Energies

26 pages, 4600 KB

Open AccessArticle

Integrated Multi-Scale Spectral Framework for Tropical Cyclone Dynamics: Implications for Offshore Wind Energy Resilience in the Atlantic Caribbean Basin

by Mario Eduardo Carbonó dela Rosa, Adalberto Ospino-Castro, Carlos Robles-Algarín, Diego Restrepo-Leal and Victor Olivero-Ortiz

Energies 2026, 19(10), 2473; https://doi.org/10.3390/en19102473 (registering DOI) - 21 May 2026

Abstract

The development of offshore wind energy in tropical cyclone-prone regions requires analytical frameworks that capture non-stationary climate dynamics. This study presents a multi-scale spectral approach to characterize Atlantic tropical cyclone variability and assess implications for offshore wind resilience in the Caribbean Basin. The [...] Read more.

The development of offshore wind energy in tropical cyclone-prone regions requires analytical frameworks that capture non-stationary climate dynamics. This study presents a multi-scale spectral approach to characterize Atlantic tropical cyclone variability and assess implications for offshore wind resilience in the Caribbean Basin. The methodology integrates Fast Fourier Transform (FFT) and Continuous Wavelet Transform (CWT) to resolve temporal variability in sea surface temperature, cyclone frequency, and intensity, complemented by two-dimensional kernel density estimation (KDE) and non-stationarity analysis. Using NOAA and National Hurricane Center datasets, results identify dominant periodicities at annual and ENSO (2–7 year) scales, a post-1995 spectral energy shift associated with the positive AMO phase, and a thermodynamically consistent energy corridor along 12–16° N. A statistically significant change point in 1987 (Pettitt test, p < 0.05) is detected, although spatial displacement is not significant. An integrated Wind Risk Index highlights the central-western Caribbean as a high-exposure zone overlapping offshore wind development areas. Exceedance analysis shows that 39.8% of observations surpass 25 m/s, 6.0% exceed 50 m/s, and 1.3% approach 70 m/s, indicating relevant design considerations. These findings support the need for non-stationary, multi-scale approaches in offshore wind risk assessment under tropical cyclone influence. Full article

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

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33 pages, 2587 KB

Open AccessArticle

A Study on Emission Reduction Strategies for Freight Trucks in the Context of China’s Carbon Neutrality Objectives

by Peihong Chen, Qi Chen, Ruitian Yao and Zhaoxia Kang

Energies 2026, 19(10), 2472; https://doi.org/10.3390/en19102472 (registering DOI) - 21 May 2026

Abstract

Road freight contributes over half of China’s transport carbon emissions, making its decarbonization critical for carbon neutrality. This study combines total cost of ownership (TCO) and life cycle assessment (LCA) to analyze the economic efficiency and carbon emission effects of diesel, electric, and [...] Read more.

Road freight contributes over half of China’s transport carbon emissions, making its decarbonization critical for carbon neutrality. This study combines total cost of ownership (TCO) and life cycle assessment (LCA) to analyze the economic efficiency and carbon emission effects of diesel, electric, and hydrogen fuel cell trucks. Combined with the LSTM neural network and vehicle ownership model, this study predicts the fleet emission reduction potential from 2020 to 2050. The results show that all new energy trucks can achieve TCO parity with diesel trucks before 2050, and electrification shows better economic competitiveness than hydrogen fuel cell technology across all vehicle types in the Chinese context. Fuel cell trucks powered via solar-powered water electrolysis exhibit the lowest carbon intensity, and grid decarbonization can significantly improve the emission reduction effects of electric and fuel cell trucks. Freight fleet carbon emissions are expected to peak around 2030. In an ideal scenario, emission reductions of 19.5%, 41.9%, and 82.9% can be achieved by 2030, 2040, and 2050, respectively. Heavy-duty trucks are the main emission contributors (47–58%) and the main target of emission reduction strategies. Short-term reduction depends on fuel economy, while long-term reduction prioritizes new energy substitution. Policy recommendations include promoting alternative fuel trucks, upgrading emission standards, and adopting differential taxation. Full article

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

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23 pages, 4001 KB

Open AccessArticle

Data-Driven Tailpipe Emission Prediction for Heavy-Duty Diesel Engines During B7–B20 Fuel Transition

by Anna Borucka, Mariusz Klimas, Jerzy Merkisz and Adam Sordyl

Energies 2026, 19(10), 2471; https://doi.org/10.3390/en19102471 (registering DOI) - 21 May 2026

Abstract

The use of biodiesel blends in heavy-duty diesel engines changes the relationship between engine operating conditions, fuel properties, and exhaust emissions, which may limit the reliability of data-driven emission models trained under a single fuel condition. This study investigates the cross-fuel transferability of [...] Read more.

The use of biodiesel blends in heavy-duty diesel engines changes the relationship between engine operating conditions, fuel properties, and exhaust emissions, which may limit the reliability of data-driven emission models trained under a single fuel condition. This study investigates the cross-fuel transferability of virtual emission sensors for a heavy-duty diesel engine operating on B7 and B20 fuel blends. The analysis was carried out for three target signals: nitrogen oxides concentration, hydrocarbon concentration, and dry carbon dioxide concentration, using data from the World Harmonized Transient Cycle (WHTC) and World Harmonized Stationary Cycle (WHSC) tests. A structured modelling workflow was developed, including signal time alignment, construction of baseline, dynamic, and memory-based features, feature selection, and separate evaluation scenarios: within-domain, cross-cycle, and cross-fuel transfer. Three tree-based regression algorithms were compared: Random Forest (RF), Histogram-Based Gradient Boosting (HGB), and Extreme Gradient Boosting (XGBoost). XGBoost achieved the best predictive performance in the source domain and was selected as the reference model. The results showed that a change in cycle characteristics led to a significant decrease in predictive performance, whereas the transition from B7/WHTC to B20/WHTC resulted in a clearly smaller drop in the evaluation metrics. The relationship between engine operating signals and emission response remained partially transferable across fuels. The highest stability was observed for carbon dioxide, intermediate stability for nitrogen oxides, and the lowest stability for hydrocarbons. The findings support the development of robust data-driven virtual sensing methods for emission monitoring and calibration of heavy-duty diesel engines operating with biodiesel blends. Full article

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

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26 pages, 1065 KB

Open AccessArticle

Urban Circular Economy and Energy Efficiency Improvement: Evidence from China’s “Zero-Waste City” Pilot Program

by Rui Li and Jiajun Xu

Energies 2026, 19(10), 2470; https://doi.org/10.3390/en19102470 (registering DOI) - 21 May 2026

Abstract

The circular economy offers a key pathway to achieve the joint improvement of resource conservation and carbon reduction, yet its causal effect on urban energy efficiency remains insufficiently examined. This paper takes China’s Zero-Waste City (ZWC) policy as a quasi-natural experiment and uses [...] Read more.

The circular economy offers a key pathway to achieve the joint improvement of resource conservation and carbon reduction, yet its causal effect on urban energy efficiency remains insufficiently examined. This paper takes China’s Zero-Waste City (ZWC) policy as a quasi-natural experiment and uses panel data from prefecture-level cities between 2006 and 2023. By applying staggered difference-in-differences and double machine learning methods, we evaluate the effect of urban circular economy transformation on energy efficiency. The results reveal four main findings: (1) The ZWC policy significantly improves energy efficiency in pilot cities. (2) The policy operates through three mechanisms: resource circulation, structural optimization, and innovation compensation. (3) Policy effects are stronger in environmentally regulated cities, large cities, and regions with higher artificial intelligence development. (4) The policy also generates broader benefits beyond energy savings, including coordinated fiscal, economic, and environmental gains. Overall, this paper highlights the spillover benefits of the circular economy from waste reduction to energy conservation and provides policy implications for coordinating waste management and energy transition at the urban level. Full article

(This article belongs to the Special Issue Circular Economy Mechanisms for Improving Energy Efficiency)

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16 pages, 8786 KB

Open AccessArticle

The Use of a Supercapacitor as a Supplementary Storage of Electricity in a Trolleybus

by Piotr Hołyszko, Dariusz Zieliński, Joanna Rymarz, Andrzej Niewczas and Ewa Dębicka

Energies 2026, 19(10), 2469; https://doi.org/10.3390/en19102469 (registering DOI) - 21 May 2026

Abstract

The article presents the concept of using supercapacitor as an energy storage in a trolleybus in order to ensure the continuity of power supply to on-board trolleybus devices during the passage through isolated sections of the overhead contact line. A mathematical model of [...] Read more.

The article presents the concept of using supercapacitor as an energy storage in a trolleybus in order to ensure the continuity of power supply to on-board trolleybus devices during the passage through isolated sections of the overhead contact line. A mathematical model of the on-board power supply system and an example of the power limit calculation have been described. The required capacity of the supercapacitor has been determined. A series of simulation studies were conducted, which made it possible to analyze and evaluate the potential capabilities and limitations of the proposed methods for maintaining the operation of auxiliary equipment. The results of simulation studies showed that the proposed model can be effectively used under typical trolleybus traction conditions. The use of a supercapacitor can ensure an uninterrupted power supply to auxiliary equipment across the entire range of operating speeds and power requirements of the trolleybus. Full article

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

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28 pages, 1208 KB

Open AccessArticle

Resilience-Driven Overload Protection Framework for Mitigating Cascading Failures in Power Systems

by Gourab Schmidt-Banerjee, Christian Hachmann and Martin Braun

Energies 2026, 19(10), 2468; https://doi.org/10.3390/en19102468 (registering DOI) - 21 May 2026

Abstract

Multiple-fault events can initiate overload propagation and cascading outages, resulting in severe load loss and reduced system resilience. Therefore, beyond conventional protection concepts based on the (n − 1) criterion, there is also a need to address multiple-fault events to minimize loss of [...] Read more.

Multiple-fault events can initiate overload propagation and cascading outages, resulting in severe load loss and reduced system resilience. Therefore, beyond conventional protection concepts based on the (n − 1) criterion, there is also a need to address multiple-fault events to minimize loss of load. This paper presents an optimized overload tripping scheme to mitigate cascading outages in high-voltage grids under multiple-fault conditions, where selected line switches or circuit breakers are opened in a controlled manner to isolate limited grid sections, minimize interrupted load, and prevent further overload propagation. The method combines inverse definite minimum time relay modeling with a heuristic graph-search algorithm implemented in pandapower to identify feasible switching actions that minimize load loss while preventing overload propagation. The approach is demonstrated on SimBench high-voltage urban and mixed benchmark grids under double-line fault scenarios. In the urban grid, the proposed scheme reduces the maximum load loss from 34.0% to 2.4%, while in the mixed grid, the reduction is from 50.3% to 5.2%. A SAIFI-inspired resilience proxy is introduced to quantify the reduction in customer/load interruptions, showing a resilience improvement factor of about 3.6 for cascading scenarios. In addition, thermal inertia analysis indicates that corrective switching must be completed within approximately 5 min to remain within line-temperature limits. The analysis is based on quasi-steady-state power-flow and relay simulations; transient stability effects are outside the scope of this study. The results demonstrate that the optimized overload tripping scheme is a promising adaptive protection strategy for improving grid resilience under severe contingency conditions. Full article

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

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19 pages, 1447 KB

Open AccessArticle

Robust MILP Optimization of Renewable Power Plants: The Role of BESS Sizing in Uncertainty Mitigation

by Tommaso Dieci, Corrado Maria Caminiti, Matteo Spiller and Marco Merlo

Energies 2026, 19(10), 2467; https://doi.org/10.3390/en19102467 (registering DOI) - 21 May 2026

Abstract

The reduction of carbon dioxide related to the energy sector is one of the greatest challenges of this century. To ensure a proper transition towards a sustainable electric power system, innovative solutions are fundamental for the efficient integration of renewable energy sources. Hybrid [...] Read more.

The reduction of carbon dioxide related to the energy sector is one of the greatest challenges of this century. To ensure a proper transition towards a sustainable electric power system, innovative solutions are fundamental for the efficient integration of renewable energy sources. Hybrid Renewable Energy Systems (HRES) play a crucial role in this scenario; they can ensure a stable and reliable electricity supply thanks to the combination of different renewable technologies, particularly thanks to the integration of storage systems. However, the optimal sizing process of such systems is a complex challenge due to the multiple uncertainties that can be present, involving demand fluctuations and electricity zonal price variations. The aim of this work was to develop a Mixed-Integer Linear Programming (MILP) optimization approach for the robust sizing of a HRES under multiple sources of uncertainty. The developed hybrid model consists of a wind farm, a photovoltaic (PV) plant, a Battery Energy Storage System (BESS), and an industrial load with the entire infrastructure for connection to the national power grid. Additionally, the model includes the capability to manage the over-generation of renewable resources through curtailment mechanisms. The objective of the sizing tool is to minimize the Net Present Cost (NPC) of the plant, while ensuring the reliability of the system. The developed tool can represent a useful assistant for the evaluation of different possible configurations, helping the decision-making process during the design of a HRES. The results will show the best trade-off between economic and reliability aspects, highlighting the impact that the uncertainty has on the optimal size of the plant. In particular, the best configuration analyzed is able to reduce the NPC of more than 50% compared to a plant with a single renewable source. Full article

(This article belongs to the Special Issue Advances in Battery Modelling, Applications, and Technology)

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19 pages, 7951 KB

Open AccessArticle

Secondary Voltage Drops in Dry-Type Transformers Caused by Coupled Magnetic Flux Effects of Voltage Unbalance and Harmonics in Isolated Offshore Power Systems

by Byung Chul Sung and Seongil Kim

Energies 2026, 19(10), 2466; https://doi.org/10.3390/en19102466 - 21 May 2026

Abstract

This paper investigates abnormal secondary voltage drops in dry-type transformers operating in isolated offshore power systems. While conventional analyses primarily attribute voltage deviations to load conditions and transformer impedance, this study shows that noticeable voltage drops can also occur under no-load conditions due [...] Read more.

This paper investigates abnormal secondary voltage drops in dry-type transformers operating in isolated offshore power systems. While conventional analyses primarily attribute voltage deviations to load conditions and transformer impedance, this study shows that noticeable voltage drops can also occur under no-load conditions due to the combined effects of voltage unbalance, harmonic distortion, and residual magnetic flux. A comprehensive approach integrating on-site measurements, PSCAD simulations, and laboratory experiments is employed to systematically analyze this phenomenon. The results indicate a coupled electromagnetic effect in which source-side voltage imperfections induce asymmetric core flux distribution, which is associated with reduced secondary voltage. In addition, a relationship between synchronous generator winding pitch and harmonic voltage distortion is observed, suggesting its influence on power quality in isolated grids. Simulation results show that the interaction of these factors can lead to a secondary voltage drop of approximately 4–6 V under no-load conditions, even in the absence of transformer defects. Finally, mitigation strategies based on voltage balancing and harmonic reduction are experimentally validated, restoring the secondary voltage to 1.002 pu. These findings provide practical insights for improving voltage stability and power quality in offshore and other isolated power systems. Full article

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

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22 pages, 3599 KB

Open AccessArticle

Coordinated Short-Term Scheduling and Control Integration in Microgrids Using Dual-Layer Deep Reinforcement Learning

by Kamelia Norouzi, Hao Xu and Wenxin Liu

Energies 2026, 19(10), 2465; https://doi.org/10.3390/en19102465 - 21 May 2026

Abstract

To optimize microgrid performance, both short-term and real-time operational objectives must be addressed, typically through energy scheduling and power control. Short-term scheduling maximizes the benefits of battery energy storage systems (BESS) by leveraging forecasted load and renewable generation conditions. However, real-time adjustments are [...] Read more.

To optimize microgrid performance, both short-term and real-time operational objectives must be addressed, typically through energy scheduling and power control. Short-term scheduling maximizes the benefits of battery energy storage systems (BESS) by leveraging forecasted load and renewable generation conditions. However, real-time adjustments are required to account for prediction errors, as neglecting these can lead to a loss of short-term optimality and visibility in overall system performance. The challenge of coordinating scheduling with control remains underexplored due to the limited timescale difference and decoupling of optimization and control. To address this problem, a bi-level deep reinforcement learning (DRL) method is presented. The upper-level DRL optimizes short-term generation and charging/discharging schedules for synchronous generators (SGs) and BESS, respectively. The lower-level DRL implements the schedules while maintaining stability and optimality. The two DRL levels learn together in a dynamic environment to ensure the short-term and real-time operational objectives are well coordinated. Simulation results demonstrate the effectiveness of the proposed algorithm. The effectiveness of the proposed algorithm is demonstrated on the studied microgrid system. Extension to larger and more complex systems is considered as future work. Full article

(This article belongs to the Special Issue Advanced Control and Operation of Distributed Energy Resources in Modern Power Systems)

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23 pages, 2120 KB

Open AccessArticle

Wind Potential Assessment of Polokwane, South Africa, Using Statistical Models for Wind Power Density Estimation

by Ngwarai Shambira and Patrick Mukumba

Energies 2026, 19(10), 2464; https://doi.org/10.3390/en19102464 - 21 May 2026

Abstract

This study evaluates the wind energy potential of Polokwane, South Africa, using statistical distribution models to estimate wind power density (WPD) and assess turbine performance under low-wind inland conditions. Hourly wind speed and direction data (2015–2024) measured at a 10 m height above [...] Read more.

This study evaluates the wind energy potential of Polokwane, South Africa, using statistical distribution models to estimate wind power density (WPD) and assess turbine performance under low-wind inland conditions. Hourly wind speed and direction data (2015–2024) measured at a 10 m height above ground level (AGL) were analysed to characterise wind behaviour and assess energy availability. Four probability distributions, namely generalised logistic (GLD), generalised extreme value (GEVD), Gumbel (GD), and Weibull (WD), were fitted using the maximum likelihood (ML) method. Model performance was evaluated using Kolmogorov–Smirnov (KS), Anderson–Darling (AD), and Chi-square

(χ^{2})

tests, while wind power density accuracy was assessed using wind power density error (WPDE). The results showed that Polokwane is characterised by low wind speeds, with an overall mean wind speed of 2.72 m/s at 10 m AGL, reaching a low of 3.88 m/s at a hub height of 125 m. The GEVD model produced the most accurate wind power density estimate of 32.37 W/m², classifying the site within the poor wind resource category. Wind direction analysis revealed a dominant northeast sector with seasonal shifts toward the south. Wind turbine performance analysis showed improved energy generation at higher hub heights, with the Gamesa G136-4.5 MW turbine identified as the most suitable option for the site, achieving the highest net annual energy production (AEP) of 10.82 GWh/yr and the highest net capacity factor (CF) of 27.44%. These results indicate that the Polokwane site is suitable for low-to-moderate wind energy applications and small-scale distributed wind generation rather than large-scale commercial wind farm development. Full article

(This article belongs to the Special Issue Integration of Power Generation and Wind Energy)

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26 pages, 2709 KB

Open AccessArticle

Buckley–Leverett Solution for Two-Phase Displacement in a Composite Porous–Cavernous–Porous System

by Fang-Fang Chen, Xu-Jian Jiang, Ting Yan, Xiao-Ping Ma, Zhen-Yu Zhang, Ming-Jie Li and Zhao-Qin Huang

Energies 2026, 19(10), 2463; https://doi.org/10.3390/en19102463 - 20 May 2026

Abstract

Fluid flow in fractured-vuggy carbonate reservoirs is characterized by extreme multiscale heterogeneity, where the coexistence of tight matrix rock and macroscopic cave challenges traditional Darcy-based continuum models. This paper presents a semi-analytical solution for two-phase immiscible displacement in a one-dimensional composite porous–cavernous–porous (PCP) [...] Read more.

Fluid flow in fractured-vuggy carbonate reservoirs is characterized by extreme multiscale heterogeneity, where the coexistence of tight matrix rock and macroscopic cave challenges traditional Darcy-based continuum models. This paper presents a semi-analytical solution for two-phase immiscible displacement in a one-dimensional composite porous–cavernous–porous (PCP) system. The main feature of the model is that the cave region is treated separately from the porous domains: classical Darcy flow is used in the surrounding matrix, whereas an idealized free-flow representation is introduced for open caves based on a simplified one-dimensional treatment of the cave momentum balance. To elucidate the impact of distinct flow regimes on displacement dynamics, three physical models are compared for the cave region: (1) an open-cave model represented by a simplified free-flow formulation; (2) a filled-cave non-Darcy model governed by the Forchheimer equation using the Ergun correlation; and (3) a creeping-flow model governed by Darcy’s law. A piecewise semi-analytical solution procedure is established to enforce flux continuity, characterize interfacial state remapping, and determine the downstream front under global water-balance closure. The results show that both cave geometry and internal cave-flow mechanism critically control water-front advancement. While the open-cave model exhibits piston-like displacement behavior with high local displacement efficiency but stronger preferential flow, the Forchheimer model shows that inertial resistance can modify the saturation profile and delay breakthrough relative to the Darcy prediction. The proposed framework provides an idealized theoretical reference for benchmarking numerical simulators and for interpreting waterflooding behavior in complex vuggy reservoirs under one-dimensional, incompressible, gravity-free, and capillarity-free conditions. Full article

(This article belongs to the Special Issue New Advances in Oil, Gas and Geothermal Reservoirs—3rd Edition)

21 pages, 4536 KB

Open AccessArticle

Techno-Economic Assessment of Electrochemical CO₂ Reduction to Ethylene: A Cu₁₀–Sn Catalyst Case Study and Performance Targets

by Kuquan Xiao, Ping Zhou and Xiqiang Zhao

Energies 2026, 19(10), 2462; https://doi.org/10.3390/en19102462 - 20 May 2026

Abstract

Electrocatalytic CO₂ reduction reaction (CO₂RR) to ethylene (C₂H₄) has emerged as a promising approach for converting CO₂ into valuable chemicals while utilizing renewable electricity. To facilitate the commercialization of this technology, a process-level techno-economic assessment [...] Read more.

Electrocatalytic CO₂ reduction reaction (CO₂RR) to ethylene (C₂H₄) has emerged as a promising approach for converting CO₂ into valuable chemicals while utilizing renewable electricity. To facilitate the commercialization of this technology, a process-level techno-economic assessment (TEA) is constructed for a plant producing 100 tons/day of C₂H₄ from coal-power flue gas CO₂ using a membrane electrode assembly (MEA) electrolyzer and downstream gas separations. The model integrates (i) flue gas CO₂ capture by chemical absorption, (ii) CO₂RR to C₂H₄ with H₂ as the only co-product, and (iii) cathode off-gas separation by pressure swing adsorption (PSA) plus anode off-gas CO₂ recovery and recycle. A Cu₁₀–Sn catalyst measured in an H-cell is projected to MEA operation by scaling current density by 10×, yielding a “Case Study in This Article” scenario of j = 246 mA·cm⁻² and FE(C₂H₄) = 48.74%. Under this scenario, the total cost is 592.61 thousand USD/day (5926 USD/ton), dominated by electricity (39.8%). Scenario analysis shows that the total cost can decrease to 76,755.0 USD/day (767.6 USD/ton) under a future-outlook case with improved electrolyzer performance and low-cost power, enabling a net profit of 19,945.0 USD/day at an ethylene selling price of 967 USD/ton. Sensitivity analysis identifies FE(C₂H₄), full-cell voltage, and electricity price as the most influential variables. The results translate laboratory catalyst metrics into industrial cost drivers and clarify quantitative performance targets for commercialization. Full article

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

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35 pages, 1637 KB

Open AccessArticle

Optimizing High-Resolution CSP–PV Hybrid Power Plant Configurations for Morocco: A Techno-Economic Study

by Nicholas Chandler, Daniel Marshal, Melisa Klein, Anna Heimsath, Christof Wittwer, Werner Platzer and Gregor Bern

Energies 2026, 19(10), 2461; https://doi.org/10.3390/en19102461 - 20 May 2026

Abstract

Hybridizing concentrating solar power (CSP) with photovoltaics (PV) offers a pathway to combine low-cost daytime generation with dispatchable nighttime supply. This study compares two CSP–PV hybridization concepts for Midelt, Morocco, under a common tender-style design framework: (i) a co-located configuration in which PV [...] Read more.

Hybridizing concentrating solar power (CSP) with photovoltaics (PV) offers a pathway to combine low-cost daytime generation with dispatchable nighttime supply. This study compares two CSP–PV hybridization concepts for Midelt, Morocco, under a common tender-style design framework: (i) a co-located configuration in which PV and CSP interact at the grid level and (ii) an EH-integrated configuration in which an electric heater (EH) uses PV electricity to heat molten salt in a topping cycle. The main contribution of this study lies in the two-stage optimization workflow, in which leading candidates are selectively re-simulated at higher temporal resolution. This workflow is applied to a common design framework that compares EH-integrated and co-located concepts while considering multiple PV technologies and a broad set of interdependent sizing variables. A surrogate-assisted genetic algorithm evaluates more than 200,000 candidate designs across PV technology, inverter size, TES capacity, EH capacity, and battery energy storage system (BESS) size. The optimization minimizes the levelized cost of energy (LCOE) subject to a

200 {MW}_{el}

export limit, a CAPEX ceiling, and a nighttime-delivery constraint of

{CF}_{night} \geq 39 %

. Candidate designs are screened at 600 s and selectively re-simulated at 120 s, showing that temporal refinement affects not only KPI values but also candidate feasibility, final ranking, and preferred component sizing. The lowest-LCOE solution is the EH-integrated bifacial configuration, achieving 64.5% overall capacity factor,

{CF}_{night} = 39.1 %

, less than 0.1% curtailment, a specific CAPEX of $4698/kW, and an LCOE of 7.29 ¢/kWh. Pareto-front and parameter-trend analyses further show that stricter nighttime-delivery targets shift the dominant sizing levers and define a neighborhood of near-optimal solutions rather than a single fixed design. Full article

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

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18 pages, 5306 KB

Open AccessArticle

Particle Swarm-Based Active Power Command Correction Virtual Synchronous Generator Control for Inverters with Current Limiting Capability and Enhanced Transient Stability

by Qiang Wang, Min Shi, Hao Lv, Fei-Fei Zhang, Yan Gao, Chen-Miao Lv, Xiao-Qi Yin and Juan Yan

Energies 2026, 19(10), 2460; https://doi.org/10.3390/en19102460 - 20 May 2026

Abstract

When a fault occurs in the power grid to which the Virtual Synchronous Generator (VSG) is connected, it leads to overcurrent phenomena, which threatens the safety of the inverter and easily results in device damage. Although existing direct current limiting unit (CLU) control [...] Read more.

When a fault occurs in the power grid to which the Virtual Synchronous Generator (VSG) is connected, it leads to overcurrent phenomena, which threatens the safety of the inverter and easily results in device damage. Although existing direct current limiting unit (CLU) control strategies can restrict the fault current, the input active power command far exceeds the power output, causing the virtual rotor to continuously accelerate. This leads to power angle divergence and a subsequent loss of synchronization. To address the conflict between direct current-limiting control and system transient stability, this paper proposes a control strategy based on the Particle Swarm Optimization (PSO) algorithm to modify the active power command, building upon existing direct current-limiting VSG control. During grid faults, the output current is constrained to its maximum value, leading to a reduction in the system’s output power. By leveraging the PSO algorithm, the proposed strategy decreases the active power command to minimize the power mismatch between the command and the output. This maximizes the system’s transient stability by minimizing the rotor acceleration torque and effectively suppressing excessive power angle deviation. Meanwhile, the active power command reduction is introduced as a penalty term to maximize the active power output capability during the fault period. Simulation results demonstrate that, compared to VSG with only direct current-limiting control, the proposed strategy significantly enhances the transient stability and transmission efficiency of the VSG under long-term fault conditions across various grid voltage sag scenarios. Furthermore, it ensures a seamless transition from the fault state to normal operation during short-term faults. Full article

(This article belongs to the Special Issue Advanced Control Methods for Power Electronics, Energy Storage, Photovoltaics, and Microgrids)

35 pages, 6936 KB

Open AccessArticle

Role-Aware Hierarchical Primary Frequency Regulation of Heterogeneous Source–Grid–Load Energy Storage System

by Hongwei Deng, Jun He, Penghui Yan, Xiaoyu Nie, Yifan Lv and Shuyi Wang

Energies 2026, 19(10), 2459; https://doi.org/10.3390/en19102459 - 20 May 2026

Abstract

With high renewable penetration, primary frequency regulation (PFR) in low-inertia power systems faces a critical challenge of balancing frequency security with sustainable energy storage system (ESS) utilization. Existing ESS-based PFR studies mainly focus on single-sided resource support or homogeneous modeling, which cannot address [...] Read more.

With high renewable penetration, primary frequency regulation (PFR) in low-inertia power systems faces a critical challenge of balancing frequency security with sustainable energy storage system (ESS) utilization. Existing ESS-based PFR studies mainly focus on single-sided resource support or homogeneous modeling, which cannot address the cross-side coordination demands arising from heterogeneous ESS on the source, grid, and load sides. This paper extends ESS-based PFR to a synergistic scenario involving heterogeneous three-sided ESS. A unified modeling framework is established, explicitly incorporating differences in capacity, functional roles, participation priority, and security boundaries. Based on this, a hierarchical decoupling control structure is proposed, separating system-level frequency regulation from side-level energy coordination. The upper level uses a low-dimensional equivalent representation to reduce the optimization burden from modeling numerous ESS units, while the lower level achieves complementary advantages and orderly task allocation among the three sides through differentiated coordination. Simulations show that the method maintains system frequency performance while achieving rational PFR responsibility allocation across source-, grid-, and load-side ESS, effectively leveraging multi-sided heterogeneous ESS for synergistic regulation, and verifying the hierarchical decoupling framework as an effective approach for coordinating multi-side energy storage. Full article

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

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17 pages, 9185 KB

Open AccessArticle

Sheath-to-Ground Fault Impedance Calculation and Localization Method in Cross-Bonded High-Voltage Cable Systems

by Hang Wang, Bo Li, Liqiang Wang, Jing Tu, Shuai Yang and Jun Chen

Energies 2026, 19(10), 2458; https://doi.org/10.3390/en19102458 - 20 May 2026

Abstract

Abnormal circulating current induced by sheath grounding faults in cross-bonded high-voltage cables is a major cause of single-phase grounding faults. For the early detection and localization of sheath grounding faults, this paper constructs an equivalent circuit model for three-phase nine-section cross-bonded cables. Circuit [...] Read more.

Abnormal circulating current induced by sheath grounding faults in cross-bonded high-voltage cables is a major cause of single-phase grounding faults. For the early detection and localization of sheath grounding faults, this paper constructs an equivalent circuit model for three-phase nine-section cross-bonded cables. Circuit model parameters are estimated via online monitoring data. The relational equation between sheath electrical quantities, fault impedance, and distance is derived for typical sheath grounding faults. Using the Adam algorithm, the solution of fault impedance and location is converted into the minimization of an optimization objective function. Simulation results show that under the influences of phase current imbalance, measurement error, and fault impedance fluctuation, the Adam algorithm exhibits superior optimization accuracy and computational efficiency in comparison with the ED and GA algorithms. Experimental results show that for low-resistance sheath grounding, the proposed method has a fault impedance calculation error ≤ 0.59% and a fault positioning error ≤ 1.89%. For metallic sheath grounding with zero resistance, the positioning error is ≤1.37%. Field test results demonstrate that the proposed method performs similarly to the time-domain reflectometry method, with a positioning deviation ≤ 0.15 m, and can meet online monitoring requirements. Full article

33 pages, 14977 KB

Open AccessArticle

A Modular C++/Eigen Aero-Elastic Simulation Code for Multi-Rotor Wind Turbines

by Chaozhi Qiu, Shigeo Yoshida, Zhiqiang Hu, Hongzhong Zhu and Amr Ismaiel

Energies 2026, 19(10), 2457; https://doi.org/10.3390/en19102457 - 20 May 2026

Abstract

This paper presents AeroelasticQ, a modular, high-performance aeroelastic simulation code for wind turbines, with particular emphasis on future applicability to multi-rotor configurations. The framework is organized into three core components: a flexible-blade structural solver, an airfoil-based aerodynamic solver, and a two-mesh aero-structural mapping [...] Read more.

This paper presents AeroelasticQ, a modular, high-performance aeroelastic simulation code for wind turbines, with particular emphasis on future applicability to multi-rotor configurations. The framework is organized into three core components: a flexible-blade structural solver, an airfoil-based aerodynamic solver, and a two-mesh aero-structural mapping module for transferring loads and kinematics between the aerodynamic and structural discretization. The implementation is written in C++17 using the Eigen linear algebra library (v5.0.0), and OpenMP (v5.1) is employed to enable rotor-level parallel execution for multi-rotor applications. The structural dynamics are formulated using Kane’s dynamic method combined with modal superposition, while the aerodynamic loads are computed using three-dimensional blade element momentum theory. The coupled and uncoupled modules are validated in the time domain against OpenFAST (v4.1.2) AeroDyn, ElastoDyn, and the coupled AeroDyn–ElastoDyn configuration using the NREL 5 MW reference wind turbine. The rotor-level aerodynamic validation gives mean absolute errors of 8.94 × 10⁻⁴, 2.82 × 10⁻⁴, and 2.71 × 10⁻⁵ for C_t, C_p, and C_q, respectively, while the coupled aeroelastic cases show close agreement in blade tip deflections, blade root loads, and aerodynamic power. A rigid three-rotor verification confirms the multi-rotor load-aggregation framework, with tower base thrust and overturning moment errors below 1.5% and 2% NRMSE, respectively, in both all rotors operating and one operating/two-parked configurations. In single-thread benchmarks, AeroelasticQ achieves speedups of 5.23×, 19.69×, and 3.65× in the aerodynamic-only, structural-only, and fully coupled modes, respectively. In the multi-rotor benchmark, the five-rotor case achieves a parallel speedup of 2.55× with a parallel efficiency of 51%. Full article

(This article belongs to the Special Issue Wind Turbine Aeromechanics: Theory, Methods and Applications)

18 pages, 1748 KB

Open AccessArticle

A Two-Stage Sequential Configuration Strategy of PPF and APF for Wind Farm Harmonic Mitigation

by Huajia Wang, Yan Zhang, Wenbin Ci, Fan Xiao and Jiawei Luo

Energies 2026, 19(10), 2456; https://doi.org/10.3390/en19102456 - 20 May 2026

Abstract

Large-scale wind integration introduces significant harmonic degradation and resonance risks. Traditional strategies primarily targeting Total Harmonic Distortion (THD) often struggle with individual node violations and high investment costs. To address these challenges, this paper proposes a two-stage sequential coordination strategy for Passive Power [...] Read more.

Large-scale wind integration introduces significant harmonic degradation and resonance risks. Traditional strategies primarily targeting Total Harmonic Distortion (THD) often struggle with individual node violations and high investment costs. To address these challenges, this paper proposes a two-stage sequential coordination strategy for Passive Power Filters (PPFs) and Active Power Filters (APFs). First, stochastic harmonic emission and frequency-domain power flow models are developed to characterize wind-induced harmonic propagation. Second, a sequential optimization framework is established to minimize Life Cycle Cost (LCC). In the first stage, PPF siting and sizing are optimized for cost-effective, system-wide mitigation of low-order harmonics while ensuring THD compliance. The second stage utilizes targeted APF deployment to precisely suppress residual high-order violations and localized resonance. Chance-constrained programming is incorporated to manage wind power uncertainty, enhancing the scheme’s robustness. Simulations on an IEEE 17-bus system demonstrate that the proposed method effectively balances harmonic suppression performance with economic efficiency, providing a robust and cost-effective solution for wind farm power quality management. Full article

(This article belongs to the Special Issue High Efficiency, Quality, and Stable Operation Technology for Flexible Distribution Networks)

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18 pages, 23562 KB

Open AccessArticle

Using Ultrasonic to Study the Overcharge Damage Threshold of Lithium-Ion Batteries

by Shihao Wang, Jifeng Song, Zhengye Yang, Weisheng Zhao, Mingzhe Du and Hui Yang

Energies 2026, 19(10), 2455; https://doi.org/10.3390/en19102455 - 20 May 2026

Abstract

Monitoring the internal structural evolution and gas generation in lithium-ion batteries is critical for effective battery management; however, conventional electrical and thermal sensing techniques lack the sensitivity to capture these dynamic changes accurately. To address this limitation, we apply ultrasonic diagnostic techniques—specifically A-scan [...] Read more.

Monitoring the internal structural evolution and gas generation in lithium-ion batteries is critical for effective battery management; however, conventional electrical and thermal sensing techniques lack the sensitivity to capture these dynamic changes accurately. To address this limitation, we apply ultrasonic diagnostic techniques—specifically A-scan and C-scan modalities—to characterize the acoustic responses of pouch-type LFP batteries subjected to a range of current densities (0.5C–5C) and overcharge conditions defined by cutoff voltage and SOC. Our findings show that ultrasonic signals are highly sensitive to concentration polarization and electrode lithiation processes occurring during charge–discharge cycles. At elevated current densities (>2C), an imbalance in the Li⁺ intercalation/deintercalation process occurs. Overcharge tests reveal that 4.2 V can serve as the threshold voltage for early warning during ultrasonic testing of LFP batteries When SOC exceeds 110%, internal gas generation and mechanical degradation significantly accelerate and become irreversible. Full article

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

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