimize the total cost while meeting the demand difference of EV users. Full article
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Article
Tracing and Evaluating Life-Cycle Carbon Emissions of Urban Multi-Energy Systems
Energies 2022, 15(8), 2946; https://doi.org/10.3390/en15082946 - 17 Apr 2022
Viewed by 451
Abstract
With the acceleration of urbanization, urban multi-energy systems (UMESs) generate more and more carbon emissions, causing severe environmental issues. The carbon generated by UMESs includes not only emissions from the consumption of fossil fuels for electricity generation during operation phases, but also those [...] Read more.
With the acceleration of urbanization, urban multi-energy systems (UMESs) generate more and more carbon emissions, causing severe environmental issues. The carbon generated by UMESs includes not only emissions from the consumption of fossil fuels for electricity generation during operation phases, but also those from the transportation, extraction, and recycling of materials during construction phases. Meanwhile, as carbon emissions are delivered with the energy flow among devices in the UMES, they are distributed differently across devices. Under this background, analyzing the carbon emissions of UMESs considering different life-cycle phases (i.e., operation and construction) and carbon flow characteristics is essential for carbon reduction and environmental protection. Considering that, a novel framework for tracing and evaluating life-cycle carbon emissions of UMESs is proposed in this paper. Firstly, the carbon emission models of different devices in UMESs, including energy sources and energy hub (EH), are established considering both the construction and operation phases. On this basis, the carbon flow matrixes of EHs coupled with the energy flow model are formulated to trace the distribution of life-cycle carbon emissions in UMESs. Moreover, different evaluation indices including the device carbon distribution factor (DCDF) and consumer carbon distribution factor (CCDF) are proposed to quantify the carbon emissions of devices and consumers in UMESs. The case study results based on a typical test UMES are presented to verify the effectiveness of the proposed framework. The analysis results of the test system show that about 60% of carbon emissions are delivered to electricity loads and the construction-produced carbon emissions of energy sources and EH devices account for nearly 35% of total carbon emissions at some periods. Full article
(This article belongs to the Special Issue Frontiers in Smart Grids and Microgrids)
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Article
Identifying the Determinants of Crude Oil Market Volatility by the Multivariate GARCH-MIDAS Model
Energies 2022, 15(8), 2945; https://doi.org/10.3390/en15082945 - 17 Apr 2022
Viewed by 514
Abstract
Many macro-level variables have been used in forecasting crude oil price volatility. This article aims to identify which variables have the greatest impact and give more accurate predictions. The GARCH-MIDAS model with variable selection enables us to incorporate many variables in a single [...] Read more.
Many macro-level variables have been used in forecasting crude oil price volatility. This article aims to identify which variables have the greatest impact and give more accurate predictions. The GARCH-MIDAS model with variable selection enables us to incorporate many variables in a single model. By combining the log-likelihood function with adaptive lasso penalty, three most informative determinants have been identified, namely, macroeconomic uncertainty, financial uncertainty and default yield spread. Out-of-sample results show that using these three variables significantly improves prediction accuracy compared to baseline models. However, the variables widely studied by other scholars, such as the supply and demand of crude oil, industrial production index, etc., were not selected, indicating that the impact of these variables may be overestimated. When studying crude oil price volatility, macroeconomic and financial market uncertainties can be used as effective predictors for investors and market analysts. Crude oil market participants should focus on macroeconomic and financial market uncertainties to make risk management more efficient. Full article
(This article belongs to the Topic Frontier Research in Energy Forecasting)
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Article
Advantage of a Thermoelectric Generator with Hybridization of Segmented Materials and Irregularly Variable Cross-Section Design
Energies 2022, 15(8), 2944; https://doi.org/10.3390/en15082944 - 17 Apr 2022
Cited by 1 | Viewed by 450
Abstract
As a direct energy converter between heat and electricity, thermoelectric generators (TEGs) have potential applications including recovery of waste heat, and solar thermoelectric power generation. Geometric parameter and material are two critical factors to improve the TEG performance. However, the strategies base on [...] Read more.
As a direct energy converter between heat and electricity, thermoelectric generators (TEGs) have potential applications including recovery of waste heat, and solar thermoelectric power generation. Geometric parameter and material are two critical factors to improve the TEG performance. However, the strategies base on structure design and material development are always separated. There are limited studies on the effects of consolidating them simultaneously. Here, an idea of segmented material coupled with irregularly variable cross-section design was conceived to further improve the TEG output power. The performance of TEGs with rectangular leg, segmented leg, variable cross-sectional leg, and the new design are compared. The coupling effects between various mechanisms are revealed, which are responsible for the superior performance provided by the developed design. Based on this knowledge, a multiparameters optimization was performed through the genetic algorithm to reach the optimal combination of design parameters. The results show that, with a constraint of certain material volume, the optimal performance of the TEG can be further enhanced by coupling segmented material and irregularly variable cross-section design. An improvement of 51.71% was achieved when compared with the conventional counterpart. This work offers a simple route to enhance the TEG performance when the device materials are specified, without an increase in the cost of manufacturing. Full article
(This article belongs to the Topic Thermoelectric Energy Harvesting)
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Article
SOC Balancing and Coordinated Control Based on Adaptive Droop Coefficient Algorithm for Energy Storage Units in DC Microgrid
Energies 2022, 15(8), 2943; https://doi.org/10.3390/en15082943 - 17 Apr 2022
Cited by 1 | Viewed by 506
Abstract
In order to achieve a state-of-charge (SOC) balance among multiple energy storage units (MESUs) in an islanded DC microgrid, a SOC balancing and coordinated control strategy based on the adaptive droop coefficient algorithm for MESUs is proposed. When the SOC deviation is significant, [...] Read more.
In order to achieve a state-of-charge (SOC) balance among multiple energy storage units (MESUs) in an islanded DC microgrid, a SOC balancing and coordinated control strategy based on the adaptive droop coefficient algorithm for MESUs is proposed. When the SOC deviation is significant, the droop coefficient for an energy storage unit (ESU) with a higher (or lower) SOC is set to a minimum value when discharging (or charging). The ESU with the higher (or lower) SOC is controlled to discharge (or charge) with the rated power, while the other ESU compensates for the remaining power when the demanded discharging (or charging) power is greater than the rated power of the individual ESU. Otherwise, when the demanded discharging (or charging) power is lower than the rated power of either ESU, the ESU with the higher (or lower) SOC releases (or absorbs) almost all the required power while the other ESU barely absorbs or releases power, thus quickly realizing SOC balancing. When the SOC deviation is slight, the fuzzy logic algorithm dynamically adjusts the droop coefficient and changes the power distribution relationship to balance the SOC accurately. Furthermore, a bus voltage recovery control scheme is employed to regulate the bus voltage, thus improving the voltage quality. The energy coordinated management strategy is adopted to ensure the power balance and stabilize the bus voltage in the DC microgrid. A simulation model is built in MATLAB/Simulink, and the simulation results demonstrate the effectiveness of the proposed control strategy in achieving fast and accurate SOC balance and regulating the bus voltage. Full article
(This article belongs to the Special Issue Microgrids and the Integration of Energy Storage Systems)
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Article
Simulation about the Effect of the Height-to-Stroke Ratios of Ports on Power and Emissions in an OP2S Engine Using Diesel/Methanol Blends
Energies 2022, 15(8), 2942; https://doi.org/10.3390/en15082942 - 17 Apr 2022
Cited by 1 | Viewed by 479
Abstract
Zero carbon emissions will dominate the future of internal combustion engines (ICEs). Existing technology has pushed the performance of ICEs operating on traditional working principles to almost reach their limit. The new generation of ICEs needs to explore new efficient combustion modes. For [...] Read more.
Zero carbon emissions will dominate the future of internal combustion engines (ICEs). Existing technology has pushed the performance of ICEs operating on traditional working principles to almost reach their limit. The new generation of ICEs needs to explore new efficient combustion modes. For new combustion modes to simplify the emission after treatment, the opposed-piston, two-stroke (OP2S) diesel engine is a powertrain with great potential value. Combined with dual-fuel technology, the OP2S diesel engine can effectively reduce carbon emissions to achieve clean combustion. Hence, methanol/diesel dual fuel was burnt in the OP2S engine to create a clean combustion mode for future demands. In the present work, a 1D simulation model of an OP2S diesel engine was established and verified. We investigated the influence of port height to stroke ratio (HSR) on power and emission performances of the OP2S diesel engine under different methanol ratios. The results show that the methanol ratio extremely influences the indicated power (IP) with the HSR of intake ports increasing. The IP decreases by about 1.8–2.0% for every 5% increase in methanol. Correspondingly, the methanol ratio extremely influences the indicated thermal efficiency (ITE), with the HSR of exhaust ports increasing. The ITE increases by about 2.1–3.1% for every 5% increase in methanol. The increasing methanol ratio reduces the HSR of ports for the optimal IP and ITE. To balance power performance and emission performance, the methanol ratio should be kept to 10–15%. Full article
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Article
New Insights into Abnormal Combustion Phenomena Induced by Diesel Spray-Wall Impingement under Engine-Relevant Conditions
Energies 2022, 15(8), 2941; https://doi.org/10.3390/en15082941 - 17 Apr 2022
Viewed by 442
Abstract
High altitude and low temperature is the common extreme environment for internal combustion engines. Under such operating conditions, heavy-duty diesel engines often suffer from serious abnormal combustion, such as knocking combustion, which results in piston crown breakdown and cylinder head erosion. Spray-wall impingement [...] Read more.
High altitude and low temperature is the common extreme environment for internal combustion engines. Under such operating conditions, heavy-duty diesel engines often suffer from serious abnormal combustion, such as knocking combustion, which results in piston crown breakdown and cylinder head erosion. Spray-wall impingement and pool fires are considered potential causes; however, the detailed mechanism remains poorly understood owing to the lack of research data. In this study, for the first time, the destructive abnormal combustion induced by diesel spray-wall impingement was identified using an optical rapid compression machine under engine-relevant conditions at high altitudes. Combining instantaneous pressure and temperature measurements with simultaneously recorded high-speed photography gives useful insights into understanding the detailed combustion processes. The experimental results show that depending on the extent of diesel spray-wall impingement, supersonic detonation-like reaction fronts featuring bright luminosity can be observed. The propagation of these reaction fronts in-cylinder results in severe pressure oscillations with an amplitude approaching hundreds of atmospheres, which is like the super-knock events in boosted direct-injection spark-ignition engines. Further parametric analysis indicates that the interplay between the diffusion combustion controlled by diesel spray and the premixed combustion dominated by attached film evaporation results in the formation of abnormal combustion. Destructive reaction fronts tend to occur at a prolonged ignition delay time, which facilitates the mixing between diesel evaporation and hot air. Full article
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Review
Biogas and Biomethane Production and Usage: Technology Development, Advantages and Challenges in Europe
Energies 2022, 15(8), 2940; https://doi.org/10.3390/en15082940 - 17 Apr 2022
Cited by 2 | Viewed by 1121
Abstract
In line with the low-carbon strategy, the EU is expected to be climate-neutral by 2050, which would require a significant increase in renewable energy production. Produced biogas is directly used to produce electricity and heat, or it can be upgraded to reach the [...] Read more.
In line with the low-carbon strategy, the EU is expected to be climate-neutral by 2050, which would require a significant increase in renewable energy production. Produced biogas is directly used to produce electricity and heat, or it can be upgraded to reach the “renewable natural gas”, i.e., biomethane. This paper reviews the applied production technology and current state of biogas and biomethane production in Europe. Germany, UK, Italy and France are the leaders in biogas production in Europe. Biogas from AD processes is most represented in total biogas production (84%). Germany is deserving for the majority (52%) of AD biogas in the EU, while landfill gas production is well represented in the UK (43%). Biogas from sewage sludge is poorly presented by less than 5% in total biogas quantities produced in the EU. Biomethane facilities will reach a production of 32 TWh in 2020 in Europe. There are currently 18 countries producing biomethane (Germany and France with highest share). Most of the European plants use agricultural substrate (28%), while the second position refers to energy crop feedstock (25%). Sewage sludge facilities participate with 14% in the EU, mostly applied in Sweden. Membrane separation is the most used upgrading technology, applied at around 35% of biomethane plants. High energy prices today, and even higher in the future, give space for the wider acceptance of biomethane use. Full article
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Article
Smart Wireless Climate Sensor Node for Indoor Comfort Quality Monitoring Application
Energies 2022, 15(8), 2939; https://doi.org/10.3390/en15082939 - 16 Apr 2022
Viewed by 633
Abstract
The indoor environment climate should be controlled by continuously maintaining the temperature and relative humidity to achieve thermal comfort. A monitoring system of both parameters is the first step to improving indoor comfort quality. This paper presents a smart wireless climate sensor node [...] Read more.
The indoor environment climate should be controlled by continuously maintaining the temperature and relative humidity to achieve thermal comfort. A monitoring system of both parameters is the first step to improving indoor comfort quality. This paper presents a smart wireless climate sensor node for indoor temperature and humidity monitoring with a powering strategy and design approach for autonomous operation. The data logging results are sent to the cloud using Internet of Things protocol for thermal comfort monitoring and analysis. The monitoring and analysis results are useful to monitor and control the indoor thermal comfort condition for room occupants. A sensor node was designed that includes a low-power mode and compact size features. It consists of a built-in AVR-based microcontroller, a temperature and humidity sensor, and a wireless module with a supercapacitor as the power storage. A low-power algorithm and Internet of Things system were implemented to reduce the total energy consumption as low as possible during operation while improving the thermal comfort quality. This developed sensor node has a small error for temperature, and relative humidity sensed values resulting from calibration. At the same time, it also consumes low power for one cycle of data acquisition. The device was integrated with an Internet of Things monitoring system to monitor indoor thermal comfort in the field experiment. The experiment results showed that the indoor temperature and relative humidity were measured and recorded in the range of 25–30 °C and 30–40%, respectively. This prototype is a preliminary design to achieve an autonomous sensor node with a low-power energy consumption goal. Thus, with this feature, the developed sensor node has potential to couple with a micro energy harvester module toward a fully autonomous active node in further development. Full article
(This article belongs to the Special Issue Smart Home Technologies Based on IoT Concepts)
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