Energies

24 pages, 33328 KiB

Open AccessArticle

Energy-Saving Renovation of Existing Buildings: Balancing Thermal Performance and Visual Performance—A Case Study of a University Sports Training Annex in Guangzhou

by Fengdeng Wan, Huazhao Li, Ziqiao Li, Li Li and Xiaomiao Xiao

Energies 2025, 18(9), 2186; https://doi.org/10.3390/en18092186 (registering DOI) - 24 Apr 2025

Abstract

Energy conservation renovation of existing buildings is a crucial aspect of sustainable energy development. This study examines the annex of a university sports training building in Guangzhou, highlighting the conflict between maintaining landscape visibility and mitigating excessive solar radiation and thermal conditions following [...] Read more.

Energy conservation renovation of existing buildings is a crucial aspect of sustainable energy development. This study examines the annex of a university sports training building in Guangzhou, highlighting the conflict between maintaining landscape visibility and mitigating excessive solar radiation and thermal conditions following renovation without external shading. Specifically, the analysis focuses on scenarios where the building’s primary orientation aligns with the region’s unfavorable solar orientation. To address this challenge, five facade optimization strategies are proposed, four of which incorporate external shading solutions: horizontal shading, vertical baffle shading, inclined baffle shading, and a comprehensive shading system. Performance simulations were conducted using Ladybug and Honeybee tools within the Grasshopper platform to evaluate the multi-objective optimization of the building’s thermal and visual performance under energy conservation constraints. The findings demonstrate that an integrated shading system significantly influences both building energy consumption and thermal performance. Notably, the 46° inclined baffle shading scheme proves particularly effective in the Guangzhou context, successfully reducing solar radiation, improving indoor lighting quality, and lowering energy consumption, while minimizing visual obstruction. These results provide valuable insights for developing energy-efficient renovation strategies for similar buildings in the region. Full article

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

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17 pages, 5677 KiB

Open AccessArticle

Volt/Var Control of Electronic Distribution Network Based on Hierarchical Coordination

by Zijie Huang, Kun Yu, Xingying Chen, Bu Xue, Liangxi Guo, Jiarou Li and Xiaolan Yang

Energies 2025, 18(9), 2185; https://doi.org/10.3390/en18092185 - 24 Apr 2025

Abstract

With the increasing penetration of high-proportion renewable energy sources and large-scale integration of power electronic devices, distribution networks are evolving towards power-electronized systems. The integration of high-proportion renewable energy introduces challenges such as bidirectional power flow and voltage violations. Unlike traditional voltage regulation [...] Read more.

With the increasing penetration of high-proportion renewable energy sources and large-scale integration of power electronic devices, distribution networks are evolving towards power-electronized systems. The integration of high-proportion renewable energy introduces challenges such as bidirectional power flow and voltage violations. Unlike traditional voltage regulation devices with slow and discrete adjustment characteristics, power electronic devices can continuously and rapidly respond to voltage fluctuations in distribution networks. However, the integration of power electronic devices alters the operational paradigm of distribution networks, necessitating adaptive voltage-reactive power control methods tailored to the regulation characteristics of both power electronic devices and discrete equipment. To fully exploit the real-time regulation capabilities of power electronic devices, this paper established a hierarchical coordinated control model for power-electronized distribution networks to achieve optimal voltage-reactive power control. A three-stage hierarchical coordinated control architecture is proposed based on the distinct response speeds of different devices. A variable-slope linear droop control method based on voltage boundary parameter optimization is employed for real-time adjustment of soft open point (SOP) and inverter outputs. To address uncertainties in PV generation and load demand, a rolling optimization strategy is implemented for centralized control, supplemented by probabilistic modeling to generate multiple representative scenarios for hierarchical coordinated control. Case studies demonstrate optimized operational results across centralized and local control stages, with comparative analyses against existing voltage-reactive power control methods confirming the superiority of the proposed hierarchical coordinated control framework. Full article

(This article belongs to the Special Issue Optimal Reliability-Oriented Techniques in Power-Electronic-Based Smart Grids)

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28 pages, 928 KiB

Open AccessArticle

Enhancing Energy Sustainability in Remote Mining Operations Through Wind and Pumped-Hydro Storage; Application to Raglan Mine, Canada

by Adrien Tardy, Daniel R. Rousse, Baby-Jean Robert Mungyeko Bisulandu and Adrian Ilinca

Energies 2025, 18(9), 2184; https://doi.org/10.3390/en18092184 - 24 Apr 2025

Abstract

The Raglan mining site in northern Quebec relies on diesel for electricity and heat generation, resulting in annual emissions of 105,500 tons of CO₂ equivalent. This study investigates the feasibility of decarbonizing the site’s power generation system by integrating a renewable energy [...] Read more.

The Raglan mining site in northern Quebec relies on diesel for electricity and heat generation, resulting in annual emissions of 105,500 tons of CO₂ equivalent. This study investigates the feasibility of decarbonizing the site’s power generation system by integrating a renewable energy network of wind turbines and a pumped hydro storage plant (PHSP). It uniquely integrates PHSP modeling with a dynamic analysis of variable wind speeds and extreme climatic conditions, providing a novel perspective on the feasibility of renewable energy systems in remote northern regions. MATLAB R2024b-based simulations assessed the hybrid system’s technical and economic performance. The proposed system, incorporating a wind farm and PHSP, reduces greenhouse gas (GHG) emissions by 50%, avoiding 68,500 tons of CO₂ equivalent annually, and lowers diesel consumption significantly. The total investment costs are estimated at 2080 CAD/kW for the wind farm and 3720 CAD/kW for the PHSP, with 17.3 CAD/MWh and 72.5 CAD/kW-year operational costs, respectively. The study demonstrates a renewable energy share of 52.2% in the energy mix, with a payback period of approximately 11 years and substantial long-term cost savings. These findings highlight the potential of hybrid renewable energy systems to decarbonize remote, off-grid industrial operations and provide a scalable framework for similar projects globally. Full article

(This article belongs to the Special Issue Recent Advances and New Challenges in Solar–Wind Hybrid Energy Systems)

19 pages, 10000 KiB

Open AccessArticle

Adaptive Line Resistance Estimation and Compensation for Accurate Power Sharing of Droop-Controlled DC Microgrids

by Xiangyu Qin, Zhengyu Lin, Wei Jiang and Hazel Lee

Energies 2025, 18(9), 2183; https://doi.org/10.3390/en18092183 - 24 Apr 2025

Abstract

For a DC microgrid with a traditional droop control strategy, achieving accurate power sharing among power converters is challenging due to mismatched line resistance. In a multi-bus DC microgrid system, changes in the power flow can further lead to variation in the equivalent [...] Read more.

For a DC microgrid with a traditional droop control strategy, achieving accurate power sharing among power converters is challenging due to mismatched line resistance. In a multi-bus DC microgrid system, changes in the power flow can further lead to variation in the equivalent line resistance of each power converter. To improve power sharing accuracy, an adaptive line resistance estimation method is proposed in this paper, which can accurately estimate line resistance without additional hardware. The estimated line resistances are then used to compensate the droop coefficient of each power converter to ensure accurate power sharing between power converters. Simulation and experimental results are presented to demonstrate the effectiveness of the proposed method for single bus, multi-bus, and ring-bus DC microgrid systems. Full article

(This article belongs to the Topic Optimal Planning, Integration and Control of Smart Grids and Microgrids Systems, 2nd Edition)

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26 pages, 5014 KiB

Open AccessArticle

Heat Transfer Coefficient of a Building: A Constant with Limited Variability or Dynamically Variable?

by Ljubomir Jankovic, Grant Henshaw, Christopher Tsang, Xinyi Zhang, Richard Fitton and William Swan

Energies 2025, 18(9), 2182; https://doi.org/10.3390/en18092182 - 24 Apr 2025

Abstract

The heat transfer coefficient, or the HTC, is an industry-standard indicator of building energy performance. It is predicated on an assumption that it is of a constant value, and several different methods have been developed to measure and calculate the HTC as a [...] Read more.

The heat transfer coefficient, or the HTC, is an industry-standard indicator of building energy performance. It is predicated on an assumption that it is of a constant value, and several different methods have been developed to measure and calculate the HTC as a constant. Whilst there are limited variations in the results obtained from these different methods, none of these methods consider a possibility that the HTC could be dynamically variable. Our experimental work shows that the HTC is not a constant. The experimental evidence based on our environmental chambers, which contain detached houses and in which the ambient air temperature can be controlled between −24 °C and +51 °C, with additional relative humidity control and with weather rigs that can introduce solar radiation, rain, and snow, shows that the HTC is dynamically variable. The analysis of data from the fully instrumented and monitored houses in combination with calibrated simulation models and data processing scripts based on genetic algorithm optimization provide experimental evidence of the dynamic variability of the HTC. This research increases the understanding of buildings physics properties and has the potential to change the way the heat transfer coefficient is used in building performance analysis. Full article

(This article belongs to the Special Issue Sustainable Built Environment: Energy Efficiency Technologies, Performance Evaluation and Indoor Environment Quality)

15 pages, 896 KiB

Open AccessArticle

Hydrothermal Liquefaction (HTL) of Lignin: The Adsorption Separation of Catechol Guaiacol and Phenol

by Emmanuel Bala, Ursel Hornung and Nicolaus Dahmen

Energies 2025, 18(9), 2181; https://doi.org/10.3390/en18092181 - 24 Apr 2025

Abstract

The complex nature of the hydrothermal liquefaction (HTL) of lignin product downstream requires an effective separation strategy. In this study, the use of adsorption separation was undertaken using deep eutectic solvent (DES)-modified amberlite XAD-4 adsorbents to achieve this goal. XAD-4 was modified with [...] Read more.

The complex nature of the hydrothermal liquefaction (HTL) of lignin product downstream requires an effective separation strategy. In this study, the use of adsorption separation was undertaken using deep eutectic solvent (DES)-modified amberlite XAD-4 adsorbents to achieve this goal. XAD-4 was modified with a choline chloride: ethylene glycol DES and characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and the Brunauer–Emmett–Teller (BET) test. In addition, the HTL product was characterized using Gas Chromatography with Flame Ionization Detection (GC-FID). The performance of unmodified and DES-modified adsorbents was initially tested on the model compounds of guaiacol, phenol and catechol, followed by the HTL product in a batch adsorption system. The Freundlich model best described the model compound adsorption system with a preferential affinity for guaiacol (k_f = 12.52), outperforming phenol and catechol. Adsorption experiments showed an increase in capacity and selectivity for all species when the DES-modified adsorbents were used at all mass loadings. GC-FID analytics showed the DES-modified XAD-4 (300 mg) as having the highest selectivity for guaiacol, with an equilibrium concentration of 121.45 mg/L representing an 85.25% uptake, while catechol was the least favorably adsorbed. These results demonstrate the potential of DES-functionalized XAD-4 adsorbents in selectively isolating high-value aromatics from the HTL of the lignin product stream. Full article

(This article belongs to the Special Issue Selected Papers from the 32nd European Biomass Conference and Exhibition (EUBCE 2024))

22 pages, 553 KiB

Open AccessArticle

The Impact of Energy Efficiency Technologies, Political Stability and Environmental Taxes on Biocapacity in the USA

by Mihaela Simionescu

Energies 2025, 18(9), 2180; https://doi.org/10.3390/en18092180 - 24 Apr 2025

Abstract

The increasing human demand for natural resources is leading to critical resource depletion. This depletion is exacerbated by exceeding the Earth’s biological regeneration rate, threatening ecosystems’ ability to renew biomass. This ecological challenge hinders the potential for simultaneous economic, social, and environmental progress. [...] Read more.

The increasing human demand for natural resources is leading to critical resource depletion. This depletion is exacerbated by exceeding the Earth’s biological regeneration rate, threatening ecosystems’ ability to renew biomass. This ecological challenge hinders the potential for simultaneous economic, social, and environmental progress. This study investigates the complex relationships between the USA’s per capita income, energy efficiency innovations, environmental taxation, political stability, and its biocapacity. Using annual data from 1990 to 2024, the paper employs a comprehensive causality testing framework that accounts for the nonlinear nature of the data, as asymmetric effects are observed. This framework includes the Quantile Autoregressive Distributed Lags model (Q-ARDL), the Wald test for parameter consistency, and the Granger-causality in Quantiles test (GC-Q), enabling the estimation of unique parameter vectors for each quantile. A key finding reveals that the impact of per capita GDP on biocapacity is significantly larger than that of other regulatory mechanisms. This suggests that carbon pricing and energy efficiency technologies require widespread implementation to offset the environmental impact of economic growth. The quantile regression reveals complex short-run impacts on biocapacity with persistent positive effects from its lag, contrasting with the diminishing negative influence of GDP and positive influence of energy efficiency at higher quantiles, while long-run analysis shows a consistent negative impact of GDP and varying positive or nonlinear effects of other factors. Granger-causality tests indicate significant unidirectional positive effects from energy efficiency and political stability to biocapacity, a bidirectional relationship for environmental taxes in upper quantiles and GDP across all quantiles. The associated methodological and policy implications aim to assist policymakers in achieving a better balance between the benefits and costs of natural resource use in the USA, promoting sustainable development. Full article

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

25 pages, 17509 KiB

Open AccessArticle

Development and Application of a Sensitivity and Uncertainty Analysis Framework for Safety Analysis of Molten Salt Reactors

by Haijun Liu, Rui Li, Xiandi Zuo, Maosong Cheng, Shichao Chen and Zhimin Dai

Energies 2025, 18(9), 2179; https://doi.org/10.3390/en18092179 - 24 Apr 2025

Abstract

To provide reliable safety margins in reactor design and safety analysis, the best estimate plus uncertainty (BEPU) analysis, which is recommended by the International Atomic Energy Agency (IAEA), has drawn increasing attention worldwide. In order to systematically evaluate the sensitivity and uncertainty in [...] Read more.

To provide reliable safety margins in reactor design and safety analysis, the best estimate plus uncertainty (BEPU) analysis, which is recommended by the International Atomic Energy Agency (IAEA), has drawn increasing attention worldwide. In order to systematically evaluate the sensitivity and uncertainty in the design and safety analysis of molten salt reactors (MSRs), a sensitivity and uncertainty analysis framework has been developed by integrating the reactor system safety analysis code RELAP5-TMSR with the data analysis code RAVEN. The framework is tested using the transient scenarios of the molten salt reactor experiment (MSRE): reactivity insertion accident (RIA) and station blackout (SBO). The testing results demonstrate that the proposed framework effectively conducts sensitivity and uncertainty analysis. Sensitivity analyses identify key input parameters, including the primary exchanger parameters, air radiator parameters, initial temperatures, delayed neutron parameters and volumetric heat capacity of the INOR-8 alloy. Uncertainty quantification provides 95% confidence intervals for the figures of merit (FOMs) and the steady-state and RIA scenarios remained within safety limits. The developed framework enables automated, efficient, and high-capacity sensitivity and uncertainty analysis across multiple parameters and transient scenarios. The systematic analysis provides sensitivity indicators and uncertainty distributions, offering quantitative insights into the safety margins and supporting the design and safety analysis of MSRs. Full article

(This article belongs to the Special Issue Advances in Nuclear Power Plants and Nuclear Safety)

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20 pages, 2505 KiB

Open AccessArticle

Anaerobic Co-Digestion of Common Reed and Plant-Based Biowaste from Households

by Robert Czubaszek and Agnieszka Wysocka-Czubaszek

Energies 2025, 18(9), 2178; https://doi.org/10.3390/en18092178 - 24 Apr 2025

Abstract

Organic wastes from households, private gardens, the maintenance of urban greenery, and active nature conservation measures are often difficult to manage. This lignocellulosic biomass may be suitable for anaerobic digestion (AD). However, the mono-digestion of plant material, such as waste from active conservation [...] Read more.

Organic wastes from households, private gardens, the maintenance of urban greenery, and active nature conservation measures are often difficult to manage. This lignocellulosic biomass may be suitable for anaerobic digestion (AD). However, the mono-digestion of plant material, such as waste from active conservation measures for wetlands, results in a low methane (CH₄) yield. The aim of this study was to assess the feasibility of using common reed silage for co-digestion with plant-based biowaste from households. The specific methane yield (SMY) was determined in biochemical methane potential (BMP) tests performed on biowaste, reed silage, and combinations of reed silage with 10%, 30%, 50%, 70%, and 90% of biowaste on a fresh weight basis. The lowest SMY was observed for the mono-digestion of reed silage (160.40 ± 4.09 NL kg_VS⁻¹), while biowaste had the highest CH₄ yield (284.03 ± 7.03 NL kg_VS⁻¹). The subsequent addition of biowaste enhanced CH₄ production from 158.57 ± 7.88 NL kg_VS⁻¹ (10% of biowaste) to 233.28 ± 11.91 NL kg_VS⁻¹ (90% of biowaste). A key advantage of biogas production is its role in reducing CO₂ emissions into the atmosphere, which result from the use of conventional fuels for energy generation. The avoided CO₂ emissions generated in electricity and heat production range between 378.62 kgCO₂ t_TS⁻¹ and 676.36 kgCO₂ t_TS⁻¹ depending on the reed silage-to-biowaste ratio used for biogas production. This study reveals that reed silage is not an optimal feedstock for biogas production, and its share in co-digestion with biowaste should not exceed 10% of the total input to the biogas plant. Full article

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

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16 pages, 954 KiB

Open AccessArticle

Technological Advancements and Economic Growth as Key Drivers of Renewable Energy Production in Saudi Arabia: An ARDL and VECM Analysis

by Faten Derouez

Energies 2025, 18(9), 2177; https://doi.org/10.3390/en18092177 - 24 Apr 2025

Abstract

This study examines the short- and long-term effects of various economic, environmental, and policy factors on renewable energy production (REP) in Saudi Arabia from 1990 to 2024, using the Autoregressive Distributed Lag (ARDL) approach and Vector Error Correction Model (VECM) techniques. The analysis [...] Read more.

This study examines the short- and long-term effects of various economic, environmental, and policy factors on renewable energy production (REP) in Saudi Arabia from 1990 to 2024, using the Autoregressive Distributed Lag (ARDL) approach and Vector Error Correction Model (VECM) techniques. The analysis focuses on fossil fuel consumption (FFC), renewable energy investment (REI), carbon emissions (CEs), energy prices (EPs), government policies (GPs), technological advancements (TAs), socioeconomic factors (SEFs), and economic growth (EG) as determinants of REP, measured as electricity generated from solar power sources in kilowatt-hours (kWh). Short-term findings reveal a positive momentum effect, where prior REP levels significantly influence current production, driven by factors such as learning by doing, economies of scale, and consistent policy support. However, FFC negatively impacts REP, highlighting resource competition and market dynamics favoring fossil fuels. Positive short-term influences include REI, CEs, EPs, GPs, TAs, SEFs, and EG, which collectively enhance renewable energy adoption through investments, technological innovation, policy incentives, and economic development. Long-term analysis underscores a strong negative relationship between FFC and REP, with a 7503-unit decline in REP associated with increased fossil fuel dependency. Conversely, REP benefits from REI, CEs, EPs, GPs, TAs, and EG, with significant contributions from technological advancements (3769-unit increase) and economic growth (9191-unit increase). However, SEFs exhibit a slight negative impact, suggesting that rapid urbanization and population growth may outpace renewable infrastructure development. Overall, the study highlights the complex interplay of factors shaping renewable energy production, emphasizing the importance of sustained investments, supportive policies, and technological innovation, while addressing challenges posed by fossil fuel reliance and socioeconomic pressures. These insights provide valuable implications for policymakers and stakeholders aiming to accelerate the transition to renewable energy in Saudi Arabia. Full article

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

24 pages, 38545 KiB

Open AccessArticle

A Novel Hybrid FEM–Dynamic Modeling Approach for Enhanced Vibration Diagnostics in a Two-Stage Spur Gearbox

by Amine El Amli, Bilal El Yousfi, Abdenour Soualhi and François Guillet

Energies 2025, 18(9), 2176; https://doi.org/10.3390/en18092176 - 24 Apr 2025

Abstract

The condition monitoring of gearboxes is crucial to ensuring the reliability and efficiency of modern industrial machinery. The accurate estimation of Time-Varying Mesh Stiffness (TVMS) is a key aspect of modeling gear meshing behavior and generating vibration signals used for fault diagnosis. In [...] Read more.

The condition monitoring of gearboxes is crucial to ensuring the reliability and efficiency of modern industrial machinery. The accurate estimation of Time-Varying Mesh Stiffness (TVMS) is a key aspect of modeling gear meshing behavior and generating vibration signals used for fault diagnosis. In this study, TVMS is calculated by using the Refined Finite Element Method (R-FEM), which captures detailed gear-body compliance and distributed load effects. The dynamic model of a two-stage gearbox is then used to generate vibration responses under both healthy and faulty conditions. A comprehensive parametric sensitivity analysis is conducted on critical gear modeling parameters, including tooth profile deviations, mesh convergence in contact zones, assembly tolerance-induced interaxial variations, load-dependent stiffness variations, and hub-radius effects. Experimental validation using a gearbox test bench confirms that the proposed methodology accurately reproduces fault-specific harmonic components. These results indicate that the hybrid FEM–dynamic modeling approach effectively balances accuracy and computational efficiency, thereby providing a robust framework for advanced fault detection and maintenance strategies in gear systems. Full article

(This article belongs to the Special Issue Failure Diagnosis and Prognosis of AC Rotating Machines)

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15 pages, 9464 KiB

Open AccessArticle

Molecular Simulation Study of Gas–Water Adsorption Behavior and Mobility Evaluation in Ultra-Deep, High-Pressure Fractured Tight Sandstone Reservoirs

by Yongfu Liu, Xuehao Pei, Fenglai Yang, Junjie Zhong, Li Dai, Cuili Wang, Tingya Zhou, Yijia Li and Sa Xiao

Energies 2025, 18(9), 2175; https://doi.org/10.3390/en18092175 - 24 Apr 2025

Abstract

Under high-temperature and high-pressure conditions, understanding the competitive adsorption and mobilization mechanisms of gas and water in fractured tight sandstone gas reservoirs is crucial for optimizing the recovery factor. This study employs molecular dynamics simulation to investigate the adsorption behavior and mobilization characteristics [...] Read more.

Under high-temperature and high-pressure conditions, understanding the competitive adsorption and mobilization mechanisms of gas and water in fractured tight sandstone gas reservoirs is crucial for optimizing the recovery factor. This study employs molecular dynamics simulation to investigate the adsorption behavior and mobilization characteristics of H₂O and CH₄ in 10 nm quartz nanopores under the conditions of the Keshen fractured tight sandstone gas reservoir. The results indicate that H₂O exhibits strong adsorption on the quartz surface, forming two high-density adsorption layers with a thickness of approximately 0.6 nm, whereas CH₄ forms three adsorption layers with a thickness of about 1.1 nm. Under gas–water coexistence conditions, the competitive adsorption effect of the water phase significantly influences the distribution of CH₄. Due to the hydrophilicity of the quartz wall, H₂O molecules preferentially adsorb onto the wall surface, forming a stable water film that significantly inhibits CH₄ adsorption. When the water saturation reaches 35%, water molecules form liquid bridges within the pores, segmenting the gas phase into different regions. As water saturation further increases, more stable liquid bridge structures develop, and microscopic water lock effects emerge, further restricting gas flow. During depletion development, H₂O remains difficult to mobilize due to strong wall adsorption, with a recovery factor of only 7%. In contrast, CH₄ exhibits high mobility, with a recovery factor of up to 75%. However, as water saturation increases from 30% to 70%, the recovery factor of CH₄ decreases significantly from 75% to 29%, indicating that the water phase not only occupies pore space, but also exerts a blocking effect that significantly inhibits CH₄ percolation and production. This study provides important theoretical support for the development strategies of ultra-deep fractured tight sandstone gas reservoirs and offers key insights for improving the ultimate recovery factor under gas–water coexistence conditions. Full article

(This article belongs to the Special Issue New Advances in Low-Energy Processes for Geo-Energy Development)

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24 pages, 10711 KiB

Open AccessArticle

Solid Oxide Fuel Cell Voltage Prediction by a Data-Driven Approach

by Hristo Ivanov Beloev, Stanislav Radikovich Saitov, Antonina Andreevna Filimonova, Natalia Dmitrievna Chichirova, Egor Sergeevich Mayorov, Oleg Evgenievich Babikov and Iliya Krastev Iliev

Energies 2025, 18(9), 2174; https://doi.org/10.3390/en18092174 - 24 Apr 2025

Abstract

A solid oxide fuel cell (SOFC) is an electrochemical energy conversion device that provides higher thermoelectric efficiency than traditional cogeneration systems. Current research in this field highlights a variety of mathematical models. These models are based on complex physicochemical and electrochemical reactions, enabling [...] Read more.

A solid oxide fuel cell (SOFC) is an electrochemical energy conversion device that provides higher thermoelectric efficiency than traditional cogeneration systems. Current research in this field highlights a variety of mathematical models. These models are based on complex physicochemical and electrochemical reactions, enabling accurate simulation and optimal control of fuel cells. However, these models require substantial computational resources, leading to high processing times. White box and gray box models are unable to achieve real-time optimization of control parameters. A potential solution involves using data-driven machine learning (ML) black-box models. This study examines three ML models: artificial neural network (ANN), random forest (RF), and extreme gradient boosting (XGB). The training dataset consisted of experimental results from SOFC laboratory experiments, comprising 32,843 records with 47 control parameters. The study evaluated the effectiveness of input matrix dimensionality reduction using the following feature importance evaluation methods: mean decrease in impurity (MDI), permutation importance (PI), principal component analysis (PCA), and Shapley additive explanations (SHAP). The application of ML models revealed a complex nonlinear relationship between the SOFC output voltage and the control parameters of the system. The default XGB model achieved the optimal balance between accuracy (MSE = 0.9940) and training speed (τ = 0.173 s/it), with performance capabilities that enable real-time enhancement of SOFC thermoelectric characteristics during system operation. Full article

(This article belongs to the Section F5: Artificial Intelligence and Smart Energy)

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12 pages, 3627 KiB

Open AccessArticle

Nitrogen-Free Co-Gasification of Fermentation Residues

by Clemens Schmittmann, Felix Öffner and Peter Quicker

Energies 2025, 18(9), 2173; https://doi.org/10.3390/en18092173 - 24 Apr 2025

Abstract

The limited usage of fermentation residues, due to increasingly stringent legal requirements, demands novel routes of utilization for these feedstocks. To the best of our knowledge, for the first time, a mixture of fermentation residues and wood chips is used as feedstock in [...] Read more.

The limited usage of fermentation residues, due to increasingly stringent legal requirements, demands novel routes of utilization for these feedstocks. To the best of our knowledge, for the first time, a mixture of fermentation residues and wood chips is used as feedstock in a fixed-bed gasifier, using only O₂/CO₂ mixtures as gasifying agent. The maximum O₂ concentration achieved was 31.6 Vol.-%. Pronounced process stability was achieved with a cold gas efficiency of about 94%, possibly due to CO₂ conversion within the process. The heating value of the produced synthesis gas was 8.5 MJ/m³_i.N.dry, with increased amounts of carbon monoxide and methane when compared to air-blown operations. Full article

(This article belongs to the Special Issue Advanced Bioenergy, Biomass and Waste Conversion Technologies)

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14 pages, 1262 KiB

Open AccessArticle

Method of Quality Control of Nuclear Reactor Element Tightness to Improve Environmental Safety

by Eduard Khomiak, Roman Trishch, Joanicjusz Nazarko, Miloslav Novotný and Vladislavas Petraškevičius

Energies 2025, 18(9), 2172; https://doi.org/10.3390/en18092172 - 24 Apr 2025

Abstract

Low carbon dioxide (CO₂) emissions make nuclear energy crucial in decarbonizing the economy. In this context, nuclear safety, and especially the operation of nuclear power plants, remains a critical issue. This article presents a new fractal cluster method of control that [...] Read more.

Low carbon dioxide (CO₂) emissions make nuclear energy crucial in decarbonizing the economy. In this context, nuclear safety, and especially the operation of nuclear power plants, remains a critical issue. This article presents a new fractal cluster method of control that improves the quality of assessing fuel element cladding integrity, which is critical for nuclear and environmental safety. The proposed non-destructive testing method allows for detecting defects on the inner and outer cladding surfaces without removing the elements from the nuclear reactor, which ensures prompt response and prevention of radiation leakage. Studies have shown that the fractal dimension of the cladding surface, which varies from 2.1 to 2.5, indicates significant heterogeneity caused by mechanical damage or corrosion, which can affect its integrity. The density analysis of defect clusters allows quantifying their concentration per unit area, which is an important indicator for assessing the risks associated with the operation of nuclear facilities. The data obtained are used to assess the impact of defects on the vessel’s integrity and, in turn, on nuclear safety. The monitoring results are transmitted in real time to the operator’s automated workstation, allowing for timely decision making to prevent radioactive releases and improve environmental safety. The proposed method is a promising tool for ensuring reliable quality control of the fuel element cladding condition and improving nuclear and environmental safety. While the study is based on VVER-1000 reactor data, the flexibility of the proposed methodology suggests its potential applicability to other reactor types, opening avenues for broader implementation in diverse nuclear systems. Full article

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

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16 pages, 9363 KiB

Open AccessArticle

Internal Model Current Decoupling Control Strategy for Induction Motors

by Qiuyue Xie, Qiwei Xu, Tao Yang and Yuxiaoying Tu

Energies 2025, 18(9), 2171; https://doi.org/10.3390/en18092171 - 24 Apr 2025

Abstract

In order to improve the current dynamic performance of induction motor (IM) drive systems, an internal model current decoupling control strategy is proposed to suppress the stator’s internal coupling effect. First, the IM mathematical model in the complex frequency domain is established, and [...] Read more.

In order to improve the current dynamic performance of induction motor (IM) drive systems, an internal model current decoupling control strategy is proposed to suppress the stator’s internal coupling effect. First, the IM mathematical model in the complex frequency domain is established, and the expressions of the coupling terms are derived. Then, according to the zero-pole distribution diagram and Bode plots, the design details for the structure and parameters of the internal model controller are presented in a continuous domain, and the impact of stator inductance mismatch on decoupling performance is analyzed. In addition to considering sampling and control delays, the IM mathematical model is established in the discrete domain, and the principle of the controller parameter is presented. Finally, the experimental results prove that the proposed internal model current decoupling control strategy can effectively improve the dynamic performance of IMs. Compared with the traditional feedforward current decoupling control strategy, the proposed method has superior decoupling performance under the operating conditions of low switching frequency. At the same time, a better steady-state performance is obtained by the proposed internal model control strategy. Full article

(This article belongs to the Special Issue Recent Advances in Control Algorithms for a Fault-Tolerant PMSM Drives)

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16 pages, 3592 KiB

Open AccessArticle

Research on the Frequency Stability Analysis of Grid-Connected Double-Fed Induction Generator Systems

by Peng Jia, Yun Sun, Linlin Yu, Jing Zhang, Xiaoliang Jiang and Gaojun Meng

Energies 2025, 18(9), 2170; https://doi.org/10.3390/en18092170 - 24 Apr 2025

Abstract

Existing approaches insufficiently analyze the quantitative relationship between frequency stability indices and wind power penetration rates. This limitation impedes rapid and accurate assessments of wind power’s grid integration potential. This paper first analyzed the impact mechanism of wind power integration on system inertia [...] Read more.

Existing approaches insufficiently analyze the quantitative relationship between frequency stability indices and wind power penetration rates. This limitation impedes rapid and accurate assessments of wind power’s grid integration potential. This paper first analyzed the impact mechanism of wind power integration on system inertia and static power-frequency characteristics from different aspects of the influence of double-fed induction generators (DFIGs) on the operating modes of synchronous machines. Subsequently, based on this analysis, the paper derived the quantitative relationship between key indicators reflecting transient frequency response characteristics during power shortages and wind power penetration rates. It also rapidly calculated the maximum wind power penetration rate based on constraints of frequency change rate and maximum frequency deviation, thereby enabling a quantitative evaluation of wind power grid connection capability. Finally, the IEEE 39-bus test system was used for case analysis. The research results indicate that the proposed method can accurately quantify the impact of wind power variation on system frequency stability and rapidly determine the maximum wind power penetration rate to ensure frequency stability, thereby improving the accuracy of the wind power grid connection capability assessment. Full article

(This article belongs to the Special Issue Clean and Efficient Use of Energy: 2nd Edition)

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13 pages, 405 KiB

Open AccessArticle

Understanding People’s Intentions Towards the Adoption of Biogas Technology: Applying the Diffusion of Innovation Theory and the Theory of Planned Behavior

by Regina Kulugomba, Harold W. T. Mapoma, Gregory Gamula, Stanley Mlatho and Richard Blanchard

Energies 2025, 18(9), 2169; https://doi.org/10.3390/en18092169 - 23 Apr 2025

Abstract

The objective of the study was to investigate factors that influence people’s intentions to adopt biogas technology in Malawi. The study adopted variables of the diffusion of innovation theory (DIT) (relative advantage, compatibility, complexity, and observability) and the theory of planned behavior (TPB) [...] Read more.

The objective of the study was to investigate factors that influence people’s intentions to adopt biogas technology in Malawi. The study adopted variables of the diffusion of innovation theory (DIT) (relative advantage, compatibility, complexity, and observability) and the theory of planned behavior (TPB) (subjective norms, perceived behavioral control, and attitude) to assess the intention. The study utilized a quantitative methodology, gathering primary data from 98 potential biogas adopters in five districts in Malawi using a questionnaire with a five-point Likert scale. After data collection, a reliability test was conducted to determine the questionnaire’s reliability. A multiple regression analysis was performed to establish the relationship between independent and dependent variables. The subjective norms, perceived behavioral control, and attitude were taken as independent variables while the intention to adopt biogas technology was the dependent variable. The study’s results indicated that only compatibility and subjective norms were significant predictors and independently contributed to predicting the individuals’ intentions to adopt biogas technology. This will assist policy makers to provide technologies that will be compatible to people’s culture and lifestyle, hence preventing the wasting of resources. At the same time, the involvement of important people in society will help to raise awareness of the importance of biogas technology. Full article

(This article belongs to the Special Issue Bioenergy Economics: Analysis, Modeling and Application, 2nd Edition)

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16 pages, 8471 KiB

Open AccessArticle

Study on Purge Strategy of Hydrogen Supply System with Dual Ejectors for Fuel Cells

by Yueming Liang and Changqing Du

Energies 2025, 18(9), 2168; https://doi.org/10.3390/en18092168 - 23 Apr 2025

Abstract

The exhaust purge on the anode side is a critical step in the operation of fuel cell systems, and optimizing the exhaust interval time is essential for enhancing stack efficiency and hydrogen utilization. This paper proposed a method to determine the purge strategy [...] Read more.

The exhaust purge on the anode side is a critical step in the operation of fuel cell systems, and optimizing the exhaust interval time is essential for enhancing stack efficiency and hydrogen utilization. This paper proposed a method to determine the purge strategy of hydrogen supply system based on theoretical and simulation analysis. To investigate the impact of anode purge strategy on the performance of automotive fuel cells, a model of a 100 kW fuel cell stack and a dual-ejector hydrogen supply system was developed in MATLAB/Simulink(R2022b) using principles of fluid dynamics, simulation, and experimental data. This model effectively captures the accumulation and exhaust of hydrogen, nitrogen, and vapor within the anode. Simulations were conducted under seven different exhaust interval times at varying current densities to study the effect of exhaust interval on the performance of the fuel cell. The results indicate that for a 100 kW fuel cell, the exhaust interval time should be controlled within 25 s and should decrease as the current density increases. At low current density, increasing the exhaust interval has a more significant effect on improving hydrogen utilization. At high current density, reducing the exhaust interval helps maintain a stable hydrogen excess ratio and shortens the time required for the output voltage to reach a stable state. Full article

(This article belongs to the Special Issue Advances in Hydrogen Energy and Fuel Cell Technologies)

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19 pages, 5281 KiB

Open AccessArticle

Bidirectional Energy Transfer Between Electric Vehicle, Home, and Critical Load

by Ștefan-Andrei Lupu and Dan Floricău

Energies 2025, 18(9), 2167; https://doi.org/10.3390/en18092167 - 23 Apr 2025

Abstract

In the transition to a sustainable energy system, the integration of electric vehicles into residential energy systems is an innovative solution for increasing energy resilience and optimizing electricity consumption. This article presents a bidirectional AC/DC converter capable of charging the electric vehicle battery [...] Read more.

In the transition to a sustainable energy system, the integration of electric vehicles into residential energy systems is an innovative solution for increasing energy resilience and optimizing electricity consumption. This article presents a bidirectional AC/DC converter capable of charging the electric vehicle battery under normal conditions, while providing power to a critical consumer in the event of a power grid outage. The simulations performed show us the functionality of this converter, demonstrating its efficiency in ensuring the continuity of supply. Full article

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

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13 pages, 2333 KiB

Open AccessArticle

Optimization of Hydrogen Internal Combustion Engines Equipped with Turbocompound Technology for Enhanced Performance and Efficiency

by Pier Paolo Brancaleoni, Enrico Corti, Federico Di Prospero, Davide Di Battista, Roberto Cipollone and Vittorio Ravaglioli

Energies 2025, 18(9), 2166; https://doi.org/10.3390/en18092166 - 23 Apr 2025

Abstract

Hydrogen Internal Combustion Engines (H₂ICEs) offer significant potential in reducing the CO₂ emissions of the heavy-duty transport sector in the pursuit of the European Green Deal targets. However, the challenges associated with hydrogen energy density require advanced technologies for fuel [...] Read more.

Hydrogen Internal Combustion Engines (H₂ICEs) offer significant potential in reducing the CO₂ emissions of the heavy-duty transport sector in the pursuit of the European Green Deal targets. However, the challenges associated with hydrogen energy density require advanced technologies for fuel efficiency enhancement. Hybrid powertrains, equipped with innovative energy recovery systems, allow optimizing the engine working point while recovering otherwise wasted energy. In particular, Turbocompound (TCo) systems allow recovering the energy content in the exhaust gases, improving the overall efficiency of the powertrain. Optimizing both engine operation and TCo recovery presents a significant challenge, as it requires balancing the dynamic interaction between the engine’s combustion process and TCo (which increases backpressure). This paper presents a novel approach aimed at optimizing the performance of a hybrid hydrogen-fueled internal combustion engine by integrating a TCo system. The TCo allows extracting a 9 kW extra power peak with respect to the baseline configuration. The performance assessment of the optimized working point for series hybrid powertrains underscores the capability of the strategy to reduce hydrogen consumption up to 6.8%. Full article

(This article belongs to the Section J: Thermal Management)

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22 pages, 12626 KiB

Open AccessArticle

Comparative Studies of Three-Dimensional Complex Flow Field Designs in a Proton Exchange Membrane Hydrogen Fuel Cell

by Dilyan Gavrailov and Silviya Boycheva

Energies 2025, 18(9), 2165; https://doi.org/10.3390/en18092165 - 23 Apr 2025

Abstract

The performance and durability of proton-exchange membrane fuel cells (PEMFCs) are dependent on fuel flow, humidifying water, and outgoing water management. Unlike conventional flow fields with linear channels, the complex 3D flow field—featuring repeating baffles along the channel, known as the baffle design—induces [...] Read more.

The performance and durability of proton-exchange membrane fuel cells (PEMFCs) are dependent on fuel flow, humidifying water, and outgoing water management. Unlike conventional flow fields with linear channels, the complex 3D flow field—featuring repeating baffles along the channel, known as the baffle design—induces a micro-scale interface flux between the gas diffusion layer (GDL) and the flow fields. Thus, an intensive oxygen flow is created that removes excess water from the GDL, thereby improving the fuel cell efficiency. Another approach for channel design is the Turing flow field, which resembles the organization of fluid flows in natural objects such as leaves, lungs, and the blood system. This design enhances the distribution of inlet flow significantly compared with traditional designs. The present study aims to combine the advantages of both Turing and baffle flow field designs and to provide model investigations on the influence of the mixed flow field design on the efficiency of PEMFCs. It was established that the mixed design achieves the highest electrode current density of 1.2 A/cm², outperforming the other designs. Specifically, it achieves 20% improvement over the Turing design, reaching 1.0 A/cm² and generating three times more current than the baffle design, which delivers 0.4 A/cm². In contrast, the conventional serpentine designs exhibit the lowest current density. The mixed flow field design provides better oxygen utilization in the electrochemical reaction, offers optimal membrane hydration, and contributes to superior electrode current density performance. These data illustrate how flow field structure directly impacts fuel cell efficiency through enhancement of current density. Full article

(This article belongs to the Special Issue Renewable Fuels and Chemicals)

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23 pages, 1945 KiB

Open AccessArticle

Tuning of ILADRC for CFB Boiler Combustion System Based on LF-DCSSA Algorithm

by Qi Wang, Chi Zhang, Aoqi Xiao, Xinchun Jia, Shikui Chen and Rongsen Fan

Energies 2025, 18(9), 2164; https://doi.org/10.3390/en18092164 - 23 Apr 2025

Abstract

Aiming at the problem that it is difficult to adjust the parameters of the controller in the circulating fluidized bed (CFB) boiler combustion system due to its multivariable and strong coupling, an improved linear active disturbance rejection controller (ILADRC) parameter tuning strategy based [...] Read more.

Aiming at the problem that it is difficult to adjust the parameters of the controller in the circulating fluidized bed (CFB) boiler combustion system due to its multivariable and strong coupling, an improved linear active disturbance rejection controller (ILADRC) parameter tuning strategy based on the Lévy flight double chaotic sparrow search algorithm (LF-DCSSA) is proposed. The LF-DCSSA algorithm is used to tune the parameters of the ILADRC controller in the multivariable coupled combustion control system of the CFB boiler built by Simulink, so that its control effect can reach the best state. The step response simulation and perturbation simulation are carried out with the theoretically tuned PID and ILADRC. The simulation results show that LF-DCSSA-ILADRC has obvious advantages in the three indexes of time–domain response, such as adjustment time, overshoot, and ITAE, which is more efficient and accurate than that of the theoretical setting, providing a new strategy for the control of the CFB boiler combustion system. Full article

(This article belongs to the Section L: Energy Sources)

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25 pages, 6656 KiB

Open AccessArticle

Energy Efficiency Improvement of Hydraulic Indirect Elevator

by Łukasz Stawiński, Andrzej Kosucki, Justyna Skowrońska and Piotr Malenta

Energies 2025, 18(9), 2163; https://doi.org/10.3390/en18092163 - 23 Apr 2025

Abstract

This article addresses the current issue of energy consumption in the hydraulic drive systems of working machines, with particular emphasis on elevators. This paper describes the results of experimental comparative research and estimation of energy and time consumption for two drive systems of [...] Read more.

This article addresses the current issue of energy consumption in the hydraulic drive systems of working machines, with particular emphasis on elevators. This paper describes the results of experimental comparative research and estimation of energy and time consumption for two drive systems of a hydraulic indirect elevator. The purpose of this article is to compare the energy consumption of a typical multi-valve system (MV) system with that of an innovative new electro-hydraulic drive (EHD) system with a variable speed pump. The EHD system uses a frequency converter with an energy recovery module to control the speed of the car in both directions and the return of potential energy during the lowering cycle. The comparison of these drive systems was performed under the same conditions, realizing the same elevator work cycles. This paper proposes methods for estimating the energy consumption of an MV system based on measurement data collected during an experiment. The results indicate that the EHD system was less energy-intensive, even at below 60%. The smaller the load mass, the shorter the operating time of the EHD system compared to the MV system. The introduced coefficients defining the energy consumption per unit of mass and payload displacement showed more than twice the decrease in energy demand during lifting and energy recovery possibility during lowering. The EHD system provides the same coefficient values regardless of the distance traveled, which makes it a predictable system, in contrast to the MV system, especially during lowering cycles. The benefits of the EHD also include a less complex hydraulic system (elimination of most valves). Full article

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

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13 pages, 3476 KiB

Open AccessArticle

Preparation of Highly Efficient and Stable All-Inorganic Perovskite Solar Cells in Atmosphere Environment

by Yufan Jiang, Dongdong Deng and Jingjing Dong

Energies 2025, 18(9), 2162; https://doi.org/10.3390/en18092162 - 23 Apr 2025

Abstract

All-inorganic CsPbX₃ perovskites have significant potential for applications in the photovoltaic field. However, during their preparation, the slow evaporation rate of the precursor solution limits the extent of solution supersaturation, leading to porous perovskite films that substantially impair device performance. Anti-solvent engineering, [...] Read more.

All-inorganic CsPbX₃ perovskites have significant potential for applications in the photovoltaic field. However, during their preparation, the slow evaporation rate of the precursor solution limits the extent of solution supersaturation, leading to porous perovskite films that substantially impair device performance. Anti-solvent engineering, which introduces a secondary solvent to modulate the crystallization process, is a well established technique in perovskite photovoltaic research. This study systematically examines the effects of four different anti-solvents on perovskite films and corresponding devices. It also investigates the optimal dipping-time of (trifluoromethyl)benzene as an anti-solvent, as well as the impact of varying amounts of anti-solvent additive perfluorinated acid. The optimized devices achieved a maximum power conversion efficiency of 12.68%. Full article

(This article belongs to the Special Issue Advanced Developments of Photovoltaic Devices and Perovskite Solar Cells: 2nd Edition)

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15 pages, 3330 KiB

Open AccessArticle

Efficiency Performance of 7-Level Multiplexed and 3-Level Neutral Point Clamped (NPC) Converters

by Shafquat Hussain, Simone Cosso, Massimiliano Passalacqua, Luis Ramon Vaccaro, Andrea Formentini and Mario Marchesoni

Energies 2025, 18(9), 2161; https://doi.org/10.3390/en18092161 - 23 Apr 2025

Abstract

In medium-voltage AC applications, multilevel converters are essential due to their ability to achieve high efficiency and significantly reduce total harmonic distortion (THD), ensuring improved performance and power quality. This paper presents a detailed analysis of the efficiency, power loss, and THD characteristics [...] Read more.

In medium-voltage AC applications, multilevel converters are essential due to their ability to achieve high efficiency and significantly reduce total harmonic distortion (THD), ensuring improved performance and power quality. This paper presents a detailed analysis of the efficiency, power loss, and THD characteristics of multiplexed multilevel converters and neutral point clamped converters. Using MATLAB^®Simulink 2024b, the switching and conduction losses of both multiplexed multilevel converters and NPC converters are calculated. The three-level NPC converter offers advantages of a simpler design, reduced component count, and cost effectiveness with the drawback of low voltage quality. Simulation results validate the THD, power losses, and efficiency for the conventional three-phase three-level NPC converter and the three-phase multiplexed multilevel converter, and a detailed comparison is performed. Full article

(This article belongs to the Collection Editorial Board Members’ Collection Series: Advances in Power Converters)

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23 pages, 1783 KiB

Open AccessArticle

Day-Ahead Scheduling of IES Containing Solar Thermal Power Generation Based on CNN-MI-BILSTM Considering Source-Load Uncertainty

by Kun Ding, Yalu Sun, Boyang Chen, Jing Chen, Lixia Sun, Yingjun Wu and Yusheng Xia

Energies 2025, 18(9), 2160; https://doi.org/10.3390/en18092160 - 23 Apr 2025

Abstract

The fluctuating uncertainty of load demand as an influencing factor for day-ahead scheduling of an integrated energy system with photovoltaic (PV) power generation may cause an imbalance between supply and demand, and to solve this problem, this paper proposes a day-ahead optimal scheduling [...] Read more.

The fluctuating uncertainty of load demand as an influencing factor for day-ahead scheduling of an integrated energy system with photovoltaic (PV) power generation may cause an imbalance between supply and demand, and to solve this problem, this paper proposes a day-ahead optimal scheduling model considering uncertain loads and electric heating appliance (EH)–PV energy storage. The model fuses the multi-interval uncertainty set with the CNN-MI-BILSTM neural network prediction technique, which significantly improves the accuracy and reliability of load prediction and overcomes the limitations of traditional methods in dealing with load volatility. By integrating the EH–photothermal storage module, the model achieves efficient coupled power generation and thermal storage operation, aiming to optimize economic targets while enhancing the grid’s peak-shaving and valley-filling capabilities and utilization of renewable energy. The validity of the proposed model is verified by algorithm prediction simulation and day-ahead scheduling experiments under different configurations. Full article

(This article belongs to the Special Issue Renewable Energy Power Generation and Power Demand Side Management)

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20 pages, 920 KiB

Open AccessArticle

Comprehensive Benefit Evaluation Analysis of Multi-Energy Complementary Off-Grid System Operation

by Yu Lei, Xiaobin Yan, Shenhao Yang, Yu Fan, Chao Ma, Qingsong Li, Yuanfeng Huang and Wei Yang

Energies 2025, 18(9), 2159; https://doi.org/10.3390/en18092159 - 23 Apr 2025

Abstract

In the future, China’s demand for centralized industrial development in remote areas will gradually increase, but the operation evaluation analysis of off-grid systems applicable to the development of such areas has not yet matured, and it is an urgent challenge to improve the [...] Read more.

In the future, China’s demand for centralized industrial development in remote areas will gradually increase, but the operation evaluation analysis of off-grid systems applicable to the development of such areas has not yet matured, and it is an urgent challenge to improve the operation mechanism of off-grid systems and then conduct a comprehensive benefit evaluation of off-grid systems. First of all, this paper focuses on the problem that the existing dimensions of the benefit evaluation of multi-energy complementary off-grid systems are not refined and comprehensive enough, and takes into account their high safety and reliability requirements, as well as the potential impacts on local industries and people’s lives after their completion, and then constructs a more complete comprehensive benefit evaluation indicator system for multi-energy complementary off-grid systems. Secondly, the subjective and objective weighting method based on the combination of the AHP (analytic hierarchy process) and AEM (anti-entropy method) is used to assign weights to the evaluation indicators. Finally, based on the TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) comprehensive evaluation method, a comprehensive benefit evaluation of a multi-energy complementary off-grid system under different operation schemes is conducted, and the example results show that the size of the relative closeness under different operation schemes has a maximum difference of 0.5592, which verifies that the proposed evaluation indicator system and the multilevel evaluation method can comprehensively evaluate and analyze the strengths and weaknesses of multi-energy complementary off-grid systems under different operation schemes, and provide theoretical guidance and decision-making support for the further promotion and construction of multi-energy complementary off-grid systems. Full article

(This article belongs to the Special Issue Leveraging Flexibility Resources to Enhance Renewable Energy Integration and Grid Stability)

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25 pages, 8244 KiB

Open AccessArticle

Sustainable Energy Storage Systems: Polypyrrole-Filled Polyimide-Modified Carbon Nanotube Sheets with Remarkable Energy Density

by Andekuba Andezai and Jude O. Iroh

Energies 2025, 18(9), 2158; https://doi.org/10.3390/en18092158 - 23 Apr 2025

Abstract

Organic hybrid materials are gaining traction as electrode candidates for energy storage due to their structural tunability and environmental compatibility. This study investigates polyimide/carbon nanotube/polypyrrole (PI/CNTs/PPy) hybrid nanocomposites, focusing on the correlation between thermal imidization temperature, polypyrrole deposition time, and the resulting electrochemical [...] Read more.

Organic hybrid materials are gaining traction as electrode candidates for energy storage due to their structural tunability and environmental compatibility. This study investigates polyimide/carbon nanotube/polypyrrole (PI/CNTs/PPy) hybrid nanocomposites, focusing on the correlation between thermal imidization temperature, polypyrrole deposition time, and the resulting electrochemical properties. By modulating PI processing temperatures (90 °C, 180 °C, 250 °C) and PPy deposition durations (60–700 s), this research uncovers critical structure–function relationships governing charge storage behavior. Scanning electron microscopy and electrochemical impedance spectroscopy reveal that low-temperature imidization preserves porosity and enables ion-accessible pathways, while moderate PPy deposition enhances electrical conductivity without blocking pore networks. The optimized composite, processed at 90 °C with 60 s PPy deposition, demonstrates superior specific capacitance (850 F/g), high redox contribution (~70% of total charge), low charge transfer resistance, and enhanced energy/power density. In contrast, high-temperature processing and prolonged PPy deposition result in structural densification, increased resistance, and diminished performance. These findings highlight a synergistic design approach that leverages partial imidization and controlled doping to balance ionic diffusion, electron transport, and redox activity. The results provide a framework for developing scalable, high-performance, and sustainable electrode materials for next-generation lithium-ion batteries and supercapacitors. Full article

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

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13 pages, 1759 KiB

Open AccessReview

Load Mismatch Compensation of Load-Modulated Power Amplifiers: A Comprehensive Review

by Yufeng Zang, Weimin Shi, Jinting Liu, Tian Qi and Mingyu Li

Energies 2025, 18(9), 2157; https://doi.org/10.3390/en18092157 - 23 Apr 2025

Abstract

With the diversification, acceleration, and arraying of wireless communication systems, power amplifiers (PAs) face stricter demands in terms of RF operation bandwidth, high-efficiency power range, and load mismatch compensation. After years of development, load-modulated PAs (LMPAs) can maintain high efficiency over a wide [...] Read more.

With the diversification, acceleration, and arraying of wireless communication systems, power amplifiers (PAs) face stricter demands in terms of RF operation bandwidth, high-efficiency power range, and load mismatch compensation. After years of development, load-modulated PAs (LMPAs) can maintain high efficiency over a wide bandwidth and a larger output back-off (OBO) range. However, there is obvious performance degradation when the load impedance of the current LMPAs is mismatched. To ensure the perfect application of power amplifiers in wireless communication systems, load mismatch compensation methods should be developed for LMPAs. Therefore, this paper gives a comprehensive review on the load mismatch compensation techniques of LMPAs, including the Doherty power amplifier and load-modulated balanced amplifier. Full article

(This article belongs to the Special Issue Renewable Energy Management System and Power Electronic Converters)

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Energies, Volume 18, Issue 9 (May-1 2025) – 43 articles

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