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Previous energy strategies for Serbia had various goals in terms of renewable energy sources with the quantification of type of power plants by type, but the national energy planning did not go to the level of determining specific locations for power plants, namely photovoltaic. This caused difficulties for the responsible ministry and public companies to decide which power plants will be connected and which not. Additionally, due to a drop in investment costs, connection requests dramatically increased. In the beginning of 2023 applications for the construction of power plants totaling 14 GW in capacity were under review at public transmission company which further caused delays and stagnation in the construction of these power plants. At the same time, electricity prices for households and industries had increased by 18 and 27% respectively. During the year 2022, only 6 MW of new power plants were realized even with granting the monthly net-metering to the industry and households, which is far below the possible and realistic dynamic of Serbia's energy transition implementation. It was announced in early 2023, with the changes in legislative towards implementing the auctions principles, that the first permits will be issued for the construction of large photovoltaic power plants on land to progress towards meeting an overall capacity goal of 2-3 GW. To guide in selecting sites that will help meet this goal, we mapped 100 suitable photovoltaic power plant locations prioritized not only by energy yield, but also to prevent possible conflicts with other activities (i.e., agriculture, protected areas and cultural heritage). The mapping was carried out using available energy yield data, and geographically specific data of importance for the construction of larger photovoltaic power plants up to 10 MW in size. The 100 locations were selected as best among a much larger number of possible ones. These 100 sites occupy less than 25 km2 of land and would be enough to cover about 5% of household consumption in Serbia. Dosadašnje energetske strategije Srbije su imale različite ciljeve u pogledu obnovljivih izvora energije sa kvantifikacijom pojedinih tipova elektrana, ali nacionalno energetsko planiranje nije išlo do nivoa određivanja konkretnih lokacija, posebno za fotonaponske elektrane. Ovo je izazvalo poteškoće nadležnom ministarstvu i javnim preduzećima jer je pad investicionih troškova ohrabrio veliki broj aplikanata za dozvole za izgradnju elektrana na pogodnim lokacijama od ukupno 14 GW, što je dodatno izazvalo zastoje i stagnaciju u izgradnji ovih elektroenergetskih objekata na zemlji. U isto vreme došlo je do poskupljenja troškova snabdevanja električnom energijom za domaćinstva 18% i 27% za privredu tokom 2022. a iste godine kroz mehanizam neto-merenja realizovano je samo oko 6 MW novih elektrana što je kao rezultat daleko ispod mogućeg, realnog nivoa i neophodne brzine sprovođenja energetske tranzicije Srbije. Početkom 2023. godine, uz izmene zakona u pravcu sprovođenja aukcija, najavljeno je da će biti izdate prve dozvole za izgradnju velikih fotonaponskih elektrana na zemljištu i ulaganja u projekte veličine nekoliko (2-3) GW. Stoga je potrebno izvršiti mapiranje i odabiranje 100 lokacija fotonaponskih elektrana kako bi se bolje razumele pogodne lokacije ne samo sa stanovišta prinosa energije, već i kako bi se predupredili eventualni konflikti sa drugim aktivnostima (poljoprivreda, zaštićena područja, kulturno nasleđe). Mapiranje je sprovedeno korišćenjem raspoloživih podataka o energetskim prinosu, kao i geografski specifičnih podataka od značaja za izgradnju većih fotonaponskih elektrana do 10 MW. Odabrano je 100 najboljih lokacija među mnogo većim brojem mogućih. Količina proizvedene energije na površini koja zauzima manje od 25 km2 bila bi dovoljna da pokrije oko 5% potrošnje domaćinstava u Srbiji.

The paper includes a general discussion of reasons for the application of heat storage and phase change material as storage medium. A part of experimental results obtained by measuring during the process of paraffin phase change was presented. It was observed that in order to obtain lower temperature stratification during the heating process it is necessary to increase the number of volume heat sources in the thermal storage. .

Brewer’s spent grain is the major by-product in beer production. It is produced in large quantities (20 kg per 100 liters of produced beer) throughout the year at a low cost or no cost, and due to its high protein and carbohydrates content it can be used as a raw material in biotechnology. Biotechnological processes based on renewable agro-industrial by-products have ecological (zero CO2 emission, eco-friendly by-products) and economical (cheap raw materials and reduction of storage costs) advantages. The use of brewer’s spent grain is still limited, being basically used as animal feed. Researchers are trying to improve the application of brewer’s spent grain by finding alternative uses apart from the current general use as an animal feed. Its possible applications are in human nutrition, as a raw material in biotechnology, energy production, charcoal production, paper manufacture, as a brick component, and adsorbent. In biotechnology brewer’s spent grain could be used as a substrate for cultivation of microorganisms and enzyme production, additive of yeast carrier in beer fermentation, raw material in production of lactic acid, bioethanol, biogas, phenolic acids, xylitol, and pullulan. Some possible applications for brewer’s spent grain are described in this article including pre-treatment conditions (different procedures for polysaccharides, hemicelluloses, and cellulose hydrolysis), working microorganisms, fermentation parameters and obtained yields. The chemical composition of brewer’s spent grain varies according to barley variety, harvesting time, malting and mashing conditions, and a quality and type of unmalted raw material used in beer production. Brewer’s spent grain is lignocellulosic material rich in protein and fibre, which account for approximately 20 and 70% of its composition, respectively.

The rapid depletion of the world petroleum supply and the increasing problem of greenhouse gas effects have strenghtened the worldwide interest in alternative, nonpetroleum sources of energy. Bioethanol accounts for the majority of biofuel use worldwide, either as a fuel or a gasoline enhancer. Utilization of bioethanol can significantly reduce petroleum use and exhaust greenhouse gas emission. The production of this fuel is increasing over the years, and has reached the level of 73.9 billion liters during the year 2009. Even though ethanol production for decades mainly depended on energy crops containing starch and sugar (corn, sugar cane etc.), new technologies for converting lignocellulosic biomass into ethanol are under development today. The use of lignocellulosic biomass, such as agricultural residues, forest and municipial waste, for the production of biofuels will be unavoidable if liquid fossil fuels are to be replaced by renewable and sustainable alternatives. For biological conversion of lignocellulosic biomass, pretreatment plays a central role affecting all unit operations in the process and is also an important cost deterrent to the comercial viability of the process. The key obstacles are: pretreatment selection and optimization; decreasing the cost of the enzymatic hydrolysis; maximizing the conversion of sugars (including pentoses) to ethanol; process scale-up and integration to minimize energy and water demand; characterization and evaluation of the lignin co-product; and lastly, the use of the representative and reliable data for cost estimation, and the determination of environmental and socio-economic impacts. Currently, not all pretreatments are capable of producing biomass that can be converted to sugars in high enough yield and concentration, while being economically viable. For the three main types of feedstocks, the developement of effective continuous fermentation technologies with near to 100% yields and elevated volumetric productivities is one of the main research subjects in the ethanol industry. The application of new, engineered enzyme systems for cellulose hydrolysis, the construction of inhibitor tolerant pentose fermenting strains, combined with optimized process integration promise significant improvements.

The paper shows results of researching the market of glued laminated timber as the most frequent innovative timber product in constructing timber framed residential facilities in Europe and Serbia. The research included the development of production, consumption and trade flows for the most significant countries in the European Union and Serbia. Additionally, the paper gives characteristics of this innovative timber product regarding dimensions, allowed deviations of dimensions defined in adequate European standard, wood species it is made of and fire resistance. The last part of the paper shows results of econometric modeling of the impact of building timber-framed houses on the consumption of glued laminated timber in Austria as one of the countries belonging to the group of the largest consumers of this innovative timber product in Europe. Taking into consideration that the substitution of classic building materials, primarily concrete, steel and aluminum, with glued laminated timber in residential construction contributes to the reduction of carbon-dioxide emission and climate change mitigation, research results of the effects of such substitution are presented in the last chapter in this paper. [Projekat Ministarstva nauke Republike Srbije, br. III43007: Istraživanje klimatskih promena na životnu sredinu: praćenje uticaja, adaptacija i ublažavanje]

Energy security and independence, increase and fluctuation of the oil price, fossil fuel resources depletion and global climate change are some of the greatest challanges facing societies today and in incoming decades. Sustainable economic and industrial growth of every country and the world in general requires safe and renewable resources of energy. It has been expected that re-arrangement of economies towards biofuels would mitigate at least partially problems arised from fossil fuel consumption and create more sustainable development. Of the renewable energy sources, bioenergy draws major and particular development endeavors, primarily due to the extensive availability of biomass, already-existence of biomass production technologies and infrastructure, and biomass being the sole feedstock for liquid fuels. The evolution of biofuels is classified into four generations (from 1st to 4th) in accordance to the feedstock origin; if the technologies of feedstock processing are taken into account, than there are two classes of biofuels - conventional and advanced. The conventional biofuels, also known as the 1st generation biofuels, are those produced currently in large quantities using well known, commercially-practiced technologies. The major feedstocks for these biofuels are cereals or oleaginous plants, used also in the food or feed production. Thus, viability of the 1st generation biofuels is questionable due to the conflict with food supply and high feedstocks’ cost. This limitation favoured the search for non-edible biomass for the production of the advanced biofuels. In a general and comparative way, this paper discusses about various definitions of biomass, classification of biofuels, and brief overview of the biomass conversion routes to liquid biofuels depending on the main constituents of the biomass. Liquid biofuels covered by this paper are those compatible with existing infrastructure for gasoline and diesel and ready to be used in mixture with them as „drop-in“ fuels: bioethanol, celullosic ethanol, biodiesel, renewable diesel and BtL diesel; their major advantages and drawbacks are compared. [Projekat Ministarstva nauke Republike Srbije, br. 172050]

In recent years, more attention has been paid to the use of third generation feedstocs for the production of biodiesel. One of the most promising sources of oil for biodiesel production are microalgae. They are unicellular or colonial photosynthetic organisms, with permanently increasing industrial application in the production of not only chemicals and nutritional supplements but also biodiesel. Biodiesel productivity per hectare of cultivation area can be up to 100 times higher for microalgae than for oil crops. Also, microalgae can grow in a variety of environments that are often unsuitable for agricultural purposes. Microalgae oil content varies in different species and can reach up to 77% of dry biomass, while the oil productivity by the phototrophic cultivation of microalgae is up to 122 mg/l/d. Variations of the growth conditions and the implementation of the genetic engineering can induce the changes in the composition and productivity of microalgal oil. Biodiesel from microalgae can be produced in two ways: by transesterification of oil extracted from biomass or by direct transesterification of algal biomass (so called in situ transesterification). This paper reviews the curent status of microalgae used for the production of biodiesel including their isolation, cultivation, harvesting and conversion to biodiesel. Because of high oil productivity, microalgae will play a significant role in future biodiesel production. The advantages of using microalgae as a source for biofuel production are increased efficiency and reduced cost of production. Also, microalgae do not require a lot of space for growing and do not have a negative impact on the global food and water supplies. Disadvantages of using microalgae are more difficult separation of biomass and the need for further research to develop standardized methods for microalgae cultivation and biodiesel production. Currently, microalgae are not yet sustainable option for the commercial production of biodiesel. First of all, the price of biodiesel from microalgae is still higher than the price of diesel due to high production costs. [Projekat Ministarstva nauke Republike Srbije, br. III 45001]

The aim of this study was to evaluate the chemical composition of the back fat tissue of mangalitsa pig and meaty pig breeds and their crosses, and the pigs that were fed with feed that was enriched or unenriched with oil, from the aspect of the production of biodiesel, where the starting material for the fuel would be the fat tissue of pigs. By examining the impact of breed and oil content in feed, it was found that chemical parameters (fat, water, protein, saturated and unsaturated fatty acids) show statistically significant variation under the influence of these factors. The highest fat content (89.39%), which is essential for conversion of fat into biodiesel, was found in back adipose tissue of mangalitsa breed, while the lowest fat content (86.10%) was found in the back fat tissue of meaty breeds and their crosses. Favorable ratio of saturated to unsaturated fatty acids (37.92% : 62.07%), on which some physical properties of the fuel depend, was found in the back fat tissue of pigs that were fed with feed enriched with oil, and the largest proportion of saturated fatty acids, i.e. the most unfavorable fatty acid composition (40.90% : 59.09%) was found in the back fat tissues of pigs that were fed with feed unenriched with oil. The lowest content of saturated fatty acids and water (7.44%), as the key factors that determine the cetane number of the fuel and the fuel production process, indicates that the most suitable raw material for the production of biodiesel is the fat tissue of pigs that were fed with food that contained a certain amount of oil.

In Serbia, the ash from power plants has long been labelled as hazardous waste. With the adoption of the appropriate legislation this ash became secondary raw material with the potential usage. In this paper an analysis of the fly and bottom ash composition, which are disposed of in the power plant “Nikola Tesla A” landfill, is presented. Thirty samples, divided into three sets, were analyzed for trace elements As, Ba, Be, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Ti, V and Zn. The first and second set of samples were taken at the depth of 0.0-0.6 m, from cassette III, at the place of waste discharge (set I) and in the centre of the cassette (set II).The third set of samples was taken from the same cassette spot but at the different depth. The estimated variations in quality within individual sets, as well as the comparison between sets I and II, were done. The repeatability of results by the depth of cassette (set III) was also analyzed. The mixture consisting of 79.4% limestone, 17% clay, 0.5% sand, 0.55% iron ore, 0.55% from steel mill waste and 2% ash from the thermal power plant "Nikola Tesla A" was adopted as the reputable mixture for cement making. For concrete making, the same cement mixture was used but with 2.1% of the same ash material added. The results showed possibility of further fly and bottom ash use as the cement and concrete material.

The paper analyses how a fast advance in technology can ease both discovering and exploitation of alternative energy resources available in space, and at the same time can open new long-term conflicts over supremacy in commercialisation of space resources. The author considers viability of actual and planned projects of members of the prestigious club of “space nations”-the United States, Japan, Russia and the European Union. Global energy demand growth stimulates technologically advanced countries to explore more intensively the technical feasibility and economic viability of renewable energy sources in space. Along with advancement in space technology in the foreseeable future, astro-resources could be used as an alternative or at least a supplement to the existing resource base. The author argues that the increasing space technology ambitions of China, India and, to some extent Iran, create a potential knot of new geopolitical and geoeconomical international conflicts. In conclusion, the author emphasizes that the extraterrestrial sources for the Earth's energy needs will not only stay an important alternative basis for energy security in decades to come, but space itself is likely to become rather a new battlefield of the great powersʼ strategic interests than a part of the common heritage of mankind, equally accessible to all nations.