Energies

22 pages, 1975 KB

Open AccessArticle

TO-SYN-FUEL Project to Convert Sewage Sludge in Value-Added Products: A Comparative Life Cycle Assessment

by Serena Righi, Filippo Baioli, Andrea Contin and Diego Marazza

Energies 2025, 18(19), 5283; https://doi.org/10.3390/en18195283 (registering DOI) - 5 Oct 2025

Second-, third-, and fourth-generation biofuels represent an important response to the challenges of clean energy supply and climate change. In this context, the Horizon 2020 “TO-SYN-FUEL” project aimed to produce advanced biofuels together with phosphorus from municipal wastewater sludge through a combination of [...] Read more.

Second-, third-, and fourth-generation biofuels represent an important response to the challenges of clean energy supply and climate change. In this context, the Horizon 2020 “TO-SYN-FUEL” project aimed to produce advanced biofuels together with phosphorus from municipal wastewater sludge through a combination of technologies including a Thermo-Catalytic Reforming system, Pressure Swing Adsorption for hydrogen separation, Hydrodeoxygenation, and biochar gasification for phosphorous recovery. This article presents the environmental performance results of the demonstrator installed in Hohenberg (Germany), with a capacity of 500 kg per hour of dried sewage sludge. In addition, four alternative scenarios are assessed, differing in the source of additional thermal energy used for sludge drying: natural gas, biogas, heat pump, and a hybrid solar greenhouse. The environmental performance of these scenarios is then compared with that of conventional fuel. The comparative study of these scenarios demonstrates that the biofuel obtained through wood gasification complies with the Renewable Energy Directive, while natural gas remains the least sustainable option. Heat pumps, biogas, and greenhouse drying emerge as promising alternatives to align biofuel production with EU sustainability targets. Phosphorus recovery from sewage sludge ash proves essential for compliance, offering clear environmental benefits. Although sewage sludge is challenging due to its high water content, it represents a valuable feedstock whose sustainable management can enhance both energy recovery and nutrient recycling. Full article

(This article belongs to the Special Issue From Waste to Energy: Towards Resource Recovery Optimization from Waste)

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24 pages, 13326 KB

Open AccessReview

Applications of Heat Pipes in Thermal Management

by Milan Malcho, Jozef Jandačka, Richard Lenhard, Katarína Kaduchová and Patrik Nemec

Energies 2025, 18(19), 5282; https://doi.org/10.3390/en18195282 (registering DOI) - 5 Oct 2025

Abstract

The paper explores the application of heat pipes in thermal management for efficient heat dissipation, particularly in electrical equipment with high heat loads. Heat pipes are devices that transfer heat with high efficiency through the phase transition of the working medium (e.g., water, [...] Read more.

The paper explores the application of heat pipes in thermal management for efficient heat dissipation, particularly in electrical equipment with high heat loads. Heat pipes are devices that transfer heat with high efficiency through the phase transition of the working medium (e.g., water, alcohol, ammonia) between the evaporator and the condenser, while they have no moving parts and are distinguished by their simplicity of construction. Different types of heat pipes—gravity, capillary, and closed loop (thermosiphon loop)—are suitable according to specific applications and requirements for the working position, temperature range, and condensate return transport. An example of an effective application is the removal of heat from the internal winding of a static energy converter transformer, where the use of a gravity heat pipe has enabled effective cooling even through epoxy insulation and kept the winding temperature below 80 °C. Other applications include the cooling of mounting plates, power transistors, and airtight cooling of electrical enclosures with the ability to dissipate lost thermal power in the order of 102 to 103 W. A significant advantage of heat pipes is also the ability to dust-tightly seal equipment and prevent the build-up of dirt, thereby increasing the reliability of the electronics. In the field of environmental technology, systems have been designed to reduce the radiant power of fireplace inserts by up to 40%, or to divert their heat output of up to about 3 kW into hot water storage tanks, thus optimising the use of the heat produced and preventing overheating of the living space. The use of nanoparticles in the working substances (e.g., Al₂O₃ in water) makes it possible to intensify the boiling process and thus increase the heat transfer intensity by up to 30% compared to pure water. The results of the presented research confirm the versatility and high efficiency of the use of heat pipes for modern cooling requirements in electronics and environmental engineering. Full article

(This article belongs to the Special Issue Advances in Numerical and Experimental Heat Transfer)

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47 pages, 14121 KB

Open AccessArticle

Systematic Development and Hardware-in-the-Loop Testing of an IEC 61850 Standard-Based Monitoring and Protection System for a Modern Power Grid Point of Common Coupling

by Sinawo Nomandela, Mkhululi E. S. Mnguni and Atanda K. Raji

Energies 2025, 18(19), 5281; https://doi.org/10.3390/en18195281 (registering DOI) - 5 Oct 2025

Abstract

This paper presents a systematic approach to the development and validation of a monitoring and protection system based on the IEC 61850 standard, evaluated through hardware-in-the-loop (HIL) testing. The study utilized an already existing model of a modern power grid consisting of the [...] Read more.

This paper presents a systematic approach to the development and validation of a monitoring and protection system based on the IEC 61850 standard, evaluated through hardware-in-the-loop (HIL) testing. The study utilized an already existing model of a modern power grid consisting of the IEEE 9-bus power system integrated with a large-scale wind power plant (LSWPP). The SEL-487B Relay was configured to protect the PCC using a low-impedance busbar differential monitoring and protection system equipped with adaptive setting group logic that automatically transitions between Group 1 and Group 2 based on system loading conditions. Significant steps were followed for selecting and configuring instrument transformers and implementing relay logic in compliance with IEEE and IEC standards. Real-time digital simulation using Real-Time Digital Simulator (RTDS) hardware and its software, Real-time Simulation Computer-Aided Design (RSCAD), was used to assess the performance of the overall monitoring and protection system, focusing on the monitoring and publishing of the selected electrical and mechanical measurements from a selected wind turbine generator unit (WTGU) on the LSWPP side through the IEC 61850 standard network, and on the behavior of the monitoring and protection system under initial and increased load conditions through monitoring of differential and restraint currents. The overall monitoring and protection system was tested under both initial and increased load conditions, confirming its capability to reliably publish analog values from WTGU13 for availability on the IEC 61850 standard network while maintaining secure protection operation. Quantitatively, the measured differential (operate) and restraint currents were 0.32 PU and 4.38 PU under initial loading, and 1.96 PU and 6.20 PU under increased loading, while total fault clearance times were 606.667 ms and 706.667 ms for faults under initial load and increased load demand conditions, respectively. These results confirm that the developed framework provides accurate real-time monitoring and reliable operation for faults, while demonstrating a practical and replicable solution for monitoring and protection at transmission-level PCCs within renewable-integrated networks. Full article

(This article belongs to the Special Issue Planning, Operation, and Control of New Power Systems: 2nd Edition)

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15 pages, 1622 KB

Open AccessArticle

Rate Transient Analysis for Commingled Production Wells with Multiple Channel Sand Layers in Tight Gas Reservoirs

by Naichao Feng, Guoting Wang, Tong Xu, Sen Chang, Shaohui Duan, Fangxuan Chen, Shuai Zheng and Yunxuan Zhu

Energies 2025, 18(19), 5280; https://doi.org/10.3390/en18195280 (registering DOI) - 5 Oct 2025

Abstract

To address the challenges of characterizing commingled production from multiple channel sand layers with varying boundaries and shapes in tight gas reservoirs, a novel Rate Transient Analysis (RTA) model was established based on the principle of equivalent seepage volume (ESV). This model enables [...] Read more.

To address the challenges of characterizing commingled production from multiple channel sand layers with varying boundaries and shapes in tight gas reservoirs, a novel Rate Transient Analysis (RTA) model was established based on the principle of equivalent seepage volume (ESV). This model enables the determination of boundary sizes and permeabilities of individual channel sand layers within commingled tight reservoirs using modern production decline analysis theory. The production decline behavior under different channel sizes, numbers, and configurations was systematically investigated through type curve analysis. The results reveal the existence of five distinct stages in the production decline curves for unequal-width channel sands. The intermediate transient flow stage serves as a diagnostic indicator for identifying boundary disparities among layers. Furthermore, reservoirs with smaller boundary distances, fewer wide channel sand layers, and lower thickness proportions of wider channels exhibit poorer productivity and tend to experience accelerated production decline during early and middle transient flow stages. The proposed method provides an effective approach for characterizing boundary parameters of commingled tight reservoirs and offers a theoretical foundation for evaluating individual layer contributions and productivity. Full article

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16 pages, 3768 KB

Open AccessArticle

Analysis of Real and Simulated Energy Produced by a Photovoltaic Installations Located in Poland

by Ewa Hołota, Anna Życzyńska and Grzegorz Dyś

Energies 2025, 18(19), 5279; https://doi.org/10.3390/en18195279 (registering DOI) - 5 Oct 2025

Abstract

In recent years, the amount of electricity produced by photovoltaic systems in Poland has increased significantly. This paper presents an evaluation of commercial software (PVGIS 5.3, ENERAD, and PVGIS 24) used for simulating energy produced by four photovoltaic installations. The results of the [...] Read more.

In recent years, the amount of electricity produced by photovoltaic systems in Poland has increased significantly. This paper presents an evaluation of commercial software (PVGIS 5.3, ENERAD, and PVGIS 24) used for simulating energy produced by four photovoltaic installations. The results of the simulation were compared with the real energy production. The installations differ in terms of panel orientation (S, SE, SE-NW), tilt angle (12°, 25°, 37°) and location (roof- or ground-mounted). The average annual electricity production per 1 kW of module power for each installation was as follows: PV1—1104 kWh·kW⁻¹, PV2—1169 kWh·kW⁻¹, PV3—927 kWh·kW⁻¹, and PV4—831 kWh·kW⁻¹. The highest values were recorded for ground-mounted installations facing south. Simulations carried out using computer programs show differences between simulated and real electricity production values of 35–41% for the ENERAD software, 3–13% for the PVGIS 5.3 software, and 3–32% for the PVGIS 24 software. The most accurate forecasts were obtained for the PV2 system in the PVGIS 24 software (MPE 3%, RMSE 12%), and the most unfavorable for the same installation in the ENERAD software (MPE 41%, RMSE 48%). Full article

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

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26 pages, 6127 KB

Open AccessArticle

The Vertical City Paradigm as Sustainable Response to Urban Densification and Energy Challenges: Case Studies from Asian Megacities

by Anna Piętocha, Wei Li and Eugeniusz Koda

Energies 2025, 18(19), 5278; https://doi.org/10.3390/en18195278 (registering DOI) - 5 Oct 2025

Abstract

Due to rapid economic development, high energy consumption, and the depletion of natural resources, resulting in climate change, urban planners and architects face the difficult task of creating a new type of sustainable city that takes into account rapid population growth. The aim [...] Read more.

Due to rapid economic development, high energy consumption, and the depletion of natural resources, resulting in climate change, urban planners and architects face the difficult task of creating a new type of sustainable city that takes into account rapid population growth. The aim of this article is to examine the development of contemporary forms of high-rise architecture and the role of the vertical city in responding to shrinking space and developing a realistic strategy for sustainable urban development. Literature analysis, case studies, and multidisciplinary analysis are used. Pro-ecological solutions are identified and analyzed using the most representative buildings in Asia and a theoretical example in Nanjing. The examples are characterized by above-average height, unusual shapes, and the use of advanced pro-ecological strategies. Greenery plays a key role, including regulating the temperature inside the building. Vertical multifunctionality is becoming an increasingly common response to increasing spatial needs. The apparent lack of understanding of the development of high-rise buildings in cities around the world, extending beyond individual skyscrapers, constitutes a research gap. This article discusses Chongqing, an example of a vertical city, which is understood not only in terms of individual high-rise buildings but also as a whole structure. The study addresses the issue of a new type of compact city: the vertical city. The article provides key guidelines and constraints for creating densely populated, yet sustainable and environmentally friendly cities of the future. The practical application of the study can be utilized by urban planners and decision-makers. Full article

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16 pages, 809 KB

Open AccessArticle

Energy Efficiency Assessment of Wastewater Treatment Plants: Analyzing Energy Consumption and Biogas Recovery Potential

by Artur Mielcarek, Roksana Lubińska, Joanna Rodziewicz and Wojciech Janczukowicz

Energies 2025, 18(19), 5277; https://doi.org/10.3390/en18195277 (registering DOI) - 5 Oct 2025

Abstract

Directive (EU) 2024/3019 on urban wastewater treatment requires municipal wastewater treatment plants (WWTPs) to achieve energy neutrality by 2045. This study assessed the energy efficiency of a WWTP in central Poland over eight years (2015–2022), considering influent variability, electricity use and cost, and [...] Read more.

Directive (EU) 2024/3019 on urban wastewater treatment requires municipal wastewater treatment plants (WWTPs) to achieve energy neutrality by 2045. This study assessed the energy efficiency of a WWTP in central Poland over eight years (2015–2022), considering influent variability, electricity use and cost, and biogas recovery. The facility served 41,951–44,506 inhabitants, with treated wastewater volumes of 3.08–3.93 million m³/year and a real population equivalent (PE) of 86,602–220,459. Over the study period, the specific energy demand remained stable at 0.92–1.20 kWh/m³ (average 1.04 ± 0.09 kWh/m³), equivalent to 17.4–36.3 kWh/PE∙year. Energy efficiency indicators (EEIs) per pollutant load removed averaged 1.12 ± 0.28 kWh/kgBODrem, 0.53 ± 0.12 kWh/kgCODrem, 1.18 ± 0.36 kWh/kgTSSrem, 12.1 ± 1.5 kWh/kgTNrem, and 62.3 ± 11.7 kWh/kgTPrem. EEI per cubic meter of treated wastewater proved to be the most reliable metric for predicting energy demand under variable influent conditions. Electricity costs represented 4.48–13.92% of the total treatment costs, whereas co-generation from sludge-derived biogas covered 18.1–68.4% (average 40.8 ± 13.8%) of the total electricity demand. Recommended pathways to energy neutrality include co-digestion with external substrates, improving anaerobic digestion efficiency, integrating photovoltaics, and optimizing electricity use. Despite fluctuations in influent quality and load, the ultimate effluent quality consistently complied with legal requirements, except for isolated cases of exceeded phosphorus levels. Full article

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15 pages, 5237 KB

Open AccessArticle

Effect of Pressure on Pyrolytic and Oxidative Coking of JP-10 in Near-Isothermal Flowing Reactor

by Qian Zhang, Maogang He, Yabin Jin, Zizhen Huang, Tiantian Xu and Long Li

Energies 2025, 18(19), 5276; https://doi.org/10.3390/en18195276 (registering DOI) - 4 Oct 2025

Abstract

JP-10 (exo-tetrahydrodicyclopentadiene) is a high-energy-density hydrocarbon broadly used in advanced aerospace propulsion as a regenerative cooling fluid; in this study, we aimed to clarify how fuel pressure affects its thermal degradation (oxidative and pyrolytic) in near-isothermal flowing reactor. Experiments were performed under oxidative [...] Read more.

JP-10 (exo-tetrahydrodicyclopentadiene) is a high-energy-density hydrocarbon broadly used in advanced aerospace propulsion as a regenerative cooling fluid; in this study, we aimed to clarify how fuel pressure affects its thermal degradation (oxidative and pyrolytic) in near-isothermal flowing reactor. Experiments were performed under oxidative conditions (wall temperature 623.15 K, p = 0.708–6.816 MPa) and pyrolytic conditions (wall temperature 793.15 K, p = 2.706–7.165 MPa); carbon deposits were quantified by LECO analysis, oxidation activity was assessed by temperature-programmed oxidation (TPO), and morphology was performed by FESEM and EDS. Results show that oxidative coking is minimal (5.37–14.95 μg·cm²) and largely insensitive to pressure in the liquid phase (1.882–6.816 MPa), whereas at 0.708 MPa (gas/phase-change conditions), deposition increases, implicating phase and local heat-transfer effects. Under oxidative conditions, deposits are predominantly amorphous carbon with a disordered structure, formed at relatively low temperatures, with only a few fiber-like metal sulfides identified by EDS. In contrast, under pyrolysis conditions, the deposits are predominantly carbon nanotubes, exhibiting well-defined tubular morphology formed at elevated temperatures via metal-catalyzed growth. The pyrolysis coking yield is substantially higher (66.88–221.89 μg·cm⁻²) and increases with pressure. The findings imply that the pressure influences the coking of JP-10 via phase state under oxidative conditions and residence time under pyrolytic conditions, while basic morphologies of coke deposits remain similar; operationally, maintaining the working pressure higher than the saturated vapor pressure can mitigate oxidation coking associated with phase transitions, and minimizing residence time can mitigate pyrolytic coking. Full article

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

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54 pages, 3027 KB

Open AccessArticle

Numerical Analysis of Aerodynamics and Aeroacoustics in Heterogeneous Vehicle Platoons: Impacts on Fuel Consumption and Environmental Emissions

by Wojciech Bronisław Ciesielka and Władysław Marek Hamiga

Energies 2025, 18(19), 5275; https://doi.org/10.3390/en18195275 (registering DOI) - 4 Oct 2025

Abstract

The systematic economic development of European Union member states has resulted in a dynamic increase in road transport, accompanied by adverse environmental impacts. Consequently, research efforts have focused on identifying technical solutions to reduce fuel and/or energy consumption. One promising approach involves the [...] Read more.

The systematic economic development of European Union member states has resulted in a dynamic increase in road transport, accompanied by adverse environmental impacts. Consequently, research efforts have focused on identifying technical solutions to reduce fuel and/or energy consumption. One promising approach involves the formation of homogeneous and heterogeneous vehicle platoons. This study presents the results of numerical simulations and analyses of aerodynamic and aeroacoustic phenomena generated by heterogeneous vehicle platoons composed of passenger cars, delivery vans, and trucks. A total of 54 numerical models were developed in various configurations, considering three vehicle speeds and three inter-vehicle distances. The analysis was conducted using Computational Fluid Dynamics (CFD) methods with the following two turbulence models: the k–ω Shear Stress Transport (SST) model and Large Eddy Simulation (LES), combined with the Ffowcs Williams–Hawkings acoustic analogy to determine sound pressure levels. Verification calculations were performed using methods dedicated to environmental noise analysis, supplemented by acoustic field measurements. The results conclusively demonstrate that vehicle movement in specific platoon configurations can lead to significant fuel and/or energy savings, as well as reductions in harmful emissions. This solution may be implemented in the future as an integral component of Intelligent Transportation Systems (ITSs) and Intelligent Environmental Management Systems (IEMSs). Full article

(This article belongs to the Special Issue Challenges and Future Trends of Energy Management Systems for Electric Vehicles)

14 pages, 1223 KB

Open AccessArticle

Heat Pipe Heating and Cooling Building Modules: Thermal Properties and Possibilities of Their Use in Polish Climatic Conditions

by Karolina Durczak and Bernard Zawada

Energies 2025, 18(19), 5274; https://doi.org/10.3390/en18195274 (registering DOI) - 4 Oct 2025

Abstract

The subject of this paper is an analysis of the use of wall heating and cooling modules with heat pipes for efficient space heating and cooling. The modules under consideration constitute a structural element installed in the room’s partition structure and consist of [...] Read more.

The subject of this paper is an analysis of the use of wall heating and cooling modules with heat pipes for efficient space heating and cooling. The modules under consideration constitute a structural element installed in the room’s partition structure and consist of heat pipes embedded in a several-centimeter layer of concrete. Water-based central heating and chilled water systems were used as the heat and cooling source. The heat pipes are filled with a thermodynamic medium that changes state in repeated gas–liquid cycles. The advantage of this solution is the use of heat pipes as a heating and cooling element built into the wall, instead of a traditional water system. This solution offers many operational benefits, such as reduced costs for pumping the heat medium. This paper presents an analysis of the potential of using heat pipe modules for heating and cooling in real-world buildings in Poland. Taking into account the structural characteristics of the rooms under consideration (i.e., internal wall area, window area), an analysis was conducted to determine the potential use of the modules for space heating and cooling. The analysis was based on rooms where, according to the authors, the largest possible use of internal and external wall surfaces is possible, such as hotels and schools. Based on the simulations and calculations, it can be concluded that the modules can be effectively used in Poland as a real heating and cooling element: standalone, covering the entire heating and cooling demand of a room, e.g., a hotel room, or as a component working with an additional system, e.g., air cooling and heating in school buildings. The changes in outdoor air temperature, during the year analyzed in the article, were in the range of −24/+32 °C. Full article

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47 pages, 6818 KB

Open AccessSystematic Review

Modelling, Simulation and Performance Analysis of Floating Photovoltaic Systems—A Systematic Review and Meta-Analysis

by Oreoluwa Lawale, Simon P. Philbin and Sahand Hosouli

Energies 2025, 18(19), 5273; https://doi.org/10.3390/en18195273 (registering DOI) - 4 Oct 2025

Abstract

Research into floating photovoltaics (FPV) has seen a significant increase in recent years. Still, the observed outputs are poorly quantified, isolated, and occasionally contradictory, with reported cooling-induced efficiency increases varying widely across sources. To address the need for consensus in the field, a [...] Read more.

Research into floating photovoltaics (FPV) has seen a significant increase in recent years. Still, the observed outputs are poorly quantified, isolated, and occasionally contradictory, with reported cooling-induced efficiency increases varying widely across sources. To address the need for consensus in the field, a systematic literature review (SLR) and meta-analysis were conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) framework to provide a comprehensive overview of the current state-of-the-art in FPV systems. 3751 articles were identified through Boolean queries on three databases (Scopus, Web of Science, and Google Scholar). Using Python programming to ensure objectivity and replicability, the dataset was screened to 109 publications (subject to a manual, full-text review) relating strictly to modelling, simulation, and performance analysis of FPV systems with regard to the observed effect of reduced operating temperature. Focusing on these areas, this study provides a fundamental understanding of the temperature-based performance, as well as insights into the operation and simulation of FPV systems. Consistent temperature reductions were observed between ground-mounted and floating systems. Experimental data on FPV temperature were subject to a regression analysis, and the resulting equation was found to correspond well to a reported relation in the literature. The article concludes with a set of informed research directions to underpin the further development and implementation of FPV technology. Full article

(This article belongs to the Special Issue Renewable and Sustainable Energy in Light of Energy Transition Processes—2nd Edition)

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18 pages, 8209 KB

Open AccessArticle

A Direct-Drive Rotary Actuator Based on Modular FSPM Topology for Large-Inertia Payload Transfer

by Jianlong Zhu, Zhe Wang, Minghao Tong, Longmiao Chen and Linfang Qian

Energies 2025, 18(19), 5272; https://doi.org/10.3390/en18195272 (registering DOI) - 4 Oct 2025

Abstract

This paper proposes a novel direct-drive rotary actuator based on a modular five-phase outer-rotor flux-switching permanent magnet (FSPM) machine to overcome the limitations of conventional actuators with gear reducers, such as mechanical complexity and low reliability. The research focused on a synergistic design [...] Read more.

This paper proposes a novel direct-drive rotary actuator based on a modular five-phase outer-rotor flux-switching permanent magnet (FSPM) machine to overcome the limitations of conventional actuators with gear reducers, such as mechanical complexity and low reliability. The research focused on a synergistic design of a lightweight, high-torque-density motor and a precise control strategy. The methodology involved a structured topology evolution to create a modular stator architecture, followed by finite element analysis-based electromagnetic optimization. To achieve precision control, a multi-vector model predictive current control (MPCC) scheme was developed. This optimization process contributed to a significant performance improvement, increasing the average torque to 13.33 Nm, reducing torque ripple from 9.81% to 2.36% and obtaining a maximum position error under 1 mil. The key result was experimentally validated using an 8 kg inertial load, confirming the actuator’s feasibility for industrial deployment. Full article

(This article belongs to the Special Issue Advanced Structures, Fault Diagnosis and Tolerant Control of Permanent Magnet Synchronous Motors: 2nd Edition)

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15 pages, 3389 KB

Open AccessArticle

Photovoltaic Decomposition Method Based on Multi-Scale Modeling and Multi-Feature Fusion

by Zhiheng Xu, Peidong Chen, Ran Cheng, Yao Duan, Qiang Luo, Huahui Zhang, Zhenning Pan and Wencong Xiao

Energies 2025, 18(19), 5271; https://doi.org/10.3390/en18195271 (registering DOI) - 4 Oct 2025

Abstract

Deep learning-based Non-Intrusive Load Monitoring (NILM) methods have been widely applied to residential load identification. However, photovoltaic (PV) loads exhibit strong non-stationarity, high dependence on weather conditions, and strong coupling with multi-source data, which limit the accuracy and generalization of existing models. To [...] Read more.

Deep learning-based Non-Intrusive Load Monitoring (NILM) methods have been widely applied to residential load identification. However, photovoltaic (PV) loads exhibit strong non-stationarity, high dependence on weather conditions, and strong coupling with multi-source data, which limit the accuracy and generalization of existing models. To address these challenges, this paper proposes a multi-scale and multi-feature fusion framework for PV disaggregation, consisting of three modules: Multi-Scale Time Series Decomposition (MTD), Multi-Feature Fusion (MFF), and Temporal Attention Decomposition (TAD). These modules jointly capture short-term fluctuations, long-term trends, and deep dependencies across multi-source features. Experiments were conducted on real residential datasets from southern China. Results show that, compared with representative baselines such as SGN-Conv and MAT-Conv, the proposed method reduces MAE by over 60% and SAE by nearly 70% for some users, and it achieves more than 45% error reduction in cross-user tests. These findings demonstrate that the proposed approach significantly enhances both accuracy and generalization in PV load disaggregation. Full article

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24 pages, 6085 KB

Open AccessArticle

Heat Pump Optimization—Comparative Study of Different Optimization Algorithms and Heat Exchanger Area Approximations

by Eivind Brodal

Energies 2025, 18(19), 5270; https://doi.org/10.3390/en18195270 - 3 Oct 2025

Abstract

More energy efficient heat pumps can be designed if the industry is able to identify reliable optimization schemes able to predict how a fixed amount of money is best spent on the different individual components. For example, how to optimally design and size [...] Read more.

More energy efficient heat pumps can be designed if the industry is able to identify reliable optimization schemes able to predict how a fixed amount of money is best spent on the different individual components. For example, how to optimally design and size the different heat exchangers (HEs) in a heat pump with respect to cost and performance. In this work, different optimization algorithms and HE area integral approximations are compared for heat pumps with two and three HEs, with or without ejectors. Since the main goal is to identify optimal numerical schemes, not optimal designs, heat transfer is simplified, assuming a constant U-value for all HEs, which reduces the computational work significantly. Results show that high-order HE area approximations are

10 - 400

times faster than conventional trapezoidal and adaptive integral methods. High-order schemes with

45

grid points (

N

) obtained

80 - 100

% optimization success rates. For subcritical processes, the LMTD method produced accurate results with

N \leq 5

, but such schemes are unreliable and difficult to extend to real HE models with non-constant U. Results also show that constrained gradient-based optimizations are

10

times faster than particle swarm, and that conventional GA optimizations are extremely inefficient. This study therefore recommends applying high-order HE area approximations and gradient-based optimizations methods developing accurate optimization schemes for the industry, which include realistic heat transfer coefficients. Full article

(This article belongs to the Special Issue Advancements and Future Prospects of Heat Exchangers in Thermal and Energy Management)

30 pages, 2458 KB

Open AccessArticle

Smart Metering as a Regulatory and Technological Enabler for Flexibility in Distribution Networks: Incentives, Devices, and Protocols

by Matias A. Kippke Salomón, José Manuel Carou Álvarez, Lucía Súárez Ramón and Pablo Arboleya

Energies 2025, 18(19), 5269; https://doi.org/10.3390/en18195269 - 3 Oct 2025

Abstract

The digital transformation of low-voltage distribution networks demands a renewed perspective on both regulatory frameworks and metering technologies. This article explores the intersection between incentive structures and metering technologies, focusing on how smart metering can act as a strategic enabler for flexibility in [...] Read more.

The digital transformation of low-voltage distribution networks demands a renewed perspective on both regulatory frameworks and metering technologies. This article explores the intersection between incentive structures and metering technologies, focusing on how smart metering can act as a strategic enabler for flexibility in electricity distribution. Starting with the Spanish regulatory evolution and European benchmarking, the shift from asset-based regulation and how it can be complemented with performance-oriented incentives to support advanced metering functionalities is analyzed. On the technical side, the capabilities of smart meters and the performance of communication protocols (such as PRIME, G3-PLC, and 6LoWPAN) highlighting their suitability for real-time observability and control are examined. The findings identify a way to enhance regulatory frameworks for fully harnessing the operational potential of smart metering systems. This article calls for a hybrid, context-aware approach that integrates regulatory evolution with metering structures innovation to unlock the full value of smart metering in the energy transition. Full article

(This article belongs to the Section A1: Smart Grids and Microgrids)

25 pages, 1904 KB

Open AccessArticle

Has the “Belt and Road Initiative” Promoted Chinese OFDI in Green Energy? Evidence from Chinese Energy Engagement in BRI Countries

by Yuli Liu, Min Xu, Yu Huang and Ningning Fu

Energies 2025, 18(19), 5268; https://doi.org/10.3390/en18195268 - 3 Oct 2025

Abstract

The advancement of green energy is a crucial mechanism for balancing economic growth with environmental sustainability, helping to mitigate conflicts between development and ecological preservation. This paper assesses the policy effects of the Belt and Road Initiative (BRI) on China’s overseas green energy [...] Read more.

The advancement of green energy is a crucial mechanism for balancing economic growth with environmental sustainability, helping to mitigate conflicts between development and ecological preservation. This paper assesses the policy effects of the Belt and Road Initiative (BRI) on China’s overseas green energy projects (including gas) using the difference-in-difference (DID) model from 2009 to 2022. The findings show that, overall, the BRI has notably augmented China’s green energy projects in the BRI countries. This result remains robust after excluding potential interference from Nationally Determined Contributions (NDCs). Specifically, its promotional effect shows heterogeneity. Firstly, the BRI has shown significant regional differences in promoting the development of China’s overseas green energy projects. Secondly, the BRI is more effective in promoting green energy projects in developing and low-risk countries compared to developed and high-risk countries. Additionally, it indicates that the BRI boosts green energy projects in BRI countries by enhancing their infrastructure quality, encompassing transportation, energy, communication, and financial infrastructure. Finally, based on the above findings, this paper provides context-specific recommendations aimed at enhancing the effectiveness of the BRI in promoting sustainable green energy cooperation. Full article

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

22 pages, 13067 KB

Open AccessArticle

Numerical Modeling of Photovoltaic Cells with the Meshless Global Radial Basis Function Collocation Method

by Murat Ispir and Tayfun Tanbay

Energies 2025, 18(19), 5267; https://doi.org/10.3390/en18195267 - 3 Oct 2025

Abstract

Accurate prediction of photovoltaic performance hinges on resolving the electron density in the P-region and the hole density in the N-region. Motivated by this need, we present a comprehensive assessment of a meshless global radial basis function (RBF) collocation strategy for the steady [...] Read more.

Accurate prediction of photovoltaic performance hinges on resolving the electron density in the P-region and the hole density in the N-region. Motivated by this need, we present a comprehensive assessment of a meshless global radial basis function (RBF) collocation strategy for the steady current continuity equation, covering a one-dimensional two-region P–N junction and a two-dimensional single-region problem. The study employs Gaussian (GA) and generalized multiquadric (GMQ) bases, systematically varying shape parameter and node density, and presents a detailed performance analysis of the meshless method. Results map the accuracy–stability–computation-time landscape: GA achieves faster convergence but over a narrower stability window, whereas GMQ exhibits greater robustness to shape-parameter variation. We identify stability plateaus that preserve accuracy without severe ill-conditioning and quantify the runtime growth inherent to dense global collocation. A utopia-point multi-objective optimization balances error and computation time to yield practical node-count guidance; for the two-dimensional case with equal weighting, an optimum of 19 intervals per side emerges, largely insensitive to the RBF choice. Collectively, the results establish global RBF collocation as a meshless, accurate, and systematically optimizable alternative to conventional mesh-based solvers for high-fidelity carrier-density prediction in P-N junctions, thereby enabling more reliable performance analysis and design of photovoltaic devices. Full article

(This article belongs to the Topic Numerical Methods and Computer Simulations in Energy Analysis, 3rd Edition)

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15 pages, 4551 KB

Open AccessArticle

Solar Energy: An Optical Analysis for Regions Located in Intertropical Zones

by Omar F. Rojas-Moreno, Leonel Paredes-Madrid, Carlos Ramón Batista-Rodríguez, Luis Fernando Castañeda-Melo and Felipe M. Galleguillos-Madrid

Energies 2025, 18(19), 5266; https://doi.org/10.3390/en18195266 - 3 Oct 2025

Abstract

The sun represents a potential opportunity for sustainable energy production. The study of solar energy harvesting reinforces this promise, with studies simulating different operating environments by estimating the sun’s orientation toward the south or north, depending on the planet’s location. However, studies for [...] Read more.

The sun represents a potential opportunity for sustainable energy production. The study of solar energy harvesting reinforces this promise, with studies simulating different operating environments by estimating the sun’s orientation toward the south or north, depending on the planet’s location. However, studies for latitudes between 23° South and 23° North are a little-explored area. This research investigates different energy harvesting scenarios in flat-plate collectors, combining different possibilities throughout the year, analyzing the amount of energy captured using algorithms and Monte Carlo simulation. The methodology allows predicting efficiencies above 36% simply by rotating the harvesting devices from north to south or vice versa just twice a year. Full article

(This article belongs to the Special Issue Advances in Solar Systems and Energy Efficiency: 2nd Edition)

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24 pages, 2442 KB

Open AccessArticle

Development of a Novel Weighted Maximum Likelihood-Based Parameter Estimation Technique for Improved Annual Energy Production Estimation of Wind Turbines

by Woobeom Han, Kanghee Lee, Jonghwa Kim and Seungjae Lee

Energies 2025, 18(19), 5265; https://doi.org/10.3390/en18195265 - 3 Oct 2025

Abstract

Conventional statistical models consider all wind speed ranges as equally important, causing significant prediction errors, particularly in wind speed intervals that contribute the most to wind turbine power generation. To overcome this limitation, this study proposes a novel parameter estimation method—Weighted Maximum Likelihood [...] Read more.

Conventional statistical models consider all wind speed ranges as equally important, causing significant prediction errors, particularly in wind speed intervals that contribute the most to wind turbine power generation. To overcome this limitation, this study proposes a novel parameter estimation method—Weighted Maximum Likelihood Estimation (WMLE)—to improve the accuracy of annual energy production (AEP) predictions for wind turbine systems. The proposed WMLE incorporates wind-speed-specific weights based on power generation contribution, along with a weighting amplification factor (β), to construct a power-oriented wind distribution model. WMLE performance was validated by comparing four offshore wind farm candidate sites in Korea—each exhibiting distinct wind characteristics. Goodness-of-fit evaluations against conventional wind statistical models demonstrated the improved distribution fitting performance of WMLE. Furthermore, WMLE consistently achieved relative AEP errors within ±2% compared to those of time-series-based methods. A sensitivity analysis identified the optimal β value, which narrowed the distribution fit around high-energy-contributing wind speeds, thereby enhancing the reliability of AEP predictions. In conclusion, WMLE provides a practical and robust statistical framework that bridges the gap between statistical distribution fitting and time-series-based methods for AEP. Moreover, the improved accuracy of AEP predictions enhances the reliability of wind farm feasibility assessments, reduces investment risk, and strengthens financial bankability. Full article

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

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