Energies

15 pages, 4160 KiB

Open AccessArticle

Novel Single-Core Phase-Shifting Transformer: Configuration, Analysis and Application in Loop Closing

by Yong Xu, Fangchen Huang, Yu Diao, Chongze Bi, Xiaokuan Jin and Jianhua Wang

Energies 2025, 18(17), 4500; https://doi.org/10.3390/en18174500 (registering DOI) - 24 Aug 2025

Phase-shifting transformers (PST) are widely used to control power flows. However, conventional designs can vary only the phase angle, leaving the voltage magnitude unaffected or requiring structurally complex devices. This study proposes a compact PST topology that realizes simultaneous, decoupled control of both [...] Read more.

Phase-shifting transformers (PST) are widely used to control power flows. However, conventional designs can vary only the phase angle, leaving the voltage magnitude unaffected or requiring structurally complex devices. This study proposes a compact PST topology that realizes simultaneous, decoupled control of both voltage magnitude and phase angle through two coordinated sets of windings. Closed-form equations are derived to link the phase-shifting and voltage regulation windings turn ratios to any target magnitude ratio and phase-shift angle, providing a unified design framework that guarantees the full practical operating range. Steady-state tests verify that the device can change the phase or adjust the magnitude independently without cross-coupling. Dynamic tests demonstrate that, when a tap command is issued, the line currents and active power converge to new set-points within a few fundamental periods and with minimal oscillation. Furthermore, the PST’s application to loop closing operations in 220 kV networks is investigated, where simulation results show it can suppress loop closing currents by over 90% under adverse voltage mismatch conditions. These results confirm that the proposed PST offers a fast, economical alternative to Flexible AC Transmission Systems (FACTS) equipment for real-time power flow balancing, renewable integration and inter-area exchange in modern transmission networks. Full article

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

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48 pages, 1710 KiB

Open AccessArticle

Optimal Placement of a Unified Power Quality Conditioner (UPQC) in Distribution Systems Using Exhaustive Search to Improve Voltage Profiles and Harmonic Distortion

by Juan S. Espinosa Gutiérrez and Alexander Aguila Téllez

Energies 2025, 18(17), 4499; https://doi.org/10.3390/en18174499 (registering DOI) - 24 Aug 2025

Abstract

This paper presents an exhaustive search approach to determine the optimal placement of a Unified Power Quality Conditioner (UPQC) in a distribution system that integrates a distributed generation (DG) unit based on photovoltaic (PV) panels. The main objective is to enhance voltage profiles [...] Read more.

This paper presents an exhaustive search approach to determine the optimal placement of a Unified Power Quality Conditioner (UPQC) in a distribution system that integrates a distributed generation (DG) unit based on photovoltaic (PV) panels. The main objective is to enhance voltage profiles and reduce total harmonic distortion (THD) in the presence of nonlinear loads. A multi-objective optimization model is formulated, combining THD minimization and voltage deviation reduction through a weighted cost function. Two case studies are conducted using the IEEE 33-bus test system modeled in MATLAB Simulink, considering different scenarios: one with nonlinear loads and another with additional DG integration. The UPQC is tested at critical nodes to assess its impact on power quality indicators. Results show that placing the UPQC at node 14 yields the lowest cost function value in both cases, with THD reductions exceeding 90% at the installation node and notable improvements across the system. These findings confirm that brute-force optimization is a reliable and effective strategy for UPQC siting, especially in distribution networks subjected to nonlinear disturbances and renewable-based DG. The proposed methodology provides a practical framework for power quality enhancement and supports decision-making in modern smart grid environments. Full article

(This article belongs to the Special Issue Advances in Electrical Power System Quality)

18 pages, 3941 KiB

Open AccessArticle

Enhancing Renewable Energy Integration via Robust Multi-Energy Dispatch: A Wind–PV–Hydrogen Storage Case Study with Spatiotemporal Uncertainty Quantification

by Qilong Zhang, Guangming Li, Xiangping Chen, Anqian Yang and Kun Zhu

Energies 2025, 18(17), 4498; https://doi.org/10.3390/en18174498 (registering DOI) - 24 Aug 2025

Abstract

This paper addresses the challenge of renewable energy curtailment, which stems from the inherent uncertainty and volatility of wind and photovoltaic (PV) generation, by developing a robust model predictive control (RMPC)-based scheduling strategy for an integrated wind–PV–hydrogen storage multi-energy flow system. By building [...] Read more.

This paper addresses the challenge of renewable energy curtailment, which stems from the inherent uncertainty and volatility of wind and photovoltaic (PV) generation, by developing a robust model predictive control (RMPC)-based scheduling strategy for an integrated wind–PV–hydrogen storage multi-energy flow system. By building a “wind–PV–hydrogen storage–fuel cell” collaborative system, the time and space complementarity of wind and PV is used to stabilize fluctuations, and the electrolyzer–hydrogen production–gas storage tank–fuel cell chain is used to absorb surplus power. A multi-time scale state-space model (SSM) including power balance equation, equipment constraints, and opportunity constraints is established. The RMPC scheduling framework is designed, taking the wind–PV joint probability scene generated by Copula and improved K-means and SSM state variables as inputs, and the improved genetic algorithm is used to solve the min–max robust optimization problem to achieve closed-loop control. Validation using real-world data from Xinjiang demonstrates a 57.83% reduction in grid power fluctuations under extreme conditions and a 58.41% decrease in renewable curtailment rates, markedly enhancing the local system’s capacity to utilize wind and solar energy. Full article

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16 pages, 4102 KiB

Open AccessArticle

Research on Active Defense System for Transformer Early Fault Based on Fiber Leakage Magnetic Field Measurement

by Junchao Wang, Yaqi Liu, Jian Mao, Shaoyong Liu, Zhixiang Tong, Xiangli Deng and Wenbin Tan

Energies 2025, 18(17), 4497; https://doi.org/10.3390/en18174497 (registering DOI) - 24 Aug 2025

Abstract

In the early faults of transformer windings, there are obvious variation characteristics of the spatial leakage magnetic field. Taking the leakage magnetic field as the fault characteristic quantity can establish an active defense system for transformer defects and faults, thereby increasing the service [...] Read more.

In the early faults of transformer windings, there are obvious variation characteristics of the spatial leakage magnetic field. Taking the leakage magnetic field as the fault characteristic quantity can establish an active defense system for transformer defects and faults, thereby increasing the service life of the equipment. However, the installation method of the optical fiber leakage magnetic field sensor, the principle of leakage magnetic field protection, the research and development of the protection device, and the dynamic model testing of the protection device are all key links in realizing the leakage magnetic field monitoring and active defense system. This paper first analyzes the symmetry of the winding leakage magnetic field, proposes invasive and non-invasive installation methods for optical fiber sensors based on different application scenarios, presents the principle of leakage magnetic field differential protection, and develops a protection device. The feasibility of the protection scheme proposed in this paper was verified through dynamic model experiments, and the early fault active defense system was put into actual on-site operation. Full article

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20 pages, 11744 KiB

Open AccessArticle

Simulation Study on Key Controlling Factors of Productivity of Multi-Branch Horizontal Wells for CBM: A Case Study of Zhina Coalfield, Guizhou, China

by Shaolei Wang, Yu Xiong, Huazhou Huang, Shiliang Zhu, Junhui Zhu and Xiaozhi Zhou

Energies 2025, 18(17), 4496; https://doi.org/10.3390/en18174496 (registering DOI) - 24 Aug 2025

Abstract

The multi-branch horizontal well for coalbed methane (CBM) is a core technical means to achieve efficient CBM extraction, and its productivity is jointly restricted by geological and engineering factors. To accurately grasp the main controlling factors of the productivity of multi-branch horizontal wells [...] Read more.

The multi-branch horizontal well for coalbed methane (CBM) is a core technical means to achieve efficient CBM extraction, and its productivity is jointly restricted by geological and engineering factors. To accurately grasp the main controlling factors of the productivity of multi-branch horizontal wells and provide a scientific basis for the optimized design of CBM development, this study takes Well W1 in the Wenjiaba Coal Mine of the Zhina Coalfield in Guizhou, China, as an engineering example and comprehensively uses three-dimensional geological modeling and reservoir numerical simulation methods to systematically explore the key influencing factors of the productivity of multi-branch horizontal wells for CBM. This study shows that coal seam thickness, permeability, gas content, and branch borehole size are positively correlated with the productivity of multi-branch horizontal wells. With the simulation time set to 1500 days, when the coal seam thickness increases from 1.5 m to 4 m, the cumulative gas production increases by 166%; when the permeability increases from 0.2 mD to 0.8 mD, the cumulative gas production increases by 123%; when the coal seam gas content increases from 8 m³/t to 18 m³/t, the cumulative gas production increases by 543%; and when the wellbore size increases from 114.3 mm to 177.8 mm, the cumulative gas production increases by 8%. However, the impact of branch angle and spacing on productivity exhibits complex nonlinear trends: when the branch angle is in the range of 15–30°, the cumulative gas production shows an upward trend during the simulation period, while in the range of 30–75°, the cumulative gas production decreases during the simulation period; the cumulative gas production with branch spacing of 100 m and 150 m is significantly higher than that with spacing of 50 m and 200 m. Quantitative analysis through sensitivity coefficients reveals that the coal seam gas content is the most important geological influencing factor, with a sensitivity coefficient of 2.5952; a branch angle of 30° and a branch spacing of 100 m are the optimal engineering conditions for improving productivity, with sensitivity coefficients of 0.2875 and 0.273, respectively. The research results clarify the action mechanism of geological and engineering factors on the productivity of multi-branch horizontal wells for CBM, providing a theoretical basis for the optimized deployment of well locations, wellbore structure, and drilling trajectory design of multi-branch horizontal wells for CBM in areas with similar geological conditions. Full article

(This article belongs to the Special Issue Research on Coalbed Methane and Coal-Measure Gas: Exploration, Exploitation, and Utilization)

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18 pages, 7380 KiB

Open AccessArticle

Attention Mechanism-Based Micro-Terrain Recognition for High-Voltage Transmission Lines

by Ke Mo, Hualong Zheng, Zhijin Zhang, Xingliang Jiang and Ruizeng Wei

Energies 2025, 18(17), 4495; https://doi.org/10.3390/en18174495 (registering DOI) - 24 Aug 2025

Abstract

With the continuous expansion of power grids and the advancement of ultra-high voltage (UHV) projects, transmission lines are increasingly traversing areas characterized by micro-terrain. These localized topographic features can intensify meteorological effects, thereby increasing the risks of hazards such as conductor icing and [...] Read more.

With the continuous expansion of power grids and the advancement of ultra-high voltage (UHV) projects, transmission lines are increasingly traversing areas characterized by micro-terrain. These localized topographic features can intensify meteorological effects, thereby increasing the risks of hazards such as conductor icing and galloping, directly threatening operational stability. Enhancing the disaster resilience of transmission lines in such environments requires accurate and efficient terrain identification. However, conventional recognition methods often neglect the spatial alignment of the transmission lines, limiting their effectiveness. This paper proposes a deep learning-based recognition framework that incorporates a dual-branch network architecture and a cross-branch spatial attention mechanism to address this limitation. The model explicitly captures the spatial correlation between transmission lines and surrounding terrain by utilizing line alignment information to guide attention along the line corridor. A semi-synthetic dataset, comprising 6495 simulated samples and 130 real-world samples, was constructed to facilitate model training and evaluation. Experimental results show that the proposed model achieves classification accuracies of 94.6% on the validation set and 92.8% on real-world test cases, significantly outperforming conventional baseline methods. These findings demonstrate that explicitly modeling the spatial relationship between transmission lines and terrain features substantially improves recognition accuracy, offering important support for hazard prevention and resilience enhancement in UHV transmission systems. Full article

(This article belongs to the Special Issue Testing, Monitoring and Diagnostic of High Voltage Equipment, 3rd Edition)

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19 pages, 4246 KiB

Open AccessArticle

Accuracy of Core Losses Estimation in PMSM: A Comparison of Empirical and Numerical Approximation Models

by Michael Nye, Matilde D’Arpino and Luigi Pio Di Noia

Energies 2025, 18(17), 4494; https://doi.org/10.3390/en18174494 (registering DOI) - 23 Aug 2025

Abstract

The estimation of core loss in permanent magnet synchronous machines (PMSMs) is a fundamental step for the optimization of the performance of PMSM drives. However, there is a lack of literature which fully demonstrates the goodness of some of the empirical approximations that [...] Read more.

The estimation of core loss in permanent magnet synchronous machines (PMSMs) is a fundamental step for the optimization of the performance of PMSM drives. However, there is a lack of literature which fully demonstrates the goodness of some of the empirical approximations that are commonly used in industrial and automotive sectors. This work investigates how different approximations for the core loss estimation of PMSMs can lead to considerable error across the entire machine operating domain. An interior PMSM (IPMSM) is modeled in finite element analysis (FEA) and used to calibrate the coefficients of the Bertotti equation. Approximations of the Bertotti equation are then made, which are calculated from a simple algebraic expression of measurable states, and these are used to estimate machine core loss in the whole direct-quadrature (

d - q

) domain of operation. The estimated core loss obtained with the approximations are finally compared to FEA core loss results. The approximations are shown to have considerable variability in their accuracy compared to FEA results. The results of this work can be used as guidance during the development of estimation algorithms for PMSM losses and the development of control strategies. Full article

(This article belongs to the Special Issue Design and Production Process Optimization for High Performance and Energy Efficiency in Electrical Machines—2nd Edition)

13 pages, 949 KiB

Open AccessArticle

Applicability Evaluation of an Online Parameter Identification Method: From Lithium-Ion to Lithium–Sulfur Batteries

by Ning Gao, You Gong, Xiaobei Yang, Disai Yang, Yao Yang, Bingyu Wang and Haifei Long

Energies 2025, 18(17), 4493; https://doi.org/10.3390/en18174493 (registering DOI) - 23 Aug 2025

Abstract

While Forgetting Factor Recursive Least Square (FFRLS) algorithms with evaluation mechanisms have been developed to address SOC-dependent parameter mapping shifts and their efficacy has been proven in Li-ion batteries, their applicability to lithium–sulfur (Li-S) batteries remains uncertain due to different electrochemical characteristics. This [...] Read more.

While Forgetting Factor Recursive Least Square (FFRLS) algorithms with evaluation mechanisms have been developed to address SOC-dependent parameter mapping shifts and their efficacy has been proven in Li-ion batteries, their applicability to lithium–sulfur (Li-S) batteries remains uncertain due to different electrochemical characteristics. This study critically evaluates the applicability of a Fisher information matrix-constrained FFRLS framework for online parameter identification in Li-S battery equivalent circuit network (ECN) models. Experimental validation using distinct drive cycles showed that the identification results of polarization-related parameters are significantly biased between different current excitations, and root mean square error (RMSE) variations diverge by 100%, with terminal voltage estimation errors more than 0.05 V. The parametric uncertainty under variable excitation profiles and voltage plateau estimation deficiencies confirms the inadequacy of such approaches, constraining model-based online identification viability for Li-S automotive applications. Future research should therefore prioritize hybrid estimation architectures integrating electrochemical knowledge with data-driven observers, alongside excitation capturing specifically optimized for Li-S online parameter observability requirements and cell nonuniformity and aging condition consideration. Full article

(This article belongs to the Special Issue Lithium-Ion and Lithium-Sulfur Batteries for Vehicular Applications)

24 pages, 8411 KiB

Open AccessArticle

Investigations on Solidification and Melting Processes of the Solar Salt Mixture in Evacuated and Non-Evacuated Receiver Tubes

by Valeria Russo, Giuseppe Napoli, Francesco Rovense, Primo Di Ascenzi, Gianremo Giorgi, Luigi Mongibello, Carmine Cancro, Gabriele Ciniglio and Walter Gaggioli

Energies 2025, 18(17), 4492; https://doi.org/10.3390/en18174492 (registering DOI) - 23 Aug 2025

Abstract

Parabolic trough collector (PTC) plants that use solar salt as a heat transfer fluid face operational challenges due to the salt’s relatively high solidification temperature of around 240 °C, which can compromise reliability if solidification occurs within receiver tubes or piping. While electric [...] Read more.

Parabolic trough collector (PTC) plants that use solar salt as a heat transfer fluid face operational challenges due to the salt’s relatively high solidification temperature of around 240 °C, which can compromise reliability if solidification occurs within receiver tubes or piping. While electric tracing cables are typically used to heat piping, they cannot be installed on PTC receivers due to the presence of external glass covers. As an alternative, impedance heating can be employed, applying voltage directly to the steel receivers, which act as resistive heaters. This study presents experimental results on the phase-change behavior of solar salt within receivers, focusing on melting and solidification times. Tests were conducted using two dedicated receivers under vacuum and non-vacuum conditions. Under vacuum, complete melting was achieved at 4.5 V and 1.43 kW in 5.5 h, while solidification from 270 °C took about 4 h, progressing inward from the tube connections. For non-evacuated receivers, 7 V and 3.2 kW were needed for melting in 5.6 h, and solidification at 270 °C was completed in 1.45 h. These outcomes illustrate that non-evacuated tubes require nearly twice the power and have a 2.8-fold increase in heat loss rate, offering quantitative guidance for vacuum loss detection in PTC systems. Full article

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

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19 pages, 6860 KiB

Open AccessArticle

Online Anomaly Detection for Nuclear Power Plants via Hybrid Concept Drift

by Jitao Li, Jize Guo, Chao Guo, Tianhao Zhang and Xiaojin Huang

Energies 2025, 18(17), 4491; https://doi.org/10.3390/en18174491 (registering DOI) - 23 Aug 2025

Abstract

Timely detection of anomalies in nuclear power plants (NPPs) is essential for operational safety, especially under conditions where process signals deviate gradually or abruptly from nominal patterns. Traditional detection methods often struggle to adapt under transient conditions or in the absence of well-labeled [...] Read more.

Timely detection of anomalies in nuclear power plants (NPPs) is essential for operational safety, especially under conditions where process signals deviate gradually or abruptly from nominal patterns. Traditional detection methods often struggle to adapt under transient conditions or in the absence of well-labeled fault data. To address this challenge, we propose KD-ADWIN, an adaptive concept drift-detection framework designed for unsupervised anomaly detection in dynamic industrial environments. The method integrates three core components: a Kalman-based prediction module to extract smoothed signal trends, a multi-channel detection strategy combining statistical and derivative-based drift indicators, and an adaptive thresholding mechanism that tunes detection sensitivity based on local signal variability. Evaluations on a synthetic dataset show that KD-ADWIN accurately detects both abrupt and gradual drifts, outperforming classical baselines. Further validation using full-scope simulation data from a modular high-temperature gas-cooled reactor (MHTGR) demonstrates its effectiveness in identifying concept drifts under realistic actuator and sensor fault conditions. Full article

(This article belongs to the Special Issue New Challenges in Safety Analysis of Nuclear Reactors)

18 pages, 891 KiB

Open AccessArticle

A Study on the Environmental and Economic Benefits of Flexible Resources in Green Power Trading Markets Based on Cooperative Game Theory: A Case Study of China

by Liwei Zhu, Xinhong Wu, Zerong Wang, Yuexin Li, Lifei Song and Yongwen Yang

Energies 2025, 18(17), 4490; https://doi.org/10.3390/en18174490 (registering DOI) - 23 Aug 2025

Abstract

This paper addresses the synergy between environmental and economic benefits in the green power trading market by constructing a collaborative game model for environmental rights value and electricity energy value. Based on this, a model for maximizing the benefits of flexible resource operation [...] Read more.

This paper addresses the synergy between environmental and economic benefits in the green power trading market by constructing a collaborative game model for environmental rights value and electricity energy value. Based on this, a model for maximizing the benefits of flexible resource operation is proposed. Through the combination of non-cooperative and cooperative games, the conflict and synergy mechanisms of multiple stakeholders are quantified, and the Shapley value allocation rule is designed to achieve Pareto optimality. Simultaneously, considering the spatiotemporal regulation capability of flexible resources, dynamic weight adjustment, cross-period environmental rights reserve, and risk diversification strategies are proposed. Simulation results show that under the scenario of a carbon price of 50 CNY/ton (≈7.25 USD/ton) and a peak–valley electricity price difference of 0.9 CNY/kWh (≈0.13 USD/kWh), when the environmental weight coefficient α = 0.5, the total revenue reaches 6.857 × 10⁷ CNY (≈9.94 × 10⁶ USD), with environmental benefits accounting for 90%, a 15.3% reduction in carbon emission intensity, and a 1.74-fold increase in energy storage cycle utilization rate. This research provides theoretical support for green power market mechanism design and resource optimization scheduling under “dual-carbon” goals. Full article

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

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20 pages, 1744 KiB

Open AccessArticle

Deep Reinforcement Learning Approaches the MILP Optimum of a Multi-Energy Optimization in Energy Communities

by Vinzent Vetter, Philipp Wohlgenannt, Peter Kepplinger and Elias Eder

Energies 2025, 18(17), 4489; https://doi.org/10.3390/en18174489 (registering DOI) - 23 Aug 2025

Abstract

As energy systems transition toward high shares of variable renewable generation, local energy communities (ECs) are increasingly relevant for enabling demand-side flexibility and self-sufficiency. This shift is particularly evident in the residential sector, where the deployment of photovoltaic (PV) systems is rapidly growing. [...] Read more.

As energy systems transition toward high shares of variable renewable generation, local energy communities (ECs) are increasingly relevant for enabling demand-side flexibility and self-sufficiency. This shift is particularly evident in the residential sector, where the deployment of photovoltaic (PV) systems is rapidly growing. While mixed-integer linear programming (MILP) remains the standard for operational optimization and demand response in such systems, its computational burden limits scalability and responsiveness under real-time or uncertain conditions. Reinforcement learning (RL), by contrast, offers a model-free, adaptive alternative. However, its application to real-world energy system operation remains limited. This study explores the application of a Deep Q-Network (DQN) to a real residential EC, which has received limited attention in prior work. The system comprises three single-family homes sharing a centralized heating system with a thermal energy storage (TES), a PV installation, and a grid connection. We compare the performance of MILP and RL controllers across economic and environmental metrics. Relative to a reference scenario without TES, MILP and RL reduce energy costs by 10.06% and 8.78%, respectively, and both approaches yield lower total energy consumption and CO

_{2}

-equivalent emissions. Notably, the trained RL agent achieves a near-optimal outcome while requiring only 22% of the MILP’s computation time. These results demonstrate that DQNs can offer a computationally efficient and practically viable alternative to MILP for real-time control in residential energy systems. Full article

(This article belongs to the Special Issue Smart Energy Management and Sustainable Urban Communities)

20 pages, 2842 KiB

Open AccessArticle

A Transient Multi-Feed-In Short Circuit Ratio-Based Framework for East China: Insights into Grid Adaptability to UHVDC Integration

by Fan Li, Hengyi Li, Yan Wang, Jishuo Qin and Peicheng Chen

Energies 2025, 18(17), 4488; https://doi.org/10.3390/en18174488 (registering DOI) - 23 Aug 2025

Abstract

Amid escalating climate challenges, China’s carbon neutrality objectives necessitate energy electrification as a pivotal strategy. As a critical load hub, East China demonstrates significant trends toward cleaner energy—marked by growing renewable energy penetration and accelerated cross-regional direct current (DC) transmission deployment. Ensuring stable [...] Read more.

Amid escalating climate challenges, China’s carbon neutrality objectives necessitate energy electrification as a pivotal strategy. As a critical load hub, East China demonstrates significant trends toward cleaner energy—marked by growing renewable energy penetration and accelerated cross-regional direct current (DC) transmission deployment. Ensuring stable and efficient grid operation requires rigorous assessment of the impacts of ultra-high voltage DC (UHVDC) integration on grid stability. This study introduces the transient multi-feed-in short circuit ratio (TMSCR), a novel metric for evaluating new DC transmission systems’ influence on grid performance. We systematically investigate UHVDC integration within the East China power grid, emphasizing strategic DC landing point placement. Using TMSCR, the effects of diverse DC incorporation methods are analyzed. Furthermore, this research examines impacts of new DC connections on local and main grids, proposing targeted mitigation measures to enhance grid resilience. This comprehensive UHVDC impact analysis addresses a critical literature gap, providing actionable insights for East China power grid planning and establishing a foundation for subsequent grid planning and DC project feasibility studies during the ‘15th Five-Year Plan’ period. Full article

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53 pages, 1783 KiB

Open AccessReview

A Comprehensive Review of Heat Transfer Fluids and Their Velocity Effects on Ground Heat Exchanger Efficiency in Geothermal Heat Pump Systems

by Khaled Salhein, Abdulgani Albagul and C. J. Kobus

Energies 2025, 18(17), 4487; https://doi.org/10.3390/en18174487 (registering DOI) - 23 Aug 2025

Abstract

This study reviews heat transfer fluids (HTFs) and their velocity effects on the thermal behavior of ground heat exchangers (GHEs) within geothermal heat pump (GHP) applications. It examines the classification, thermophysical properties, and operational behavior of standard working fluids, including water–glycol mixtures, as [...] Read more.

This study reviews heat transfer fluids (HTFs) and their velocity effects on the thermal behavior of ground heat exchangers (GHEs) within geothermal heat pump (GHP) applications. It examines the classification, thermophysical properties, and operational behavior of standard working fluids, including water–glycol mixtures, as well as emerging nanofluids. Fundamental heat exchange mechanisms are discussed, with emphasis on how conductivity, viscosity, and heat capacity interact with fluid velocity to influence energy transfer performance, hydraulic resistance, and system reliability. Special attention is given to nanofluids, whose enhanced thermal behavior depends on nanoparticle type, concentration, dispersion stability, and flow conditions. The review analyzes stabilization strategies, including surfactants, functionalization, and pH control, for maintaining long-term performance. It also highlights the role of velocity optimization in balancing convective benefits with pumping energy demands, providing velocity ranges suited to different GHE configurations. Drawing from recent experimental and numerical studies, the review offers practical guidelines for integrating nanofluid formulation with engineered operating conditions to maximize energy efficiency and extend system lifespan. Full article

(This article belongs to the Special Issue Advances in Fluid Dynamics and Thermal Transport in Geothermal Energy Systems)

18 pages, 1211 KiB

Open AccessReview

Insight into the Potential Use of Biochar as a Substitute for Fossil Fuels in Energy-Intensive Industries on the Example of the Iron and Steel Industry

by Agata Wajda and Ewa Brągoszewska

Energies 2025, 18(17), 4486; https://doi.org/10.3390/en18174486 (registering DOI) - 23 Aug 2025

Abstract

Actions related to reducing CO₂ emissions have led to the development of technologies using raw materials in the form of broadly understood biomass as CO₂-neutral fuels. There has been a rapid development of pyrolysis processes (carbonization, dry distillation) of various [...] Read more.

Actions related to reducing CO₂ emissions have led to the development of technologies using raw materials in the form of broadly understood biomass as CO₂-neutral fuels. There has been a rapid development of pyrolysis processes (carbonization, dry distillation) of various types of biomass toward the production of biochar for industrial applications. Particularly high hopes are associated with the use of biochar as a substitute for fossil fuel in energy-intensive sectors of the economy, especially the metallurgical and steel industries. This paper characterizes the current state and potential for biochar application, using the iron and steel industry as a case study. The analysis focuses primarily on the characteristics of biochar production and its industrial application potential. The characterization includes the diversity of biomass feedstocks, processing methods, and reactor types, the influence of operational parameters on biochar yield, as well as the properties and applications of biochar. As part of the analysis of biomass use potential in the iron and steel industry, the study reviews the current levels of coal substitution achieved at the laboratory scale and presents examples of biochar implementation in existing industrial facilities. In addition, key factors limiting the feasibility of coal substitution in the iron and steel industry are identified. The summary includes the main directions for further research aimed at increasing the use of biochar in industry. Full article

(This article belongs to the Special Issue Decarbonization and Sustainability in Industrial and Tertiary Sectors)

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18 pages, 1279 KiB

Open AccessArticle

The Optimal Energy Management of Virtual Power Plants by Considering Demand Response and Electric Vehicles

by Chia-Sheng Tu and Ming-Tang Tsai

Energies 2025, 18(17), 4485; https://doi.org/10.3390/en18174485 (registering DOI) - 23 Aug 2025

Abstract

This paper aims to explore Virtual Power Plants (VPPs) in combination with Demand Response (DR) concepts, integrating solar power generation, Electric Vehicle (EV) charging and discharging, and user loads to establish an optimal energy management scheduling system. Willingness curves for load curtailment are [...] Read more.

This paper aims to explore Virtual Power Plants (VPPs) in combination with Demand Response (DR) concepts, integrating solar power generation, Electric Vehicle (EV) charging and discharging, and user loads to establish an optimal energy management scheduling system. Willingness curves for load curtailment are derived based on the consumption patterns of industrial, commercial, and residential users, enabling VPPs to design DR mechanisms under Time-of-Use (TOU), two-stage, and critical peak pricing periods. An energy management model for a VPP is developed by integrating DR, EV charging and discharging, and user loads. To solve this model and optimize economic benefits, this paper proposes an Improved Wolf Pack Search Algorithm (IWPSA). Based on the original Wolf Pack Search Algorithm (WPSA), the Improved Wolf Pack Search Algorithm (IWPSA) enhances the key behaviors of detection and encirclement. By reinforcing the attack strategy, the algorithm achieves better search performance and improved stability. IWPSA provides a parameter optimization mechanism with global search capability, enhancing searching efficiency and increasing the likelihood of finding optimal solutions. It is used to simulate and analyze the maximum profit of the VPP under various scenarios, such as different seasons, incentive prices, and DR periods. The verification analysis in this paper demonstrates that the proposed method can not only assist decision makers in improving the operation and scheduling of VPPs, but also serve as a valuable reference for system architecture planning and more effectively evaluating the performance of VPP operation management. Full article

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16 pages, 2692 KiB

Open AccessArticle

Experimental Investigation of Flash Spray Cooling for Power Electronics

by Dimitrios Kotsopoulos, Panagiotis Parissis, Athanasios Giannadakis, Konstantinos Perrakis, Giouli Mihalakakou, Thrassos Panidis, Bin Chen, Zhifu Zhou and Alexandros Romaios

Energies 2025, 18(17), 4484; https://doi.org/10.3390/en18174484 (registering DOI) - 23 Aug 2025

Abstract

Power electronics convert and control electrical power in applications ranging from electric motors to telecommunications and computing. Ongoing efforts to miniaturize these systems and boost power density demand advanced thermal management solutions to maintain optimal cooling and temperature control. Spray cooling offers an [...] Read more.

Power electronics convert and control electrical power in applications ranging from electric motors to telecommunications and computing. Ongoing efforts to miniaturize these systems and boost power density demand advanced thermal management solutions to maintain optimal cooling and temperature control. Spray cooling offers an effective means of removing high heat fluxes and keeping power electronics within safe operating temperatures. This study presents an experimental investigation of flash spray cooling in a closed-loop system using R410A refrigerant. In particular, two nozzles with different spraying angles are used to study the effects of the distance between the spray nozzle and a heated flat surface, as well as the mass flow rate of the coolant. Results indicate that three key flow-pattern factors—surface coverage, impingement intensity, and liquid film dynamics—govern the heat transfer mechanisms and determine cooling efficiency. Flash spray cooling using refrigerants like R410A demonstrates strong potential as a high-performance thermal management strategy for next-generation power electronics. Full article

(This article belongs to the Special Issue Advanced Thermal Simulation of Energy Systems: 2nd Edition)

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20 pages, 3582 KiB

Open AccessArticle

Enhancement of Thermal Comfort and Energy Performance of Educational Buildings in the Warm Season: The Case Study of Two Public Schools in Bolzano, Italy

by Angelica El Hokayem, Giovanni Pernigotto and Andrea Gasparella

Energies 2025, 18(17), 4483; https://doi.org/10.3390/en18174483 (registering DOI) - 23 Aug 2025

Abstract

Most educational buildings in the north of Italy, whether of dated or recent construction, were designed to comply with the thermal comfort and energy performance requirements set for the heating season due to limited use in the summer months. In the latest years, [...] Read more.

Most educational buildings in the north of Italy, whether of dated or recent construction, were designed to comply with the thermal comfort and energy performance requirements set for the heating season due to limited use in the summer months. In the latest years, however, with greater frequency, school buildings have been used to host indoor summer activities, and, due to the warm temperature conditions and heat waves, indoor thermal discomfort is often experienced, with negative impacts on occupants’ task performance. Consequently, the need to guarantee adequate indoor thermal comfort in schools in the warm season is becoming a growing concern for local public authorities. In this context, this work examines a set of strategies for the enhancement of the energy performance and indoor thermal comfort of public school buildings in the cooling season. Thus, two case study public school buildings of dated and recent construction located in Bolzano, Italy, were analyzed and compared. This study shows the potential of passive and semi-passive measures in improving indoor thermal comfort in the spring–summer months and the limit beyond which mechanical cooling and ventilation systems are required to ensure adequate levels of indoor environmental quality and task performance in the warmest months. Full article

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20 pages, 5185 KiB

Open AccessArticle

Relationship Between Energy Efficiency and Color Consistency in LED Lighting

by Irena Fryc and Maciej Listowski

Energies 2025, 18(17), 4482; https://doi.org/10.3390/en18174482 (registering DOI) - 23 Aug 2025

Abstract

This study presents the first comprehensive investigation establishing the relationship between color consistency and luminous efficacy of radiation (LER) in phosphor-converted light-emitting diodes (LEDs), introducing novel selection criteria for energy-efficient applications. A systematic analysis of LED sources with nominal correlated color temperature (CCT) [...] Read more.

This study presents the first comprehensive investigation establishing the relationship between color consistency and luminous efficacy of radiation (LER) in phosphor-converted light-emitting diodes (LEDs), introducing novel selection criteria for energy-efficient applications. A systematic analysis of LED sources with nominal correlated color temperature (CCT) values of 3000 K and 4000 K across color-rendering index (CRI Ra) thresholds (≥60 and ≥80) was conducted, evaluating spectral power distributions (SPD) and chromaticities relative to 3-step, 5-step color-consistency circles, and 7-step American National Standards Institute (ANSI) quadrangles. Novel findings reveal a previously uncharacterized strong positive correlation between color consistency and luminous efficacy across all analyzed LED sources. LEDs with chromaticities within 3-step color-consistency circles consistently demonstrated superior LER values compared to 5-step boundaries, while sources outside established circles showed significantly inferior energy performance despite meeting nominal CCT requirements. The research establishes that tighter color-consistency tolerances directly correlate with enhanced luminous efficacy, revealing an intrinsic relationship between color quality and energy performance. These breakthrough findings introduce a paradigm shift in LED selection methodology, providing lighting professionals with evidence-based criteria that simultaneously optimize color consistency and energy efficiency, enabling more sustainable lighting solutions through integrated quality–performance assessment. Full article

(This article belongs to the Special Issue Advances in Indoor Environmental Quality and Energy Efficiency in Buildings)

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20 pages, 6299 KiB

Open AccessArticle

State-Set-Optimized Finite Control Set Model Predictive Control for Three-Level Non-Inverting Buck–Boost Converters

by Mingxia Xu, Hongqi Ding, Rong Han, Xinyang Wang, Jialiang Tian, Yue Li and Zhenjiang Liu

Energies 2025, 18(17), 4481; https://doi.org/10.3390/en18174481 (registering DOI) - 23 Aug 2025

Abstract

Three-level non-inverting buck–boost converters are promising for electric vehicle charging stations due to their wide voltage regulation capability and bidirectional power flow. However, the number of three-level operating states is four times that of two-level operating states, and the lack of a unified [...] Read more.

Three-level non-inverting buck–boost converters are promising for electric vehicle charging stations due to their wide voltage regulation capability and bidirectional power flow. However, the number of three-level operating states is four times that of two-level operating states, and the lack of a unified switching state selection mechanism leads to serious challenges in its application. To address these issues, a finite control set model predictive control (FCS-MPC) strategy is proposed, which can determine the optimal set and select the best switching state from the excessive number of states. Not only does the proposed method achieve fast regulation over a wide voltage range, but it also maintains the input- and output-side capacitor voltage balance simultaneously. A further key advantage is that the number of switching actions in adjacent cycles is minimized. Finally, a hardware-in-the-loop experimental platform is built, and the proposed control method can realize smooth transitions between multiple operation modes without the need for detecting modes. In addition, the state polling range and the number of switching actions are superior to conventional predictive control, which provides an effective solution for high-performance multilevel converter control in energy systems. Full article

(This article belongs to the Special Issue Control and Optimization of Power Converters)

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16 pages, 1484 KiB

Open AccessArticle

Determination of the Control Criterion for Centralized Heat Supply of the City on the Basis of the Production Function with Complex Variables

by Gulmira Bazil, Waldemar Wójcik, Fariza Zaynolda, Laulasyn Abzhanova and Sholpan Sagyndykova

Energies 2025, 18(17), 4480; https://doi.org/10.3390/en18174480 (registering DOI) - 23 Aug 2025

Abstract

The aim of this work is to determine the production function using the method of complex-valued economics as a criterion for the management of the centralized heat supply of a city. This paper used the methodology of using stepped production functions of complex [...] Read more.

The aim of this work is to determine the production function using the method of complex-valued economics as a criterion for the management of the centralized heat supply of a city. This paper used the methodology of using stepped production functions of complex variables with real coefficients as a tool to perform dynamic analysis and forecasting of production results, allowing the performance of Manufacturing Execution System tasks of the heat supply system to be tracked. Based on this, a justified selection of a management criterion was made, objectively reflecting both the passive and active components of the administrative and economic activities of the heat supply enterprise. A comparative analysis of production functions was conducted to identify a predictive model for resource provision in the process of heat energy generation. A predictive model of resource provision was developed based on the capital/labor ratio of the enterprise, using a production function with complex variables. In other words, determining the production function allows the analysis of both the quantity and quality of resources used to produce 1 Gcal of energy, as well as the forecast of resource procurement to ensure a reliable and cost-effective heat supply. Full article

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19 pages, 1547 KiB

Open AccessArticle

The Impact of Climate Risk on China’s Energy Security

by Zhiyong Zhang, Xiaokai Liu, Rula Sa, Meng Wang, Xianli Liu, Peiji Hu, Zhen Gao, Peixue Xing, Yan Zhao and Yong Geng

Energies 2025, 18(17), 4479; https://doi.org/10.3390/en18174479 - 22 Aug 2025

Abstract

Energy security has emerged as a critical concern amid intensifying climate risks and surging energy demand driven by economic growth. This study examines the impact of climate risk on energy security by constructing a panel dataset covering 30 Chinese provinces from 2006 to [...] Read more.

Energy security has emerged as a critical concern amid intensifying climate risks and surging energy demand driven by economic growth. This study examines the impact of climate risk on energy security by constructing a panel dataset covering 30 Chinese provinces from 2006 to 2022. Using the instrumental variable generalized method of moments (IV-GMM) model, we estimate the marginal impact of climate risk on energy security and further investigate its asymmetric, direct, and indirect relationships via panel quantile regression and mediation analysis. Our key findings are as follows: (1) Climate risk exerts a significant negative impact on energy security, indicating an inverse relationship. (2) The effect of climate risk is asymmetric, with a stronger adverse impact in regions with lower levels of energy security. (3) Climate risk undermines energy security by reducing energy accessibility, affordability, sustainability, and technological efficiency. (4) Energy transition and energy efficiency serve as critical mediators in the relationship between climate risk and energy security, offering insights into potential mitigation pathways. Unlike previous studies that primarily examine energy security in isolation or focus on single dimensions, this research integrates a multidimensional indicator system and advanced econometric techniques to uncover both direct and mediated pathways, thereby filling a key gap in understanding the climate–energy nexus at the provincial level in China. Based on these findings, we propose targeted policy recommendations to enhance energy security by improving climate resilience, accelerating the deployment of renewable energy, and optimizing energy infrastructure investments. Full article

(This article belongs to the Section B1: Energy and Climate Change)

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23 pages, 10932 KiB

Open AccessArticle

Dynamic CO₂ Leakage Risk Assessment of the First Chinese CCUS-EGR Pilot Project in the Maokou Carbonate Gas Reservoir in the Wolonghe Gas Field

by Jingwen Xiao, Chengtao Wei, Dong Lin, Xiao Wu, Zexing Zhang and Danqing Liu

Energies 2025, 18(17), 4478; https://doi.org/10.3390/en18174478 - 22 Aug 2025

Abstract

Existing CO₂ leakage risk assessment frameworks for CO₂ capture, geological storage and utilization (CCUS) projects face limitations due to subjective biases and poor adaptability to long-term scale sequestration. This study proposed a dynamic risk assessment method for CO₂ leakage based [...] Read more.

Existing CO₂ leakage risk assessment frameworks for CO₂ capture, geological storage and utilization (CCUS) projects face limitations due to subjective biases and poor adaptability to long-term scale sequestration. This study proposed a dynamic risk assessment method for CO₂ leakage based on a timeliness analysis of different leakage paths and accurate time-dependent numerical simulations, and it was applied to the first CO₂ enhanced gas recovery (CCUS-EGR) pilot project of China in the Maokou carbonate gas reservoir in the Wolonghe gas field. A 3D geological model of the Maokou gas reservoir was first developed and validated. The CO₂ leakage risk under different scenarios including wellbore failure, caprock fracturing, and new fracture activation were evaluated. The dynamic CO₂ leakage risk of the CCUS-EGR project was then quantified using the developed method and numerical simulations. The results revealed that the CO₂ leakage risk was observed to be the most pronounced when the caprock integrity was damaged by faults or geologic activities. This was followed by leakage caused by wellbore failures. However, fracture activation in the reservoir plays a neglected role in CO₂ leakage. The CO₂ leakage risk and critical risk factors dynamically change with time. In the short term (at 5 years), the project has a low risk of CO₂ leakage, and well stability and existing faults are the major risk factors. In the long term (at 30 years), special attention should be paid to the high permeable area due to its high CO₂ leakage risk. Factors affecting the spatial distribution of CO₂, such as the reservoir permeability and porosity, alternately dominate the leakage risk. This study established a method bridging gaps in the ability to accurately predict long-term CO₂ leakage risks and provides a valuable reference for the security implementation of other similar CCUS-EGR projects. Full article

(This article belongs to the Special Issue Application and Optimization of CCUS Technology in Shale Gas Production and Storage)

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19 pages, 1633 KiB

Open AccessArticle

Temporal-Alignment Cluster Identification and Relevance-Driven Feature Refinement for Ultra-Short-Term Wind Power Forecasting

by Yan Yan and Yan Zhou

Energies 2025, 18(17), 4477; https://doi.org/10.3390/en18174477 - 22 Aug 2025

Abstract

Ultra-short-term wind power forecasting is challenged by high volatility and complex temporal patterns, with traditional single-model approaches often failing to provide stable and accurate predictions under diverse operational scenarios. To address this issue, a framework based on the TCN-ELM hybrid model with temporal [...] Read more.

Ultra-short-term wind power forecasting is challenged by high volatility and complex temporal patterns, with traditional single-model approaches often failing to provide stable and accurate predictions under diverse operational scenarios. To address this issue, a framework based on the TCN-ELM hybrid model with temporal alignment clustering and feature refinement is proposed for ultra-short-term wind power forecasting. First, dynamic time warping (DTW)–K-means is applied to cluster historical power curves in the temporal alignment space, identifying consistent operational patterns and providing prior information for subsequent predictions. Then, a correlation-driven feature refinement method is introduced to weight and select the most representative meteorological and power sequence features within each cluster, optimizing the feature set for improved prediction accuracy. Next, a TCN-ELM hybrid model is constructed, combining the advantages of temporal convolutional networks (TCNs) in capturing sequential features and an extreme learning machine (ELM) in efficient nonlinear modelling. This hybrid approach enhances forecasting performance through their synergistic capabilities. Traditional ultra-short-term forecasting often focuses solely on historical power as input, especially with a 15 min resolution, but this study emphasizes reducing the time scale of meteorological forecasts and power samples to within one hour, aiming to improve the reliability of the forecasting model in handling sudden meteorological changes within the ultra-short-term time horizon. To validate the proposed framework, comparisons are made with several benchmark models, including traditional TCN, ELM, and long short-term memory (LSTM) networks. Experimental results demonstrate that the proposed framework achieves higher prediction accuracy and better robustness across various operational modes, particularly under high-variability scenarios, out-performing conventional models like TCN and ELM. The method provides a reliable technical solution for ultra-short-term wind power forecasting, grid scheduling, and power system stability. Full article

(This article belongs to the Special Issue AI-Enhanced Operation and Management of Renewable Energy-Integrated Power Systems)

37 pages, 617 KiB

Open AccessReview

Trends, Challenges, and Viability in Green Hydrogen Initiatives

by Mario Iamarino and Antonio D’Angola

Energies 2025, 18(17), 4476; https://doi.org/10.3390/en18174476 - 22 Aug 2025

Abstract

This review explores the current status of green hydrogen integration into energy and industrial ecosystems. By considering notable examples of existing and developing green hydrogen initiatives, combined with insights from the relevant scientific literature, this paper illustrates the practical implementation of those systems [...] Read more.

This review explores the current status of green hydrogen integration into energy and industrial ecosystems. By considering notable examples of existing and developing green hydrogen initiatives, combined with insights from the relevant scientific literature, this paper illustrates the practical implementation of those systems according to their main end use: power and heat generation, mobility, industry, or their combination. Main patterns are highlighted in terms of sectoral applications, geographical distribution, development scales, storage solutions, electrolyzer technology, grid interaction, and financial viability. Open challenges are also addressed, including the high production costs, an underdeveloped transport and distribution infrastructure, the geopolitical aspects and the weak business models, with the industrial sector appearing as the most favorable environment where such challenges may first be overcome in the medium term. Full article

(This article belongs to the Section A: Sustainable Energy)

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35 pages, 1314 KiB

Open AccessReview

Dry Anaerobic Digestion of Selectively Collected Biowaste: Technological Advances, Process Optimization and Energy Recovery Perspectives

by Beata Bień, Anna Grobelak, Jurand Bień, Daria Sławczyk, Kamil Kozłowski, Klaudia Wysokowska and Mateusz Rak

Energies 2025, 18(17), 4475; https://doi.org/10.3390/en18174475 - 22 Aug 2025

Abstract

Given the increasing volume of selectively collected bio-waste and the requirement to increase waste treatment system energy efficiency, dry anaerobic digestion (DAD) represents a more sustainable choice for the treatment of municipal organic fraction instead of conventional technologies. The current paper provides an [...] Read more.

Given the increasing volume of selectively collected bio-waste and the requirement to increase waste treatment system energy efficiency, dry anaerobic digestion (DAD) represents a more sustainable choice for the treatment of municipal organic fraction instead of conventional technologies. The current paper provides an overview of the existing knowledge on DAD of green waste or kitchen waste collected selectively. Key substrates characteristics (chemical composition, methane potential), novel reactor design and process conditions relevant to effective digestion at elevated dry matter content are considered. Of special interest is the process intensification techniques, impact of contamination and co-fermentation opportunity with other biodegradable wastes. This article also discusses energy and economic performance of DAD plants and puts their environmental burden in perspective versus other bio-waste treatment processes. The current legislation and DAD’s role in the circular economy are also considered. Selectively collected biowaste has significant energy potential and dry anaerobic digestion is an effective technology, especially in areas with limited water availability, offering both waste volume reduction and minimized energy losses. The aim of this work is to introduce the potential of this technology as a sustainable option within the context of renewable energy and modern waste management. Full article

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

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23 pages, 977 KiB

Open AccessArticle

Fast Voltage Stability Margin Computation via a Second-Order Power Flow Supported by a Linear Voltage Stability Index and Sensitivity Analysis

by Wilmer E. Barreto and Carlos A. Castro

Energies 2025, 18(17), 4474; https://doi.org/10.3390/en18174474 - 22 Aug 2025

Abstract

One of the crucial types of information needed to guarantee the secure operation of power systems is their voltage stability condition. This is particularly true for power systems operating at peak hours or under abnormal conditions, such as contingencies. The literature shows several [...] Read more.

One of the crucial types of information needed to guarantee the secure operation of power systems is their voltage stability condition. This is particularly true for power systems operating at peak hours or under abnormal conditions, such as contingencies. The literature shows several methods for voltage stability assessment; however, they are either accurate and computationally burdensome or less accurate and computationally efficient. The main goal of this research work is to propose methods that are both accurate and fast, features that are especially important in strict real-time operating conditions. Two new methods for computing the maximum loadability and the voltage stability margin of power systems are proposed. Both methods use a powerful, second-order, and non-divergent power flow with an optimally computed step size; however, each of them is initialized differently. Very high-quality initializations are obtained by using a linear voltage stability index and sensitivity analysis factors. This combination leads to a fast, robust, and accurate method, suited for strict real-time power system operation. The proposed methods require 90% fewer power flow runs compared with conventional methods, such as the continuation method for small systems, and tend to require even fewer power flow runs for larger systems. Computer simulations of the proposed methods use small benchmarks to large realistic power systems, showing that the requirements for real-time use—namely accuracy, robustness, and computational efficiency—are met. Full article

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

39 pages, 2781 KiB

Open AccessArticle

Evaluation of Technological Alternatives for the Energy Transition of Coal-Fired Power Plants, with a Multi-Criteria Approach

by Jessica Valeria Lugo, Norah Nadia Sánchez Torres, Renan Douglas Lopes da Silva Cavalcante, Taynara Geysa Silva do Lago, João Alves de Lima, Jorge Javier Gimenez Ledesma and Oswaldo Hideo Ando Junior

Energies 2025, 18(17), 4473; https://doi.org/10.3390/en18174473 - 22 Aug 2025

Abstract

This paper investigates technological pathways for the conversion of coal-fired power plants toward sustainable energy sources, using an integrated multi-criteria decision-making approach that combines Proknow-C, AHP, and PROMETHEE. Eight alternatives were identified: full conversion to natural gas, full conversion to biomass, coal and [...] Read more.

This paper investigates technological pathways for the conversion of coal-fired power plants toward sustainable energy sources, using an integrated multi-criteria decision-making approach that combines Proknow-C, AHP, and PROMETHEE. Eight alternatives were identified: full conversion to natural gas, full conversion to biomass, coal and natural gas hybridization, coal and biomass hybridization, electricity and hydrogen cogeneration, coal and solar energy hybridization, post-combustion carbon capture systems, and decommissioning with subsequent reuse. The analysis combined bibliographic data (26 scientific articles and 13 patents) with surveys from 14 energy experts, using Total Decision version 1.2.1041.0 and Visual PROMETHEE version 1.1.0.0 software tools. Based on six criteria (environmental, structural, technical, technological, economic, and social), the most viable option was full conversion to natural gas (ϕ = +0.0368), followed by coal and natural gas hybridization (ϕ = +0.0257), and coal and solar hybridization (ϕ = +0.0124). These alternatives emerged as the most balanced in terms of emissions reduction, infrastructure reuse, and cost efficiency. In contrast, decommissioning (ϕ = −0.0578) and carbon capture systems (ϕ = −0.0196) were less favorable. This study proposes a structured framework for strategic energy planning that supports a just energy transition and contributes to the United Nations Sustainable Development Goals (SDGs) 7 and 13, highlighting the need for public policies that enhance the competitiveness and scalability of sustainable alternatives. Full article

(This article belongs to the Special Issue Advanced Energy Conversion Technologies Based on Energy Physics)

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24 pages, 5995 KiB

Open AccessArticle

Influence of Inlet Temperature Differentials on Aerothermal Characteristics and Mass Flow Distribution in Multi-Inlet and Multi-Outlet Corotating-Disc Cavities

by Clarence Jia Cheng Chai, Xueying Li and Jing Ren

Energies 2025, 18(17), 4472; https://doi.org/10.3390/en18174472 - 22 Aug 2025

Abstract

To facilitate the development of next-generation gas turbine cooling systems, the present study systematically investigates the influence of inlet temperature differentials on the aerothermal characteristics and mass flow distribution within multi-inlet, multi-outlet corotating-disc cavities, for which inlet temperature differentials of 10 K, 30 [...] Read more.

To facilitate the development of next-generation gas turbine cooling systems, the present study systematically investigates the influence of inlet temperature differentials on the aerothermal characteristics and mass flow distribution within multi-inlet, multi-outlet corotating-disc cavities, for which inlet temperature differentials of 10 K, 30 K, and 50 K were applied. Steady-state Reynolds-averaged Navier–Stokes (RANS) simulations using the Shear Stress Transport (SST) k-ω model were performed across a range of flow conditions corresponding to Rossby numbers from 0.01 to 0.10, by varying the rotational and axial Reynolds numbers. This study finds that the inlet temperature differentials are a secondary driver of the aerothermal characteristics in the corotating cavity. Meanwhile, Rossby number dictates the main flow structure of radially stratified vortices and governs the thermal mixing between hot and cold streams. A higher Rossby number enhances mixing, causing the radial outlet temperature to rise significantly, while the axial outlet remains cool. A larger inlet temperature differential can induce secondary vortices at high Rossby numbers. Furthermore, the differential is revealed to increase cavity pressure, slightly reducing the radial outlet’s mass flow by up to 2.5% and its discharge coefficient by nearly 5% at high Rossby numbers. These insights allow engine designers to develop more precise and optimized cooling strategies. Full article

(This article belongs to the Section J1: Heat and Mass Transfer)

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20 pages, 3234 KiB

Open AccessArticle

Thermal Performance Enhancement in Pool Boiling on Copper Surfaces: Contact Angle and Surface Tension Analysis

by Robert Kaniowski and Sylwia Wciślik

Energies 2025, 18(17), 4471; https://doi.org/10.3390/en18174471 - 22 Aug 2025

Abstract

The electronics industry has significantly contributed to the development of efficient heat dissipation systems. One widely used technique is pool boiling, a simple method requiring no moving parts or complex structures. It enables the removal of large amounts of heat at relatively low [...] Read more.

The electronics industry has significantly contributed to the development of efficient heat dissipation systems. One widely used technique is pool boiling, a simple method requiring no moving parts or complex structures. It enables the removal of large amounts of heat at relatively low temperature differences. Enhancing pool boiling performance involves increasing the critical heat flux and the heat transfer coefficient, which defines how effectively a surface can transfer heat to a cooling fluid. This method is commonly applied in cooling electronic devices, digital circuits, and power systems. In this study, pool boiling at atmospheric pressure was investigated using copper surfaces. To validate the Rohsenow model used to estimate the maximum bubble departure diameter, a planimetric approach was applied. Measurements included average contact angle (CA), surface tension (σ), and droplet diameter for four working fluids: deionised water, ethanol, Novec-649, and FC-72. For each fluid, at least 15 measurements of CA and σ were conducted using the Young–Laplace model. This study provides a comprehensive analysis of the influence of contact angle and surface tension on nucleate boiling using four different fluids on copper surfaces. The novelty lies in combining high-precision experimental measurements with validation of the Rohsenow model, offering new insights into surface-fluid interactions critical for thermal system performance. Full article

(This article belongs to the Special Issue Modeling, Optimization and Experimental Investigation of Heat Exchangers for Power Plants)

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Energies, Volume 18, Issue 17 (September-1 2025) – 43 articles

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