Energies

23 pages, 1156 KB

Open AccessArticle

Assessing Policy Contagion in China’s Wind Power Industry Chain

by Hao Lyu, Jiayu Zhang, Cody Yu-Ling Hsiao and Yi-Bin Chiu

Energies 2025, 18(23), 6328; https://doi.org/10.3390/en18236328 (registering DOI) - 1 Dec 2025

Wind power has become a strategic cornerstone of China’s renewable-energy transition and industrial upgrading, making it essential to understand how policy interventions shape the behaviour of its industry chain. This study examines how major wind power policies issued between 2015 and 2024 transmit [...] Read more.

Wind power has become a strategic cornerstone of China’s renewable-energy transition and industrial upgrading, making it essential to understand how policy interventions shape the behaviour of its industry chain. This study examines how major wind power policies issued between 2015 and 2024 transmit shocks across nine upstream, midstream, and downstream sectors. Using four contagion tests based on higher-order co-moments, combined with a policy sensitivity index, the analysis identifies distinct transmission patterns across policy types. The results show that market-mechanism reforms induce the strongest and most systemic contagion effects, reflecting their ability to align financial incentives with renewable-integration objectives. Upstream sectors—particularly equipment and key material industries—exhibit the highest responsiveness, while midstream construction and downstream operation and maintenance display more moderate and delayed adjustments. Development and construction policies generate broader but less intensive contagion, whereas industry-support measures trigger selective, sector-specific responses. These findings offer practical guidance for improving policy coordination, investment planning, and industrial upgrading within China’s wind power value chain. Future research could extend the analysis by incorporating firm-level data, longer policy cycles, and interactions with other structural shocks such as electricity-market reforms and climate-related risks. Full article

(This article belongs to the Special Issue Sustainable Energy Futures: Economic Policies and Market Trends)

26 pages, 819 KB

Open AccessArticle

A Global Construction Embodied Energy Emission Index (CEEEI): A Data-Driven Assessment of Carbon and Energy Efficiency Across 148 Countries (2000–2023)

by Ibrahim Mosly

Energies 2025, 18(23), 6327; https://doi.org/10.3390/en18236327 (registering DOI) - 1 Dec 2025

Abstract

This study establishes the Construction Embodied Energy and Emissions Index (CEEEI) to assess the comprehensive environmental impacts of construction work in 148 countries from 2000 to 2023. The index combines data on material, energy, and carbon intensity from four international open databases. The [...] Read more.

This study establishes the Construction Embodied Energy and Emissions Index (CEEEI) to assess the comprehensive environmental impacts of construction work in 148 countries from 2000 to 2023. The index combines data on material, energy, and carbon intensity from four international open databases. The three latent components derived from Principal Component Analysis (PCA) account for 72.1% of the total variance. They are categorized into the following factors: Economic–Urban Development, Carbon Governance, Industrial Carbon and Material Intensity, and Energy Source and Decarbonization Structure. The CEEEI adjusted (CEEEI_adj) evaluates countries based on their embodied efficiency, revealing that developed nations, including the UK, Netherlands, and Sweden, have the lowest embodied emissions, whereas fast-urbanizing, fossil-dependent countries perform poorly. The regression analysis shows that GDP per capita, urbanization rates, and fossil energy consumption ratios are vital determinants of embodied intensity. This study offers a reproducible open-data system that enables construction organizations worldwide to develop decarbonization policies. Full article

18 pages, 529 KB

Open AccessReview

Graphene Nanoplatelets for Advanced Energy Storage Applications

by Aleksandra Tatara and Ewa Klugmann-Radziemska

Energies 2025, 18(23), 6326; https://doi.org/10.3390/en18236326 (registering DOI) - 1 Dec 2025

Abstract

Graphene nanoplatelets (GNPs) represent a promising class of carbon nanomaterials bridging the gap between graphite and monolayer graphene. Their unique combination of high electrical conductivity, large specific surface area, mechanical strength, and chemical stability makes them attractive for advanced energy storage applications. This [...] Read more.

Graphene nanoplatelets (GNPs) represent a promising class of carbon nanomaterials bridging the gap between graphite and monolayer graphene. Their unique combination of high electrical conductivity, large specific surface area, mechanical strength, and chemical stability makes them attractive for advanced energy storage applications. This review summarizes recent developments in the synthesis, functionalization, characterization, and application of GNPs in supercapacitors, batteries, and hybrid systems. The influence of key structural parameters—such as flake thickness, lateral size, surface chemistry, and defect density—on electrochemical performance is discussed, highlighting structure–property correlations. Particular emphasis is placed on scalable production methods, including mechanical, liquid-phase, and electrochemical exfoliation, as well as edge functionalization and heteroatom doping strategies. Comparative analyses show that GNP-based electrodes can significantly improve specific capacitance, conductivity, and cycling stability, especially when used in composites with polymers or metal oxides. The review also addresses current challenges related to aggregation, dispersion, standardization, and environmental impact. Finally, prospects for the development of sustainable, low-emission GNP production and its integration into next-generation energy storage systems are outlined. Full article

(This article belongs to the Special Issue Renewable Energy Development in Distribution Networks: Optimization, Assessment and Design of Renewable Plants)

14 pages, 2827 KB

Open AccessArticle

Analysis of Heat Transfer Characteristics in a Latent Heat Storage Module Using Circular-Finned Tubes

by Ji-Woon Ko, Tae Hwan Song, Jong-Hoon Lee, Jong Hyeon Peck and Seung Jin Oh

Energies 2025, 18(23), 6325; https://doi.org/10.3390/en18236325 (registering DOI) - 1 Dec 2025

Abstract

Latent heat thermal energy storage (LHTES) using inorganic salt hydrates is a promising technology for buffering renewable energy fluctuations; however, phase-dependent heat transfer remains insufficiently understood for design optimization. In this study, a shell-and-tube storage module with a circular-finned tube was constructed and [...] Read more.

Latent heat thermal energy storage (LHTES) using inorganic salt hydrates is a promising technology for buffering renewable energy fluctuations; however, phase-dependent heat transfer remains insufficiently understood for design optimization. In this study, a shell-and-tube storage module with a circular-finned tube was constructed and filled with 13.17 kg of barium hydroxide octahydrate (BHO). Discharge tests were conducted with heat transfer fluid (HTF) inlet temperatures ranging from 20 °C to 50 °C and flow rates of 10–25 L/min, while charging was performed at 90 °C. The overall heat transfer coefficient (

U_{o}

) was derived using the logarithmic mean temperature difference method, the inside coefficient (h_i) was calculated by the Petukhov correlation, and the outside coefficient (h_o) was obtained via thermal-resistance network. Results show that the average discharge energy was approximately 1.027 kWh (except 0.859 kWh at 50 °C inlet), with a mean utilization efficiency of 79.25%. The

U_{o}

was consistently highest in the liquid phase, followed by the latent and solid phases, with ranges of 0.257–0.863, 0.025–0.072, and 0.015–0.044 kW/m²·°C, respectively. Sensitivity analysis revealed that the HTF flow rate strongly influenced U_o across all phases, whereas inlet temperature played only a minor role. The outside coefficient

h_{o}

was 0.033–0.162 kW/m²·°C in the latent regime and 0.018–0.064 kW/m²·°C in the solid regime, with a notable peak around Reynolds number 1.3 × 10⁴ in the latent phase. These findings provide detailed phase-resolved

U_{o}

and

h_{o}

data for inorganic salt hydrate storage and highlight design insights such as the diminishing returns of flow rate increase beyond a threshold, offering valuable guidelines for sizing and operation of LHTES in Power-to-Heat applications. Full article

(This article belongs to the Special Issue Heat Transfer Analysis: Recent Challenges and Applications—2nd Edition)

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22 pages, 4302 KB

Open AccessArticle

Vehicle Vibration Characteristics of an Additional-Flow-Path-Type Magnetorheological Damper Using a Frequency-Tuned Proportional-Integral Controller

by Seongjae Won, Sukju Kim, Chanyoung Jin and Jinwook Lee

Energies 2025, 18(23), 6324; https://doi.org/10.3390/en18236324 (registering DOI) - 1 Dec 2025

Abstract

Magnetorheological (MR) dampers provide tunable, fast-response damping for semi-active suspension systems. However, their nonlinear flow behavior can limit stability and energy efficiency under broadband road excitation. This study proposes an additional-flow-path-type MR damper integrated with a frequency-domain proportional-integral (PI) controller that captures the [...] Read more.

Magnetorheological (MR) dampers provide tunable, fast-response damping for semi-active suspension systems. However, their nonlinear flow behavior can limit stability and energy efficiency under broadband road excitation. This study proposes an additional-flow-path-type MR damper integrated with a frequency-domain proportional-integral (PI) controller that captures the dominant spectral characteristics of ISO-standard road profiles. A quarter-car simulation model developed in AMESim was used to assess the dynamic performance of the integrated system. The controller gains were tuned using representative excitation frequencies obtained through spectral analysis, allowing the damping force to be shaped in accordance with the primary vibration bandwidth. This approach combines structural modifications that enhance internal flow linearity with a control strategy aligned with the statistical nature of real road disturbances. Simulation results show that the proposed method reduces vertical acceleration of the sprung mass while simultaneously lowering the average damping-force demand compared with a passive suspension. These findings indicate that the combined structural control framework improves both ride comfort and mechanical energy dissipation efficiency. Full article

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22 pages, 2838 KB

Open AccessArticle

Hybrid Mono–Bipolar HVDC System with Control Strategy for Offshore Wind Power Integration

by Xingning Han, Zhuyi Peng, Wenjia Zhang, Wentao Sun, Qian Wu and Zhenjian Xie

Energies 2025, 18(23), 6323; https://doi.org/10.3390/en18236323 (registering DOI) - 1 Dec 2025

Abstract

The ever-growing scale of offshore wind power integration has led coastal provincial power grids to face the common issue of insufficient AC grid structure capacity. An effective solution involves constructing an offshore–onshore mono–bipolar hybrid high voltage DC (HVDC) system by integrating an offshore [...] Read more.

The ever-growing scale of offshore wind power integration has led coastal provincial power grids to face the common issue of insufficient AC grid structure capacity. An effective solution involves constructing an offshore–onshore mono–bipolar hybrid high voltage DC (HVDC) system by integrating an offshore wind monopolar HVDC with an onshore embedded bipolar HVDC. Firstly, the limitations of existing AC structures in coastal grids when undertaking offshore wind power integration are analyzed through N-1 security verification, and the applicability of conventional power evacuation approaches is assessed from both theoretical and practical engineering standpoints. Subsequently, an offshore–onshore mono–bipolar hybrid HVDC system is proposed. Meanwhile, based on operational requirements and the analysis of the structural features, a coordinated control strategy for the hybrid HVDC system under both symmetric and asymmetric operation modes is designed. Finally, a simulation model is built on the PSCAD/EMTDC platform to verify the feasibility of the hybrid HVDC system control strategy in the coastal power grid and the effectiveness of the system to improve the wind power consumption capacity of the coastal power grid. Full article

(This article belongs to the Special Issue Integration of Renewable Energy Systems in Power Grid)

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24 pages, 12417 KB

Open AccessArticle

Conjugate Heat Transfer and Thermal Stress Analysis of a Gas Turbine Double-Wall Cooling System with a Diamond-Type TPMS Effusion

by Kirttayoth Yeranee, Chao Xu, Yuli Cheng and Yu Rao

Energies 2025, 18(23), 6322; https://doi.org/10.3390/en18236322 (registering DOI) - 1 Dec 2025

Abstract

This research numerically investigates the cooling performance of Diamond-type triply periodic minimal surface (TPMS) networks as a gas turbine effusion cooling layer, augmented with various jet impingement configurations. The study analyzes the internal and external flow characteristics, pressure loss, and overall cooling effectiveness [...] Read more.

This research numerically investigates the cooling performance of Diamond-type triply periodic minimal surface (TPMS) networks as a gas turbine effusion cooling layer, augmented with various jet impingement configurations. The study analyzes the internal and external flow characteristics, pressure loss, and overall cooling effectiveness using conjugate heat transfer simulations. The Diamond design is compared to conventional film cooling and micro-hole models within a blowing ratio range of 0.5 to 2.0. The jet hole diameter and jet-to-plate distance are varied to identify an optimal double-wall cooling configuration. The results reveal that the Diamond hole mitigates the strong discharge of coolant, resulting in a more adherent cooling film, which provides excellent surface coverage. While jet impingement enhances internal heat transfer, its contribution to cooling effectiveness is minor compared to the benefit of film coverage. At an equivalent total pressure loss coefficient, the Diamond with impinging jets demonstrates 101% higher cooling effectiveness than the film hole. The thermal-mechanical analysis indicates that the Diamond model exhibits a more uniform distribution of thermal stress and displacement. The average stress is reduced by 44.7% compared to the film hole. This work confirms the TPMS-based effusion as an advanced cooling solution for next-generation gas turbines. Full article

(This article belongs to the Special Issue Thermal Design, Thermodynamic Analysis, and Optimization of Aero-Engines and Gas Turbines—2nd Edition)

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30 pages, 1247 KB

Open AccessArticle

Impact of the Deadlock Handling Method on the Energy Efficiency of a System of Multiple Automated Guided Vehicles in a Production Environment Described as a Square Topology

by Waldemar Małopolski, Jerzy Zając, Wojciech Klein and Rafał Cupek

Energies 2025, 18(23), 6321; https://doi.org/10.3390/en18236321 (registering DOI) - 1 Dec 2025

Abstract

Efficient control a system of multiple Automated Guided Vehicles (AGVs) is crucial for modern intralogistics given the growing importance of energy consumption and operating costs. This study investigates the impact of two deadlock handling methods: Chain Of Reservations (COR) and Structural On-line Control [...] Read more.

Efficient control a system of multiple Automated Guided Vehicles (AGVs) is crucial for modern intralogistics given the growing importance of energy consumption and operating costs. This study investigates the impact of two deadlock handling methods: Chain Of Reservations (COR) and Structural On-line Control Policy (SOCP), on the energy efficiency and performance of AGV systems operating in a production environment described as square topology. A simulation model developed in FlexSim implemented both methods using real AGV data on electricity consumption during various tasks. The analysis also discusses the adopted battery charging strategy. Simulation experiments combined each deadlock handling method with two path-planning strategies: shortest path and fastest path. Pseudocode algorithms for determining these paths in an environment described as square topology are provided. System performance was evaluated across a wide range of AGV fleet sizes, focusing on key indicators such as total energy consumption, time to complete transportation tasks, and AGV utilization rate. Multi-criteria optimization reduced the problem to two conflicting objectives: energy consumption and completion time, with Pareto fronts generated for each configuration studied. The results demonstrate that both the deadlock handling strategy and the selected pathfinding algorithm significantly influence the evaluation criteria. This original research integrates solving the deadlock problem with controlling energy efficiency and task completion time in structured transportation environments that are not deadlock-free by design. Full article

(This article belongs to the Special Issue New Solutions in Electric Machines and Motor Drives: 2nd Edition)

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16 pages, 8077 KB

Open AccessArticle

Algorithmic Design of Modular Two-Layer Multiphase Windings Based on Number Theory

by Bohdan Kharchyshyn, Oleksandr Makarchuk, Dariusz Całus, Mykhailo Khai and Oleh Babei

Energies 2025, 18(23), 6320; https://doi.org/10.3390/en18236320 (registering DOI) - 1 Dec 2025

Abstract

Many electromechanical specialists have attempted to move away from the classical method of designing windings of electrical machines using the star of slot electromotive forces, but their approaches are not always simple or universal. This article proposes a straightforward algorithmic method of winding [...] Read more.

Many electromechanical specialists have attempted to move away from the classical method of designing windings of electrical machines using the star of slot electromotive forces, but their approaches are not always simple or universal. This article proposes a straightforward algorithmic method of winding synthesis based on number theory, which makes it possible to compute the distribution table of symmetrical multiphase, multimodular windings. Analytical expressions are provided for determining the assignment of coils to the corresponding phases, phase zones, and winding modules by sampling coils from a closed-ring structure. The method allows one to determine the direction of coil connections within a phase and covers both overlapping and non-overlapping windings. Three characteristic cases of the relationship between the number of coils and the number of pole pairs in multiphase alternating-current electrical machines are analyzed from the perspective of number theory. Conditions for implementing symmetrical windings are presented. The distribution factors of modular windings for higher field harmonics are evaluated. To validate the approach, examples of application and experimental results are provided. Full article

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31 pages, 1585 KB

Open AccessArticle

Inverting Two-Stage Step-Up Converters

by Felix A. Himmelstoss

Energies 2025, 18(23), 6319; https://doi.org/10.3390/en18236319 (registering DOI) - 30 Nov 2025

Abstract

Apart from combining two converters by connecting them in parallel at the input and the output sides, one can connect them in parallel at the inputs and in series at the outputs of the stages to increase the power rate and to modify [...] Read more.

Apart from combining two converters by connecting them in parallel at the input and the output sides, one can connect them in parallel at the inputs and in series at the outputs of the stages to increase the power rate and to modify the voltage transformation ratio. Four converter topologies with a limited duty-cycle range are studied for their application as stages for a converter combination, which operates as an inverting two-stage step-up converter. The operation of the converter combinations is studied in the steady state, and the dynamic models (for large and small signals) are derived. The start-up of the converters is analyzed. The stress across the components is calculated, and hints for dimensioning are given. The considerations are proved by LTSpice simulations. The advantages and the disadvantages of the four converters are included. Full article

44 pages, 6410 KB

Open AccessArticle

Experimental Assessment and Digital Twin Modeling of Integrated AEM Electrolyzer–PEM Fuel Cell–BESS for Smart Hydrogen Energy Applications

by A. H. Samitha Weerakoon and Mohsen Assadi

Energies 2025, 18(23), 6318; https://doi.org/10.3390/en18236318 (registering DOI) - 30 Nov 2025

Abstract

Rising energy demand, fossil fuel depletion, and global warming are accelerating research into sustainable energy solutions, with growing interest in hydrogen as a promising alternative. This research presents a detailed experimental investigation and novel digital twin (DT) models for an integrated hydrogen-based energy [...] Read more.

Rising energy demand, fossil fuel depletion, and global warming are accelerating research into sustainable energy solutions, with growing interest in hydrogen as a promising alternative. This research presents a detailed experimental investigation and novel digital twin (DT) models for an integrated hydrogen-based energy system consisting of an Anion Exchange Membrane Electrolyzer (AEMEL), Proton Exchange Membrane Fuel Cell (PEMFC), hydrogen storage, and Battery Energy Storage System (BESS). Conducted at a real-world facility in Risavika, Norway, the study employed commercial units: the Enapter EL 4.1 AEM electrolyzer and Intelligent Energy IE-Lift 1T/1U PEMFC. Experimental tests under dynamic load conditions demonstrated stable operation, achieving hydrogen production rates of up to 512 NL/h and a specific power consumption of 4.2 kWh/Nm³, surpassing the manufacturer’s specifications. The PEMFC exhibited a unique cyclic operational mechanism addressing cathode water flooding, a critical issue in fuel cell systems, achieving steady-state efficiencies around 43.6% under prolonged (190 min) rated-power operation. Subsequently, advanced DT models were developed for both devices: a physics-informed interpolation model for the AEMEL, selected due to its linear and steady operational behavior, and an ANN-based model for the PEMFC to capture its inherently nonlinear, dynamically fluctuating characteristics. Both models were validated, showing excellent predictive accuracy (<3.8% deviation). The DTs integrated manufacturer constraints, accurately modeling transient behaviors, safety logic, and operational efficiency. The round-trip efficiency of the integrated system was calculated (~27%), highlighting the inherent efficiency trade-offs for autonomous hydrogen-based energy storage. This research significantly advances our understanding of integrated H₂ systems, providing robust DT frameworks for predictive diagnostics, operational optimization, and performance analysis, supporting the broader deployment and management of hydrogen technologies. Full article

(This article belongs to the Section A5: Hydrogen Energy)

17 pages, 3219 KB

Open AccessArticle

Investigation of Torque Enhancement in PMSMs for LEV Propulsion Using Magnet Segmentation

by Ali Sinan Cabuk and Ozgur Ustun

Energies 2025, 18(23), 6317; https://doi.org/10.3390/en18236317 (registering DOI) - 30 Nov 2025

Abstract

In this paper, the effect of eddy-current losses of permanent magnets (PMs) is studied by conducting analyses and experiments. PM segmentation is used to reduce eddy-current losses. Nowadays, many researchers are focusing on improving the efficiency and torque of permanent magnet synchronous motors [...] Read more.

In this paper, the effect of eddy-current losses of permanent magnets (PMs) is studied by conducting analyses and experiments. PM segmentation is used to reduce eddy-current losses. Nowadays, many researchers are focusing on improving the efficiency and torque of permanent magnet synchronous motors (PMSMs), particularly in electric vehicle applications. This study evaluates PM eddy-current losses of an in-wheel-type PMSM designed for light electric vehicle (LEV) propulsion. Improving output torque and efficiency is essential in this type of direct-drive application. The eddy-current losses of PMs can be reduced by forming PMs as electrically isolated magnet segments. PM segmentation leads to shorter paths and reduces the values of eddy-currents, creating reduced magnetic losses. The improvement in torque production capability also implies an improvement in efficiency. To investigate the validity of PM segmentation, a three-dimensional (3D) finite element analysis (FEA) software is used for non-segmented (monolithic) and segmented cases. The experimental study is conducted using monolithic PM and segmented PM rotor assemblies. This study demonstrates the contribution of PM segmentation to torque production. Full article

(This article belongs to the Special Issue New Solutions in Electric Machines and Motor Drives: 2nd Edition)

20 pages, 546 KB

Open AccessArticle

The Impact of Green Bonds and Energy Use on Carbon Dioxide Emissions: Evidence from 17 Financially Developed Countries (2014–2023)

by Bartosz Jóźwik, Ayşegül Toy, Murat Tekbas, Mesut Dogan and Filip Krauze

Energies 2025, 18(23), 6316; https://doi.org/10.3390/en18236316 (registering DOI) - 30 Nov 2025

Abstract

This study investigates how green bond issuance, energy use, renewable energy, and economic growth relate to per capita CO₂ emissions in 17 financially developed countries that are active in green bond markets over the period 2014–2023. We construct an annual panel for [...] Read more.

This study investigates how green bond issuance, energy use, renewable energy, and economic growth relate to per capita CO₂ emissions in 17 financially developed countries that are active in green bond markets over the period 2014–2023. We construct an annual panel for Australia, Austria, Canada, Mainland China, Finland, France, Germany, Italy, Japan, Luxembourg, New Zealand, Norway, Spain, Sweden, the United Kingdom, and the United States, and apply panel-corrected standard errors (PCSEs) together with Method of Moments Quantile Regression (MMQR). Diagnostic tests based on Pesaran’s CIPS unit root and Westerlund’s cointegration procedures indicate that the variables are I(1) and cointegrated, while Pesaran-type dependence and slope heterogeneity tests justify the use of robust panel methods. The PCSE results show that total energy consumption is the strongest factor associated with higher emissions, renewable energy consumption is consistently associated with lower emissions, economic growth is positively linked to emissions, and green bond issuance is associated with lower emissions, although the magnitude of this relationship is modest. MMQR estimates reveal that these relationships are heterogeneous across the CO₂ distribution. Green bonds are associated with lower emissions only in low-emission country–years, while this association becomes statistically weak at higher quantiles. Renewable energy is linked to lower emissions across all quantiles, with stronger associations in the lower part of the distribution, and the growth–emissions relationship weakens at the top, consistent with an Environmental Kuznets Curve pattern. These findings suggest that expanding renewables and improving the carbon content of energy use remain central for decarbonization, while green bonds may support emission reductions, particularly in cleaner, institutionally advanced economies. Full article

(This article belongs to the Special Issue Energy Economics, Finance and Policy Towards Sustainable Energy: 2nd Edition)

16 pages, 2062 KB

Open AccessArticle

An Indicator for Assessing the Hosting Capacity of Low-Voltage Power Networks for Distributed Energy Resources

by Grzegorz Hołdyński, Zbigniew Skibko and Andrzej Firlit

Energies 2025, 18(23), 6315; https://doi.org/10.3390/en18236315 (registering DOI) - 30 Nov 2025

Abstract

The article analyses the hosting capacity of low-voltage (LV) power grids for connecting distributed energy sources (DER), mainly photovoltaic installations (PV), considering technical limitations imposed by power system operating conditions. The main objective of the research was to develop a simple equation that [...] Read more.

The article analyses the hosting capacity of low-voltage (LV) power grids for connecting distributed energy sources (DER), mainly photovoltaic installations (PV), considering technical limitations imposed by power system operating conditions. The main objective of the research was to develop a simple equation that enables the quick estimation of the maximum power of an energy source that can be safely connected at a given point in the network without causing excessive voltage rise or overloading the transformer and line cable. The analysis was performed on the basis of relevant calculation formulas and simulations carried out in DIgSILENT PowerFactory, where a representative low-voltage grid model was developed. The network model included four transformer power ratings (40, 63, 100, and 160 kVA) and four cable cross-sections (25, 35, 50, and 70 mm²), which made it possible to assess the impact of these parameters on grid hosting capacity as a function of the distance from the transformer station. Based on this, the P_HCI indicator was developed to determine the hosting capacity of a low-voltage network, using only the transformer rating and the length and cross-section of the line for the calculations. A comparison of the results obtained using the proposed equation with detailed calculations showed that the approximation error does not exceed 15%, which confirms the high accuracy and practical applicability of the proposed approach. Full article

(This article belongs to the Special Issue New Technologies and Materials in the Energy Transformation)

15 pages, 588 KB

Open AccessArticle

Closing the Loop on Solar: A Sustainability Assessment of Photovoltaic Recycling in Greece

by Kyriaki Kiskira, Angeliki Lalopoulou, Konstantinos Kalkanis and George Vokas

Energies 2025, 18(23), 6314; https://doi.org/10.3390/en18236314 (registering DOI) - 30 Nov 2025

Abstract

This paper examines the sustainability of photovoltaic (PV) panel recycling through a case study in Greece. It traces the evolution of PVs and outlines the main construction characteristics, emphasizing that although PV systems reduce greenhouse gas emissions, they also generate substantial end-of-life (EoL) [...] Read more.

This paper examines the sustainability of photovoltaic (PV) panel recycling through a case study in Greece. It traces the evolution of PVs and outlines the main construction characteristics, emphasizing that although PV systems reduce greenhouse gas emissions, they also generate substantial end-of-life (EoL) waste containing both valuable and potentially hazardous materials. The study estimates Greece’s annual PV waste generation and evaluates its environmental, social, and economic impacts. It focuses on advanced disassembly and recycling methods by PV types and calculates material-recovery rates. Using national installation data from 2009–2023, the analysis quantifies the potential mass of recoverable materials and assesses the sustainability of PV recycling in terms of environmental protection, public health, and economic feasibility. Results show high recovery rates: silicon (85%), aluminum (100%), silver (98–100%), glass (95%), copper (97%), and tin (32%). Although current recycling economics remain challenging, the environmental and health benefits are significant. This research contributes to the existing literature by providing the first detailed quantification of recoverable raw materials embedded in Greece’s PV stock and by highlighting the need for technological innovation and supportive policies to enable a circular and sustainable solar economy. Full article

(This article belongs to the Special Issue A Circular Economy Perspective: From Waste to Energy)

21 pages, 2110 KB

Open AccessArticle

Control of an Energy Storage System in the Prosumer’s Installation Under Dynamic Tariff Conditions

by Paweł Kelm, Rozmysław Mieński and Irena Wasiak

Energies 2025, 18(23), 6313; https://doi.org/10.3390/en18236313 (registering DOI) - 30 Nov 2025

Abstract

In accordance with the European common rules for the internal electricity market, suppliers offer end users contracts with dynamic energy prices. To reduce energy costs, prosumers must manage their installations with energy storage devices (ESSs). The authors propose a novel control strategy with [...] Read more.

In accordance with the European common rules for the internal electricity market, suppliers offer end users contracts with dynamic energy prices. To reduce energy costs, prosumers must manage their installations with energy storage devices (ESSs). The authors propose a novel control strategy with a relatively simple simulation-based algorithm that effectively reduces daily energy costs by managing the ESS charging and discharging schedule under different types of dynamic energy tariffs. The algorithm operates in a running window mode to ensure ongoing control updates in response to the changing conditions of the prosumer’s installation operation and dynamically changing energy prices. A feature of the control system is its ability to regulate the power exchanged with the supply network in response to an external signal from a superior control system or a network operator. This feature allows the control system to participate in regulatory services provided by the prosumer to the DSO. The effectiveness of the proposed control algorithm was verified in the PSCAD V4 Professional environment and with the MS Excel SOLVER for Office 365 optimisation tool. The results showed good accuracy with respect to the cost reduction algorithm and confirmed that the additional regulatory service can be effectively implemented within the same prosumer ESS control system. Full article

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

38 pages, 2935 KB

Open AccessArticle

Household Challenges in Solar Retrofitting to Optimize Energy Usage in Subtropical Climates

by Richard Hyde, David Wadley and John Hyde

Energies 2025, 18(23), 6312; https://doi.org/10.3390/en18236312 (registering DOI) - 30 Nov 2025

Abstract

This study investigates the architectural design factors that influence the adoption of eco-friendly solar energy technologies for the partial retrofitting of older residential buildings in densely populated urban areas in a developed country. This research study employs a mixed-method approach, combining quantitative and [...] Read more.

This study investigates the architectural design factors that influence the adoption of eco-friendly solar energy technologies for the partial retrofitting of older residential buildings in densely populated urban areas in a developed country. This research study employs a mixed-method approach, combining quantitative and qualitative frameworks along with comparative analysis and utilizing standard fact-finding procedures to examine the adoption of eco-friendly energy systems and their integration into existing infrastructures. The feasibility study, complemented by a detailed technical investigation, identifies several significant factors affecting the intention to undertake sustainable solar retrofitting. These factors include performance expectations, facilitating conditions, motivation, price/value perceptions, and environmental knowledge. This study highlights key constraints and tipping points that influence households’ decisions to implement light retrofitting and explores three distinct system configurations to enhance cost-effectiveness. The insights gained from this research study are valuable for a range of stakeholders, including homeowners, designers, technology developers and manufacturers, real estate developers, builders, and government entities. The findings guide effective strategies to encourage eco-friendly retrofits through both passive and active systems, contributing to future environmental sustainability goals. This research study addresses a gap in the literature regarding the environmental sustainability of solar retrofitting in densely populated urban settings in developed countries. Addressing the pressing issue of global warming contributes to advancing sustainable solar housing technologies and provides a comprehensive foundation for the early stages of the design process. Full article

(This article belongs to the Special Issue Advanced Studies in Energy Efficiency of Buildings and Urban Built Environment)

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20 pages, 8449 KB

Open AccessArticle

Research on the Alternating Current Properties of Cellulose–Innovative Bio-Oil Nanocomposite as the Fundamental Component of Power Transformer Insulation—Determination of Nanodroplet Dimensions and the Distances Between Them

by Konrad Kierczyński, Tomasz N. Kołtunowicz, Vitalii Bondariev, Paweł Okal, Marek Zenker, Marek Szrot, Paweł Molenda, Andrzej Cichoń and Paweł Żukowski

Energies 2025, 18(23), 6311; https://doi.org/10.3390/en18236311 (registering DOI) - 30 Nov 2025

Abstract

The paper presents measurements of frequency dependence of conductivity and real components of complex permittivity of a nanocomposite consisting of electrical pressboard, bio-insulating oil and water nanodroplets with moisture content ranging from 0.6 wt.% to 5 wt.%. Bio-oil meets high environmental requirements—it is [...] Read more.

The paper presents measurements of frequency dependence of conductivity and real components of complex permittivity of a nanocomposite consisting of electrical pressboard, bio-insulating oil and water nanodroplets with moisture content ranging from 0.6 wt.% to 5 wt.%. Bio-oil meets high environmental requirements—it is fully biodegradable, and its combustion products are significantly less harmful than those of mineral oil. In addition, the use of bio-oil reduces the carbon footprint of power transformer production. The quantum mechanical phenomenon of electron tunnelling between potential wells created by water nanodroplets was used to analyze the experimental results obtained. The study determined the effect of moisture content on the relative relaxation time values. On this basis, the number of water molecules in nanodroplets, their diameters and the concentration of nanodroplets depending on moisture content were determined. The distances over which electrons tunnel in moist pressboard impregnated with bio-oil were determined. These values are the expected values of the probability distribution of the distance between neighbouring nanodroplets. The values of the number of water molecules in nanodroplets are also the expected values of the probability distribution of the number of molecules in nanodroplets. It has been established that during many years of transformer life, several parallel processes occur as the moisture content in bio-oil-impregnated pressboard increases. One of them involves the accumulation of water molecules collected in the pressboard in nanodroplets. The second is an increase in the concentration of nanodroplets. The third is an increase in the average number of water molecules in nanodroplets. Full article

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

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44 pages, 4291 KB

Open AccessArticle

A Physics-Informed Reinforcement Learning Framework for HVAC Optimization: Thermodynamically-Constrained Deep Deterministic Policy Gradients with Simulation-Based Validation

by Sattar Hedayat, Tina Ziarati and Matteo Manganelli

Energies 2025, 18(23), 6310; https://doi.org/10.3390/en18236310 (registering DOI) - 30 Nov 2025

Abstract

This paper presents a physics-informed reinforcement learning framework that embeds thermodynamic constraints directly into the policy network of a continuous control agent for HVAC optimization. We introduce a Thermodynamically-Constrained Deep Deterministic Policy Gradient (TC-DDPG) algorithm that operates on continuous actions and enforces physical [...] Read more.

This paper presents a physics-informed reinforcement learning framework that embeds thermodynamic constraints directly into the policy network of a continuous control agent for HVAC optimization. We introduce a Thermodynamically-Constrained Deep Deterministic Policy Gradient (TC-DDPG) algorithm that operates on continuous actions and enforces physical feasibility through a differentiable constraint layer coupled with physics-regularized loss functions. In a simulation-based evaluation using a custom Python multi-zone resistance-capacitance (RC) thermal model, the proposed method achieves a 34.7% reduction in annual HVAC electricity consumption relative to a rule-based baseline (95% CI: 31.2–38.1%, n = 50 runs) and outperforms standard DDPG by 16.1 percentage points. Thermal comfort during occupied hours maintains PMV∈ [−0.5, 0.5] for 98.3% of operational time, peak demand decreases by 35.8%, and simulated coefficient of performance (COP) improves from 2.87 ± 0.08 to 4.12 ± 0.10. Physics constraint violations are reduced by approximately 98.6% compared to unconstrained DDPG, demonstrating the effectiveness of architectural enforcement mechanisms within the simulation environment. We present a reference prototype and commit to a future public release of the code, configurations, and hyperparameters sufficient to reproduce the reported results. The paper explicitly addresses the limitations of simulation-based studies and presents a staged roadmap toward hardware-in-the-loop testing and pilot deployments in real buildings. Full article

(This article belongs to the Special Issue New Insights into Hybrid Renewable Energy Systems in Buildings)

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