Energies

17 pages, 2886 KiB

Open AccessArticle

Online Pre-Diagnosis of Multiple Faults in Proton Exchange Membrane Fuel Cells by Convolutional Neural Network Based Bi-Directional Long Short-Term Memory Parallel Model with Attention Mechanism

by Junyi Chen, Huijun Ran, Ziyang Chen, Trevor Hocksun Kwan and Qinghe Yao

Energies 2025, 18(10), 2669; https://doi.org/10.3390/en18102669 - 21 May 2025

Viewed by 151

Abstract

Proton exchange membrane fuel cell (PEMFC) fault diagnosis faces two critical limitations: conventional offline methods lack real-time predictive capability, while existing prediction approaches are confined to single fault types. To address these gaps, this study proposes an online multi-fault prediction framework integrating three [...] Read more.

Proton exchange membrane fuel cell (PEMFC) fault diagnosis faces two critical limitations: conventional offline methods lack real-time predictive capability, while existing prediction approaches are confined to single fault types. To address these gaps, this study proposes an online multi-fault prediction framework integrating three novel contributions: (1) a sensor fusion strategy leveraging existing thermal/electrochemical measurements (voltage, current, temperature, humidity, and pressure) without requiring embedded stack sensors; (2) a real-time sliding window mechanism enabling dynamic prediction updates every 1 s under variable load conditions; and (3) a modified CNN-based Bi-LSTM parallel model with attention mechanism (ConvBLSTM-PMwA) architecture featuring multi-input multi-output (MIMO) capability for simultaneous flooding/air-starvation detection. Through comparative analysis of different neural architectures using experimental datasets, the optimized ConvBLSTM-PMwA achieved 96.49% accuracy in predicting dual faults 64.63 s pre-occurrence, outperforming conventional LSTM models in both temporal resolution and long-term forecast reliability. Full article

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Graphical abstract

37 pages, 8641 KiB

Open AccessArticle

Experimental Investigations of Moored OWC Wave Energy Converters in Cyclonic Conditions: Survivability Versus Operational Performance

by Eric Gubesch, Nagi Abdussamie, Irene Penesis and Christopher Chin

Energies 2025, 18(10), 2668; https://doi.org/10.3390/en18102668 - 21 May 2025

Viewed by 110

Abstract

This study experimentally evaluates the survivability and hydrodynamic performance of a moored oscillating water column (OWC) wave energy converter (WEC) subjected to extreme cyclonic wave conditions emulating tropical cyclone Oma (2019). Laboratory tests recreated realistic cyclonic sea states using focused wave groups through [...] Read more.

This study experimentally evaluates the survivability and hydrodynamic performance of a moored oscillating water column (OWC) wave energy converter (WEC) subjected to extreme cyclonic wave conditions emulating tropical cyclone Oma (2019). Laboratory tests recreated realistic cyclonic sea states using focused wave groups through the NewWave theory, combining singular and embedded focused waves within irregular seas to simulate extreme crests, troughs, and transient slamming events. Three mooring systems, including catenary, vertical-taut, and taut with 45° tendons, were tested to quantify their influence on structural response, chamber pressures, mooring tensions, and motion dynamics. The results revealed a critical trade-off: mooring configurations optimised for energy capture efficiency (e.g., taut systems) exhibited reduced survivability during extreme waves, while survivability-focused designs (e.g., catenary) compromised operational performance. Slamming pressures and transient loads were highly sensitive to wave group and mooring stiffness, with vertical taut systems experiencing the largest peak tensions. By integrating localised slamming pressure data with global mooring load measurements, this work provides a novel framework for balancing energy production and storm resilience in OWC design. Full article

(This article belongs to the Special Issue Advances in Ocean Energy Technologies and Applications)

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19 pages, 1806 KiB

Open AccessArticle

A Study on Non-Contact Multi-Sensor Fusion Online Monitoring of Circuit Breaker Contact Resistance for Operational State Awareness

by Zheng Wang, Hua Zhang, Yiyang Zhang, Haoyong Zhang, Jing Chen, Shuting Feng, Jie Guo and Yanpeng Lv

Energies 2025, 18(10), 2667; https://doi.org/10.3390/en18102667 - 21 May 2025

Viewed by 115

Abstract

The contact condition of circuit breaker contacts directly affects their operational reliability, while circuit resistance, as a key performance indicator, reflects physical changes such as wear, oxidation, and ablation. Traditional offline measurement methods fail to accurately represent the real-time operating state of equipment [...] Read more.

The contact condition of circuit breaker contacts directly affects their operational reliability, while circuit resistance, as a key performance indicator, reflects physical changes such as wear, oxidation, and ablation. Traditional offline measurement methods fail to accurately represent the real-time operating state of equipment due to large errors and high randomness, limiting their effectiveness for state awareness and precision maintenance. To address this, a non-contact multi-sensor fusion method for the online monitoring of circuit breaker circuit resistance is proposed, aimed at enhancing operational state awareness in power systems. The method integrates Hall effect current sensors, infrared temperature sensors, and electric field sensors to extract multiple sensing signals, combined with high-precision signal processing algorithms to enable the real-time identification and evaluation of circuit resistance changes. Experimental validation under various scenarios—including normal load, overload impact, and high-temperature and high-humidity environments—demonstrates excellent system performance, with a fast response time (≤200 ms), low measurement error (<1.5%), and strong anti-interference capability (SNR > 60 dB). In field applications, the system successfully identifies circuit resistance increases caused by contact oxidation and issues early warnings, thereby preventing unplanned outages and demonstrating a strong potential for application in the fault prediction and intelligent maintenance of power grids. Full article

(This article belongs to the Special Issue Advances in Diagnostic Analysis, Strategic Management, and Proactive Maintenance of Electrical Equipment)

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34 pages, 5896 KiB

Open AccessArticle

Networked Multi-Agent Deep Reinforcement Learning Framework for the Provision of Ancillary Services in Hybrid Power Plants

by Muhammad Ikram, Daryoush Habibi and Asma Aziz

Energies 2025, 18(10), 2666; https://doi.org/10.3390/en18102666 - 21 May 2025

Viewed by 125

Abstract

Inverter-based resources (IBRs) are becoming more prominent due to the increasing penetration of renewable energy sources that reduce power system inertia, compromising power system stability and grid support services. At present, optimal coordination among generation technologies remains a significant challenge for frequency control [...] Read more.

Inverter-based resources (IBRs) are becoming more prominent due to the increasing penetration of renewable energy sources that reduce power system inertia, compromising power system stability and grid support services. At present, optimal coordination among generation technologies remains a significant challenge for frequency control services. This paper presents a novel networked multi-agent deep reinforcement learning (N—MADRL) scheme for optimal dispatch and frequency control services. First, we develop a model-free environment consisting of a photovoltaic (PV) plant, a wind plant (WP), and an energy storage system (ESS) plant. The proposed framework uses a combination of multi-agent actor-critic (MAAC) and soft actor-critic (SAC) schemes for optimal dispatch of active power, mitigating frequency deviations, aiding reserve capacity management, and improving energy balancing. Second, frequency stability and optimal dispatch are formulated in the N—MADRL framework using the physical constraints under a dynamic simulation environment. Third, a decentralised coordinated control scheme is implemented in the HPP environment using communication-resilient scenarios to address system vulnerabilities. Finally, the practicality of the N—MADRL approach is demonstrated in a Grid2Op dynamic simulation environment for optimal dispatch, energy reserve management, and frequency control. Results demonstrated on the IEEE 14 bus network show that compared to PPO and DDPG, N—MADRL achieves 42.10% and 61.40% higher efficiency for optimal dispatch, along with improvements of 68.30% and 74.48% in mitigating frequency deviations, respectively. The proposed approach outperforms existing methods under partially, fully, and randomly connected scenarios by effectively handling uncertainties, system intermittency, and communication resiliency. Full article

(This article belongs to the Collection Artificial Intelligence and Smart Energy)

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20 pages, 2085 KiB

Open AccessArticle

Steady-State Model Enabled Dynamic PEMFC Performance Degradation Prediction via Recurrent Neural Network

by Qiang Liu, Weihong Zang, Wentao Zhang, Yang Zhang, Yuqi Tong and Yanbiao Feng

Energies 2025, 18(10), 2665; https://doi.org/10.3390/en18102665 - 21 May 2025

Viewed by 100

Abstract

Proton exchange membrane fuel cells (PEMFC), distinguished by rapid refueling capability and zero tailpipe emissions, have emerged as a transformative energy conversion technology for automotive applications. Nevertheless, their widespread commercialization remains constrained by technical limitations mainly in operational longevity. Precise prognostics of performance [...] Read more.

Proton exchange membrane fuel cells (PEMFC), distinguished by rapid refueling capability and zero tailpipe emissions, have emerged as a transformative energy conversion technology for automotive applications. Nevertheless, their widespread commercialization remains constrained by technical limitations mainly in operational longevity. Precise prognostics of performance degradation could enable real-time optimization of operation, thereby extending service life. This investigation proposes a hybrid prognostic framework integrating steady-state modeling with dynamic condition. First, a refined semi-empirical steady-state model was developed. Model parameters’ identification was achieved using grey wolf optimizer. Subsequently, dynamic durability testing data underwent systematic preprocessing through a correlation-based screening protocol. The processed dataset, comprising model-calculated reference outputs under dynamic conditions synchronized with filtered operational parameters, served as inputs for a recurrent neural network (RNN). Comparative analysis of multiple RNN variants revealed that the hybrid methodology achieved superior prediction fidelity, demonstrating a root mean square error of 0.6228%. Notably, the integration of steady-state physics could reduce the RNN structural complexity while maintaining equivalent prediction accuracy. This model-informed data fusion approach establishes a novel paradigm for PEMFC lifetime assessment. The proposed methodology provides automakers with a computationally efficient framework for durability prediction and control optimization in vehicular fuel cell systems. Full article

(This article belongs to the Special Issue Advances in Fuel Cells: Materials, Technologies, and Applications)

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21 pages, 1338 KiB

Open AccessArticle

Parameter Estimation-Based Output Voltage or Current Regulation for Double-LCC Hybrid Topology in Wireless Power Transfer Systems

by Thaís M. Tolfo, Rafael de S. Silva, Ruben B. Godoy, Moacyr A. G. de Brito and Witória S. de Souza

Energies 2025, 18(10), 2664; https://doi.org/10.3390/en18102664 - 21 May 2025

Viewed by 73

Abstract

In Wireless Power Transfer Systems (WPTS), variations in a load connected to a receiver can cause instability in the waveforms of output voltage and current due to their sensitivity to changes in load impedance. To overcome such drawbacks, this paper presents a control [...] Read more.

In Wireless Power Transfer Systems (WPTS), variations in a load connected to a receiver can cause instability in the waveforms of output voltage and current due to their sensitivity to changes in load impedance. To overcome such drawbacks, this paper presents a control scheme for regulating voltage and current at the output of a WPTS system with the Double-LCC topology. The proposed method is based on estimating secondary-side parameters while assuming a constant coupling coefficient that remains close to its intended value during operation. The methodology begins with the mathematical modeling of the primary and secondary resonant circuits. By measuring the input voltage and current, the system estimates the load impedance, which is then used to derive the expected output voltage and a reference for the input voltage. To maintain a stable output, the system dynamically adjusts the input voltage, ensuring that it aligns with the theoretical reference value. Analytical calculations and simulations were performed using the MATLAB/Simulink platform to validate the proposed approach. Simulations confirmed the theoretical predictions for a wireless system operating at 120 kHz with a power transfer of 100 W. The results demonstrated that the load voltage remains stable at 32 V, even under varying load conditions, while the output current remains at 3 A despite fluctuations in battery voltage. Full article

(This article belongs to the Section F1: Electrical Power System)

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23 pages, 3159 KiB

Open AccessArticle

Accounting Factors and Spatio-Temporal Differences of the Carbon Footprint Factor in China’s Power System

by Ao Li, Zhen Wang, Xingyu Sun and Fei Ma

Energies 2025, 18(10), 2663; https://doi.org/10.3390/en18102663 - 21 May 2025

Viewed by 150

Abstract

The carbon footprint factor of a power system is a crucial basis for calculating carbon emissions from electricity consumption. However, the current carbon footprint factor of China’s power system faces several issues, such as a limited spatial range, outdated updates, an incomplete accounting [...] Read more.

The carbon footprint factor of a power system is a crucial basis for calculating carbon emissions from electricity consumption. However, the current carbon footprint factor of China’s power system faces several issues, such as a limited spatial range, outdated updates, an incomplete accounting scope, and unclear accounting methods. To make the power system’s carbon footprint accounting method and its temporal and spatial scope more comprehensive, this study reconstructs the accounting method based on the emission factor method, adding factors such as transmission losses, power transmission across spatial ranges, and Sulfur hexafluoride (SF₆) gas leakage. This study’s analysis reveals that these three accounting factors have a significant impact on the power system’s carbon footprint factor. In terms of the time dimension, the carbon footprint factor has decreased by more than 20% over the past 18 years, and when the time interval is refined to a monthly scale, the carbon footprint factor exhibits significant seasonal fluctuations. In the spatial dimension, the coefficient of variation (CV) for regional and provincial power system carbon footprint factors reached 27.38% and 29.98%, respectively, in 2022. For the same geographic location, the difference in carbon footprint factors between provincial and regional levels ranged from −73.98% to 119.95%. This study shows that the current carbon footprint factor of the power system has limitations, and there is an urgent need to improve the accounting factors, establish multi-level spatial division standards for provincial and regional scales, and shorten the update intervals while ensuring data timeliness. This will enhance the temporal and spatial accuracy of the carbon footprint factor, providing scientific support for precise carbon emission management. Full article

(This article belongs to the Section B: Energy and Environment)

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22 pages, 1780 KiB

Open AccessArticle

Investigation on Pressure Drop Characteristics During Refrigerants Condensation Inside Internally Threaded Tubes

by Xiangrui Meng, Jian Wang, Qian Sun and Xinling Ma

Energies 2025, 18(10), 2662; https://doi.org/10.3390/en18102662 - 21 May 2025

Viewed by 98

Abstract

This study investigates the influence of geometric parameters of internally threaded tubes on heat transfer and resistance characteristics. Experimental analyses were conducted on pressure drop for 9.52 mm outer diameter tubes with various industry-standard geometric parameter combinations. Using R410A as the working fluid [...] Read more.

This study investigates the influence of geometric parameters of internally threaded tubes on heat transfer and resistance characteristics. Experimental analyses were conducted on pressure drop for 9.52 mm outer diameter tubes with various industry-standard geometric parameter combinations. Using R410A as the working fluid under turbulent flow conditions (Re = 20,000–60,000), experimental parameters included the following: mass velocity 50–600 kg/(m²·s), condensation temperature 45 ± 0.2 °C, and geometric ranges of thread height (e = 0.0001–0.0003 m), helix angle (α = 17–46°), crest angle (β = 16–53°), and number of ribs (Ns = 50–70). Results demonstrate that the newly developed correlation based on Webb and Ravigururajan friction factor models shows improved prediction accuracy for R410A condensation pressure drop in ribbed tubes. Model II achieved a mean absolute percentage error (MAPE) of 7.08%, with maximum and minimum errors of 27.66% and 0.76%, respectively. The standard deviation decreased from 0.0619 (Webb-based Model I) to 0.0362. Integration of SVR machine learning further enhanced tube selection efficiency through optimized correlation predictions. Full article

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15 pages, 11519 KiB

Open AccessArticle

PID Sliding Mode Control of PMSM Based on Improved Terminal Sliding Mode Reaching Law

by Guodong Qin, Min Wang, Guizhou Cao, Qi Wang and Yuefeng Liao

Energies 2025, 18(10), 2661; https://doi.org/10.3390/en18102661 - 21 May 2025

Viewed by 79

Abstract

In order to enhance the dynamic performance and anti-disturbance ability of speed control for a permanent magnet synchronous motor (PMSM), a sliding mode control method based on a PID sliding surface and an improved terminal sliding mode reaching law (ITSMRL) is proposed. Firstly, [...] Read more.

In order to enhance the dynamic performance and anti-disturbance ability of speed control for a permanent magnet synchronous motor (PMSM), a sliding mode control method based on a PID sliding surface and an improved terminal sliding mode reaching law (ITSMRL) is proposed. Firstly, an ITSMRL is proposed to increase the reaching speed and reduce chattering; moreover, it has been verified that the reaching law (RL) can achieve a sliding mode surface in finite time. Then, based on the dynamic model of PMSMs with uncertainties, an extended state observer (ESO) is used to estimate the lumped disturbance, and it is proven that the estimated error is bounded. Finally, on the basis of the observed feedforward disturbance, to enhance the disturbance rejection ability of PMSMs, a controller that combines the PID sliding mode surface and the ITSMRL is proposed. Moreover, the stability of the closed-loop system is proven. The composite method has the characteristics of a fast reaching speed, small chattering and strong robustness, and is verified by experiments. Full article

(This article belongs to the Special Issue Linear/Planar Motors and Other Special Motors)

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43 pages, 1501 KiB

Open AccessReview

State and Perspectives of Biomethane Production and Use—A Systematic Review

by Małgorzata Pawłowska, Magdalena Zdeb, Marta Bis and Lucjan Pawłowski

Energies 2025, 18(10), 2660; https://doi.org/10.3390/en18102660 - 21 May 2025

Viewed by 233

Abstract

In the face of increasingly frequent natural disasters resulting from climate change and disruptions in the supply chains of energy resources, the demand for energy carriers based on locally sourced renewable resources is growing. Biomethane, derived from biomass and having multiple uses in [...] Read more.

In the face of increasingly frequent natural disasters resulting from climate change and disruptions in the supply chains of energy resources, the demand for energy carriers based on locally sourced renewable resources is growing. Biomethane, derived from biomass and having multiple uses in the energy sector, fully meets these conditions. Analyses of the development and spatial distribution of biomethane production plants, the prevalence of methods of its production, and directions of applications, made on the basis of the data gained from official databases and research papers, are the main subjects of the paper. Additionally, the advantages and disadvantages of biomethane production, taking into account the results of the life cycle assessments, and the prospects for development of the biomethane market, facing regulatory and policy challenges, are considered. The results of the review indicate that biomethane production is currently concentrated in Europe and North America, which together generate over 80% of the globally produced biomethane. An exponential growth of the number of biomethane plants and their production capacities has been observed over the last decade. Assuming that the global strategies currently adopted and the resulting regional and national regulations on environmental and socio-economic policies are maintained, the further intensive development of the biomethane market will be expected in the near future. Full article

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52 pages, 4396 KiB

Open AccessReview

A Review of CO₂ Clathrate Hydrate Technology: From Lab-Scale Preparation to Cold Thermal Energy Storage Solutions

by Sai Bhargav Annavajjala, Noah Van Dam, Devinder Mahajan and Jan Kosny

Energies 2025, 18(10), 2659; https://doi.org/10.3390/en18102659 - 21 May 2025

Viewed by 163

Abstract

Carbon dioxide (CO₂) clathrate hydrate is gaining attention as a promising material for cold thermal energy storage (CTES) due to its high energy storage capacity and low environmental footprint. It shows strong potential in building applications, where space cooling accounts for [...] Read more.

Carbon dioxide (CO₂) clathrate hydrate is gaining attention as a promising material for cold thermal energy storage (CTES) due to its high energy storage capacity and low environmental footprint. It shows strong potential in building applications, where space cooling accounts for nearly 40% of total energy use and over 85% of electricity demand in developed countries. CO₂ hydrates are also being explored for use in refrigeration, cold chain logistics, supercomputing, biomedical cooling, and defense systems. With the growing number of applications in mind, this review focuses on the thermal behavior of CO₂ hydrates and their environmental impact. It highlights recent efforts to reduce formation pressure and temperature using chemical promoters and surfactants. This paper also reviews key experimental techniques used to study hydrate properties, including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), high-pressure differential scanning calorimetry (HP-DSC), and the T-history method. In lifecycle comparisons, CO₂ hydrate systems show better energy efficiency and lower carbon emissions than traditional ice or other phase-change materials (PCMs). This review also discusses current commercialization challenges such as high energy input during formation and promoter toxicity. Finally, practical strategies to move CO₂ hydrate-based CTES from lab-scale studies to real-world cooling and temperature control applications are discussed. Full article

(This article belongs to the Special Issue New Advances in Indoor Acoustics and Thermal Comfort for Sustainable Buildings)

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13 pages, 846 KiB

Open AccessArticle

A Probabilistic Reserve Decision-Making Method Based on Cumulative Probability Approximation for High-Penetration Renewable Energy Power System

by Yun Yang, Zichao Meng, Guobing Wu, Zhanxin Yang and Ruipeng Guo

Energies 2025, 18(10), 2658; https://doi.org/10.3390/en18102658 - 21 May 2025

Viewed by 68

Abstract

Probabilistic modeling of net load forecast errors is an important approach for reserve decision-making in power systems with a high penetration of renewable energy. However, existing probabilistic modeling methods face issues such as insufficient estimation accuracy in the small probability interval of the [...] Read more.

Probabilistic modeling of net load forecast errors is an important approach for reserve decision-making in power systems with a high penetration of renewable energy. However, existing probabilistic modeling methods face issues such as insufficient estimation accuracy in the small probability interval of the tails or increased complexity in probability decision-making problems. A probabilistic reserve decision-making method based on cumulative probability approximation is proposed. By using key points on the cumulative probability distribution curve of net load forecast error samples, this method enhances the fitting accuracy of the normal distribution model in the small probability interval of the tail, resulting in an optimal reserve outcome with the desired comprehensive expected profit. Using relevant renewable energy output and load data from actual transmission networks in Guangdong Province, China, the proposed method demonstrates good practical value. Full article

(This article belongs to the Special Issue Energy, Electrical and Power Engineering: 4th Edition)

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18 pages, 11864 KiB

Open AccessArticle

Characteristics of Mine Pressure Behavior and Zoned Support Technology for Advancing Working Face in Ultra-Close Coal Seams

by Qi Xu, Baisheng Zhang, Junqing Guo, Zetian Li, Taoyu Liu, Fan Li and Dong Duan

Energies 2025, 18(10), 2657; https://doi.org/10.3390/en18102657 - 21 May 2025

Viewed by 126

Abstract

To address the issues of severe surrounding-rock failure and ground support component failure in advancing working-face driving roadways (AWFDRs) in ultra-close coal seams, this study used the 5202 air-return roadway in Huaye Coal Mine as a case study and for engineering background. Numerical [...] Read more.

To address the issues of severe surrounding-rock failure and ground support component failure in advancing working-face driving roadways (AWFDRs) in ultra-close coal seams, this study used the 5202 air-return roadway in Huaye Coal Mine as a case study and for engineering background. Numerical simulation, theoretical analysis, and industrial application methods were adopted to analyze the laws of the dynamic evolution of vertical stress in such roadways. The mine pressure behaviors of AWFDRs in ultra-close coal seams were also clarified, thereby enabling the proposal of a solution; namely, zoned support technology. The results show that the 5202 air-return roadway, as an AWFDR in an ultra-close coal seam, exhibits five different characteristic behaviors of mine pressure zones during excavation. Zone 1 is influenced by the adjacent working-face mining under goaf; Zone 2 is influenced by the adjacent goaf lateral abutment stress under goaf; Zone 3 is influenced by the stress of the overlying solid coal; Zone 4 is influenced by the adjacent goaf lateral abutment stress under the overlying solid coal; and Zone 5 is influenced by stabilized stress under the overlying solid coal. The mine pressure behaviors of these zones were ranked, from most intense to weakest, as follows: Zone 3 > Zone 1 > Zone 4 > Zone 2 > Zone 5. Based on this, a basic support scheme was proposed, which involves using bolt–mesh–beam supports combined with shed supports under the goaf and bolt–mesh–beam supports combined with roof anchor cables under the overlying solid coal. Additionally, in Zones 1 and 3, roof anchor cables or rib anchor cables were supplemented as reinforcing supports, which were combined with the basic support scheme described above to form a zoned support scheme for the AWFDR. The analysis of mine pressure behavior and implementation of a zoned support scheme for AWFDRs in ultra-close coal seams provides technical and engineering references for roadway supports under similar mining conditions. Full article

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27 pages, 7892 KiB

Open AccessArticle

Model of a Switched Reluctance Generator Considering Iron Losses, Mutual Coupling and Remanent Magnetism

by Šime Grbin, Dinko Vukadinović and Mateo Bašić

Energies 2025, 18(10), 2656; https://doi.org/10.3390/en18102656 - 21 May 2025

Viewed by 66

Abstract

In this paper, an advanced model of a switched reluctance generator (SRG) with mutual coupling, iron losses, and remanent magnetism is presented. The proposed equivalent circuit for each SRG phase is represented by the winding resistance, phase inductance and electromotive forces (EMFs) induced [...] Read more.

In this paper, an advanced model of a switched reluctance generator (SRG) with mutual coupling, iron losses, and remanent magnetism is presented. The proposed equivalent circuit for each SRG phase is represented by the winding resistance, phase inductance and electromotive forces (EMFs) induced by mutual flux-linkage and remanent magnetism. In the advanced SRG model, the phase inductance and equivalent iron-loss resistance need not be known, as the components of the phase current flowing through them are determined directly from appropriate look-up tables, making the advanced SRG model simpler. Both the magnitude of the mutual flux-linkage and its time derivative are considered in the advanced model. The proposed model only requires knowledge of data that can be obtained using the DC excitation method and does not require knowledge of the SRG material properties. For the first time, the remanent magnetic flux of the SRG is modeled and the induced EMS caused by it is included in the advanced SRG model. Stray losses within the SRG are considered negligible. Connection to an asymmetric bridge converter is assumed. Magnetization angles of individual SRG phases are provided by the terminal voltage controller. The results obtained with the advanced SRG model are compared with experiments carried out in the steady-state of the 8/6 SRG with a rated power of 1.1 kW SRG over a wide range of load, terminal voltage, turn-on angle, and rotor speed in single-pulse mode suitable for high-speed applications. Full article

(This article belongs to the Special Issue Recent Advances in Power Quality Analysis and Robust Control of Renewable Energy Sources in Power Grids: 2nd Edition)

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12 pages, 3403 KiB

Open AccessArticle

Elimination Methods for High-Frequency Harmonics on the DC Side of Modular Multilevel Converters from the Perspective of Valve Control

by Qing Huai, Yirun Ji, Minxiang Yang, Ziyao Jie, Xi Yuan and Xiang Xu

Energies 2025, 18(10), 2655; https://doi.org/10.3390/en18102655 - 21 May 2025

Viewed by 100

Abstract

Modular multilevel converter (MMC)-based HVDC systems have become one promising way to integrate a large amount of renewable energy. However, the high-frequency harmonics problem could seriously affect the safety and stable operation level of MMC-HVDCs. Aiming at the high-frequency harmonics issues in MMC-HVDC [...] Read more.

Modular multilevel converter (MMC)-based HVDC systems have become one promising way to integrate a large amount of renewable energy. However, the high-frequency harmonics problem could seriously affect the safety and stable operation level of MMC-HVDCs. Aiming at the high-frequency harmonics issues in MMC-HVDC projects, this study investigates the influence of the valve-level controller modulation control on the DC high-frequency harmonics of MMCs. Firstly, the mechanism of high-frequency DC voltage harmonics generated by carrier quantization errors is revealed. Research results demonstrate that carrier quantization errors alter the switching instants of upper and lower arm submodules, inducing wideband high-frequency DC voltage harmonics ranging from several kilohertz to hundreds of kilohertz. In addition, a discrete carrier compensation method based on amplitude symmetry is proposed to eliminate the impact of carrier quantization errors on DC voltage harmonics. Lastly, a carrier phase-shifted (CPS)-modulated MMC simulation model is built in Matlab/Simulink to validate the impact of carrier quantization errors on DC high-frequency harmonics and the effectiveness of the proposed discrete carrier compensation method. Full article

(This article belongs to the Collection Advanced Control and Applications of Power Electronics and Power Converters)

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23 pages, 6428 KiB

Open AccessReview

A Critical Review of the Carbon–Energy Nexus Within the Construction Sector’s Embodied Emissions: A Case Study in the United Arab Emirates

by Yara Al Jundi and Hassam Nasarullah Chaudhry

Energies 2025, 18(10), 2654; https://doi.org/10.3390/en18102654 - 21 May 2025

Viewed by 242

Abstract

This review maps the complex relationship between embodied carbon emissions and energy within the construction sector, aiming to generate insights that facilitate more informed and sustainable decision-making for new construction projects. It addresses the challenges associated with the variability in standards, methodologies, and [...] Read more.

This review maps the complex relationship between embodied carbon emissions and energy within the construction sector, aiming to generate insights that facilitate more informed and sustainable decision-making for new construction projects. It addresses the challenges associated with the variability in standards, methodologies, and emission factors used in embodied carbon assessments, which contribute to discrepancies and impede the development of cohesive carbon reduction strategies. The paper identifies key drivers of embodied emissions, with a particular emphasis on energy consumption, and represents the findings in the form of a detailed graph, elucidating the interplay between energy use and embodied emissions and providing actionable insights to enhance sustainability selections. Additionally, a case study of four residential low-rise projects in Abu Dhabi is conducted to analyze the energy-based carbon emissions of construction projects, examine their patterns over the entire construction period, and determine the energy-based carbon emission intensity of projects typically powered by diesel generators. This work expands the existing knowledge base by offering actionable insights into how energy-related decisions can significantly influence embodied carbon outcomes and aims to guide stakeholders in optimizing selections to advance sustainability practices within the construction industry. Full article

(This article belongs to the Section B3: Carbon Emission and Utilization)

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25 pages, 5127 KiB

Open AccessArticle

Comparative Analysis of Insulation Aging in Cross-Linked Polyethylene and Ethylene–Propylene Rubber Cables Through the Progression Rate of Partial Discharge

by Andréia C. Domingos, Leandro Duarte, Alan P. Pinheiro, Fabrício A. M. Moura, Lorenço Vasconcelos, Daniel P. de Carvalho, Fernando E. de F. Fadel and Patrícia N. Sakai

Energies 2025, 18(10), 2653; https://doi.org/10.3390/en18102653 - 21 May 2025

Viewed by 154

Abstract

In order to ensure the continuous and reliable supply of electrical energy to the power grid, it is necessary to evaluate and monitor the degree of impairment of the insulation of electrical cables, as throughout its service life, insulation around cables suffers degradation [...] Read more.

In order to ensure the continuous and reliable supply of electrical energy to the power grid, it is necessary to evaluate and monitor the degree of impairment of the insulation of electrical cables, as throughout its service life, insulation around cables suffers degradation due to numerous stress factors, which can arise from both environmental and operational causes. This aspect has aroused deep interest among energy professionals, as well as the industrial sector, with focus mainly placed on the undesirable effect caused by unexpected and sudden process stoppages, as well as their consequent financial and social impacts. That said, this article presents a methodology for evaluating the degree of insulation aging using the partial discharge progression curve. For this purpose, a thermal oven was duly constructed, in accordance with the technical premises presented in the literature, capable of homogeneously heating conductor samples. After thermal cycles, these conductors were aptly handled and tested in a controlled laboratory environment to determine the partial discharge progression curve. Through accurate data processing, a correlation was obtained between the degradation of the insulation and the rate of increase in partial discharge. The results are promising, as they provide support for maintenance agents’ ability to monitor and intervene regarding conductors. Full article

(This article belongs to the Section F1: Electrical Power System)

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22 pages, 12898 KiB

Open AccessArticle

Topology Optimization Design of Phase Change Liquid Cooling Composite Plate

by Xinqiang Xia, Jiancheng Luo, Jiabao Li and Lixia Wei

Energies 2025, 18(10), 2652; https://doi.org/10.3390/en18102652 - 20 May 2025

Viewed by 130

Abstract

To address the challenges of high flow resistance and poor temperature uniformity in conventional PCM–liquid cooling hybrid heat exchangers—which significantly impair the performance and lifespan of electronic devices—a topology optimization approach was adopted. A dual-objective function, aimed at minimizing the average temperature and [...] Read more.

To address the challenges of high flow resistance and poor temperature uniformity in conventional PCM–liquid cooling hybrid heat exchangers—which significantly impair the performance and lifespan of electronic devices—a topology optimization approach was adopted. A dual-objective function, aimed at minimizing the average temperature and pressure drop, was introduced to reconstruct the cooling channel layout and PCM filling region. A two-dimensional transient thermo-fluid model coupling the solid–liquid phase-change process with coolant flow and heat transfer was established, alongside the development of an experimental platform. A comprehensive comparison was performed against a conventional liquid cooling plate with straight channels. The results showed that the topology-optimized cooling plate exhibited a pressure drop of 15.80 Pa and a pumping power of 1.19 × 10⁻⁴ W, representing reductions of 38.28% and 38.02%, respectively. The PCM solidification time was shortened by 6 min. Under these conditions, the convective heat transfer coefficient (h_w) and performance evaluation criterion (j/f) of the optimized plate reached 1319.06 W/(m²·K) and 0.56, which corresponded to increases of 60.71% and 47.5%, respectively. The topology-optimized configuration significantly improved temperature uniformity and overall cooling performance. As the inlet velocity increased from 0.05 m/s to 0.2 m/s, h_w increased by 38.65%; however, j/f decreased by 57.14%, due to the limited thermal conductivity of the PCMs, resulting in only a slight reduction in the average PCM temperature. Furthermore, the topology-optimized cooling plate demonstrated stronger steady-state regulation capability under fluctuating thermal loads. This study provides valuable insights and design guidance for the development of high-efficiency hybrid liquid cooling plates. Full article

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20 pages, 1397 KiB

Open AccessArticle

Toward Sustainable Development: Energy Transition Scenarios for Oil-Dependent Countries, with Iran as a Case Study

by Bahareh Heidary, Mohammad Ali Kiani and Farzin Golzar

Energies 2025, 18(10), 2651; https://doi.org/10.3390/en18102651 - 20 May 2025

Viewed by 161

Abstract

Oil-dependent countries face persistent challenges, such as energy supply–demand imbalances, overreliance on fossil fuels, declining economic diversification, and environmental degradation. In response, policymakers are increasingly advocating for comprehensive energy transitions to enhance energy and environmental security while promoting sustainable development. This study evaluates [...] Read more.

Oil-dependent countries face persistent challenges, such as energy supply–demand imbalances, overreliance on fossil fuels, declining economic diversification, and environmental degradation. In response, policymakers are increasingly advocating for comprehensive energy transitions to enhance energy and environmental security while promoting sustainable development. This study evaluates Iran’s energy transition through the modeling of five scenarios using the EnergyPLAN software V16.3. These scenarios, ranging from increased fossil fuel production to renewable energy deployment, subsidy reform, and energy efficiency, were developed based on a systematic literature review and expert interviews. Key indicators such as carbon emissions, primary energy demand, and supply–demand balance were used to assess the long-term impacts of each scenario through 2040. The Transition Scenario Policy (TSP), which integrates elements of all other scenarios, emerged as the most effective pathway for reducing emissions, correcting supply–demand imbalances, and aligning with sustainable development goals. The novelty of this study lies in its mixed-method approach, combining qualitative stakeholder insights with quantitative modeling, offering a replicable framework for energy transition planning in similar oil-dependent contexts. The practical implications support evidence-based policy making, while the results open avenues for future research on adaptive energy governance, policy trade-offs, and resilience under global uncertainty. Full article

(This article belongs to the Special Issue Research on Energy, Environment, and Sustainable Development)

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19 pages, 2510 KiB

Open AccessArticle

Efficiency Optimization Control Strategies for High-Voltage-Ratio Dual-Active-Bridge (DAB) Converters in Battery Energy Storage Systems

by Hui Ma, Jianhua Lei, Geng Qin, Zhihua Guo and Chuantong Hao

Energies 2025, 18(10), 2650; https://doi.org/10.3390/en18102650 - 20 May 2025

Viewed by 154

Abstract

This article introduces a high-efficiency, high-voltage-ratio bidirectional DC–DC converter based on the Dual-Active-Bridge (DAB) topology, specifically designed for applications involving low-voltage, high-capacity cells. Addressing the critical challenge of enhancing bidirectional power transfer efficiency under ultra-high step-up ratios, which is essential for integrating renewable [...] Read more.

This article introduces a high-efficiency, high-voltage-ratio bidirectional DC–DC converter based on the Dual-Active-Bridge (DAB) topology, specifically designed for applications involving low-voltage, high-capacity cells. Addressing the critical challenge of enhancing bidirectional power transfer efficiency under ultra-high step-up ratios, which is essential for integrating renewable energy sources and battery storage systems into modern power grids, an optimized control strategy is proposed. This strategy focuses on refining switching patterns and minimizing conduction losses to improve overall system efficiency. Theoretical analysis revealed significant enhancements in efficiency across various operating conditions. Simulation results further confirmed that the converter achieved exceptional performance in terms of efficiency at extremely high voltage conversion ratios, showcasing full-range Zero-Voltage Switching (ZVS) capabilities and reduced circulating reactive power. Specifically, the proposed method reduced circulating reactive power by up to 22.4% compared to conventional fixed-frequency control strategies, while achieving over 35% overload capability. These advancements reinforce the role of DAB as a key topology for next-generation high-performance power conversion systems, facilitating more efficient integration of renewable energy and energy storage solutions, and thereby contributing to the stability and sustainability of contemporary energy systems. Full article

(This article belongs to the Special Issue Advances in Energy Storage Systems for Renewable Energy: 2nd Edition)

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25 pages, 2927 KiB

Open AccessArticle

Research on Measures to Limit Short-Circuit Current by Renovating the Equipment of the Power Grid

by Shuqin Sun, Guanghao Zhou, Zaihua Li, Xiaojun Tang, Yuguang Zhou and Zhenghai Yuan

Energies 2025, 18(10), 2649; https://doi.org/10.3390/en18102649 - 20 May 2025

Viewed by 111

Abstract

This paper addresses the increasingly severe issue of exceeding short-circuit current limits brought about by the rapid development of large power grids. It investigates the principles of short-circuit current control and methods to limit short-circuit current through the modification of grid equipment. Building [...] Read more.

This paper addresses the increasingly severe issue of exceeding short-circuit current limits brought about by the rapid development of large power grids. It investigates the principles of short-circuit current control and methods to limit short-circuit current through the modification of grid equipment. Building on the current state of research, this study introduces different types of impedances to analyze their effects on the control of short-circuit currents, thereby exploring the principles of short-circuit current control based on the composition of actual grid short-circuit currents. Regarding the issue of controlling short-circuit current levels in large power grids, a detailed analysis is conducted of the operational principles, advantages, and disadvantages of five types of modified grid equipment for limiting short-circuit current: high-impedance generators, high-impedance transformers, current-limiting reactors, fault current limiters (FCLs), and a generator–transformer–line group unit. This study identifies the applicable conditions for each short-circuit current-limiting measure and presents specific engineering simulation cases to validate their effectiveness in limiting short-circuit currents, thus determining the control effects of each limiting measure. The results indicate that this research plays an important role in controlling short-circuit currents in power systems, maintaining the safe and stable operation of power systems, and improving the structural framework of power systems. Full article

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15 pages, 1550 KiB

Open AccessArticle

Fermentation of Sugar Beet Pulp by E. coli for Enhanced Biohydrogen and Biomass Production

by Gayane Mikoyan, Liana Vanyan, Akerke Toleugazykyzy, Roza Bekbayeva, Kamila Baichiyeva, Kairat Bekbayev and Karen Trchounian

Energies 2025, 18(10), 2648; https://doi.org/10.3390/en18102648 - 20 May 2025

Viewed by 376

Abstract

This study investigates the potential of sugar beet pulp (SBP), a lignocellulosic by-product of sugar production, as a low-cost substrate for biohydrogen and biomass generation using Escherichia coli under dark fermentation conditions. Two strains—BW25113 wild-type and a genetically engineered septuple mutant—were employed. SBP [...] Read more.

This study investigates the potential of sugar beet pulp (SBP), a lignocellulosic by-product of sugar production, as a low-cost substrate for biohydrogen and biomass generation using Escherichia coli under dark fermentation conditions. Two strains—BW25113 wild-type and a genetically engineered septuple mutant—were employed. SBP was pretreated via thermochemical hydrolysis, and the effects of substrate concentration, dilution, and glycerol supplementation were evaluated. Hydrogen production was highly dependent on substrate dilution and nutrient balance. The septuple mutant achieved the highest H₂ yield in 30 g L⁻¹ SBP hydrolysate (0.75% sulfuric acid) at 5× dilution with glycerol, reaching 12.06 mmol H₂ (g sugar)⁻¹ and 0.28 mmol H₂ (g waste)⁻¹, while the wild type under the same conditions yielded 3.78 mmol H₂ (g sugar)⁻¹ and 0.25 mmol H₂ (g waste)⁻¹. In contrast, undiluted hydrolysates favored biomass accumulation over H₂ production, with the highest biomass yield (0.3 g CDW L⁻¹) obtained using the septuple mutant in 30 g L⁻¹ SBP hydrolysate without glycerol. These findings highlight the potential of genetically optimized E. coli and optimized hydrolysate conditions to enhance the valorization of agro-industrial waste, supporting future advances in sustainable hydrogen bioeconomy and integrated waste biorefineries. Full article

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15 pages, 1786 KiB

Open AccessArticle

Comparison and Application of Pore Pressure Prediction Methods for Carbonate Formations: A Case Study in Luzhou Block, Sichuan Basin

by Wenzhe Li, Pingya Luo, Yatian Li, Jinghong Zhou, Xihui Hu, Qiutong Wang, Yiguo He and Yi Zhang

Energies 2025, 18(10), 2647; https://doi.org/10.3390/en18102647 - 20 May 2025

Viewed by 120

Abstract

The Luzhou Block in the Sichuan Basin hosts a widely distributed high-quality shale gas reservoir. However, the overlying carbonate strata pose considerable engineering challenges, including severe risks of subsurface fluid loss and wellbore collapse. These challenges are primarily attributed to inaccuracies in pore [...] Read more.

The Luzhou Block in the Sichuan Basin hosts a widely distributed high-quality shale gas reservoir. However, the overlying carbonate strata pose considerable engineering challenges, including severe risks of subsurface fluid loss and wellbore collapse. These challenges are primarily attributed to inaccuracies in pore pressure prediction, which significantly constrains the safety and efficiency of drilling operations in carbonate formations. To address this issue, this study systematically investigates and compares three classical pore pressure prediction approaches—namely, the equivalent depth method, the Eaton method, and the effective stress method—within the geological context of the Luzhou Block. A novel fitting strategy based on laboratory core experimental data is introduced, whereby empirical relationships between field-measured parameters and rock mechanical properties are established to improve model robustness in geologically complex formations. The optimized effective stress model is subsequently applied to the carbonate reservoir interval, and its prediction outcomes are evaluated against measured pore pressure data. The results demonstrate that the effective stress method achieves the highest prediction accuracy, with a maximum deviation of 8.4% and an average deviation of 5.3%. In comparison, the equivalent depth and Eaton methods yield average errors of 12.5% and 12.2%, respectively. These findings suggest that the effective stress method exhibits superior adaptability and reliability for pore pressure prediction in carbonate formations of the Luzhou Block, and holds significant potential for guiding mud density design and improving the operational safety of drilling programs. Full article

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20 pages, 2596 KiB

Open AccessArticle

Adsorption Equilibria and Systematic Thermodynamics Analysis of Carbon Dioxide Sequestration on South African Coals Using Nonlinear Three-Parameter Models: Sips, Tóth, and Dubinin–Astakhov

by Major Melusi Mabuza and Mandlenkosi George Robert Mahlobo

Energies 2025, 18(10), 2646; https://doi.org/10.3390/en18102646 - 20 May 2025

Viewed by 231

Abstract

Carbon dioxide (CO₂) injection into geologic formations has gained global traction, including in South Africa, to mitigate anthropogenic emissions through carbon capture, utilisation, and storage technology. These technological and technical developments require a comprehensive and reliable study of CO₂ sorption [...] Read more.

Carbon dioxide (CO₂) injection into geologic formations has gained global traction, including in South Africa, to mitigate anthropogenic emissions through carbon capture, utilisation, and storage technology. These technological and technical developments require a comprehensive and reliable study of CO₂ sorption equilibria under in situ unmineable coal reservoir conditions. This paper presents novel findings on the study of the equilibrium adsorption of CO₂ on two South African coals measured at four temperatures between 30 and 60 °C and pressures up to 9.0 MPa using the volumetric technique. Additionally, the sorption mechanism and thermodynamic nature of the process were studied by fitting the experimental data into Langmuir–Freundlich (Sips), Tóth, and Dubinin–Astakhov (DA) isotherm models, and the Clausius–Clapeyron equation. The findings indicate that the sorption process is highly exothermic, as presented by a negative temperature effect, with the maximum working capacity estimated to range between 3.46 and 4.16 mmol/g, which is also rank- and maceral composition-dependent, with high-rank vitrinite-rich coal yielding more sorption capacity than low-rank inertinite-rich coal. The experimental data fit well in Sips and Tóth models, confirming their applicability in describing the CO₂ sorption behaviour of the coals under the considered conditions. The isosteric heat of adsorption varied from 7.518 to 37.408 kJ/mol for adsorbate loading ranging from 0.4 to 3.6 mmol/g. Overall, the coals studied demonstrate well-developed sorption properties that characteristically make them viable candidates for CO₂ sequestration applications for environmental sustainability. Full article

(This article belongs to the Special Issue CO₂ Capture, Utilization and Storage)

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14 pages, 5559 KiB

Open AccessArticle

Classification of Rolling Bearing Defects Based on the Direct Analysis of Phase Currents

by Oliwia Frankiewicz, Maciej Skowron, Jeremi Jan Jarosz, Sebastien Weisse, Jerome Valire and Krzysztof Szabat

Energies 2025, 18(10), 2645; https://doi.org/10.3390/en18102645 - 20 May 2025

Viewed by 126

Abstract

Electric machines are gaining popularity in transport and replacing internal combustion engines. However, the diagnosis of their faults remains an ongoing problem. Traditional diagnostic methods, such as vibration, sound, and temperature analysis, have limitations in practical applications, particularly because of external interference and [...] Read more.

Electric machines are gaining popularity in transport and replacing internal combustion engines. However, the diagnosis of their faults remains an ongoing problem. Traditional diagnostic methods, such as vibration, sound, and temperature analysis, have limitations in practical applications, particularly because of external interference and the need for additional sensors. This paper presents a new diagnostic approach based on convolutional neural networks (CNNs) and direct analysis of current signals. The proposed solution allows for a significant reduction in the number of samples required for effective diagnostics. The neural network, operating on 500 signal samples, achieved a classification efficiency of 99.85–100% for each category of damage investigated. Tests were conducted to determine the effect of noise on the accuracy of the system. This study compares applications based on mechanical vibration signals and the proposed algorithm based on phase current signals. The results indicate that the proposed approach can be successfully applied to real-world monitoring systems for electrical machinery, offering a high-efficiency diagnostic tool while fulfilling the limitations of demanding measurement systems. Full article

(This article belongs to the Special Issue Developments in Automatic Control in Drives and Power Electronics)

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20 pages, 716 KiB

Open AccessArticle

Heavy Metal Control and Dry Matter Assessment in Digested Sewage Sludge for Biogas Production

by Krzysztof Michalski, Magdalena Kóska-Wolny, Krzysztof Chmielowski, Michał Gąsiorek, Klaudiusz Grübel, Konrad Kalarus and Wiktor Halecki

Energies 2025, 18(10), 2644; https://doi.org/10.3390/en18102644 - 20 May 2025

Viewed by 168

Abstract

The expansion of sewage networks and treatment facilities results in considerable amounts of municipal sludge, which is essential for biogas production as part of energy diversification efforts. Principal Component Analysis (PCA) demonstrated a strong correlation between biogas production and its utilization in power [...] Read more.

The expansion of sewage networks and treatment facilities results in considerable amounts of municipal sludge, which is essential for biogas production as part of energy diversification efforts. Principal Component Analysis (PCA) demonstrated a strong correlation between biogas production and its utilization in power generation units. Modernization efforts led to an increase in biogas utilization in power units but a decrease in boiler utilization, independent of the overall biogas production levels. The general linear model (GLM) further confirmed that biogas production was positively influenced by the amount of waste digested, while utilization in power units increased post modernization. A repeated measures ANOVA (Analysis of Variance) indicated significant increases in both dry matter and mineral content in digested sludge compared to raw sludge. SIMPER (Similarity Percentage) analysis revealed that the addition of glycerin water significantly reduced the nitrogen, ammonium nitrogen, and calcium content, while modernization increased these elements and slightly decreased the magnesium concentration. Multivariate dispersion analysis showed that samples treated with glycerin water exhibited less variability in metal content. Regression models explored the factors influencing mineral elements and dry mass in fermented sludge. The zinc content was positively associated with mineral content, while copper showed a negative correlation. The addition of glycerin water increased the mineral content, whereas modernization had the opposite effect. The nitrogen content was negatively correlated with dry mass. These findings provide valuable insights into optimizing sewage sludge treatment and biogas production processes by underlining the approaches for enhancing sludge properties to support efficient biogas production. Full article

(This article belongs to the Special Issue New Challenges in Biogas Production from Organic Waste)

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81 pages, 13040 KiB

Open AccessReview

Thermochemical Energy Storage Based on Salt Hydrates: A Comprehensive Review

by Tomasz Spietz, Rafał Fryza, Janusz Lasek and Jarosław Zuwała

Energies 2025, 18(10), 2643; https://doi.org/10.3390/en18102643 - 20 May 2025

Viewed by 241

Abstract

Thermal energy storage technologies are essential for balancing energy demand and supply. There are three main types: sensible heat, latent heat, and thermochemical energy storage. Among them, thermochemical energy storage offers the highest energy density (1–3 GJ/m³) and long-term storage capability. [...] Read more.

Thermal energy storage technologies are essential for balancing energy demand and supply. There are three main types: sensible heat, latent heat, and thermochemical energy storage. Among them, thermochemical energy storage offers the highest energy density (1–3 GJ/m³) and long-term storage capability. Salt hydrates have attracted attention as energy storage materials due to their low cost, wide availability, and operating temperatures being well-suited for residential and low-temperature applications. This review focuses on the use of salt hydrates in sorption-based thermochemical energy storage systems. It summarizes the current state of knowledge, including screening studies of various salt hydrates, their thermodynamic and operational limitations, advantages, and performance in composite materials. This review also covers recent projects and common reactor designs used in TCES applications. Based on the literature analysis, the most promising salt hydrates for sorption-based TCES systems include SrCl₂, SrBr₂, K₂CO₃, MgSO₄, MgCl₂, and CaCl₂. Despite the high theoretical energy density of many salt hydrates, future work should focus on experimental studies in large-scale reactor systems to better evaluate the practical discharge behavior of the energy storage system beyond theoretical hydration enthalpies or small-scale thermal analyses. Full article

(This article belongs to the Section D: Energy Storage and Application)

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22 pages, 2863 KiB

Open AccessArticle

Predicting Thermal Performance of Aquifer Thermal Energy Storage Systems in Depleted Clastic Hydrocarbon Reservoirs via Machine Learning: Case Study from Hungary

by Hawkar Ali Abdulhaq, János Geiger, István Vass, Tivadar M. Tóth, Tamás Medgyes, Gábor Bozsó, Balázs Kóbor, Éva Kun and János Szanyi

Energies 2025, 18(10), 2642; https://doi.org/10.3390/en18102642 - 20 May 2025

Viewed by 281

Abstract

This study presents an innovative approach for repurposing depleted clastic hydrocarbon reservoirs in Hungary as High-Temperature Aquifer Thermal Energy Storage (HT-ATES) systems, integrating numerical heat transport modeling and machine learning optimization. A detailed hydrogeological model of the Békési Formation was built using historical [...] Read more.

This study presents an innovative approach for repurposing depleted clastic hydrocarbon reservoirs in Hungary as High-Temperature Aquifer Thermal Energy Storage (HT-ATES) systems, integrating numerical heat transport modeling and machine learning optimization. A detailed hydrogeological model of the Békési Formation was built using historical well logs, core analyses, and production data. Heat transport simulations using MODFLOW/MT3DMS revealed optimal dual-well spacing and injection strategies, achieving peak injection temperatures around 94.9 °C and thermal recovery efficiencies ranging from 81.05% initially to 88.82% after multiple operational cycles, reflecting an efficiency improvement of approximately 8.5%. A Random Forest model trained on simulation outputs predicted thermal recovery performance with high accuracy (R² ≈ 0.87) for candidate wells beyond the original modeling domain, demonstrating computational efficiency gains exceeding 90% compared to conventional simulations. The proposed data-driven methodology significantly accelerates optimal site selection and operational planning, offering substantial economic and environmental benefits and providing a scalable template for similar geothermal energy storage initiatives in other clastic sedimentary basins. Full article

(This article belongs to the Special Issue Energy, Engineering and Materials 2024)

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16 pages, 5681 KiB

Open AccessArticle

Reactive Power Compensation for Single-Phase AC Motors Using Integral Power Theory

by Grzegorz Kosobudzki, Daniel Dusza, Marek Pawel Ciurys and Aleksander Leicht

Energies 2025, 18(10), 2641; https://doi.org/10.3390/en18102641 - 20 May 2025

Viewed by 139

Abstract

The paper investigates an alternative approach to measuring and compensating reactive power in electric machines, particularly under non-sinusoidal voltage and current waveforms. Traditional power definitions, such as those introduced by Budeanu and Fryze, as well as the power triangle, are discussed alongside integral [...] Read more.

The paper investigates an alternative approach to measuring and compensating reactive power in electric machines, particularly under non-sinusoidal voltage and current waveforms. Traditional power definitions, such as those introduced by Budeanu and Fryze, as well as the power triangle, are discussed alongside integral definitions of reactive power, which account for waveform distortions. This approach is novel and has not been previously applied in the context of electric machines. A digital algorithm for reactive power calculation, based on the integral definition, is proposed. It requires minimal computational resources and is easy to implement. Experimental measurements conducted on a single-phase induction motor demonstrate the impact of capacitive compensation on current waveforms. The results confirm the validity of the adopted definition of reactive power. With full reactive power compensation, the RMS value of the current drawn by the motor is minimized, which is not always the case with the classical approach to improving the power factor. The findings highlight the importance of accurate reactive power measurement and compensation in enhancing the performance and energy efficiency of electrical machines. The proposed approach is applicable not only to single-phase motors but also more broadly in determining the reactive power drawn by electric machines and in measuring electric energy, particularly in the presence of distorted voltages and currents. Full article

(This article belongs to the Special Issue Energy, Electrical and Power Engineering: 4th Edition)

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30 pages, 3404 KiB

Open AccessReview

Optimizing Solar–Biomass Pyrolysis: Innovations in Reactor Design and Thermal–Solar System Efficiency

by Fahim Ullah, Kamran Hasrat, Mao Mu, Shuang Wang and Sunel Kumar

Energies 2025, 18(10), 2640; https://doi.org/10.3390/en18102640 - 20 May 2025

Viewed by 238

Abstract

To promote renewable energy sources, we focus on optimizing the design of solar–biomass pyrolysis systems. This study suggests the best reactor orientation that creates effective thermal–solar systems for pyrolysis. Solar–biomass pyrolysis uses solar energy to create valuable products like syngas, tar, and char [...] Read more.

To promote renewable energy sources, we focus on optimizing the design of solar–biomass pyrolysis systems. This study suggests the best reactor orientation that creates effective thermal–solar systems for pyrolysis. Solar–biomass pyrolysis uses solar energy to create valuable products like syngas, tar, and char from biomass. This process promotes energy sustainability. We analyze different solar reactors based on their design, operation, heat transfer rate, efficiency, residence time for biomass retention inside the reactor, and biomass conversion efficiency. A thorough analysis of the existing technologies helps to pinpoint the difficulties and most recent developments in the sector, making decision making more manageable and providing information on the viability and sustainability of biomass conversion technologies. Full article

(This article belongs to the Special Issue Advancements in Sustainable Energy Technologies: Innovations, Integration, and Impact)

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Energies, Volume 18, Issue 10 (May-2 2025) – 263 articles

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