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Energies, Volume 18, Issue 3 (February-1 2025) – 112 articles

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13 pages, 3968 KiB  
Article
One-Step Synthesis CuCoNiSxO4−x Thio/Oxy Spinel on Ni Foam for High-Performance Asymmetric Supercapacitors
by Anastassiya A. Migunova, Renata R. Nemkayeva, Yeldar A. Zhakanbayev and Yuriy Zh. Tuleushev
Energies 2025, 18(3), 561; https://doi.org/10.3390/en18030561 (registering DOI) - 24 Jan 2025
Abstract
Mixed transition metal sulfides are promising materials for positive electrodes of asymmetric supercapacitors because they have a large potential for increasing the electrical characteristics of these devices. The paper presents the results of a study of a material based on spinel CuCoNiSx [...] Read more.
Mixed transition metal sulfides are promising materials for positive electrodes of asymmetric supercapacitors because they have a large potential for increasing the electrical characteristics of these devices. The paper presents the results of a study of a material based on spinel CuCoNiSxO4−x with both sulfide and oxide sublattices, prepared by a one-step hydrothermal method directly on nickel foam, forming an array of whiskers. Electrochemical studies showed that a positive electrode, CuCoNiS2O2, exhibited a high specific capacitance of 3612 F g−1 at a current density of 1 A g−1. The assembled asymmetric supercapacitor with activated carbon as a negative electrode achieved a specific capacitance of 133.5 F g−1 at 1 A g−1 and a potential window of 1.7 V. Its energy density was 53.6 Wh kg−1 at a power density of 805 W kg−1 and the power density reached 17,000 W kg−1 at an energy density of 18.9 W h kg−1. The assembled device exhibits 52% of capacitance retention after the 20,000 cycles at a current density of 10 A g−1 with 97% coulombic efficiency. These results demonstrate that the CuCoNiSxO4−x system is competitive with other quaternary transition metal sulfides, and this type of spinel is a perspective electrode material for high-performance supercapacitors. Full article
(This article belongs to the Section D2: Electrochem: Batteries, Fuel Cells, Capacitors)
►▼ Show Figures

Figure 1

Figure 1
<p>SEM images of CuCoNiS<sub>2</sub>O<sub>2</sub> on fragment of Ni foam (<b>a</b>) and its EDS spectrum (<b>b</b>).</p> Full article ">Figure 2
<p>XRD patterns of the CuCoNiS<sub>2</sub>O<sub>2</sub>/NF samples (<b>a</b>) and typical Raman spectrum of the spinel phase (<b>b</b>).</p> Full article ">Figure 3
<p>Evaluation of the electrochemical performance of the CuCoNiS<sub>2</sub>O<sub>2</sub>/NF electrode in a three-electrode cell: (<b>a</b>) CV curves of the electrode at different scan rates; (<b>b</b>) GCD curves of the electrode at various current densities; (<b>c</b>) rate capability of the electrode; (<b>d</b>) Nyquist plot of the electrode.</p> Full article ">Figure 4
<p>CV curves of the CuCoNiS<sub>2</sub>O<sub>2</sub>//AC ACS at various scan rates ranging from 5 to 100 mV s<sup>−1</sup> (<b>a</b>); CV curves collected in various potential windows at current density 1 A g<sup>−1</sup> (<b>b</b>); GCD curves of the device collected at different potential (<b>c</b>); Nyquist plot of the ASC before and after 20,000 cycles (<b>d</b>); cycling performances of ASC at a current density of 10 A g<sup>−1</sup> (<b>e</b>); Ragone plot of the CuCoNiS<sub>2</sub>O<sub>2</sub>//AC compared with other energy storage devices (<b>f</b>) (S. Guo 2018 [<a href="#B5-energies-18-00561" class="html-bibr">5</a>], W. Chen 2019 [<a href="#B18-energies-18-00561" class="html-bibr">18</a>], S.K. Shinde 2021 [<a href="#B19-energies-18-00561" class="html-bibr">19</a>], S. Q. Gao 2019 [<a href="#B24-energies-18-00561" class="html-bibr">24</a>]).</p> Full article ">Figure 4 Cont.
<p>CV curves of the CuCoNiS<sub>2</sub>O<sub>2</sub>//AC ACS at various scan rates ranging from 5 to 100 mV s<sup>−1</sup> (<b>a</b>); CV curves collected in various potential windows at current density 1 A g<sup>−1</sup> (<b>b</b>); GCD curves of the device collected at different potential (<b>c</b>); Nyquist plot of the ASC before and after 20,000 cycles (<b>d</b>); cycling performances of ASC at a current density of 10 A g<sup>−1</sup> (<b>e</b>); Ragone plot of the CuCoNiS<sub>2</sub>O<sub>2</sub>//AC compared with other energy storage devices (<b>f</b>) (S. Guo 2018 [<a href="#B5-energies-18-00561" class="html-bibr">5</a>], W. Chen 2019 [<a href="#B18-energies-18-00561" class="html-bibr">18</a>], S.K. Shinde 2021 [<a href="#B19-energies-18-00561" class="html-bibr">19</a>], S. Q. Gao 2019 [<a href="#B24-energies-18-00561" class="html-bibr">24</a>]).</p> Full article ">
17 pages, 855 KiB  
Article
Lessons Learned from Four Real-Life Case Studies: Energy Balance Calculations for Implementing Positive Energy Districts
by Helmut Bruckner, Svitlana Alyokhina, Simon Schneider, Manuela Binder, Zain Ul Abdin, Rudi Santbergen, Maarten Verkou, Miro Zeman, Olindo Isabella, Marco Pagliarini, Cristiana Botta and Ana Streche
Energies 2025, 18(3), 560; https://doi.org/10.3390/en18030560 - 24 Jan 2025
Abstract
Positive Energy Districts (PEDs) are integral to achieving sustainable urban development by enhancing energy self-sufficiency and reducing carbon emissions. This paper explores energy balance calculations in four diverse case study districts within different climatic conditions—Fiat Village in Settimo Torinese (Italy), Großschönau (Austria), Beursplain [...] Read more.
Positive Energy Districts (PEDs) are integral to achieving sustainable urban development by enhancing energy self-sufficiency and reducing carbon emissions. This paper explores energy balance calculations in four diverse case study districts within different climatic conditions—Fiat Village in Settimo Torinese (Italy), Großschönau (Austria), Beursplain in Amsterdam (Netherlands), and Lunca Pomostului in Reşiţa (Romania)—as part of the SIMPLY Positive project. Each district faces unique challenges, such as outdated infrastructure or heritage protection, which we address through tailored strategies including building renovations and the integration of renewable energy systems. Additionally, we employ advanced simulation methodologies to assess energy performance. Simulation results highlight the significance of innovative technologies like photovoltaic-thermal (PVT) systems, application of demand-side actions, and flexible grid usage. Furthermore, mobility assessments and resident-driven initiatives demonstrate the critical role of community engagement in reducing carbon footprints. This study underscores the adaptability of PED frameworks across varied urban contexts and provides actionable insights for scaling similar strategies globally, supporting net-zero energy targets. Full article
(This article belongs to the Special Issue Advanced Energy Systems in Energy Resilient, Zero/Positive Energy Buildings, Communities and Districts)
22 pages, 2849 KiB  
Article
Study on the Effect of Mixed-Phase Icing on the Aerodynamic Characteristics of Wind Turbine Airfoil
by Xiang Wang, Yiyao Ru, Huanyu Zhao and Zhengzhi Wang
Energies 2025, 18(3), 559; https://doi.org/10.3390/en18030559 - 24 Jan 2025
Abstract
Wind turbines operating in high-altitude and cold regions are susceptible to icing phenomenon, which is a serious threat to the power generation efficiency and operational safety. On the basis of the current research on supercooled droplet icing, mixed-phase icing is investigated. Based on [...] Read more.
Wind turbines operating in high-altitude and cold regions are susceptible to icing phenomenon, which is a serious threat to the power generation efficiency and operational safety. On the basis of the current research on supercooled droplet icing, mixed-phase icing is investigated. Based on icing numerical simulations under mixed-phase conditions, the aerodynamic characteristics of wind turbine airfoils before and after icing are analyzed. The results indicate that as the icing thickness increases, the aerodynamic characteristics of the airfoil gradually deteriorate, with the lift decreasing by 40.2% and the drag increasing by 135.2%. The aerodynamic characteristics of airfoil after icing are analyzed under both glaze and rime ice conditions and compared to those of the clear airfoil. The results show that icing leads to a decrease in the lift coefficient and an increase in the drag coefficient of the airfoil. This deterioration is primarily due to the fact that icing causes premature separation of the airfoil airflow, and icing can cause obstruction at the leading edge, which leads to the formation of local vortices and a decline in aerodynamic performance. The effects of icing on the aerodynamic characteristics of wind turbine airfoils under glaze and rime ice conditions are compared, and the lift-to-drag ratio decreases by 87.9% under the glaze ice condition and by 62.4% under rime ice conditions. The results show that the effects of mixed-phase icing under glaze ice conditions has a more severe impact than under rime ice conditions. Full article
(This article belongs to the Section A3: Wind, Wave and Tidal Energy)
26 pages, 1372 KiB  
Article
Catalytic Methane Decomposition for the Simultaneous Production of Hydrogen and Low-Reactivity Biocarbon for the Metallurgic Industry
by Roger A. Khalil, Sethulakshmy Jayakumari, Halvor Dalaker, Liang Wang, Pål Tetlie and Øyvind Skreiberg
Energies 2025, 18(3), 558; https://doi.org/10.3390/en18030558 - 24 Jan 2025
Abstract
To reach agreed-on climate goals, it is necessary to develop new energy carriers and industrial materials that are carbon-neutral. To combat global warming and keep Earth’s temperature from increasing by 1.5 °C, some of these solutions need to be carbon-negative. This study fulfills [...] Read more.
To reach agreed-on climate goals, it is necessary to develop new energy carriers and industrial materials that are carbon-neutral. To combat global warming and keep Earth’s temperature from increasing by 1.5 °C, some of these solutions need to be carbon-negative. This study fulfills this criterion by producing clean hydrogen and biocarbon suitable for the metallurgic industry through the thermal decomposition of methane using biocarbon as a catalyst. Five different biomass samples were used to prepare biocarbons at a pyrolysis temperature of 1000 °C with a holding time of 90 min. When methane was cracked at 1100 °C with a holding time of 90 min, the highest hydrogen production was 105 mol/kg biocarbon, achieved using birch bark. The lowest hydrogen yield, of 68 mol/kg biocarbon, was achieved with steam-explosion pellets. All the biocarbons showed substantial carbon deposition from cracked methane on their surfaces, with the highest deposition on birch bark and spruce wood biocarbons of 42% relative to the biocarbon start weight. The carbon deposition increased with the decomposition temperature, the methane share in the purge gas and the holding time. The steam-explosion pellets, after deactivation, had a CO2 reactivity that was comparable to coke, a reducing agent that is commonly used in manganese-producing industries. About 90% of the potassium and sodium were removed from the biocarbon during catalytic decomposition of methane performed at 1100 °C. The alkali removal was calculated relative to the biocarbon produced under the same conditions, but with 100% N2 purge instead of CH4. After catalytic decomposition, the surface area of the biocarbon was reduced by 11–34%, depending on the biocarbon type. Full article
(This article belongs to the Section B: Energy and Environment)
18 pages, 4820 KiB  
Review
Research and Application of Oxygen-Reduced-Air-Assisted Gravity Drainage for Enhanced Oil Recovery
by Jiangfei Wei, Hongwei Yu, Ming Gao, Peifeng Yan, Kesheng Tan, Yutong Yan, Keqiang Wei, Mingyan Sun, Xianglong Yu, Zhihua Chen and Qiang Chen
Energies 2025, 18(3), 557; https://doi.org/10.3390/en18030557 - 24 Jan 2025
Abstract
This paper summarizes the research progress and applications of oxygen-reduced-air-assisted gravity drainage (OAGD) in enhanced oil recovery (EOR). The fundamental principles and key technologies of OAGD are introduced, along with a review of domestic and international field trials. Factors influencing displacement performance, including [...] Read more.
This paper summarizes the research progress and applications of oxygen-reduced-air-assisted gravity drainage (OAGD) in enhanced oil recovery (EOR). The fundamental principles and key technologies of OAGD are introduced, along with a review of domestic and international field trials. Factors influencing displacement performance, including low-temperature oxidation reactions, injection rates, and reservoir dip angles, are discussed in detail. The findings reveal that low-temperature oxidation significantly improves the recovery efficiency through the dynamic balance of light hydrocarbon volatilization and fuel deposition, coupled with the synergistic optimization of the reservoir temperature, pressure, and oxygen concentration. Proper control of the injection rate stabilizes the oil–gas interface, expands the swept volume, and delays gas channeling. High-dip reservoirs, benefiting from enhanced gravity segregation, demonstrate superior displacement efficiency. Finally, the paper highlights future directions, including the optimization of injection parameters, deepening studies on reservoir chemical reaction mechanisms, and integrating intelligent gas injection technologies to enhance the effectiveness and economic viability of OAGD in complex reservoirs. Full article
(This article belongs to the Special Issue Petroleum and Natural Gas Engineering)
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Figure 1

Figure 1
<p>Structural flow chart of the OAGD review.</p> Full article ">Figure 2
<p>Schematic diagram of the GAGD process.</p> Full article ">Figure 3
<p>Cryogenic separation process flow. 1—air compressor, 2—pre-cooling unit, 3—molecular sieve adsorber, 4—electric heater, 5—cold box, 6—turbo expander, 7—main heat exchanger, 8—rectification column, and 9—condenser evaporator.</p> Full article ">Figure 4
<p>Process flow of membrane separation method. 1—air compressor, 2—filter, 3—dryer, 4—electric heater, and 5—membrane module.</p> Full article ">Figure 5
<p>Pressure swing adsorption process flow. 1—air compressor, 2—filter, 3—dryer, 4—PSA tower, and 5—buffer tank.</p> Full article ">Figure 6
<p>Mechanism of LTO [<a href="#B18-energies-18-00557" class="html-bibr">18</a>].</p> Full article ">Figure 7
<p>Reaction pathways of crude oil during LTO [<a href="#B55-energies-18-00557" class="html-bibr">55</a>].</p> Full article ">Figure 8
<p>Comparison of the gas injection rate on oil saturation before the breakthrough time [<a href="#B60-energies-18-00557" class="html-bibr">60</a>].</p> Full article ">Figure 9
<p>Stable nitrogen flooding process diagram [<a href="#B10-energies-18-00557" class="html-bibr">10</a>].</p> Full article ">Figure 10
<p>Relationship between oil recovery factor and injected gas volume at different injection rates [<a href="#B67-energies-18-00557" class="html-bibr">67</a>].</p> Full article ">Figure 11
<p>Relationship between gravity number and oil recovery factor in oxygen-reduced air gravity drainage [<a href="#B68-energies-18-00557" class="html-bibr">68</a>].</p> Full article ">
20 pages, 11324 KiB  
Article
Power Quality Improvement with Three-Phase Shunt Active Power Filter Prototype Based on Harmonic Component Separation Method with Low-Pass Filter
by Marian Gaiceanu, Silviu Epure, Razvan Constantin Solea and Razvan Buhosu
Energies 2025, 18(3), 556; https://doi.org/10.3390/en18030556 - 24 Jan 2025
Abstract
This work contributes to both Romania’s and the European Union’s energy policies by highlighting the research results obtained within the Dunarea de Jos University of Galati, but also through the technological transfer of this knowledge to the industry. In order to improve the [...] Read more.
This work contributes to both Romania’s and the European Union’s energy policies by highlighting the research results obtained within the Dunarea de Jos University of Galati, but also through the technological transfer of this knowledge to the industry. In order to improve the power quality of the nonlinear loads connected to the electrical grid, a three-phase shunt active power filter prototype based on the Harmonic Component Separation Method with a Low-Pass Filter was used. The active power filter is connected at the Point of Common Coupling to compensate for individual loads or even all of them simultaneously. Therefore, active power filters can be used to compensate for the power factor and reduce the harmonic distortion of power supplies, or for processes subsequently connected to additional nonlinear loads, thus improving the energy efficiency. The shunt active power filter prototype is composed of the power side (three-phase insulated gate bipolar transistor bridge, DC link capacitor precharge system, inductive filter) and the control side (gate drive circuits, control subsystems, signal acquisition system). The filter control strategy is based on the principle of separating harmonic components with a low-pass filter, implemented by the authors on the industrial prototype. In this paper, the main technical features of the industrial shunt active power filter prototype are specified. The authors of this paper involved three cascaded control loops: the DC link voltage control loop, the shunt active power filter current control loop and the phase-locked loop. Both simulation and experimental results for the shunt-type active power filter prototype were obtained. By analyzing the obtained waveforms of the power supply source in two cases (with and without an active power filter), a decrease in the total harmonic distortion was demonstrated, both the voltage harmonic distortion factor THDu and the current harmonic distortion factor THDi in the case of the active power filter connection. By using the Field-Programmed Gate Array processing platform, the powerful computational speed features were exploited to implement the active shunt power filter control on an experimental test bench. Conducting source current harmonics mitigation increased the efficiency of the power system by decreasing the respective harmonic Joule losses. The energy-saving feature led to the increased added value of the parallel active power filter. Through the performed laboratory tests, the authors demonstrated the feasibility of the proposed control solution for the industrial prototype. In accordance with the European Union’s Research and Technological Development Policy, the development of an innovation ecosystem was taken into consideration. The unified and efficient integration of all the specific actors (enterprises, research institutes, universities and entrepreneurs) in innovation was achieved. Full article
(This article belongs to the Section F: Electrical Engineering)
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Figure 1

Figure 1
<p>The Harmonic Component Separation Method with a Low-Pass Filter.</p> Full article ">Figure 2
<p>The MATLAB-Simulink implementation of the harmonic improvement power system (HCSLPF).</p> Full article ">Figure 3
<p>Block diagram of the generation of current references for the active power filter using Harmonic Component Extraction.</p> Full article ">Figure 4
<p>The MATLAB-Simulink implementation of the harmonic improvement control system by using the HCSLPF control method.</p> Full article ">Figure 5
<p>The operation of the DC voltage loop of the SAPF.</p> Full article ">Figure 6
<p>The power supply waveforms: three phase voltages (blue) and three phase currents (red).</p> Full article ">Figure 7
<p>The nonlinear three-phase load currents.</p> Full article ">Figure 8
<p>The three-phase reference currents generated by the HCSLPF.</p> Full article ">Figure 9
<p>The measured three-phase SAPF currents.</p> Full article ">Figure 10
<p>The selected FFT window (red line) from the power supply phase current analysis (blue line) without an SAPF connection (red marked signal).</p> Full article ">Figure 11
<p>The FFT analyses of the power supply phase current without an SAPF connection.</p> Full article ">Figure 12
<p>The selected FFT window (red line) from the power supply phase current (blue line) analysis with an SAPF connection (red marked signal).</p> Full article ">Figure 13
<p>The FFT analyses of the power supply phas1 current with an SAPF connection.</p> Full article ">Figure 14
<p>Comparative side-by-side THD analyses of the power supply phase current (<b>a</b>) without an SAPF connection and (<b>b</b>) with an SAPF connection.</p> Full article ">Figure 15
<p>The FPGA control loop implementation of the SAPF industrial prototype.</p> Full article ">Figure 16
<p>The implemented three-phase FPGA PWM signal generator.</p> Full article ">Figure 17
<p>The implemented FPGA PLL circuit.</p> Full article ">Figure 18
<p>The grid three-phase voltage with a nonlinear load.</p> Full article ">Figure 19
<p>The grid phasor harmonics.</p> Full article ">Figure 20
<p>The grid phase voltage and phase current without an SAPF connection.</p> Full article ">Figure 21
<p>The nonlinear three-phase load current system.</p> Full article ">Figure 22
<p>The harmonics content of the load current, THD<sub>i</sub> = 29.1%.</p> Full article ">Figure 23
<p>The harmonics content of the power supply voltage, THD<sub>u</sub> = 0.9%, without an SAPF connection.</p> Full article ">Figure 24
<p>The grid three-phase voltage system with an SAPF connection.</p> Full article ">Figure 25
<p>The harmonics content of the grid phase current with an SAPF connection: THD<sub>i</sub> = 5.6%.</p> Full article ">Figure 26
<p>The harmonics content of the grid phase voltage with an SAPF connection: THD<sub>u</sub> = 0.2%.</p> Full article ">Figure 27
<p>The grid phase voltage and current with an SAPF connection.</p> Full article ">Figure 28
<p>Comparative experimental results of the harmonic distortion (without the SAPF and with the SAPF) for grid current signals.</p> Full article ">Figure 29
<p>Comparative experimental results of the harmonic distortion (without the SAPF and with the SAPF) for grid voltage signals.</p> Full article ">Figure 30
<p>The Human Machine Interface on the front of the SAPF prototype (<b>a</b>) and the Point of Common Coupling (<b>b</b>).</p> Full article ">
16 pages, 1862 KiB  
Article
The Potential of a Thermoelectric Heat Dissipation System: An Analytical Study
by Xuechun Li, Rujie Shi and Kang Zhu
Energies 2025, 18(3), 555; https://doi.org/10.3390/en18030555 - 24 Jan 2025
Abstract
Thermoelectric heat dissipation systems offer unique advantages over conventional systems, including vibration-free operation, environmental sustainability, and enhanced controllability. This study examined the benefits of incorporating a thermoelectric cooler (TEC) into conventional heat sinks and investigated strategies to improve heat dissipation efficiency. A theoretical [...] Read more.
Thermoelectric heat dissipation systems offer unique advantages over conventional systems, including vibration-free operation, environmental sustainability, and enhanced controllability. This study examined the benefits of incorporating a thermoelectric cooler (TEC) into conventional heat sinks and investigated strategies to improve heat dissipation efficiency. A theoretical model introducing a dimensionless evaluation index () is proposed to assess the system’s performance, which measures the ratio of the heat dissipation density of a conventional heat dissipation system to that of a thermoelectric heat dissipation system. Here, we subjectively consider 0.9 as a cutoff, and when , the thermoelectric heat dissipation system shows substantial superiority over conventional ones. In contrast, for , the advantage of the thermoelectric system weakens, making conventional systems more attractive. This analysis examined the effects of engineering leg length (), the heat transfer allocation ratio (), and temperature difference () on heat dissipation capabilities. The results indicated that under a fixed heat source temperature, heat sink temperature, and external heat transfer coefficient, an optimal engineering leg length exists, maximizing the system’s heat dissipation performance. Furthermore, a detailed analysis revealed that the thermoelectric system demonstrated exceptional performance under small temperature differences, specifically when the temperature difference was below 32 K with the current thermoelectric (TE) materials. For moderate temperature differences between 32 K and 60 K, the system achieved optimal performance when . This work establishes a theoretical foundation for applying thermoelectric heat dissipation systems and provides valuable insights into optimizing hybrid heat dissipation systems. Full article
(This article belongs to the Special Issue Recent Advances in Thermoelectric Energy Conversion)
24 pages, 9949 KiB  
Article
Voltage Unbalance Control Strategy for Local Shading Photovoltaic Grid-Connected System
by Pingye Wan, Miao Huang, Jinshan Mou, Lili Tao, Shuping Zhang and Zhihua Hu
Energies 2025, 18(3), 554; https://doi.org/10.3390/en18030554 - 24 Jan 2025
Abstract
In view of the sudden grid voltage distortions, such as voltage sags and unbalances, that may occur in photovoltaic (PV) grid-connected systems under local shading conditions, this paper proposes a control strategy integrating a linear active disturbance rejection controller (LADRC)-based virtual synchronous generator [...] Read more.
In view of the sudden grid voltage distortions, such as voltage sags and unbalances, that may occur in photovoltaic (PV) grid-connected systems under local shading conditions, this paper proposes a control strategy integrating a linear active disturbance rejection controller (LADRC)-based virtual synchronous generator (VSG) and an active disturbance rejection controller (ADRC)-based dynamic voltage restorer (DVR). To enhance the stability and response speed of the PV inverter system, a novel LADRC-based voltage–current dual closed-loop control strategy with pre-synchronization is designed, ensuring stable operation of the inverter and load. To address the overshooting issues found in traditional PI control under local shading, the ADRC-based DVR compensates for PV system voltage fluctuations, achieving rapid voltage distortion compensation and ensuring grid-connected system safety. Simulink experiments verify the feasibility and effectiveness of the proposed control strategy in improving transient voltage quality in PV systems affected by local shading. The total harmonic distortion rates of voltage and current are both less than 0.5%, which significantly improves the performance compared to existing research. Full article
(This article belongs to the Topic Power System Modeling and Control, 2nd Edition)
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Figure 1

Figure 1
<p>The topology of the PV inverter grid-connected system. Vinj is the DVR feedback voltage.</p> Full article ">Figure 2
<p>The equivalent model of the PV module photovoltaic cells [<a href="#B28-energies-18-00554" class="html-bibr">28</a>].</p> Full article ">Figure 3
<p>The structure of the VSI with an LC filter.</p> Full article ">Figure 4
<p>Three-phase DVR topology.</p> Full article ">Figure 5
<p>The specific PV input signal.</p> Full article ">Figure 6
<p>Main circuit and control structure diagram of the three-phase grid-connected inverter. The symbol * represents the reference value.</p> Full article ">Figure 7
<p>Voltage vectoring and sectorization of the VSI.</p> Full article ">Figure 8
<p>GSA-MPPT algorithm process.</p> Full article ">Figure 9
<p>Dynamic voltage restorer DVR schematic.</p> Full article ">Figure 10
<p>Simulink simulation diagram of the dynamic voltage restorer.</p> Full article ">Figure 11
<p>DVR control process.</p> Full article ">Figure 12
<p>Simulink model diagram of DVR control.</p> Full article ">Figure 13
<p>Model diagram of the DVR in Simulink. The symbol * represents the reference value.</p> Full article ">Figure 14
<p>The waveforms of the voltage signals in condition A. The red line represents the selected area of FFT, while the blue line is not.</p> Full article ">Figure 15
<p>Four experimental voltages THD in operating condition A.</p> Full article ">Figure 16
<p>The waveforms of the current signals in condition A. The red line represents the selected area of FFT, while the blue line is not.</p> Full article ">Figure 17
<p>Four experimental current THD in operating condition A.</p> Full article ">Figure 18
<p>The waveforms of the voltage signals in condition B. The red line represents the selected area of FFT, while the blue line is not.</p> Full article ">Figure 19
<p>Four experimental voltages THD in operating condition B.</p> Full article ">Figure 20
<p>The waveforms of the current signals in condition B. The red line represents the selected area of FFT, while the blue line is not.</p> Full article ">Figure 21
<p>Four experimental current THD in operating condition B.</p> Full article ">
14 pages, 1338 KiB  
Article
Performance Comparison Between Microstepping and Field-Oriented Control for Hybrid Stepper Motors
by Emilio Carfagna, Giovanni Migliazza, Marcello Medici and Emilio Lorenzani
Energies 2025, 18(3), 553; https://doi.org/10.3390/en18030553 - 24 Jan 2025
Abstract
With their cost-effective manufacturing process, hybrid stepper motors (HSMs) are a popular choice for position control in low-power industrial applications. These versatile motors offer a compelling solution for reducing system costs and size since at standstill/low speeds, HSMs typically have higher torque density [...] Read more.
With their cost-effective manufacturing process, hybrid stepper motors (HSMs) are a popular choice for position control in low-power industrial applications. These versatile motors offer a compelling solution for reducing system costs and size since at standstill/low speeds, HSMs typically have higher torque density with respect to low-power permanent magnet (PM) motors. This higher torque density determines a reduced use of rare-earth PMs and, therefore, a lower environmental footprint. In practical applications, the commonly used microstepping control faces low efficiency, low dynamic performance, vibrations, and a variable maximum continuous torque depending on the working point. In this paper, the operating region of an HSM is extended in the field-weakening (FW) region, showing how field-oriented control (FOC) with FW allows one to strongly increase the drive performance with a slight cost increase thanks to the availability of low-cost magnetic encoders. Due to the fact that FOC provides only the requested current, the HSM faces lower temperatures, lower insulation degradation, and lower permanent magnet demagnetization issues. An experimental evaluation comparing the commonly used microstepping and the proposed FOC with FW is performed on four commercial HSMs with different DC voltage power supplies using an industrial test bench. In particular, the experimental campaign has a focus on steady-state conditions in the case of the maximum continuous torque, showing the advantages of FOC with FW because the advantages in transient conditions are well known. Full article
(This article belongs to the Section F3: Power Electronics)
34 pages, 1560 KiB  
Review
Overview of the e-Fuels Market, Projects, and the State of the Art of Production Facilities
by Olaf Dybiński, Łukasz Szabłowski, Aliaksandr Martsinchyk, Arkadiusz Szczęśniak, Jarosław Milewski, Andrzej Grzebielec and Pavel Shuhayeu
Energies 2025, 18(3), 552; https://doi.org/10.3390/en18030552 - 24 Jan 2025
Abstract
E-fuels, or synthetic fuels produced from green hydrogen and captured CO2, are a promising solution for achieving climate neutrality by replacing fossil fuels in transportation and industry. They help reduce greenhouse gas emissions and efficiently utilize renewable energy surpluses. This study [...] Read more.
E-fuels, or synthetic fuels produced from green hydrogen and captured CO2, are a promising solution for achieving climate neutrality by replacing fossil fuels in transportation and industry. They help reduce greenhouse gas emissions and efficiently utilize renewable energy surpluses. This study aims to assess the current state and future potential of e-fuel production technologies, focusing on their scalability and market integration. A comprehensive literature review and market trend analysis, including modeling based on historical data and growth forecasts, were used to estimate market penetration. Results indicate that e-fuels could reach a 10% market share within the next 5 years, potentially reaching 30% in 20 years, particularly in aviation, maritime transport, and the steel industry. Ongoing projects expected to be completed this decade may cover about 20% of the global liquid fuel demand for transportation. However, challenges such as high costs, scalability, and recent project terminations due to funding shortages highlight the need for substantial investment, regulatory support, and innovation. Global collaboration and policy alignment are essential for the successful development and integration of e-fuels as a critical pathway to decarbonization. Full article
(This article belongs to the Special Issue Renewable Fuels for Internal Combustion Engines: 2nd Edition)
11 pages, 5898 KiB  
Article
Analysis of Water Injection and Heat Recovery Potential of Abandoned Oil Wells Transformed into Geothermal Wells in Northern Shaanxi
by Huagui Yu, Shi Liu, Yanyan Pang, Peng Wang and Qian Gao
Energies 2025, 18(3), 551; https://doi.org/10.3390/en18030551 - 24 Jan 2025
Abstract
The Chang 2 bottom water reservoir area in the western part of northern Shaanxi constitutes one of the key oil-producing regions within the Ordos Basin. A principal reservoir here is the Triassic Yanchang Formation’s Chang 2 reservoir, which is characterized by favorable physical [...] Read more.
The Chang 2 bottom water reservoir area in the western part of northern Shaanxi constitutes one of the key oil-producing regions within the Ordos Basin. A principal reservoir here is the Triassic Yanchang Formation’s Chang 2 reservoir, which is characterized by favorable physical properties, dynamic edge and bottom water activity, and a high geothermal gradient. This study employs the STARS module of the CMG reservoir numerical simulation software to model water intake and heat recovery processes in the target region. It analyzes the heat recovery rate and efficiency of three water production methods—direct water extraction, four-injection–one-production, and one-injection–four-production—under varying injection pressures. The results indicate that direct water extraction from the bottom water reservoir is challenging. However, the annual heat recovery per well for the four-injection–one-production and one-injection–four-production methods equates to a standard coal production ranging between 190 and 420 tons, suggesting that there is significant potential for water injection and heat recovery in the Chang 2 reservoir in the western part of northern Shaanxi. Full article
(This article belongs to the Special Issue Heat Transfer and Fluid Flows for Industry Applications)
33 pages, 7541 KiB  
Article
Analysis of Rail Pressure Stability in an Electronically Controlled High-Pressure Common Rail Fuel Injection System via GT-Suite Simulation
by Hongfeng Jiang, Zhejun Li, Feng Jiang, Shulin Zhang, Yan Huang and Jie Hu
Energies 2025, 18(3), 550; https://doi.org/10.3390/en18030550 - 24 Jan 2025
Abstract
The high-pressure common rail (HPCR) injection system, a key technology for enhancing diesel engine performance, plays a decisive role in ensuring fuel injection precision and combustion efficiency through rail pressure stability. This study establishes a coupled simulation model of an electronically controlled HPCR [...] Read more.
The high-pressure common rail (HPCR) injection system, a key technology for enhancing diesel engine performance, plays a decisive role in ensuring fuel injection precision and combustion efficiency through rail pressure stability. This study establishes a coupled simulation model of an electronically controlled HPCR injection system and a diesel engine, using GT-Suite to systematically investigate the effects of fuel supply pressure, camshaft speed, high-pressure pump plunger parameters, and inlet and outlet valve characteristics on rail pressure fluctuations. Gray relational analysis quantifies the correlation between these factors and rail pressure variations. The results demonstrate that increasing camshaft speed, injection pulse width, plunger mass, plunger length, plunger spring preload, inlet valve spring preload, and outlet valve body mass reduces rail pressure fluctuations, while variations in fuel supply pressure, plunger spring stiffness, and valve spring stiffness have minimal impact. Notably, the influence of outlet valve spring preload, inlet valve spring stiffness, and inlet valve body mass on rail pressure is nonlinear, with optimal values observed. Gray relational analysis further identifies inlet valve spring preload as having the highest correlation with rail pressure fluctuations (0.815), followed by inlet valve spring stiffness (0.625), with outlet valve spring preload (0.551) and stiffness (0.527) showing relatively lower correlations. This study provides valuable insights for optimizing the HPCR injection system design and contributes to advancements in diesel engine technology. Full article
(This article belongs to the Section I2: Energy and Combustion Science)
14 pages, 1597 KiB  
Article
Use of Pressure Transient Analysis Method to Assess Fluid Soaking in Multi-Fractured Shale Gas Wells
by Jun Zhang, Boyun Guo and Majid Hussain
Energies 2025, 18(3), 549; https://doi.org/10.3390/en18030549 - 24 Jan 2025
Abstract
Multi-stage hydraulic fracturing is a key technology adopted in the energy industry to make shale gas and shale oil fields profitable. Post-frac fluid soaking before putting wells into production has been found essential for enhancing well productivity. Finding the optimum time to terminate [...] Read more.
Multi-stage hydraulic fracturing is a key technology adopted in the energy industry to make shale gas and shale oil fields profitable. Post-frac fluid soaking before putting wells into production has been found essential for enhancing well productivity. Finding the optimum time to terminate the fluid-soaking process is an open problem to solve. Post-frac shut-in pressure data from six wells in two shale gas fields were investigated in this study based on pressure transient analysis (PTA) to reveal fluid-soaking performance. It was found that pressure-derivative data become scattering after 1 day of well shut in. The overall trend of pressure-derivative data after the first day of well shut in should reflect the effectiveness of fluid soaking. Two wells exhibited flat (zero-slope) pressure derivatives within one week of fluid soaking, indicating adequate time of fluid soaking. Four wells exhibited increasing pressure derivatives within one week of fluid soaking, indicating inadequate time of fluid soaking. This observation is consistent with the reported well’s Estimated Ultimate Recovery (EUR). This study presents a new approach to the assessment of post-frac fluid-soaking performance with real-time shut-in pressure data. Full article
(This article belongs to the Special Issue Petroleum and Natural Gas Engineering)
22 pages, 4589 KiB  
Review
Tree-Related High-Impedance Fault in Distribution Systems: Modeling, Detection, and Ignition Risk Assessment (Review)
by Chunlan Yang, Wenhai Zhang, Rui Tang and Xianyong Xiao
Energies 2025, 18(3), 548; https://doi.org/10.3390/en18030548 - 24 Jan 2025
Abstract
Tree-related high-impedance faults (THIFs) in medium voltage distribution systems represent a typical fault, especially where an overhead line crosses a forested area. The arc caused by THIFs could ignite nearby combustibles, significantly increasing the risk of forest fires. THIF detection remains a significant [...] Read more.
Tree-related high-impedance faults (THIFs) in medium voltage distribution systems represent a typical fault, especially where an overhead line crosses a forested area. The arc caused by THIFs could ignite nearby combustibles, significantly increasing the risk of forest fires. THIF detection remains a significant challenge because this type of fault has weak characteristics, as the fault impedance can reach hundreds of kΩ. Many previous studies have investigated reducing the risk of wildfires caused by THIFs. This paper reviews the existing literature on THIF modeling, detection, and ignition risk assessment. The modeling focuses on the distinctions and connections among electrical models of tree structures, traditional high-impedance fault (HIF) models, and THIF models. Detailed reviews and comparisons are conducted on THIF detection methods, encompassing fault analysis, fault feature extraction, and fault identification. The experiments and methods for assessing THIF ignition risk are also introduced and discussed. The review reveals critical research gaps. In modeling, there is a lack of frameworks that simultaneously elucidate underlying mechanisms and support detection algorithms. In detection algorithms, the existing methods have not been adequately validated under complex environmental conditions. In ignition risk assessment, current studies do not account for a comprehensive range of influencing variables. Finally, this paper proposes future research directions for THIF, aiming to provide a comprehensive reference for researchers and practitioners in this field. Full article
(This article belongs to the Special Issue Advances in Power Distribution Systems)
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<p>(<b>a</b>) THIF schematic. (<b>b</b>) Tree cross-section structure. (<b>c</b>) Schematic diagram of current path.</p> Full article ">Figure 2
<p>Typical plant tissue electrical model. (<b>a</b>) Hayden model [<a href="#B20-energies-18-00548" class="html-bibr">20</a>]; (<b>b</b>) Double-shell model [<a href="#B22-energies-18-00548" class="html-bibr">22</a>].</p> Full article ">Figure 3
<p>(<b>a</b>) Distributed model of plant tissue [<a href="#B24-energies-18-00548" class="html-bibr">24</a>]; (<b>b</b>) The EIS of the tree under the distribution model [<a href="#B26-energies-18-00548" class="html-bibr">26</a>,<a href="#B27-energies-18-00548" class="html-bibr">27</a>].</p> Full article ">Figure 4
<p>Typical HIF models. (<b>a</b>) Single-variable resistor [<a href="#B28-energies-18-00548" class="html-bibr">28</a>]; (<b>b</b>) Single-variable resistor with inductor [<a href="#B30-energies-18-00548" class="html-bibr">30</a>]; (<b>c</b>) Dual-variable resistor [<a href="#B31-energies-18-00548" class="html-bibr">31</a>,<a href="#B32-energies-18-00548" class="html-bibr">32</a>]; (<b>d</b>) Diode-DC power supply model [<a href="#B33-energies-18-00548" class="html-bibr">33</a>].</p> Full article ">Figure 5
<p>(<b>a</b>) Schematic diagram of THIF experiment. [<a href="#B34-energies-18-00548" class="html-bibr">34</a>]; (<b>b</b>) THIF model proposed in reference [<a href="#B34-energies-18-00548" class="html-bibr">34</a>]; (<b>c</b>) Segmented model of THIF [<a href="#B38-energies-18-00548" class="html-bibr">38</a>].</p> Full article ">Figure 6
<p>THIF models based on tree structure [<a href="#B42-energies-18-00548" class="html-bibr">42</a>]. (<b>a</b>) Complex Version; (<b>b</b>) Simplified Version.</p> Full article ">Figure 7
<p>THIF models based on heat input. (<b>a</b>) The model proposed in reference [<a href="#B44-energies-18-00548" class="html-bibr">44</a>]; (<b>b</b>) The model proposed in reference [<a href="#B45-energies-18-00548" class="html-bibr">45</a>].</p> Full article ">Figure 8
<p>Typical THIF leakage current waveforms: (<b>a</b>) prolonged waveforms; (<b>b</b>) localized waveforms (red box in (<b>a</b>)).</p> Full article ">Figure 9
<p>Schematic diagram of magnetic field signal acquisition.</p> Full article ">Figure 10
<p>Schematic diagram of partial-discharge signal acquisition.</p> Full article ">Figure 11
<p>Schematic diagram of tree ignition process.</p> Full article ">Figure 12
<p>Statistical chart of the publication years of relevant literature.</p> Full article ">Figure 13
<p>Statistical chart of the keywords of the relevant literature.</p> Full article ">
24 pages, 10275 KiB  
Article
New Nusselt Number Correlation and Turbulent Prandtl Number Model for Turbulent Convection with Liquid Metal Based on Quasi-DNS Results
by Hao Fu, Juan Chen, Yanjun Tong, Sifan Peng, Fang Liu, Xuefeng Lyu and Houjian Zhao
Energies 2025, 18(3), 547; https://doi.org/10.3390/en18030547 - 24 Jan 2025
Abstract
Liquid metal is widely used as the primary coolant in many advanced nuclear energy systems. Prandtl number of liquid metal is much lower than that of the conventional coolant of water or gas. Based on the Reynolds analogy, the turbulent Prandtl number is [...] Read more.
Liquid metal is widely used as the primary coolant in many advanced nuclear energy systems. Prandtl number of liquid metal is much lower than that of the conventional coolant of water or gas. Based on the Reynolds analogy, the turbulent Prandtl number is assumed to be a constant around unity. For the turbulent convection of liquid metal, dissipations of half the temperature variance are larger than those of turbulent kinetic energies. The dissimilarity between the thermal and momentum fields increases as Pr decreases. The turbulent Prandtl number is larger than one for the liquid metal. In the current investigation, the turbulent convection of liquid metal in the channel is quasi-directly simulated with OpenFOAM-7. The turbulent statistics of the momentum and the thermal field are compared with the existing database to validate the numerical model. The power law for dimensionless temperature distribution with different Prandtl numbers is obtained by regression analysis of numerical results. A new Nusselt number correlation is derived based on the power law. The new Nusselt number correlation agrees well with the DNS results in the literature. The momentum mixing process between different layers in the cross section is compared with the thermal mixing process. The effects of the Prandtl number on the difference between the turbulence time scale and scalar time scale are analyzed. A new turbulent Prandtl number model with local parameters is obtained for turbulent convection with liquid metal. Combined with the k−ω model, the temperature distributions with the new turbulent Prandtl number model agree well with the DNS results in the literature. The new turbulent Prandtl number model can be used for turbulent convection with different Prandtl and different Reynolds numbers. Full article
(This article belongs to the Special Issue Thermal Hydraulics and Safety Research for Nuclear Reactors)
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<p>Nusselt number calculated by different correlations [<a href="#B12-energies-18-00547" class="html-bibr">12</a>,<a href="#B13-energies-18-00547" class="html-bibr">13</a>,<a href="#B14-energies-18-00547" class="html-bibr">14</a>,<a href="#B15-energies-18-00547" class="html-bibr">15</a>,<a href="#B16-energies-18-00547" class="html-bibr">16</a>].</p> Full article ">Figure 2
<p>Turbulent Prandtl number calculated by different models [<a href="#B6-energies-18-00547" class="html-bibr">6</a>,<a href="#B8-energies-18-00547" class="html-bibr">8</a>,<a href="#B20-energies-18-00547" class="html-bibr">20</a>,<a href="#B21-energies-18-00547" class="html-bibr">21</a>,<a href="#B22-energies-18-00547" class="html-bibr">22</a>,<a href="#B23-energies-18-00547" class="html-bibr">23</a>,<a href="#B24-energies-18-00547" class="html-bibr">24</a>,<a href="#B26-energies-18-00547" class="html-bibr">26</a>,<a href="#B27-energies-18-00547" class="html-bibr">27</a>].</p> Full article ">Figure 3
<p>Computational domain.</p> Full article ">Figure 4
<p>Statistically averaged temperature and velocity distributions [<a href="#B8-energies-18-00547" class="html-bibr">8</a>,<a href="#B18-energies-18-00547" class="html-bibr">18</a>].</p> Full article ">Figure 5
<p>Budgets of the transporting equation for turbulent kinetic energy [<a href="#B8-energies-18-00547" class="html-bibr">8</a>].</p> Full article ">Figure 6
<p>Budgets of the transporting equation for the half temperature variance [<a href="#B8-energies-18-00547" class="html-bibr">8</a>].</p> Full article ">Figure 7
<p>Turbulent Prandtl number distributions [<a href="#B8-energies-18-00547" class="html-bibr">8</a>].</p> Full article ">Figure 8
<p>Temperature distributions with different Prandtl numbers.</p> Full article ">Figure 9
<p>The Nusselt number calculated by the numerical result and power law for the temperature distribution.</p> Full article ">Figure 10
<p>Validation of the new Nusselt number correlation.</p> Full article ">Figure 11
<p>Turbulent momentum and energy exchange process.</p> Full article ">Figure 12
<p>Turbulent Prandtl number model validation [<a href="#B18-energies-18-00547" class="html-bibr">18</a>].</p> Full article ">Figure 13
<p>Validations of the new turbulent Prandtl number model.</p> Full article ">Figure 14
<p>Comparison of the Nusselt number between the current <math display="inline"><semantics> <mrow> <mi>P</mi> <msub> <mi>r</mi> <mi>t</mi> </msub> </mrow> </semantics></math> model, <math display="inline"><semantics> <mrow> <mi>P</mi> <msub> <mi>r</mi> <mi>t</mi> </msub> <mo>=</mo> <mn>0.85</mn> </mrow> </semantics></math> and DNS results in the literature.</p> Full article ">
21 pages, 3965 KiB  
Article
Photovoltaic-Thermal Side-Absorption Concentrated Module with Micro-Structures as Spectrum-Division Component for a Hybrid-Collecting Reflection Solar System
by Jyh-Rou Sze and An-Chi Wei
Energies 2025, 18(3), 546; https://doi.org/10.3390/en18030546 - 24 Jan 2025
Abstract
A photovoltaic-thermal side-absorption concentrated module (PT-SACM) based on spectrum division for photovoltaic-thermal hybrid applications is carried out. In order to reduce the absorption by materials and the axial-chromatic aberration caused by the transmissive optical system and to improve the performance of the entire [...] Read more.
A photovoltaic-thermal side-absorption concentrated module (PT-SACM) based on spectrum division for photovoltaic-thermal hybrid applications is carried out. In order to reduce the absorption by materials and the axial-chromatic aberration caused by the transmissive optical system and to improve the performance of the entire system, a reflective system, the parabolic mirror array, fabricated by the ultra-precision diamond turning technology, is proposed herein. For the purposes of spectrum division, thinner volume, lightweight, and wide acceptance angle, the proposed module is designed with a diffraction optical element (DOE), a light-guide plate with a micro-structure array and a parabolic mirror array. Among them, the DOE can separate the solar spectrum into the visible band, which is converted to electrical energy via photovoltaics, and the infrared band, whose thermal energy is collected. Experimental measurements show that the overall optical efficiency of the entire system reached 38.32%, while a deviation percentage of 3.5% is calculated based on the simulation. The system has successfully demonstrated the separation of visible and infrared bands of the solar spectrum. Meanwhile, the lateral displacement between the micro-structures of the light-guide plate and the focus of the parabolic mirror array can be used to compensate for the angular deviation of the sun incidence, thereby achieving wide-angle acceptance via the proposed solar concentration system. Full article
(This article belongs to the Special Issue Photovoltaic-Thermal (PVT) and Concentrated Photovoltaic-Thermal (CPVT) Solar Collectors)
21 pages, 1003 KiB  
Article
Neural Network Based Power Meter Wiring Fault Recognition of Smart Grids Under Abnormal Reactive Power Compensation Scenarios
by Huizhe Zheng, Zhongshuo Lin, Huan Lin, Chaokai Huang, Xiaoqi Huang, Suna Ji and Xiaoshun Zhang
Energies 2025, 18(3), 545; https://doi.org/10.3390/en18030545 - 24 Jan 2025
Abstract
This paper explores the challenges of detecting wiring anomalies in three-phase, four-wire energy metering devices, especially when large amounts of reactive power compensation are involved. Traditional methods, such as the hexagon phasor diagram technique, perform well under standard loads, but struggle to adapt [...] Read more.
This paper explores the challenges of detecting wiring anomalies in three-phase, four-wire energy metering devices, especially when large amounts of reactive power compensation are involved. Traditional methods, such as the hexagon phasor diagram technique, perform well under standard loads, but struggle to adapt to new situations, such as over- or under-compensation. To overcome these limitations, this paper proposes a hybrid approach that combines mechanism-based knowledge with data-driven technologies, including backpropagation neural networks (BPNNs). This method improves the accuracy and efficiency of anomaly detection and can better adapt to a dynamic power environment. The result is improved universality of anomaly detection, which helps to achieve safer, more accurate, and more efficient smart grid operation in complex situations. Full article
(This article belongs to the Topic Intelligent, Flexible, and Effective Operation of Smart Grids with Novel Energy Technologies and Equipment)
29 pages, 3098 KiB  
Article
A Novel Decision-Support Framework for Supporting Renewable Energy Technology Siting in the Early Design Stage of Microgrids: Considering Geographical Conditions and Focusing on Resilience and SDGs
by Bharath Kumar Sugumar and Norma Anglani
Energies 2025, 18(3), 544; https://doi.org/10.3390/en18030544 - 24 Jan 2025
Abstract
This research is focused on microgrid design supporting tools and presents an innovative framework for renewable energy (RE) sources’ site selection, integrating multicriteria decision-making (MCDM) methods with resilience considerations and alignment to the Sustainable Development Goals (SDGs). It addresses present climatic challenges, identifies [...] Read more.
This research is focused on microgrid design supporting tools and presents an innovative framework for renewable energy (RE) sources’ site selection, integrating multicriteria decision-making (MCDM) methods with resilience considerations and alignment to the Sustainable Development Goals (SDGs). It addresses present climatic challenges, identifies key causes of possible power failures, and develops strategies to mitigate their effects, while providing tools for energy managers and decision-makers to select suitable RE sources/technologies, based on geographical and sustainability criteria. The framework categorizes criteria into quantitative and qualitative types, adopting a cost (C)- and benefit (B)-based approach. The Analytic Hierarchy Process (AHP) calculates criteria weights to ensure accuracy and compatibility in decision-making, integrating SDG objectives into the evaluation process. This study focuses on five major RE options, photovoltaic (PV), wind, wave, tidal, and geothermal, analyzing more than 50 criteria for each energy type. This evaluation incorporates the expertise of over 50 experts and case studies, making it one of the most extensive research efforts in RE site selection. By systematically addressing resilience challenges and linking them with SDG priorities, this study provides a robust framework for evaluating and optimizing RE options. Its methodologies offer significant contributions to advancing sustainable energy development and enhancing energy systems’ resilience to climate and infrastructural challenges. Full article
(This article belongs to the Special Issue Planning, Operation, Control and Economics of Renewable and Smart Energy Systems)
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<p>Resilience criteria flowchart for microgrid renewable energy selection. Grey-colored boxes indicate future work.</p> Full article ">Figure 2
<p>Classification of criteria.</p> Full article ">Figure 3
<p>Integration of Sustainable Development Goals (SDGs) into site selection criteria for renewable energy projects.</p> Full article ">Figure 4
<p>Criteria aligned with SDGs.</p> Full article ">Figure 5
<p>Division of criteria.</p> Full article ">Figure 6
<p>PV criteria weight.</p> Full article ">Figure 7
<p>Wind energy criteria weight.</p> Full article ">Figure 8
<p>Wave energy criteria weight.</p> Full article ">Figure 9
<p>Tidal energy criteria weight.</p> Full article ">Figure 10
<p>Geothermal energy criteria weight.</p> Full article ">
17 pages, 6048 KiB  
Article
Machine Learning Prediction of Photovoltaic Hydrogen Production Capacity Using Long Short-Term Memory Model
by Qian He, Mingbin Zhao, Shujie Li, Xuefang Li and Zuoxun Wang
Energies 2025, 18(3), 543; https://doi.org/10.3390/en18030543 - 24 Jan 2025
Abstract
The yield of photovoltaic hydrogen production systems is influenced by a number of factors, including weather conditions, the cleanliness of photovoltaic modules, and operational efficiency. Temporal variations in weather conditions have been shown to significantly impact the output of photovoltaic systems, thereby influencing [...] Read more.
The yield of photovoltaic hydrogen production systems is influenced by a number of factors, including weather conditions, the cleanliness of photovoltaic modules, and operational efficiency. Temporal variations in weather conditions have been shown to significantly impact the output of photovoltaic systems, thereby influencing hydrogen production. To address the inaccuracies in hydrogen production capacity predictions due to weather-related temporal variations in different regions, this study develops a method for predicting photovoltaic hydrogen production capacity using the long short-term memory (LSTM) neural network model. The proposed method integrates meteorological parameters, including temperature, wind speed, precipitation, and humidity into a neural network model to estimate the daily solar radiation intensity. This approach is then integrated with a photovoltaic hydrogen production prediction model to estimate the region’s hydrogen production capacity. To validate the accuracy and feasibility of this method, meteorological data from Lanzhou, China, from 2013 to 2022 were used to train the model and test its performance. The results show that the predicted hydrogen production agrees well with the actual values, with a low mean absolute percentage error (MAPE) and a high coefficient of determination (R2). The predicted hydrogen production in winter has a MAPE of 0.55% and an R2 of 0.985, while the predicted hydrogen production in summer has a slightly higher MAPE of 0.61% and a lower R2 of 0.968, due to higher irradiance levels and weather fluctuations. The present model captures long-term dependencies in the time series data, significantly improving prediction accuracy compared to conventional methods. This approach offers a cost-effective and practical solution for predicting photovoltaic hydrogen production, demonstrating significant potential for the optimization of the operation of photovoltaic hydrogen production systems in diverse environments. Full article
(This article belongs to the Special Issue Advances in Fuel Cells and Hydrogen Storage Technologies)
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<p>Structures of photovoltaic hydrogen production system. (<b>a</b>) Off-grid photovoltaic hydrogen production system; (<b>b</b>) grid-connected photovoltaic hydrogen production system.</p> Full article ">Figure 2
<p>LSTM network structure.</p> Full article ">Figure 3
<p>Distribution of ground meteorological elements in the Third Pole region.</p> Full article ">Figure 4
<p>Daily solar irradiance variations from 2013 to 2022.</p> Full article ">Figure 5
<p>Correlation analysis of ground meteorological element variables. Abbreviations: IR—Solar Irradiance (W/m<sup>2</sup>); PP—Precipitation (mm/h); P—Atmospheric Pressure (hPa); RH—Relative Humidity (kg/kg); T—Temperature (K); WS—Wind Speed (m/s).</p> Full article ">Figure 6
<p>Normalization of the meteorological parameters: (<b>a</b>) original values; (<b>b</b>) normalized values.</p> Full article ">Figure 7
<p>Loss variation curve.</p> Full article ">Figure 8
<p>Comparison between predicted and actual solar irradiance values: (<b>a</b>) original values; (<b>b</b>) normalized values (the dashed line represents the predictions matching the true values).</p> Full article ">Figure 9
<p>Prediction results of daily average photovoltaic hydrogen production capacity in summer and winter.</p> Full article ">
28 pages, 24642 KiB  
Article
Prediction for Coastal Wind Speed Based on Improved Variational Mode Decomposition and Recurrent Neural Network
by Muyuan Du, Zhimeng Zhang and Chunning Ji
Energies 2025, 18(3), 542; https://doi.org/10.3390/en18030542 - 24 Jan 2025
Abstract
Accurate and comprehensive wind speed forecasting is crucial for improving efficiency in offshore wind power operation systems in coastal regions. However, raw wind speed data often suffer from noise and missing values, which can undermine the prediction performance. This study proposes a systematic [...] Read more.
Accurate and comprehensive wind speed forecasting is crucial for improving efficiency in offshore wind power operation systems in coastal regions. However, raw wind speed data often suffer from noise and missing values, which can undermine the prediction performance. This study proposes a systematic framework, termed VMD-RUN-Seq2Seq-Attention, for noise reduction, outlier detection, and wind speed prediction by integrating Variational Mode Decomposition (VMD), the Runge–Kutta optimization algorithm (RUN), and a Sequence-to-Sequence model with an Attention mechanism (Seq2Seq-Attention). Using wind speed data from the Shidao, Xiaomaidao, and Lianyungang stations as case studies, a fitness function based on the Pearson correlation coefficient was developed to optimize the VMD mode count and penalty factor. A comparative analysis of different Intrinsic Mode Function (IMF) selection ratios revealed that selecting a 50% IMF ratio effectively retains the intrinsic information of the raw data while minimizing noise. For outlier detection, statistical methods were employed, followed by a comparative evaluation of three models—LSTM, LSTM-KAN, and Seq2Seq-Attention—for multi-step wind speed forecasting over horizons ranging from 1 to 12 h. The results consistently showed that the Seq2Seq-Attention model achieved superior predictive accuracy across all forecast horizons, with the correlation coefficient of its prediction results greater than 0.9 in all cases. The proposed VMD-RUN-Seq2Seq-Attention framework outperformed other methods in the denoising, data cleansing, and reconstruction of the original wind speed dataset, with a maximum improvement of 21% in accuracy, producing highly accurate and reliable results. This approach offers a robust methodology for improving data quality and enhancing wind speed forecasting accuracy in coastal environments. Full article
(This article belongs to the Section A3: Wind, Wave and Tidal Energy)
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<p>(<b>a</b>) Location of three buoys at Yellow Sea, China. (<b>b</b>) Time series of raw wind speed. (<b>c</b>) Rose chart of raw wind speed from buoys of (<b>i</b>) Shidao (<b>ii</b>) Xiaomaidao, and (<b>iii</b>) Lianyungang from July 2020 to July 2023.</p> Full article ">Figure 2
<p>Flowchart for the wind speed data processing.</p> Full article ">Figure 3
<p>Long Short-Term Memory network mode (reproduced from Ref. [<a href="#B30-energies-18-00542" class="html-bibr">30</a>]).</p> Full article ">Figure 4
<p>Illustration of the LSTM-KAN model (reproduced from Ref. [<a href="#B31-energies-18-00542" class="html-bibr">31</a>]).</p> Full article ">Figure 5
<p>Illustration of the Seq2Seq-Attention-Attention model (reproduced from Refs. [<a href="#B32-energies-18-00542" class="html-bibr">32</a>,<a href="#B33-energies-18-00542" class="html-bibr">33</a>]).</p> Full article ">Figure 6
<p>The best result mean changes with the number of iterations (<span class="html-italic">M</span>).</p> Full article ">Figure 7
<p>Different optimization algorithms.</p> Full article ">Figure 8
<p>VMD and IMFs for Shidao station.</p> Full article ">Figure 9
<p>Histograms of wind speed distribution and fitted Gamma distribution.</p> Full article ">Figure 10
<p>Autocorrelation coefficient of wind speed data.</p> Full article ">Figure 11
<p>The input, target and predicted output of different deep learning algorithms (<b>a</b>) LSTM and LSTM-KAN, (<b>b</b>) Seq2Seq-Attention.</p> Full article ">Figure 12
<p>Regression line for 12 h wind speed prediction on train data for Shidao by using models (<b>a</b>) LSTM, (<b>b</b>) LSTM-KAN, (<b>c</b>) Seq2Seq-Attention.</p> Full article ">Figure 13
<p>Comparison between models for prediction horizon 12 h wind speed prediction for three buoys at a selected time span of 300 h (<b>a</b>) Shidao, (<b>b</b>) Xiaomaidao, (<b>c</b>) Lianyungang.</p> Full article ">Figure 13 Cont.
<p>Comparison between models for prediction horizon 12 h wind speed prediction for three buoys at a selected time span of 300 h (<b>a</b>) Shidao, (<b>b</b>) Xiaomaidao, (<b>c</b>) Lianyungang.</p> Full article ">Figure 14
<p>Comparison of models with different error types for 1–12 h wind speed prediction for three buoys. (<b>a</b>) Shidao, (<b>b</b>) Xiaomaidao, (<b>c</b>) Lianyungang.</p> Full article ">Figure 14 Cont.
<p>Comparison of models with different error types for 1–12 h wind speed prediction for three buoys. (<b>a</b>) Shidao, (<b>b</b>) Xiaomaidao, (<b>c</b>) Lianyungang.</p> Full article ">Figure 15
<p>Outlier imputation for three buoys (<b>a</b>) Shidao, (<b>b</b>) Xiaomaidao, (<b>c</b>) Lianyungang.</p> Full article ">
16 pages, 5171 KiB  
Article
The Assessment of Electricity Self-Sufficiency Potential of Facade-Applied Photovoltaic Systems Based on Design Scenarios: A Case Study of an Apartment Complex in the Republic of Korea
by Hyomun Lee, Tien Nhat Tran, Ruda Lee, Dongsu Kim, Hyunkyu Choi and Jongho Yoon
Energies 2025, 18(3), 541; https://doi.org/10.3390/en18030541 - 24 Jan 2025
Abstract
The performance of facade-applied photovoltaic (FPV) systems in high-rise apartment complexes varies based on the height and layout of the buildings, influencing the overall energy efficiency of the complex. This study assesses the potential of FPV systems to achieve electricity self-sufficiency in apartment [...] Read more.
The performance of facade-applied photovoltaic (FPV) systems in high-rise apartment complexes varies based on the height and layout of the buildings, influencing the overall energy efficiency of the complex. This study assesses the potential of FPV systems to achieve electricity self-sufficiency in apartment complexes. Focusing on a single apartment complex in Seoul, South Korea, the geometry and layout of each building are used to estimate electricity consumption and assess the impact of FPV systems. The electricity consumption of the apartment complex was estimated based on the electricity energy use intensity derived from the analysis of public data and the gross floor area of the apartment complex, yielding an annual electricity consumption of 1803.7 MWh. Two types of photovoltaic (PV) systems were considered: rooftop-mounted photovoltaic (RFPV) systems and FPV systems installed on the south-facing facades of buildings. Three FPV design scenarios were examined (Scenario A: full facade coverage; Scenario B: horizontal-only installation; Scenario C: vertical-only installation), with no design variations for the RFPV system. The RFPV system was estimated to contribute 30.7% (553.8 MWh/yr) of the complex’s electricity consumption. The remaining electricity consumption, 1249.9 MWh/yr, is met by the FPV systems, with self-sufficiency rates under the three FPV design scenarios found to be 83.3% for Scenario A, 33.6% for Scenario B, and 64.6% for Scenario C. These findings highlight the need for additional PV installations or the incorporation of other renewable energy technologies to achieve full electricity self-sufficiency. This study provides a foundational model for applying PV systems to high-rise apartment complexes, offering insights for further research and real-world implementation. Full article
(This article belongs to the Section A2: Solar Energy and Photovoltaic Systems)
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<p>The research process.</p> Full article ">Figure 2
<p>Bird’s eye view and layout of each building in the apartment complex.</p> Full article ">Figure 3
<p>The hourly shading pattern for December 22nd.</p> Full article ">Figure 4
<p>The annual irradiation at the center of the facade for each floor of the buildings.</p> Full article ">Figure 5
<p>The design scenarios for PV arrays on apartment facades.</p> Full article ">Figure 6
<p>Daily EUI for each month based on electricity consumption of the filtered suitable apartment complexes.</p> Full article ">Figure 7
<p>The monthly and annual power generation for each FPV system design scenario.</p> Full article ">Figure 8
<p>The electricity balance of the apartment complex with RFPV systems.</p> Full article ">Figure 9
<p>The final residual electricity consumption of the apartment complex and contribution ratio of FPV systems in each scenario.</p> Full article ">
21 pages, 3124 KiB  
Review
Recent Advances in Cooling Technology for the Leading Edge of Gas Turbine Blades
by Shixing Zhu, Yan Li, Junyang Yan and Chao Zhang
Energies 2025, 18(3), 540; https://doi.org/10.3390/en18030540 - 24 Jan 2025
Abstract
As the inlet temperature of the gas turbine exceeds the high temperature limit of the blade materials, efficient leading edge cooling technologies are crucial for the further development of gas turbines. Therefore, this paper reviews the research progress on external cooling technology, internal [...] Read more.
As the inlet temperature of the gas turbine exceeds the high temperature limit of the blade materials, efficient leading edge cooling technologies are crucial for the further development of gas turbines. Therefore, this paper reviews the research progress on external cooling technology, internal cooling technology, and composite cooling technology for gas turbine rotating blade leading edge cooling. It focuses on the impact of the geometric shape, arrangement, and flow parameters of film cooling holes on external cooling performance, the influence of jet hole design, configuration, crossflow, ribs on internal cooling efficiency, and the characteristics and influencing factors of composite cooling technologies are also discussed. Among the most promising composite cooling techniques, the impingement jet film composite cooling technology and swirl film composite cooling technology stand out. For impingement jet film composite cooling technology, this paper explores the effects of blowing ratio, nozzle parameters, jet hole characteristics, and flow field parameters on the overall cooling performance of the rotating blade leading edge. Impingement jet film composite cooling technology has been shown to significantly improve the cooling performance of the leading edge compared to traditional single cooling techniques. For applications requiring large area cooling or maintaining film integrity, swirl film composite cooling technology not only enhances heat transfer efficiency but also improves the uniformity of heat transfer. The design of swirl nozzles, coolant flow rate, Reynolds number, and jet temperature all have significant effects on the heat transfer efficiency of swirl film composite cooling. To further advance the development of gas turbine rotating blade leading edge cooling technologies, it is recommended to focus on the study of film composite cooling techniques, particularly investigating the effects of various parameters of impingement, swirl on composite cooling performance. Full article
(This article belongs to the Section J: Thermal Management)
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<p>Schematic diagram of impingement cooling hole geometry [<a href="#B3-energies-18-00540" class="html-bibr">3</a>].</p> Full article ">Figure 2
<p>Geometry of the tested blade with impingement cooling [<a href="#B14-energies-18-00540" class="html-bibr">14</a>].</p> Full article ">Figure 3
<p>Internal cooling at the leading edge of a gas turbine blade with a simplified design employing multiple jets [<a href="#B21-energies-18-00540" class="html-bibr">21</a>].</p> Full article ">Figure 4
<p>Leading Edge Impact-Film Composite Cooling Structure [<a href="#B45-energies-18-00540" class="html-bibr">45</a>].</p> Full article ">Figure 5
<p>Slotted and arrayed hole inlet channel cooling chamber configurations [<a href="#B61-energies-18-00540" class="html-bibr">61</a>].</p> Full article ">Figure 6
<p>Schematic of swirl impingement cooling strategy for the turbine blade leading edge [<a href="#B62-energies-18-00540" class="html-bibr">62</a>].</p> Full article ">Figure 7
<p>A novel double-wall with composite swirl/film cooling structure [<a href="#B63-energies-18-00540" class="html-bibr">63</a>].</p> Full article ">Figure 8
<p>Serpentine swirl/film double wall cooling [<a href="#B64-energies-18-00540" class="html-bibr">64</a>].</p> Full article ">Figure 9
<p>Film/multi-channel wall jet cooling structure: (<b>a</b>) computational domain, (<b>b</b>) sketch of cooling structure in blade, and (<b>c</b>) scheme of bended cooling channel [<a href="#B65-energies-18-00540" class="html-bibr">65</a>].</p> Full article ">
17 pages, 3504 KiB  
Article
Discussion on AC Resistance and Temperature of ACSR Based on Finite Element Model Assistance
by Jianbo Yu, Changqing Wu, Hao Huang, Dexin Xie, Feixiang Qin, Jian Jiang and Gaohui He
Energies 2025, 18(3), 539; https://doi.org/10.3390/en18030539 - 24 Jan 2025
Viewed by 71
Abstract
In overhead wire transmission systems, the presence of AC resistance results in increased energy dissipation, adversely affecting the lines’ capacity to conduct current. This paper employs a finite element aluminum conductor steel-reinforced (ACSR) model, combined with electrical measurement techniques, to investigate AC resistance. [...] Read more.
In overhead wire transmission systems, the presence of AC resistance results in increased energy dissipation, adversely affecting the lines’ capacity to conduct current. This paper employs a finite element aluminum conductor steel-reinforced (ACSR) model, combined with electrical measurement techniques, to investigate AC resistance. By applying varying levels of AC current, the model is employed to determine the AC resistance which closely aligns with theoretical values estimated using the Morgan algorithm. The trends observed in the parameters are consistent, thereby validating the accuracy of the model. Following simulations and analyses regarding both AC resistance and temperature variations within the conductors—and incorporating empirical measurement results—it is demonstrated that, when environmental factors are not considered, any increase in the conductor temperature can be integrated into a revised model. This updated model is subsequently compared against test results obtained from an experimental platform; the findings confirm that the estimation errors remain within an acceptable range. Overall, this simulation model serves as a valuable reference for assessing AC losses in existing conductors, as well as contributing to reduced experimental costs while mitigating the associated risks and challenges. In summary, this simulation model serves as an essential reference for assessing AC losses in current conductors and aids in reducing experimental costs while addressing the associated risks and challenges. Full article
(This article belongs to the Special Issue Power Cables in Energy Systems)
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<p>Refinement of the experimental platform setup: (<b>a</b>) the structure of a transmission line tower and (<b>b</b>) 60 m tested ACSR.</p> Full article ">Figure 2
<p>Experimental circuit wiring diagram.</p> Full article ">Figure 3
<p>Three-dimensional modeling diagram: (<b>a</b>) two-layer steel core radius <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="normal">R</mi> <mrow> <mi>steel</mi> </mrow> </msub> </mrow> </semantics></math> and three-layer aluminum stranded wire <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="normal">R</mi> <mrow> <mi>Al</mi> </mrow> </msub> </mrow> </semantics></math> and (<b>b</b>) measured pitch length.</p> Full article ">Figure 4
<p>Graph typing grid: (<b>a</b>) end face (extremely fine precision) and (<b>b</b>) side sweep (number of units 60).</p> Full article ">Figure 5
<p>Finite element simulation of temperature and resistivity under five AC currents: (<b>a</b>) JL3/G1A 300/25 and (<b>b</b>) JL/G1A 400/35.</p> Full article ">Figure 6
<p>Analysis chart of error bands: (<b>a</b>) JL/G1A 300/25; (<b>b</b>) JL3/G1A 300/25; and (<b>c</b>) JL/G1A 400/35.</p> Full article ">Figure 7
<p>Measured temperature curves.</p> Full article ">Figure 8
<p>Simulation temperature fitting curves.</p> Full article ">Figure 9
<p>The steady-state temperatures rise fitting curves.</p> Full article ">Figure 10
<p>Analysis chart of error bands after temperature revision: (<b>a</b>) JL/G1A 300/25; (<b>b</b>) JL3/G1A 300/25; and (<b>c</b>) JL/G1A 400/35.</p> Full article ">Figure 10 Cont.
<p>Analysis chart of error bands after temperature revision: (<b>a</b>) JL/G1A 300/25; (<b>b</b>) JL3/G1A 300/25; and (<b>c</b>) JL/G1A 400/35.</p> Full article ">
19 pages, 9490 KiB  
Article
Research on the Randomness of Low-Voltage AC Series Arc Faults Based on the Improved Cassie Model
by Yao Wang, Yuying Liu, Xin Ning, Dejie Sheng and Tianle Lan
Energies 2025, 18(3), 538; https://doi.org/10.3390/en18030538 - 24 Jan 2025
Viewed by 75
Abstract
Low-voltage AC power lines are prone to arc faults, and an arc current presents as a random and complicated signal. The amplitude of the line current remains relatively unchanged during the occurrence of series arcs, hence complicating the detection of series arc faults. [...] Read more.
Low-voltage AC power lines are prone to arc faults, and an arc current presents as a random and complicated signal. The amplitude of the line current remains relatively unchanged during the occurrence of series arcs, hence complicating the detection of series arc faults. In this work, we developed a low-voltage series arc fault test platform to analyze the digital features of low-voltage series arc currents and the morphology of arc combustion, as the current model fails to capture the high-frequency and randomness of arc currents. An analysis of the physical causes and influencing factors of the random distribution of AC arc zero-crossing times was conducted. A time-domain simulation model for arc fault currents was developed by enhancing the time constant of the Cassie arc model, while the high-frequency features of arc currents were simulated using a segmented noise model. The measured arc current data were utilized to validate the model through the analysis of the zero-crossing time distribution of arc current, the correlation coefficient of the arc current frequency-domain signal, and the similarity of the time-domain waveforms. When comparing the similarity of the simulated waveforms of the arc model presented in this research and those of other traditional arc models, it was found that the suggested model effectively characterizes the time-/frequency-domain features of low-voltage AC series arc fault currents. The suggested model enhances the features of randomness in low-voltage AC series arc faults and is important in extracting essential aspects and reliably recognizing low-voltage series arc faults. Full article
(This article belongs to the Section F: Electrical Engineering)
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<p>Series arc fault experimental platform.</p> Full article ">Figure 2
<p>Real test platform photo.</p> Full article ">Figure 3
<p>Waveforms of the voltage between the electrodes and the circuit current during arc development.</p> Full article ">Figure 4
<p>The spectrum of the arc fault current.</p> Full article ">Figure 5
<p>The arc current zero-crossing time distribution of the 5 A arc current.</p> Full article ">Figure 6
<p>The arc current zero-crossing time distribution of different arc currents.</p> Full article ">Figure 7
<p>The arc voltage and current curves when τ changes. (<b>a</b>) <math display="inline"><semantics> <mrow> <mi>τ</mi> </mrow> </semantics></math> = 3 × <math display="inline"><semantics> <mrow> <msup> <mrow> <mn>10</mn> </mrow> <mrow> <mo>−</mo> <mn>3</mn> </mrow> </msup> </mrow> </semantics></math> s; (<b>b</b>) <math display="inline"><semantics> <mrow> <mi>τ</mi> </mrow> </semantics></math> = 3 × <math display="inline"><semantics> <mrow> <msup> <mrow> <mn>10</mn> </mrow> <mrow> <mo>−</mo> <mn>4</mn> </mrow> </msup> </mrow> </semantics></math> s; (<b>c</b>) <math display="inline"><semantics> <mrow> <mi>τ</mi> </mrow> </semantics></math> = 3 × <math display="inline"><semantics> <mrow> <msup> <mrow> <mn>10</mn> </mrow> <mrow> <mo>−</mo> <mn>5</mn> </mrow> </msup> </mrow> </semantics></math> s.</p> Full article ">Figure 8
<p>The arc voltage and current curves when <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>u</mi> </mrow> <mrow> <mi>c</mi> </mrow> </msub> </mrow> </semantics></math> changes.</p> Full article ">Figure 9
<p>The arc current time constant simulation results.</p> Full article ">Figure 10
<p>Comparison of the simulated and actual arc current zero-crossing time distributions.</p> Full article ">Figure 11
<p>Comparison of the simulated and actual arc current spectrums.</p> Full article ">Figure 12
<p>Comparison of the simulated and actual arc current waveforms with linear load. (<b>a</b>) Arc current waveforms of 5 A. (<b>b</b>) Arc current waveforms of 16 A.</p> Full article ">Figure 13
<p>Comparison of the simulated and actual arc current waveforms with nonlinear load.</p> Full article ">Figure 14
<p>The influence of different parameters on model precision. (<b>a</b>) The influence of <math display="inline"><semantics> <mrow> <mi>τ</mi> </mrow> </semantics></math>. (<b>b</b>) The influence of the parameters of the high-frequency model.</p> Full article ">
22 pages, 2718 KiB  
Article
Closing the Loop of Biowaste Composting by Anaerobically Co-Digesting Leachate, a By-Product from Composting, with Glycerine
by Thi Cam Tu Le, Katarzyna Bernat, Tomasz Pokój and Dorota Kulikowska
Energies 2025, 18(3), 537; https://doi.org/10.3390/en18030537 - 24 Jan 2025
Viewed by 100
Abstract
To achieve the required recycling rates, organic recycling via composting should be widely introduced in Poland for selectively collected biowaste. However, this process not only produces compost but also leachate (LCB), a nitrogen- and organics-rich liquid by-product. So far there has [...] Read more.
To achieve the required recycling rates, organic recycling via composting should be widely introduced in Poland for selectively collected biowaste. However, this process not only produces compost but also leachate (LCB), a nitrogen- and organics-rich liquid by-product. So far there has been limited information on the application of anaerobic digestion (AD) for treating LCB, which has fermentative potential. However, for effective methane production (MP) via AD, the ratio of chemical oxygen demand to total Kjeldahl nitrogen (COD/TKN) and pH of LCB are too low; thus, it should be co-digested with other organics-rich waste, e.g., glycerine (G). The present study tested the effect of G content in feedstock (in the range of 3–5% (v/v)) on the effectiveness of co-digestion with LCB, based on MP and the removal of COD. MP was accessed by using an automatic methane potential test system (AMPTS). Regardless of the feedstock composition (LCB, or LCB with G), the efficiency of COD removal was over 91%. Co-digestion not only increased MP by 6–15%, but also the methane content in the biogas by 4–14% compared to LCB only (353 NL/kg CODadded, 55%). MP and COD removal proceeded in two phases. During co-digestion in the 1st phase, volatile fatty acids (VFA) accumulated up to 2800 mg/L and the pH decreased below 6.8. The presence of G altered the shares of individual VFA and promoted the accumulation of propionic acid in contrast to LCB only, where caproic acid predominated. An initial accumulation of propionic acid and acidification in the mixtures decreased the kinetic constants of MP (from 0.79 to 0.54 d−1) and the rate of COD removal (from 2193 to 1603 mg/(L·d)). In the 2nd phase, the pH recovered, VFA concentrations decreased, and MP was no longer limited by these factors. However, it should be noted that excessive amounts of G, especially in reactors with constant feeding, may cause VFA accumulation to a greater extent and create a toxic environment for methanogens, inhibiting biogas production. In contrast, digestion of LCB only may lead to ammonium buildup if the COD/TKN ratio of the feedstock is too low. Despite these limitations, the use of AD in the treatment of LCB as a sustainable “closed-loop nutrient” technology closes the loop in composting of biowaste. Full article
(This article belongs to the Special Issue New Challenges in Waste-to-Energy and Bioenergy Systems)
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<p>The AMPTS II: water bath, CO<sub>2</sub> absorption trap, and gas flow-measuring device.</p> Full article ">Figure 2
<p>Biochemical oxygen demand (BOD<sub>7</sub>) for oxidation of organics in L<sub>CB</sub> (<b>a</b>), G (<b>e</b>), and their mixtures (<b>b</b>–<b>d</b>); the equations for the first-order kinetic models used to describe the BOD for oxidation of the organics in the substrates and their mixtures are given, and a summary of kinetic parameters are presented (<b>f</b>).</p> Full article ">Figure 3
<p>Changes in VFA/TA ratio and in the concentrations of COD and total VFA in the supernatant from L<sub>CB</sub> (<b>a</b>), L<sub>CB</sub>+3%G (<b>b</b>), L<sub>CB</sub>+4%G (<b>c</b>), and L<sub>CB</sub>+5%G (<b>d</b>) during measurements of MP; the equations for the zero-order kinetic models used to describe a decrease in the concentrations of COD and VFA, and a summary of the kinetic parameters of the decrease in the concentrations of COD and VFA are given (<b>e</b>). The dark grey area indicates the 1st phase of COD removal; the light grey area indicates the 2nd phase of COD removal; red arrow means the day to reach a maximal MP.</p> Full article ">Figure 4
<p>Changes in the individual VFA concentrations in the supernatant from L<sub>CB</sub> (<b>a</b>), L<sub>CB</sub>+3%G (<b>b</b>), L<sub>CB</sub>+4%G (<b>c</b>), and L<sub>CB</sub>+5%G (<b>d</b>), and the comparison of VFA concentrations depending on the feedstock composition in time (<b>e</b>) during measurements of MP.</p> Full article ">Figure 5
<p>Changes in pH and TA, and increasing trends in N-NH<sub>4</sub> concentration (dotted line described equation of y = ax + b) in the supernatant from L<sub>CB</sub> (<b>a</b>,<b>b</b>), L<sub>CB+</sub>3%G (<b>c</b>,<b>d</b>), L<sub>CB+</sub>4%G (<b>e</b>,<b>f</b>), and L<sub>CB+</sub>5%G (<b>g</b>,<b>h</b>) during measurements of MP. Dotted blue arrow means the day to reach a maximal MP.</p> Full article ">Figure 6
<p>Methane production (MP) and the changes in total VFA concentration in the supernatant of L<sub>CB</sub> (<b>a</b>), L<sub>CB+</sub>3%G (<b>b</b>), L<sub>CB+</sub>4%G (<b>c</b>), and L<sub>CB+</sub>5%G (<b>d</b>); the equations for the first-order kinetic models used to describe MP (two phases: 1st (the grey area), 2nd) are given; dotted blue arrow means the day to reach a maximal MP; a summary of kinetic parameters of the MP are given (<b>e</b>).</p> Full article ">
23 pages, 2009 KiB  
Review
Microalga-Based Electricity Production: A Comprehensive Review
by Wid Alrashidi, Safiah Alhazmi, Fotoon Sayegh and Sherif Edris
Energies 2025, 18(3), 536; https://doi.org/10.3390/en18030536 - 24 Jan 2025
Viewed by 74
Abstract
This review evaluates the feasibility of using microalgal culture for sustainable energy production, emphasizing microbial fuel cells (MFCs) and biophotovoltaics (BPVs). This study’s uniqueness is rooted in its thorough examination of recent developments (2014–present) in microalgal strain selection, bioreactor design, and electrode materials. [...] Read more.
This review evaluates the feasibility of using microalgal culture for sustainable energy production, emphasizing microbial fuel cells (MFCs) and biophotovoltaics (BPVs). This study’s uniqueness is rooted in its thorough examination of recent developments (2014–present) in microalgal strain selection, bioreactor design, and electrode materials. Furthermore, this review combines microalga cultivation with wastewater treatment, highlighting its importance. Notably, it examines advanced methodologies, such as the use of genetic engineering to enhance microalgal traits, nanotechnology to optimize electrode efficacy, and artificial intelligence (AI) to optimize bioelectrochemical systems. In addition, this study identifies possible future research avenues by examining microalga–bacterium consortia and cascaded biobattery systems. Consequently, the incorporation of case studies illustrating microalga biobatteries’ practical applications in low-power devices and wastewater treatment underscores the technology’s promise. Similarly, this study examines significant problems with enhancing farming methods, reconciling cost and yield, and integrating renewable energy sources with the grid, offering vital insights for academics and policymakers. Ultimately, this review emphasizes the need for economical cultivation methods, waste stream utilization, and scalable bioreactor designs, thereby considerably advancing sustainable energy options. Full article
(This article belongs to the Section F: Electrical Engineering)
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<p>Essential stages of biochemistry-driven biobattery production using microalgae. (<b>A</b>) Microalgal cultivation shows the significance of selecting certain strains, designing efficient bioreactors, providing adequate nutrients, and exploring potential improvements in genetic engineering. (<b>B</b>) Biobattery assembly emphasizes the distinctions between microbial fuel cells (MFCs) and biophotovoltaics (BPVs). The MFC has a bioreactor with two separate compartments for the anode and cathode. In contrast, the BPV employs a single chamber where microalgae directly interact with specialized electrodes. The arrows represent the movement of CO<sub>2</sub> used by microalgae and the production of O<sub>2</sub> during photosynthesis.</p> Full article ">Figure 2
<p>The fundamental stages of producing a biobattery utilizing microalgae as the primary component. (<b>A</b>) The direct insertion of live microalgal cells into the biobattery. (<b>B</b>) The use of microalgal biomass as a component of the biobattery: The procedure starts by cultivating microalgae under controlled conditions, harvesting the biomass, and extracting the targeted lipids from the cells. The lipids extracted are further purified and transformed into fatty acid methyl esters (FAMEs) via transesterification. The refined FAMEs undergo polymerization to create a biocompatible polymer suitable for electrode material use. Once the polymer has undergone additional purification, it is transformed into electrodes. These electrodes are combined with other battery components to construct a fully operational biobattery that utilizes microalgae.</p> Full article ">Figure 3
<p>Renewable electricity capacity additions by technology and segment, 2016–2028. The values for 2023 are approximated. Capacity additions are synonymous with net additions. The historical and projected solar photovoltaic (PV) capacity may vary from earlier renewable-energy market report versions. The photovoltaic (PV) data for all nations in 2023 were switched from alternating current (AC) to direct current (DC), thus increasing the capacity of countries that report in AC. The conversions were derived from an extensive study conducted by the International Energy Agency (IEA) across more than 80 nations and interviews conducted with photovoltaic (PV) industry associations. Solar PV systems harness sunlight through photovoltaic cells and transform it into direct current (DC) electricity. Subsequently, direct current (DC) electricity is typically transformed using an inverter, given that alternating current (AC) is the preferred form of electrical energy for most devices and power systems. Before around 2010, the AC and DC capacities of most photovoltaic (PV) systems were comparable. However, advancements in PV system sizing have led to a potential difference of up to 40% between these two values, particularly in utility-scale installations. The increases in solar PV and wind capacity include the specialized capacity required for the manufacture of hydrogen [<a href="#B3-energies-18-00536" class="html-bibr">3</a>].</p> Full article ">
15 pages, 2447 KiB  
Article
Sustainability in Public Lighting: The Methodology for Identifying Environmentally Optimal Solutions in Replacement Planning—A Case Study
by Fabrizio Cumo, Elisa Pennacchia and Adriana Scarlet Sferra
Energies 2025, 18(3), 535; https://doi.org/10.3390/en18030535 - 24 Jan 2025
Viewed by 62
Abstract
The urban public lighting system plays a fundamental role in enhancing safety and shaping the nocturnal identity of the city. Efficient lighting is also a key factor in reducing energy consumption and lowering atmospheric emissions. In the context of sustainable development goals, increasing [...] Read more.
The urban public lighting system plays a fundamental role in enhancing safety and shaping the nocturnal identity of the city. Efficient lighting is also a key factor in reducing energy consumption and lowering atmospheric emissions. In the context of sustainable development goals, increasing attention is being directed towards the energy, social, economic, and environmental benefits associated with the adoption of LED lighting systems. This paper aims to assess the environmental impacts of two different public outdoor lighting replacement planning scenarios. The methodology employed in this study calculates the environmental impacts using a life cycle approach, incorporating data from the Environmental Product Declarations (EPDs) of the lighting systems. It involves a systematic census and categorization of lighting fixtures based on their installation year to determine both their quantity and average efficiency. This methodology, applied to a case study, demonstrates that it is possible to reduce the CO2-equivalent emissions by approximately 7% depending on the technical and environmental performance of the fixtures and the timing of their replacements. These results provide a scientific foundation for supporting both the preparation of planning tools by governance entities and the technical and economic feasibility of designing and implementing interventions aimed at improving the environmental performance of public lighting. These efforts could contribute to achieving climate neutrality, conserving biodiversity, and mitigating the effects of climate change. Full article
(This article belongs to the Special Issue Sustainable Buildings and Green Design)
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<p>Schematic of the research methodology.</p> Full article ">Figure 2
<p>Classification of existing fixtures based on installation year and evaluation of luminous efficiency (luminous efficiency lm/W on the left and number of fixtures on the right).</p> Full article ">Figure 3
<p>Improved performance through the replacement of existing fixtures.</p> Full article ">Figure 4
<p>Comparison between the two scenarios S1 and S2 in terms of kgCO<sub>2</sub>eq emitted.</p> Full article ">
44 pages, 3781 KiB  
Review
Fault Detection of Permanent Magnet Synchronous Machines: An Overview
by Henghui Li, Zi-Qiang Zhu, Ziad Azar, Richard Clark and Zhanyuan Wu
Energies 2025, 18(3), 534; https://doi.org/10.3390/en18030534 - 24 Jan 2025
Viewed by 81
Abstract
These days, as the application of permanent magnet synchronous machines (PMSMs) and drive systems becomes popular, the reliability issue of PMSMs gains more and more attention. To improve the reliability of PMSMs, fault detection is one of the practical techniques that enables the [...] Read more.
These days, as the application of permanent magnet synchronous machines (PMSMs) and drive systems becomes popular, the reliability issue of PMSMs gains more and more attention. To improve the reliability of PMSMs, fault detection is one of the practical techniques that enables the early interference and mitigation of the faults and subsequently reduces the impact of the faults. In this paper, the state-of-the-art fault detection methods of PMSMs are systematically reviewed. Three typical faults, i.e., the inter-turn short-circuit fault, the PM partial demagnetization fault, and the eccentricity fault, are included. The existing methods are firstly classified into signal-, model-, and data-based methods, while the focus of this paper is laid on the signal sources and the signatures utilized in these methods. Based on this perspective, this paper intends to provide a new insight into the inherent commonalities and differences among these detection methods and thus inspire further innovation. Furthermore, comparison is conducted between methods based on different signatures. Finally, some issues in the existing methods are discussed, and future work is highlighted. Full article
(This article belongs to the Special Issue New Journey of Energy and Electric Vehicle Revolutions-Infinities Possibilities in the Science World: In Honor of Prof. Dr. C.C. Chan’s 90th Birthday)
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<p>Classification of faults in the PMSM drive system. The detailed explanation of inter-turn short-circuit fault, partial demagnetization fault, and rotor eccentricity fault is shown in <a href="#sec2dot1-energies-18-00534" class="html-sec">Section 2.1</a>, <a href="#sec3dot1-energies-18-00534" class="html-sec">Section 3.1</a> and <a href="#sec4dot1-energies-18-00534" class="html-sec">Section 4.1</a>.</p> Full article ">Figure 2
<p>Classification of detection methods for ITSC, PD, and eccentricity faults.</p> Full article ">Figure 3
<p>Illustration of fault detection procedure of signal-, model-, and data-based methods.</p> Full article ">Figure 4
<p>Illustration of ITSC fault. (<b>a</b>) Illustration; (<b>b</b>) equivalent circuit.</p> Full article ">Figure 5
<p>Classification of signal-based methods for ITSC detection.</p> Full article ">Figure 6
<p>Illustration of typical mounting placing of flux sensors for fault detection. (<b>a</b>) Invasive methods; (<b>b</b>) less-invasive methods.</p> Full article ">Figure 7
<p>Classification of model-based methods for ITSC detection.</p> Full article ">Figure 8
<p>Classification of data-based methods for ITSC detection.</p> Full article ">Figure 9
<p>Illustration of demagnetization curve of a PM.</p> Full article ">Figure 10
<p>Classification of signal-based methods for PD detection.</p> Full article ">Figure 11
<p>Classification of model-based methods for PD detection.</p> Full article ">Figure 12
<p>Classification of data-based methods for PD detection.</p> Full article ">Figure 13
<p>Illustration of eccentricity. (<b>a</b>) SE; (<b>b</b>) DE.</p> Full article ">Figure 14
<p>Classification of signal-based methods for eccentricity detection.</p> Full article ">Figure 15
<p>Classification of data-based methods for eccentricity detection.</p> Full article ">Figure 16
<p>Illustration of existing challenges and future work.</p> Full article ">
17 pages, 6367 KiB  
Article
Coordinated Frequency Control for Electric Vehicles and a Thermal Power Unit via an Improved Recurrent Neural Network
by Jianhua Zhang and Yongyue Wang
Energies 2025, 18(3), 533; https://doi.org/10.3390/en18030533 - 24 Jan 2025
Viewed by 114
Abstract
With the advancement of intelligent power generation and consumption technologies, an increasing number of renewable energy sources (RESs), smart loads, and electric vehicles (EVs) are being integrated into smart grids. This paper proposes a coordinated frequency control strategy for hybrid power systems with [...] Read more.
With the advancement of intelligent power generation and consumption technologies, an increasing number of renewable energy sources (RESs), smart loads, and electric vehicles (EVs) are being integrated into smart grids. This paper proposes a coordinated frequency control strategy for hybrid power systems with RESs, smart loads, EVs, and a thermal power unit (TPU), in which EVs and the TPU participate in short-term frequency regulation (FR) jointly. All EVs provide FR auxiliary services as controllable loads; specifically, the EV aggregations operate in charging mode when participating in FR. The proposed coordinated frequency control strategy is implemented by an improved recurrent neural network (IRNN), which combines a recurrent neural network with a functional-link layer. The weights and biases of the IRNN are trained by an improved backpropagation through time (BPTT) algorithm, in which a chaotic competitive swarm optimizer (CCSO) is proposed to optimize the learning rates. Finally, the simulation results verify the superiority of the coordinated frequency control strategy. Full article
(This article belongs to the Section E: Electric Vehicles)
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<p>Schematic view of EV-integrated hybrid power system.</p> Full article ">Figure 2
<p>Equivalent battery model of EV.</p> Full article ">Figure 3
<p>Coordinated frequency control strategy for EV aggregators and a TPU.</p> Full article ">Figure 4
<p>General concept of CSO.</p> Full article ">Figure 5
<p>The flow chart of the proposed CCSO.</p> Full article ">Figure 6
<p>Distribution graph of chaotic maps.</p> Full article ">Figure 7
<p>The system frequency response curve.</p> Full article ">Figure 8
<p>Output power change of turbine under load disturbance.</p> Full article ">Figure 9
<p>Output power change of EVs under load disturbance.</p> Full article ">Figure 10
<p>Non-Gaussian disturbances from wind energy.</p> Full article ">Figure 11
<p>Non-Gaussian disturbances from solar energy.</p> Full article ">Figure 12
<p>System frequency response under non-Gaussian disturbances.</p> Full article ">Figure 13
<p>PDF of the frequency deviation with the FLRNN + CCSO-based control strategy.</p> Full article ">Figure 14
<p>Output power change of thermal turbine under non-Gaussian disturbances.</p> Full article ">Figure 15
<p>Output power change of EVs under non-Gaussian disturbances.</p> Full article ">
18 pages, 3752 KiB  
Article
Magnetic Gear Wireless Power Transfer System: Prototype and Electric Vehicle Charging
by Caleb Dunlap and Charles W. Van Neste
Energies 2025, 18(3), 532; https://doi.org/10.3390/en18030532 - 24 Jan 2025
Viewed by 118
Abstract
This paper investigates the potential of a magnetic gear wireless power transfer (WPT) system for electric vehicle (EV) charging, with the advantages of low-frequency operation, low foreign object interference, low electromagnetic emissions, and high misalignment tolerance. The study explores the novel impact of [...] Read more.
This paper investigates the potential of a magnetic gear wireless power transfer (WPT) system for electric vehicle (EV) charging, with the advantages of low-frequency operation, low foreign object interference, low electromagnetic emissions, and high misalignment tolerance. The study explores the novel impact of Halbach arrays that enhance the flux density in desirable locations while decreasing the flux in undesirable locations, which provides the benefit of decreased foreign object attraction. The initial prototype results demonstrate that the Halbach system can transmit approximately 34.65 W with a transfer efficiency of 64% across a gap of 104 mm. The Halbach system is experimentally compared to a conventional magnet arrangement, which achieved a maximum power transfer of 88 W over 104 mm. The Halbach system is applied to a personal mobility EV to enable wireless charging at low frequency. The axial design of this WPT system has the unique benefit of a 360° radial coupling angle that maintains constant, near-maximum levels of power transfer and efficiency. This full circle coupling angle allows the personal EV to park in any direct vicinity of the charger and achieve the same level of charging given a certain distance. This study delivers important contributions to advancing a low-frequency wireless EV charging technology based on magnetic gears, that sets the stage for future innovations focused on optimizing efficiency, increasing safety, and simplifying the charging process. Full article
(This article belongs to the Special Issue Advanced Technologies for Electrified Transportation and Robotics)
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<p>(<b>a</b>) General single wire loop approximation. (<b>b</b>) Single wire loop approximation applied to a cubic permanent magnet.</p> Full article ">Figure 2
<p>Diagram of the torque measurement setup.</p> Full article ">Figure 3
<p>Plot of measured and theoretical torque vs. axial separation for the Halbach and regular magnet arrays.</p> Full article ">Figure 4
<p>Diagram of the magnetic gear WPT system with (<b>a</b>) a Halbach array arrangement and (<b>b</b>) a regular magnetic array arrangement.</p> Full article ">Figure 5
<p>TX designs. (<b>a</b>) Directly coupled motor and TX magnet. (<b>b</b>) Custom BLDC motor based on the TX magnet with driving coil around TXPM. (<b>c</b>) Pulley system between motor and magnets.</p> Full article ">Figure 6
<p>Image of bench top set up.</p> Full article ">Figure 7
<p>Oscilloscope screen of the output voltage of the system.</p> Full article ">Figure 8
<p>Maximum power transfer is shown in green. The individual load tests are also shown. (<b>a</b>) Power output for the Halbach array. (<b>b</b>) Power output for the regular array.</p> Full article ">Figure 9
<p>Plot of maximum power output with theoretical based on <math display="inline"><semantics> <mrow> <mi>P</mi> <mo>=</mo> <mi>T</mi> <mo>∗</mo> <mi>ω</mi> </mrow> </semantics></math> and observed power from testing.</p> Full article ">Figure 10
<p>(<b>a</b>) Image of magnetic gear WPT attached to personal EV. (<b>b</b>) Diagram of guaranteed planar and axis alignment with 360° of coupling when using vertical axes.</p> Full article ">Figure 11
<p>Plot of the magnetic flux measured on the axis of rotation for the regular and Halbach arrays.</p> Full article ">
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