Green Synthesis of Core/Shell Phase Change Materials: Applications in Industry and Energy Sectors
Modeling Retail Buildings Within Renewable Energy Communities: Generation and Implementation of Reference Energy Use Profiles
Introduction to ORC–VCC Systems: A Review
Offshore Wind Power—Seawater Electrolysis—Salt Cavern Hydrogen Storage Coupling System: Potential and Challenges
Unsteady Loading on a Tidal Turbine Due to the Turbulent Wake of an Upstream Turbine Interacting with a Seabed Ridge

Journal Description

Energies

Energies is a peer-reviewed, open access journal of related scientific research, technology development, engineering policy, and management studies related to the general field of energy, from technologies of energy supply, conversion, dispatch, and final use to the physical and chemical processes behind such technologies. Energies is published semimonthly online by MDPI. The European Biomass Industry Association (EUBIA), Association of European Renewable Energy Research Centres (EUREC), Institute of Energy and Fuel Processing Technology (ITPE), International Society for Porous Media (InterPore), CYTED and others are affiliated with Energies and their members receive a discount on the article processing charges.

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, SCIE (Web of Science), Ei Compendex, RePEc, Inspec, CAPlus / SciFinder, and other databases.
Journal Rank: CiteScore - Q1 (Control and Optimization)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 16.8 days after submission; acceptance to publication is undertaken in 2.9 days (median values for papers published in this journal in the second half of 2024).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Sections: published in 41 topical sections.
Testimonials: See what our editors and authors say about Energies.
Companion journals for Energies include: Gases, Nanoenergy Advances, Solar, Wind, Energy Storage and Applications and Bioresources and Bioproducts.

Impact Factor: 3.0 (2023); 5-Year Impact Factor: 3.0 (2023)

Imprint Information Journal Flyer Open Access ISSN: 1996-1073

Latest Articles

22 pages, 2229 KiB

Open AccessArticle

A Structured Data Model for Asset Health Index Integration in Digital Twins of Energy Converters

by Juan F. Gómez Fernández, Eduardo Candón Fernández and Adolfo Crespo Márquez

Energies 2025, 18(12), 3148; https://doi.org/10.3390/en18123148 (registering DOI) - 16 Jun 2025

Abstract

A persistent challenge in digital asset management is the lack of standardized models for integrating health assessment—such as the Asset Health Index (AHI)—into Digital Twins, limiting their extended implementation beyond individual projects. Asset managers in the energy sector face challenges of digitalization such as digital environment selection, employed digital modules (absence of an architecture guide) and their interconnection, sources of data, and how to automate the assessment and provide the results in a friendly decision support system. Thus, for energy systems, the integration of Asset Assessment in virtual replicas by Digital Twins is a complete way of asset management by enabling real-time monitoring, predictive maintenance, and lifecycle optimization. Another challenge in this context is how to compound in a structured assessment of asset condition, where the Asset Health Index (AHI) plays a critical role by consolidating heterogeneous data into a single, actionable indicator easy to interpret as a level of risk. This paper tries to serve as a guide against these digital and structured assessments to integrate AHI methodologies into Digital Twins for energy converters. First, the proposed AHI methodology is introduced, and after a structured data model specifically designed, orientated to a basic and economic cloud implementation architecture. This model has been developed fulfilling standardized practices of asset digitalization as the Reference Architecture Model for Industry 4.0 (RAMI 4.0), organizing asset-related information into interoperable domains including physical hierarchy, operational monitoring, reliability assessment, and risk-based decision-making. A Unified Modeling Language (UML) class diagram formalizes the data model for cloud Digital Twin implementation, which is deployed on Microsoft Azure Architecture using native Internet of Things (IoT) and analytics services to enable automated and real-time AHI calculation. This design and development has been realized from a scalable point of view and for future integration of Machine-Learning improvements. The proposed approach is validated through a case study involving three high-capacity converters in distinct operating environments, showing the model’s effective assistance in anticipating failures, optimizing maintenance strategies, and improving asset resilience. In the case study, AHI-based monitoring reduced unplanned failures by 43% and improved maintenance planning accuracy by over 30%. Full article

(This article belongs to the Section A1: Smart Grids and Microgrids)

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16 pages, 5881 KiB

Open AccessArticle

High-Performance Carbon Black/Fe₃O₄/Epoxy Nanodielectrics for Electrostatic Energy Storage and Harvesting Solutions

by Sotirios Stavropoulos, Aikaterini Sanida and Georgios Psarras

Energies 2025, 18(12), 3147; https://doi.org/10.3390/en18123147 (registering DOI) - 16 Jun 2025

Abstract

The present study explores the energy storage and harvesting properties of nanocomposite systems reinforced with carbon black and magnetite nanoparticles (Fe₃O₄). The systems’ energy storage performance was evaluated under both AC and DC conditions to analyze the impact of temperature, DC charging voltage levels, and varying filler contents on the stored and recovered energy. The experimental findings demonstrated that these systems are capable of efficiently storing and releasing energy on demand via a rapid charge–discharge mechanism. Dynamic mechanical and dielectric analyses revealed significant enhancements in the storage modulus and the energy efficiency of these materials due to the synergistic effects of the nanoparticles and the interactions between them and the polymer matrix. The incorporation of the carbon black and magnetite nanoparticles improves the energy-storage capabilities, supported by augmented interfacial polarization phenomena, which facilitate charge migration and accumulation. These systems exhibit rapid charge and discharge behavior, making them suitable for applications requiring high power density and fast energy storage and recovery cycling. These findings underscore the aptitude of these nanocomposites for high-performance energy-storage solutions, emphasizing their adaptability to applications requiring both high energy density and efficient recovery in tandem with adequate thermomechanical performance. Full article

(This article belongs to the Special Issue Research on Advanced Energy Materials for Meeting Global Energy Challenges)

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21 pages, 2990 KiB

Open AccessReview

Geothermal Lithium Extraction Technology: Research Status and Prospects

by Bo Zhang, Feng Wang, Ronggang Wang, Yuhan Shang, Feng Li, Mengjiao Li and Tao Wang

Energies 2025, 18(12), 3146; https://doi.org/10.3390/en18123146 (registering DOI) - 16 Jun 2025

Abstract

With the explosive growth in global lithium demand driven by the new energy industry, traditional lithium extraction methods face critical challenges such as resource scarcity, environmental pressure, and high energy consumption, necessitating sustainable alternatives. Under such circumstances, geothermal brine has emerged as a critical lithium resource, attracting significant attention due to advancements in efficient extraction technologies. This review establishes a comprehensive framework for analyzing geothermal lithium extraction technologies, with the following key contributions: an in-depth analysis of resource characteristics and development advantages, an innovative technical evaluation and performance comparison, and strategic pathways for technological synergy and industrial integration. This article reviews the global distribution and characteristics of lithium resources, analyzes the advantages and primary methods of geothermal lithium extraction, and examines key challenges such as high energy consumption and environmental impacts. Furthermore, future development directions are outlined. Currently, applicable technologies for geothermal lithium extraction include evaporation–crystallization, chemical precipitation, adsorption, solvent extraction, electrochemical methods, and membrane separation. Among these, membrane separation, particularly forward osmosis (FO), is identified as a pivotal research focus. The industrialization of geothermal lithium extraction and its integration with other industries are expected to shape future trends. This review not only provides critical insights and optimization strategies for geothermal lithium resource development, but also establishes a theoretical foundation for the green transition and sustainable utilization of resources in the global new energy industry. Full article

(This article belongs to the Section H: Geo-Energy)

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25 pages, 3539 KiB

Open AccessArticle

Deceptive Cyber-Resilience in PV Grids: Digital Twin-Assisted Optimization Against Cyber-Physical Attacks

by Bo Li, Xin Jin, Tingjie Ba, Tingzhe Pan, En Wang and Zhiming Gu

Energies 2025, 18(12), 3145; https://doi.org/10.3390/en18123145 (registering DOI) - 16 Jun 2025

Abstract

The increasing integration of photovoltaic (PV) systems into smart grids introduces new cybersecurity vulnerabilities, particularly against cyber-physical attacks that can manipulate grid operations and disrupt renewable energy generation. This paper proposes a multi-layered cyber-resilient PV optimization framework, leveraging digital twin-based deception, reinforcement learning-driven cyber defense, and blockchain authentication to enhance grid security and operational efficiency. A deceptive cyber-defense mechanism is developed using digital twin technology to mislead adversaries, dynamically generating synthetic PV operational data to divert attack focus away from real assets. A deep reinforcement learning (DRL)-based defense model optimizes adaptive attack mitigation strategies, ensuring real-time response to evolving cyber threats. Blockchain authentication is incorporated to prevent unauthorized data manipulation and secure system integrity. The proposed framework is modeled as a multi-objective optimization problem, balancing attack diversion efficiency, system resilience, computational overhead, and energy dispatch efficiency. A non-dominated sorting genetic algorithm (NSGA-III) is employed to achieve Pareto-optimal solutions, ensuring high system resilience while minimizing computational burdens. Extensive case studies on a realistic PV-integrated smart grid test system demonstrate that the framework achieves an attack diversion efficiency of up to 94.2%, improves cyberattack detection rates to 98.5%, and maintains an energy dispatch efficiency above 96.2%, even under coordinated cyber threats. Furthermore, computational overhead is analyzed to ensure that security interventions do not impose excessive delays on grid operation. The results validate that digital twin-based deception, reinforcement learning, and blockchain authentication can significantly enhance cyber-resilience in PV-integrated smart grids. This research provides a scalable and adaptive cybersecurity framework that can be applied to future renewable energy systems, ensuring grid security, operational stability, and sustainable energy management under adversarial conditions. Full article

(This article belongs to the Special Issue Big Data Analysis and Application in Power System)

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20 pages, 2393 KiB

Open AccessArticle

Thermal Conductivity of Sustainable Earthen Materials Stabilized by Natural and Bio-Based Polymers: An Experimental and Statistical Analysis

by Rizwan Shoukat, Marta Cappai, Giorgio Pia, Tadeusz Kubaszek, Roberto Ricciu, Łukasz Kolek and Luca Pilia

Energies 2025, 18(12), 3144; https://doi.org/10.3390/en18123144 (registering DOI) - 15 Jun 2025

Abstract

The natural and sustainable ability of earthen building materials makes them highly valuable. Bio-stabilization involves using biological materials or processes in earthen construction to enhance the performance and characteristics of earthen materials. The main objective of bio-stabilization is to substitute high-energy-intensive building materials with more green, thermally efficient substitutions, ultimately reducing indirect emissions. The large-scale use of earth presents a viable alternative due to its extensive availability and, more importantly, its low embodied energy. The aim of this work is to investigate the thermal conductivity of earth stabilized with Opuntia Ficus-Indica (OFI), a natural biopolymer, and to assess how these properties vary based on mix design. A comparative analysis is performed to evaluate the thermal performance of bio-based polymer-stabilized earthen materials (S-30, S-40, D-30, and D-40) alongside natural biopolymer-stabilized earth (OFI-30 and OFI-40) under dry conditions, employing an experimental method. A scanning electron microscope was employed to examine the microstructure of bio-stabilized earthen materials from the samples. Statistical analysis was conducted on the collected data using ANOVA with a significance level of 0.05. The Tukey test was applied to identify specific mean pairings that demonstrate significant differences in the characteristics of the mixtures at each replacement level, maintaining a confidence interval of 95%. The experimental and statistical findings reveal that the OFI-30, D-40, and S-40 mixtures exhibit strong bonding with earthen materials and high thermal performance compared to all other mix designs in environmental samples. Additionally, these mix designs show further improvement in thermal performance in the dry conditions. Full article

(This article belongs to the Special Issue Biomass and Municipal Solid Waste Thermal Conversion Technologies: 3rd Edition)

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29 pages, 8083 KiB

Open AccessArticle

DC-Link Voltage Stabilization and Capacitor Size Reduction in Active Neutral-Point-Clamped Inverters Using an Advanced Control Method

by Ahmet Yuksel, Ibrahim Sefa and Necmi Altin

Energies 2025, 18(12), 3143; https://doi.org/10.3390/en18123143 (registering DOI) - 15 Jun 2025

Abstract

This study examines the impact of midpoint voltage fluctuations on the performance of multilevel converters and proposes an advanced control strategy to reduce the required DC bus capacitance while maintaining system stability. The research demonstrates that active voltage imbalance control in active neutral-point-clamped (ANPC) topologies allows for stable operation with significantly reduced capacitor values. A hybrid control approach, combining fuzzy logic control and third-harmonic injection PWM (THIPWM), is developed to enhance voltage balancing, and modulation techniques are systematically optimized. Both simulation and experimental analyses confirm the efficacy of the proposed method, which achieves superior voltage regulation compared to conventional PI-based control schemes. Specifically, experimental results show a reduction in peak-to-peak DC-link voltage fluctuation from 116 V to just 4 V, and the phase current THD is reduced from 3.6% to 0.8%. The results indicate a substantial reduction in voltage fluctuations, contributing to a total harmonic distortion (THD) as low as 0.8%. Furthermore, the proposed strategy facilitates an approximate 26-fold decrease in DC bus capacitor size without compromising system stability. The reduction in capacitance not only lowers the overall system costs and hardware complexity but also improves reliability. The inverter was tested at a rated power of 62.5 kW using 0.3 mF capacitors instead of the theoretically required 7.8 mF. This work advances power electronics by presenting an efficient voltage balancing methodology, offering a cost-effective and robust solution for multilevel converter applications. The findings are validated through comprehensive simulations and experimental tests, ensuring practical applicability. Full article

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19 pages, 4244 KiB

Open AccessArticle

Modular-Multi-Port-Converter-Based Battery Energy Storage System with Integrated Battery Management Functions

by Bortecene Yildirim, Mohammed A. Elgendy, Andrew Smith, Mehmet C. Kulan and Bahadir Akbal

Energies 2025, 18(12), 3142; https://doi.org/10.3390/en18123142 (registering DOI) - 15 Jun 2025

Abstract

Modular converters offer an effective solution for battery energy storage systems (BESSs) by lowering battery pack voltage levels and enabling additional functionalities, such as state of charge (SoC) and state of health (SoH) balancing, temperature regulation, and improved system reliability. However, conventional modular designs often require numerous additional components, including passive elements, switches, and sensing circuits. This paper proposes a modular multi-port converter (MMPC) BESS that combines energy conversion and battery management functions, leveraging the benefits of both modular and multi-port architectures. The proposed system demonstrates promising scalability and adaptability within the tested voltage and power ranges, with potential for extension to higher voltage and power applications through modular expansion. It also introduces an additional control layer, enhancing flexibility for control optimization and cost-effectiveness while improving reliability by reducing dependency on bypass switches. A prototype utilizing three dual-port converters managing six battery packs was developed. The experimental results confirm that the MMPC-based BESS achieves energy conversion and effectively balances the SoC among battery packs during both charging and discharging, under initial SoC mismatches. Full article

(This article belongs to the Section F3: Power Electronics)

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14 pages, 1465 KiB

Open AccessArticle

Comparative Study of the Lubricity of Hydrotreated Vegetable Oil, Diesel, and Their Blends Using Four-Ball Testing: Focus on Scuffing Load

by Hubert Kuszewski, Artur Jaworski and Dariusz Szpica

Energies 2025, 18(12), 3141; https://doi.org/10.3390/en18123141 (registering DOI) - 15 Jun 2025

Abstract

The search for low-emission fuels has increased interest in hydrotreated vegetable oil (HVO) as a renewable diesel substitute. This study examines the lubricity of HVO, diesel, and their blends using a four-ball tester, with scuffing load as the main evaluation criterion. Five fuel samples were tested: diesel, neat HVO, and blends containing 25%, 50%, and 75% HVO by volume. The results show that blending HVO with diesel improves lubricity at moderate concentrations, with the 25% HVO blend exhibiting the highest scuffing load. In contrast, neat HVO demonstrated significantly reduced lubricity—its scuffing load was 24% lower than diesel’s—confirming the negative impact of the absence of polar and aromatic compounds. The scuffing load did not decrease linearly with increasing HVO content, suggesting synergistic effects in certain blends. Viscosity increased with HVO content, but it did not directly correlate with improved lubricity. These findings indicate that chemical composition plays a dominant role over viscosity in determining lubricating performance. The study provides new insights into the tribological behavior of HVO–diesel blends and demonstrates that scuffing load testing offers a practical method for preliminary lubricity assessment of renewable fuels. Full article

(This article belongs to the Special Issue Internal Combustion Engines: Research and Applications—3rd Edition)

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18 pages, 4257 KiB

Open AccessArticle

Comprehensive Experimental Study of Steam Flooding for Offshore Heavy Oil Recovery After Water Flooding

by Wei Zhang, Yigang Liu, Jian Zou, Qiuxia Wang, Zhiyuan Wang, Yongbin Zhao and Xiaofei Sun

Energies 2025, 18(12), 3140; https://doi.org/10.3390/en18123140 (registering DOI) - 15 Jun 2025

Abstract

The objective of this study is to investigate the feasibility of steam flooding (SF) as an alternative method for offshore heavy oil reservoirs after water flooding (WF). A series of experiments was performed by using specially designed one-dimensional (1-D) and three-dimensional (3-D) experimental systems to prove the feasibility of SF and to study the effects of the timing of SF, the steam injection rate, and the addition of chemical agents (the nitrogen foams and displacing agents) on the performance of SF after WF. The results showed that, for offshore heavy oil reservoirs after WF processes, the SF process is a viable enhanced oil recovery method, which should start as early as possible if the economic conditions permit. It is extremely important to choose an appropriate steam injection rate for SF after the WF process. Compared with the pure SF process, the final oil recovery of the SF process with the addition of the nitrogen foam or the displacing agent increased by 12.83% and 7.58% in the 1-D experiments, respectively. The nitrogen foam and displacing agent have synergistic effects on the performance of the SF after WF processes. The final oil recovery of the SF process with the addition of the two chemical agents at the steam injection rate of 10 mL/min was 37.64%, which was 5.47% higher than that of the pure SF process in the 3-D experiments. Full article

(This article belongs to the Section H: Geo-Energy)

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31 pages, 26167 KiB

Open AccessArticle

Optimization of Vertical Axis Wind Turbine Systems to Capture Vehicle-Induced Highway Winds

by Aydin Ulus and Stefan Ilie Moldovan

Energies 2025, 18(12), 3139; https://doi.org/10.3390/en18123139 (registering DOI) - 14 Jun 2025

Abstract

This study introduces an innovative set of guide vanes that increase the efficiency of Vertical Axis Wind Turbines (VAWT) using winds generated by vehicles traveling on highways. The increase in efficiency is based on enhancing the airflow interaction as the vehicle moves past the turbine. Initial Computational Fluid Dynamics (CFD) simulations with two guide vanes setups demonstrated a 56.81% increase in power output under wind generated by passenger vehicles. Further design enhancements, incorporating three guide vanes with optimized geometries, led to a 242% improvement in power generation. Additional simulations evaluated the performance under wind conditions generated by larger vehicles, such as buses. The three guide vanes configuration yielded a 102% increase in energy capture efficiency in these scenarios. The findings suggest that vehicle-induced winds—typically an untapped energy source—can be effectively harvested using tailored turbine system designs. By integrating passive flow control strategies such as guide vanes, VAWTs can operate more efficiently in highway environments. This research highlights a novel pathway for enhancing renewable energy systems and supports broader efforts toward sustainable energy development through the utilization of unconventional wind sources. This performance enhancement is primarily due to the aerodynamic redirection of airflow toward the advancing blade and away from the returning blade, reducing drag and improving torque generation. Full article

(This article belongs to the Special Issue Vertical Axis Wind Turbines: Current Technologies and Future Trends)

41 pages, 7139 KiB

Open AccessReview

Analysis of Failures and Protective Measures for Core Rods in Composite Long-Rod Insulators of Transmission Lines

by Guohui Pang, Zhijin Zhang, Jianlin Hu, Qin Hu, Hualong Zheng and Xingliang Jiang

Energies 2025, 18(12), 3138; https://doi.org/10.3390/en18123138 (registering DOI) - 14 Jun 2025

Abstract

Composite insulators are deployed globally for outdoor insulation owing to their light weight, excellent pollution resistance, good mechanical strength, ease of installation, and low maintenance costs. The core rod in composite long-rod insulators plays a critical role in both mechanical load-bearing and internal insulation for overhead transmission lines, and its performance directly affects the overall operational condition of the insulator. However, it remains susceptible to failures induced by complex actions of mechanical, electrical, thermal, and environmental stresses. This paper systematically reviews the major failure modes of core rods, including mechanical failures (normal fracture, brittle fracture, and decay-like fracture) and electrical failures (flashunder and abnormal heating of the core rod). Through analysis of extensive field data and research findings, key failure mechanisms are identified. Preventive strategies encompassing material modification (such as superhydrophobic coatings, self-diagnostic materials, and self-healing epoxy resin), structural optimization (like the optimization of grading rings), and advanced inspection methods (such as IRT detection, Terahertz (THz) detection, X-ray computed tomography (XCT)) are proposed. Furthermore, the limitations of current technologies are discussed, emphasizing the need for in-depth studies on deterioration mechanisms, materials innovation, and defect detection technologies to enhance the long-term reliability of composite insulators in transmission networks. Full article

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25 pages, 1579 KiB

Open AccessArticle

Properties of Pellets from Forest and Agricultural Biomass and Their Mixtures

by Mariusz Jerzy Stolarski, Michał Krzyżaniak and Ewelina Olba-Zięty

Energies 2025, 18(12), 3137; https://doi.org/10.3390/en18123137 (registering DOI) - 14 Jun 2025

Abstract

Pellets can be produced not only from forest dendromass but also from agricultural dendromass derived from short rotation coppice (SRC) plantations, as well as surplus straw from cereal and oilseed crops. This study aimed to determine the thermophysical properties and elemental composition of 16 types of pellets produced from four types of forest biomass (Scots pine I, alder, beech, and Scots pine II), four types of agricultural biomass (SRC willow, SRC poplar, wheat straw, and rapeseed straw), and eight types of pellets from mixtures of wood biomass and straw. Another aim of the study was to demonstrate which pellet types met the parameters specified in three standards, categorizing pellets into thirteen different classes. As expected, pellets produced from pure Scots pine sawdust exhibited the best quality. The quality of the pellets obtained from mixtures of dendromass and straw deteriorated with an increase in the proportion of cereal straw or rapeseed straw in relation to pure Scots pine sawdust and SRC dendromass. The bulk density of the pellets ranged from 607.9 to 797.5 kg m⁻³, indicating that all 16 pellet types met the requirements of all six classes of the ISO standard. However, it was determined that four types of pellets (rapeseed, wheat, and two others from biomass mixtures) did not meet the necessary requirements of the Premium and Grade 1 classes. The ash content ranged from 0.44% DM in pellets from pure Scots pine sawdust to 5.00% DM in rapeseed straw pellets. Regarding ash content, only the pellets made from pure Scots pine sawdust met the stringent requirements of the highest classes, A1, Premium, and Grade 1. In contrast, all 16 types of pellets fulfilled the criteria for the lower classes, i.e., Utility and Grade 4. Concerning the nitrogen (N) content, seven types of pellets met the strict standards of classes A1 and Grade 1, while all the pellets satisfied the less rigorous requirements of classes B and Grade 4. Full article

(This article belongs to the Section A4: Bio-Energy)

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25 pages, 4300 KiB

Open AccessArticle

Photovoltaic Power Generation Forecasting Based on Secondary Data Decomposition and Hybrid Deep Learning Model

by Liwei Zhang, Lisang Liu, Wenwei Chen, Zhihui Lin, Dongwei He and Jian Chen

Energies 2025, 18(12), 3136; https://doi.org/10.3390/en18123136 (registering DOI) - 14 Jun 2025

Abstract

Accurate forecasting of photovoltaic (PV) power generation is crucial for optimizing grid operation and ensuring a reliable power supply. However, the inherent volatility and intermittency of solar energy pose significant challenges to grid stability and energy management. This paper proposes a learning model named CECSVB-LSTM, which integrates several advanced techniques: a bidirectional long short-term memory (BILSTM) network, Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN), variational mode decomposition (VMD), and the Sparrow Search Algorithm (CSSSA) incorporating circle chaos mapping and the Sine Cosine Algorithm. The model first uses CEEMDAN to decompose PV power data into Intrinsic Mode Functions (IMFs), capturing complex nonlinear features. Then, the CSSSA is employed to optimize VMD parameters, particularly the number of modes and the penalty factor, ensuring optimal signal decomposition. Subsequently, BILSTM is used to model time dependencies and predict future PV power output. Empirical tests on a PV dataset from an Australian solar power plant show that the proposed CECSVB-LSTM model significantly outperforms traditional single models and combination models with different decomposition methods, improving R² by more than 7.98% and reducing the root mean square error (RMSE) and mean absolute error (MAE) by at least 60% and 55%, respectively. Full article

(This article belongs to the Section A2: Solar Energy and Photovoltaic Systems)

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15 pages, 2925 KiB

Open AccessArticle

Estimation and Application for Line Impedance Between IBR and POM

by Woo-Hyun Kim, Ye-Chan Kim and Seung-Ho Song

Energies 2025, 18(12), 3135; https://doi.org/10.3390/en18123135 (registering DOI) - 14 Jun 2025

Abstract

With the increasing integration of Inverter-Based Resources (IBRs) into power grids, accurate estimation of line impedance between the Point of Connection (POC) and the Point of Measurement (POM) has become critical to ensure stable and efficient reactive power control. However, conventional impedance estimation methods often face challenges such as power quality degradation and sensitivity to voltage unbalance. This paper presents a method to improve the reactive power control performance of Inverter-Based Resources (IBRs) by estimating the line impedance between the Point of Connection (POC) and the Point of Measurement (POM) and utilize the estimated impedance into control. The impact of voltage drop caused by line impedance on reactive power delivery is analyzed, and a compensation method is designed to mitigate the resulting control errors. The line impedance is estimated through a negative-sequence current injection technique, under the condition that the voltage phases at the two measurement points are synchronized. To address potential voltage unbalance issues that may arise during the injection process, a dedicated compensation algorithm is also proposed. The proposed algorithm is validated through both simulations and lab-scale experiments, demonstrating that the line impedance can be estimated with an error of less than 2%, while effectively compensating for reactive power distortion at the POM. Full article

(This article belongs to the Special Issue Renewable and Sustainable Energy in Light of Energy Transition Processes—2nd Edition)

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17 pages, 2876 KiB

Open AccessArticle

Research on the Oil Cooling Structure Design Method of Permanent Magnet Synchronous Motors for Electric Vehicles

by Shijun Chen, Cheng Miao, Xinyu Chen, Wei Qian and Songchao Chu

Energies 2025, 18(12), 3134; https://doi.org/10.3390/en18123134 (registering DOI) - 14 Jun 2025

Abstract

Permanent magnet synchronous motors for electric vehicles (EVs) prioritize high power density and lightweight design, leading to elevated thermal flux density. Consequently, cooling methods and heat conduction in stator windings become critical. This paper proposes a compound cooling structure combining direct oil spray cooling on stator windings and housing oil channel cooling (referred to as the winding–housing composite oil cooling system) for permanent synchronous motors in EVs. A systematic design methodology for oil jet nozzles and housing oil channels is investigated, determining the average convective heat transfer coefficient on end-winding surfaces and the heat dissipation factor of the oil channels. Finite element analysis (FEA) was employed to simulate the thermal field of a 48-slot 8-pole oil-cooled motor, with further analysis on the effects of oil temperature and flow rate on motor temperature. Based on these findings, an optimized oil-cooled structure is proposed, demonstrating enhanced thermal management efficiency. The results provide valuable references for the design of cooling systems in oil-cooled motors for EV applications. Full article

(This article belongs to the Special Issue Advances in Permanent Magnet Motor and Motor Control)

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17 pages, 8225 KiB

Open AccessArticle

Numerical Study on the Influence of Cooling-Fin Geometry on the Aero-Thermal Behavior of a Rotating Tire

by Kyoungmi Yu and SangWook Lee

Energies 2025, 18(12), 3133; https://doi.org/10.3390/en18123133 (registering DOI) - 14 Jun 2025

Abstract

An excessive temperature rise in vehicle tires during driving can degrade dynamic performance, safety, and fuel efficiency by increasing rolling resistance and softening materials. To mitigate these issues, it is essential to enhance the cooling performance of tires without inducing significant aerodynamic penalties. In this study, we propose the use of sidewall-mounted cooling fins and investigate their aero-thermal effects under both ground-contact and no-ground-contact conditions. Seven fin configurations were tested, with installation angles ranging from −67.5° to 67.5°, with positive angles indicating an orientation opposite to the direction of wheel rotation and negative angles indicating alignment with the direction of rotation. High-fidelity unsteady Reynolds-averaged Navier–Stokes simulations were conducted using the SST k-w turbulence model. The sliding mesh technique was employed to capture the transient flow behavior induced by tire rotation. The results showed that, under no-ground-contact conditions, the 45° configuration achieved a 16.8% increase in convective heat transfer with an increase in drag less than 3%. Under ground-contact conditions, the 22.5° configuration increased heat transfer by over 13% with a minimal aerodynamic penalty (~1.7%). These findings provide valuable guidance for designing passive cooling solutions that improve tire heat dissipation performance without compromising aerodynamic efficiency. Full article

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23 pages, 17229 KiB

Open AccessArticle

Comprehensive Performance Assessment of Conventional and Sequential Predictive Control for Grid-Tied NPC Inverters: A Hardware-in-the-Loop Study

by Jakson Bonaldo, Beichen Duan, Marco Rivera, K. V. Ling, Camila Fantin and Patrick Wheeler

Energies 2025, 18(12), 3132; https://doi.org/10.3390/en18123132 (registering DOI) - 14 Jun 2025

Abstract

Model Predictive Control (MPC) has become very attractive for the efficient control of power converters. This paper compares Classical MPC (C-MPC) and Sequential MPC (S-MPC) for a three-level NPC converter. Although C-MPC is simple to implement, it faces challenges such as switching frequency variations and complex weighting factor tuning. S-MPC addresses these issues by prioritizing control objectives sequentially, eliminating weighting factors, and simplifying controller design. Simulation results show that S-MPC improves the tracking of output currents, reduces harmonic distortion, and enhances the balancing of dc–link voltages under steady-state and transient conditions. These findings establish S-MPC as a robust alternative to C-MPC, improving power quality and system performance in multilevel converter applications. Full article

20 pages, 539 KiB

Open AccessReview

Positive Energy Districts Enabling Smart Energy Communities

by Dimitrios Siakas, Harjinder Rahanu, Elli Georgiadou, Kerstin Siakas and Georgios Lampropoulos

Energies 2025, 18(12), 3131; https://doi.org/10.3390/en18123131 (registering DOI) - 14 Jun 2025

Abstract

Energy transitions concentrated on a neighborhood or district scale represent a fairly new area of focus at the European (EU) level, aiming to combat future global warming and to reduce anthropogenic greenhouse gas (GHG) emissions. In the EU energy transition policy agenda, positive energy districts (PEDs) refer to urban areas where more renewable/zero-emissions energy is produced annually than is consumed. PEDs have increasingly grown in recognition and significance, as a societal solution geared towards a low-carbon future. The relevant aims include the utilization of 100 PEDs by 2025 and alignment with the EU, which seeks to become a climate-neutral continent by 2050. However, this target raises questions regarding the means of achieving fast and consistent adoption across various socio-technical contexts. Defining the opportunities, challenges, and key issues to address short-term project timelines is vital to implementing fit-for-purpose solutions and bringing PEDs into the mainstream. Proactive knowledge sharing, adaptive learning, and collaboration across disciplines and sectors will bring know-how for understanding the requirements in different contexts. The need for practical approaches to facilitate PED implementation is crucial. This study aims to elucidate the opportunities for and barriers to successful PED design and implementation by compiling and synthesizing experiences from 61 PED projects, identifying key drivers, challenges, enablers, and ethical considerations. In addition, the authors present a framework, consisting of moral principles, which can help present the issues concerning the development and deployment of PED in an ethical context. Full article

(This article belongs to the Special Issue Renewable and Sustainable Energy in Light of Energy Transition Processes—2nd Edition)

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24 pages, 6176 KiB

Open AccessArticle

Study of Ignition Process in an Aero Engine Combustor Based on Droplet Evaporation Characteristics Analyses

by Lei Sun, Rui Feng, Fangliang Wang and Xiwei Wang

Energies 2025, 18(12), 3130; https://doi.org/10.3390/en18123130 (registering DOI) - 14 Jun 2025

Abstract

To study the coupling mechanism between droplet evaporation characteristics and flame propagation, in this paper, the ignition process in a single dome lean direct injection combustor is simulated by the Large Eddy Simulation (LES) method. A new concept, i.e., available droplet, and a new parameter, i.e., available equivalence ratio, are innovatively introduced to accurately quantify fuel–air mixing characteristics and reveal flame propagation mechanisms. Simulation results show that the temporal variations in the locally available equivalence ratio during the ignition process can serve as a reliable indicator to identify the flame propagation direction. Moreover, the results show that during the ignition process, available droplets are mainly distributed in the regions where temperatures range from 650 K to 1200 K. The number percentage of available droplets in the combustor increases approximately exponentially to about 2.5% after 40 ms from the ignition. Additionally, the temperature fields and distributions of the available equivalence ratio at different moments during the ignition are also computed and analyzed. The results show that the volume percentage of flammable regions gradually increases from the ignition and eventually stabilizes at about 10% after 8 ms from the ignition. This result shows that during the ignition, the increase in regions whose available equivalence ratios fit flammability is a critical factor for ensuring stable flame development. The available droplet and available equivalence ratio can bridge the gap between droplet-scale evaporation and combustor-scale ignition dynamics, offering an analytical tool for optimizing ignition criteria in aero engine combustors. By analyzing the distributions and evolutions of available fuel rather than fuel vapor, this work can be utilized in design strategies for reliable ignition in extreme conditions. Full article

(This article belongs to the Special Issue Heat and Mass Transfer: Theory, Methods, and Applications)

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25 pages, 2402 KiB

Open AccessArticle

Research on Different Energy Transition Pathway Analysis and Low-Carbon Electricity Development: A Case Study of an Energy System in Inner Mongolia

by Boyi Li, Richao Cong, Toru Matsumoto and Yajuan Li

Energies 2025, 18(12), 3129; https://doi.org/10.3390/en18123129 (registering DOI) - 14 Jun 2025

Abstract

To achieve carbon neutrality targets in the power sector, regions with rich coal and renewable energy resources are facing unprecedented pressure. This paper explores the decarbonization pathway in the power sector in Inner Mongolia, China, under different energy transition scenarios based on the Long-Range Energy Alternatives Planning System (LEAP) model. This includes renewable energy expansion, carbon capture and storage (CCS) applications, demand response, and economic regulation scenarios. Subsequently, a combination of the Logarithmic Mean Divisia Index (LMDI) and Slack-Based Measure Data Envelopment Analysis (SBM-DEA) model was developed to investigate the influencing factors and power generation efficiency in low-carbon electricity. The results revealed that this region emphasizes first developing renewable energy and improving the carbon and green electricity market and then accelerating CCS technology. Its carbon emissions are among the lowest, at about 77.29 million tons, but the cost could reach CNY 229.8 billion in 2060. We also found that the influencing factors of carbon productivity, low-carbon electricity structures, and carbon emissions significantly affected low-carbon electricity generation; their cumulative contribution rate is 367–588%, 155–399%, and −189–−737%, respectively. Regarding low-carbon electricity efficiency, the demand response scenario is the lowest at about 0.71; other scenarios show similar efficiency values. This value could be improved by optimizing the energy consumption structure and the installed capacity configuration. Full article

(This article belongs to the Special Issue Energy Transition and Environmental Sustainability: 3rd Edition)

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