Energies

23 pages, 803 KB

Open AccessArticle

Evaluation of Renewable Energy Sources Sector Development in the European Union

by Laima Okunevičiūtė Neverauskienė, Alina Kvietkauskienė, Manuela Tvaronavičienė, Irena Danilevičienė and Dainora Gedvilaitė

Energies 2025, 18(17), 4786; https://doi.org/10.3390/en18174786 - 8 Sep 2025

Viewed by 518

Abstract

The global energy landscape is transforming, driven by the urgent need to address climate change, reduce dependency on fossil fuels, and promote sustainable economic growth. Renewable energy sources (RESs) have emerged as a cornerstone of this transition, offering environmental benefits and significant potential [...] Read more.

The global energy landscape is transforming, driven by the urgent need to address climate change, reduce dependency on fossil fuels, and promote sustainable economic growth. Renewable energy sources (RESs) have emerged as a cornerstone of this transition, offering environmental benefits and significant potential to catalyze economic development. By harnessing inexhaustible natural resources, such as solar, wind, hydro, and biomass, renewable energy systems provide a pathway to achieving energy security, fostering innovation, and generating new economic opportunities. In this article, the economic effect on the RES sector development was examined. The authors defined the set from seven indicators: real GDP growth, unemployment rate, inflation rate, exports of goods and services, government debt, foreign direct investments, and labor cost index, which allowed them to evaluate the EU countries’ economic situation and rank the countries by economic stability level. The results, which were obtained using a multi-criteria evaluation method, show that the EU countries whose economies are the strongest according to the evaluated macroeconomic indicators are Luxembourg, Malta, Estonia, and Ireland. The countries with the lowest scores are Greece, Italy, and Spain. Seeking to evaluate the development level of the RES sector in all ranked EU countries, the analysis of RES sector development during the 2012–2022 period, using these RES indicators—share of renewable energy in gross final energy consumption by sector—in general, in transport, in electricity, and in heating and cooling, was carried out and, through a different multi-criteria method, the countries were ranked by RES development. After the analysis was carried out, it could be stated that the economic situation stability in the country does not directly affect the growth of the RES sector development, and the two rankings by different indicators are heavily uncorrelated. RES sector development can be affected by many other circumstances. RES development is still stagnating in some countries, despite macroeconomic stability, for several reasons: institutional and political barriers, differences in the availability of finance, infrastructure limitations, and technological and human resource shortages. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Economic Growth, Energy Consumption and Carbon Emission)

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28 pages, 2703 KB

Open AccessArticle

Theoretical Approaches to the Heating of an Extensive Homogeneous Plate with Convective Cooling

by Paweł Jabłoński, Tomasz Kasprzak, Sławomir Gryś and Waldemar Minkina

Energies 2025, 18(17), 4785; https://doi.org/10.3390/en18174785 - 8 Sep 2025

Viewed by 289

Abstract

The article presents a mathematical description of the thermal phenomena occurring both inside and on the surfaces of a homogeneous plate subjected to an external heat flux on one side. Analytical formulae for thermal excitation, with a given duration and constant power, are [...] Read more.

The article presents a mathematical description of the thermal phenomena occurring both inside and on the surfaces of a homogeneous plate subjected to an external heat flux on one side. Analytical formulae for thermal excitation, with a given duration and constant power, are derived, enabling the determination of temperature increases on both the heated and unheated surfaces of the plate under specific heat transfer conditions to the surroundings. Convective heat transfer, with individual heat transfer coefficients on both sides of the slab, is considered; however, radiative heat loss can also be included. The solution of the problem obtained using two methods is presented: the method of separation of variables (MSV) and the Laplace transform (LT). The advantages and disadvantages of both analytical formulae, as well as the impact of various factors on the accuracy of the solution, are discussed. Among others, the MSV solution works well for a sufficiently long time, whereas the LT solution is better for a sufficiently short time. The theoretical considerations are illustrated with diagrams for several configurations, each representing various heat transfer conditions on both sides of the plate. The presented solution can serve as a starting point for further analysis of more complex geometries or multilayered structures, e.g., in non-destructive testing using active thermography. The developed theoretical model is verified for a determination of the thermal diffusivity of a reference material. The model can be useful for analyzing the method’s sensitivity to various factors occurring during the measurement process, or the method can be adapted to a pulse of known duration and constant power, which is much easier to implement technically than a very short impulse (Dirac) with high energy. Full article

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

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19 pages, 2416 KB

Open AccessArticle

Time Delay Stability Analysis and Control Strategy of Wind Farm for Active Grid Frequency Support

by Xin Yao, Qingguang Yu, Ding Liu, Leidong Yuan, Min Guo and Xiaoyu Li

Energies 2025, 18(17), 4784; https://doi.org/10.3390/en18174784 - 8 Sep 2025

Viewed by 365

Abstract

With the rapid development of wind turbines and rising penetration levels, grid codes now require wind farms to provide active frequency support. However, time delays in fast power response reduce the stability of system frequency modulation. This study focuses on integrated inertia control [...] Read more.

With the rapid development of wind turbines and rising penetration levels, grid codes now require wind farms to provide active frequency support. However, time delays in fast power response reduce the stability of system frequency modulation. This study focuses on integrated inertia control and droop control of wind turbines with explicit consideration of time delays. First, the frequency modulation process is analyzed, and the main sources of time delay are identified. A system frequency response model is then developed, incorporating the time delay link into the state-space equations. Based on this model, frequency-domain and linear matrix inequality methods are applied to analyze delay-independent stability and time delay margins of wind turbines. A PI controller for the synchronous unit is designed, and compensation parameters for wind turbine delay are calculated to enhance system stability. Simulation results show that with a wind penetration level of 50%, the system becomes unstable when the delay reaches 0.32 s. By applying the proposed strategy, stability can be maintained even with a delay of 0.5 s. These results confirm the effectiveness of the proposed strategy and highlight its potential for improving frequency regulation in high-renewable power systems. Full article

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

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22 pages, 6100 KB

Open AccessArticle

A Hybrid Control Strategy Combining Reinforcement Learning and MPC-LSTM for Energy Management in Building

by Amal Azzi, Meryem Abid, Ayoub Hanif, Hassna Bensag, Mohamed Tabaa, Hanaa Hachimi and Mohamed Youssfi

Energies 2025, 18(17), 4783; https://doi.org/10.3390/en18174783 - 8 Sep 2025

Viewed by 329

Abstract

Aware of the nefarious effects of excessive exploitation of natural resources and the greenhouse gases emissions linked to building sector, the concept of smart buildings emerged, referring to a building that uses clean energy efficiently. This requires intelligent control systems to manage the [...] Read more.

Aware of the nefarious effects of excessive exploitation of natural resources and the greenhouse gases emissions linked to building sector, the concept of smart buildings emerged, referring to a building that uses clean energy efficiently. This requires intelligent control systems to manage the use of residential energy consuming devices, namely the HVAC (Heating, Ventilation, Air-conditioning) system. This system consumes up to 50% of the total energy used by a building. In this paper, we introduce a RL (Reinforcement Learning) and MPC-LSTM (Model Predictive Control-Long-Short Term Memory) hybrid control system that combines DNNs (Deep Neural Networks), through RL, with LSTM’s long-short memory technique and MPC’s control characteristics. The goal of our model is to maintain thermal comfort of residents while optimizing energy consumption. Consequently, to train and test our model, we generate our own dataset using a building model of a corporate building in Casablanca, Morocco, combined with weather data of the same city. Simulations confirm the robustness of our model as it outperforms basic control methods in terms of thermal comfort and energy consumption especially during summer. Compared to conventional methods, our approach resulted in a 45.4% and 70.9% reduction in energy consumption, in winter and summer, respectively. Our approach also resulted in 26 less comfort violations during winter. On the other hand, during summer, our approach found a compromise between energy consumption and comfort with no more than 2.5 °C above ideal temperature limit. Full article

(This article belongs to the Section G: Energy and Buildings)

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15 pages, 2477 KB

Open AccessArticle

An Improved Two-Degree-of-Freedom Speed Controller for Permanent-Magnet Synchronous Motors

by Chaoming Huang, Jinyang Wu, Ping Lin, Kai Lin and Yuan Gao

Energies 2025, 18(17), 4782; https://doi.org/10.3390/en18174782 - 8 Sep 2025

Viewed by 304

Abstract

For the traditional one-degree-of-freedom controller, there is a trade-off between the tracking performance and disturbance rejection performance. The traditional two-degree-of-freedom controller can achieve disturbance rejection and tracking simultaneously, when there are one tracking channel and one disturbance rejection channel. To overcome the limitations [...] Read more.

For the traditional one-degree-of-freedom controller, there is a trade-off between the tracking performance and disturbance rejection performance. The traditional two-degree-of-freedom controller can achieve disturbance rejection and tracking simultaneously, when there are one tracking channel and one disturbance rejection channel. To overcome the limitations of the one-degree-of-freedom controller and the traditional two-degree-of-freedom controller, an improved two-degree-of-freedom controller is designed for the speed regulation system of a permanent-magnet synchronous motor (PMSM) for use in electric aircraft scenarios and PMSM control applications. This proposed controller includes three elements: a proportional forward element, a proportional–integral feedback element, and a linear extended state observer element. The proportional forward element is used for tracking, and the proportional–integral feedback element and linear extended state observer element are used for disturbance rejection. The controller can simultaneously achieve tracking and disturbance rejection. The proportional forward element guarantees tracking performance, while the proportional–integral feedback and linear extended state observer elements enhance disturbance rejection. The stability of the proposed controller is experimentally demonstrated, and the results show that the improved controller offers superior tracking and disturbance rejection compared to traditional 1-DoF and 2-DoF controllers. Full article

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

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14 pages, 4531 KB

Open AccessArticle

A Permanent Magnet Synchronous Machine with Mechanically Controlled Excitation Flux

by Piotr Paplicki

Energies 2025, 18(17), 4781; https://doi.org/10.3390/en18174781 - 8 Sep 2025

Viewed by 305

Abstract

This paper presents the initial design of a permanent magnet synchronous machine with mechanically controlled excitation flux using the linear sliding motion of an additional excitation source placed inside a hollow shaft in the rotor. A new rotor design concept and assembling method [...] Read more.

This paper presents the initial design of a permanent magnet synchronous machine with mechanically controlled excitation flux using the linear sliding motion of an additional excitation source placed inside a hollow shaft in the rotor. A new rotor design concept and assembling method are described and presented in detail. On the basis of 3D-FE analysis results, the principle of adjusting reluctance, magnetic flux distribution, flux linkage, field weakening rate, no-load back EMF waveforms, electromagnetic torque, magnetic tension, and the effectiveness of the excitation adjustment of the presented machine design are discussed. The presented machine concept enables the design of permanent magnet excited machines with a good flux control range operating in changing load conditions under variable rotor speed. Full article

(This article belongs to the Special Issue Magnetic Field Computations and Energy Efficiency Studies in Electrical Machines, 2nd Edition)

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21 pages, 1183 KB

Open AccessArticle

A Performance Evaluation and Feasibility Study of Mine Thermal Energy Storage in Glace Bay, Nova Scotia

by Sara Sohrabikhah and Larry Hughes

Energies 2025, 18(17), 4780; https://doi.org/10.3390/en18174780 - 8 Sep 2025

Viewed by 338

Abstract

Mine Thermal Energy Storage (MTES) offers a promising solution for sustainable heating by repurposing abandoned, water-filled mines as underground thermal reservoirs. This study assesses the feasibility of implementing MTES in Nova Scotia, with a focus on the Sydney coalfield region, particularly Glace Bay. [...] Read more.

Mine Thermal Energy Storage (MTES) offers a promising solution for sustainable heating by repurposing abandoned, water-filled mines as underground thermal reservoirs. This study assesses the feasibility of implementing MTES in Nova Scotia, with a focus on the Sydney coalfield region, particularly Glace Bay. The research combines geological analysis, residential heat demand estimation, thermal storage capacity estimation, and cost–benefit evaluation to determine whether abandoned coal mines can support district heating applications. Results show that MTES can deliver substantial heating cost reductions compared to oil-based systems, while significantly lowering greenhouse gas emissions. The study also explores the integration of MTES with local renewable energy sources, including wind and solar, to enhance energy system flexibility and reliability. International case studies from Springhill (Canada), Heerlen (Netherlands), and Bochum (Germany) are referenced to contextualize the analysis and demonstrate how the findings of this study align with broader MTES scalability, performance, and operational challenges. Key technical barriers, such as water quality management, infrastructure investment, and seasonal variability in heat demand, are discussed. Overall, the findings highlight MTES as a viable and sustainable energy storage approach for Nova Scotia and other regions with legacy mining infrastructure. Full article

(This article belongs to the Special Issue Advances in Thermal Energy Storage Systems: Methods and Applications)

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92 pages, 3238 KB

Open AccessReview

Machine Learning-Based Electric Vehicle Charging Demand Forecasting: A Systematized Literature Review

by Maher Alaraj, Mohammed Radi, Elaf Alsisi, Munir Majdalawieh and Mohamed Darwish

Energies 2025, 18(17), 4779; https://doi.org/10.3390/en18174779 - 8 Sep 2025

Viewed by 435

Abstract

The transport sector significantly contributes to global greenhouse gas emissions, making electromobility crucial in the race toward the United Nations Sustainable Development Goals. In recent years, the increasing competition among manufacturers, the development of cheaper batteries, the ongoing policy support, and people’s greater [...] Read more.

The transport sector significantly contributes to global greenhouse gas emissions, making electromobility crucial in the race toward the United Nations Sustainable Development Goals. In recent years, the increasing competition among manufacturers, the development of cheaper batteries, the ongoing policy support, and people’s greater environmental awareness have consistently increased electric vehicles (EVs) adoption. Nevertheless, EVs charging needs—highly influenced by EV drivers’ behavior uncertainty—challenge their integration into the power grid on a massive scale, leading to potential issues, such as overloading and grid instability. Smart charging strategies can mitigate these adverse effects by using information and communication technologies to optimize EV charging schedules in terms of power systems’ constraints, electricity prices, and users’ preferences, benefiting stakeholders by minimizing network losses, maximizing aggregators’ profit, and reducing users’ driving range anxiety. To this end, accurately forecasting EV charging demand is paramount. Traditionally used forecasting methods, such as model-driven and statistical ones, often rely on complex mathematical models, simulated data, or simplifying assumptions, failing to accurately represent current real-world EV charging profiles. Machine learning (ML) methods, which leverage real-life historical data to model complex, nonlinear, high-dimensional problems, have demonstrated superiority in this domain, becoming a hot research topic. In a scenario where EV technologies, charging infrastructure, data acquisition, and ML techniques constantly evolve, this paper conducts a systematized literature review (SLR) to understand the current landscape of ML-based EV charging demand forecasting, its emerging trends, and its future perspectives. The proposed SLR provides a well-structured synthesis of a large body of literature, categorizing approaches not only based on their ML-based approach, but also on the EV charging application. In addition, we focus on the most recent technological advances, exploring deep-learning architectures, spatial-temporal challenges, and cross-domain learning strategies. This offers an integrative perspective. On the one hand, it maps the state of the art, identifying a notable shift toward deep-learning approaches and an increasing interest in public EV charging stations. On the other hand, it uncovers underexplored methodological intersections that can be further exploited and research gaps that remain underaddressed, such as real-time data integration, long-term forecasting, and the development of adaptable models to different charging behaviors and locations. In this line, emerging trends combining recurrent and convolutional neural networks, and using relatively new ML techniques, especially transformers, and ML paradigms, such as transfer-, federated-, and meta-learning, have shown promising results for addressing spatial-temporality, time-scalability, and geographical-generalizability issues, paving the path for future research directions. Full article

(This article belongs to the Topic Electric Vehicles Energy Management, 2nd Volume)

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27 pages, 2518 KB

Open AccessArticle

Costs of Modernization and Improvement in Energy Efficiency in Polish Buildings in Light of the National Building Renovation Plans

by Edyta Plebankiewicz, Apolonia Grącka and Jakub Grącki

Energies 2025, 18(17), 4778; https://doi.org/10.3390/en18174778 - 8 Sep 2025

Viewed by 495

Abstract

Long-term renovation strategies (LTRSs) play a central role in achieving the European Union’s objective of a climate-neutral building stock by 2050. In Poland, the challenge is particularly acute: a majority of the building stock was constructed before 1990 and does not even meet [...] Read more.

Long-term renovation strategies (LTRSs) play a central role in achieving the European Union’s objective of a climate-neutral building stock by 2050. In Poland, the challenge is particularly acute: a majority of the building stock was constructed before 1990 and does not even meet basic thermal performance standards. In view of the state of the buildings in Poland and the assumptions made about obtaining the necessary energy parameters in the coming years, it is necessary to undertake thermal modernization measures. The purpose of the paper is to assess the economic efficiency of the variants of modernization of building stock in Poland, taking into account the constraints related to improving energy efficiency. Additionally, the article also points out the problem of discrepancies resulting from climate zones that may significantly affect the final primary energy results (on average, 5–15%). In order to achieve the objectives, the paper focuses on the analysis of energy sources. According to the overall score in the analytic hierarchy process (AHP) method, the best solutions, with a global priority of 0.46, are renewable energy sources (RESs). The evaluation of selected fuel types in the 2055 perspective, using the technique for order preference by similarity to ideal solution (TOPSIS) method, indicate favorable environmental performance by sources based on electricity, i.e., air-source heat pumps, ground-source heat pumps, and electric heating, which achieved the highest relative closeness to the ideal solution. Heat pump systems can reduce energy consumption by 26–41% depending on the building and heat pump type. The final analysis in the paper concerns different options for thermal modernization of a model single-family house, taking into account different energy sources and stages of thermal modernization work. The scenario involves the simultaneous implementation of all renovation measures at an early stage, resulting in the lowest investment burden over time and the most favorable economic performance. Full article

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

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24 pages, 4324 KB

Open AccessArticle

Power System Modeling and Simulation for Distributed Generation Integration: Honduras Power System as a Case Study

by Jhonny Ismael Ramos-Gómez, Angel Molina-García and Jonathan Muñoz-Tabora

Energies 2025, 18(17), 4777; https://doi.org/10.3390/en18174777 - 8 Sep 2025

Viewed by 504

Abstract

This paper presents a case study of the Honduran electricity system and evaluates the technical impact of integrating distributed generation through modeling and simulation using Pandapower, (version 3.1.0) an open-source Python tool. A multi-criteria methodology was applied to select connection nodes considering the [...] Read more.

This paper presents a case study of the Honduran electricity system and evaluates the technical impact of integrating distributed generation through modeling and simulation using Pandapower, (version 3.1.0) an open-source Python tool. A multi-criteria methodology was applied to select connection nodes considering the voltage sensitivity (∆V/MW), loss factor, available thermal capacity (headroom), and hosting capacity. The analysis focused on voltage stability, power losses, and line loading under various distributed generation scenarios. This methodology prioritized buses with critical voltages and significant loads. The case study model included official data from the Honduran National Dispatch Center. The simulations included a redispatch scheme for conventional generators to maintain power balance in all scenarios (20–100% distributed generation profiles), using GEN (controllable output) and SGEN (fixed output) components. The results show that with 50% distributed generation relative to local demand, voltages at critical buses improved by up to 0.14 p.u. Total active losses decreased by 9%, and reactive losses decreased by 44%. Additionally, indirect improvements were observed in non-intervened buses, as well as load relief in lines and transformers. These results confirm that strategic distributed generation injections combined with redispatch can improve supply quality and operational efficiency in weak and radial network topologies. The proposed methodology is scalable and able to be replicated in other power systems, providing technical input for energy planning and renewable energy integration in developing countries. Full article

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42 pages, 8471 KB

Open AccessReview

Comprehensive Evaluation of Agrivoltaics Research: Breadth, Depth, and Insights for Future Research

by Kai Lepley, Hanna Fields, Chong Seok Choi, Thomas Hickey, Benny Towner, Brittany Staie, James McCall, Julia Chamberland and Jordan Macknick

Energies 2025, 18(17), 4776; https://doi.org/10.3390/en18174776 - 8 Sep 2025

Viewed by 749

Abstract

Agrivoltaics integrates agricultural production with solar energy generation to address challenges related to land use, food security, and renewable energy development. This study provides the most comprehensive evaluation to date of global agrivoltaic research, aiming to classify the literature, identify strengths and gaps, [...] Read more.

Agrivoltaics integrates agricultural production with solar energy generation to address challenges related to land use, food security, and renewable energy development. This study provides the most comprehensive evaluation to date of global agrivoltaic research, aiming to classify the literature, identify strengths and gaps, and guide future work. We systematically screened over 3000 English-language publications through 2023 for relevant agrivoltaic publications. A total of 670 studies were categorized in the InSPIRE Data Portal across five agrivoltaic activities and multiple hierarchical themes, including physical, biological, technological, social, and crosscutting domains. We found that research was concentrated on crop production, microclimate dynamics, and PV performance, with gaps in areas like human health, wildlife, policy, and standardized methodologies. Although the U.S. emphasizes animal grazing and habitat-based systems in practice, most U.S.-based studies focused disproportionately on crop production. The analysis revealed uneven geographic and topical representation and highlighted a lack of integrated, interdisciplinary approaches. This study concludes that while agrivoltaic research has grown rapidly, more coordinated efforts could support standardized data collection, address overlooked ecological and social impacts, and align research focus with real-world system implementation, ultimately improving the scalability and successful deployment of agrivoltaic systems. Full article

(This article belongs to the Special Issue Renewable Energy Integration into Agricultural and Food Engineering)

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27 pages, 2932 KB

Open AccessArticle

Increasing the Ecological Efficiency of Monocrystalline Photovoltaic Power Plants by Management Their Life Cycle Assessment

by Adam Idzikowski, Patryk Leda, Izabela Piasecka, Tomasz Cierlicki and Magdalena Mazur

Energies 2025, 18(17), 4775; https://doi.org/10.3390/en18174775 - 8 Sep 2025

Viewed by 497

Abstract

This study’s objectives were to evaluate the life cycle of a 2 MW solar power plant in northern Poland and provide suggestions for enhancing this kind of installation’s environmental performance. Eight years of operating data were examined under the assumption that 2000 MWh [...] Read more.

This study’s objectives were to evaluate the life cycle of a 2 MW solar power plant in northern Poland and provide suggestions for enhancing this kind of installation’s environmental performance. Eight years of operating data were examined under the assumption that 2000 MWh of energy was produced annually on average. The evaluation took into account two waste management scenarios—landfill and recycling—and was carried out in accordance with the ReCiPe 2016 methodology. Human health and water resource usage had the most environmental effects (7.08 × 10⁵ Pt—landfill), but recycling greatly reduced these effects (−3.08 × 10⁵ Pt). Terrestrial ecosystems were negatively impacted by the turbines’ water consumption (8.94 × 10⁵ Pt—landfill), which was lessened in the recycling scenario. The water and soil environment was greatly impacted by released pollutants, such as zinc and chlorinated hydrocarbons, whose emissions were greatly decreased by material recovery. Particularly detrimental was sulfur dioxide (SO₂), which is the cause of PM 2.5 particle matter, which is dangerous to the public’s health. Recycling has helped to lower these pollutants and enhance the quality of the air. Reducing methane and other greenhouse gas emissions can help reduce CO₂ emissions, which were the most significant factor in the context of climate change (1.91 × 10⁴ Pt—landfilling). Recycling lessened these impacts and decreased the need to acquire virgin raw materials, but landfilling was linked to soil acidification and the depletion of mineral resources. According to the findings, even “green” technology, like photovoltaics, can have detrimental effects on the environment if they are not properly handled at the end of their useful lives. Recycling is turning out to be a crucial instrument for lowering negative effects on the environment, increasing resource efficiency, and safeguarding public health. Full article

(This article belongs to the Special Issue Energy Management and Life Cycle Assessment for Sustainable Energy)

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19 pages, 14884 KB

Open AccessArticle

Microscopic Transport During Carbon Dioxide Injection in Crude Oil from Jimsar Oilfield Using Microfluidics

by Huiying Guo, Jianxiang Wang, Yuankai Zhang, Ning Xu, Zhaowen Jiang and Bo Bao

Energies 2025, 18(17), 4774; https://doi.org/10.3390/en18174774 - 8 Sep 2025

Viewed by 411

Abstract

During the process of oil extraction, the urgent need for unconventional oil resources is driven by escalating global demand and the progressive depletion of conventional reserves. Shale oil represents a critical unconventional resource, with recovery efficiency being fundamentally constrained by the multiscale heterogeneity [...] Read more.

During the process of oil extraction, the urgent need for unconventional oil resources is driven by escalating global demand and the progressive depletion of conventional reserves. Shale oil represents a critical unconventional resource, with recovery efficiency being fundamentally constrained by the multiscale heterogeneity of shale reservoirs characterized by intricate networks of microscale fractures and nanoscale pores. To unravel pore structure impacts on microscopic transport phenomena, this study employed microfluidic chips replicating authentic shale pore architectures with pore depths as small as 200 nm to conduct immiscible flooding, constant volume depletion, and huff-n-puff experiments under representative reservoir conditions, with experiments reaching a maximum pressure of 40 MPa. The results show that large-pore and fine-throat structures create dual flow restrictions: the abrupt change in pore throat size amplifies the local flow resistance relative to the homogeneous structure, leading to a 78.09% decline in displacement velocity, while Jamin effect-induced capillary resistance reduces recovery efficiency, and even prevents some crude oil in the pore from being driven out. Slug flow occurred in the experiment, with calculated capillary numbers (Ca) of 0.0015 and 0.0026. This slug flow impedes microscopic transport efficiency, and lower Ca values yield more distinct liquid slugs. CO₂ exhibited effective extraction capabilities for light crude oil components, enriching residual heavy components that impeded subsequent extraction. When contact time was tripled under experimental conditions, this ultimately led to a 25.6% reduction in recovery rate. This investigation offers valuable insights into microscopic transport mechanisms within shale oil systems and provides practical guidance for optimizing shale reservoir development strategies. Full article

(This article belongs to the Section H1: Petroleum Engineering)

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14 pages, 1132 KB

Open AccessArticle

Hydrothermal Liquefaction of Structurally Diverse Lignins: Insights into Biocrude Yield, Fuel Properties, and Reaction Mechanisms

by Md Mostafizur Rahman and Toufiq Reza

Energies 2025, 18(17), 4773; https://doi.org/10.3390/en18174773 - 8 Sep 2025

Viewed by 471

Abstract

Lignin holds significant promise as a feedstock for biocrude production via hydrothermal liquefaction (HTL). Although lignin HTL has been widely studied, the specific depolymerization pathways associated with distinct lignin structures remain largely unexplored. This study investigates the HTL of four structurally diverse lignins: [...] Read more.

Lignin holds significant promise as a feedstock for biocrude production via hydrothermal liquefaction (HTL). Although lignin HTL has been widely studied, the specific depolymerization pathways associated with distinct lignin structures remain largely unexplored. This study investigates the HTL of four structurally diverse lignins: alkaline (AL), dealkaline (DAL), organosolv (OL), and lignosulfonate (LS) across 270–310 °C to elucidate structure-specific mechanisms governing biocrude yield and composition. AL and OL achieved the highest yields (16.8 ± 0.3% and 16.8 ± 2.5%), with AL-derived biocrude showing the highest carbon content (70.2 ± 0.0%) and HHV (31.0 ± 0.2 MJ/kg). In contrast, DAL and LS produced lower yields and inferior fuel quality due to higher sulfur content and lower carbon enrichment. The structures of AL and DAL, containing fewer methoxy groups, produced guaiacol-rich biocrudes (46.6% and 69.5%). Methylation in AL formed alkyl guaiacols and veratroles, while DAL favored side-chain oxidation. OL retained complex structures, forming syringols and desaspidinol, which contributed to heavier biocrude compounds. Sulfonate groups in LS were stabilized mostly as sulfides, leading to elevated sulfur content. These findings provide mechanistic insight into how lignin structure governs HTL behavior, enabling targeted control of biocrude yield and quality for renewable fuel production. Full article

(This article belongs to the Special Issue Advances in Bioenergy and Bioproducts Innovation)

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32 pages, 10952 KB

Open AccessArticle

Study on the Gas–Liquid Two-Flow Characteristics Inside a Three-Stage Centrifugal Pump

by Xiang Zhang and Weidong Cao

Energies 2025, 18(17), 4772; https://doi.org/10.3390/en18174772 - 8 Sep 2025

Viewed by 459

Abstract

This paper takes a small three-stage centrifugal pump as the research object. Based on the RNG k-ε turbulence model and the TFM two-phase flow model, the numerical simulation of the internal gas–liquid two-phase flow was carried out, and the influence of the inlet [...] Read more.

This paper takes a small three-stage centrifugal pump as the research object. Based on the RNG k-ε turbulence model and the TFM two-phase flow model, the numerical simulation of the internal gas–liquid two-phase flow was carried out, and the influence of the inlet gas content rate of the small multistage centrifugal pump on its internal flow was analyzed. The research results show that the head and efficiency of the multistage centrifugal pump will decrease with the increase in the inlet gas content rate. As the gas content increases from 0% to 5%, the head of the multistage centrifugal pump decreases by 3% and its efficiency drops by 5%. The trend of the continuous increase in the pressure on the blade surface does not change with the increase in the inlet gas content rate. The bubble area on the surface of the first-stage impeller blade increases with the increase in the gas content rate. When the inlet gas content rate condition reaches 5%, the bubbles cover the middle section of the blade suction surface. The flow vortex structure is mainly composed of blade separation vortices and mouth ring clearance leakage vortices. The vortices inside the impeller are concentrated in the blade outlet and rim area, while the vortices inside the guide vanes are located in the flow channel area of the anti-guide vanes. With the increase in the gas content rate, the amplitude of pressure pulsation in the flow channel inside the pump decreases. Full article

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22 pages, 8363 KB

Open AccessArticle

Off-Design Performance Modeling of the Natural Gas-Fired Allam Cycle

by Federico D’Ambrosio, Lorenzo Colleoni and Silvia Ravelli

Energies 2025, 18(17), 4771; https://doi.org/10.3390/en18174771 - 8 Sep 2025

Viewed by 424

Abstract

This work focuses on modeling the performance of the natural gas-fired Allam cycle under off-design conditions. Key thermodynamic parameters, such as turbine inlet pressure (TIP), turbine inlet temperature (TIT), and turbine outlet temperature (TOT), were evaluated at part-load and varying environmental conditions. In [...] Read more.

This work focuses on modeling the performance of the natural gas-fired Allam cycle under off-design conditions. Key thermodynamic parameters, such as turbine inlet pressure (TIP), turbine inlet temperature (TIT), and turbine outlet temperature (TOT), were evaluated at part-load and varying environmental conditions. In the former case, different control strategies were implemented in the simulation code (Thermoflex^®) to reduce the power output. In the latter case, the impact of ambient temperature (T_amb) on the minimum cycle temperature (T_min) was evaluated. The ultimate goal is to predict the thermal efficiency (η_th) and its decrease due to partial load operation and warm climate, without thermal recovery from the air separation unit (ASU). With the most efficient partial load strategy, η_th decreased from 50.4% at full load to 40.3% at about 30% load, at nominal T_min. The penalty caused by the increase in T_min due to hot weather, up to T_amb = 30 °C, was significant at loads above 60%, but limited to 0.5 percentage points (pp). Full article

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24 pages, 6123 KB

Open AccessArticle

Multifactor Coupling Effects on Permeability Evolution During Reinjection in Sandstone Geothermal Reservoirs: Insights from Dynamic Core Flow Experiments

by Miaoqing Li, Sen Zhang, Yanting Zhao, Yun Cai, Ming Zhang, Zheng Liu, Pengtao Li, Bing Wang, Bowen Xu, Jian Shen and Bo Feng

Energies 2025, 18(17), 4770; https://doi.org/10.3390/en18174770 - 8 Sep 2025

Viewed by 417

Abstract

Efficient reinjection is critical for maintaining reservoir pressure and ensuring the sustainable development of sandstone geothermal systems. However, complex thermal–hydraulic–chemical (THC) interactions often lead to progressive permeability reduction, significantly impairing injection performance. This study systematically investigates the coupled effects of injection flow rate, [...] Read more.

Efficient reinjection is critical for maintaining reservoir pressure and ensuring the sustainable development of sandstone geothermal systems. However, complex thermal–hydraulic–chemical (THC) interactions often lead to progressive permeability reduction, significantly impairing injection performance. This study systematically investigates the coupled effects of injection flow rate, temperature, and suspended particle size on permeability evolution during geothermal reinjection. Laboratory-scale core flow-through experiments were conducted using sandstone samples from the Guantao Formation in the Huanghua Depression, Bohai Bay Basin. The experimental schemes included graded flow rate tests, temperature-stepped injections, particle size control, long-term seepage, and reverse-flow backflushing operations. The results reveal that permeability is highly sensitive to injection parameters. Flow rates exceeding 6 mL/min induce irreversible clogging and pore structure damage, while lower rates yield more stable injection behavior. Injection at approximately 35 °C resulted in a permeability increase of 15.7%, attributed to reduced fluid viscosity and moderate clay swelling and secondary precipitation. Particles larger than 3 μm were prone to bridging and persistent clogging, whereas smaller particles exhibited more reversible behavior. During long-term seepage, reverse injection implemented upon permeability decline restored up to 98% of the initial permeability, confirming its effectiveness in alleviating pore throat blockage. Based on these findings, a combined reinjection strategy is recommended, featuring low flow rate (≤5 mL/min), moderate injection temperature (~35 °C), and fine filtration (≤3 μm). In addition, periodic backflushing should be considered when permeability loss exceeds 30% or a sustained injection pressure rise is observed. This study provides robust experimental evidence and practical guidance for optimizing geothermal reinjection operations. Full article

(This article belongs to the Special Issue Recent Advances in Geothermal Energy Systems and Reservoir Engineering)

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42 pages, 1089 KB

Open AccessReview

A Overview of Energy Management Strategies for Hybrid Power Systems

by Guoyu Feng, Zhishu Feng, Peng Sun, Lulu Guo and Zhiyong Chen

Energies 2025, 18(17), 4769; https://doi.org/10.3390/en18174769 - 8 Sep 2025

Viewed by 532

Abstract

This paper systematically reviews and analyzes various energy management strategies, as well as the characteristics, core challenges, and general processes of energy management for hybrid vehicles, aircraft, and ships. It also Analyzes the application scenarios, advantages, and limitations of rule-based energy management strategies. [...] Read more.

This paper systematically reviews and analyzes various energy management strategies, as well as the characteristics, core challenges, and general processes of energy management for hybrid vehicles, aircraft, and ships. It also Analyzes the application scenarios, advantages, and limitations of rule-based energy management strategies. Based on the characteristics, design challenges, and general processes of optimized energy management strategies, a comparative analysis was conducted of mainstream strategies such as dynamic programming algorithms, Pontryagin’s minimum principle, equivalent energy consumption minimization, and multi-objective prediction. The focus was on analyzing intelligent control energy management strategies, including hybrid power system energy management strategies and their control effects based on neural network control, adaptive dynamic programming, reinforcement learning, and deep reinforcement learning. Finally, this paper addresses the challenges in applying energy management strategies, the limitations of modeling approaches, the validation of their effectiveness, and future research directions. Full article

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

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17 pages, 3299 KB

Open AccessArticle

Co-Pyrolysis Behavior of Energetic Materials and Pine Sawdust

by Cui Quan, Yufen Wang and Ningbo Gao

Energies 2025, 18(17), 4768; https://doi.org/10.3390/en18174768 - 8 Sep 2025

Viewed by 385

Abstract

Incineration is a widely adopted method for the disposal of waste energetic materials (SP). Nevertheless, this approach is associated with considerable thermal energy loss and significant environmental pollution. To address these limitations, this study proposes a co-pyrolysis process incorporating pine sawdust (SD) with [...] Read more.

Incineration is a widely adopted method for the disposal of waste energetic materials (SP). Nevertheless, this approach is associated with considerable thermal energy loss and significant environmental pollution. To address these limitations, this study proposes a co-pyrolysis process incorporating pine sawdust (SD) with SP. This technique utilizes the exothermic decomposition of energetic substances and the endothermic pyrolysis of biomass. Through this synergistic thermal interaction, the process enables efficient energy recovery and facilitates the resource valorization of SP. The pyrolysis kinetics and thermodynamics of SP, SD, and their blends were investigated. Synchronous thermal analysis examined the co-pyrolysis reaction heat at varying blend ratios, while the temperature’s effects on the gas–liquid–solid product distribution were explored. The results indicate that the apparent activation energy (E_a) required for co-pyrolysis of the SP and SD exhibits an initial increase followed by a decrease in both Stage 1 and Stage 2. Furthermore, the mean apparent activation energy (E_avg) during Stage 1 (FWO: 101.87 kJ/mol; KAS: 94.02 kJ/mol) is lower than that in Stage 2 (FWO: 110.44 kJ/mol; KAS: 100.86 kJ/mol). Co-pyrolysis reaction heat calculations indicated that SD addition significantly mitigates the exothermic intensity, shifts decomposition to higher temperatures (the primary exothermic zone shifted from 180–245 °C to 265–400 °C), and moderates heat release. Elevated temperatures increase the gas yield (CO and H₂ are dominant). High temperatures promote aromatic bond cleavage and organic component release; the char’s calorific value correlates positively with the carbon content. Higher co-pyrolysis temperatures increase the nitrogenous compounds in the oil, while the aldehyde content peaks then declines. This work proposes a resource recovery pathway for SP, providing fundamental data for co-pyrolysis valorization or the development of catalytic conversion precursors. Full article

(This article belongs to the Special Issue Development and Technologies of Biomass Conversion Process, Biofuel Production and Biorefinery)

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17 pages, 1718 KB

Open AccessArticle

A Fifth-Generation-Based Synchronized Measurement Method for Urban Distribution Networks

by Jie Zhang, Bo Pang, Linghao Zhang and Sihao Tang

Energies 2025, 18(17), 4767; https://doi.org/10.3390/en18174767 - 8 Sep 2025

Viewed by 402

Abstract

This work proposes a 5G-based synchronized measurement method for urban distribution networks. First, downlink frequency synchronization is achieved by cross-correlating the Primary and Secondary Synchronization Signals (PSSs/SSSs) within gNB-broadcast Synchronization Signal Blocks (SSBs), enabling accurate alignment with the 5G system clock. Then, uplink [...] Read more.

This work proposes a 5G-based synchronized measurement method for urban distribution networks. First, downlink frequency synchronization is achieved by cross-correlating the Primary and Secondary Synchronization Signals (PSSs/SSSs) within gNB-broadcast Synchronization Signal Blocks (SSBs), enabling accurate alignment with the 5G system clock. Then, uplink phase synchronization is refined using Timing Advance (TA) feedback to compensate for propagation delays. Based on the recovered 5G Pulse Per Second (PPS) signal, a dynamic compensation algorithm is applied to discipline the SAR ADC sampling process. This algorithm tracks crystal oscillator drift, accumulates sub-cycle deviations, and corrects integer timer counts only when the error exceeds

\pm 0.5

. Simulations under a 228 MHz oscillator and 1200 samples per cycle demonstrate that the accumulated phase error remains below 0.00008°, satisfying IEEE C37.118 precision requirements. Compared with traditional GPS-based synchronization methods, the proposed solution offers greater deployment flexibility and can operate reliably in GPS-denied environments such as indoors and urban canyons. Full article

(This article belongs to the Special Issue Advances in Stability Analysis and Control of Power Systems: 2nd Edition)

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25 pages, 5336 KB

Open AccessArticle

Experimental Energy and Exergy Performance Evaluation of a Novel Pumpless Rankine Cycle (PRC) Unit Employing Low-Temperature Heat Sources

by Evangelos Syngounas, John Konstantaras, Nikolaos Arapkoules, Dimitrios Tsimpoukis, Maria K. Koukou and Michail Gr. Vrachopoulos

Energies 2025, 18(17), 4766; https://doi.org/10.3390/en18174766 - 8 Sep 2025

Viewed by 373

Abstract

The current study experimentally investigates the performance of a novel pumpless Rankine cycle (PRC) configuration utilizing low-temperature heat sources. Precisely, a 1 kW_e PRC configuration using R245fa refrigerant is tested under different heat source and heat sink temperature levels. The energetic and [...] Read more.

The current study experimentally investigates the performance of a novel pumpless Rankine cycle (PRC) configuration utilizing low-temperature heat sources. Precisely, a 1 kW_e PRC configuration using R245fa refrigerant is tested under different heat source and heat sink temperature levels. The energetic and exergetic performance indexes are calculated using validated simulation models developed in MATLAB incorporating the CoolProp library. The derived efficiency results are compared with the corresponding indexes of a conventional ORC system used as the baseline. The findings show that for a hot water heat source temperature of 90 °C and a cold water heat sink temperature of 10 °C as the working conditions, the time-averaged thermal efficiency maximizes at 4.5%, while the corresponding time-averaged exergy efficiency is calculated at 31%. Additionally, the innovative PRC topology shows higher efficiency rates compared to the conventional ORC solution for all the working scenarios tested. For a heat sink of 40 °C and a heat source of 90 °C, the thermal efficiency and the exergy efficiency calculated for the PRC are 7.7% and 7.5% higher, respectively, than the baseline ORC system, showing improved exploitation potential. Full article

(This article belongs to the Special Issue Advances in Waste Heat Utilization Systems)

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32 pages, 8114 KB

Open AccessArticle

An Improved Calibration for Satellite Estimation of Flared Gas Volumes from VIIRS Nighttime Data

by Mikhail Zhizhin, Christopher D. Elvidge, Tamara Sparks, Tilottama Ghosh, Morgan Bazilian and Feng-Chi Hsu

Energies 2025, 18(17), 4765; https://doi.org/10.3390/en18174765 - 8 Sep 2025

Viewed by 463

Abstract

The VIIRS Nightfire (VNF) data product is particularly useful for monitoring of global natural gas flaring and estimation of flared gas volumes. Advantages of VIIRS include the collection of nightly global coverage with the inclusion of four daytime channels in the near and [...] Read more.

The VIIRS Nightfire (VNF) data product is particularly useful for monitoring of global natural gas flaring and estimation of flared gas volumes. Advantages of VIIRS include the collection of nightly global coverage with the inclusion of four daytime channels in the near and shortwave infrared that cover the wavelengths of peak radiant emissions from flares. VNF calculates flare temperatures, source areas, and radiant heat using physical laws. For more than a decade, the Earth Observation Group has estimated flared gas volumes based on radiant heat with a calibration based on reported annual flared and vented natural gas volumes from Cedigaz. The calibration was tuned with an exponent of 0.7 placed on the VNF source areas to achieve the highest regression correlation coefficient. The Cedigaz calibration has wide error bars attributed to unresolvable reporting errors in the Cedigaz data. In this paper we report on the development of an empirical calibration for estimating flared gas volumes based on VIIRS observations of flares running at low, medium, and high flared gas volumes. Tests were run with both single and double flares, with and without atmospheric correction. The new calibrations were applied to VIIRS detection profiles for metered flares located in the North Sea, Arabian Peninsula, and Gulf of Mexico. The results indicate the following: (1) the exponent is unnecessary and causes flared gas volumes to be overestimated for small flares and underestimated for large flares, (2) the calibration can be applied to sites having either single or multiple flares, and (3) flared gas volume estimates can be improved by applying an atmospheric correction to account for regional difference in band-specific transmissivity levels. The new calibration has a prediction interval (error bars) seventy times smaller than the Cedigaz calibration. Full article

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

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26 pages, 1261 KB

Open AccessArticle

Speculators and Price Inertia in a Day-Ahead Electricity Market: An Irish Case Study

by Joseph Collins, Andreas Amann and Kieran Mulchrone

Energies 2025, 18(17), 4764; https://doi.org/10.3390/en18174764 - 8 Sep 2025

Viewed by 437

Abstract

Short-term dynamics in auction-based Day-Ahead electricity markets remain insufficiently studied. This paper investigates two such aspects in the Irish Day-Ahead market. First, we address an empirical gap by examining the extent of speculator (financial trader) participation and its evolution over time in a [...] Read more.

Short-term dynamics in auction-based Day-Ahead electricity markets remain insufficiently studied. This paper investigates two such aspects in the Irish Day-Ahead market. First, we address an empirical gap by examining the extent of speculator (financial trader) participation and its evolution over time in a European Day-Ahead setting. Using granular participant-level order and trade data, we quantify speculators’ share of overall market activity and assess how often they are marginal in the auction. Although their share of orders and trades is relatively small, speculators are marginal in a substantial proportion of trading periods and their behaviour changes significantly following a Brexit-related structural shift in market coupling. Second, we introduce a sensitivity-based measure of price inertia defined as the resistance of prices to small changes in demand or supply, adapted to the Day-Ahead auction context, a dimension of market behaviour that has received little prior attention. We find that inertia levels vary considerably and also shift following the structural change. Taken together, these analyses provide empirical evidence that speculators play a non-negligible role in a European auction-based Day-Ahead market, while price inertia offers an additional lens through which to examine short-term market dynamics and their evolution under different market conditions. Full article

(This article belongs to the Special Issue Economic Analysis and Policies in the Energy Sector—2nd Edition)

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24 pages, 4143 KB

Open AccessArticle

Optimisation of a Kind of Vertical Axis Darrieus Turbine—Davidson Hill Venturi Cross-Flow Turbines

by Han Wang, Mark Hill and Joseph Burchell

Energies 2025, 18(17), 4763; https://doi.org/10.3390/en18174763 - 8 Sep 2025

Viewed by 527

Abstract

Vertical axis turbines (VATs) have grown in popularity over the past decade, owing to their lower cost of energy (CoE) when installed in remote offshore locations. The Davidson Hill Venturi system, as a kind of vertical axis tidal turbine technology, has been tested [...] Read more.

Vertical axis turbines (VATs) have grown in popularity over the past decade, owing to their lower cost of energy (CoE) when installed in remote offshore locations. The Davidson Hill Venturi system, as a kind of vertical axis tidal turbine technology, has been tested and proved to increase the power generation by the effect from the venturi structure. Based on the Computational Fluid Dynamic simulation (Ansys 2021R1) software, the present project develops a complete and improved 3D model to calculate the influence from different parameter adjustments on the turbine. The angle of the hydrofoil on the side panel was investigated in a previous study, while the new hydrofoil and different number of blades on the centre rotor can also affect the power generation of the tidal turbines. With this accurately created design, a sizing procedure is developed, and several 3D turbine models with a new hydrofoil or different number of blades are established. Both three-dimensional and two-dimensional section results are compared with the model with adjusting parameters. The 2D section view obtained from a static 3D model without a centre rotor is used to compare with the previous research, while the different number of blades is simulated by the dynamic 3D model without the hydrofoil. An analytical optimisation demonstrates that the new hydrofoil GOE-222 performed better than the material used in a previous study. The optimal number of blades between four blades and eight blades for use in the DHV turbine is also confirmed to be four. Full article

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

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16 pages, 6288 KB

Open AccessArticle

Experimental Study and Calculation of Condensation Heat Transfer in Flue Gas of Gas-Fired Boiler

by Ziyang Cheng, Shuo Peng, Haofei Cai, Ye Bai, Bingfeng Zhou, Xiaoju Wang and Shifeng Deng

Energies 2025, 18(17), 4762; https://doi.org/10.3390/en18174762 - 8 Sep 2025

Viewed by 520

Abstract

The wide application of natural gas will help to achieve the goal of double carbon. The potential of energy saving and carbon reduction after deep condensation of a natural gas flue gas can reach as much as 10~12%. In this paper, the interplay [...] Read more.

The wide application of natural gas will help to achieve the goal of double carbon. The potential of energy saving and carbon reduction after deep condensation of a natural gas flue gas can reach as much as 10~12%. In this paper, the interplay between sensible and latent heat transfer in the process of condensation heat transfer was explored by adjusting the flue gas temperature, relative humidity, cooling water temperature, and other parameters entering the condensation heat exchanger by the condensation heat transfer experimental platform of a gas-fired boiler. The Ln number presents the proportion of water vapor condensation in flue gas, and the P number shows the total amount of water vapor condensation. The increase in Ln and p values promotes the enhancement of water vapor condensation, and the condensation heat transfer coefficient can reach about three to eight times that of a sensible heat transfer coefficient. As the Ln number increases from 0 to 0.35, the promoting effect of sensible heat is enhanced, up to a maximum of 2.5 times. However, from 0.35 to 0.75, the promotion gradually weakens. When the Ln number exceeds 0.75, sensible heat transfer begins to be suppressed, with a minimum coefficient of 0.7. The correction term of the sensible and latent heat transfer coefficient is added to the existing empirical correlation of pure convection heat transfer, which is applicable to various heat exchanger structures and verified by experiments. The micro-element superposition calculation method of the condensing heat exchanger is proposed to realize the digital accurate design of the condensing heat exchanger, which lays the foundation for the extensive promotion and application of the flue gas condensing heat exchanger. Full article

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16 pages, 1932 KB

Open AccessArticle

Analysis of the Dynamic Properties of the Rogowski Coil to Improve the Accuracy in Power and Electromechanical Systems

by Krzysztof Tomczyk, Maciej Gibas and Marek S. Kozień

Energies 2025, 18(17), 4761; https://doi.org/10.3390/en18174761 - 7 Sep 2025

Viewed by 1240

Abstract

This paper presents an analysis of the dynamic properties of the Rogowski coil, primarily by determining the dynamic errors for several selected test signals and the upper bound of the dynamic error for two quality criteria: the integral-square error and the absolute error. [...] Read more.

This paper presents an analysis of the dynamic properties of the Rogowski coil, primarily by determining the dynamic errors for several selected test signals and the upper bound of the dynamic error for two quality criteria: the integral-square error and the absolute error. A procedure for filtering and reproducing these signals is also presented. The foundation of the presented research is an equivalent circuit model of the Rogowski coil, developed primarily for applications in electrical power and electromechanical systems. Two novel aspects of this work are the determination of dynamic errors for the Rogowski coil and a graphical and quantitative comparison of their values. The research results presented in this paper may serve as a foundation for enhancing the accuracy and dynamic reliability of both the Rogowski coil and other devices (e.g., transformers and current transformers) used in the power industry and mechanical engineering, particularly in the condition monitoring of a broad range of power equipment and in the experimental analysis of electromechanical systems operating under variable load conditions. The findings also highlight the importance of accurate current measurement in modern energy systems, where transient and high-frequency components increasingly affect performance and reliability. Consequently, the presented methodology provides a useful framework for guiding sensor selection and signal processing strategies in advanced monitoring and control applications. Full article

(This article belongs to the Special Issue Digital Measurement Procedures for the Energy Industry)

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27 pages, 3553 KB

Open AccessArticle

Experimental-Numerical Method for Determining Heat Transfer Correlations in the Plate-and-Frame Heat Exchanger

by Dawid Taler, Ewelina Ziółkowska, Jan Taler, Tomasz Sobota, Magdalena Jaremkiewicz, Mateusz Marcinkowski and Tomasz Cieślik

Energies 2025, 18(17), 4760; https://doi.org/10.3390/en18174760 - 7 Sep 2025

Viewed by 484

Abstract

Plate heat exchangers are used in heat substations for domestic hot water preparation and building heating in municipal central heating systems. Water from the municipal water supply is heated by hot water from a district heating network. This paper presents a numerical method [...] Read more.

Plate heat exchangers are used in heat substations for domestic hot water preparation and building heating in municipal central heating systems. Water from the municipal water supply is heated by hot water from a district heating network. This paper presents a numerical method for simultaneously determining heat transfer correlations on the cold and hot water sides based on flow-thermal measurements of the plate heat exchanger. The unknown parameters in the functions approximating the Nusselt numbers, which depend on the Reynolds and Prandtl numbers, are determined using the least-squares method, so the sum of the squares of the differences in the calculated and measured temperatures at the heat exchanger outlet reaches a minimum. One or two correlations were sought for a plate heat exchanger, and the total number of parameters sought is between three and six. The limits of the 95% confidence intervals for all estimated parameters were also determined. Correlations for Nusselt numbers determined experimentally for a clean plate heat exchanger can be used in the online monitoring of the degree of fouling of plate heat exchangers installed in the substations of a large urban district heating network. Full article

(This article belongs to the Special Issue Heat Transfer Analysis: Recent Challenges and Applications)

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22 pages, 2841 KB

Open AccessArticle

Application of PVDF Transducers for Piezoelectric Energy Harvesting in Unmanned Aerial Vehicles

by Laís dos Santos Gonçalves, Ricardo Morais Leal Pereira, Rafael Salomão Tyszler, Maria Clara A. M. Morais and Carlos Roberto Hall Barbosa

Energies 2025, 18(17), 4759; https://doi.org/10.3390/en18174759 - 7 Sep 2025

Viewed by 633

Abstract

The demand for sustainable energy generation and storage methods has become inevitable. As a result, numerous sectors are investing in research focused on energy harvesting (EH) techniques. In this context, a promising area involves integrating piezoelectric materials into unmanned aerial vehicles (UAVs)—an application [...] Read more.

The demand for sustainable energy generation and storage methods has become inevitable. As a result, numerous sectors are investing in research focused on energy harvesting (EH) techniques. In this context, a promising area involves integrating piezoelectric materials into unmanned aerial vehicles (UAVs)—an application that enables electrical energy generation from the kinetic energies produced during flight. This article aims to use polyvinylidene fluoride (PVDF) piezoelectric transducers coupled to an EH power management unit (LTC3588-1) to convert and store electrical energy generated by wind from the propellers and motor vibration. Methodologically, the motor and transducers are characterized, a model is developed using LTSpice^®, and experimental validation of the performance of this coupling is carried out for output voltages (V_out) of 1.8 V, 2.5 V, 3.3 V, and 3.6 V. With a motor rotation speed of 3975 rpm, the transducers generated a voltage amplitude of 17.3 V, enabling the capacitor coupled to the EH power management unit—adjusted to the highest V_out—to be charged in approximately 162 s. Thus, this study demonstrated the feasibility of using PVDF as a piezoelectric nanogenerator in UAVs, enabling onboard electronic circuits and sensors to be powered while reserving the battery solely for propulsion, thereby increasing flight autonomy. Full article

(This article belongs to the Special Issue Emerging Trends in Energy Harvesting Materials and Technologies for Sustainable Energy)

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24 pages, 14557 KB

Open AccessArticle

Numerical Investigation of Hydrogen Production via Methane Steam Reforming in Tubular Packed Bed Reactors Integrated with Annular Metal Foam Gas Channels

by Yifan Han, Zihui Zhang, Zhen Wang and Guanmin Zhang

Energies 2025, 18(17), 4758; https://doi.org/10.3390/en18174758 - 7 Sep 2025

Viewed by 563

Abstract

Methane steam reforming is the most widely adopted hydrogen production technology. To address the challenges associated with the large radial thermal resistance and low mass transfer rates inherent in the tubular packed bed reactors during the MSR process, this study proposes a structural [...] Read more.

Methane steam reforming is the most widely adopted hydrogen production technology. To address the challenges associated with the large radial thermal resistance and low mass transfer rates inherent in the tubular packed bed reactors during the MSR process, this study proposes a structural design optimization that integrates annular metal foam gas channels along the inner wall of the reforming tubes. Utilizing multi-physics simulation methods and taking the conventional tubular reactor as a baseline, a comparative analysis was performed on physical parameters that characterize flow behavior, heat transfer, and reaction in the reforming process. The integration of the annular channels induces a radially non-uniform distribution of flow resistance in the tubes. Since the metal foam exhibits lower resistance, the fluid preferentially flows through the annular channels, leading to a diversion effect that enhances both convective heat transfer and mass transfer. The diversion effect redirects the central flow toward the near-wall region, where the higher reactant concentration promotes the reaction. Additionally, the higher thermal conductivity of the metal foam strengthens radial heat transfer, further accelerating the reaction. The effects of operating parameters on performance were also investigated. While a higher inlet velocity tends to hinder the reaction, in tubes integrated with annular channels, it enhances the diversion effect and convective heat transfer. This offsets the adverse impact, maintaining high methane conversion with lower pressure drop and thermal resistance than the conventional tubular reactor does. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) Study for Heat Transfer)

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67 pages, 11035 KB

Open AccessReview

A Comprehensive Review of Well Integrity Challenges and Digital Twin Applications Across Conventional, Unconventional, and Storage Wells

by Ahmed Ali Shanshool Alsubaih, Kamy Sepehrnoori, Mojdeh Delshad and Ahmed Alsaedi

Energies 2025, 18(17), 4757; https://doi.org/10.3390/en18174757 - 6 Sep 2025

Viewed by 2298

Abstract

Well integrity is paramount for the safe, environmentally responsible, and economically viable operation of wells throughout their lifecycle, encompassing conventional oil and gas production, unconventional resource extraction (e.g., shale gas and tight oil), and geological storage applications (CO₂, H₂, [...] Read more.

Well integrity is paramount for the safe, environmentally responsible, and economically viable operation of wells throughout their lifecycle, encompassing conventional oil and gas production, unconventional resource extraction (e.g., shale gas and tight oil), and geological storage applications (CO₂, H₂, and natural gas). This review presents a comprehensive synthesis of well integrity challenges, failure mechanisms, monitoring technologies, and management strategies across these operational domains. Key integrity threats—including cement sheath degradation (chemical attack, debonding, cracking, microannuli), casing failures (corrosion, collapse, burst, buckling, fatigue, wear, and connection damage), sustained casing pressure (SCP), and wellhead leaks—are examined in detail. Unique challenges posed by hydraulic fracturing in unconventional wells and emerging risks in CO₂ and hydrogen storage, such as corrosion, carbonation, embrittlement, hydrogen-induced cracking (HIC), and microbial degradation, are also highlighted. The review further explores the evolution of integrity standards (NORSOK, API, ISO), the implementation of Well Integrity Management Systems (WIMS), and the integration of advanced monitoring technologies such as fiber optics, logging tools, and real-time pressure sensing. Particular emphasis is placed on the role of digital technologies—including artificial intelligence, machine learning, and digital twin systems—in enabling predictive maintenance, early failure detection, and lifecycle risk management. The novelty of this review lies in its integrated, cross-domain perspective and its emphasis on digital twin applications for continuous, adaptive well integrity surveillance. It identifies critical knowledge gaps in modeling, materials qualification, and data integration—especially in the context of long-term CO₂ and H₂ storage—and advocates for a proactive, digitally enabled approach to lifecycle well integrity. Full article

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