Energies

25 pages, 4102 KB

Open AccessArticle

Theoretical and Simulation-Based Approach to BIPV Systems Integrated with Modular Building

by Julia Brenk, Barbara Ksit and Bożena Orlik-Kożdoń

Energies 2025, 18(16), 4457; https://doi.org/10.3390/en18164457 - 21 Aug 2025

Viewed by 535

This study presents a simulation-based analysis of a steel modular building that integrates technologies that support the energy transition in the built environment. The focus is placed on the implementation of building-integrated photovoltaics (BIPVs), with photovoltaic modules incorporated into the façade and balcony [...] Read more.

This study presents a simulation-based analysis of a steel modular building that integrates technologies that support the energy transition in the built environment. The focus is placed on the implementation of building-integrated photovoltaics (BIPVs), with photovoltaic modules incorporated into the façade and balcony railings. Several modern photovoltaic façade systems were examined. In addition, the study considers the application of photovoltaic glazing enhanced with active quantum coatings. Seven distinct BIPV modules were analysed, each characterised by unique features, with particular emphasis on the influence of colour in tinted variants. A performance degradation analysis was conducted for railing-mounted modules with varying glass tints. The simulation results were correlated with the building’s electricity demand. Full article

(This article belongs to the Special Issue Energy Efficiency and Energy Saving in Buildings)

► Show Figures

Figure 1

20 pages, 1680 KB

Open AccessArticle

Simulation of a Natural Gas Solid Oxide Fuel Cell System Based on Rated Current Density Input

by Wenxian Hu, Xudong Sun and Yating Qin

Energies 2025, 18(16), 4456; https://doi.org/10.3390/en18164456 - 21 Aug 2025

Viewed by 510

Abstract

Solid Oxide Fuel Cells (SOFCs) offer high-efficiency electrochemical conversion of fuels like natural gas, yet detailed modeling is crucial for optimization. This paper presents a simulation study of a natural gas-fueled SOFC system, developed using Aspen Plus with Fortran integration. Distinct from prevalent [...] Read more.

Solid Oxide Fuel Cells (SOFCs) offer high-efficiency electrochemical conversion of fuels like natural gas, yet detailed modeling is crucial for optimization. This paper presents a simulation study of a natural gas-fueled SOFC system, developed using Aspen Plus with Fortran integration. Distinct from prevalent paradigms assuming rated power output, this work adopts rated current density as the primary input, enabling a more direct investigation of the cell’s electrochemical behavior. We conducted a comprehensive sensitivity analysis of key parameters, including fuel utilization, water-carbon ratio, and current density, and further investigated the impact of different interconnection configurations on overall module performance. Results demonstrate that a single unit operating at a current density of 180 mA/cm², a fuel utilization of 0.75, and a water-carbon ratio of 1.5 can achieve a maximum net stack-level electrical efficiency of 54%. Furthermore, optimizing the interconnection of a 400 kW module by combining series and parallel units boosts the overall net system-level electrical efficiency to 59%, a 5-percentage-point increase over traditional parallel setups. This is achieved by utilizing a bottoming cycle for exhaust heat recovery. This research validates the rated current density approach for SOFC modeling, offering novel insights into performance optimization and modular design for integrated energy systems. Full article

► Show Figures

Figure 1

19 pages, 4456 KB

Open AccessArticle

Numerical Analysis on Thermal and Flow Performance of Honeycomb-Structured Microchannel Cooling Plate for IGBT

by Guangtao Zhai, Hao Yang, Wu Gong, Fan Wu, Junxiong Zeng, Xiaojin Fu and Tieyu Gao

Energies 2025, 18(16), 4455; https://doi.org/10.3390/en18164455 - 21 Aug 2025

Viewed by 433

Abstract

In high-power insulated gate bipolar transistor (IGBT) module thermal management, the structural design of microchannel cooling plates plays a crucial role in determining heat dissipation efficiency and temperature uniformity. This study focuses on the effects of honeycomb-structured unit dimensions and arrangements, as well [...] Read more.

In high-power insulated gate bipolar transistor (IGBT) module thermal management, the structural design of microchannel cooling plates plays a crucial role in determining heat dissipation efficiency and temperature uniformity. This study focuses on the effects of honeycomb-structured unit dimensions and arrangements, as well as inlet/outlet configurations of the cooling plate on its thermal and flow performance. Additionally, the influence of different coolant inlet velocities and temperatures is investigated. Under constant coolant flow rate and boundary conditions, four design configurations with varying pore widths and channel spacings were evaluated numerically. The results indicate that the optimized honeycomb structure can reduce the module’s peak temperature by approximately 8.7 K while significantly improving temperature uniformity and maintaining a moderate pressure drop. Moreover, increasing the number of inlets and outlets effectively lowers the pressure drop and enhances thermal uniformity. Although increasing the coolant flow rate and reducing the inlet temperature can further improve cooling performance, these measures also lead to notable increases in energy consumption and pressure loss. Therefore, a trade-off between thermal enhancement and system energy efficiency must be considered in practical applications. The findings of this study provide practical guidance for the design optimization of high-efficiency microchannel liquid cooling systems in power electronic applications. Full article

(This article belongs to the Topic Enhanced Heat Transfer and Advanced Energy Conversion Technology, 2nd Edition)

► Show Figures

Figure 1

23 pages, 3591 KB

Open AccessArticle

Identification of Key Parameters and Construction of Empirical Formulas for Isentropic and Volumetric Efficiency of High-Temperature Heat Pumps Based on XGBoost-MLR Algorithm

by Shuaiqi Li, Fengming Wu, Wenye Lin, Wenji Song and Ziping Feng

Energies 2025, 18(16), 4454; https://doi.org/10.3390/en18164454 - 21 Aug 2025

Viewed by 396

Abstract

High-temperature heat pumps (HTHPs) have gradually begun to play an essential role in using heat in industry for waste heat recovery and providing higher-grade heat. The isentropic efficiency and volumetric efficiency of HTHPs are significantly affected by high-temperature operating conditions, which take the [...] Read more.

High-temperature heat pumps (HTHPs) have gradually begun to play an essential role in using heat in industry for waste heat recovery and providing higher-grade heat. The isentropic efficiency and volumetric efficiency of HTHPs are significantly affected by high-temperature operating conditions, which take the pressure ratio (PR) as the key parameter, with limited consideration of other factors such as temperature. Relying on the experimental data obtained from the industrial-grade HTHP system experimental platform, this work proposed an XGBoost-MLR algorithm-based method to identify the key parameters of HTHP isentropic efficiency and volumetric efficiency. High-precision (R² > 0.95) prediction models were established to determine the effect of temperature variables on isentropic efficiency and volumetric efficiency. After the key parameters were identified, the empirical equation of isentropic efficiency and volumetric efficiency applicable to this operation condition were constructed. The average relative errors of the two empirical formulas were 5.95% and 5.28%, respectively. Finally, the generalizability of empirical formulas was verified using experimental data from other researchers. The isentropic empirical formula had a relative deviation of less than 10% under twin-screw compressor conditions. However, the applicability of the volumetric efficiency empirical formula was unstable in compressors of different sizes. The feasibility of the method was also discussed. Full article

(This article belongs to the Special Issue Optimization and Integrated Design of Sustainable and Renewable Energy Systems)

► Show Figures

Figure 1

32 pages, 1892 KB

Open AccessArticle

Gasification Processes of Portuguese Biomass: Theoretical Analysis of Hydrogen Production Potential

by Leonel J. R. Nunes

Energies 2025, 18(16), 4453; https://doi.org/10.3390/en18164453 - 21 Aug 2025

Viewed by 378

Abstract

Portugal’s commitment to carbon neutrality by 2050 has intensified the search for renewable energy alternatives, with biomass gasification emerging as a promising pathway for hydrogen production. This comprehensive review analyzes the potential of 39 Portuguese biomass species for gasification processes, based on extensive [...] Read more.

Portugal’s commitment to carbon neutrality by 2050 has intensified the search for renewable energy alternatives, with biomass gasification emerging as a promising pathway for hydrogen production. This comprehensive review analyzes the potential of 39 Portuguese biomass species for gasification processes, based on extensive laboratory characterization data including proximate analysis, ultimate analysis, heating values, and metal content. The studied biomasses encompass woody shrubland species (matos arbustivos lenhosos), forest residues, and energy crops representative of Portugal’s diverse biomass resources. Results indicate significant variability in gasification potential, with moisture content ranging from 0.5% to 14.9%, ash content from 0.5% to 5.5%, and higher heating values between 16.8 and 21.2 MJ/kg. Theoretical hydrogen yield calculations suggest that Portuguese biomasses could produce between 85 and 120 kg H₂ per ton of dry biomass, with species such as Eucalyptus globulus, Pinus pinaster, and Cytisus multiflorus showing the highest potential. Statistical analysis reveals strong negative correlations between moisture content and hydrogen yield potential (r = −0.63), while carbon content shows positive correlation with gasification efficiency. The comprehensive characterization provides essential data for optimizing gasification processes and establishing Portugal’s biomass-to-hydrogen production capacity, contributing to the national hydrogen strategy and renewable energy transition. Full article

► Show Figures

Figure 1

18 pages, 2621 KB

Open AccessArticle

Convective Heat Loss Prediction Using the Concept of Effective Wind Speed for Dynamic Line Rating Studies

by Yuxuan Wang, Fulin Fan, Yu Wang, Ke Wang, Jinhai Jiang, Chuanyu Sun, Rui Xue and Kai Song

Energies 2025, 18(16), 4452; https://doi.org/10.3390/en18164452 - 21 Aug 2025

Viewed by 426

Abstract

Dynamic line rating (DLR) is an effective technique for real-time assessments on current-carrying capacities of overhead lines (OHLs), improving efficiencies and preventing overloads of transmission networks. Most research related to DLR forecasting mainly translates predictions of weather conditions into DLR forecasts or directly [...] Read more.

Dynamic line rating (DLR) is an effective technique for real-time assessments on current-carrying capacities of overhead lines (OHLs), improving efficiencies and preventing overloads of transmission networks. Most research related to DLR forecasting mainly translates predictions of weather conditions into DLR forecasts or directly trains artificial intelligence models from DLR observations. Less attention has been given to the predictability of effective wind speeds (EWS) that describe overall convective cooling effects of varying weather conditions along OHLs, which could increase the reliability of DLR forecasts. To assess the effectiveness of EWS concepts in improving DLR predictions, this paper develops an EWS-based method for convective cooling predictions which are critical parameters dominating DLRs of overhead conductors. The EWS is first calculated from actual measurements of wind speeds and directions relative to OHL orientation based on the thermal model of overhead conductors. Then, an autoregressive model along with the Fourier series is employed to predict ultra-short-term EWS variations for up to three 10-min steps ahead, which are eventually converted into predictions of convective cooling effects along OHLs. The proposed EWS-based method is tested based on wind condition measurements in proximity to an OHL. Furthermore, to examine the impacts of angles between wind directions and line orientation on EWS estimation and thus EWS-based convective cooling predictions, the forecasting performance is assessed in the context of different line orientations. Results demonstrate that EWS-based ultra-short-term convective cooling predictions consistently outperform traditional forecasts from original wind conditions across all the tested line orientations. This highlights the significance of the EWS concept in reducing the complexity of DLR forecasting caused by the circular nature of wind directions, and in enhancing the accuracy of convective cooling predictions. Full article

► Show Figures

Figure 1

24 pages, 8122 KB

Open AccessArticle

Heat Exchange Effectiveness and Influence Mechanism of Coaxial Downhole in the Alpine Region of Xining City, Qinghai Province

by Zhen Zhao, Xinkai Zhan, Baizhong Yan, Guangxiong Qin and Yanbo Yu

Energies 2025, 18(16), 4451; https://doi.org/10.3390/en18164451 - 21 Aug 2025

Viewed by 389

Abstract

To enhance the development efficiency of medium–deep geothermal resources in cold regions, this study focuses on a coaxial borehole heat exchanger (CBHE) located in Dapuzi Town, Xining City, Qinghai Province. Based on field-scale heat exchange experiments, a three-dimensional numerical model of the CBHE [...] Read more.

To enhance the development efficiency of medium–deep geothermal resources in cold regions, this study focuses on a coaxial borehole heat exchanger (CBHE) located in Dapuzi Town, Xining City, Qinghai Province. Based on field-scale heat exchange experiments, a three-dimensional numerical model of the CBHE was developed using COMSOL Multiphysics 6.2, incorporating both conductive heat transfer in the surrounding geological formation and convective heat transfer within the wellbore. The model was calibrated and validated against measured data. On this basis, the effects of wellhead injection flow rate, injection temperature, and the thermal conductivity of the inner pipe on heat exchange performance were systematically analyzed. The results show that in cold regions with high altitudes (2000–3000 m) and medium–deep low-temperature geothermal reservoirs (68.8 °C), using a coaxial heat exchange system for space heating delivers good heat extraction performance, with a maximum average power output of 282.37 kW. Among the parameters, the injection flow rate has the most significant impact on heat extraction. When the flow rate increases from 10 m³/h to 30 m³/h, the heat extraction power increases by 57.58%. An increase in injection temperature helps suppress thermal short-circuiting and improves the effluent temperature, but excessively high temperatures lead to a decline in heat extraction. Additionally, increasing the thermal conductivity of the inner pipe significantly intensifies thermal short-circuiting and reduces overall heat exchange capacity. Under constant reservoir conditions, the thermal influence radius expands with both depth and operating time, reaching a maximum of 10.04 m by the end of the heating period. For the CBHE system in Dapuzi, maintaining an injection flow rate of 20–25 m³/h and an injection temperature of approximately 20 °C can achieve an optimal balance between effluent temperature and heat extraction. Full article

► Show Figures

Figure 1

35 pages, 1684 KB

Open AccessArticle

Advancements in Tokamak Technology for Fusion Energy: A Bibliometric and Patent Trend Analysis (2014–2024)

by Horng Jinh Chang and Shih Wei Wang

Energies 2025, 18(16), 4450; https://doi.org/10.3390/en18164450 - 21 Aug 2025

Viewed by 595

Abstract

Tokamak technology, as the cornerstone of nuclear fusion energy, holds immense potential in achieving efficient plasma confinement and high energy densities. To comprehensively map the rapidly evolving landscape of this field, this study employs bibliometric analysis to systematically examine the research and development [...] Read more.

Tokamak technology, as the cornerstone of nuclear fusion energy, holds immense potential in achieving efficient plasma confinement and high energy densities. To comprehensively map the rapidly evolving landscape of this field, this study employs bibliometric analysis to systematically examine the research and development trends of tokamak technology from 2014 to 2024. The data are drawn from 7702 academic publications in the Scopus database, representing a global research effort. Additionally, the study incorporates 2299 tokamak-related patents from Google Patents over the same period, analyzing their technological trends to highlight the growing significance of tokamak devices. Using the R language and the Bibliometric package, the analysis explores research hotspots, institutional influences, and keyword evolution. The results reveal a multifaceted global landscape: China leads in publication output, and the United States maintains a leading role in citation impacts and technological innovation, with other notable contributions from Germany, Japan, South Korea, and various European countries. Patent trend analysis further reveals the rapid expansion of tokamak applications, particularly with significant innovations in high-temperature superconducting magnets and plasma control technologies. Nevertheless, the study identifies major challenges in the commercialization process, including plasma stability control, material durability, and the sustainability of long-term operations. To address these, the study proposes concrete future directions, emphasizing international collaboration and interdisciplinary integration. These efforts are crucial in accelerating tokamak commercialization, thereby providing a strategic roadmap for researchers, policymakers, and industry stakeholders to advance the global deployment of clean energy solutions. Full article

(This article belongs to the Section B4: Nuclear Energy)

► Show Figures

Figure 1

15 pages, 3536 KB

Open AccessArticle

Large Temperature Difference Heat Pump System for Long-Distance Heat Transportation: Experimental Study and Feasibility Analysis

by Qing Miao, Minxia Li, Chaobin Dang, Beiran Hou and Shigang Zhang

Energies 2025, 18(16), 4449; https://doi.org/10.3390/en18164449 - 21 Aug 2025

Viewed by 415

Abstract

With the increasing depletion of fossil fuels, it is urgent to build an efficient regional heating scheme. Long-distance heating transportation schemes are important for the integration and utilization of low-grade heat resources. It is worth noting that when implementing the long-distance heating transportation [...] Read more.

With the increasing depletion of fossil fuels, it is urgent to build an efficient regional heating scheme. Long-distance heating transportation schemes are important for the integration and utilization of low-grade heat resources. It is worth noting that when implementing the long-distance heating transportation scheme, a heat pump system with large temperature differences and high flexibility is required. However, the conventional vapor compression heat pump system is generally based on a single-stage cycle construction, which has the problems of poor heating capacity and a narrow operation range. In this study, a novel large temperature difference heat pump system is proposed. The heat transfer process of the novel heat pump system is serrated, and the pressure ratio of the compressor is similar under different working conditions. Through experimental study, the energy efficiency performance of the system is explored. Taking the conventional heat pump as the comparison object, the annual performance of the system is analyzed. The results show that the novel system can reduce carbon emissions and operation costs by more than 50%. Full article

(This article belongs to the Special Issue Advances in Refrigeration and Heat Pump Technologies)

► Show Figures

Figure 1

32 pages, 1588 KB

Open AccessReview

Comprehensive Review of Hydrogen and Tyre Pyrolysis Oil as Sustainable Fuels for HCCI Engines

by Dilip S. Borkar, Sushant Satputaley, Santosh Alone and Magdalena Dudek

Energies 2025, 18(16), 4448; https://doi.org/10.3390/en18164448 - 21 Aug 2025

Viewed by 494

Abstract

This review article provides an overview of the use of hydrogen and tyre pyrolysis oil as fuels for homogeneous charge compression ignition (HCCI) engines. It discusses their properties, the ways they are produced and their sustainability, which is of particular importance in the [...] Read more.

This review article provides an overview of the use of hydrogen and tyre pyrolysis oil as fuels for homogeneous charge compression ignition (HCCI) engines. It discusses their properties, the ways they are produced and their sustainability, which is of particular importance in the present moment. Both fuels have certain advantages but also throw up many challenges, which complicate their application in HCCI engines. The paper scrutinises engine performance with hydrogen and tyre pyrolysis oil, respectively, and compares the fuels’ emissions, a crucial focus from an environmental perspective. It also surveys related technologies that have recently emerged, their effects and environmental impacts, and the rules and regulations that are starting to become established in these areas. Furthermore, it provides a comparative discussion of various engine performance data in terms of combustion behaviour, emission levels, fuel economy and potential costs or savings in real terms. The analysis reveals significant research gaps, and recommendations are provided as to areas for future study. The paper argues that hydrogen and tyre pyrolysis oil might sometimes be used together or in complementary ways to benefit HCCI engine performance. The importance of life-cycle assessment is noted, acknowledging also the requirements of the circular economy. The major findings are summarised with some comments on future perspectives for the use of sustainable fuels in HCCI engines. This review article provides a helpful reference for researchers working in this area and for policymakers concerned with establishing relevant legal frameworks, as well as for companies in the sustainable transport sector. Full article

(This article belongs to the Special Issue Advances in Hydrogen Production and Hydrogen-Based Power Systems)

► Show Figures

Figure 1

22 pages, 9175 KB

Open AccessArticle

Bi-Level Optimization-Based Bidding Strategy for Energy Storage Using Two-Stage Stochastic Programming

by Kui Hua, Qingshan Xu, Lele Fang and Xin Xu

Energies 2025, 18(16), 4447; https://doi.org/10.3390/en18164447 - 21 Aug 2025

Viewed by 442

Abstract

Energy storage will play an important role in the new power system with a high penetration of renewable energy due to its flexibility. Large-scale energy storage can participate in electricity market clearing, and knowing how to make more profits through bidding strategies in [...] Read more.

Energy storage will play an important role in the new power system with a high penetration of renewable energy due to its flexibility. Large-scale energy storage can participate in electricity market clearing, and knowing how to make more profits through bidding strategies in various types of electricity markets is crucial for encouraging its market participation. This paper considers differentiated bidding parameters for energy storage in a two-stage market with wind power integration, and transforms the market clearing process, which is represented by a two-stage bi-level model, into a single-level model using Karush–Kuhn–Tucker conditions. Nonlinear terms are addressed using binary expansion and the big-M method to facilitate the model solution. Numerical verification is conducted on the modified IEEE RTS-24 and 118-bus systems. The results show that compared to bidding as a price-taker and with marginal cost, the proposed mothod can bring a 16.73% and 13.02% increase in total market revenue, respectively. The case studies of systems with different scales verify the effectiveness and scalability of the proposed method. Full article

(This article belongs to the Special Issue Modeling and Optimization of Energy Storage in Power Systems)

► Show Figures

Figure 1

39 pages, 1131 KB

Open AccessArticle

Reproducible Method for Modifying a Published Electricity Network Model for Transmission Expansion Planning

by Peter Haigh, Cecilia Wallmark and Math Bollen

Energies 2025, 18(16), 4446; https://doi.org/10.3390/en18164446 - 21 Aug 2025

Viewed by 443

Abstract

Transmission network-expansion planning research requires reproducibility of results and comparability of research from various sources. This paper presents a process for modifying a published electricity network model so that the model can be used for exploration of transmission expansion planning problems for different [...] Read more.

Transmission network-expansion planning research requires reproducibility of results and comparability of research from various sources. This paper presents a process for modifying a published electricity network model so that the model can be used for exploration of transmission expansion planning problems for different load and generation profiles. Nodal voltages and branch currents are kept within performance limits by following the applicable planning codes, with reinforcements selected based on a defined strategy to achieve compliance with the applicable standards. The process can be applied to any published model and any set of planning standards to result in a base model that is suitably up to date and realistic for transmission network-expansion planning research. A case study is presented, whereby the process is followed for the “Nordic-32”—a popular reference model based on the Swedish transmission network of the 1980s—with the result being a reproducible and updatable model suitable for exploring transmission expansion planning using 2024 generation-and-demand assumptions from Sweden and network design guidelines based on the Nordel Grid Code. Full article

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

► Show Figures

Figure 1

20 pages, 5507 KB

Open AccessArticle

A Control Strategy for Enhancing Transient-State Stability of Interior Permanent Magnet Synchronous Motors for xEV Applications

by Yangjin Shin, Suyeon Cho and Ju Lee

Energies 2025, 18(16), 4445; https://doi.org/10.3390/en18164445 - 21 Aug 2025

Viewed by 402

Abstract

This study proposes a current control strategy to enhance the control stability of an interior permanent magnet synchronous motor (IPMSM) under transient conditions, such as rapid acceleration or deceleration in electric vehicle (EV) applications. Conventional current control methods provide optimal steady-state current references [...] Read more.

This study proposes a current control strategy to enhance the control stability of an interior permanent magnet synchronous motor (IPMSM) under transient conditions, such as rapid acceleration or deceleration in electric vehicle (EV) applications. Conventional current control methods provide optimal steady-state current references corresponding to torque commands using a lookup table (LUT)-based approach. However, during transitions between these reference points, particularly in the field-weakening region at high speeds, the voltage limit may be exceeded. When the voltage limit is exceeded, unstable overmodulation states may occur, degrading stability and resulting in overshoot of the inverter input current. Although ramp generators are commonly employed to interpolate between current references, a fixed ramp slope may fail to ensure a sufficient voltage margin during rapid transients. In this study, a method is proposed to dynamically adjust the rate of change of the d-axis current reference in real time based on the difference between the inverter output voltage and its voltage limit. By enabling timely field-weakening before rapid changes in speed or q-axis current, the proposed strategy maintains control stability within the voltage limit. The effectiveness of the proposed method was verified through simulations based on real vehicle driving profiles and dynamometer experiments using a 38 kW class IPMSM for a hybrid electric vehicle (HEV), demonstrating reduced input DC current overshoot, improved voltage stability, and enhanced torque tracking performance under high-speed transient conditions. Full article

(This article belongs to the Special Issue Drive System and Control Strategy of Electric Vehicle)

► Show Figures

Figure 1

19 pages, 1939 KB

Open AccessArticle

Development and Optimization of Chemical Kinetic Mechanisms for Ethanol–Gasoline Blends Using Genetic Algorithms

by Filipe Cota, Clarissa Martins, Raphael Braga and José Baeta

Energies 2025, 18(16), 4444; https://doi.org/10.3390/en18164444 - 21 Aug 2025

Viewed by 462

Abstract

Reduced chemical kinetic mechanisms are essential for enabling the use of complex fuels in 3D CFD combustion simulations. This study presents the development and optimization of a compact mechanism capable of accurately modeling ethanol–gasoline blends, including Brazilian Type-C gasoline (27% ethanol by volume) [...] Read more.

Reduced chemical kinetic mechanisms are essential for enabling the use of complex fuels in 3D CFD combustion simulations. This study presents the development and optimization of a compact mechanism capable of accurately modeling ethanol–gasoline blends, including Brazilian Type-C gasoline (27% ethanol by volume) and up to pure ethanol (E100). An initial mechanism was constructed using the Directed Relation Graph with Error Propagation (DRGEP) method applied to detailed mechanisms selected for each surrogate component. The resulting mechanism was then refined through three global iterations of a genetic algorithm targeting ignition delay time (IDT) and laminar flame speed (LFS) performance. Five candidate versions (Mec1 to Mec5), each containing 179 species and 771 reactions, were generated. Mec4 was identified as the optimal configuration based on quantitative error analysis across all tested conditions and blend ratios. The final mechanism offers a balance between predictive accuracy and computational feasibility, making it well-suited for high-fidelity simulations in complex geometries involving multi-component ethanol–gasoline fuels. Full article

► Show Figures

Figure 1

19 pages, 2907 KB

Open AccessArticle

Optimization of Rear-Side Energy Contribution in Bifacial PV Panels: A Parametric Analysis on Albedo, Tilt, Height, and Mounting Configuration

by Furkan Dincer and Emre Ozer

Energies 2025, 18(16), 4443; https://doi.org/10.3390/en18164443 - 21 Aug 2025

Viewed by 654

Abstract

Bifacial photovoltaic panels are preferred over monofacial panels due to the ability of their back surfaces to absorb radiation and generate electricity. However, optimizing the rear-side energy contribution remains a critical area of research. This study systematically investigates how four key parameters (albedo, [...] Read more.

Bifacial photovoltaic panels are preferred over monofacial panels due to the ability of their back surfaces to absorb radiation and generate electricity. However, optimizing the rear-side energy contribution remains a critical area of research. This study systematically investigates how four key parameters (albedo, tilt angle, panel height, and mounting configuration) affect rear-side energy generation and overall panel efficiency. In the first scenario, the impact of surface reflectivity was evaluated. High-reflectivity materials such as aluminum (21.2%) and fresh snow (20.5%) significantly increased rear-side energy yield. The second scenario examined tilt angle, showing that increasing the tilt up to 50° enhanced back-side generation, reaching a gain of 5.5%. The third scenario focused on the effect of panel height, revealing a linear relationship with energy generation. The fourth assessed orientation, comparing horizontal and vertical installations. Horizontal mounting provided a higher rear-side energy yield (4.5%) due to increased exposure to ground-reflected radiation. The findings of this study provide important information for the optimization of bifacial photovoltaic panels and the information will provide guidance for easier and more efficient installation of solar power plants. Full article

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

► Show Figures

Figure 1

27 pages, 2500 KB

Open AccessArticle

Powering the Woods Hole X-Spar Buoy with Ocean Wave Energy—A Control Co-Design Feasibility Study

by Daniel T. Gaebele, Ryan G. Coe, Giorgio Bacelli, Thomas Lanagan, Paul Fucile, Umesh A. Korde and John Toole

Energies 2025, 18(16), 4442; https://doi.org/10.3390/en18164442 - 21 Aug 2025

Viewed by 524

Abstract

Despite its success in measuring air–sea exchange, the Woods Hole Oceanographic Institution’s (WHOI) X-Spar Buoy faces operational limitations due to energy constraints, motivating the integration of an energy harvesting apparatus to improve its deployment duration and capabilities. This work explores the feasibility of [...] Read more.

Despite its success in measuring air–sea exchange, the Woods Hole Oceanographic Institution’s (WHOI) X-Spar Buoy faces operational limitations due to energy constraints, motivating the integration of an energy harvesting apparatus to improve its deployment duration and capabilities. This work explores the feasibility of an augmented, self-powered system in two parts. Part 1 presents the collaborative design between X-Spar developers and wave energy researchers translating user needs into specific functional requirements. Based on requirements like desired power levels, deployability, survivability, and minimal interference with environmental data collection, unsuitable concepts are pre-eliminated from further feasibility study consideration. In part 2, we focus on one of the promising concepts: an internal rigid body wave energy converter. We apply control co-design methods to consider commercial of the shelf hardware components in the dynamic models and investigate the concept’s power conversion capabilities using linear 2-port wave-to-wire models with concurrently optimized control algorithms that are distinct for every considered hardware configuration. During this feasibility study we utilize two different control algorithms, the numerically optimal (but acausal) benchmark and the optimized damping feedback. We assess the sensitivity of average power to variations in drive-train friction, a parameter with high uncertainty, and analyze stroke limitations to ensure operational constraints are met. Our results indicate that a well-designed power take-off (PTO) system could significantly extend the WEC-Spar’s mission by providing additional electrical power without compromising data quality. Full article

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

► Show Figures

Figure 1

20 pages, 558 KB

Open AccessReview

Energy Transition 2024–2025: New Demand Vectors, Technology Oversupply, and Shrinking Net-Zero 2050 Premium

by Henryk Wojtaszek

Energies 2025, 18(16), 4441; https://doi.org/10.3390/en18164441 - 21 Aug 2025

Viewed by 1097

Abstract

The global energy transition is accelerating, yet new and underestimated challenges have emerged since 2024. Rising electricity demand—driven by artificial intelligence data centres, extreme heatwaves, and the electrification of transport—has exceeded earlier projections and shifted the system’s pressure point from generation to flexibility. [...] Read more.

The global energy transition is accelerating, yet new and underestimated challenges have emerged since 2024. Rising electricity demand—driven by artificial intelligence data centres, extreme heatwaves, and the electrification of transport—has exceeded earlier projections and shifted the system’s pressure point from generation to flexibility. At the same time, an oversupply of solar PV panels and lithium-ion batteries is lowering costs but increasing the risk of trade conflicts and supply chain concentration. This article presents a meta-analysis of 12 energy scenarios from 2024 to 2025, based on institutional outlooks (IEA, BNEF, and WEF) and peer-reviewed publications selected using transparent quality criteria (TRL thresholds, JRC guidance, and data transparency). A difference-in-differences method is applied to identify changes between editions. Results show a demand increase of over 2200 TWh by 2035, a decline in the “Net-Zero premium” from 19% to 15%, and a pressing need to redirect investment from gas infrastructure to grids, storage, and hydrogen. A case study for Central and Eastern Europe reveals that Poland will require USD 5–6 billion annually, primarily for transmission networks. These findings support a capital shift toward resilient and socially acceptable decarbonisation pathways. Full article

(This article belongs to the Section C: Energy Economics and Policy)

► Show Figures

Figure 1

26 pages, 15026 KB

Open AccessArticle

Interactive Optimization of Electric Bus Scheduling and Overnight Charging

by Zvonimir Dabčević and Joško Deur

Energies 2025, 18(16), 4440; https://doi.org/10.3390/en18164440 - 21 Aug 2025

Viewed by 537

Abstract

The transition to fully electric bus (EB) fleets introduces new challenges in coordinating daily operations and managing charging energy needs, while accounting for infrastructure constraints. The paper proposes a three-stage optimization framework that integrates EB scheduling with overnight charging under realistic depot layout [...] Read more.

The transition to fully electric bus (EB) fleets introduces new challenges in coordinating daily operations and managing charging energy needs, while accounting for infrastructure constraints. The paper proposes a three-stage optimization framework that integrates EB scheduling with overnight charging under realistic depot layout constraints. In the first stage, a mixed-integer linear program (MILP) determines the minimum number of EBs with ample batteries and related schedules to complete all timetabled trips. With the fleet size fixed, the second stage minimizes the EB battery capacity by optimizing trip assignments. In the third stage, charging schedules are iteratively optimized for different numbers of chargers to minimize charger power capacity and charging cost, while ensuring each EB is fully recharged before its first trip on the following day. The matrix-shape depot layout imposes spatial and operational constraints that restrict the charging and movement of EBs based on their parking positions, with EBs remaining stationary overnight. The entire process is repeated by incrementing the fleet size until a saturation point is reached, beyond which no further reduction in battery capacity is observed. This results in a Pareto frontier showing trade-offs between required battery capacity, number of chargers, charger power capacity, and charging cost. The proposed method is applied to a real-world airport parking shuttle service, demonstrating its potential to reduce the battery size and charging infrastructure demands while maintaining full operational feasibility. Full article

(This article belongs to the Special Issue Integrated Solutions for Transportation and Energy Systems: Advancing Sustainable Mobility and Power Infrastructure)

► Show Figures

Figure 1

11 pages, 8468 KB

Open AccessArticle

Nuclear Thermal Rocket Emulator for a Hardware-in-the-Loop Test Bed

by Brandon A. Wilson, Jono McConnell, Wesley C. Williams, Nick Termini, Craig Gray, Charles E. Taylor and N. Dianne Ezell Bull

Energies 2025, 18(16), 4439; https://doi.org/10.3390/en18164439 - 21 Aug 2025

Viewed by 691

Abstract

To support NASA’s mission to use nuclear thermal rockets for future Mars missions, an instrumentation and control test bed has been built at Oak Ridge National Laboratory. The system is designed as a hardware-in-the-loop test bed for testing control elements and autonomous control [...] Read more.

To support NASA’s mission to use nuclear thermal rockets for future Mars missions, an instrumentation and control test bed has been built at Oak Ridge National Laboratory. The system is designed as a hardware-in-the-loop test bed for testing control elements and autonomous control algorithms for nuclear thermal propulsion rockets. The mock reactor system consists of a modular and scalable framework, using inexpensive components and open-source software. The hardware system consists of a two-phase flow loop and a mock reactor with six control drums. A single-board computer (NVIDIA Jetson) handles reactor core emulation and hosts a message queuing telemetry transport broker that allows user-deployed control algorithms to interact with the system hardware. The reactor emulator receives sensor data from the hardware and provides the simulated performance of the reactor under steady-state, transient, and fault conditions. The emulator uses a reactivity lookup table and the point kinetics equations to solve for the reactor dynamics in real time. Emulated reactor dynamics and sensor input inform the autonomous control algorithm’s decision-making in a closed-loop manner. The current system is capable of operating at 10 Hz, but faster cycle rates are an area of ongoing research. This test bed will enable NASA and other space vendors to rigorously test their autonomous control systems for NTP rockets under transient (reactor startup and shutdown), steady-state, and fault conditions to reduce development time and risk for autonomous control systems in future missions. Full article

(This article belongs to the Special Issue Advanced Control for Nuclear Energy Systems: Intelligent Control and Operation Strategies)

► Show Figures

Figure 1

23 pages, 3768 KB

Open AccessArticle

Research on Mode Transition Control of Power-Split Hybrid Electric Vehicle Based on Fixed Time

by Hongdang Zhang, Hongtu Yang, Fengjiao Zhang, Xuhui Liao and Yanyan Zuo

Energies 2025, 18(16), 4438; https://doi.org/10.3390/en18164438 - 20 Aug 2025

Viewed by 510

Abstract

In this paper, we address the problem of jerk and disturbance suppression during mode transitions in power-split hybrid electric vehicles. First, a transient switching model of the PS-HEV is developed. Next, the mechanisms underlying shock generation and the influence of disturbances on transition [...] Read more.

In this paper, we address the problem of jerk and disturbance suppression during mode transitions in power-split hybrid electric vehicles. First, a transient switching model of the PS-HEV is developed. Next, the mechanisms underlying shock generation and the influence of disturbances on transition smoothness are analyzed. Based on this, a fixed-time dynamic coordinated control strategy is proposed, comprising a novel sliding mode control law and a fixed-time extended state observer. The proposed fixed-time sliding mode control law is independent of initial state values and ensures superior convergence performance. Meanwhile, the fixed-time extended state observer enables real-time estimation of external disturbances, thereby reducing the conservatism of the control law. Finally, simulation and hardware-in-the-loop results demonstrate that the proposed strategy markedly improves mode transition performance under various disturbance scenarios. This work provides a new perspective on hybrid mode transition control and effectively enhances transition smoothness. Full article

► Show Figures

Figure 1

22 pages, 1805 KB

Open AccessArticle

Fault Diagnosis of Wind Turbine Pitch Bearings Based on Online Soft-Label Meta-Learning and Gaussian Prototype Network

by Lianghong Wang, Zhongzhuang Bai, Hongxiang Li, Panpan Yang, Jie Tao, Xuemei Zou, Jinliang Zhao and Chunwei Wang

Energies 2025, 18(16), 4437; https://doi.org/10.3390/en18164437 - 20 Aug 2025

Viewed by 428

Abstract

Meta-learning has demonstrated significant advantages in small-sample tasks and has attracted considerable attention in wind turbine fault diagnosis. However, due to extreme operating conditions and equipment aging, the monitoring data of wind turbines often contain false alarms or missed detections. This results in [...] Read more.

Meta-learning has demonstrated significant advantages in small-sample tasks and has attracted considerable attention in wind turbine fault diagnosis. However, due to extreme operating conditions and equipment aging, the monitoring data of wind turbines often contain false alarms or missed detections. This results in inaccurate fault sample labeling. In meta-learning, these erroneous labels not only fail to help models quickly adapt to new meta-test tasks, but they also interfere with learning for new tasks, which leads to “negative transfer” phenomena. To address this, this paper proposes a novel method called Online Soft-Labeled Meta-learning with Gaussian Prototype Networks (SL-GPN). During training, the method dynamically aggregates feature similarities across multiple tasks or samples to form online soft labels. They guide model training process and effectively solve small-sample bearing fault diagnosis challenges. Experimental tests on small-sample data under various operating conditions and error labels were carried out. The results show that the proposed method improves diagnostic accuracy in small-sample environments, reduces false alarm rates, and demonstrates excellent generalization performance. Full article

► Show Figures

Figure 1

19 pages, 2944 KB

Open AccessArticle

Analysis of Thermal Cycles with an Isothermal Turbine for Use in Low-Temperature Systems

by Krzysztof Kosowski and Marian Piwowarski

Energies 2025, 18(16), 4436; https://doi.org/10.3390/en18164436 - 20 Aug 2025

Viewed by 414

Abstract

The article discusses the current challenges facing the energy sector in the context of climate policy, technological transformation, and the urgent need to increase energy efficiency while reducing greenhouse gas emissions. Modern thermal energy conversion technologies are analyzed, including supercritical steam and gas–steam [...] Read more.

The article discusses the current challenges facing the energy sector in the context of climate policy, technological transformation, and the urgent need to increase energy efficiency while reducing greenhouse gas emissions. Modern thermal energy conversion technologies are analyzed, including supercritical steam and gas–steam cycles, as well as distributed systems using renewable fuels and microturbines. Particular attention is given to innovative systems with isothermal expansion, which theoretically allow operation close to the efficiency limit defined by the Carnot cycle. The study presents calculation results for conventional systems (steam, gas with regeneration, and Organic Rankine Cycle) and proposes a novel isothermal air turbine cycle. In a combined gas–steam configuration, the proposed cycle achieved an efficiency exceeding 43% at a relatively low heat source temperature of 700 K, clearly outperforming conventional steam and ORC systems under the same thermal conditions. The use of a simple working medium (air), combined with the potential for integration with renewable energy sources, makes this concept a promising and viable alternative to traditional Rankine and Brayton cycles in thermally constrained applications. Full article

(This article belongs to the Special Issue Advanced Methods for the Design and Optimization of Turbomachinery)

► Show Figures

Figure 1

22 pages, 7110 KB

Open AccessArticle

Flow and Heat Transfer in an Axial Throughflow Rotating Disk Cavity with Dual Inlets Under Variable Conditions

by Jianfei Li, Xueying Li and Jing Ren

Energies 2025, 18(16), 4435; https://doi.org/10.3390/en18164435 - 20 Aug 2025

Viewed by 419

Abstract

The flow and heat transfer in a rotating disk cavity with dual axial inlets are investigated under a range of operating conditions. A full 360° computational fluid dynamics model is employed, with 40 simulation cases varying the rotational Reynolds number (Re_ω [...] Read more.

The flow and heat transfer in a rotating disk cavity with dual axial inlets are investigated under a range of operating conditions. A full 360° computational fluid dynamics model is employed, with 40 simulation cases varying the rotational Reynolds number (Re_ω= 1.9 × 10⁶–3.1 × 10⁶) and axial throughflow Reynolds number (Re_z = 7.3 × 10⁵–1.2 × 10⁶). The results show that elevated rotation intensifies turbulent mixing and significantly enhances convective cooling on the upstream disk, whereas increasing throughflow improves heat transfer on the downstream disk by promoting deeper coolant penetration. However, an excessive axial flow rate can induce local thermal stratification near the upstream disk, which offsets its heat transfer gains, and strong rotation diminishes the marginal benefits of higher throughflow on downstream cooling. Overall, the study reveals distinct cooling behaviors on the upstream and downstream disk surfaces governed by the interplay between rotation and throughflow. These findings provide insight into optimizing dual-inlet cavity designs and underscore the importance of balancing rotational speed and coolant flow distribution for effective thermal management in gas turbine disk cavities. Full article

► Show Figures

Figure 1

21 pages, 1242 KB

Open AccessArticle

Smart Monitoring and Management of Local Electricity Systems with Renewable Energy Sources

by Olexandr Kyrylenko, Serhii Denysiuk, Halyna Bielokha, Artur Dyczko, Beniamin Stecuła and Yuliya Pazynich

Energies 2025, 18(16), 4434; https://doi.org/10.3390/en18164434 - 20 Aug 2025

Viewed by 566

Abstract

Smart monitoring of local electricity systems (LESs) with sources based on renewable energy resources (RESs) from the point of view of the requirements of the functions of an intelligent system are hardware and software systems that can solve the tasks of both analysis [...] Read more.

Smart monitoring of local electricity systems (LESs) with sources based on renewable energy resources (RESs) from the point of view of the requirements of the functions of an intelligent system are hardware and software systems that can solve the tasks of both analysis (optimization) and synthesis (design, planning, control). The article considers the following: a functional scheme of smart monitoring of LESs, describing its main components and scope of application; an assessment of the state of the processes and the state of the equipment of generators and loads; dynamic pricing and a dynamic assessment of the state of use of primary fuel and/or current costs of generators; economic efficiency of generator operation and loads; an assessment of environmental acceptability, in particular, the volume of CO₂ emissions; provides demand-side management, managing maximum energy consumption; a forecast of system development; an assessment of mutual flows of electricity; system resistance to disturbances; a forecast of metrological indicators, potential opportunities for generating RESs (wind power plants, solar power plants, etc.); an assessment of current costs; the state of electromagnetic compatibility of system elements and operation of electricity storage devices; and ensures work on local electricity markets. The application of smart monitoring in the formation of tariffs on local energy markets for transactive energy systems is shown by conducting a combined comprehensive assessment of the energy produced by each individual power source with graphs of the dependence of costs on the generated power. Algorithms for the comprehensive assessment of the cost of electricity production in a transactive system for calculating planned costs are developed, and the calculation of the cost of production per 1 kW is also presented. A visualization of the results of applying this algorithm is presented. Full article

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

► Show Figures

Figure 1

15 pages, 2081 KB

Open AccessArticle

Levelized Cost of Electricity Prediction and End-User Price Deduction Model for Power Systems with High Renewable Energy Penetration

by Wenqin Song, Zhuxiu Wang, Xu Yan, Xumin Liu, Zhongfu Tan and Yuan Feng

Energies 2025, 18(16), 4433; https://doi.org/10.3390/en18164433 - 20 Aug 2025

Viewed by 424

Abstract

With the rapid growth in the scale of high-percentage new energy generation, the structure of the new power system is changing. Influenced by the uncertainty and zero marginal cost characteristics of new energy, the security cost required by the power system under the [...] Read more.

With the rapid growth in the scale of high-percentage new energy generation, the structure of the new power system is changing. Influenced by the uncertainty and zero marginal cost characteristics of new energy, the security cost required by the power system under the high proportion of new energy access has increased dramatically. How to accurately measure the cost of the power system and assess the trend of the system cost changes and the impact on its end-user price has become critical. Accordingly, this paper creatively proposes a levelized cost of electricity (LCOE) prediction and end-user price deduction model for power systems with high renewable energy penetration. Firstly, the power system factor cost prediction model is constructed from the three dimensions of power-side, grid-side, and system operation cost. Secondly, a levelized cost of electricity prediction model is constructed based on the above model. Again, based on the analysis of the end-user price composition, the end-user price deduction model is proposed. Finally, the data of Gansu Province is selected for example analysis, and the results show that, in 2060, the power LCOE will be 0.064 USD/kWh, the system LCOE will be 0.103 USD/kWh, and the end-user price will rise to 0.1 USD/kWh. Full article

(This article belongs to the Topic Intelligent, Flexible, and Effective Operation of Smart Grids with Novel Energy Technologies and Equipment)

► Show Figures

Figure 1

22 pages, 4773 KB

Open AccessArticle

Equivalent Modeling and Simulation of Fracture Propagation in Deep Coalbed Methane

by Cong Xiao, Jiayuan He, Lin Meng, Rusheng Zhang and Dong Xiong

Energies 2025, 18(16), 4432; https://doi.org/10.3390/en18164432 - 20 Aug 2025

Viewed by 469

Abstract

Deep coalbed methane (CBM) is challenging to develop due to considerable burial depth, high ground stress, and complex geological structures. However, modeling deep CBM in complex formations and setting reasonable simulation parameters to obtain reasonable results still needs exploration. This study presents a [...] Read more.

Deep coalbed methane (CBM) is challenging to develop due to considerable burial depth, high ground stress, and complex geological structures. However, modeling deep CBM in complex formations and setting reasonable simulation parameters to obtain reasonable results still needs exploration. This study presents a comprehensive equivalent finite element modeling method for deep CBM. The method is based on the cohesive element with pore pressure of the zero-thickness (CEPPZ) model to simulate hydraulic fracture propagation and characterize the effects of bedding interfaces and natural fractures. Taking Ordo’s deep CBM in China as an example, a comprehensive equivalent model for hydraulic fracturing was developed for the limestone layer–coal seam–mudstone layer. Then, the filtration parameters of the CEPPZ model and the permeability parameters of the deep CBM reservoir matrix were inverted and calibrated using on-site data from fracturing tests. Finally, the propagation path of hydraulic fractures was simulated under varying ground stress, construction parameters, and perforation positions. The results show that the hydraulic fractures are more likely to expand into layers with low minimum horizontal stress; the effect of a sizable fluid injection rate on the increase in hydraulic fracture length is noticeable; the improvement effect on fracture length and area gradually weakens with the increased fracturing fluid volume and viscosity; and when directional roof limestone/floor mudstone layer perforation is used, and the appropriate perforation location is selected, hydraulic fractures can communicate the coal seam to form a roof limestone/floor mudstone layer indirect fracturing. The results can guide the efficient development of deep CBM, improving the human society’s energy structure. Full article

► Show Figures

Figure 1

27 pages, 4682 KB

Open AccessArticle

Optimal Configuration for Photovoltaic and Energy Storage in Distribution Network Using Comprehensive Evaluation Model

by Rui Gao, Dan Wang, Chengxiong Mao, Bin Liu, Bingzhao Zhu, Jiawei Huang and Shengjun Wu

Energies 2025, 18(16), 4431; https://doi.org/10.3390/en18164431 - 20 Aug 2025

Viewed by 549

Abstract

To enhance the efficiency of renewable energy consumption and reduce reliance on fossil fuels, the study addresses the challenges of distributed photovoltaic and energy storage integration in distribution networks, such as voltage fluctuations, safety risks, and insufficient converter considerations to the distribution network. [...] Read more.

To enhance the efficiency of renewable energy consumption and reduce reliance on fossil fuels, the study addresses the challenges of distributed photovoltaic and energy storage integration in distribution networks, such as voltage fluctuations, safety risks, and insufficient converter considerations to the distribution network. Through a four-dimensional comprehensive evaluation system including grid-strength quantification indicators like the generalized short-circuit ratio, a multi-objective mathematical model-based performance evaluation system using an analytic hierarchy process and criteria importance through the intercriteria correlation method has been established, and an optimization model for the configuration of photovoltaic and energy storage equipment is optimized. The study innovatively proposes a multi-type synchronous control framework enabling dynamic GFL/GFM converter selection at different nodes, overcoming traditional single-control limitations. The simulation results show that the proposed optimal configuration scheme can effectively improve the operating states and reduce the energy consumption of the distribution network. Full article

(This article belongs to the Special Issue Searching for Ways of Optimizing the Attainment and Use of Energy)

► Show Figures

Figure 1

29 pages, 9911 KB

Open AccessArticle

A Novel Integrated System for Coupling an Externally Compressed Air Separation Unit with Liquid Air Energy Storage and Its Performance Analysis

by Yunong Liu, Xiufen He, Zhongqi Zuo, Lifang Zheng and Li Wang

Energies 2025, 18(16), 4430; https://doi.org/10.3390/en18164430 - 20 Aug 2025

Viewed by 546

Abstract

Air separation units (ASUs) are power-intensive devices on the electricity demand side with significant potential for large-scale energy storage. Liquid air energy storage (LAES) is currently a highly promising large-scale energy storage technology. Coupling ASU with LAES equipment can not only reduce the [...] Read more.

Air separation units (ASUs) are power-intensive devices on the electricity demand side with significant potential for large-scale energy storage. Liquid air energy storage (LAES) is currently a highly promising large-scale energy storage technology. Coupling ASU with LAES equipment can not only reduce the initial investment for LAES, but also significantly lower the operating electricity costs of the ASU. This study proposes a novel modular-integrated process for coupling an externally compressed ASU (ECAS) with LAES. The core advantages of this integrated process are as follows: the liquefaction unit’s storage capacity is not constrained by the ASU surplus load capacity and it integrates cold, heat, electricity, and material utilization. Taking an integrated system with 40,000 Nm³/h oxygen production capacity as an example, under liquefaction pressure of 90 bar and discharge expansion pressure of 110 bar, the system achieves its highest electrical round trip efficiency of 55.3%. Its energy storage capacity reaches 31.32 MWh/10⁴ Nm³ O₂, exceeding the maximum capacity of existing energy storage systems of the ECAS by 1.7 times. Based on a peak-flat-valley electricity price ratio of 3.4:2:1, an optimal economic performance is attained at 100 bar liquefaction pressure, delivering a 7.21% in cost saving rate compared to conventional ASUs. The liquefaction unit’s payback period is 6.39 years—68.1% shorter than conventional LAES. This study aims to enhance both the energy storage capacity and economic performance of integrated systems combining ECAS with LAES. Full article

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

► Show Figures

Figure 1

15 pages, 1687 KB

Open AccessArticle

Catalytic Role of Nickel in Hydrogen Storage and Release Using Dibenzyltoluene as a Liquid Organic Hydrogen Carrier

by Jesús Rodríguez Ruiz, Nuria García-Mancha, Roberto Campana and Carlos Tardío

Energies 2025, 18(16), 4429; https://doi.org/10.3390/en18164429 - 20 Aug 2025

Viewed by 600

Abstract

Liquid Organic Hydrogen Carriers (LOHCs) represent a promising technology for the safe storage and transport of hydrogen. Its technical development largely depends on the catalysts used in the hydrogenation and dehydrogenation processes. Typically, noble metal-based monometallic catalysts are employed, although they present limitations [...] Read more.

Liquid Organic Hydrogen Carriers (LOHCs) represent a promising technology for the safe storage and transport of hydrogen. Its technical development largely depends on the catalysts used in the hydrogenation and dehydrogenation processes. Typically, noble metal-based monometallic catalysts are employed, although they present limitations in terms of cost and availability. This study uses the DBT system to explore the potential of nickel (Ni) as a catalytic alternative. In dehydrogenation, its role as an additive in low-loaded Pt-based catalysts (0.25 wt%) was evaluated, showing a significant increase in activity, with dehydrogenation levels exceeding 95%, compared to 82% obtained with monometallic Pt catalysts. This improvement is attributed to the formation of Pt-Ni alloys. On the other hand, although the bimetallic systems were not effective in hydrogenation, a commercial Ni/Al₂O₃-SiO₂ catalyst was tested, achieving hydrogenation degrees of 80% in just 40 min, after pressure and catalyst loading optimization. These results position Ni as a key component in LOHC catalysis, either as an effective additive in Pt-based systems or as an active metal itself, due to its excellent performance and low cost. This paves the way for economically viable and efficient catalytic solutions for hydrogen storage applications, bridging the gap between performance and practicality. Full article

(This article belongs to the Special Issue Advanced Energy Storage Technologies)

► Show Figures

Figure 1

25 pages, 3878 KB

Open AccessArticle

Thermodynamic Evaluation of Low-GWP A1 Refrigerants for Ultra-Low Temperature Refrigeration Applications

by Pau Giménez-Prades, Cosmin-Mihai Udroiu, Joaquín Navarro-Esbrí and Adrián Mota-Babiloni

Energies 2025, 18(16), 4428; https://doi.org/10.3390/en18164428 - 20 Aug 2025

Viewed by 510

Abstract

Slow market development has caused the lack of low-GWP A1 refrigerants for ultra-low temperature (ULT) refrigeration. Consequently, the high-GWP refrigerant R23 (GWP = 14,600) remains widely used within the ULT sector. For this reason, this paper proposes a comprehensive thermodynamic analysis of recently [...] Read more.

Slow market development has caused the lack of low-GWP A1 refrigerants for ultra-low temperature (ULT) refrigeration. Consequently, the high-GWP refrigerant R23 (GWP = 14,600) remains widely used within the ULT sector. For this reason, this paper proposes a comprehensive thermodynamic analysis of recently developed CO₂-based mixtures as low-GWP A1 alternatives to R23 for ULT applications, R469A (GWP = 1357), R472B (GWP = 526), R472A (GWP = 353), and R473A (GWP = 1830). In addition, three system configurations are analysed, the basic two-stage cascade system, and configurations incorporating internal heat exchangers (IHXs). Keeping a constant high-temperature stage (HTS) condensation temperature at 35 °C, three low-temperature stage (LTS) evaporation temperatures are considered, −70, −60, and −50 °C. The highest coefficient of performance (COP) is reached by R23 across all operating conditions and configurations. Among the alternative refrigerants, R473A exhibits the highest COP (0.74% to 1.26% lower than R23). The implementation of IHX results in a reduced COP compared to the basic cycle. R472B is the refrigerant least negatively affected by the IHX implementation due to its high glide. Finally, the environmental impact of R23 is notably reduced by all the alternative refrigerants (up to 95%). This paper’s findings highlight the potential of alternative refrigerants as replacements for R23 in ULT applications. Full article

(This article belongs to the Section J2: Thermodynamics)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Energies, Volume 18, Issue 16 (August-2 2025) – 248 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI