Energies

33 pages, 7876 KiB

Open AccessEditor’s ChoiceArticle

Methods for the Investigation and Mitigation of Conducted Differential-Mode Electromagnetic Interference in Commercial Electrical Vehicles

by Per Widek and Mats Alaküla

Energies 2025, 18(4), 859; https://doi.org/10.3390/en18040859 - 12 Feb 2025

Viewed by 782

Abstract

One of the main challenges as the market for fully commercial electrified vehicles quickly expands is predicting the electromagnetic interference (EMI) in traction voltage systems (TVSs) in differential mode (DM) and common mode (CM). The number of subsystems connected to vehicle TVSs is [...] Read more.

One of the main challenges as the market for fully commercial electrified vehicles quickly expands is predicting the electromagnetic interference (EMI) in traction voltage systems (TVSs) in differential mode (DM) and common mode (CM). The number of subsystems connected to vehicle TVSs is increasing, and thus, so are the electromagnetic compatibility (EMC) requirements. These requirements should make sure that neither the function nor lifetime of any source or load is affected by another, but experience shows that they are often insufficient. The purpose of this article is to show how circuit simulations can complement these requirements and that a generalized artificial network/line impedance stabilization network (LISN) is insufficient to correctly predict the EMI situation of a real vehicle. This article presents a method for complexity reduction in TVS DM simulations and a comparison with the usage of LISN to predict the EMI between subsystems; the article also addresses how to mitigate the EMI with DM filters for the subsystems. The proposed method creates a foundation for a faster and safer development process. The simulation model’s development includes a traction battery and TVS subsystems. It is found that a standardized LISN does not reflect the behavior of a commercial TVS and cannot be used solely to judge if a subsystem will operate as intended within a TVS without creating EMI. A change in switching frequency in the DUT can cause severe resonance between TVS subsystems, but this is not seen with a LISN. The conclusion of the article is that LISN can provide a false sense of security and that calibrated simulation models of a complete TVS are necessary to predict the behavior in that TVS; this study also highlights the importance of using DM filters to ensure protection against resonance frequencies. Full article

(This article belongs to the Special Issue Novel Applications of Power Converters for Energy Storage and Grid Integration)

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24 pages, 9516 KiB

Open AccessEditor’s ChoiceArticle

Review on Noise Generation Issues and Noise Mitigation Methods in Electric Vehicle Charging Systems

by Marcin Jarnut, Jacek Kaniewski and Mariusz Buciakowski

Energies 2025, 18(4), 778; https://doi.org/10.3390/en18040778 - 7 Feb 2025

Cited by 1 | Viewed by 945

Abstract

This paper presents an overview of issues related to noise generation in electric vehicle (EV) charging systems. It discusses the requirements for noise reduction in locations where charging stations are most commonly installed. The primary sources of noise in EV charging stations are [...] Read more.

This paper presents an overview of issues related to noise generation in electric vehicle (EV) charging systems. It discusses the requirements for noise reduction in locations where charging stations are most commonly installed. The primary sources of noise in EV charging stations are identified, considering their design and configuration. The results of acoustic tests for specific noise sources and entire charging stations are presented, including measurements of sound pressure level (SPL), acoustic imaging, and the generated acoustic spectrum. The paper also describes noise reduction methods and proposes solutions aimed at minimizing the noise generated by charging infrastructure. Additionally, the results of tests illustrating the effectiveness of these methods are presented. Full article

(This article belongs to the Collection "Electric Vehicles" Section: Review Papers)

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77 pages, 4903 KiB

Open AccessEditor’s ChoiceReview

State of the Art in Electric Batteries’ State-of-Health (SoH) Estimation with Machine Learning: A Review

by Giovane Ronei Sylvestrin, Joylan Nunes Maciel, Marcio Luís Munhoz Amorim, João Paulo Carmo, José A. Afonso, Sérgio F. Lopes and Oswaldo Hideo Ando Junior

Energies 2025, 18(3), 746; https://doi.org/10.3390/en18030746 - 6 Feb 2025

Cited by 2 | Viewed by 3704

Abstract

The sustainable reuse of batteries after their first life in electric vehicles requires accurate state-of-health (SoH) estimation to ensure safe and efficient repurposing. This study applies the systematic ProKnow-C methodology to analyze the state of the art in SoH estimation using machine learning [...] Read more.

The sustainable reuse of batteries after their first life in electric vehicles requires accurate state-of-health (SoH) estimation to ensure safe and efficient repurposing. This study applies the systematic ProKnow-C methodology to analyze the state of the art in SoH estimation using machine learning (ML). A bibliographic portfolio of 534 papers (from 2018 onward) was constructed, revealing key research trends. Public datasets are increasingly favored, appearing in 60% of the studies and reaching 76% in 2023. Among 12 identified sources covering 20 datasets from different lithium battery technologies, NASA’s Prognostics Center of Excellence contributes 51% of them. Deep learning (DL) dominates the field, comprising 57.5% of the implementations, with LSTM networks used in 22% of the cases. This study also explores hybrid models and the emerging role of transfer learning (TL) in improving SoH prediction accuracy. This study also highlights the potential applications of SoH predictions in energy informatics and smart systems, such as smart grids and Internet-of-Things (IoT) devices. By integrating accurate SoH estimates into real-time monitoring systems and wireless sensor networks, it is possible to enhance energy efficiency, optimize battery management, and promote sustainable energy practices. These applications reinforce the relevance of machine-learning-based SoH predictions in improving the resilience and sustainability of energy systems. Finally, an assessment of implemented algorithms and their performances provides a structured overview of the field, identifying opportunities for future advancements. Full article

(This article belongs to the Section K: State-of-the-Art Energy Related Technologies)

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16 pages, 2888 KiB

Open AccessEditor’s ChoiceArticle

Rheological Properties of Crude Oil and Produced Emulsion from CO₂ Flooding

by Mingzheng Qiao, Fan Zhang and Weiqi Li

Energies 2025, 18(3), 739; https://doi.org/10.3390/en18030739 - 6 Feb 2025

Cited by 1 | Viewed by 703

Abstract

Carbon Capture, Utilization and Storage (CCUS) technology is recognized as a pivotal strategy to mitigate global climate change. The CO₂ storage and enhanced oil recovery (CCUS-EOR) technology not only enhances oil recovery rates but also contributes to significant reductions in CO₂ [...] Read more.

Carbon Capture, Utilization and Storage (CCUS) technology is recognized as a pivotal strategy to mitigate global climate change. The CO₂ storage and enhanced oil recovery (CCUS-EOR) technology not only enhances oil recovery rates but also contributes to significant reductions in CO₂ emissions, with significant social and economic benefits. This paper examines the application of CO₂-EOR technology in both enhancing oil recovery and facilitating geological CO₂ storage, and analyzes its implementation status and differences in the United States and China. Through experimental investigations conducted in a specific oilfield, we analyze the effects of dissolved CO₂ on the viscosity–temperature characteristics, yield value under pressure, stability, and rheological properties of crude oil and produced fluids. Additionally, we assess the demulsification effectiveness of various demulsifiers. Our findings indicate that both dissolved CO₂ in crude oil and emulsions exhibit non-Newtonian fluid behavior characterized by shear thinning, and the viscosity decreases with the increase in temperature and pressure. Furthermore, the presence of dissolved CO₂ exacerbates the oil–water separation phenomenon in produced fluids, thereby diminishing emulsion stability. The increase in emulsion concentration and the increase in emulsification temperature are both conducive to improving the emulsification rate. These research results provide critical insights for pipeline design and pump selection in oilfield production processes. Full article

(This article belongs to the Special Issue Low Carbon Energy Generation and Utilization Technologies)

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23 pages, 629 KiB

Open AccessEditor’s ChoiceArticle

Few-Shot Load Forecasting Under Data Scarcity in Smart Grids: A Meta-Learning Approach

by Georgios Tsoumplekas, Christos Athanasiadis, Dimitrios I. Doukas, Antonios Chrysopoulos and Pericles Mitkas

Energies 2025, 18(3), 742; https://doi.org/10.3390/en18030742 - 6 Feb 2025

Cited by 2 | Viewed by 1026

Abstract

Despite the rapid expansion of smart grids and large volumes of data at the individual consumer level, there are still various cases where adequate data collection to train accurate load forecasting models is challenging or even impossible. This paper proposes adapting an established [...] Read more.

Despite the rapid expansion of smart grids and large volumes of data at the individual consumer level, there are still various cases where adequate data collection to train accurate load forecasting models is challenging or even impossible. This paper proposes adapting an established Model-Agnostic Meta-Learning algorithm for short-term load forecasting in the context of few-shot learning. Specifically, the proposed method can rapidly adapt and generalize within any unknown load time series of arbitrary length using only minimal training samples. In this context, the meta-learning model learns an optimal set of initial parameters for a base-level learner recurrent neural network. The proposed model is evaluated using a dataset of historical load consumption data from real-world consumers. Despite the examined load series’ short length, it produces accurate forecasts outperforming transfer learning and task-specific machine learning methods by

12.5 %

. To enhance robustness and fairness during model evaluation, a novel metric, mean average log percentage error, is proposed that alleviates the bias introduced by the commonly used MAPE metric. Finally, a series of studies to evaluate the model’s robustness under different hyperparameters and time series lengths is also conducted, demonstrating that the proposed approach consistently outperforms all other models. Full article

(This article belongs to the Special Issue Machine Learning for Energy Load Forecasting)

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32 pages, 2280 KiB

Open AccessEditor’s ChoiceReview

Underground Hydrogen Storage: Transforming Subsurface Science into Sustainable Energy Solutions

by Kwamena Opoku Duartey, William Ampomah, Hamid Rahnema and Mohamed Mehana

Energies 2025, 18(3), 748; https://doi.org/10.3390/en18030748 - 6 Feb 2025

Cited by 4 | Viewed by 1953

Abstract

As the global economy moves toward net-zero carbon emissions, large-scale energy storage becomes essential to tackle the seasonal nature of renewable sources. Underground hydrogen storage (UHS) offers a feasible solution by allowing surplus renewable energy to be transformed into hydrogen and stored in [...] Read more.

As the global economy moves toward net-zero carbon emissions, large-scale energy storage becomes essential to tackle the seasonal nature of renewable sources. Underground hydrogen storage (UHS) offers a feasible solution by allowing surplus renewable energy to be transformed into hydrogen and stored in deep geological formations such as aquifers, salt caverns, or depleted reservoirs, making it available for use on demand. This study thoroughly evaluates UHS concepts, procedures, and challenges. This paper analyzes the most recent breakthroughs in UHS technology and identifies special conditions needed for its successful application, including site selection guidelines, technical and geological factors, and the significance of storage characteristics. The integrity of wells and caprock, which is important for safe and efficient storage, can be affected by the operating dynamics of the hydrogen cycle, notably the fluctuations in pressure and stress within storage formations. To evaluate its potential for broader adoption, we also examined economic elements such as cost-effectiveness and the technical practicality of large-scale storage. We also reviewed current UHS efforts and identified key knowledge gaps, primarily in the areas of hydrogen–rock interactions, geochemistry, gas migration control, microbial activities, and geomechanical stability. Resolving these technological challenges, regulatory frameworks, and environmental sustainability are essential to UHS’s long-term and extensive integration into the energy industry. This article provides a roadmap for UHS research and development, emphasizing the need for further research to fully realize the technology’s promise as a pillar of the hydrogen economy. Full article

(This article belongs to the Special Issue Advances in Hydrogen Energy IV)

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23 pages, 3913 KiB

Open AccessEditor’s ChoiceArticle

Socio-Economic Impact Assessment of Hydrogen Injection in the Natural Gas Network

by Spyros Kyrimis, Petros Dimas, Dimitrios Stamopoulos and Aggelos Tsakanikas

Energies 2025, 18(3), 725; https://doi.org/10.3390/en18030725 - 5 Feb 2025

Viewed by 698

Abstract

This study explores the feasibility parameters of a potential investment plan for injecting “green” hydrogen into the existing natural gas supply network in Greece. To this end, a preliminary profitability optimization analysis was conducted through key performance indicators such as the cost of [...] Read more.

This study explores the feasibility parameters of a potential investment plan for injecting “green” hydrogen into the existing natural gas supply network in Greece. To this end, a preliminary profitability optimization analysis was conducted through key performance indicators such as the cost of hydrogen and the socio-environmental benefit of carbon savings, followed by break-even and sensitivity analyses. The identification of the major impact drivers of the assessment was based on the examination of a set of operational scenarios of varying hydrogen and natural gas flow rates. The results show that high natural gas capacities with a 5% hydrogen content by volume are the optimal case in terms of socio-economic viability, but the overall profitability is too sensitive to hydrogen pricing, rendering it unfeasible without additional motives, measures and pricing strategies. The results feed into the main challenge of implementing commercial “green” hydrogen infrastructures in the market in a sustainable and feasible manner. Full article

(This article belongs to the Special Issue Techno-Economic Analysis and Optimization for Energy Systems: 2nd Edition on the Way to Green Transition)

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31 pages, 3689 KiB

Open AccessEditor’s ChoiceArticle

Comparative Evaluation of the Effect of Exhaust Gas Recirculation Usage on the Performance Characteristics and Emissions of a Natural Gas/Diesel Compression-Ignition Engine Operating at Part-Load Conditions

by Nikolaos Rizopoulos and Roussos Papagiannakis

Energies 2025, 18(3), 710; https://doi.org/10.3390/en18030710 - 4 Feb 2025

Cited by 2 | Viewed by 667

Abstract

The use of natural gas as an alternative fuel in dual-fuel compression-ignition engines can lead to a substantial reduction in the majority of pollutant emissions compared to fossil fuels, while the thermal efficiency of the engine can be maintained at adequate levels. Its [...] Read more.

The use of natural gas as an alternative fuel in dual-fuel compression-ignition engines can lead to a substantial reduction in the majority of pollutant emissions compared to fossil fuels, while the thermal efficiency of the engine can be maintained at adequate levels. Its usage has increased widely in recent years, and significant efforts have been made to investigate the inherent physical and chemical processes that take place during this engine’s combustion, as well as the parameters that affect the operation of the engine and use natural gas as energy source. The scope of this study is to investigate the effect of EGR temperature (cold and hot) and rate (10% and 20%) on the performance characteristics and emissions of a dual-fuel compression-ignition engine operating at a specific engine operating point under dual-fuel (diesel–natural gas) conditions. For this reason, a phenomenological two-zone combustion model was developed. The results of the model were validated against the experimental data obtained from a single-cylinder direct-injection, turbocharged compression-ignition dual-fuel research engine operated under part-load conditions (IMEP = 0.52 Mpa and engine speed = 1500 rpm) and at various replacement percentages of diesel using methane (which was treated as a natural gas surrogate). The model results were in good agreement with the experimental results, revealing the ability of the model to be used in the aforementioned EGR analysis. The results of the study revealed that engine operation with 10% cold EGR does not significantly affect the engine performance characteristics, and combined with the addition of 80% gaseous fuel energy, can lead to a substantial reduction in NO and soot emissions, with a moderate increase in CO emissions. On the other hand, a significant finding of the present work is that engine operation with hot EGR under the investigated operating conditions, even though it had a beneficial effect on NO-specific emissions, led to a reduction in engine efficiency and may raise issues regarding the mechanical strength of the engine. Full article

(This article belongs to the Special Issue Internal Combustion Engine Performance 2024)

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53 pages, 4256 KiB

Open AccessEditor’s ChoiceReview

Nanofluids in Thermal Energy Storage Systems: A Comprehensive Review

by Mohamed Shameer Peer, Mario Cascetta, Luca Migliari and Mario Petrollese

Energies 2025, 18(3), 707; https://doi.org/10.3390/en18030707 - 4 Feb 2025

Cited by 2 | Viewed by 1284

Abstract

Nanofluids, which consist of nanosized particles dispersed in a base fluid, represent a promising solution to improve the performance of thermal energy storage systems. This review offers a comprehensive overview of nanofluids and their applications in thermal energy storage systems, discussing their thermal [...] Read more.

Nanofluids, which consist of nanosized particles dispersed in a base fluid, represent a promising solution to improve the performance of thermal energy storage systems. This review offers a comprehensive overview of nanofluids and their applications in thermal energy storage systems, discussing their thermal properties, heat transfer mechanisms, synthesis techniques, and application in latent heat storage systems. Various types of nanofluids are examined, including metal oxide, carbon-based, and metallic nanofluids, highlighting their effects on thermal conductivity, latent heat and the phase change temperature. A review of experimental and numerical studies showcases the performance of thermal energy storage systems incorporating nanofluids and the factors influencing their thermophysical characteristics and energy storage capacity. Finally, the key findings of current research are summarized, as well as the challenges and the potential future directions in nanofluid-based thermal energy storage systems research, emphasizing the need to optimize nanoparticle concentration and long-term durability. Full article

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

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41 pages, 1629 KiB

Open AccessEditor’s ChoiceReview

Production and Storage of Hydrogen from Biomass and Other Sources: Technologies and Policies

by Georgios Giakoumakis and Dimitrios Sidiras

Energies 2025, 18(3), 650; https://doi.org/10.3390/en18030650 - 30 Jan 2025

Cited by 1 | Viewed by 2469

Abstract

Hydrogen has emerged as a critical energy carrier for achieving global decarbonization and supporting a sustainable energy future. This review explores key advancements in hydrogen production technologies, including electrolysis, biomass gasification, and thermochemical processes, alongside innovations in storage methods like metal hydrides and [...] Read more.

Hydrogen has emerged as a critical energy carrier for achieving global decarbonization and supporting a sustainable energy future. This review explores key advancements in hydrogen production technologies, including electrolysis, biomass gasification, and thermochemical processes, alongside innovations in storage methods like metal hydrides and liquid organic hydrogen carriers (LOHCs). Despite its promise, challenges such as high production costs, scalability issues, and safety concerns persist. Biomass gasification stands out for its dual benefits of waste management and carbon neutrality yet hurdles like feedstock variability and energy efficiency need further attention. This review also identifies opportunities for improvement, such as developing cost-effective catalysts and hybrid storage systems, while emphasizing future research on improving storage efficiency and tackling production bottlenecks. By addressing these challenges, hydrogen can play a central role in the global transition to cleaner energy systems. Full article

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

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15 pages, 5535 KiB

Open AccessEditor’s ChoiceArticle

Numerical Simulation of the Transition to Detonation in a Hydrogen–Air Mixture Due to Shock Wave Focusing on a 90-Degree Wedge

by Jose Bermudez De La Hoz, Wojciech Rudy and Andrzej Teodorczyk

Energies 2025, 18(3), 619; https://doi.org/10.3390/en18030619 - 29 Jan 2025

Cited by 2 | Viewed by 800

Abstract

This study numerically explores the initiation of detonation through shock wave reflection and focusing on a 90-degree wedge in varying mixtures of hydrogen–air. The simulations were conducted using the ddtFoam code, an integral part of the OpenFOAM open-source Computational Fluid Dynamics (CFD) package [...] Read more.

This study numerically explores the initiation of detonation through shock wave reflection and focusing on a 90-degree wedge in varying mixtures of hydrogen–air. The simulations were conducted using the ddtFoam code, an integral part of the OpenFOAM open-source Computational Fluid Dynamics (CFD) package of density-based code for solving the unsteady, compressible Navier–Stokes equations. The simulation results unveil three potential outcomes in the corner post-reflection: deflagrative ignition in the corner, deflagrative ignition with intermediate transient phases leading to a delayed transition to detonation in the trailing combustion zone close to the apex of the wedge, and ignition with an immediate transition to detonation, resulting in the formation of a detonation wave in the corner tip. In the experimental investigation, the transition velocity for the stoichiometric mixture stood at approximately 719 m/s. In contrast, the numerical simulation indicated a transition velocity of 664 m/s for the same stoichiometric mixture, reflecting a 5.5% decrease in velocity. Such an underestimation level of 5–8% by the simulation results was observed for mixtures of 25–45% H₂ in air. Full article

(This article belongs to the Section I2: Energy and Combustion Science)

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39 pages, 3474 KiB

Open AccessEditor’s ChoiceReview

Hydrogen as a Renewable Fuel of Non-Biological Origins in the European Union—The Emerging Market and Regulatory Framework

by Andrzej Graczyk, Paweł Brusiło and Alicja Małgorzata Graczyk

Energies 2025, 18(3), 617; https://doi.org/10.3390/en18030617 - 29 Jan 2025

Cited by 1 | Viewed by 1091

Abstract

The European Union continues to lead global efforts toward climate neutrality by developing a cohesive regulatory and market framework for alternative fuels, including renewable hydrogen. This review article critically examines the recent evolution of the EU’s policy landscape specifically for hydrogen as a [...] Read more.

The European Union continues to lead global efforts toward climate neutrality by developing a cohesive regulatory and market framework for alternative fuels, including renewable hydrogen. This review article critically examines the recent evolution of the EU’s policy landscape specifically for hydrogen as a renewable fuel of non-biological origin (RFNBO), highlighting its growing importance in hard-to-abate sectors such as industry and transportation. We assess the interplay of market-based mechanisms (e.g., EU ETS II), direct mandates (e.g., FuelEU Maritime, RED III), and support auction-based measures (e.g., the European Hydrogen Bank) that collectively shape both the demand and the supply of hydrogen as RFNBO fuel. The article also addresses emerging cost, capacity, and technical barriers—ranging from constrained electrolyzer deployment to complex certification requirements—that hinder large-scale adoption and market rollout. The article aims to discuss advancing and changing regulatory and market environment for the development of infrastructure and market for hydrogen as RFNBO fuel in the EU in 2019–2024. Synthesizing current research and policy developments, we propose targeted recommendations, including enhanced cross-border coordination and capacity-based incentives, to accelerate investment and infrastructure development. This review informs policymakers, industry stakeholders, and researchers on critical success factors for integrating hydrogen as a cornerstone of the EU’s climate neutrality efforts. Full article

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

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24 pages, 1117 KiB

Open AccessEditor’s ChoiceReview

Navigating the Intersection of Microgrids and Hydrogen: Evolutionary Trends, Challenges, and Future Strategies

by Bawantha Indrajith and Kosala Gunawardane

Energies 2025, 18(3), 614; https://doi.org/10.3390/en18030614 - 28 Jan 2025

Viewed by 1069

Abstract

Growing interest in sustainable energy has gathered significant attention for alternative technologies, with hydrogen-based solutions emerging as a crucial component in the transition to cleaner and more resilient energy systems. Following that, hydrogen-based microgrids, integrated with renewable energy sources including wind and solar, [...] Read more.

Growing interest in sustainable energy has gathered significant attention for alternative technologies, with hydrogen-based solutions emerging as a crucial component in the transition to cleaner and more resilient energy systems. Following that, hydrogen-based microgrids, integrated with renewable energy sources including wind and solar, have gained substantial attention as an upcoming pathway toward long-term energy sustainability. Hydrogen, produced through processes such as electrolysis and steam methane reforming, can be stored in various forms including compressed gas, liquid, or solid-state hydrides, and later utilized for electricity generation through fuel cells and gas turbines. This dynamic energy system offers highly flexible, scalable, and resilient solutions for various applications. Specifically, hydrogen-based microgrids are particularly suitable for offshore and islanded applications, with geographical factors, adverse environmental conditions, and limited access to conventional energy solutions. This is critical for energy independence, long-term storage capacity, and grid stability. This review explores topological and functional-based classifications of microgrids, advancements in hydrogen generation, storage, and utilization technologies, and their integration with microgrid systems. It also critically evaluates the key challenges of each technology, including cost, efficiency, and scalability, which impact the feasibility of hydrogen microgrids. Full article

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

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29 pages, 5384 KiB

Open AccessEditor’s ChoiceArticle

Analysis and Evaluation of a TCO₂ Electrothermal Energy Storage System with Integration of CO₂ Geological Storage

by Aristeidis Stoikos, Alexios-Spyridon Kyriakides, Júlio Carneiro, Dounya Behnous, Georgios Gravanis, Ioannis N. Tsimpanogiannis, Panos Seferlis and Spyros Voutetakis

Energies 2025, 18(3), 601; https://doi.org/10.3390/en18030601 - 27 Jan 2025

Viewed by 702

Abstract

The goal to reduce greenhouse gas emissions necessitates the increase in RES utilization. To accomplish this goal, energy storage solutions are required. This study investigates the performance of an electrothermal energy storage system, the CEEGS, which consists of an above-surface energy storage system [...] Read more.

The goal to reduce greenhouse gas emissions necessitates the increase in RES utilization. To accomplish this goal, energy storage solutions are required. This study investigates the performance of an electrothermal energy storage system, the CEEGS, which consists of an above-surface energy storage system and a below-surface geological system. The focus is set initially on the analysis of the above-surface system to gain insight into its operation. Then, steady-state optimization is utilized to identify the operating conditions that maximize the system performance, before investigating the below-surface system integration and the effect that the geological conditions have on system performance. For the above-surface system, efficiency (η_R-T) up to 46.89% is calculated. For systems integrated with CO₂ geological storage, two case studies are examined, presenting higher η_R-T compared to the above-surface system (Case study 1: 50.37%, Case study 2: 67.39%). The optimal η_R-T for Case study 2 is achieved for higher injection/production pressures and temperatures conditions and minimal ΔP and ΔT between injection and production. In conclusion, it is the selection of the geological storage conditions that contribute the most to the optimal η_R-T; thus, the selection of the appropriate geological storage formation is imperative. Full article

(This article belongs to the Collection Renewable Energy and Energy Storage Systems)

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37 pages, 3837 KiB

Open AccessEditor’s ChoiceReview

Review: Overview of Organic Cathode Materials in Lithium-Ion Batteries and Supercapacitors

by Andekuba Andezai and Jude O. Iroh

Energies 2025, 18(3), 582; https://doi.org/10.3390/en18030582 - 26 Jan 2025

Cited by 1 | Viewed by 1171

Abstract

Organic materials have emerged as promising candidates for cathode materials in lithium-ion batteries and supercapacitors, offering unique properties and advantages over traditional inorganic counterparts. This review investigates the use of organic compounds as cathode materials in energy storage devices, focusing on their application [...] Read more.

Organic materials have emerged as promising candidates for cathode materials in lithium-ion batteries and supercapacitors, offering unique properties and advantages over traditional inorganic counterparts. This review investigates the use of organic compounds as cathode materials in energy storage devices, focusing on their application in lithium-ion batteries and supercapacitors. The review covers various types of organic materials, organosulfur compounds, organic free radical compounds, organic carbonyl compounds, conducting polymers, and imine compounds. The advantages, challenges, and ongoing developments in this area are examined and the potential of organic cathode materials to achieve higher energy density, improved cycling stability, and environmental sustainability is highlighted. The comprehensive analysis of organic cathode materials provides insights into their electrochemical performance, electrode reaction mechanisms, and design strategies such as molecular structure modification, hybridization with inorganic components, porous architectures, conductive additives, electrolyte optimization, binder selection, and electrode architecture to improve their efficiency and performance. In addition, future research in the field of organic cathode materials should focus on addressing current limitations such as low energy density, cycling stability, poor discharge capability, potential safety concerns and improving their performance. To do this, it will be necessary to improve structural stability, conductivity, cycle life, and capacity fading, explore new redox-active organic compounds, and pave the way for the next generation of high-performance energy storage devices. For organic cathode materials to be commercially viable, it is also essential to develop scalable and economical manufacturing processes. Full article

(This article belongs to the Topic Advanced Polymeric Composites: Processing, Characterization and Mechanical Behavior)

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29 pages, 12145 KiB

Open AccessEditor’s ChoiceArticle

Influence of Biodiesel from Used Cooking Oil and Sunflower Oil on Engine Efficiency and Emission Profiles

by Ruxandra-Cristina Stanescu, Adrian Soica and Cristian-Ioan Leahu

Energies 2025, 18(3), 583; https://doi.org/10.3390/en18030583 - 26 Jan 2025

Cited by 1 | Viewed by 654

Abstract

This study evaluates the performance and emissions characteristics of a compression ignition engine fueled with biodiesel blends derived from used cooking oil (UO) and sunflower oil (SF) at concentrations of 5%, 10%, 20%, and 50%. Tests were conducted under different load conditions (20%, [...] Read more.

This study evaluates the performance and emissions characteristics of a compression ignition engine fueled with biodiesel blends derived from used cooking oil (UO) and sunflower oil (SF) at concentrations of 5%, 10%, 20%, and 50%. Tests were conducted under different load conditions (20%, 50%, and 100%) across engine speeds ranging from 1500 to 3600 rpm, focusing on effective power, torque, brake specific fuel consumption (BSFC), and emissions of NOx, CO, HC, particulate matter (PM), smoke, and CO₂. Consistent engine operating conditions were maintained for all fuel blends. The results indicated that increasing the biodiesel concentration led to a decrease in brake power and torque—up to 3.18% reduction for SF50 compared to diesel—due to the lower calorific value of biodiesel. For SF biodiesel, the BSFC increased with higher biodiesel content, while for UO biodiesel the results varied across concentrations. Emissions analysis revealed lower CO and HC at 2500 rpm for all biodiesel blends relative to diesel, while NOx emissions varied depending on fuel type and concentration. In terms of particles, both PM and smoke were measured, and while PM showed different results across blends, smoke was lower for all blends compared to diesel. Our overall analysis shows that biodiesel blends up to 20% can be effectively used in diesel engines without substantial modifications, offering a balance between performance and reduced emissions. Full article

(This article belongs to the Special Issue Renewable Fuels for Internal Combustion Engines: 2nd Edition)

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41 pages, 6644 KiB

Open AccessEditor’s ChoiceReview

Phase Change Materials in Electrothermal Conversion Systems: A Review

by Rafał Twaróg, Piotr Szatkowski and Kinga Pielichowska

Energies 2025, 18(3), 569; https://doi.org/10.3390/en18030569 - 25 Jan 2025

Cited by 1 | Viewed by 886

Abstract

Green energy harvesting is one of the most important and evolving research areas. Solar energy is an inexhaustible and environmentally friendly energy source, and phase change materials (PCMs) are capable of improving photovoltaic devices by heat storage and could have a positive impact [...] Read more.

Green energy harvesting is one of the most important and evolving research areas. Solar energy is an inexhaustible and environmentally friendly energy source, and phase change materials (PCMs) are capable of improving photovoltaic devices by heat storage and could have a positive impact on sustainable energy utilization. This review presents the current state of the art on PCMs and their modifications for electrothermal energy conversion applications. The paper focuses on PCMs characteristics and their properties required for electrothermal energy conversion systems, and it presents various methods of PCMs modification intended to obtain multifunctional systems based on these materials as well as electrothermal conversion and energy storage mechanisms and selected applications. The goal of this review is to present different types of PCM modifications to obtain multifunctional PCM-based systems for electrothermal energy conversion. Full article

(This article belongs to the Collection Renewable Energy and Energy Storage Systems)

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38 pages, 6187 KiB

Open AccessEditor’s ChoiceReview

A Review of Reliability Assessment and Lifetime Prediction Methods for Electrical Machine Insulation Under Thermal Aging

by Jian Zhang, Jiajin Wang, Hongbo Li, Qin Zhang, Xiangning He, Cui Meng, Xiaoyan Huang, Youtong Fang and Jianwei Wu

Energies 2025, 18(3), 576; https://doi.org/10.3390/en18030576 - 25 Jan 2025

Cited by 1 | Viewed by 1384

Abstract

The thermal aging of insulation systems in electrical machines is a critical factor influencing their reliability and lifetime, particularly in modern high-performance electrical equipment. However, evaluating and predicting insulation lifetime under thermal aging poses significant challenges due to the complex aging mechanisms. Thermal [...] Read more.

The thermal aging of insulation systems in electrical machines is a critical factor influencing their reliability and lifetime, particularly in modern high-performance electrical equipment. However, evaluating and predicting insulation lifetime under thermal aging poses significant challenges due to the complex aging mechanisms. Thermal aging not only leads to the degradation of macroscopic properties such as dielectric strength and breakdown voltage but also causes progressive changes in the microstructure, making the correlation between aging stress and aging indicators fundamental for lifetime evaluation and prediction. This review first summarizes the performance indicators reflecting insulation thermal aging. Subsequently, it systematically reviews current methods for reliability assessment and lifetime prediction in the thermal aging process of electrical machine insulation, with a focus on the application of different modeling approaches such as physics-of-failure (PoF) models, data-driven models, and stochastic process models in insulation lifetime modeling. The theoretical foundations, modeling processes, advantages, and limitations of each method are discussed. In particular, PoF-based models provide an in-depth understanding of degradation mechanisms to predict lifetime, but the major challenge remains in dealing with complex failure mechanisms that are not well understood. Data-driven methods, such as artificial intelligence or curve-fitting techniques, offer precise predictions of complex nonlinear relationships. However, their dependence on high-quality data and the lack of interpretability remain limiting factors. Stochastic process models, based on Wiener or Gamma processes, exhibit clear advantages in addressing the randomness and uncertainty in degradation processes, but their applicability in real-world complex operating conditions requires further research and validation. Furthermore, the potential applications of thermal lifetime models, such as electrical machine design optimization, fault prognosis, health management, and standard development are reviewed. Finally, future research directions are proposed, highlighting opportunities for breakthroughs in model coupling, multi-physical field analysis, and digital twin technology. These insights aim to provide a scientific basis for insulation reliability studies and lay the groundwork for developing efficient lifetime prediction tools. Full article

(This article belongs to the Special Issue Power Electronic Converter and Its Control)

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29 pages, 3098 KiB

Open AccessEditor’s ChoiceArticle

A Novel Decision-Support Framework for Supporting Renewable Energy Technology Siting in the Early Design Stage of Microgrids: Considering Geographical Conditions and Focusing on Resilience and SDGs

by Bharath Kumar Sugumar and Norma Anglani

Energies 2025, 18(3), 544; https://doi.org/10.3390/en18030544 - 24 Jan 2025

Cited by 1 | Viewed by 937

Abstract

This research is focused on microgrid design supporting tools and presents an innovative framework for renewable energy (RE) sources’ site selection, integrating multicriteria decision-making (MCDM) methods with resilience considerations and alignment to the Sustainable Development Goals (SDGs). It addresses present climatic challenges, identifies [...] Read more.

This research is focused on microgrid design supporting tools and presents an innovative framework for renewable energy (RE) sources’ site selection, integrating multicriteria decision-making (MCDM) methods with resilience considerations and alignment to the Sustainable Development Goals (SDGs). It addresses present climatic challenges, identifies key causes of possible power failures, and develops strategies to mitigate their effects, while providing tools for energy managers and decision-makers to select suitable RE sources/technologies, based on geographical and sustainability criteria. The framework categorizes criteria into quantitative and qualitative types, adopting a cost (

C

)- and benefit (

B

)-based approach. The Analytic Hierarchy Process (AHP) calculates criteria weights to ensure accuracy and compatibility in decision-making, integrating SDG objectives into the evaluation process. This study focuses on five major RE options, photovoltaic (PV), wind, wave, tidal, and geothermal, analyzing more than 50 criteria for each energy type. This evaluation incorporates the expertise of over 50 experts and case studies, making it one of the most extensive research efforts in RE site selection. By systematically addressing resilience challenges and linking them with SDG priorities, this study provides a robust framework for evaluating and optimizing RE options. Its methodologies offer significant contributions to advancing sustainable energy development and enhancing energy systems’ resilience to climate and infrastructural challenges. Full article

(This article belongs to the Special Issue Planning, Operation, Control and Economics of Renewable and Smart Energy Systems)

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19 pages, 9490 KiB

Open AccessEditor’s ChoiceArticle

Research on the Randomness of Low-Voltage AC Series Arc Faults Based on the Improved Cassie Model

by Yao Wang, Yuying Liu, Xin Ning, Dejie Sheng and Tianle Lan

Energies 2025, 18(3), 538; https://doi.org/10.3390/en18030538 - 24 Jan 2025

Cited by 1 | Viewed by 625

Abstract

Low-voltage AC power lines are prone to arc faults, and an arc current presents as a random and complicated signal. The amplitude of the line current remains relatively unchanged during the occurrence of series arcs, hence complicating the detection of series arc faults. [...] Read more.

Low-voltage AC power lines are prone to arc faults, and an arc current presents as a random and complicated signal. The amplitude of the line current remains relatively unchanged during the occurrence of series arcs, hence complicating the detection of series arc faults. In this work, we developed a low-voltage series arc fault test platform to analyze the digital features of low-voltage series arc currents and the morphology of arc combustion, as the current model fails to capture the high-frequency and randomness of arc currents. An analysis of the physical causes and influencing factors of the random distribution of AC arc zero-crossing times was conducted. A time-domain simulation model for arc fault currents was developed by enhancing the time constant of the Cassie arc model, while the high-frequency features of arc currents were simulated using a segmented noise model. The measured arc current data were utilized to validate the model through the analysis of the zero-crossing time distribution of arc current, the correlation coefficient of the arc current frequency-domain signal, and the similarity of the time-domain waveforms. When comparing the similarity of the simulated waveforms of the arc model presented in this research and those of other traditional arc models, it was found that the suggested model effectively characterizes the time-/frequency-domain features of low-voltage AC series arc fault currents. The suggested model enhances the features of randomness in low-voltage AC series arc faults and is important in extracting essential aspects and reliably recognizing low-voltage series arc faults. Full article

(This article belongs to the Section F: Electrical Engineering)

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16 pages, 1763 KiB

Open AccessEditor’s ChoiceArticle

Lessons Learned from Four Real-Life Case Studies: Energy Balance Calculations for Implementing Positive Energy Districts

by Helmut Bruckner, Svitlana Alyokhina, Simon Schneider, Manuela Binder, Zain Ul Abdin, Rudi Santbergen, Maarten Verkou, Miro Zeman, Olindo Isabella, Marco Pagliarini, Cristiana Botta and Ana Streche

Energies 2025, 18(3), 560; https://doi.org/10.3390/en18030560 - 24 Jan 2025

Cited by 1 | Viewed by 1102

Abstract

Positive Energy Districts (PEDs) are integral to achieving sustainable urban development by enhancing energy self-sufficiency and reducing carbon emissions. This paper explores energy balance calculations in four diverse case study districts within different climatic conditions—Fiat Village in Settimo Torinese (Italy), Großschönau (Austria), Beursplain [...] Read more.

Positive Energy Districts (PEDs) are integral to achieving sustainable urban development by enhancing energy self-sufficiency and reducing carbon emissions. This paper explores energy balance calculations in four diverse case study districts within different climatic conditions—Fiat Village in Settimo Torinese (Italy), Großschönau (Austria), Beursplain in Amsterdam (Netherlands), and Lunca Pomostului in Reşiţa (Romania)—as part of the SIMPLY Positive project. Each district faces unique challenges, such as outdated infrastructure or heritage protection, which we address through tailored strategies including building renovations and the integration of renewable energy systems. Additionally, we employ advanced simulation methodologies to assess energy performance. Simulation results highlight the significance of innovative technologies like photovoltaic-thermal (PVT) systems, application of demand-side actions, and flexible grid usage. Furthermore, mobility assessments and resident-driven initiatives demonstrate the critical role of community engagement in reducing carbon footprints. This study underscores the adaptability of PED frameworks across varied urban contexts and provides actionable insights for scaling similar strategies globally, supporting net-zero energy targets. Full article

(This article belongs to the Special Issue Advanced Energy Systems in Energy Resilient, Zero/Positive Energy Buildings, Communities and Districts)

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34 pages, 7894 KiB

Open AccessEditor’s ChoiceReview

Comprehensive Review of Bearing Currents in Electrical Machines: Mechanisms, Impacts, and Mitigation Techniques

by Tianyi Pei, Hengliang Zhang, Wei Hua and Fengyu Zhang

Energies 2025, 18(3), 517; https://doi.org/10.3390/en18030517 - 23 Jan 2025

Cited by 2 | Viewed by 1442

Abstract

The present paper deals with a review on bearing currents in electrical machines, with major emphasis on mechanisms, impacts, and mitigation strategies. High-frequency common-mode voltages from the inverter-driven system have been found to be the main reason for bearing current leading to motor [...] Read more.

The present paper deals with a review on bearing currents in electrical machines, with major emphasis on mechanisms, impacts, and mitigation strategies. High-frequency common-mode voltages from the inverter-driven system have been found to be the main reason for bearing current leading to motor bearing degradation and eventual failure. This paper deals with bearing currents—electrical discharge machining (EDM) currents, circulating bearing currents, and rotor-to-ground bearing currents—and the various methods of their generation and effects that are harmful to the bearings and lubricants of a motor. Mitigation techniques, among which the following have been taken into account, are studied in this context: the optimization of PWM modulation, and the use of shaft grounding brushes, insulated bearings, and passive or active filters. Finally, advantages, limitations, and implementation challenges are discussed. A review comparing three-phase and dual three-phase inverters showed that, due to the increased degree of freedom in modulation strategies, it is possible to eliminate common-mode voltages through active modulation techniques. Such added flexibility will reduce the risk of bearing currents effectively. It also highlights future research directions in bearing current suppression, including the development of multi-phase motor systems, real-time monitoring technologies with artificial intelligence, and the use of new insulation materials for the enhancement of bearing reliability. The results obtained should guide future research and engineering practices in suppressing bearing currents to improve motor durability with high performance. Full article

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

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43 pages, 4744 KiB

Open AccessEditor’s ChoiceReview

A Detailed Review of Organic Rankine Cycles Driven by Combined Heat Sources

by Dimitra Gonidaki and Evangelos Bellos

Energies 2025, 18(3), 526; https://doi.org/10.3390/en18030526 - 23 Jan 2025

Cited by 1 | Viewed by 2174

Abstract

The Organic Rankine Cycle (ORC) is an effective method for transforming low- and medium-grade heat into electricity that has recently gained significant attention. Several review studies in the literature are focused on working fluids, system architecture, and the individual utilization of renewable and [...] Read more.

The Organic Rankine Cycle (ORC) is an effective method for transforming low- and medium-grade heat into electricity that has recently gained significant attention. Several review studies in the literature are focused on working fluids, system architecture, and the individual utilization of renewable and alternative heat sources in ORCs, like solar irradiation, geothermal, biomass, and waste heat energy. However, no studies have yet investigated ORC systems driven by two of the aforementioned sources combined. This work aims to review and explore multiple aspects of hybrid ORC systems. Such systems are categorized based on source combinations and configurations, and the results regarding their thermodynamic, thermo-economic, and environmental performance are discussed. The source arrangements follow the following three main configurations: series, parallel, and heat upgrade. Most of the examined systems include solar energy as one of the sources and only four cases involve combinations of the other three sources. The reported results show that hybrid ORCs generally perform better thermodynamically compared to their respective single-source systems, exhibiting an enhancement in power production that reaches 44%. An average levelized cost of energy (LCOE) of 0.165 USD/kWh was reported for solar–geothermal plants, 0.153 USD/kWh for solar–biomass plants, and 0.100 USD/kWh for solar–waste plants. Solar–biomass plants also reported the lowest reported LCOE value of 0.098 USD/kWh. The payback periods ranged from 2.88 to 10.5 years. Further research is proposed on multiple source combinations, the in-depth analysis of the three main configurations, the integration of polygeneration systems, the incorporation of zeotropic mixture working media and experimental research on ORCs with combined sources. Full article

(This article belongs to the Special Issue Investigations of Heat Transfer with Estimation of Temperature Uncertainty Measurements)

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26 pages, 8105 KiB

Open AccessEditor’s ChoiceReview

A Review of Ignition Characteristics and Prediction Model of Combustor Under High-Altitude Conditions

by Yuhui Zhu, Shaolin Wang, Kaixing Wang, Yushuai Liu, Cunxi Liu, Fuqiang Liu, Jinhu Yang, Yong Mu and Gang Xu

Energies 2025, 18(3), 527; https://doi.org/10.3390/en18030527 - 23 Jan 2025

Viewed by 862

Abstract

High-altitude relight is a critical challenge for aero-engines, directly impacting the safety and emergency response capabilities of aircraft. This paper systematically reviews the physical mechanisms, key factors, and relevant prediction models of high-altitude relight, highlighting the detrimental effects of extreme conditions such as [...] Read more.

High-altitude relight is a critical challenge for aero-engines, directly impacting the safety and emergency response capabilities of aircraft. This paper systematically reviews the physical mechanisms, key factors, and relevant prediction models of high-altitude relight, highlighting the detrimental effects of extreme conditions such as low pressure and temperature on fuel evaporation rates, flame propagation speeds, and turbulent combustion processes. A comprehensive overview of the current state of high-altitude relight research is presented, alongside recommendations for enhancing the ignition performance of aero-engines under extreme conditions. This paper focuses on the development of ignition prediction models, including early empirical and semi-empirical models, as well as physics-based models for turbulent flame propagation and flame kernel tracking, assessing their applicability in high-altitude relight scenarios. Although flame kernel tracking has shown satisfactory performance in predicting ignition probability, it still overly relies on manually set parameters and lacks precise descriptions of the physical processes of flame kernel generation. Future studies on some topics, including refining flame kernel modeling, strengthening the integration of experimental data and numerical simulations, and exploring the incorporation of new ignition technologies, are needed, to further improve model reliability and predictive capability. Full article

(This article belongs to the Section I2: Energy and Combustion Science)

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27 pages, 4157 KiB

Open AccessEditor’s ChoiceReview

Review of Thermal Management Techniques for Prismatic Li-Ion Batteries

by Nasim Saber, Christiaan Petrus Richter and Runar Unnthorsson

Energies 2025, 18(3), 492; https://doi.org/10.3390/en18030492 - 22 Jan 2025

Viewed by 1837

Abstract

This review presents a comprehensive analysis of battery thermal management systems (BTMSs) for prismatic lithium-ion cells, focusing on air and liquid cooling, heat pipes, phase change materials (PCMs), and hybrid solutions. Prismatic cells are increasingly favored in electric vehicles and energy storage applications [...] Read more.

This review presents a comprehensive analysis of battery thermal management systems (BTMSs) for prismatic lithium-ion cells, focusing on air and liquid cooling, heat pipes, phase change materials (PCMs), and hybrid solutions. Prismatic cells are increasingly favored in electric vehicles and energy storage applications due to their high energy content, efficient space utilization, and improved thermal management capabilities. We evaluate the effectiveness, advantages, and challenges of each thermal management technique, emphasizing their impact on performance, safety, and the lifespan of prismatic Li-ion batteries. The analysis reveals that while traditional air and liquid cooling methods remain widely used, 80% of the 21 real-world BTMS samples mentioned in this review employ liquid cooling. However, emerging technologies such as PCM and hybrid systems offer superior thermal regulation, particularly in high-power applications. However, both PCM and hybrid systems come with significant challenges; PCM systems are limited by their low thermal conductivity and material melting points. While hybrid systems face complexity, cost, and potential reliability concerns due to their multiple components nature. This review underscores the need for continued research into advanced BTMSs to optimize energy efficiency, safety, and longevity for prismatic cells in electric vehicle applications and beyond. Full article

(This article belongs to the Special Issue Challenges and Opportunities Towards Lithium-Ion Batteries)

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21 pages, 2320 KiB

Open AccessEditor’s ChoiceReview

Advancements and Challenges in Direct Air Capture Technologies: Energy Intensity, Novel Methods, Economics, and Location Strategies

by Janusz Kotowicz, Kamil Niesporek and Oliwia Baszczeńska

Energies 2025, 18(3), 496; https://doi.org/10.3390/en18030496 - 22 Jan 2025

Cited by 2 | Viewed by 2310

Abstract

Direct air capture (DAC) technology is increasingly recognized as a key tool in the pursuit of climate neutrality, enabling the removal of carbon dioxide directly from the atmosphere. Despite its potential, DAC remains in the early stages of development, with most installations limited [...] Read more.

Direct air capture (DAC) technology is increasingly recognized as a key tool in the pursuit of climate neutrality, enabling the removal of carbon dioxide directly from the atmosphere. Despite its potential, DAC remains in the early stages of development, with most installations limited to pilot or demonstration units. The main barriers to its widespread implementation include high energy demands and significant capture costs. This literature review addresses the most critical research directions related to the development of this technology, focusing on its challenges and prospects for deployment. Particular attention is given to studies aimed at developing new, cost-effective, and efficient sorbents that could significantly reduce the energy intensity and costs of the process. Alternative technologies, such as electrochemical and membrane-based processes, show promise but require further research to overcome limitations, such as sensitivity to oxygen presence or insufficient membrane selectivity. The economic feasibility of DAC remains uncertain, with current estimates subject to significant uncertainty. Governmental and regulatory support will be crucial for the technology’s success. Furthermore, the location of DAC installations should consider factors such as energy availability, options for carbon dioxide storage or utilization, and climatic conditions, which significantly affect process efficiency. This review highlights the necessity for continued research to overcome existing barriers and fully harness the potential of DAC technology. Full article

(This article belongs to the Special Issue Energy Management: Economic, Social, and Ecological Aspects)

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21 pages, 2348 KiB

Open AccessEditor’s ChoiceReview

Minimizing the Environmental Impact of Aircraft Engines with the Use of Sustainable Aviation Fuel (SAF) and Hydrogen

by Łukasz Brodzik, Wojciech Prokopowicz, Bartosz Ciupek and Andrzej Frąckowiak

Energies 2025, 18(3), 472; https://doi.org/10.3390/en18030472 - 21 Jan 2025

Cited by 2 | Viewed by 1989

Abstract

Adverse climate change has forced a deeper reflection on the scale of pollution related to human activity, including in the aviation industry. As a result, fundamental questions have arisen about the characteristics of these pollutants, the mechanisms of their formation and potential strategies [...] Read more.

Adverse climate change has forced a deeper reflection on the scale of pollution related to human activity, including in the aviation industry. As a result, fundamental questions have arisen about the characteristics of these pollutants, the mechanisms of their formation and potential strategies for reducing them. This paper provides a comprehensive overview of key technical solutions to minimize the environmental impact of aircraft engines. The solutions presented range from fuel innovations to advanced design changes and drive concepts. Particular attention was paid to sustainable aviation fuels (SAFs), which are currently an important element of the environmental strategy regulated by the European Union. It also discusses the potential use of hydrogen as a potential alternative fuel to replace traditional aviation fuels in the long term. The analysis in the article made it possible to characterize in detail possible modifications in the functioning of aircraft engines, based both on the current state of technical knowledge and on the anticipated directions of its development, which has not been a frequent issue in comprehensive research so far. The analysis shows that the type of raw material used to create SAF has a strong impact on its physical and chemical parameters and the degree of greenhouse gas emissions. This necessitates a broader analysis of the legitimacy of using a given type of fuel from the SAF group in the direction of selected air operations and areas with a higher risk of severe atmospheric pollution. These results provide the basis for further research into sustainable solutions in the aviation sector that can contribute to significantly reducing its impact on climate change. Full article

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

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34 pages, 3761 KiB

Open AccessEditor’s ChoiceArticle

Enabling Power System Restoration from Offshore Wind Power Plants in the UK

by Rui Alves, Ning Yang, Lie Xu and Agustí Egea-Àlvarez

Energies 2025, 18(2), 436; https://doi.org/10.3390/en18020436 - 20 Jan 2025

Viewed by 1183

Abstract

This paper presents the findings from the initial phases of the SIF BLADE project, focused on demonstrating the capabilities of an offshore wind power plant (OWPP) for power system restoration (PSR). It provides an overview of PSR, highlighting its challenges and operational requirements, [...] Read more.

This paper presents the findings from the initial phases of the SIF BLADE project, focused on demonstrating the capabilities of an offshore wind power plant (OWPP) for power system restoration (PSR). It provides an overview of PSR, highlighting its challenges and operational requirements, alongside the various scenarios considered in the project. The study includes a steady-state analysis to assess whether the OWPP can meet local network demands for both active and reactive power. Results indicate that the OWPP can operate within an envelope that covers all local power requirements. Additionally, electromagnetic transient (EMT) analysis was conducted to evaluate different percentages of grid-forming (GFM) converter penetration during the energisation process. These analyses aimed to determine compliance with transmission system operator (TSO) requirements. Findings demonstrate that all GFM penetration levels met the necessary TSO standards. Furthermore, a novel small-signal analysis was performed to identify the optimal percentage of GFM converters for enhancing system stability during block loading. The analysis suggests that for top-up scenarios, a GFM penetration between 20% and 40% is optimal, while for anchor scenarios, 40% to 60% GFM penetration enhances stability and robustness. Full article

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

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21 pages, 1301 KiB

Open AccessEditor’s ChoiceReview

Artificial Intelligence in Automotives: ANNs’ Impact on Biodiesel Engine Performance and Emissions

by Ramozon Khujamberdiev and Haeng Muk Cho

Energies 2025, 18(2), 438; https://doi.org/10.3390/en18020438 - 20 Jan 2025

Cited by 4 | Viewed by 1374

Abstract

This paper explores the integration and advancements of artificial neural networks (ANNs) in modeling diesel engine performance, particularly focusing on biodiesel-fueled engines. ANNs have emerged as a vital tool in predicting and optimizing engine parameters, contributing to the enhancement of fuel efficiency and [...] Read more.

This paper explores the integration and advancements of artificial neural networks (ANNs) in modeling diesel engine performance, particularly focusing on biodiesel-fueled engines. ANNs have emerged as a vital tool in predicting and optimizing engine parameters, contributing to the enhancement of fuel efficiency and a reduction in emissions. The novelty of this review lies in its critical analysis of the existing literature on ANN applications in biodiesel engines, identifying gaps in optimization and emission control. While ANNs have shown promise in predicting engine parameters, fuel efficiency, and emission reduction, this paper highlights their limitations and areas for improvement, especially in the context of biodiesel-fueled engines. The integration of ANNs with big data and sophisticated algorithms paves the way for more accurate and reliable engine modeling, essential for advancing sustainable and eco-friendly automotive technologies. This research underscores the growing importance of ANNs in optimizing biodiesel-fueled diesel engines, aligning with global efforts towards cleaner and more sustainable energy solutions. Full article

(This article belongs to the Special Issue Sustainable Energy Development in Liquid Waste and Biomass: 2nd Edition)

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24 pages, 3649 KiB

Open AccessEditor’s ChoiceReview

Energy Supply Chains in the Digital Age: A Review of Current Research and Trends

by Agnieszka A. Tubis and Honorata Poturaj

Energies 2025, 18(2), 430; https://doi.org/10.3390/en18020430 - 19 Jan 2025

Cited by 1 | Viewed by 1738

Abstract

(1) Background: Digital transformation is critical in further developing the energy supply chain. The attainment of successive levels of digital maturity by chain participants translates into numerous benefits related to the efficiency, cost, and effectiveness of the energy flows implemented. However, the increasing [...] Read more.

(1) Background: Digital transformation is critical in further developing the energy supply chain. The attainment of successive levels of digital maturity by chain participants translates into numerous benefits related to the efficiency, cost, and effectiveness of the energy flows implemented. However, the increasing degree of digitalisation and automation generates an increased risk of cyberattacks and other challenges related to the operation of the smart grid. This paper presents the results of a literature review describing the phenomenon of digital transformation in the energy supply chain. (2) Methods: The literature review was performed using two review methods. First, a systematic literature review was conducted using the PRISMA method. However, due to unsatisfactory results, this review was supplemented by a search supporting a narrative review. (3) Results: Analysing the identified publications made it possible to distinguish nine leading research trends related to digital transformation in the energy supply chain. These trends were characterised based on the described research results, and all articles were classified into the corresponding categories. (4) Conclusions: The presented results provide interesting material for further research related to building resilience in the energy supply chain and selected Industry 4.0 tools for assessing and managing risks associated with the operation of the energy sector. Full article

(This article belongs to the Special Issue Blockchain, IoT and Smart Grids Challenges for Energy II)

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22 pages, 4295 KiB

Open AccessEditor’s ChoiceArticle

Spatiotemporal Variability in Wind Turbine Blade Leading Edge Erosion

by Sara C. Pryor, Jacob J. Coburn and Rebecca J. Barthelmie

Energies 2025, 18(2), 425; https://doi.org/10.3390/en18020425 - 19 Jan 2025

Viewed by 1005

Abstract

Wind turbine blade leading edge erosion (LEE) reduces energy production and increases wind energy operation and maintenance costs. Degradation of the blade coating and ultimately damage to the underlying blade structure are caused by collisions of falling hydrometeors with rotating blades. The selection [...] Read more.

Wind turbine blade leading edge erosion (LEE) reduces energy production and increases wind energy operation and maintenance costs. Degradation of the blade coating and ultimately damage to the underlying blade structure are caused by collisions of falling hydrometeors with rotating blades. The selection of optimal methods to mitigate/reduce LEE are critically dependent on the rates of coating fatigue accumulation at a given location and the time variance in the accumulation of material stresses. However, no such assessment currently exists for the United States of America (USA). To address this research gap, blade coating lifetimes at 883 sites across the USA are generated based on high-frequency (5-min) estimates of material fatigue derived using a mechanistic model and robust meteorological measurements. Results indicate blade coating failure at some sites in as few as 4 years, and that the frequency and intensity of material stresses are both highly episodic and spatially varying. Time series analyses indicate that up to one-third of blade coating lifetime is exhausted in just 360 5-min periods in the Southern Great Plains (SGP). Conversely, sites in the Pacific Northwest (PNW) exhibit the same level of coating lifetime depletion in over three times as many time periods. Thus, it may be more cost-effective to use wind turbine deregulation (erosion-safe mode) for damage reduction and blade lifetime extension in the SGP, while the application of blade leading edge protective measures may be more appropriate in the PNW. Annual total precipitation and mean wind speed are shown to be poor predictors of blade coating lifetime, re-emphasizing the need for detailed modeling studies such as that presented herein. Full article

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

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19 pages, 2202 KiB

Open AccessEditor’s ChoiceReview

Advanced Deep Learning Algorithms for Energy Optimization of Smart Cities

by Izabela Rojek, Dariusz Mikołajewski, Krzysztof Galas and Adrianna Piszcz

Energies 2025, 18(2), 407; https://doi.org/10.3390/en18020407 - 18 Jan 2025

Cited by 3 | Viewed by 3016

Abstract

Advanced deep learning algorithms play a key role in optimizing energy usage in smart cities, leveraging massive datasets to increase efficiency and sustainability. These algorithms analyze real-time data from sensors and IoT devices to predict energy demand, enabling dynamic load balancing and reducing [...] Read more.

Advanced deep learning algorithms play a key role in optimizing energy usage in smart cities, leveraging massive datasets to increase efficiency and sustainability. These algorithms analyze real-time data from sensors and IoT devices to predict energy demand, enabling dynamic load balancing and reducing waste. Reinforcement learning models optimize power distribution by learning from historical patterns and adapting to changes in energy usage in real time. Convolutional neural networks (CNNs) and recurrent neural networks (RNNs) facilitate detailed analysis of spatial and temporal data to better predict energy usage. Generative adversarial networks (GANs) are used to simulate energy usage scenarios, supporting strategic planning and anomaly detection. Federated learning ensures privacy-preserving data sharing in distributed energy systems, promoting collaboration without compromising security. These technologies are driving the transformation towards sustainable and energy-efficient urban environments, meeting the growing demands of modern smart cities. However, there is a view that if the pace of development is maintained with large amounts of data, the computational/energy costs may exceed the benefits. The article aims to conduct a comparative analysis and assess the development potential of this group of technologies, taking into account energy efficiency. Full article

(This article belongs to the Special Issue Advanced Machine Learning and Big Data Technologies for Smart Cities and Grids)

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47 pages, 2013 KiB

Open AccessEditor’s ChoiceReview

Green Hydrogen for Energy Transition: A Critical Perspective

by Ruggero Angelico, Ferruccio Giametta, Biagio Bianchi and Pasquale Catalano

Energies 2025, 18(2), 404; https://doi.org/10.3390/en18020404 - 17 Jan 2025

Cited by 10 | Viewed by 2706

Abstract

Green hydrogen (GH₂) is emerging as a key driver of global energy transition, offering a sustainable pathway to decarbonize energy systems and achieve climate objectives. This review critically examines the state of GH₂ research production technologies and their integration into [...] Read more.

Green hydrogen (GH₂) is emerging as a key driver of global energy transition, offering a sustainable pathway to decarbonize energy systems and achieve climate objectives. This review critically examines the state of GH₂ research production technologies and their integration into renewable energy systems, supported by a bibliometric analysis of the recent literature. Produced via electrolysis powered by renewable energy, GH₂ shows significant potential to decarbonize industries, enhance grid stability, and support the Power-to-X paradigm, which interlinks electricity, heating, transportation, and industrial applications. However, widespread adoption faces challenges, including high production costs, infrastructure constraints, and the need for robust regulatory frameworks. Addressing these barriers requires advancements in electrolyzer efficiency, scalable fuel cell technologies, and efficient storage solutions. Sector-coupled smart grids incorporating hydrogen demonstrate the potential to integrate GH₂ into energy systems, enhancing renewable energy utilization and ensuring system reliability. Economic analyses predict that GH₂ can achieve cost parity with fossil fuels by 2030 and will play a foundational role in low-carbon energy systems by 2050. Its ability to convert surplus renewable electricity into clean energy carriers positions it as a cornerstone for decarbonizing energy-intensive sectors, such as industry, transportation, and heating. This review underscores the transformative potential of GH₂ in creating a sustainable energy future. By addressing technical, economic, and policy challenges and through coordinated efforts in innovation and infrastructure development, GH₂ can accelerate the transition to carbon-neutral energy systems and contribute to achieving global climate goals. Full article

(This article belongs to the Special Issue Advances in Hydrogen Energy IV)

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22 pages, 9731 KiB

Open AccessEditor’s ChoiceReview

Flame–Flame Interactions and Jet–Jet Interactions in Gas Turbine Swirl Combustors

by Wei Wei, Xin Hui, Xin Xue, Qiang An and Shiyang Yu

Energies 2025, 18(2), 390; https://doi.org/10.3390/en18020390 - 17 Jan 2025

Cited by 1 | Viewed by 1205

Abstract

Annular combustors are widely used in newly developed aero-engines. Nevertheless, the development of annular combustors requires substantial air supplies and high-power heaters during testing, leading to high experimental costs. To reduce these costs during the design phase, researchers often simplify annular combustors into [...] Read more.

Annular combustors are widely used in newly developed aero-engines. Nevertheless, the development of annular combustors requires substantial air supplies and high-power heaters during testing, leading to high experimental costs. To reduce these costs during the design phase, researchers often simplify annular combustors into single-dome configurations using aerodynamic and thermodynamic similarity principles. A fundamental divergence exists between the boundary conditions of annular and simplified single-dome combustors, which is reviewed in this article. It highlights the limitations of single-dome model combustors in accurately representing the crucial features of annular combustors, particularly flame–flame interaction (FFI) and jet–jet interaction (JJI). FFI and JJI existing in annular combustors are observed to result in alternating flow patterns and the superposition of mass and energy transfer between adjacent domes, which can deteriorate flame stabilization and increase NOx emissions. This review emphasizes the characteristics of multi-dome combustors and notes a lack of research comparing single-dome and multi-dome combustors under engine-relevant conditions. Addressing this research gap in the future can better connect fundamental combustion research and engine development, providing more guidance for engine designers. Full article

(This article belongs to the Section I2: Energy and Combustion Science)

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20 pages, 4910 KiB

Open AccessEditor’s ChoiceArticle

Grid Connection of a Squirrel-Cage Induction Generator Excited by a Partial Power Converter

by Dominik A. Górski, Grzegorz Dziechciaruk and Grzegorz Iwański

Energies 2025, 18(2), 368; https://doi.org/10.3390/en18020368 - 16 Jan 2025

Cited by 1 | Viewed by 931

Abstract

This article concerns the connection process of a squirrel-cage induction generator to the grid/microgrid. Typically, the generator is unexcited, and its connection to the grid is made directly via a switch. This connection causes a high inrush current and grid voltage drop, which [...] Read more.

This article concerns the connection process of a squirrel-cage induction generator to the grid/microgrid. Typically, the generator is unexcited, and its connection to the grid is made directly via a switch. This connection causes a high inrush current and grid voltage drop, which local consumers notice. This article proposes a robust power system consisting of the squirrel-cage induction generator, a power electronic converter, and a capacitor bank, all connected in parallel. The proposed configuration and a dedicated control system eliminate the inrush current and compensate for the generator’s reactive power during grid-tied operation. The converter controls the generator voltage build-up to adjust the generator voltage to the grid voltage (controlled excitation) and connects the generator to the grid, minimising distortions. Moreover, the system is robust because the failure of the converter does not stop the power generation, unlike a system with a back-to-back converter, where the converter links the generator and the grid. Furthermore, the parallel-connected converter has a significantly reduced power rating because it is only rated for a part of the reactive generator power. The rest of the reactive generator power is delivered by the fixed capacitor bank. The article presents the system configuration, the control method, and laboratory results confirming the system’s effectiveness in maintaining high-quality grid voltage during generator-to-grid connection and high-quality power supplied to the grid. Full article

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

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23 pages, 10564 KiB

Open AccessEditor’s ChoiceArticle

Experimental and Simulation Study on Reducing the Liquid Film and Improving the Performance of a Carbon-Neutral Methanol Engine

by Yongzhi Li, Zhi Zhang, Haifeng Liu, Weide Chang, Zanqiao Shu, Hu Wang, Zunqing Zheng, Hua Zhao, Xinyan Wang and Mingfa Yao

Energies 2025, 18(2), 353; https://doi.org/10.3390/en18020353 - 15 Jan 2025

Cited by 1 | Viewed by 812

Abstract

Methanol is a potential carbon-neutral fuel. It has a high latent heat of vaporization, making it difficult to achieve evaporation and mixing, and it is prone to forming a liquid film, which in turn affects engine performance. To reduce the liquid film and [...] Read more.

Methanol is a potential carbon-neutral fuel. It has a high latent heat of vaporization, making it difficult to achieve evaporation and mixing, and it is prone to forming a liquid film, which in turn affects engine performance. To reduce the liquid film and improve engine performance, this work investigates the influence mechanism of injection strategies on the generation of liquid films in the intake port and cylinder of an inline 6-cylinder port fuel injection (PFI) spark-ignition (SI) methanol engine and further explores the optimization scheme for improving engine performance. The results show that the end of injection (EOI) influences the methanol evaporation rate and the methanol–air mixing process, thereby determining the liquid film deposition, mixture distribution, and temperature distribution in the cylinder. As the EOI advances, the higher methanol evaporation rate during the intake process reduces the amount of methanol droplets and the deposition of a liquid film in the cylinder. The in-cylinder temperature is relatively high, while the mixture inhomogeneity slightly increases. As the EOI increases from 170 °CA to 360 °CA, the higher in-cylinder temperature and properly stratified mixture accelerate the early and middle stages of combustion, shorten the ignition delay, advance the center of combustion, and improve the brake thermal efficiency (BTE). However, further advancing the EOI results in the BTE remaining basically unchanged. Optimized injection timing can enhance the BTE by 1.4% to 2.4% under various load conditions. The increase in the EOI contributes to the reduction of HC emissions due to the weakening of the crevice effect with lower masses of methanol droplets and liquid film in the cylinder, while the increase in mixture inhomogeneity leads to an increase in CO emissions. In general, controlling the EOI at around 360 °CA can maintain relatively low CO emissions under various load conditions, while significantly reducing HC emissions by 71.2–76.4% and improving the BTE. Full article

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

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24 pages, 2765 KiB

Open AccessEditor’s ChoiceArticle

Valorization of Biomass Through Anaerobic Digestion and Hydrothermal Carbonization: Integrated Process Flowsheet and Supply Chain Network Optimization

by Sanja Potrč, Aleksandra Petrovič, Jafaru M. Egieya and Lidija Čuček

Energies 2025, 18(2), 334; https://doi.org/10.3390/en18020334 - 14 Jan 2025

Cited by 1 | Viewed by 846

Abstract

Utilization of biomass through anaerobic digestion and hydrothermal carbonization is crucial to maximize resource efficiency. At the same time, supply chain integration ensures sustainable feedstock management and minimizes environmental and logistical impacts, enabling a holistic approach to a circular bioeconomy. This study presents [...] Read more.

Utilization of biomass through anaerobic digestion and hydrothermal carbonization is crucial to maximize resource efficiency. At the same time, supply chain integration ensures sustainable feedstock management and minimizes environmental and logistical impacts, enabling a holistic approach to a circular bioeconomy. This study presents an integrated approach to simultaneously optimize the biomass supply chain network and process flowsheet, which includes anaerobic digestion, cogeneration, and hydrothermal carbonization. A three-layer supply chain network superstructure was hence developed to integrate the optimization of process variables with supply chain features such as transportation modes, feedstock supply, plant location, and demand location. A mixed-integer nonlinear programming model aimed at maximizing the economic performance of the system was formulated and applied to a case study of selected regions in Slovenia. The results show a great potential for the utilization of organic biomass with an annual after tax profit of 23.13 million USD per year, with the production of 245.70 GWh/yr of electricity, 298.83 GWh/yr of heat, and 185.08 kt/yr of hydrochar. The optimal configuration of the supply chain network, including the selection of supply zones, plant locations and demand locations, transportation links, and mode of transportation is presented, along with the optimal process variables within the plant. Full article

(This article belongs to the Special Issue Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction—In Memory of Professor Habil Jiří Jaromír Klemeš)

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36 pages, 2688 KiB

Open AccessEditor’s ChoiceArticle

StegoEDCA: An Efficient Covert Channel for Smart Grids Based on IEEE 802.11e Standard

by Marek Natkaniec and Paweł Kępowicz

Energies 2025, 18(2), 330; https://doi.org/10.3390/en18020330 - 13 Jan 2025

Cited by 1 | Viewed by 854

Abstract

Smart grids are continuously evolving, incorporating modern technologies such as Wi-Fi, Zigbee, LoRaWAN or BLE. Wi-Fi are commonly used to transmit data from measurement systems, distribution control and monitoring systems, as well as network protection systems. However, since Wi-Fi networks primarily operate on [...] Read more.

Smart grids are continuously evolving, incorporating modern technologies such as Wi-Fi, Zigbee, LoRaWAN or BLE. Wi-Fi are commonly used to transmit data from measurement systems, distribution control and monitoring systems, as well as network protection systems. However, since Wi-Fi networks primarily operate on unlicensed frequency bands, this introduces significant security risks for sensitive data transmission. In this paper, we propose a novel and highly efficient covert channels that utilize IEEE 802.11 Enhanced Distributed Channel Access (EDCA) for data transmission. It is also the first ever covert channel that employ three or four independent covert mechanisms to enhance operational efficiency. The proposed mechanism is also the first to exploit the Transmission Opportunity (TXOP) period and the access categories of the EDCA function. The protocol was developed and tested using the ns-3 simulator, achieving excellent performance results. Its efficiency remains consistent even under heavy network load with additional background traffic. These covert channels provide an innovative solution for securely transmitting large volumes of data within the smart grid. Full article

(This article belongs to the Special Issue Research on Security and Data Protection for Energy Systems)

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18 pages, 3980 KiB

Open AccessEditor’s ChoiceArticle

Efficient Production of Fuel Ethanol via the Simultaneous Use of Distillery Stillage Biomass and Beet Molasses

by Katarzyna Osmolak, Dawid Mikulski and Grzegorz Kłosowski

Energies 2025, 18(2), 312; https://doi.org/10.3390/en18020312 - 12 Jan 2025

Cited by 3 | Viewed by 1100

Abstract

The integrated production of ethanol fuel through the simultaneous use of various by-products and waste materials is an intriguing concept, as it maximizes the raw material potential while addressing the challenge of managing waste biomass from different technological processes. The efficient utilization of [...] Read more.

The integrated production of ethanol fuel through the simultaneous use of various by-products and waste materials is an intriguing concept, as it maximizes the raw material potential while addressing the challenge of managing waste biomass from different technological processes. The efficient utilization of lignocellulosic waste depends on employing a pretreatment method that enhances the susceptibility of structural polysaccharides to hydrolysis. The aim of the study was to assess the possibility of the simultaneous use of corn stillage biomass and beet molasses as raw materials for the production of ethanol fuel. The research focused on optimizing the process conditions for the acid pretreatment of stillage biomass and the enzymatic hydrolysis of cellulose and evaluating the effectiveness of two fermentation strategies: SHF (Separate Hydrolysis and Fermentation) and SSF (Simultaneous Saccharification and Fermentation). The highest hydrolysis susceptibility was observed in biomass pretreated with 2% v/v H₃PO₄ for 30 min at 121 °C. The maximum glucose concentration of about 12 g/L (hydrolysis efficiency about 35.5%) was achieved even with the lowest enzyme dose, i.e., 7.5 FPU per gram of biomass. The yeast also showed high fermentation activity in media prepared from stillage biomass and molasses, producing about 50 g/L of ethanol regardless of the fermentation strategy used. The complete fermentation of carbohydrates assimilated by yeast confirmed the complementarity of the two raw materials used to prepare fermentation media, emphasizing the high potential of the proposed technological solution for ethanol fuel production. Full article

(This article belongs to the Special Issue New Challenges in Lignocellulosic Biomass Conversion)

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23 pages, 8113 KiB

Open AccessEditor’s ChoiceArticle

Artificial Neural Networks as a Tool for High-Accuracy Prediction of In-Cylinder Pressure and Equivalent Flame Radius in Hydrogen-Fueled Internal Combustion Engines

by Federico Ricci, Massimiliano Avana and Francesco Mariani

Energies 2025, 18(2), 299; https://doi.org/10.3390/en18020299 - 11 Jan 2025

Cited by 2 | Viewed by 1021

Abstract

The automotive industry is under increasing pressure to develop cleaner and more efficient technologies in response to stringent emission regulations. Hydrogen-powered internal combustion engines represent a promising alternative, offering the potential to reduce carbon-based emissions while improving efficiency. However, the accurate estimation of [...] Read more.

The automotive industry is under increasing pressure to develop cleaner and more efficient technologies in response to stringent emission regulations. Hydrogen-powered internal combustion engines represent a promising alternative, offering the potential to reduce carbon-based emissions while improving efficiency. However, the accurate estimation of in-cylinder pressure is crucial for optimizing the performance and emissions of these engines. While traditional simulation tools such as GT-POWER are widely utilized for these purposes, recent advancements in artificial intelligence provide new opportunities for achieving faster and more accurate predictions. This study presents a comparative evaluation of the predictive capabilities of GT-POWER and an artificial neural network model in estimating in-cylinder pressure, with a particular focus on improvements in computational efficiency. Additionally, the artificial neural network is employed to predict the equivalent flame radius, thereby obviating the need for repeated tests using dedicated high-speed cameras in optical access research engines, due to the resource-intensive nature of data acquisition and post-processing. Experiments were conducted on a single-cylinder research engine operating at low-speed and low-load conditions, across three distinct relative air–fuel ratio values with a range of ignition timing settings applied for each air excess coefficient. The findings demonstrate that the artificial neural network model surpasses GT-POWER in predicting in-cylinder pressure with higher accuracy, achieving an RMSE consistently below 0.44% across various conditions. In comparison, GT-POWER exhibits an RMSE ranging from 0.92% to 1.57%. Additionally, the neural network effectively estimates the equivalent flame radius, maintaining an RMSE of less than 3%, ranging from 2.21% to 2.90%. This underscores the potential of artificial neural network-based approaches to not only significantly reduce computational time but also enhance predictive precision. Furthermore, this methodology could subsequently be applied to conventional road engines exhibiting characteristics and performance similar to those of a specific optical engine used as the basis for the machine learning analysis, offering a practical advantage in real-time diagnostics. Full article

(This article belongs to the Special Issue Advancements in Hydrogen Application for Internal Combustion Engines)

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40 pages, 3051 KiB

Open AccessEditor’s ChoiceReview

Navigating the Challenges of Sustainability in the Food Processing Chain: Insights into Energy Interventions to Reduce Footprint

by Orlando Corigliano, Pietropaolo Morrone and Angelo Algieri

Energies 2025, 18(2), 296; https://doi.org/10.3390/en18020296 - 10 Jan 2025

Cited by 2 | Viewed by 2706

Abstract

This review paper examines the critical intersection of energy consumption and environmental impacts within the global food system, emphasizing the substantial footprint (including land usage, costs, food loss and waste, and carbon and water footprints) associated with current practices. The study delineates the [...] Read more.

This review paper examines the critical intersection of energy consumption and environmental impacts within the global food system, emphasizing the substantial footprint (including land usage, costs, food loss and waste, and carbon and water footprints) associated with current practices. The study delineates the high energy demands and ecological burdens of food production, trade, and consumption through a comprehensive bibliographic analysis of high-impact research papers, authoritative reports, and databases. The paper systematically analyzes and synthesizes data to characterize the food industry’s current energy use patterns and environmental impacts. The results underscore a pressing need for strategic interventions to enhance food system efficiency and reduce the footprint. In light of the projected population growth and increasing food demand, the study advocates for a paradigm shift towards more sustainable and resilient food production practices, adopting energy-efficient technologies, promoting sustainable dietary habits, and strengthening global cooperation among stakeholders to achieve the Sustainable Development Goals. Investigations have revealed that the food system is highly energy-intensive, accounting for approximately 30% of total energy consumption (200 EJ per year). The sector remains heavily reliant on fossil fuels. Associated greenhouse gas (GHG) emissions, which constitute 26% of all anthropogenic emissions, have shown a linear growth trend, reaching 16.6 Gt_CO2eq in 2015 and projected to approach 18.6 Gt_CO2eq in the coming years. Notably, 6% of these emissions result from food never consumed. While the water footprint has slightly decreased recently, its demand is expected to increase by 20% to 30%, potentially reaching between 5500 and 6000 km³ annually by 2050. Energy efficiency interventions are estimated to save up to 20%, with a favorable payback period, as evidenced by several practical implementations. Full article

(This article belongs to the Collection Energy Efficiency and Environmental Issues)

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24 pages, 2448 KiB

Open AccessEditor’s ChoiceReview

On a New Sustainable Energy Policy: Exploring a Macro-Meso-Micro Synthesis

by Dimos Chatzinikolaou and Charis Michael Vlados

Energies 2025, 18(2), 260; https://doi.org/10.3390/en18020260 - 9 Jan 2025

Cited by 2 | Viewed by 1416

Abstract

This study examines the differences between the emerging new energy policy and its predecessor, offering guidelines for an integrated approach to support a rapid and sustainable energy transition. Using a bibliometric and qualitative integrative analysis of 360 scientific articles on energy policy, ecosystems, [...] Read more.

This study examines the differences between the emerging new energy policy and its predecessor, offering guidelines for an integrated approach to support a rapid and sustainable energy transition. Using a bibliometric and qualitative integrative analysis of 360 scientific articles on energy policy, ecosystems, and entrepreneurship—supplemented by insights from 16 experts in the European energy sector and an in-depth analysis of 89 relevant business cases—this research identifies a significant shift in priorities. Traditional concerns, such as energy security, self-sufficiency, and market liberalization, are increasingly giving way to a focus on rapid, sustainable energy transitions and development at the macrolevel. The findings reveal that contemporary energy policies are progressively prioritizing integrated strategies across the macrolevel, mesolevel, and microlevel. At the macrolevel, policies are increasingly focused on enabling efficient transitions and promoting sustainable development within an ecosystemic framework. At the mesolevel, there is a growing emphasis on strengthening regional energy ecosystems. At the microlevel, the focus increasingly shifts toward empowering energy firms through innovative organizational strategies, technological advancements, and enhanced managerial practices. The proposed integrated energy policy aims to address these broader goals while fostering diverse energy ecosystems and communities at the mesolevel. Additionally, it emphasizes the importance of empowering individual energy firms by enhancing their strategies, technological capabilities, and managerial skills. These improvements are essential for driving innovation, developing green business models, strengthening corporate social responsibility, and aligning with the principles of Resilience, Adaptability, Sustainability, and Inclusiveness (RASI). Full article

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

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13 pages, 2012 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Backfill Gas Pressure on the Thermal Response of a Dry Cask for Spent Nuclear Fuel

by Michela Angelucci, Salvatore A. Cancemi, Rosa Lo Frano and Sandro Paci

Energies 2025, 18(2), 274; https://doi.org/10.3390/en18020274 - 9 Jan 2025

Cited by 1 | Viewed by 699

Abstract

Dry systems are being employed worldwide as interim storage for Spent Nuclear Fuel (SNF). Despite not being designed as permanent repositories, the safe storage of SNF must still be ensured. In this framework, few experimental campaigns have been conducted in the past. However, [...] Read more.

Dry systems are being employed worldwide as interim storage for Spent Nuclear Fuel (SNF). Despite not being designed as permanent repositories, the safe storage of SNF must still be ensured. In this framework, few experimental campaigns have been conducted in the past. However, their limited number has led to the necessity to exploit numerical simulations for the thermal characterization of the system. Since the majority of the degradation mechanisms are temperature-dependent, conducting a thermal analysis of a dry cask is essential to assess the integrity of the system itself, and of the SNF stored within it. In this regard, both heat production and heat removal mechanisms have to be taken into account. On this basis, the present paper addresses the variation in the system heat removal capacity when considering different backfill gas pressures. In particular, the analysis, carried out with the MELCOR code, investigates the thermal response of the ventilated, concrete-based HI-STORM 100S cask, currently employed for spent fuel elements of Light Water Reactors (LWRs), when imposing different initial pressures for the helium backfill gas. Results are reported primarily in terms of maximum temperature of the fuel cladding, which is the variable under regulatory surveillance. In addition, the adherence to the maximum design pressure for the canister is verified by evaluating the helium pressure as the steady state is reached. The analysis seems to suggest that the safe operation of the HI-STORM 100S cask is guaranteed only for a limited range of the initial helium pressure. Full article

(This article belongs to the Special Issue Advanced Multi-physics Modelling and Simulation for Nuclear Technology)

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21 pages, 7149 KiB

Open AccessEditor’s ChoiceArticle

Experimental Testing Results on Critical Components for Molten Salt-Based CSP Systems

by Valeria Russo, Giuseppe Petroni, Francesco Rovense, Mauro Giorgetti, Giuseppe Napoli, Gianremo Giorgi and Walter Gaggioli

Energies 2025, 18(1), 198; https://doi.org/10.3390/en18010198 - 5 Jan 2025

Cited by 1 | Viewed by 1210

Abstract

Concentrated Solar Power (CSP) plants integrated with Thermal Energy Storage (TES) represent a promising renewable energy source for generating heat and power. Binary molten salt mixtures, commonly referred to as Solar Salts, are utilized as effective heat transfer fluids and storage media due [...] Read more.

Concentrated Solar Power (CSP) plants integrated with Thermal Energy Storage (TES) represent a promising renewable energy source for generating heat and power. Binary molten salt mixtures, commonly referred to as Solar Salts, are utilized as effective heat transfer fluids and storage media due to their thermal stability and favorable thermophysical properties. However, these mixtures pose significant challenges due to their high solidification temperatures, around 240 °C, which can compromise the longevity and reliability of critical system components such as pressure sensors and bellows seal globe valves. Thus, it is essential to characterize their performance, assess their reliability under various conditions, and understand their failure mechanisms, particularly in relation to temperature fluctuations affecting the fluid’s viscosity. This article discusses experimental tests conducted on a pressure sensor and a bellows seal globe valve, both designed for direct contact with molten salts in CSP environments, at the ENEA Casaccia Research Center laboratory in Rome. The methodology for conducting these experimental tests is detailed, and guidelines are outlined to optimize plant operation. The findings provide essential insights for improving component design and maintenance to minimize unplanned plant downtime. They also offer methodologies for installing measurement instruments and electrical heating systems on the components. Full article

(This article belongs to the Special Issue Solar Thermal Heat and Power Technology: Developments and Applications)

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17 pages, 3478 KiB

Open AccessEditor’s ChoiceArticle

Enzymatic Activity in the Anaerobic Co-Digestion of Cavitated Coffee Waste and Sewage Sludge

by Elżbieta Wołejko, Urszula Wydro, Aleksandra Szaja, Agnieszka Montusiewicz and Magdalena Lebiocka

Energies 2025, 18(1), 187; https://doi.org/10.3390/en18010187 - 4 Jan 2025

Viewed by 1265

Abstract

Hydrodynamic cavitation (HDC) as a pre-treatment method is innovative and has potential for wide-scale industrial applications. The novelty of this research involves evaluating the enzymatic activity in the anaerobic co-digestion (AcD) of hydrodynamically cavitated coffee waste (CW) and municipal sewage sludge (SS) as [...] Read more.

Hydrodynamic cavitation (HDC) as a pre-treatment method is innovative and has potential for wide-scale industrial applications. The novelty of this research involves evaluating the enzymatic activity in the anaerobic co-digestion (AcD) of hydrodynamically cavitated coffee waste (CW) and municipal sewage sludge (SS) as well as its influence on the AcD performance. The effectiveness of AcD was assessed on the basis of changes in the physico-chemical composition of the feedstock and digestate as well as the biogas/methane yield, and attention was paid to the effect of coffee waste on enzyme activity, including that of β-Glucosidases (β-Glu), protease (PR), urease (URE), phosphomonoesterases acid (ACP) and alkaline (ALP). Moreover, the changes in the heavy metal content after the AcD of CW and SS were investigated. Comparing the enzymatic activity of the feedstock and digestate, we observed that the URE, ACP and ALP activities were 4.5 to 11 times higher for the feedstock than the enzyme activities in the digestate. Moreover, when using CW cavitated for 30 min, the highest enzymatic activity in both the feedstock and digestate occurred. The results indicated that the relationship between the β-Glu activity and biogas yield showed the strongest positive correlation (r = 0.98 at p ≤ 0.05). At the same time, a positive correlation between the PAC, PAL, URE and PR activity and methane yield and methane content at p ≤ 0.05 was observed. The obtained results allow us to conclude that, in the future, such a digestate could be used as a bio-fertilizer to improve degraded soil to activate microbial populations. Full article

(This article belongs to the Special Issue Energy from Waste: Towards Sustainable Development and Clean Future)

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28 pages, 6449 KiB

Open AccessEditor’s ChoiceReview

A Review of Matrix Converters in Motor Drive Applications

by Annette von Jouanne, Emmanuel Agamloh and Alex Yokochi

Energies 2025, 18(1), 164; https://doi.org/10.3390/en18010164 - 3 Jan 2025

Cited by 3 | Viewed by 1326

Abstract

A matrix converter (MC) converts an AC source voltage into a variable-voltage variable-frequency AC output voltage (direct AC-AC) without an intermediate DC-link capacitance. By eliminating the traditional DC-link capacitor, MCs can achieve higher power densities and reliability when compared to conventional AC-DC-AC converters. [...] Read more.

A matrix converter (MC) converts an AC source voltage into a variable-voltage variable-frequency AC output voltage (direct AC-AC) without an intermediate DC-link capacitance. By eliminating the traditional DC-link capacitor, MCs can achieve higher power densities and reliability when compared to conventional AC-DC-AC converters. MCs also offer the following characteristics: total semiconductor solution, sinusoidal input and output currents, bidirectional power flow and controllable input power factor. This paper reviews the history, recent developments and commercialization of MCs and discusses several technical requirements and challenges, including bidirectional switches, wide bandgap (WBG) opportunities using GaN and SiC, overvoltage protection, electromagnetic interference (EMI) and ride-through in motor drive applications. MC design solutions and operation are discussed, including a comparison of control and modulation techniques as well as the detailed development of space vector modulation (SVM) to provide a deep insight into the control implementation and results. The paper concludes with compelling motor drive innovation opportunities made possible by advanced MCs including fully integrated and multiphase systems. For conventional MCs, size reductions of 30% are reported, as well as efficiencies of 98% and low input current total harmonic distortion of 3–5%. Full article

(This article belongs to the Section F: Electrical Engineering)

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17 pages, 2098 KiB

Open AccessEditor’s ChoiceArticle

Highly Stable Inverted Organic Solar Cell Structure Using Three Efficient Electron Transport Layers

by Mohamed El Amine Boudia and Cunlu Zhao

Energies 2025, 18(1), 167; https://doi.org/10.3390/en18010167 - 3 Jan 2025

Cited by 1 | Viewed by 948

Abstract

The efficiency of organic solar cells (OSCs) is influenced by various factors, among which environmental temperature plays a significant role. Previous studies have shown that the thermal stability of these cells can be enhanced by incorporating a third component into their structure. Ternary [...] Read more.

The efficiency of organic solar cells (OSCs) is influenced by various factors, among which environmental temperature plays a significant role. Previous studies have shown that the thermal stability of these cells can be enhanced by incorporating a third component into their structure. Ternary organic solar cells, particularly, have shown promising results in improving thermal stability. A well-designed electron transport layer (ETL) can significantly bolster thermal stability by facilitating efficient charge transport and reducing charge recombination. In this study, we investigated the effect of temperature, ranging from 300 K to 400 K, on the efficiency of inverted ternary structures by using a one-dimension optoelectronic model on “Oghma-Nano 8.0.034” software. The structures examined include (S1) “FTO/SnO₂/PM6:D18:L8-BO/PEDOT: PSS/Ag”, (S2): “FTO/C₆₀/PM6:D18:L8-BO/PEDOT: PSS/Ag”, and (S3): “FTO/PC₆₀BM/PM6:D18:L8-BO/PEDOT: PSS/Ag”. Simulations using three different ETLs—SnO₂, C₆₀, and PC₆₀BM—at 340 K (66.85 °C) resulted in a main effect on open circuit voltage (V_oc) and fill factor (FF) values, in addition to an important J_sc value in terms of thermally stable devices. However, these structures retained 92% of their initial ~20% efficiency observed at 300 K, demonstrating significant thermal stability under high power conversion efficiency (PCE) conditions. Full article

(This article belongs to the Special Issue Organic and Hybrid Solar Cells for Efficient Solar Power Conversion)

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10 pages, 3719 KiB

Open AccessEditor’s ChoiceArticle

Experimental Studies of Fluid Flow Resistance in a Heat Exchanger Based on the Triply Periodic Minimal Surface

by Marcin Kruzel, Krzysztof Dutkowski and Tadeusz Bohdal

Energies 2025, 18(1), 134; https://doi.org/10.3390/en18010134 - 1 Jan 2025

Cited by 1 | Viewed by 1217

Abstract

This study describes experimental data on 3D-printed compact heat exchangers. The heat exchanger is a prototype designed and manufactured additively using 3D printing in metal—AISI 316L steel. The device’s design is based on the triply periodic minimal surface (TPMS) geometry called gyroid, which [...] Read more.

This study describes experimental data on 3D-printed compact heat exchangers. The heat exchanger is a prototype designed and manufactured additively using 3D printing in metal—AISI 316L steel. The device’s design is based on the triply periodic minimal surface (TPMS) geometry called gyroid, which can only be obtained by incremental manufacturing. This innovative heat exchange surface structure enables these devices to provide higher thermal performance while reducing their weight by up to 50%. Few publications describe thermal or flow tests in this type of device. They mainly concern computer simulations that have yet to be experimentally verified. The authors of this study conducted innovative flow tests to determine pressure drops during the flow of working fluids under conditions of variable temperature, mass flow rate and thermal load. Water was used as a heat transfer fluid during the tests. The range of parameters for the entire experiment was ṁ = 1–24 kg/h; Δp/Δl = 0.05–2 kPa; t_cold = 20 °C; t_hot = 50 °C. Flow characteristics during the single-phase heat exchange process were determined, including Δp/Δl = f(ṁ), Δp/Δl = f(Re), Δp/Δl = f(f). The experimental data will be used to determine the relationships describing flow resistance in structures based on a triply periodic minimal surface, and it also enables one to specify the energy consumption of these devices and compare the profitability of their use to conventional designs, i.e., shell-and-tube or plate heat exchangers. Full article

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

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24 pages, 10995 KiB

Open AccessEditor’s ChoiceArticle

Using RES Surpluses to Remove Overburden from Lignite Mines Can Improve the Nation’s Energy Security

by Leszek Jurdziak, Witold Kawalec, Zbigniew Kasztelewicz and Pawel Parczyk

Energies 2025, 18(1), 104; https://doi.org/10.3390/en18010104 - 30 Dec 2024

Cited by 2 | Viewed by 990

Abstract

The increasing use of renewable energy sources, such as wind and solar energy, presents challenges to the stability and efficiency of other energy sources due to their intermittent and unpredictable surpluses. The unintended consequence of stabilizing the power supply system is an increase [...] Read more.

The increasing use of renewable energy sources, such as wind and solar energy, presents challenges to the stability and efficiency of other energy sources due to their intermittent and unpredictable surpluses. The unintended consequence of stabilizing the power supply system is an increase in emissions and external costs from the suboptimal use of coal power plants. The rising number of RES curtailments needs to be addressed by either the adjusting energy supply from fossil fuel or the flexible energy consumption. In Poland’s energy mix, coal-fired power plants are a critical component in ensuring energy security for the foreseeable future. Using domestic lignite to generate a total power of 8.5 GW can stabilize the national power supply, as it is currently done in Germany, where 15 GW of lignite-fueled power units provide the power supply base for the country. The leading Belchatów power plant comprises 10 retrofitted units and one new unit, with a total rating of 5.5 GW. Access to the new coal deposit, Zloczew, is necessary to ensure its longer operation. The other domestic lignite power plants are located in Central Poland at Patnów (0.47 GW from the new unit and 0.6 GW from its three retrofitted counterparts) and located in the Lusatian lignite basin at Turów (operating a brand new unit rated at 0.5 GW and retrofitted units with a total rating of 1.5 GW). The use of this fuel is currently being penalized as a result of increasing carbon costs. However, the continuous surface mining technology that is used in lignite mines is fully electrified, and large amounts of electric energy are required to remove and dump overburden and mining coal and its conveying to power units (the transport of coal from the new lignite mine Zloczew to the Belchatów power plant would be a long-distance operation). A possible solution to this problem is to focus on the lignite fuel supply operations of these power plants, with extensive simulations of the entire supply chain. A modern lignite mine is operated by one control room, and it can balance the dynamic consumption of surplus renewable energy sources (RESs) and reduce the need for reduction. When a lignite supply chain is operated this way, a high-capacity power bank can be created with energy storage in the form of an open brown coal seam. This would enable an almost emission-free supply of cheap and domestic fossil fuel, making it insensitive to changes in the world prices of energy resources for power units operating at the base of the system. Furthermore, extending the life of relatively new and efficient lignite-fired units in Poland would facilitate the decommissioning of older and exhausted hard coal-fired units. Full article

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

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Open AccessEditor’s ChoiceReview

Impact of Coolant Operation on Performance and Heterogeneities in Large Proton Exchange Membrane Fuel Cells: A Review

by Marine Cornet, Erwan Tardy, Jean-Philippe Poirot-Crouvezier and Yann Bultel

Energies 2025, 18(1), 111; https://doi.org/10.3390/en18010111 - 30 Dec 2024

Cited by 1 | Viewed by 1086

Abstract

PEMFCs’ operation entails the presence of heterogeneities in the generation of current, heat and water along the active surface area. Indeed, PEMFCs are open systems, and as such, operating heterogeneities are inherent to their operation. A review of the literature reveals numerous attempts [...] Read more.

PEMFCs’ operation entails the presence of heterogeneities in the generation of current, heat and water along the active surface area. Indeed, PEMFCs are open systems, and as such, operating heterogeneities are inherent to their operation. A review of the literature reveals numerous attempts to achieve uniform current density distribution. These attempts are primarily focused on bipolar plate design and operating conditions, with the underlying assumption that uniform current density correlates with enhanced performance. Most studies focus on the influence of gas flow-field design and inlet hydrogen and air flow conditioning, and less attention has been paid to the coolant operating condition. However, uncontrolled temperature distribution over a large cell active surface area can lead to performance loss and localized degradations. On this latter point, we notice that studies to date have been confined to a narrow range of operating conditions. It appears that complementary durability studies are needed in order to obtain in-depth analyses of the coupled influence of temperature distribution and gas humidification in large PEMFCs. Full article

(This article belongs to the Section D2: Electrochem: Batteries, Fuel Cells, Capacitors)

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