Energies

20 pages, 3672 KiB

Open AccessArticle

Comparative Analysis of Transcritical CO₂ Heat Pump Systems With and Without Ejector: Performance, Exergy, and Economic Perspective

by Xiang Qin, Shihao Lei, Heyu Liu, Yinghao Zeng, Yajun Liu, Caiyan Pang and Jiaheng Chen

Energies 2025, 18(12), 3223; https://doi.org/10.3390/en18123223 - 19 Jun 2025

Viewed by 297

Abstract

To promote renewable energy utilization and enhance the environmental friendliness of refrigerants, this study presents a novel experimental investigation on a transcritical CO₂ double-evaporator heat pump water heater integrating both air and water sources, designed for high-temperature hot water production. A key [...] Read more.

To promote renewable energy utilization and enhance the environmental friendliness of refrigerants, this study presents a novel experimental investigation on a transcritical CO₂ double-evaporator heat pump water heater integrating both air and water sources, designed for high-temperature hot water production. A key innovation of this work lies in the integration of an ejector into the dual-source system, aiming to improve system performance and energy efficiency. This study systematically compares the conventional circulation mode and the proposed ejector-assisted circulation mode in terms of system performance, exergy efficiency, and the economic payback period. Experimental results reveal that the ejector-assisted mode not only achieves a higher water outlet temperature and reduces compressor power consumption but also improves the system’s exergy efficiency by 6.6% under the condition of the maximum outlet water temperature. Although the addition of the ejector increases initial manufacturing and maintenance costs, the payback periods of the two modes remain nearly the same. These findings confirm the feasibility and advantage of incorporating an ejector into a transcritical CO₂ compression/ejection heat pump system with integrated air and water sources, offering a promising solution for efficient and environmentally friendly high-temperature water heating applications. Full article

(This article belongs to the Special Issue Advances in Supercritical Carbon Dioxide Cycle)

► Show Figures

Figure 1

36 pages, 9026 KiB

Open AccessReview

Review on Research and Development of Magnetic Bearings

by Yuanhao Du, Gan Zhang and Wei Hua

Energies 2025, 18(12), 3222; https://doi.org/10.3390/en18123222 - 19 Jun 2025

Viewed by 353

Abstract

This paper reviews the research advancements and development in magnetic bearings. Firstly, from the technical principle, the design differences and application areas of active magnetic bearings, permanent magnetic bearings and hybrid structures are clarified. At the key technology level, focusing on electromagnetic design [...] Read more.

This paper reviews the research advancements and development in magnetic bearings. Firstly, from the technical principle, the design differences and application areas of active magnetic bearings, permanent magnetic bearings and hybrid structures are clarified. At the key technology level, focusing on electromagnetic design optimization, control strategy innovation and power-driven energy management, the breakthrough points of multi-physics coupling modeling, vibration suppression and energy efficiency improvement are revealed. Through the analysis of its engineering cases in the fields of high-speed motors, flywheel energy storage, aerospace and so on, the feasibility and economy of the technical scheme are verified. Further, the technical bottlenecks that need to be broken through are pointed out. For the future trend, this paper suggests that integration of interdisciplinary high-precision modeling, intelligent control algorithm and miniaturized integrated design should be deeply integrated to promote the large-scale application of magnetic bearing in frontier fields. This paper provides theoretical reference and engineering practice guidance for the technology iteration and cross-field integration of magnetic bearings. Full article

(This article belongs to the Special Issue Electrical Machine Systems with High Efficiency, Reliability and Integration)

► Show Figures

Figure 1

29 pages, 4263 KiB

Open AccessArticle

Modeling the Thermodynamics of Oxygen-Enriched Combustion in a GE LM6000 Gas Turbine Using CH₄/NH₃ and CH₄/H₂

by Laith Mustafa, Rafał Ślefarski, Radosław Jankowski, Mohammad Alnajideen and Sven Eckart

Energies 2025, 18(12), 3221; https://doi.org/10.3390/en18123221 - 19 Jun 2025

Viewed by 221

Abstract

Gas turbines are widely used in power generation due to their reliability, flexibility, and high efficiency. As the energy sector transitions towards low-carbon alternatives, hydrogen and ammonia are emerging as promising fuels. This study investigates the thermodynamic and combustion performance of a GE [...] Read more.

Gas turbines are widely used in power generation due to their reliability, flexibility, and high efficiency. As the energy sector transitions towards low-carbon alternatives, hydrogen and ammonia are emerging as promising fuels. This study investigates the thermodynamic and combustion performance of a GE LM6000 gas turbine fueled by methane/hydrogen and methane/ammonia fuel blends under varying levels of oxygen enrichment (21%, 30%, and 40%

O_{2}

by volume). Steady-state thermodynamic simulations were conducted using Aspen HYSYS, and combustion modeling was performed using ANSYS Chemkin-Pro, assuming a constant thermal input of 102 MW. Results show that increasing hydrogen content significantly raises flame temperature and burning velocity, whereas ammonia reduces both due to its lower reactivity. Net power output and thermal efficiency improved with higher fuel substitution, peaking at 43.46 MW and 42.7% for 100%

N H_{3}

. However,

N O_{x}

emissions increased with higher hydrogen content and oxygen enrichment, while

N H_{3}

blends exhibit more complex emission trends. The findings highlight the trade-offs between efficiency and emissions in future low-carbon gas turbine systems. Full article

(This article belongs to the Special Issue The Evolution and Future Prospects of Combustion Engines for Enhancing Energy Efficiency and Minimizing Environmental Impact)

► Show Figures

Figure 1

18 pages, 3348 KiB

Open AccessArticle

Moderate-Temperature Pyrolysis Characteristics of Lump Coal Under Varying Coal Particle Sizes

by Yuanpei Luo, Luxuan Liu, Liangguo Lv, Shengping Zhang, Fei Dai, Hongguang Jin and Jun Sui

Energies 2025, 18(12), 3220; https://doi.org/10.3390/en18123220 - 19 Jun 2025

Viewed by 247

Abstract

Pyrolysis is an important methodology for achieving efficient and clean utilization of coal. Lump coal pyrolysis demonstrates distinct advantages over pulverized coal processing, particularly in enhanced gas yield and superior coke quality. As a critical parameter in lump coal pyrolysis, particle size significantly [...] Read more.

Pyrolysis is an important methodology for achieving efficient and clean utilization of coal. Lump coal pyrolysis demonstrates distinct advantages over pulverized coal processing, particularly in enhanced gas yield and superior coke quality. As a critical parameter in lump coal pyrolysis, particle size significantly influences heat transfer and mass transfer during pyrolysis, yet its governing mechanisms remain insufficiently explored. This research systematically investigates pyrolysis characteristics of the low-rank coal from Ordos, Inner Mongolia, across graded particle sizes (2–5 mm, 5–10 mm, 10–20 mm, and 20–30 mm) through pyrolysis experiments. Real-time central temperature monitoring of coal bed coupled with advanced characterization techniques—including X-ray diffraction (XRD), Raman spectroscopy, Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy (SEM), gas chromatography (GC), and GC–mass spectrometry (GC-MS)—reveals particle-size-dependent pyrolysis mechanisms. Key findings demonstrate that the larger particles enhance bed-scale convective heat transfer, accelerating temperature propagation from reactor walls to the coal center. However, excessive sizes cause significant intra-particle thermal gradients, impeding core pyrolysis. The 10–20 mm group emerges as optimal—balancing these effects to achieve uniform thermal attainment, evidenced by 20.99 vol% peak hydrogen yield and maximum char graphitization. Tar yield first demonstrates a tendency to rise and then decline, peaking at 14.66 wt.% for 5–10 mm particles. This behavior reflects competing mechanisms: enlarging particle size can improve bed permeability (reducing tar residence time and secondary reactions), but it can also inhibit volatile release and intensify thermal cracking of tar in oversized coal blocks. The BET analysis result reveals elevated specific surface area and pore volume with increasing particle size, except for the 10–20 mm group, showing abrupt porosity reduction—attributed to pore collapse caused by intense polycondensation reactions. Contrasting previous studies predominantly focused on less than 2 mm pulverized coal, this research selects large-size (from 2 mm to 30 mm) lump coal to clarify the effect of particle size on coal pyrolysis, providing critical guidance for industrial-scale lump coal pyrolysis optimization. Full article

► Show Figures

Figure 1

18 pages, 1407 KiB

Open AccessArticle

Problems in Modeling Three-Phase Three-Wire Circuits in the Case of Non-Sinusoidal Periodic Waveforms and Unbalanced Load

by Konrad Zajkowski and Stanislaw Duer

Energies 2025, 18(12), 3219; https://doi.org/10.3390/en18123219 - 19 Jun 2025

Viewed by 138

Abstract

Asymmetry in the supply voltage in three-phase circuits disrupts the flow of currents. This worsens the efficiency of the distribution system and increases the problems in determining the mathematical model of the energy system. Among many power theories, the most accurate is the [...] Read more.

Asymmetry in the supply voltage in three-phase circuits disrupts the flow of currents. This worsens the efficiency of the distribution system and increases the problems in determining the mathematical model of the energy system. Among many power theories, the most accurate is the Currents’ Physical Components (CPC) power theory, which tries to justify the physical essence of each component. Such knowledge can be used to improve efficiency and reduce transmission losses in the power system. This article discusses the method of mathematical decomposition of current components in the case of a three-wire line connecting an asymmetric power source with linear time-invariant (LTI) loads. Special cases where irregularities appear in the results of calculations according to the CPC theory are discussed. The problem of equivalent conductance in the case of a non-zero value of the constant voltage component is discussed. The method of determining symmetrical components for periodic non-sinusoidal waveforms is also discussed. These considerations are supported by numerical examples. Full article

► Show Figures

Figure 1

16 pages, 6435 KiB

Open AccessArticle

A Switched-Capacitor-Based Quasi-H7 Inverter for Common-Mode Voltage Reduction

by Thi-Thanh Nga Nguyen, Tan-Tai Tran, Minh-Duc Ngo and Seon-Ju Ahn

Energies 2025, 18(12), 3218; https://doi.org/10.3390/en18123218 - 19 Jun 2025

Viewed by 221

Abstract

This paper proposes a novel three-phase two-level DC-AC inverter with significantly reduced common-mode voltage. The proposed inverter combines a conventional three-phase H7 configuration with a voltage multiplier network, effectively doubling the DC-link voltage relative to the input. Compared to existing solutions, the topology [...] Read more.

This paper proposes a novel three-phase two-level DC-AC inverter with significantly reduced common-mode voltage. The proposed inverter combines a conventional three-phase H7 configuration with a voltage multiplier network, effectively doubling the DC-link voltage relative to the input. Compared to existing solutions, the topology achieves a remarkably low common-mode voltage, limited to only 16.6% of the DC-link voltage. Additionally, the voltage stress across the additional switches remains at half of the DC-link voltage. The paper details the operating principles, mathematical formulation, and circuit-level analysis of the proposed inverter. Simulation results are provided to validate its performance. Furthermore, a hardware prototype has been implemented using a DSP TMS320F28379D microcontroller manufactured by Texas Instruments, headquartered in Dallas, TX, USA in conjunction with an Altera Cyclone® IV EP4CE22F17C6N FPGA-based digital control platform manufactured by Intel Corporation, headquarters in Santa Clara, CA, USA. Experimental results are presented to confirm the effectiveness and feasibility of the proposed design. Full article

(This article belongs to the Special Issue Advanced Control and Operation of Microgrids and Power Distribution Systems)

► Show Figures

Figure 1

25 pages, 1725 KiB

Open AccessReview

Analysis of the Application of Ammonia as a Fuel for a Compression-Ignition Engine

by Wojciech Tutak and Arkadiusz Jamrozik

Energies 2025, 18(12), 3217; https://doi.org/10.3390/en18123217 - 19 Jun 2025

Viewed by 191

Abstract

Piston engines used for powering automobiles as well as machinery and equipment have traditionally relied on petroleum-derived fuels. Subsequently, renewable fuels began to be used in an effort to reduce the combustion of hydrocarbon-based fuels and the associated greenhouse effect. Researchers are currently [...] Read more.

Piston engines used for powering automobiles as well as machinery and equipment have traditionally relied on petroleum-derived fuels. Subsequently, renewable fuels began to be used in an effort to reduce the combustion of hydrocarbon-based fuels and the associated greenhouse effect. Researchers are currently developing technologies aimed at eliminating fuels containing carbon in their molecular structure, which would effectively minimize the emission of carbon oxides into the atmosphere. Ammonia is considered a highly promising carbon-free fuel with broad applicability in energy systems. It serves as an excellent hydrogen carrier (NH₃), free from many of the storage and transportation limitations associated with pure hydrogen. Safety concerns regarding the storage and transport of hydrogen make ammonia an increasingly important fuel also due to its larger hydrogen storage capacity. This manuscript investigates the use of ammonia for powering a dual-fuel engine. The results indicate that the addition of ammonia improves engine performance; however, it may also lead to an increase in NO_x emissions. Due to the limitations of ammonia as a fuel, approximately 40% of the energy input must still be provided by diesel fuel to achieve optimal engine performance and acceptable NO_x emission levels. The presented research findings highlight the significant potential of NH₃ as an alternative fuel for compression-ignition engines. Proper control of the injection strategy or the adoption of alternative combustion systems may offer a promising approach to reducing greenhouse gas emissions while maintaining satisfactory engine performance parameters. Full article

(This article belongs to the Special Issue Renewable Fuels for Internal Combustion Engines: 2nd Edition)

► Show Figures

Figure 1

23 pages, 6078 KiB

Open AccessArticle

Multi-Energy Optimal Dispatching of Port Microgrids Taking into Account the Uncertainty of Photovoltaic Power

by Xiaoyong Wang, Xing Wei, Hanqing Zhang, Bailiang Liu and Yanmin Wang

Energies 2025, 18(12), 3216; https://doi.org/10.3390/en18123216 - 19 Jun 2025

Viewed by 216

Abstract

To tackle the problems of high scheduling costs and low photovoltaic (PV) accommodation rates in port microgrids, which are caused by the coupling of uncertainties in new energy output and load randomness, this paper proposes an optimized scheduling method that integrates scenario analysis [...] Read more.

To tackle the problems of high scheduling costs and low photovoltaic (PV) accommodation rates in port microgrids, which are caused by the coupling of uncertainties in new energy output and load randomness, this paper proposes an optimized scheduling method that integrates scenario analysis with multi-energy complementarity. Firstly, based on the improved Iterative Self-organizing Data Analysis Techniques Algorithm (ISODATA) clustering algorithm and backward reduction method, a set of typical scenarios that represent the uncertainties of PV and load is generated. Secondly, a multi-energy complementary system model is constructed, which includes thermal power, PV, energy storage, electric vehicle (EV) clusters, and demand response. Then, a planning model centered on economy is established. Through multi-energy coordinated optimization, supply–demand balance and cost control are achieved. The simulation results based on the port microgrid of the LEKKI Port in Nigeria show that the proposed method can significantly reduce system operating costs by 18% and improve the PV accommodation rate through energy storage time-shifting, flexible EV scheduling, and demand response incentives. The research findings provide theoretical and technical support for the low-carbon transformation of energy systems in high-volatility load scenarios, such as ports. Full article

(This article belongs to the Special Issue Renewable Energy Utilization for Energy Saving and Carbon-Emission Reduction)

► Show Figures

Figure 1

28 pages, 3433 KiB

Open AccessReview

Nearly Zero-Energy Buildings (NZEBs): A Systematic Review of the Current Status of Single-Family Houses in the EU

by Marek Borowski, Charith Madhuwantha Rathnayake and Klaudia Zwolińska-Glądys

Energies 2025, 18(12), 3215; https://doi.org/10.3390/en18123215 - 19 Jun 2025

Viewed by 282

Abstract

The building sector, responsible for approximately 40% of global energy consumption, is increasingly embracing nearly zero-energy buildings (NZEBs) to promote environmental sustainability. Focusing specifically on single-family houses, this review systematically examines current NZEB practices across Europe, aiming to identify regional adaptation strategies and [...] Read more.

The building sector, responsible for approximately 40% of global energy consumption, is increasingly embracing nearly zero-energy buildings (NZEBs) to promote environmental sustainability. Focusing specifically on single-family houses, this review systematically examines current NZEB practices across Europe, aiming to identify regional adaptation strategies and highlight performance disparities. The primary research question explored is as follows: how do design strategies, renewable energy integration, and climate adaptation measures for single-family NZEBs vary across Northern, Eastern, Southern, and Western European countries? A key gap in the literature is the lack of cross-comparative analysis of regional NZEB approaches for single-family houses, despite their significant share in Europe’s housing sector. Effective NZEB implementation depends on interdisciplinary collaboration among architects, engineers, and energy experts to optimize building design elements, including orientation, envelope insulation, and HVAC systems, tailored to regional climatic conditions. A systematic analysis of case studies was conducted, synthesizing data on primary energy consumption, CO₂ emissions, and building envelope performance. The findings reveal regional differences: Northern Europe exhibits primary energy consumption at 27–68 kWh/(m²·y) (mean: 48.2), Eastern Europe at 29–68 (mean: 42.5), Southern Europe at 35–42 (mean: 39.1), and Western Europe at 27–85 (mean: 51.5), with higher emissions in Eastern Europe compared to Denmark, for instance. These patterns underscore the role of climatic conditions and regulatory frameworks of the regions in shaping NZEB strategies. Despite shared goals of decarbonization and occupant comfort, significant knowledge gaps remain, particularly regarding long-term operational performance and regional comparison of other building types. Full article

(This article belongs to the Section G: Energy and Buildings)

► Show Figures

Figure 1

15 pages, 1729 KiB

Open AccessArticle

Theory of Quantity Value Traceability of Effective Apparent Power and Evaluation Method of Uncertainty

by Yi Luo, Jingfeng Yang, Fusheng Li, Bin Qian and Xiangyong Feng

Energies 2025, 18(12), 3214; https://doi.org/10.3390/en18123214 - 19 Jun 2025

Viewed by 185

Abstract

Apparent power and power factor are crucial metrics for evaluating the energy transmission efficiency and reactive power management in power systems. The increasing complexity of power load structures, driven by evolving energy production and consumption models, has intensified the nonlinear and unbalanced characteristics [...] Read more.

Apparent power and power factor are crucial metrics for evaluating the energy transmission efficiency and reactive power management in power systems. The increasing complexity of power load structures, driven by evolving energy production and consumption models, has intensified the nonlinear and unbalanced characteristics of circuits, presenting significant challenges to accurate apparent power measurement. The IEEE 1459-2010 standard introduces the concept of effective apparent power to enhance the assessment of energy transmission efficiency under non-sinusoidal and unbalanced conditions. However, the absence of a physical standard and a standardized traceability method for effective apparent power results in inconsistent measurement outcomes across instruments. This study proposes a novel method to trace effective apparent power measurements to the International System of Units (SI) benchmarks, based on the loss characteristics of transmission lines. The method includes a comprehensive analysis of measurement uncertainty. Simulation and experimental validation confirm that the proposed traceability circuit can achieve a measurement uncertainty of 0.0110% (coverage factor k = 2), satisfying the engineering requirement of expanded uncertainty U approximately 0.02% (k = 2). These results demonstrate the method’s practical suitability for engineering applications. Full article

► Show Figures

Figure 1

20 pages, 1200 KiB

Open AccessArticle

An Assessment of Replacing Aluminum Tubes Hosting Nuclear Fuels with Stainless Steel in a Subcritical Nuclear Reactor

by Diego Medina-Castro, Héctor René Vega-Carrillo, Antonio Baltazar-Raigosa, Tzinnia Gabriela Soto-Bernal, Régulo López-Callejas and Benjamín Gonzalo Rodríguez-Méndez

Energies 2025, 18(12), 3213; https://doi.org/10.3390/en18123213 - 19 Jun 2025

Viewed by 531

Abstract

This computational study using MCNP5 evaluated the feasibility of replacing 6061-T6 aluminum with 316L stainless steel (SS-316L) for the tubes hosting the uranium slugs in the subcritical nuclear reactor Nuclear Chicago model 9000, thereby contributing to its preservation as a key resource for [...] Read more.

This computational study using MCNP5 evaluated the feasibility of replacing 6061-T6 aluminum with 316L stainless steel (SS-316L) for the tubes hosting the uranium slugs in the subcritical nuclear reactor Nuclear Chicago model 9000, thereby contributing to its preservation as a key resource for nuclear research and education in Mexico. Simulations and dosimetric analyses (ICRP/ICRU) confirmed subcriticality in both configurations. Notably, SS-316L demonstrated an effective attenuation of peripheral gamma radiation and a reduction in the ambient neutron dose, indicating a considerable improvement in radiological safety. Although a reduction in thermal and epithermal neutron fluence was observed, the similarity in the gamma spectrum suggests no significant alteration for gamma spectroscopic experiments. In conclusion, SS-316L presents a promising alternative that enhances radiological safety and reactor longevity, making it a worthy consideration as a replacement material. Further experimental investigation is recommended to assess material activation and the gamma dose in the vicinity of the fuel. Full article

(This article belongs to the Special Issue Nuclear Engineering and Nuclear Fuel Safety)

► Show Figures

Figure 1

17 pages, 4539 KiB

Open AccessArticle

Equivalent Modeling of Temperature Field for Amorphous Alloy 3D Wound Core Transformer for New Energy

by Jianwei Han, Xiaolin Hou, Xinglong Yao, Yunfei Yan, Zonghan Dai, Xiaohui Wang, Peng Zhao, Pengzhe Zhuang and Zhanyang Yu

Energies 2025, 18(12), 3212; https://doi.org/10.3390/en18123212 - 19 Jun 2025

Viewed by 194

Abstract

It is of the utmost importance to accurately solve the transformer temperature field, as it governs the overall performance and operational stability of the transformer. However, the intricate structure of high- and low-voltage windings, insulating materials, and other components presents numerous challenges for [...] Read more.

It is of the utmost importance to accurately solve the transformer temperature field, as it governs the overall performance and operational stability of the transformer. However, the intricate structure of high- and low-voltage windings, insulating materials, and other components presents numerous challenges for modeling. Temperature exerts a significant influence on insulation aging, and elevated temperatures can notably accelerate the degradation process of insulation materials, reducing their service life and increasing the risk of electrical failures. In view of this, this paper proposes an equivalent modeling method of the temperature field of the transformer HLV winding and studies the refined modeling of the winding part. First of all, in order to reduce the difficulty of temperature field modeling, based on the principle of constant thermal resistance, the fine high- and low-voltage windings are equivalent to large conductors, and the equivalent thermal conductivity coefficient of the high- and low-voltage windings is obtained, which improves the calculation accuracy and shortens the calculation time. Secondly, we verify the feasibility of the equivalent model before and after the simulation, analyze the influence of different boundary conditions on the winding temperature field distribution, and predict the local hotspot location and temperature trend. Finally, a 50 kVA amorphous alloy winding-core transformer is tested on different prototypes to verify the effectiveness of the proposed method. Full article

► Show Figures

Figure 1

15 pages, 1550 KiB

Open AccessArticle

A Study of the Nonlinear Attenuation Behavior of Preload in the Bolt Fastening Process for Offshore Wind Turbine Blades Using Ultrasonic Technology

by Jia Han, Ke Xie, Zhaohui Yang, Lin’an Li and Ming Zhao

Energies 2025, 18(12), 3211; https://doi.org/10.3390/en18123211 - 19 Jun 2025

Viewed by 137

Abstract

The attenuation of bolt preload is a critical factor leading to bolt fatigue failure, whereas the study of the nonlinear attenuation behavior of preload and its mechanism during installation is an inevitable challenge in engineering practice. The attenuation of the preload of a [...] Read more.

The attenuation of bolt preload is a critical factor leading to bolt fatigue failure, whereas the study of the nonlinear attenuation behavior of preload and its mechanism during installation is an inevitable challenge in engineering practice. The attenuation of the preload of a bolt is mainly related to the stiffness of the bolt body as well as the stiffness of the connected parts. This study aimed to develop an experimental system to analyze the nonlinear attenuation behavior of preload during bolt tightening. First, a simulation system replicating the bolt installation process was constructed in a laboratory setting, incorporating blade and pitch bearing specimens identical to those used in a 10 MW wind turbine, restoring the stiffness coupling characteristics of the “composite-metal bearing” heterogeneous interface at the blade root through a 1:1 full-scale simulation system for the first time. Second, ultrasonic preload measurement equipment was employed to monitor preload variations during the bolt tightening process. Finally, the instantaneous preload decay rate of the wind turbine blade-root bolts and the over-draw coefficient were quantified. Experiments have shown that the preload decay rate of commonly used M36 leaf root bolts is 11–16%. If a more precise value is required, each bolt needs to be calibrated. These findings provide valuable insights for optimizing bolt installation procedures, enabling precise preload control to mitigate fatigue failures caused by abnormal preload attenuation. Full article

(This article belongs to the Section A3: Wind, Wave and Tidal Energy)

► Show Figures

Figure 1

29 pages, 3472 KiB

Open AccessArticle

Modeling of Battery Storage of Photovoltaic Power Plants Using Machine Learning Methods

by Rad Stanev, Tanyo Tanev, Venizelos Efthymiou and Chrysanthos Charalambous

Energies 2025, 18(12), 3210; https://doi.org/10.3390/en18123210 - 19 Jun 2025

Viewed by 271

Abstract

The massive integration of variable renewable energy sources (RESs) poses the gradual necessity for new power system architectures with wide implementation of distributed battery energy storage systems (BESSs), which support power system stability, energy management, and control. This research presents a methodology and [...] Read more.

The massive integration of variable renewable energy sources (RESs) poses the gradual necessity for new power system architectures with wide implementation of distributed battery energy storage systems (BESSs), which support power system stability, energy management, and control. This research presents a methodology and realization of a set of 11 BESS models based on different machine learning methods. The performance of the proposed models is tested using real-life BESS data, after which a comparative evaluation is presented. Based on the results achieved, a valuable discussion and conclusions about the models’ performance are made. This study compares the results of feedforward neural networks (FNNs), a homogeneous ensemble of FNNs, multiple linear regression, multiple linear regression with polynomial features, decision-tree-based models like XGBoost, CatBoost, and LightGBM, and heterogeneous ensembles of decision tree modes in the day-ahead forecasting of an existing real-life BESS in a PV power plant. A Bayesian hyperparameter search is proposed and implemented for all of the included models. Among the main objectives of this study is to propose hyperparameter optimization for the included models, research the optimal training period for the available data, and find the best model from the ones included in the study. Additional objectives are to compare the test results of heterogeneous and homogeneous ensembles, and grid search vs. Bayesian hyperparameter optimizations. Also, as part of the deep learning FNN analysis study, a customized early stopping function is introduced. The results show that the heterogeneous ensemble model with three decision trees and linear regression as main model achieves the highest average R² of 0.792 and the second-best nRMSE of 0.669% using a 30-day training period. CatBoost provides the best results, with an nRMSE of 0.662% for a 30-day training period, and offers competitive results for R²—0.772. This study underscores the significance of model selection and training period optimization for improving battery performance forecasting in energy management systems. The trained models or pipelines in this study could potentially serve as a foundation for transfer learning in future studies. Full article

(This article belongs to the Topic Smart Solar Energy Systems)

► Show Figures

Figure 1

23 pages, 3864 KiB

Open AccessArticle

Co-Optimization of Market and Grid Stability in High-Penetration Renewable Distribution Systems with Multi-Agent

by Dongli Jia, Zhaoying Ren and Keyan Liu

Energies 2025, 18(12), 3209; https://doi.org/10.3390/en18123209 - 19 Jun 2025

Viewed by 292

Abstract

The large-scale integration of renewable energy and electric vehicles(EVs) into power distribution systems presents complex operational challenges, particularly in coordinating market mechanisms with grid stability requirements. This study proposes a new dispatching method based on dynamic electricity prices to coordinate the relationship between [...] Read more.

The large-scale integration of renewable energy and electric vehicles(EVs) into power distribution systems presents complex operational challenges, particularly in coordinating market mechanisms with grid stability requirements. This study proposes a new dispatching method based on dynamic electricity prices to coordinate the relationship between the market and the physical characteristics of the power grid. The proposed approach introduces a multi-agent transaction model incorporating voltage regulation metrics and network loss considerations into market bidding mechanisms. For EV integration, a differentiated scheduling strategy categorizes vehicles based on usage patterns and charging elasticity. The methodological innovations primarily include an enhanced scheduling algorithm for coordinated optimization of renewable energy and energy storage, and a dynamic coordinated optimization method for EV clusters. Implemented on a modified IEEE test system, the framework demonstrates improved voltage stability through price-guided energy storage dispatch, with coordinated strategies effectively balancing peak demand management and renewable energy utilization. Case studies verify the system’s capability to align economic incentives with technical objectives, where time-of-use pricing dynamically regulates storage operations to enhance reactive power support during critical periods. This research establishes a theoretical linkage between electricity market dynamics and grid security constraints, providing system operators with a holistic tool for managing high-renewable penetration networks. By bridging market participation with operational resilience, this work contributes actionable insights for developing interoperable electricity market architectures in energy transition scenarios. Full article

► Show Figures

Figure 1

19 pages, 7758 KiB

Open AccessArticle

A Multi-Vector Modulated Model Predictive Control Based on Coordinated Control Strategy of a Photovoltaic-Storage Three-Port DC–DC Converter

by Qihui Feng, Meng Zhang, Yutao Xu, Chao Zhang, Dunhui Chen and Xufeng Yuan

Energies 2025, 18(12), 3208; https://doi.org/10.3390/en18123208 - 19 Jun 2025

Viewed by 256

Abstract

As a core component of the photovoltaic-storage microgrid systems, three-port DC–DC converters have attracted significant attention in recent years. This paper proposes a multi-vector modulated model predictive control (MVM-MPC) method based on vector analysis for a non-isolated three-port DC–DC converter formed by paralleling [...] Read more.

As a core component of the photovoltaic-storage microgrid systems, three-port DC–DC converters have attracted significant attention in recent years. This paper proposes a multi-vector modulated model predictive control (MVM-MPC) method based on vector analysis for a non-isolated three-port DC–DC converter formed by paralleling two bidirectional DC–DC converters. The proposed modulated MPC method utilizes three basic vectors to calculate the optimal switching sequence for minimizing the error vector. It can significantly minimize voltage ripple while maintaining the nonlinear and dynamic performance characteristics of a traditional MPC. MATLAB/Simulink R2024a simulations and hardware-in-loop (HIL) experimental results demonstrate that, compared with finite control set MPC and traditional two-vector modulated MPC methods, the proposed approach achieves remarkable reductions in current ripple and voltage ripple, along with excellent dynamic performance featuring smooth mode-switching. Full article

(This article belongs to the Special Issue Trends and Prospects in DC–DC/DC–AC Converters and Their Control Techniques for Renewable Energy Applications)

► Show Figures

Figure 1

15 pages, 1918 KiB

Open AccessArticle

Innovative Application of the Ritz Method to Oil-Gas Seepage Problems: A Novel Variational Approach for Solving Underground Flow Equations

by Xiongzhi Liu, Hao Yang, Lifei Dong, Ming Lei, Jie Han and Hao Kang

Energies 2025, 18(12), 3207; https://doi.org/10.3390/en18123207 - 18 Jun 2025

Viewed by 170

Abstract

State-of-the-art commercial simulators (e.g., Eclipse, CMG) predominantly employ finite difference schemes, which face persistent challenges in modeling strongly nonlinear seepage dynamics. This study explores the application of the Ritz method, grounded in variational theory, to solve underground oil seepage problems in reservoir engineering. [...] Read more.

State-of-the-art commercial simulators (e.g., Eclipse, CMG) predominantly employ finite difference schemes, which face persistent challenges in modeling strongly nonlinear seepage dynamics. This study explores the application of the Ritz method, grounded in variational theory, to solve underground oil seepage problems in reservoir engineering. The research focuses on deriving the variational form of steady-state seepage equations and presents a systematic procedure for solving these equations in finite domains. Using a one-dimensional steady-state seepage problem as a case study (which can effectively represent a wide range of typical flow regimes), the study compares the approximate solutions obtained by the Ritz method (both monomial and binomial forms) with exact solutions. The results demonstrate that the binomial approximate solution achieves high accuracy, with an average deviation of only 0.30% from the exact solution, significantly outperforming the monomial solution. The findings validate the Ritz method as an effective tool for addressing seepage problems and highlight its potential for broader applications in oil and gas reservoir modeling. Full article

(This article belongs to the Special Issue Oil and Gas Reservoirs: Phase Behavior, Seepage Mechanisms, Productivity Prediction, and Novel Modelling Methods—3rd Edition)

► Show Figures

Figure 1

21 pages, 569 KiB

Open AccessArticle

Optimization of Electricity Consumption-Associated Costs in a Medium-Sized Logistics Company

by Martins Tisenkopfs, Leo Jansons, Ineta Geipele, Sanda Lapuke and Andris Backurs

Energies 2025, 18(12), 3206; https://doi.org/10.3390/en18123206 - 18 Jun 2025

Viewed by 215

Abstract

The purpose of this research is to investigate the possibilities of electricity consumption-associated cost reduction in buildings owned by a medium-sized logistics company in Latvia (A_LV), which is a part of the larger international business ecosystem (A). The company is not using all [...] Read more.

The purpose of this research is to investigate the possibilities of electricity consumption-associated cost reduction in buildings owned by a medium-sized logistics company in Latvia (A_LV), which is a part of the larger international business ecosystem (A). The company is not using all of its facilities for its own business needs, some of them are rented out, and therefore the possibility of impacting electricity consumption in rented out buildings is limited. During the research, mixed-type approaches combining qualitative and quantitative research methods and data analysis were employed, where the quantitative methods helped to analyze the company’s electricity consumption and cost changes in different time periods, while the qualitative methods were used in a literature review. As primary data sources, A_LV’s internal electricity consumption reports and invoices for electricity payments were used, along with publicly available data on electricity consumption in Latvia and wholesale market price fluctuations. Although A_LV has numerous areas of electricity consumption optimization, this research is limited to few of them—lighting system optimization, energy management and automation applications, forklift charging regime adjustments, and choice of electricity retailer and tariff plan. Full article

(This article belongs to the Special Issue Energy Consumption in the EU Countries: 4th Edition)

► Show Figures

Figure 1

11 pages, 2137 KiB

Open AccessArticle

Design of Cobalt-Free Ni-Rich Cathodes for High-Performance Sodium-Ion Batteries Using Electrochemical Li⁺/Na⁺ Exchange

by Yao Lv, Liqiu Shi, Jianfeng Yu and Shifei Huang

Energies 2025, 18(12), 3205; https://doi.org/10.3390/en18123205 - 18 Jun 2025

Viewed by 252

Abstract

Sodium-ion batteries are renowned for their abundant reserves, cost-efficiency, safety, and eco-friendliness and are prime candidates for large-scale energy storage applications. The development of cathode materials plays a crucial role in shaping both the commercialization path and the ultimate performance capabilities of SIBs. [...] Read more.

Sodium-ion batteries are renowned for their abundant reserves, cost-efficiency, safety, and eco-friendliness and are prime candidates for large-scale energy storage applications. The development of cathode materials plays a crucial role in shaping both the commercialization path and the ultimate performance capabilities of SIBs. To overcome the intricate synthesis challenges associated with pure-phase sodium-ion cathode materials, this study introduces an innovative and streamlined electrochemical Li⁺/Na⁺ exchange process, successfully fabricating a high-capacity Ni-rich cathode material. This cathode material boasts a remarkable reversible capacity of 180 mAh g⁻¹ at 0.1 C and retains a high-rate capacity of 115 mAh g⁻¹ even at 5 C. Additionally, it exhibits exceptional cycling stability, retaining about 85% of its capacity at 1 C after 50 cycles and still maintaining a capacity greater than 60% after 100 cycles. The Na-NMA85 full cell preserves a discharge capacity of 110 mAh g⁻¹ after 100 cycles, with a capacity retention rate of 80%. This research underscores innovative strategies for designing ion-intercalation-based cathode materials that enhance battery performance, providing fresh perspectives for advancing high-performance battery technologies. Full article

(This article belongs to the Special Issue Future of Electrochemical Energy Storage Material and Technology)

► Show Figures

Figure 1

21 pages, 2735 KiB

Open AccessArticle

Price Volatility Spillovers in Energy Supply Chains: Empirical Evidence from China

by Lei Wang, Yu Sun and Jining Wang

Energies 2025, 18(12), 3204; https://doi.org/10.3390/en18123204 - 18 Jun 2025

Viewed by 193

Abstract

Based on the theoretical framework of Multivariate Stochastic Volatility (MSV), this paper combines the Dynamic Generalized Correlation (DGC) model with the t-distribution, establishes the DGC-t-MSV model, and employs the Markov Chain Monte Carlo (MCMC) algorithm based on the Bayesian principle for efficient estimation [...] Read more.

Based on the theoretical framework of Multivariate Stochastic Volatility (MSV), this paper combines the Dynamic Generalized Correlation (DGC) model with the t-distribution, establishes the DGC-t-MSV model, and employs the Markov Chain Monte Carlo (MCMC) algorithm based on the Bayesian principle for efficient estimation to investigate the price volatility spillover effects in China’s energy supply chains. The results of this study indicate the following: (1) The upstream crude oil spot price has a positive spillover effect on the midstream freight price. The downstream diesel market price, 92 gasoline market price, and 95 gasoline market price all exert positive volatility spillovers on the midstream crude oil freight price. (2) The volatility spillover effect between the upstream power coal price and the midstream coal freight price exhibits unidirectionality, and the volatility is transmitted from the power coal price to the coal freight price. (3) The upstream natural gas price and the midstream liquefied natural gas market price display asymmetric characteristics. Among them, the upstream natural gas price has a unidirectional and more pronounced positive volatility spillover effect on the midstream liquefied natural gas market price. Full article

► Show Figures

Figure 1

33 pages, 13278 KiB

Open AccessArticle

Effect of Blade Profile on Flow Characteristics and Efficiency of Cross-Flow Turbines

by Ephrem Yohannes Assefa and Asfafaw Haileselassie Tesfay

Energies 2025, 18(12), 3203; https://doi.org/10.3390/en18123203 - 18 Jun 2025

Viewed by 507

Abstract

This study presents a comprehensive numerical investigation into the influence of blade profile geometry on the internal flow dynamics and hydraulic performance of Cross-Flow Turbines (CFTs) under varying runner speeds. Four blade configurations, flat, round, sharp, and aerodynamic, were systematically evaluated using steady-state, [...] Read more.

This study presents a comprehensive numerical investigation into the influence of blade profile geometry on the internal flow dynamics and hydraulic performance of Cross-Flow Turbines (CFTs) under varying runner speeds. Four blade configurations, flat, round, sharp, and aerodynamic, were systematically evaluated using steady-state, two-dimensional Computational Fluid Dynamics (CFD) simulations. The Shear Stress Transport (SST) k–ω turbulence model was employed to resolve the flow separation, recirculation, and turbulence across both energy conversion stages of the turbine. The simulations were performed across runner speeds ranging from 270 to 940 rpm under a constant head of 10 m. The performance metrics, including the torque, hydraulic efficiency, water volume fraction, pressure distribution, and velocity field characteristics, were analyzed in detail. The aerodynamic blade consistently outperformed the other geometries, achieving a peak efficiency of 83.5% at 800 rpm, with improved flow attachment, reduced vortex shedding, and lower exit pressure. Sharp blades also demonstrated competitive efficiency within a narrower optimal speed range. In contrast, the flat and round blades exhibited higher turbulence and recirculation, particularly at off-optimal speeds. The results underscore the pivotal role of blade edge geometry in enhancing energy recovery, suppressing flow instabilities, and optimizing the stage-wise performance in CFTs. These findings offer valuable insights for the design of high-efficiency, site-adapted turbines suitable for micro-hydropower applications. Full article

(This article belongs to the Special Issue Optimization Design and Simulation Analysis of Hydraulic Turbine)

► Show Figures

Figure 1

29 pages, 12629 KiB

Open AccessArticle

Forecast-Aided Converter-Based Control for Optimal Microgrid Operation in Industrial Energy Management System (EMS): A Case Study in Vietnam

by Yeong-Nam Jeon and Jae-ha Ko

Energies 2025, 18(12), 3202; https://doi.org/10.3390/en18123202 - 18 Jun 2025

Viewed by 179

Abstract

This study proposes a forecast-aided energy management strategy tailored for industrial microgrids operating in Vietnam’s tropical climate. The core novelty lies in the implementation of a converter-based EMS that enables bidirectional DC power exchange between multiple subsystems. To improve forecast accuracy, an artificial [...] Read more.

This study proposes a forecast-aided energy management strategy tailored for industrial microgrids operating in Vietnam’s tropical climate. The core novelty lies in the implementation of a converter-based EMS that enables bidirectional DC power exchange between multiple subsystems. To improve forecast accuracy, an artificial neural network (ANN) is used to model the relationship between electric load and localized meteorological features, including temperature, dew point, humidity, and wind speed. The forecasted load data is then used to optimize charge/discharge schedules for energy storage systems (ESS) using a Particle Swarm Optimization (PSO) algorithm. The strategy is validated using real-site data from a Vietnamese industrial complex, where the proposed method demonstrates enhanced load prediction accuracy, cost-effective ESS operation, and multi-microgrid flexibility under weather variability. This integrated forecasting and control approach offers a scalable and climate-adaptive solution for EMS in emerging industrial regions. Full article

(This article belongs to the Special Issue Advanced Control and Operation of Microgrids and Power Distribution Systems)

► Show Figures

Figure 1

23 pages, 3161 KiB

Open AccessArticle

Experimental Investigation into the Energy Performance of a Biomass Recuperative Organic Rankine Cycle (ORC) for Micro-Scale Applications in Design and Off-Design Conditions

by Luigi Falbo, Angelo Algieri, Pietropaolo Morrone and Diego Perrone

Energies 2025, 18(12), 3201; https://doi.org/10.3390/en18123201 - 18 Jun 2025

Viewed by 156

Abstract

Increasing energy efficiency and promoting the use of sustainable energy sources are crucial for addressing global energy challenges. Organic Rankine cycle (ORC) technology offers a promising route for efficient decentralised power generation. This study examines the energy performance of a biomass-fired recuperative ORC [...] Read more.

Increasing energy efficiency and promoting the use of sustainable energy sources are crucial for addressing global energy challenges. Organic Rankine cycle (ORC) technology offers a promising route for efficient decentralised power generation. This study examines the energy performance of a biomass-fired recuperative ORC for micro-scale applications. The investigation proposes an extensive experimental analysis to characterise the ORC behaviour under design and off-design conditions due to the limited data in the literature. The work examines the impact of different operating parameters (e.g., pump speed, hot source temperature, superheating degree, expander inlet pressure) to provide suitable insights for the efficient design and operation of recuperative micro-generation units fuelled by biomass. The experimental analysis highlights that the micro-scale ORC properly operates under a wide range of operating conditions. Electric power ranges between 0.37 kW and 2.30 kW, and the maximum net electric efficiency reaches 8.55%. The selection of the proper operating conditions guarantees efficiency higher than 7% for power larger than 800 W, demonstrating that biomass-fired recuperative ORC systems represent a valuable option for low-carbon micro-scale generation, with good performance in design and off-design conditions. For this purpose, the pump speed and the superheating degree at the expander inlet are essential parameters to maximise the performance of the investigated recuperative ORC. Full article

► Show Figures

Figure 1

43 pages, 1295 KiB

Open AccessReview

Enhancing Building Thermal Performance: A Review of Phase Change Material Integration

by Khaled Alassaad, James Minto and Pieter de Wilde

Energies 2025, 18(12), 3200; https://doi.org/10.3390/en18123200 - 18 Jun 2025

Viewed by 434

Abstract

Buildings are responsible for over one-third of global energy use and greenhouse gas emissions, with heating and cooling being major contributors. Phase change materials (PCMs) offer a promising passive solution to improve thermal regulation and reduce heating and cooling loads. This review analyses [...] Read more.

Buildings are responsible for over one-third of global energy use and greenhouse gas emissions, with heating and cooling being major contributors. Phase change materials (PCMs) offer a promising passive solution to improve thermal regulation and reduce heating and cooling loads. This review analyses different experimental and simulation-based studies on the integration of PCMs into building structures for enhancing building energy performance. The key variables examined include melting temperature, latent heat capacity, thermal conductivity (λ), PCM positioning (interior, exterior, or embedded), thickness, and climate zone. The results show that PCMs reduce heat transfer by up to 47.6%, stabilize indoor temperatures with up to a 46% reduction in fluctuations, and decrease heating and cooling demands by as much as 31%, depending on component placement and climate. The optimal melting range for moderate climates lies between 22 °C and 28 °C. This review identifies critical trade-offs between PCM quantity, placement, and climatic suitability and provides a matrix of design recommendations for various building types. Full article

(This article belongs to the Special Issue Thermal Comfort and Energy Performance in Building)

► Show Figures

Graphical abstract

20 pages, 6509 KiB

Open AccessArticle

Investigations on the Effect of Inclination Angle on the Aerodynamic Performance of a Two-Stage Centrifugal Compressor of a Proton Exchange Membrane Fuel Cell System

by Wenke Wang, Dengfeng Yang, Li Guo, Rui Wu, Xiangyi Zhou, Qian Zhang, Qingyi Kong and Leon Hu

Energies 2025, 18(12), 3199; https://doi.org/10.3390/en18123199 - 18 Jun 2025

Viewed by 169

Abstract

This study examines how leading-edge inclination angles affect a two-stage centrifugal compressor’s aerodynamic performance using numerical and experimental methods. Five impellers with varied inclination configurations were designed for both stages. The results show that negative inclination improves the pressure ratio and efficiency under [...] Read more.

This study examines how leading-edge inclination angles affect a two-stage centrifugal compressor’s aerodynamic performance using numerical and experimental methods. Five impellers with varied inclination configurations were designed for both stages. The results show that negative inclination improves the pressure ratio and efficiency under near-choke conditions, with greater enhancements in the low-pressure stage. Positive inclination significantly boosts the pressure ratio and efficiency under near-stall conditions, particularly in the low-pressure stage. Negative inclinations optimize blade loading and choke flow capacity, while effectively reducing incidence angle deviations induced by interstage pipeline distortion and decreasing outlet pressure fluctuation amplitude in the high-pressure stage. Positive inclinations delay flow separation, suppress tip leakage vortices, and extend the stall margin. Full article

► Show Figures

Figure 1

18 pages, 1812 KiB

Open AccessReview

Cadmium-Free Buffer Layer Materials for Kesterite Thin-Film Solar Cells: An Overview

by Nafees Ahmad and Guangbao Wu

Energies 2025, 18(12), 3198; https://doi.org/10.3390/en18123198 - 18 Jun 2025

Viewed by 341

Abstract

Kesterite (CZTS/CZTSSe) thin-film solar cells are considered an eco-friendly, earth-abundant, and low-cost photovoltaic technology that can fulfill our future energy needs. Due to its outstanding properties including tunable bandgap and high absorption coefficient, the power conversion efficiency (PCE) has reached over 14%. However, [...] Read more.

Kesterite (CZTS/CZTSSe) thin-film solar cells are considered an eco-friendly, earth-abundant, and low-cost photovoltaic technology that can fulfill our future energy needs. Due to its outstanding properties including tunable bandgap and high absorption coefficient, the power conversion efficiency (PCE) has reached over 14%. However, toxic cadmium sulfide (CdS) is commonly used as an n-type buffer layer in kesterite thin-film solar cells (KTFSCs) to form a better p–n junction with the p-type CZTS/CZTSSe absorber. In addition to its toxicity, the CdS buffer layer shows parasitic absorption at low wavelengths (400–500 nm) owing to its low bandgap (2.4 eV). For the last few years, several efforts have been made to substitute CdS with an eco-friendly, Cd-free, cost-effective buffer layer with alternative large-bandgap materials such as ZnSnO, Zn (O, S), In₂Se₃, ZnS, ZnMgO, and TiO₂, which showed significant advances. Herein, we summarize the key findings of the research community using a Cd-free buffer layer in KTFSCs to provide a current scenario for future work motivating researchers to design new materials and strategies to achieve higher performance. Full article

(This article belongs to the Special Issue Interface Engineering and Stability Investigation for Organic, Perovskite, and Thin Film Solar Cells)

► Show Figures

Figure 1

17 pages, 5848 KiB

Open AccessArticle

Highly Reliable Power Circuit Configuration with SiC Chopper Module for Hybrid Fuel Cell and Battery Power System for Urban Air Mobility (UAM) Applications

by Moon-Seop Choi and Chong-Eun Kim

Energies 2025, 18(12), 3197; https://doi.org/10.3390/en18123197 - 18 Jun 2025

Viewed by 189

Abstract

This paper proposes a high-reliability power conversion system optimized for Urban Air Mobility (UAM) applications, which utilizes silicon carbide (SiC) chopper modules within a hybrid fuel cell and battery structure. The system features a redundant power configuration that employs both a main and [...] Read more.

This paper proposes a high-reliability power conversion system optimized for Urban Air Mobility (UAM) applications, which utilizes silicon carbide (SiC) chopper modules within a hybrid fuel cell and battery structure. The system features a redundant power configuration that employs both a main and an auxiliary battery to ensure continuous and stable power supply, even under emergency or fault conditions. By integrating SiC-based power converters, the proposed system achieves high efficiency, low switching losses, and enhanced thermal performance, which are crucial for the space- and weight-constrained environment of UAM platforms. Furthermore, a robust control strategy is implemented to enable smooth transitions between multiple power sources, maintaining operational stability and safety. System-level simulations were conducted using PowerSIM to validate the performance and reliability of the proposed architecture. The results demonstrate its effectiveness, making it a strong candidate for future UAM power systems requiring lightweight, efficient, and fault-tolerant power solutions. Full article

(This article belongs to the Special Issue Electric Vehicles: Latest Advances and Prospects for Sustainable Energy Systems and Sustainable Mobility)

► Show Figures

Figure 1

26 pages, 13313 KiB

Open AccessArticle

Exploring Augmented Reality HMD Telemetry Data Visualization for Strategy Optimization in Student Solar-Powered Car Racing

by Jakub Forysiak, Piotr Krawiranda, Krzysztof Fudała, Zbigniew Chaniecki, Krzysztof Jóźwik, Krzysztof Grudzień and Andrzej Romanowski

Energies 2025, 18(12), 3196; https://doi.org/10.3390/en18123196 - 18 Jun 2025

Viewed by 244

Abstract

This article explores how different modalities of presenting telemetry data can support strategy management during solar-powered electric vehicle racing. Student team members using augmented reality head-mounted displays (AR HMD) have reported significant advantages for in-race strategy monitoring and execution, yet so far, there [...] Read more.

This article explores how different modalities of presenting telemetry data can support strategy management during solar-powered electric vehicle racing. Student team members using augmented reality head-mounted displays (AR HMD) have reported significant advantages for in-race strategy monitoring and execution, yet so far, there is no published evidence to support these claims. This study shows that there are specific situations in which various visualization modes, including AR HMDs, demonstrate improved performance for users with varying levels of experience. We analyzed racing team performance for specific in-race events extracted from free and circuit-based real race datasets. These findings were compared with results obtained in a controlled, task-based user study utilizing three visualization interface conditions. Our exploration focused on how telemetry data visualizations influenced user performance metrics such as event reaction time, decision adequacy, task load index, and usability outcomes across four event types, taking into account both the interface and participant experience level. The results reveal that while traditional web application-type visualizations work well in most cases, augmented reality has the potential to improve race performance in some of the examined free-race and circuit-race scenarios. A notable novelty and key finding of this study is that the use of augmented reality HMDs provided particularly significant advantages for less experienced participants in most of the tasks, underscoring the substantial benefits of this technology for the support of novice users. Full article

► Show Figures

Figure 1

37 pages, 9432 KiB

Open AccessReview

High-Temperature Molten Salt Heat Exchanger Technology: Research Advances, Challenges, and Future Perspectives

by Chunyang Zheng, Keyong Cheng and Dongjiang Han

Energies 2025, 18(12), 3195; https://doi.org/10.3390/en18123195 - 18 Jun 2025

Viewed by 287

Abstract

Molten salt heat exchangers are pivotal components in advanced energy systems, where their high-temperature stability and efficient heat transfer performance are critical for system reliability. This paper provides a comprehensive review of recent advancements in molten salt heat exchanger technology, focusing on their [...] Read more.

Molten salt heat exchangers are pivotal components in advanced energy systems, where their high-temperature stability and efficient heat transfer performance are critical for system reliability. This paper provides a comprehensive review of recent advancements in molten salt heat exchanger technology, focusing on their application in nuclear energy, concentrated solar power, and thermal energy storage systems. Key design considerations, including thermophysical properties of molten salts and operational conditions, are analyzed to highlight performance optimization strategies. The review traces the evolution from traditional shell-and-tube heat exchangers to compact designs like printed circuit heat exchangers, emphasizing improvements in heat transfer efficiency and power density. Challenges such as material corrosion, manufacturing complexities, and flow dynamics are critically examined. Furthermore, future research directions are proposed, including the development of high-performance materials, advanced manufacturing techniques, and optimized geometries. This review aims to consolidate dispersed research findings, address technological bottlenecks, and provide a roadmap for the continued development of molten salt heat exchangers in high-temperature energy systems. Full article

(This article belongs to the Collection Advances in Heat Transfer Enhancement)

► Show Figures

Figure 1

19 pages, 3650 KiB

Open AccessArticle

Enhanced-Dueling Deep Q-Network for Trustworthy Physical Security of Electric Power Substations

by Nawaraj Kumar Mahato, Junfeng Yang, Jiaxuan Yang, Gangjun Gong, Jianhong Hao, Jing Sun and Jinlu Liu

Energies 2025, 18(12), 3194; https://doi.org/10.3390/en18123194 - 18 Jun 2025

Viewed by 232

Abstract

This paper introduces an Enhanced-Dueling Deep Q-Network (EDDQN) specifically designed to bolster the physical security of electric power substations. We model the intricate substation security challenge as a Markov Decision Process (MDP), segmenting the facility into three zones, each with potential normal, suspicious, [...] Read more.

This paper introduces an Enhanced-Dueling Deep Q-Network (EDDQN) specifically designed to bolster the physical security of electric power substations. We model the intricate substation security challenge as a Markov Decision Process (MDP), segmenting the facility into three zones, each with potential normal, suspicious, or attacked states. The EDDQN agent learns to strategically select security actions, aiming for optimal threat prevention while minimizing disruptive errors and false alarms. This methodology integrates Double DQN for stable learning, Prioritized Experience Replay (PER) to accelerate the learning process, and a sophisticated neural network architecture tailored to the complexities of multi-zone substation environments. Empirical evaluation using synthetic data derived from historical incident patterns demonstrates the significant advantages of EDDQN over other standard DQN variations, yielding an average reward of 7.5, a threat prevention success rate of 91.1%, and a notably low false alarm rate of 0.5%. The learned action policy exhibits a proactive security posture, establishing EDDQN as a promising and reliable intelligent solution for enhancing the physical resilience of power substations against evolving threats. This research directly addresses the critical need for adaptable and intelligent security mechanisms within the electric power infrastructure. Full article

(This article belongs to the Special Issue Energy, Electrical and Power Engineering: 3rd Edition)

► Show Figures

Graphical abstract

Journal Menu

Journal Browser

Energies, Volume 18, Issue 12 (June-2 2025) – 223 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI