Energies

14 pages, 3355 KiB

Open AccessArticle

Molecular Solar Thermal Fuels with High Energy Density Based on Azobenzene Derivatives

by Yan Jiang, Rui Liu, Yupeng Guo, Hai Wang, Wen Luo and Jin Huang

Energies 2025, 18(11), 2672; https://doi.org/10.3390/en18112672 (registering DOI) - 22 May 2025

Molecular solar thermal fuels (MOSTs) based on azobenzene derivatives have become one of the research hotspots for solar thermal conversion and storage due to their excellent cycling stability, resistance to photodegradation, and the capability to precisely adjust their absorption wavelengths, and other merits. [...] Read more.

Molecular solar thermal fuels (MOSTs) based on azobenzene derivatives have become one of the research hotspots for solar thermal conversion and storage due to their excellent cycling stability, resistance to photodegradation, and the capability to precisely adjust their absorption wavelengths, and other merits. Here, a novel MOST with connecting two azobenzene molecules by a short linkage (bis-AZO) has been proposed; the photoisomerization regulation and energy storage performance are studied experimentally in detail. The photoisomerization rate of the resultant MOST could be controlled by diverse irradiation intensities. The energy density for bis-AZO was 275.03 J g⁻¹ at 100% isomerization degree, with excellent thermal and photochemical cycling stability. The macroscale heat release of bis-AZO loaded on fabric reached a temperature increase of about 4.3 °C. This research offers a new design strategy for increasing the energy density in azobenzene-based molecular solar thermal fuels. Full article

(This article belongs to the Special Issue Solar Energy and Photovoltaic Systems: Prospect Development and Challenges)

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17 pages, 1000 KiB

Open AccessArticle

Beyond Traditional Grid: A Novel Quantitative Framework for Assessing Automation’s Impact on System Average Interruption Duration Index and System Average Interruption Frequency Index

by Jakub Dowejko and Jarosław Jaworski

Energies 2025, 18(11), 2671; https://doi.org/10.3390/en18112671 (registering DOI) - 22 May 2025

Abstract

The existing literature on power grid reliability extensively examines the effects of individual automation technologies, such as Smart Grids, IoT, and AI, on reducing SAIDI (System Average Interruption Duration Index) and SAIFI (System Average Interruption Frequency Index) indices. However, previous studies have largely [...] Read more.

The existing literature on power grid reliability extensively examines the effects of individual automation technologies, such as Smart Grids, IoT, and AI, on reducing SAIDI (System Average Interruption Duration Index) and SAIFI (System Average Interruption Frequency Index) indices. However, previous studies have largely focused on partial analyses, often limited to specific aspects of grid operation or isolated case studies. As a result, there is a lack of a comprehensive and integrated theoretical approach that considers the interdependencies between different automation technologies, their impact on various levels of grid management and the economic consequences of their deployment. This study presents a novel theoretical framework aimed at providing a holistic perspective on power grid automation and its impact on energy supply reliability. The key elements of this approach include developing a multidimensional mathematical model that integrates the impact of key automation technologies on SAIDI and SAIFI, allowing for a quantitative assessment of different implementation strategies and applying a probabilistic approach to predict the likelihood of power outages based on the level of automation and real-time grid conditions. This proposed framework offers a holistic view of power grid automation, integrating technical, economic and operational dimensions. It serves as a foundation for further empirical research and the implementation of intelligent grid modernisation strategies, aiming to enhance power supply stability and increase the resilience of distribution networks against outages. The introduced concept aligns with the current challenges of the energy transition, providing utilities and policymakers with analytical tools for making optimal decisions regarding the adoption of digitalisation and automation technologies in the power sector. Full article

(This article belongs to the Special Issue Advanced Control, Operation and Energy Management of Distribution Networks and Smart Grids: 2nd Edition)

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29 pages, 5625 KiB

Open AccessArticle

Lower-Carbon Substitutes for Natural Gas for Use in Energy-Intensive Industries: Current Status and Techno-Economic Assessment in Lithuania

by Aurimas Lisauskas, Nerijus Striūgas and Adolfas Jančauskas

Energies 2025, 18(11), 2670; https://doi.org/10.3390/en18112670 (registering DOI) - 22 May 2025

Abstract

Significant shortfalls in meeting the climate mitigation targets and volatile energy markets make evident the need for an urgent transition from fossil fuels to sustainable alternatives. However, the integration of zero-carbon fuels like green hydrogen and ammonia is an immense project and will [...] Read more.

Significant shortfalls in meeting the climate mitigation targets and volatile energy markets make evident the need for an urgent transition from fossil fuels to sustainable alternatives. However, the integration of zero-carbon fuels like green hydrogen and ammonia is an immense project and will take time and the construction of new infrastructure. It is during this transitional period that lower-carbon natural gas alternatives are essential. In this study, the industrial sectors of Lithuania are analysed based on their energy consumption. The industrial sectors that are the most energy-intensive are food, chemical, and wood-product manufacturing. Synthetic natural gas (SNG) has become a viable substitute, and biomethane has also become viable given a feedstock price of 21 EUR/MWh in the twelfth year of operation and 24 EUR/MWh in the eighth year, assuming an electricity price of 140 EUR/MWh and a natural gas price of 50 EUR/MWh. Nevertheless, the scale of investment in hydrogen production is comparable to the scale of investment in the production of other chemical elements; however, hydrogen production is constrained by its high electricity demand—about 3.8 to 4.4 kWh/Nm³—which makes it economically viable only at negative electricity prices. This analysis shows the techno-economic viability of biomethane and the SNG as transition pathways towards a low-carbon energy future. Full article

(This article belongs to the Special Issue International Finance and Energy Markets: Energy Supplying, Prices, Investments and Trends)

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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 (registering DOI) - 21 May 2025

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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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

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

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, 5884 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

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)

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

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, 1330 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

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)

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

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 (registering DOI) - 21 May 2025

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, 11518 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 (registering DOI) - 21 May 2025

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, 1290 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

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

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 (registering DOI) - 21 May 2025

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

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

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

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

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

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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