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Abstract Background The aim of this paper is to reconsider the necessity for the green transition and the key preconditions for the implementation of a circular economy in Western Balkan countries. With the objective of the research in mind, the method of analysis and synthesis was applied to determine (1) regulatory and institutional prerequisites for the green transition; (2) the need for the Western Balkan countries to redefine the model of sustainable economic growth towards the green transition; (3) the development opportunities for recovery defined in the Green Agenda for the Western Balkans; and (4) the possibility of implementing the circular economy in the Western Balkans. Main text The main findings of the research indicate that: (1) the countries of the Western Balkan region, following the example of the EU, should define a national strategic approach to the green transition with an accompanying action plan and regulatory framework; (2) the biggest challenge of the green transition is the reform of the energy sector and the restructuring of the energy-intensive economy; (3) the countries have untapped potential in renewable energy sources and report the improvement of energy efficiency; (4) the circular economy can boost the green transition, because the countries of the region have a five-time lower value of resource productivity than the average of the EU, while the generation of waste (excluding major mineral wastes) per GDP unit is lower compared to the EU; (5) cross-sectoral governance should be more coordinated. Conclusions The green transition might be a development opportunity for the Western Balkans, which should enable sustainable economic growth as well as energy security and environmental protection. However, the implementation of the Green Agenda is not easy, because the region faces the problem of underdeveloped regulatory and institutional capacities that might provide not only the base for long-term planning but also financial resources for the efficient implementation of projects. In addition, it is essential to understand the principles of the Green Agenda and the interaction of all activities that should enable the achievement of defined goals.

Abstract This paper summarises studies undertaken towards the development of a laminated composite aluminium/hexadecane phase change material (PCM) drywall based on previous analytical work. The study also covered the selection and testing of various types of adhesive materials and identified Polyvinyl acetate (PVA) material as a suitable bonding material. For the purpose of comparison pure hexadecane and composite aluminium/hexadecane samples were developed and tested. The test results revealed faster thermal response by the aluminium/hexadecane sample regarding the rate of heat flux and also achieved about 10% and 15% heat transfer enhancements during the charging and discharging periods respectively. Its measured effective thermal conductivity also increased remarkably to 1.25 W/mK as compared with 0.15 W/mK for pure hexadecane. However there was about 5% less total cumulative thermal energy discharged at the end of the test which indicates that its effective thermal capacity was reduced by the presence of the aluminium particles. The study has shown that some of the scientific and technical barriers associated with the development of laminated composite PCM drywall systems can be overcome but further investigations of effects of adhesive materials are needed.

Abstract A unique large scale pilot plant of the CellFlux thermal energy storage concept is experimentally investigated. This storage concept consists of a regenerator type thermal energy storage volume, which is coupled to a finned tube heat exchanger by a circulating intermediate working fluid. The system investigated in this work operates at a temperature of 390 °C and uses air as intermediate working fluid which is conveyed by a centrifugal fan. The storage volume has a bed length of over ten meters and is of a novel design, where the air flows in horizontal direction. Since this approach could cause a flow maldistribution, a thorough analysis is of major interest for the accuracy of subsequent numerical simulations. The experiments reveal that the mass flow along the centerline can be up to 20% higher than the mean bulk flow. A significant maldistribution between top and bottom area, however, is not observed. As an alternative to the typically used rock filling, the storage volume is equipped with standard hollow bricks. These bricks are cost effective but do not have a well-defined shape. Thus, the predictability of the pressure drop by correlations found in the literature is unclear. It turns out that the measured pressure drop is evenly distributed in axial flow direction but generally higher than expected from the assumption of pure channel flow. Further experiments are conducted to validate the heat capacity of the bricks and to derive a correlation for the inner heat transfer between bricks and storage walls. Eventually, the aim of the experimental investigation is a general proof of concept as basis for the numerical investigation. Thus, all specifications of the plant and the storage material are provided. The plant is analyzed towards plausibility of heat losses, showing that heat losses can be predicted well within the given uncertainties.

In this study, the effect of recycling the non-condensable gases (NCG) in the catalytic pyrolysis of hybrid poplar using FCC catalyst was investigated. A 50mm bench scale fluidized bed reactor at 475°C with a weight hourly space velocity (WHSV) of 2h(-1) and a gas recycling capability was used for the studies. Model fluidizing gas mixtures of CO/N(2), CO(2)/N(2), CO/CO(2)/N(2) and H(2)/N(2) were used to determine their independent effects. Recycling of the NCG in the process was found to potentially increase the liquid yield and decrease char/coke yield. The model fluidizing gases increased the liquid yield and the CO(2)/N(2) fluidizing gas had the lowest char/coke yield. The (13)C-NMR analysis showed that recycling of NCG increases the aromatic fractions and decreases the methoxy, carboxylic and sugar fractions. Recycling of NCG increased the higher heating value and the pH of the bio-oil as well as decreased the viscosity and density.

Researchers have been driven to investigate sustainable alternatives to cement production, such as geopolymers, due to the impact of global warming and climate change resulting from greenhouse gas emissions. Currently, they are exploring different methods and waste materials to enhance the mechanical and physical properties of geopolymer and expand its application range. This review paper offers a thorough analysis of the utilization of various waste materials in geopolymer manufacturing and shows the creative contribution of this research to the development of environmentally friendly cement substitutes. The article covers the properties, durability, and practical applications of geopolymer composites made from various waste binders. It includes a microstructure and chemical analysis. The research findings indicate that geopolymers are an effective cementitious binder substitute for cement in various applications. Additionally, the ecological and carbon footprint analysis highlights the sustainability of geopolymers compared to cement.

Heavy-duty vehicles (HDVs) are responsible for a significant amount of CO2 emissions in the transport sector. The share of these vehicles is still increasing in the European Union (EU); nevertheless, rigorous CO2 emission reduction schemes will apply in the near future. Different measures to decrease CO2 emissions are being already discussed, e.g., the electrification of the powertrain. Additionally, the impact of autonomous driving on energy consumption is being investigated. The most common types are fuel cell vehicles (FCEVs) and battery-only vehicles (BEVs). It is still unclear which type of powertrain will prevail in the future. Therefore, we developed a method to compare different powertrain options based on different scenarios in terms of primary energy consumption, CO2 emissions, and fuel costs. We compared the results with the internal combustion engine vehicle (ICEV). The model includes a model for the climatization of the driver’s cabin, which we used to investigate the impact of autonomous driving on energy consumption. It became clear that certain powertrains offer advantages for certain applications and that sensitivities exist with regard to primary energy and CO2 emissions. Overall, it became clear that electrified powertrains could reduce the CO2 emissions and the primary energy consumption of HDVs. Moreover, autonomous vehicles can save energy in most cases.

In this paper, the notion of a cohesive and self-sufficient grid is proposed. Based on a cohesive and self-sufficient virtual microgrid, an active distribution network is optimally planned, and an optimal configuration of demand-side resources, distributed generations, and energy storage systems are generated. To cope with stochastic uncertainty from forecast error in wind speed and load, flexibility reserves are needed. In this paper, the supply relation between flexibility and uncertainty is quantified and integrated in an innovative index which is defined as cohesion. The optimization objectives are a minimized operational cost and system net-ability cohesion as well as self-sufficiency, which is defined as the abilities both to supply local load and to deal with potential uncertainty. After testing the optimal configuration in the PG&E 69 bus system, it is found that with a more cohesive VM partition, the self-sufficiency of VMs is also increased. Also, a case study on uncertainty-caused system imbalance is carried out to show how flexibility resources are utilized in real-time operational balance.

With the development of smart devices and information technology, it is possible for users to optimize their usage of electrical equipment through the home energy management system (HEMS). To solve the problems of daily optimal scheduling and emergency demand response (DR) in an uncertain environment, this paper provides an opportunity constraint programming model for the random variables contained in the constraint conditions. Considering the probability distribution of the random variables, a home energy management method for DR based on chance-constrained programming is proposed. Different confidence levels are set to reflect the influence mechanism of random variables on constraint conditions. An improved particle swarm optimization algorithm is used to solve the problem. Finally, the demand response characteristics in daily and emergency situations are analyzed by simulation examples, and the effectiveness of the method is verified.