Journal of Energy Technology
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description: Journal of Energy Technology is a scientific and professional journal in the field of energy and energy technologies. The first issue of Journal of Energy Technology was launched in November 2008. The founder of the journal is University of Maribor, Faculty of Energy Technology. The journal is intended for domestic and foreign scientific, technical and general public. With the aim of increasing the recognition of the journal, the articles in journal are mainly in English. The journal is issued quarterly in both printed and electronic form. Indexing: The Journal of Energy Technology (JET) is indexed and abstracted in database INSPEC©. Participating University of Maribor Faculties: Faculty of Energy Technology
publisher: University of Maribor Press
language: en
publication name: Journal of Energy Technology
issn: 1855-5748
items: Results of the HESS project – Hybrid Energy Storage System in post-mining infrastructure
items: Stochastic modelling of a low voltage distribution network operation
items: Using a High-Temperature Heat Pump for Heating of Greenhouses
items: Design and Economic Assessment of a 19-Seat Hydrogen Fuel Cell Aircraft for Regional Aviation
items: Assessing the Potential of Electrochemical Impedance Spectroscopy as a Supporting Tool for Equivalent Circuit Modeling in Battery Management Systems
items: Environmental Assessment: Safeguarding nature and accelerating the transition to green energy
items: Approximate, numerical and experimental investigations of a water hammer in Vrhovo bulb-turbines hydropower plant
items: Operational and thermodynamic methodology for integrating a gas–steam cycle into a legacy coal-fired power block
items: Measurement-Based Evaluation of Distribution Transformer Losses Characteristics for Sustainable Voltage Regulation
items: Evaluation of the mechanical properties of steel under elevated temperature conditions
items: Radioactive Waste Management Strategy for a New Nuclear Power Plant
items: Identification and Qualitative Analysis of Liquid Effluents in the Spatial Planning Stage of a New Nuclear Power Plant Project
items: Systematic Derivation of Clarke and Park Transformations through Vector Representation in Three-Phase Systems
items: Design and fabrication of a demonstration model for promoting low-carbon energy technologies
items: Assessment of Harmonic Distortion in School Buildings Equipped with Grid-Connected PV Systems
items: Towards Digital Twinning of Electrical Motors – Simulation Models
items: Simulation-Based Study of Structural Changes in Electrical Time-Series Signals
items: Biomass Gasification Potential for Slovenia’s Green Transition
items: Consumer Protection in the Electricity Market in the European Union and Slovenia
items: THE IMPACT OF WIND POWER PLANT SIZE ON ECONOMIC VIABILITY AT THE OJSTRICA LOCATION
items: CHEMICAL ANALYSIS OF THERMALLY AGED CABLES IN NUCLEAR POWER PLANTS
items: ARTIFICIAL INTELLIGENCE -BASED EXERGY ANALYSIS OF AN ABSORPTION COOLING SYSTEM
items: ENERGY TRANSITION IN MUNICIPALITIES – A MODEL FOR SUSTAINABLE RENEWABLE ENERGY MANAGEMENT
items: FFA FW FLOW INFLUENCE AT NPP KRŠKO
items: A REVIEW OF ARTIFICIAL INTELLIGENCE IN NUCLEAR POWER PLANTS
items: THEORETICAL AND EXPERIMENTAL INVESTIGATIONS OF A WATER HAMMER IN SAVA RIVER KAPLAN TURBINE HYDROPOWER PLANTS
items: ASSESSING THE EFFECTS OF A HYDROPOWER PLANT BASIN ON FISH SPAWNING IN AN UPSTREAM RIVER TRIBUTARY
items: VERIFICATION AND VALIDATION OF STUDENT’S CFD TOOL ON THE VENTURI FLOW CASE
items: HEAVY METAL CONTENT IN VEGETABLE GARDEN SOILS IN RELATION TO THEIR NATURAL BACKGROUND
items: HEAVY METAL CONTENT IN SOILS OF SELECTED HOP PLANTATIONS IN RELATION TO THEIR NATURAL BACKGROUND

Results of the HESS project – Hybrid Energy Storage System in post-mining infrastructure
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description: The project`s aim was to develop a Hybrid Energy Storage System (HESS) consisting of three different energy storage systems: Pumped Storage Hydroelectricity (PSH), Compressed Gas – Air/CO2 Energy Storage (CAES) and Thermal Energy Storage (TES) using a post-mining infrastructure. The possibility of using geothermal energy and the use and potential storage of CO2 were also included in the research. The assumed total energy storage capacity in the HESS project was in the range of 30 MWh. On the basis of the energy demand of each HESS component, a method of thermal and mechanical integration of the entire system was investigated and developed, together with an algorithm for the mutual interaction between the elements of the energy storage system. The optimal cooperation of the various elements of the HESS was decided to be supervised by an energy router. The router also manages energy exchanges with the national power grid for the intake of low-cost green energy and peak energy production. The single HESS energy router system should take into account the possibility of the cooperation of multiple HESS systems working in a distributed system.
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creator: Sergej Jamnikar
creator: Agata Czardybon
creator: Piotr Matusiak
creator: Daniel Kowol
creator: Marcin Lutynski
creator: Jakub Ochmann
creator: Konrad Kołodziej
creator: Zbyszek Szeliga
creator: Gregor Jeromel
creator: Janez Rošer
rights: Copyright (c) 2026 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2026-07-15
publication date: 2026-07-15
starting page: 5
ending page: 30
doi: 10.18690/jet.19.1.%p.2026

Stochastic modelling of a low voltage distribution network operation
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description: Modelling a low-voltage network operation is becoming increasingly challenging. In the past, deterministic methods adopted from sub-transmission and transmission network analysis were sufficient for operators to assess the operating conditions. However, changes in customer behaviour, household appliance structure, and the growing penetration of residential photovoltaics, EV charging, heat pumps, and air conditioning are altering operating conditions in low voltage networks significantly. Given the strongly stochastic nature of individual customer consumption and generation, deterministic methods are becoming less suitable for proper grid operation analysis and development planning. This article presents a simple method for stochastic modelling of a network operation, where customer behaviour is described using a system of histograms. The presented approach enables in-depth investigation of operating conditions in low voltage networks, identifying potential operational extremes that compromise safety of operation, while also quantifying the frequency and probability of such events. Application of the method is demonstrated for a typical rural network.
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creator: Michal Baherník
creator: Marek Höger
rights: Copyright (c) 2026 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2026-07-15
publication date: 2026-07-15
starting page: 31
ending page: 54
doi: 10.18690/jet.19.1.%p.2026

Using a High-Temperature Heat Pump for Heating of Greenhouses
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description: Greenhouse heating is associated with high energy consumption and operating costs, particularly during winter conditions. This study investigates the application of a geothermal high-temperature heat pump for greenhouse heating in northeastern Slovenia. A case study greenhouse used for rose cultivation was analysed, to determine heat losses, heating demand and economic feasibility. The heat loss calculations were performed using the greenhouse geometry, the thermal properties of double-wall polycarbonate panels, and the minimum outdoor temperatures recorded between October 2023 and April 2024. The results showed that the maximum heating demand reached 91.31 kW, exceeding the capacity of the existing 80 kW electric heater. Consequently, a Thermeco2 HHR180 high-temperature heat pump was selected, with a heating capacity of 130 kW and a coefficient of performance (COP) of 4.78. An economic analysis indicated annual savings of €29,143.07 and a payback period of 6.55 years. The findings confirm that high-temperature heat pumps represent a technically feasible and economically viable solution for improving energy efficiency and sustainability in greenhouse production.
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creator: Almina Sarajlić
creator: Jurij Avsec
creator: Urška Novosel
rights: Copyright (c) 2026 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2026-07-15
publication date: 2026-07-15
starting page: 55
ending page: 68
doi: 10.18690/jet.19.1.%p.2026

Design and Economic Assessment of a 19-Seat Hydrogen Fuel Cell Aircraft for Regional Aviation
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description: This paper summarises the results from the MAHEPA project, which investigated the technological and economic feasibility of 19-seat hydrogen fuel cell aircraft and their potential deployment towards 2050. It assesses the key requirements necessary to enable their operation and long-term viability. The analysis is structured in three parts. First, it addresses the required infrastructure and safety measures for hydrogen-based regional aviation, including production and distribution. Second, it evaluates the development needs of critical technological components such as fuel cells, hydrogen storage systems and propulsion integration. Third, it examines the economic feasibility, where the direct operating costs are linked strongly to the aircraft mass characteristics. The economic results for the 2030–2050 horizon indicate potential cost competitiveness under favourable hydrogen pricing and continued technology development, supporting hydrogen fuel cell aircraft as a viable option for regional aviation.
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creator: Anita Prapotnik Brdnik
creator: Maršenka Marksel
rights: Copyright (c) 2026 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2026-07-15
publication date: 2026-07-15
starting page: 69
ending page: 82
doi: 10.18690/jet.19.1.%p.2026

Assessing the Potential of Electrochemical Impedance Spectroscopy as a Supporting Tool for Equivalent Circuit Modeling in Battery Management Systems
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description: Accurate yet computationally efficient battery models are essential for industrial battery management systems (BMS), which operate under strict constraints on sensing and processing power, as well as certification requirements. Electrical equivalent circuit models (ECMs) are therefore adopted widely in practice, while physics-based models (PBMs) provide detailed descriptions of transport, kinetic, and degradation processes, but are not yet adopted in embedded implementation. The present work assesses the potential of electrochemical impedance spectroscopy (EIS) as a supporting tool for equivalent circuit modeling in BMS applications, with an emphasis on its ability to provide frequency-resolved, process-level indications rather than direct parameter information. By separating the ohmic, charge-transfer, and diffusion-related contributions in the frequency domain, EIS offers complementary insights that are not accessible through time-domain measurements alone. The analysis addresses how such indications can guide ECM structure selection and parameter interpretation, the limitations imposed by measurement duration, noise, and temperature gradients, and the feasibility of EIS-supported modeling approaches under typical BMS constraints. The results delineate the scope within which frequency-informed modeling can enhance physical consistency and diagnostic interpretability while preserving the computational characteristics required for BMS implementation.
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creator: Denis Batiuk
creator: Igor Mele
creator: Klemen Zelič
creator: Martin Pec
creator: Tomaž Katrašnik
creator: Amor Chowdhury
rights: Copyright (c) 2026 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2026-07-15
publication date: 2026-07-15
starting page: 83
ending page: 108
doi: 10.18690/jet.19.1.83-108.2026

Environmental Assessment: Safeguarding nature and accelerating the transition to green energy
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description: The accelerated deployment of a renewable energy infrastructure is a cornerstone of the European green transition, yet the planning, assessment and permitting processes are perceived increasingly as bottlenecks. This paper examines environmental assessment as an enabling framework that can support faster, more coherent and more legitimate decision-making in the context of energy system transformation. Rather than framing environmental assessment as a procedural barrier, the paper conceptualises it as a decision-making and governance infrastructure that integrates environmental, social and health considerations into energy planning. Drawing on recent research and a synthesis of contemporary practice, the paper highlights the importance of early engagement, systems thinking and transformative approaches that move beyond narrow compliance-oriented assessment. Particular attention is given to the balance between acceleration and simplification, as well as to the role of agency, collaboration and professional capacity. The paper concludes that a well-designed environmental assessment does not slow down the green transition, but helps ensure that it is resilient, legitimate and aligned with the long-term sustainability objectives.
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creator: Matej Fike
creator: Marko Pezdevšek
creator: Andraž Roger
rights: Copyright (c) 2025 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2026-02-18
publication date: 2026-02-18
starting page: 251
ending page: 260
doi: 10.18690/jet.18.4.%p.2025

Approximate, numerical and experimental investigations of a water hammer in Vrhovo bulb-turbines hydropower plant
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description: This paper investigates effectiveness and accuracy of approximate and numerical water hammer models in the Sava River bulb turbine hydropower plants. The approximate and numerical rigid water hammer models are introduced first. The computational results are compared with the results of measurements in Vrhovo hydropower plant. Comparisons of the computed and measured results are examined for emergency shutdown case. The water hammer is controlled by appropriate adjustment of the guide vane and runner blade closing/opening laws. There is a good agreement between the approximate and numerical, and measured results.
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creator: Anton Bergant
creator: Jošt Perkolj
rights: Copyright (c) 2025 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2026-02-18
publication date: 2026-02-18
starting page: 189
ending page: 202
doi: 10.18690/jet.18.4.%p.2025

Operational and thermodynamic methodology for integrating a gas–steam cycle into a legacy coal-fired power block
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description: This paper investigates the thermodynamic integration of a gas–steam combined cycle into an existing coal-fired power block with the objective of reducing coal utilisation and associated emissions. In the baseline configuration, the legacy unit relies entirely on pulverised coal combustion, whereas the retrofit concept introduces a natural gas-fired gas turbine with heat recovery steam generation. The recovered exhaust heat is used to supplement steam production for the existing steam turbine train, thereby increasing the overall cycle efficiency and enabling partial fuel substitution. From an ecological perspective, natural gas presents a significantly lower carbon emission factor compared to coal, resulting in a proportional reduction of CO₂ and other greenhouse gas emissions at the system level. Additional benefits include lower NOₓ formation due to cleaner combustion and improved operational flexibility, enabling more efficient load following under variable renewable penetration. The results suggest that such hybridisation offers a viable decarbonisation pathway for thermal assets by leveraging the existing infrastructure while achieving meaningful reductions in specific emissions.
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creator: Dušan Strušnik
rights: Copyright (c) 2025 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2026-02-18
publication date: 2026-02-18
starting page: 213
ending page: 230
doi: 10.18690/jet.18.4.%p.2025

Measurement-Based Evaluation of Distribution Transformer Losses Characteristics for Sustainable Voltage Regulation
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description: This paper presents the characteristics of distribution transformer losses obtained on the basis of field measurements in a distribution grid. The active and reactive powers were recorded simultaneously at both 110 kV and 35 kV transformer voltage levels in different periods of the days, when the position of the on-load tap changer was changed intentionally. The variations of total transformer losses during these experiments were modelled by exponential models. The parameters of the models were grouped according to the particular daily periods, analysed statistically and compared with corresponding parameters of transformer load models. The importance was emphasised of knowing transformer losses characteristics in the networks with a significant share of distributed generation, energy storage systems and electric vehicles.
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creator: Lidija Korunovic
rights: Copyright (c) 2025 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2026-02-18
publication date: 2026-02-18
starting page: 203
ending page: 212
doi: 10.18690/jet.18.4.203-212.2025

Evaluation of the mechanical properties of steel under elevated temperature conditions
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description: This paper presents the influence of elevated temperatures on the mechanical properties of steel with varying iron content and alloying compositions. The paper combines chemical analysis and high-temperature tensile testing to examine how microstructure, chemical composition and temperature affect the yield strength, tensile strength and ductility of steel. Samples of two thicknesses (0.63 mm and 0.50 mm) and three iron levels (85 wt%, 90 wt %, and 97 wt%) were analysed and classified based on their chemical composition. Tensile tests were performed in accordance with ISO 6892-2 within the temperature range of 90 °C to 250 °C, using 20 °C increments. The findings highlight the combined effect of temperature and alloying chemistry on the hightemperature performance of steel, providing valuable insights for material selection in thermally demanding engineering applications.
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creator: Klemen Sredenšek
creator: Zdravko Praunseis
creator: Luka Barbič
rights: Copyright (c) 2025 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2026-02-18
publication date: 2026-02-18
starting page: 231
ending page: 250
doi: 10.18690/jet.18.4.%p.2025

Radioactive Waste Management Strategy for a New Nuclear Power Plant
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description: An essential early phase of any new nuclear power plant (NPP) project is drafting and preparation of a radioactive waste management strategy. The paper outlines major steps in such strategy presented in a case study approach for new NPP project in Krško (the JEK2 project). The paper includes analyses of options and strategies for radioactive waste (RAW) and spent nuclear fuel (SNF) management. This article presents a proposed management plan for RAW and SNF expected to be produced during operation and decommissioning of JEK2, together with an assessment of anticipated decommissioning and waste management costs. The document further examines the existing financing framework for radioactive waste management in Slovenia, which is legally regulated for current nuclear facilities. A similar approach is planned for JEK2, including the expansion of existing and planned facilities for waste handling and storage. Accordingly, additional financial resources will be required through contributions to the national decommissioning and disposal fund. An analysis was therefore conducted to estimate the scale of additional contributions needed to ensure adequate funding for new NPP project in Krško.
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creator: Eva Bahčič
creator: Kaja Naglič
creator: Tomaž Žagar
rights: Copyright (c) 2025 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2026-02-11
publication date: 2026-02-11
starting page: 161
ending page: 168
doi: 10.18690/jet.18.3.161-168.2025

Identification and Qualitative Analysis of Liquid Effluents in the Spatial Planning Stage of a New Nuclear Power Plant Project
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description: Planned JEK2 will generate liquid effluents during normal operation, categorized as radioactive and non-radioactive. Radioactive releases will mainly consist of tritium, while other radionuclides will be present only in trace amounts, all below the authorized limits. Non-radioactive effluents, originating from cooling and service water systems, will be treated by filtration, pH adjustment, and biocide neutralization. Thermal load of non-radioactive emissions to the Sava will be minimal to negligible levels, as the cooling tower serves as the heat sink. All effluents from JEK2 will be managed by design through defence in depth: multi-barrier treatment and holdup, controlled storage and release, and comprehensive monitoring under the ALARA principle to keep impacts low and within strict regulatory limits
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creator: Pia Fackovič
creator: Klemen Debelak
creator: Kaja Zupančič
creator: Tomaž Žagar
rights: Copyright (c) 2025 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2026-02-11
publication date: 2026-02-11
starting page: 177
ending page: 186
doi: 10.18690/jet.18.3.177-186.2025

Systematic Derivation of Clarke and Park Transformations through Vector Representation in Three-Phase Systems
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description: This paper presents a comprehensive mathematical derivation of Clarke and Park transformations from first principles through systematic vector representation. Despite over a century of widespread application in power electronics and motor control, rigorous derivations of these fundamental transformations remain scattered across literature. We address this gap by systematically progressing from three-phase voltage equations in time domain to spatial vector representation in three-dimensional space, then deriving Clarke transformation through geometric projection onto the plane where balanced quantities reside. Subsequently, we derive Park transformation as time-varying rotation of the Clarke frame. The work establishes both amplitude-invariant and power-invariant formulations, explains the geometric significance of the 35.26° angle between coordinate systems, and reveals the mathematical basis for zero-sequence component extraction. This unified treatment bridges the gap between these transformations' ubiquitous practical application and their fundamental mathematical origins.
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creator: Filip Filipović
creator: Milutin Petronijević
creator: Nebojša Mitrović
creator: Bojan Banković
creator: Anđela Stojiljković
creator: Vojkan Kostić
rights: Copyright (c) 2025 Journal of Energy Technology https://creativecommons.org/licenses/by/4.0
date: 2026-02-11
publication date: 2026-02-11
starting page: 145
ending page: 160
doi: 10.18690/jet.18.3.145-160.2025

Design and fabrication of a demonstration model for promoting low-carbon energy technologies
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description: This article presents the design, construction, and educational application of a large-scale model representing renewable energy facilities that do not yet exist. The model features a circular layout with a diameter of 2 meters, divided into two halves: the Mokrice Hydropower Plant and a nuclear power plant with an accompanying low- and intermediate-level radioactive waste repository. The Mokrice half highlights key ecological and technical features, including two fish passages and a solar power plant installation, with realistic water effects achieved using epoxy resin. The nuclear half includes a removable low- and intermediate-level radioactive waste repository, allowing viewers to explore storage arrangements via a cross-sectional view. All components were fabricated using FDM 3D printing, assembled, finished with paint and landscaping materials, and mounted on a wooden base with a metal support structure. While the model was not intended to achieve exact technical scaling, it effectively communicates complex energy infrastructures, facilitating public understanding, awareness, and dialogue about low-carbon technologies. The combination of additive manufacturing, interactive features, and detailed landscape representation demonstrates the value of models as tools for education, demonstration, and the promotion of sustainable energy solutions.
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creator: Marko Pezdevšek
creator: Garsia Kosinac
creator: Boštjan Pišotek
creator: Andrej Predin
creator: Andraž Roger
creator: Matej Fike
creator: Gorazd Hren
rights: Copyright (c) 2025 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2026-02-11
publication date: 2026-02-11
starting page: 169
ending page: 176
doi: 10.18690/jet.18.3.169-176.2025

Assessment of Harmonic Distortion in School Buildings Equipped with Grid-Connected PV Systems
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description: The integration of photovoltaic systems into power grids can impact power quality, particularly concerning voltage and current harmonics. This study investigates the power quality of a photovoltaic system integrated into the electrical system of an educational facility, focusing on harmonic distortion in both voltage and current. Comprehensive measurements were conducted across three phases and analysed according to the EN 50160 and IEEE 519 Standards. The results demonstrated that, while the voltage quality meets EN 50160 requirements consistently, indicating stable voltage levels, the current measurements revealed significant harmonic distortion. Notably, Phase 2 exhibited Total Harmonic Distortion values substantially above the acceptable limits, with Phase 1 and Phase 3 also showing elevated Total Harmonic Distortion. To address these issues, the study recommends the implementation of advanced harmonic filters and optimisation of inverter technologies. These measures are crucial for enhancing power quality, and ensuring compliance with the industry Standards in high photovoltaic penetration scenarios.
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creator: Franjo Pranjić
rights: Copyright (c) 2025 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2025-09-29
publication date: 2025-09-29
starting page: 99
ending page: 122
doi: 10.18690/jet.18.2.99-122.2025

Towards Digital Twinning of Electrical Motors – Simulation Models
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description: This paper presents a methodological framework for building a digital shadow of an induction motor based on standardized tests and a two‑axis (dq) simulation model. Tests were carried out according to IEEE Std 112 and IEC 60034‑2‑1 [10, 11]. Parameters of the equivalent circuit were identified and entered into the model. Validation was performed by comparing torque–speed and current–speed curves at 180 V and 220 V, while nominal behavior at 400 V was estimated using the model and voltage scaling. The model was then calibrated to reduce the discrepancy between simulation and measurements and the error was quantified using the root‑mean‑square error (RMSE) and mean absolute percentage error (MAPE). An automated load‑simulation setup that reproduces the torque test is also presented, enabling rapid evaluation of parameter influence. Results show a very good match in the current channel, with larger deviations in the prediction of characteristic torque points, indicating the limitations of linearized parameters and motivating nonlinear model extensions. The approach enables reliable estimates at nominal voltage when direct measurements are not feasible.
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creator: Goran Kurtović
creator: Luka Živković
creator: Tin Benšić
creator: Željko Hederić
creator: Marinko Stojkov
rights: Copyright (c) 2025 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2025-09-29
publication date: 2025-09-29
starting page: 65
ending page: 74
doi: 10.18690/jet.18.2.65-74.2025

Simulation-Based Study of Structural Changes in Electrical Time-Series Signals
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description: This paper addresses the detection of changes in electrical signals typical for industrial and power systems, using statistical indicators. A dedicated MATLAB algorithm was developed to identify change points by tracking shifts in signal behavior and statistical properties. To evaluate the method, synthetic signals were generated through simulation to reproduce common patterns observed in these systems, allowing testing under different operating conditions and varying noise levels. The results demonstrate that the algorithm reliably detects change points across multiple scenarios, showing both flexibility and robustness. This study highlights the value of simulation-based signal generation as a controlled environment for testing detection methods and provides a foundation for future application to more complex real-world electrical signal analysis tasks.
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creator: Luka Živković
creator: Željko Hederić
creator: Tin Benšić
creator: Goran Kurtović
creator: Marinko Stojkov
rights: Copyright (c) 2025 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2025-09-29
publication date: 2025-09-29
starting page: 75
ending page: 84
doi: 10.18690/jet.18.2.75-84.2025

Biomass Gasification Potential for Slovenia’s Green Transition
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description: In 2024, approximately fifty percent of the total kilometers driven by passenger vehicles in Slovenia were attributed to diesel-powered automobiles, underscoring the persistent dependence of the transportation sector on fossil fuels, which are major contributors to greenhouse gas emissions and global warming. Research further substantiates that the transportation sector constitutes the nation's predominant source of greenhouse gas emissions. In this context, e-mobility emerges as a key strategy for Slovenia’s green transition in transportation. Additionally, biomass gasification represents a sustainable and environmentally friendly energy pathway that could support the country in achieving its environmental targets, while promoting the principles of the circular economy.
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creator: Neja Hadžiselimović
creator: Tjaž Hadžiselimović
rights: Copyright (c) 2025 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2025-09-29
publication date: 2025-09-29
starting page: 85
ending page: 98
doi: 10.18690/jet.18.2.85-98.2025

Consumer Protection in the Electricity Market in the European Union and Slovenia
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description: The article examines consumer protection in the electricity market, focusing on vulnerable customers and the right to emergency supply. At EU level, it outlines the development from the energy legislative packages to Directive (EU) 2019/944, which strengthens consumer rights and requires Member States to define and protect vulnerable groups. In Slovenia, these issues are regulated by Article 33 of the Electricity Supply Act (ZOEE), implemented through the System Operating Instructions (SONDSEE) and the Energy Agency’s act on criteria for ensuring emergency supply. The article applies normative and comparative legal analysis, reviews the Energy Agency’s Annual Reports, and analyzes case law. The findings reveal a gap between regulation and practice, as only one request for emergency supply was approved in Slovenia, in 2019. It proposes clearer criteria, simpler procedures, and more effective consumer information, particularly for vulnerable groups, to ensure the right to emergency supply is realized in practice.
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creator: Nina Sotošek
creator: Peter Virtič
rights: Copyright (c) 2025 University of Maribor, University of Maribor Press https://creativecommons.org/licenses/by/4.0/
date: 2025-09-29
publication date: 2025-09-29
starting page: 123
ending page: 142
doi: 10.18690/jet.18.2.123–142.2025

THE IMPACT OF WIND POWER PLANT SIZE ON ECONOMIC VIABILITY AT THE OJSTRICA LOCATION
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description: Wind energy in Slovenia has not yet achieved a significant share in the energy resource mix, due primarily to the limited number of suitable locations and opposition from local communities. Nevertheless, interest in wind power plants is increasing, as they represent significant potential for utilising renewable energy sources. The paper analyses the economic viability of wind farm installation and electricity production at the proposed Ojstrica site in the Dravograd Municipality. Two scenarios were considered, involving wind turbines with capacities of 3.5 MW and 7 MW. Based on wind speed data, turbine power curves, and an electricity selling price of 75 EUR/MWh, the study calculated the maximum investment costs for each turbine type to ensure economic viability under the condition of a net present value (NPV) equal to zero. The results show that the maximum allowable investment is 5.99 million EUR for the 3.5 MW turbine and 15.60 million EUR for the 7 MW turbine.
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creator: Andraž Roger
creator: Matej Fike
rights: Copyright (c) 2025 Journal of Energy Technology https://creativecommons.org/licenses/by/4.0
date: 2025-06-11
publication date: 2025-06-11
starting page: 55
ending page: 64
doi: 10.18690/jet.18.1.55-64.2025

CHEMICAL ANALYSIS OF THERMALLY AGED CABLES IN NUCLEAR POWER PLANTS
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description: The paper presents findings on the implementation of various mechanical and chemical diagnostic procedures aimed at enhancing the monitoring of cable insulation conditions in Krško Nuclear Power Plant (NEK). This article introduces the advancement of four novel diagnostic testing methodologies for evaluating the mechanical and chemical properties of cable insulation: Indenter Modulus (IM), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric analysis (TGA) and X-Ray Fluorescence Spectral Analysis (XRF). Experiments were performed on diverse samples of widely used nuclear-qualified cable polymer materials, including Ethylene Propylene Rubber (EPR) and Crosslinked Polyethylene (XLPE), all with a Chlorosulphonated Polyethylene (CSPE) jacket. Samples from various vintages were subjected to additional temperature ageing in many stages, to establish field testing acceptability requirements and assess the remaining lifespan of the polymer insulation. Diagnostic tests were performed and some preliminary results are reported.
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creator: Marko Pirc
creator: Jurij Avsec
creator: Dijana Vrsaljko
rights: Copyright (c) 2025 Journal of Energy Technology https://creativecommons.org/licenses/by/4.0
date: 2025-06-11
publication date: 2025-06-11
starting page: 35
ending page: 54
doi: 10.18690/jet.18.1.%p.2025

ARTIFICIAL INTELLIGENCE -BASED EXERGY ANALYSIS OF AN ABSORPTION COOLING SYSTEM
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description: An artificial intelligence (AI)-based exergy analysis of an absorption cooling system (ACS), utilizing a lithium bromide–water refrigeration cycle, is presented in this paper. The ACS is characterised by the utilisation of the intermediatepressure (IP) extraction steam from the steam turbine for its operation. The exergy analysis of the ACS is detailed, based on AI modelling through a machine learning algorithm, which predicts and optimises the ACS performance. The machine learning algorithm is validated using real process data obtained through ACS measurements via the supervisory control and data acquisition (SCADA) system. The AI results show that the ACS generates 126.71 kW of cooling for district cooling and 279.57 kW of heat, which is used for heating demineralised water. During the analysis period, the ACS consumed an average of 152.86 kW of IP steam, and operated with an average exergy efficiency of 17.3%. The study suggests that the average exergy efficiency of the ACS could be improved by using lower-quality steam, or even hot water, for operation.
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creator: Dušan Strušnik
rights: Copyright (c) 2025 Journal of Energy Technology https://creativecommons.org/licenses/by/4.0
date: 2025-06-11
publication date: 2025-06-11
starting page: 21
ending page: 34
doi: 10.18690/jet.18.1.21-34.2025

ENERGY TRANSITION IN MUNICIPALITIES – A MODEL FOR SUSTAINABLE RENEWABLE ENERGY MANAGEMENT
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description: This study explores optimal strategies for utilizing the electricity generated from already installed PV systems at the local level, aiming to reduce electricity costs and increase revenues through the sale of surplus electricity. Two scenarios are analyzed: (1) individual consumption of the generated electricity within each building and the sale of surplus electricity at the time of production, and (2) collective energy management through a municipal energy enterprise, where surplus electricity is distributed among buildings, and the remaining surplus is sold on the free market. By analyzing existing research and case studies, the study seeks to determine which strategy is more efficient regarding energy efficiency and financial viability, and to propose a model for the collective management of electricity generated from PV systems at the municipal level.
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creator: Sara Aneva
creator: Dragan Minovski
creator: Vasilija Sarac
rights: Copyright (c) 2025 Journal of Energy Technology https://creativecommons.org/licenses/by/4.0
date: 2025-06-11
publication date: 2025-06-11
starting page: 5
ending page: 20
doi: 10.18690/jet.18.1.5–20.2025

FFA FW FLOW INFLUENCE AT NPP KRŠKO
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description: The Krško Nuclear Power Plant (NEK) operates based on a Pressurised Water Reactor (PWR), which utilises three loops for heat transfer: primary, secondary, and tertiary. Heat generation occurs in the primary loop; steam production takes place in the secondary loop; and waste heat is discharged in the tertiary loop. During outages, which occur every 18 months, the secondary systems are exposed to the atmosphere, increasing the risk of corrosion. To prevent this, in 2021, the plant used a chemical solution, Film Forming Amine (FFA), which formed a protective hydrophobic layer on the inner surfaces of the pipelines. In March 2021, during the first use of FFA, deviations were observed in the main feedwater (FW) flow measurements. This affected the reactor power calculations, leading to a 0.4–0.5 % reduction in plant output (approximately 4 MWe). The main feedwater flow is a critical parameter for secondary calorimetric calculations, and has the largest impact on error in the event of deviations. The power reduction was confirmed by comparing various process parameters, including changes in the primary loop temperature differences (ΔT), main steam flow (MS), and generator output vs. condenser vacuum. Since the measurement of the main feedwater flow contributes the most to the uncertainty of primary flow and reactor calorimetric calculations, NEK is focused on improving its accuracy. Developing a numerical model in the computer-based programming environment is proposed as part of further research. This model would enable independent calculations of the main feedwater flow, to reduce the impact of the FFA chemicals on the measurement readout and its associated calculations. The model will be based on thermodynamic equations and algorithms for determining the flow with lower uncertainty than the current system. Using this model, correction factors should be obtained to adjust the current venturi meter readings. Ultimately, this approach will ensure better plant management, r…
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creator: Robert Kelavić
creator: Jurij Avsec
rights: Copyright (c) 2024 Journal of Energy Technology
date: 2025-04-18
publication date: 2025-04-18
starting page: 46
ending page: 57
doi: 10.18690/jet.17.4.46-57.2024

A REVIEW OF ARTIFICIAL INTELLIGENCE IN NUCLEAR POWER PLANTS
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description: Nuclear power plants are recognised as complex systems, where maintenance is critical for ensuring safety and operational stability. Time-based preventive maintenance programmes are employed in most nuclear power plants, relying on periodic inspections to prevent equipment failures. However, this method is considered resource-intensive and not always efficient. An alternative is offered by Artificial Intelligence and condition-based maintenance, which allow early fault detection, reduce unnecessary maintenance tasks, and lower operational costs. The potential of Artificial Intelligence in nuclear power plants is vast, ranging from operational improvements to predictive maintenance. Techniques such as Supervised and Unsupervised Learning are highlighted as essential tools for fault detection, pattern recognition, and predictive modelling. In Supervised Learning, known input-output pairs are used to train models, while Unsupervised Learning is employed to identify hidden patterns in unlabelled data, which is particularly useful in the large, unstructured datasets found commonly in nuclear power plants. The challenges in integrating Artificial Intelligence into nuclear power plant operations shall be noted, including the lack of standardised procedures for selecting and applying algorithms. Despite these challenges, AI-driven tools, including Deep Learning and hybrid models, have shown promising results in fault detection and prediction in nuclear power plants. These advancements support the broader goal of improving safety and operational efficiency. In conclusion, although Artificial Intelligence has not yet been adopted fully across all nuclear power plants, it is seen as a promising advancement for the future of nuclear energy operations. Its implementation enhances fault detection, reduces operational risks, and ensures more reliable energy production.
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creator: Nejc Friškovec
creator: Dalibor Igrec
rights: Copyright (c) 2024 Journal of Energy Technology
date: 2025-04-18
publication date: 2025-04-18
starting page: 34
ending page: 45
doi: 10.18690/jet.17.4.34-45.2024

THEORETICAL AND EXPERIMENTAL INVESTIGATIONS OF A WATER HAMMER IN SAVA RIVER KAPLAN TURBINE HYDROPOWER PLANTS
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description: This paper deals with critical flow regimes that may induce an unacceptable water hammer in the Sava River Kaplan turbine hydropower plants. The rigid water hammer model is introduced first. The computational results are then compared with the results of measurements in two distinct hydropower plants (HPP): (i) The refurbished and upgraded Medvode HPP, and (ii) The newest Brežice HPP. Comparisons of the computed and measured results are examined for normal operating regimes. The water hammer in the two power plants is controlled by appropriate adjustment of the wicket gates and runner blades closing/opening manoeuvres. The agreement between the computed and measured results is reasonable.
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creator: Anton Bergant
creator: Jernej Mazij
creator: Jošt Pekolj
rights: Copyright (c) 2024 Journal of Energy Technology
date: 2025-04-17
publication date: 2025-04-17
starting page: 11
ending page: 20
doi: 10.18690/jet.17.4.11-20.2024

ASSESSING THE EFFECTS OF A HYDROPOWER PLANT BASIN ON FISH SPAWNING IN AN UPSTREAM RIVER TRIBUTARY
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description: This paper presents a combined modeling approach to evaluate the ecological effects on the habitat of an upstream tributary of a river with a series of hydropower plants. The influence is investigated of the last planned hydropower plant to be built, which has a large impact on the river ecosystem. The new hydropower plant basin will affect the tributary with hydropeaking in the upstream basin. A simulation was conducted of spawning conditions for two protected fish species. The analysis combined a hydro-morphological model with a fish module that considers the water depth and velocity necessary for fish reproduction. The different river discharge scenarios were simulated, incorporating the hydropeaking effects of the new hydropower plant basin on the upstream tributary. With the new hydropower plant, sustainable measures are planned to prevent the damaging negative impacts that could lead to the degradation of the river ecosystem and the destruction of the existing ecosystem at the river’s confluence. The results indicate that, after the hydropower plant begins operation, the habitat`s suitability will decrease, and the planned sustainable measures will not provide a fully satisfactory solution.
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creator: Gorazd Hren
creator: Andrej Predin
creator: Matej Fike
creator: Marko Pezdevšek
rights: Copyright (c) 2024 Journal of Energy Technology
date: 2025-04-18
publication date: 2025-04-18
starting page: 21
ending page: 33
doi: 10.18690/jet.17.4.21-33.2024

VERIFICATION AND VALIDATION OF STUDENT’S CFD TOOL ON THE VENTURI FLOW CASE
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description: The main goal of this study is to investigate the usability of the CFD software ANSYS Student 2023 R1 for students` scientific research. To carry out this investigation, a comparison was carried out of the analytically calculated flow rates through a standard venturi tube with the results obtained by simulations of the flow in the specified program. Given that it is a student, free version of the program, which comes with certain limitations, proving its usability by performing verification and validation on known geometry would be of great benefit. To ensure comparability, a 3D model of the venturi tube was created in accordance with the ISO 5167 Standard. The flow rate was calculated on that selected geometry of the venturi tube, using the well-known equations of fluid mechanics. The selected geometry of the venturi tube was discretised in the ANSYS Student 2023 program, respecting all CFD rules. Comparison of these two sets of results showed a match within 5%.
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creator: Tihomir Mihalić
creator: Ante Zaninović
creator: Srđan Medić
rights: Copyright (c) 2024 Journal of Energy Technology
date: 2025-04-16
publication date: 2025-04-16
starting page: 54
ending page: 61
doi: 10.18690/jet.17.3.54-61.2024

HEAVY METAL CONTENT IN VEGETABLE GARDEN SOILS IN RELATION TO THEIR NATURAL BACKGROUND
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description: Heavy metals (HM) are present in soil naturally [1], due to the weathering of the element-rich parent rock and by anthropogenic sources (industry, energy production, agriculture, traffic) [2– 4]. The agricultural sources of increased HM concentrations in soil are HM-containing fertilizers and pesticides. Agricultural soils are often considered polluted, and are therefore subject to soil contamination monitoring for food safety reasons. Allotments are particularly at risk from intensive gardening, the general overuse of fertilizers, soil conditioners, often seen as a means of improving soil quality, in some cases the overuse or misuse of pesticides and, in the past, the use of coal ash. In some cases, landowners are also receiving untested and potentially polluted soils from elsewhere. Therefore, the soils of the vegetable/allotment gardens are generally considered to be ‘highly anthropogenized'. According to Slovenian legislation [5], the HM concentration is considered elevated if the HM concentration in the soil is above the limit immission value (LIV), polluted if it is above the warning immission value (WIV) and critically polluted if it is above the critical immission value (CIV). The HM content was analyzed in the soils of 20 allotment gardens in the village of Legen (Municipality of Slovenj Gradec, Carinthia, Slovenia). The soil samples were dried, ground and sieved in the FEP laboratory, and analyzed ‘by Bureau Veritas Commodities (Canada) using Aqua Regia extraction to determine the 'pseudo-total content' for 37 elements (Ag, Al, As, Au, B, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, Hg, K, La, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Sc, Se, Sr, Te, Th, Ti, TI, U, V, W, and Zn), 10 of which (in the frames) are considered common HM soil contaminants. The comparison of the HM concentrations in the garden soils with the well-known rich natural geochemical background of the area showed that the values for all the compared metals, except Al, Fe, Ga, Sc, Th and Co, were higher …
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creator: Katja Črnec
creator: Ana Strmčnik
creator: Borut Vrščaj
rights: Copyright (c) 2024 Journal of Energy Technology
date: 2025-04-16
publication date: 2025-04-16
starting page: 62
ending page: 77
doi: 10.18690/jet.17.3.62-77.2024

HEAVY METAL CONTENT IN SOILS OF SELECTED HOP PLANTATIONS IN RELATION TO THEIR NATURAL BACKGROUND
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description: Heavy metals (HM) are present in soil naturally [1], due to weathering of the element-rich parent rock and anthropogenic sources (industry, agriculture, traffic, energy production) [2–4]. The agricultural source of the increased HM concentrations in soil are HM-containing fertilisers and pesticides. Agricultural soils are often considered polluted, and are, therefore, subject to soil contamination monitoring for food safety reasons. Permanent crops are particularly at risk, due to the intensive and traditional (over)use of pesticides and fertilisers. Hop plantations are a special type of economically important permanent crop in the Lower Savinja region. The product, the dried hop cones, is mainly exported. The cultivation of hops requires intensive soil tillage, fertilisation, and, above all, constant protection of the hop plant by usage of pesticides. According to Slovenian legislation [5], the HM concentration is considered elevated if the HM concentration in the soil is above the limit immission value (LIV), polluted if it is above the warning immission value (WIV), and critically polluted if it is above the critical immission value (CIV). The HM content was analysed in the soils of 10 hop plantations in the Lower Savinja region. The soil samples were dried, ground and sieved in the FVO laboratory, and analysed by Bureau Veritas Commodities (Canada) using Aqua Regia extraction to determine the 'pseudo-total content' for 37 elements (Ag, Al, As, Au, B, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, Hg, K, La, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Sc, Se, Sr, Te, Th, Ti, TI, U, V, W, and Zn), 10 of which (in the frames) are considered common HM soil contaminants. The HM concentrations in the soils of the hop plantations were within the natural background values [1] (below the LIV), with the exception of Cd, Cu and Zn, which were above the LIV in some cases. The Cd concentration was elevated in 90 % (it exceeded the LIV). The hop fields were not contaminated with Cd – as the conce…
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creator: Katja Črnec
creator: Lucija Božiljak
creator: Borut Vrščaj
rights: Copyright (c) 2024 Journal of Energy Technology
date: 2025-04-16
publication date: 2025-04-16
starting page: 39
ending page: 53
doi: 10.18690/jet.17.3.39-53.2024