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1.
A multi-level approach to circular economy progress : linking national targets with corporate implementation
Jan Drofenik, Tine Seljak, Zorka Novak-Pintarič, 2025, izvirni znanstveni članek

Opis: An integrated top-down methodology for assessing and promoting progress towards a circular economy at macro (national) and micro (company) levels is presented. It is based on the MICRON (MIcroCirculaR ecOnomy iNdex) framework developed by Baratsas et al. (2022) for companies. In this paper, it has been extended to enable a consistent assessment for companies and countries. The methodology facilitates the analysis of key categories: energy, emissions, water, materials, and waste. A quantitative analysis of circularity, including a sensitivity analysis, is conducted at the macro level, identifying critical areas and the most influential factors for the circular economy. Based on this analysis, existing national strategies are evaluated, and implementation plans with specific measures are developed. This is followed by micro-level implementation, which involves techno-economic assessment of circular projects. Using this methodology, coordinated improvements in circularity are achieved at all levels. The methodology was tested in Slovenia, where the national circularity index revealed stable performance over five years, averaging slightly above 50 points out of 100. Analysis identified significant improvement potential in areas such as energy and emissions, aligning with the country's focus on decarbonization and energy efficiency in its climate strategies. At the company level, circularity assessments highlighted critical challenges in renewable energy use and overall energy efficiency. The proposed measures showed potential for significantly improving circularity and reducing emissions, while the results provided valuable insights into the economic feasibility of these transitions.
Ključne besede: circular economy, integrated assessment framework, micro level, energy transition, renewable energy
Objavljeno v DKUM: 10.02.2025; Ogledov: 0; Prenosov: 1
.pdf Celotno besedilo (9,03 MB)

2.
Advancing energy recovery: evaluating torrefaction temperature effects on food waste properties from fruit and vegetable processing
Andreja Škorjanc, Sven Gruber, Klemen Rola, Darko Goričanec, Danijela Urbancl, 2025, izvirni znanstveni članek

Opis: Most organic waste from food production is still not used for energy production. From the perspective of energy production, one option is to valorise the properties of organic waste. The fruit juice industry is growing rapidly and generates large amounts of waste. One of the main wastes in food and fruit juice processing is peach pits and apple peels. The aim of this study was to analyse the influence of torrefaction temperature on the properties of food waste, namely apple peels, peach pits and pea shells, in order to improve their energy value and determine their potential for further use and valorisation as a renewable energy source. The aim was to analyse the influence of different torrefaction temperatures on the heating value (HHV), mass yield (MY) and energy yield (EY) in order to better understand the behavior of the thermal properties of individual selected samples. The torrefaction process was carried out at temperatures of 250 ◦C, 350 ◦C and 450 ◦C. The obtained biomass was compared with dried biomass. For apple peels, HHV after torrefaction was (28 kJ/kg), MY decreased by (66–34%), while EY fell by (97–83%). Peach pits, despite a higher HHV after torrefaction (18 kJ/kg), achieved low MY (38–89%) and EY (59–99%), which reduces their efficiency in biochar production. Pea peels had EY (82–97%) and a lower HHV after torrefaction (11 kJ/kg), but their high ash content limits their wider use. The results confirm that, with increasing temperature, MY and EY for all selected biomasses decrease, which is a consequence of the degradation of hemicellulose and cellulose and the loss of volatile compounds. In most cases, increasing the torrefaction temperature improved the resistance to moisture adsorption, as this is related to the thermal process that causes structural changes. The results showed that the torrefaction process improved the hydrophobic properties of the biomass samples. Temperature was seen to have a great impact on mass energy efficiency. Apple peels generally had the highest mass and energy yield.
Ključne besede: torrefaction, food waste, energy from waste, higher heating value, energy potential
Objavljeno v DKUM: 07.02.2025; Ogledov: 0; Prenosov: 5
.pdf Celotno besedilo (3,55 MB)

3.
International energy security risk index - analysis of the methodological settings
Iztok Podbregar, Goran Šimić, Mirjana Radovanović, Sanja Filipović, Polona Šprajc, 2020, izvirni znanstveni članek

Opis: The main objective of this paper is to analyze model settings of the International Energy Security Risk Index developed by the U.S. Chamber of Commerce. The study was performed using stepwise regression, principal component analysis, and Promax oblique rotation. The conclusion of the regression analysis shows that Crude Oil Price and Global Coal Reserves are sufficient to explain 90% of the variance of the Index. However, if a model that explains 100% of the variance of the Index is chosen and other variables are added, Global Coal Reserves loses importance due to the presence of other parameters in which it is contained. Regardless of the chosen model of analysis, it is evident that there is room for revising the Index and removing variables that do not contribute to its precision. The research showed that the main disadvantage of the variables that make up the Index rests with the fact that the variables are of different degrees of generality, that is, one parameter is contained in other parameters (unclear which other). The research covers data for 25 countries over a 26-year period, with the first year of the research being 1980 and the last 2016 (the latest available report).
Ključne besede: international energy security risk index, analysis, stepwise regression, principal component analysis, Promax oblique rotation
Objavljeno v DKUM: 04.02.2025; Ogledov: 0; Prenosov: 4
.pdf Celotno besedilo (1,04 MB)
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4.
The international energy security risk index in sustainable energy and economy transition decision making - a reliability analysis
Iztok Podbregar, Goran Šimić, Mirjana Radovanović, Sanja Filipović, Damjan Maletič, Polona Šprajc, 2020, izvirni znanstveni članek

Opis: The world economy and society are in a complex process of transition characterized by a high degree of uncertainty. Therefore, further development and management of the transition will largely depend on the quality of the decisions made and, accordingly, on the decision-making process itself. The main goal of this study is to analyze the reliability of International Energy Security Risk Index as a tool to support the process of energy and economy transition decision making, as closely related and highly interdependent phenomena. The index is composed of 29 aggregated variables (grouped into eight categories), and the research is conducted on a research sample of 25 countries over a period of 36 years. The reliability assessment is performed by using Multiple Regression Analysis. Multicollinearity test, plus Multicollinearity test with Variance Inflation Factors, is used for methodological verification. The test results indicate a high degree of unreliability of the Index, as is concluded based on the observed errors in its methodological settings. These errors primarily relate to a high degree of multicollinearity in all 29 variables, whereby independent variables lose their independence and thus jeopardize reliability of the total Index. Out of the eight groups of variables, the fuel imports group is the only one that does not show big methodological errors. The paper presents a recommendation for the improvement of the observed Index (review of the role of individual variables found to be particularly methodologically indicative), as well as a recommendation for different distribution of weighting coefficients.
Ključne besede: energy and economy transition, decision making, international energy security risk index, multiple regression analysis, multicollinearity test, multicollinearity test with variance inflation factors
Objavljeno v DKUM: 04.02.2025; Ogledov: 0; Prenosov: 2
.pdf Celotno besedilo (447,82 KB)
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Development of Methodology for Estimation of Energy-Efficient Building Renovation Using Application of MINLP-Optimized Timber–Glass Upgrade Modules
Maja Lešnik Nedelko, Stojan Kravanja, Miroslav Premrov, Vesna Žegarac Leskovar, 2025, izvirni znanstveni članek

Opis: Vertical addition to already-existing structures is an approach to energy-efficient building renovation. It presents an opportunity for the densification of built-up areas and the construction of new usable spaces. While many studies have dealt with the subject of renovating buildings with a focus on energy efficiency, far fewer studies have specifically examined the potential of vertically extending existing buildings, an approach which could be introduced in new sustainable building policies. The objective of this study is to redevelop optimal timber–glass upgrade modules, considering the ideal proportions of glazing for all cardinal directions, by using discrete Mixed-Integer Non-Linear Programming optimization. The novelty of the suggested method resides in the synchronous optimization of the upgrade modules’ daylighting and energy-efficiency performance, resulting in the creation of optimization methods that can determine the optimal glazing proportions for all cardinal directions and incorporate rational design and window measurement. The impact of the developed Mixed-Integer Non-Linear Programming-optimized upgrade modules is compared to previously designed optimized upgrade modules. Finally, a methodology for estimating the energy efficiency of building renovations incorporating vertical additions using the timber–glass upgrade modules was developed, supporting the quick assessment of the reduction in hybrid buildings’ energy consumption for heating and cooling according to boundary conditions, presuming that they undergo the suggested renovations. The findings are applicable (not exclusively) to Slovenia’s residential building stock, which makes up around 20% of the country’s current housing stock and was mainly constructed between 1946 and 1970. This offers a substantial opportunity to improve the overall sustainability and energy efficiency of the country’s housing stock. The proposed approach offers a holistic solution to drive sustainable development in the built environment by incorporating all three pillars of sustainability (environmental, social, and economic).
Ključne besede: energy efficient building renovation, energy efficiency, building vertical addition, timber–glass upgrade modules, mixed-integer non-linear programming, MINLP, optimization, visual comfort, energy sustainability
Objavljeno v DKUM: 16.01.2025; Ogledov: 0; Prenosov: 3
.pdf Celotno besedilo (9,27 MB)
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Novel GPU-accelerated high-resolution solar potential estimation in urban areas by using a modified diffuse irradiance model
Niko Lukač, Domen Mongus, Borut Žalik, Gorazd Štumberger, Marko Bizjak, 2024, izvirni znanstveni članek

Opis: In the past years various methods have been developed to estimate high-resolution solar potential in urban areas, by simulating solar irradiance over surface models that originate from remote sensing data. In general, this requires discretisation of solar irradiance models that estimate direct, reflective, and diffuse irradiances. The latter is most accurately estimated by an anisotropic model, where the hemispherical sky dome from arbitrary surface’s viewpoint consists of the horizon, the circumsolar and sky regions. Such model can be modified to incorporate the effects of shadowing from obstruction with a view factor for each sky region. However, state-of-the-art using such models for estimating solar potential in urban areas, only considers the sky view factor, and not circumsolar view factor, due to high computational load. In this paper, a novel parallelisation of solar potential estimation is proposed by using General Purpose computing on Graphics Processing Units (GPGPU). Modified anisotropic Perez model is used by considering diffuse shadowing with all three sky view factors. Moreover, we provide validation based on sensitivity analysis of the method’s accuracy with independent meteorological measurements, by changing circumsolar sky region’s half-angle and resolution of the hemispherical sky dome. Finally, the presented method using GPPGU was compared to multithreaded Central Processing Unit (CPU) approach, where on average a 70x computational speedup was achieved. Finally, the proposed method was applied over a urban area, obtained from Light Detection And Ranging (LiDAR) data, where the computation of solar potential was performed in a reasonable time.
Ključne besede: solar energy, solar potential, anisotropic diffuse irradiance, LiDAR, GPGPU
Objavljeno v DKUM: 17.12.2024; Ogledov: 0; Prenosov: 3
.pdf Celotno besedilo (8,06 MB)

10.
The impact of financial support mechanisms and geopolitical factors on the profitability of investments in solar power plants in Slovenia
Iztok Gornjak, Filip Kokalj, Niko Samec, 2024, izvirni znanstveni članek

Opis: This article examines the impact of financial support mechanisms and geopolitical factors on the profitability of investments in solar power plants within Slovenia. The European Union’s energy policy prioritizes increases in renewable energy sources, aiming to reduce dependency on unstable and volatile fossil fuel markets. Solar power plants play a vital role in this transition. The energy policy framework also includes mechanisms and support systems to operate such facilities. This article analyzes electricity price trends over the past decade and addresses which support type—guaranteed purchase or operational support—has proven more profitable for investments in solar power plants up to 50 kW in Slovenia, considering economic and geopolitical influences on the electricity market. Although the global energy market has been affected by various significant events in recent years, it was found that the COVID-19 pandemic had minimal impact on the electricity market. In contrast, the onset of the conflict in Ukraine has contributed to rising electricity prices and has influenced the support dynamics essential for the development and sustainability of renewable energy systems. Analyses from the past decade indicate a higher return on investment in solar power plants when operational support mechanisms are chosen over guaranteed purchase support.
Ključne besede: renewable energy sources, solar power plants, support system, investment profitability factors, electricity price
Objavljeno v DKUM: 16.12.2024; Ogledov: 0; Prenosov: 8
.pdf Celotno besedilo (4,96 MB)
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