RENEWABLE ENERGY AND CLIMATE CHANGE IN SERBIA AND THE REPUBLIC OF SRPSKA

This paper focuses on the use of renewable energy sources in Serbia and the Republic of Srpska and their impact on the environment and climate change. Renewable energy sources used in Serbia are hydropower, solar energy, wind energy, biomass, and biogas. Renewable energy sources used in the Republic of Srpska are hydropower, solar energy, biomass, and biogas. When using hydropower, the formed reservoirs often impact the microclimate of the environment in which they are located. Photothermal and photovoltaic solar radiation conversion installations are mostly stationary, do not emit harmful substances into the environment, and have no impact on climate change. The use of wind turbines has a certain influence on the flow of ambient air. When using biomass and biogas, combustion gases are released into the atmosphere, which has slightly negative impact on climate change. The paper concludes that the use of renewable energy sources in Serbia and the Republic of Srpska has a negligible negative impact on the environment and climate change.

TENDENCY OF GLOBAL CAPACITY DEVELOPMENT OF RENEWABLE ENERGY SOURCES IN THE WORLD IN THE LAST TEN YEARS

It is well-known that, in the past decades, the burning of fossil fuels was identified as the major cause of climate change. Climate change mitigation is becoming a central concern of global society. Limiting global warming to below 2 °C above the temperature of the pre-industrial period is the key to preserving global ecosystems and providing a secure basis for human activities, as well as reducing excessive environmental change. The ambitions increased at an accelerated pace with a dramatic expansion of net zero-emission targets. Increasing pressure from citizens and society has forced countries to intensify their climate plans, while the private sector has bought a record amount of renewable energy. An energy system based on fossil fuels must be replaced by renewable energy with low carbon emissions with improved energy efficiency. That applies to all consumers of fossil energy: cities, villages, building sectors, industry, transport, agriculture, and forestry. The paper explores and presents the strategy of energy development of renewable energy sources in the world. The application of new technologies that have led to developing renewable energy sources is presented in detail: wind energy, solar energy, small hydropower plants, biomass, and their increase in the total share of energy production, i.e., reduced fossil fuel use in energy production. Investments in new technologies used in renewable energy sources have led to increases in employment worldwide. Analysis of the trend of increased energy production from RES (Renewable Energy Sources) with investment plans, the employment rate for each energy source, and the development of renewable energy sources in the coming period are provided.

REDUCING CLIMATE CHANGE BY INSTALLING A NEW PHOTOVOLTAIC POWER PLANT IN BULGARIA

Three new roof-mounted 10 kWp grid-connected photovoltaic (PV) power plants have been constructed in the Technology Park at the Technical University of Gabrovo, Bulgaria, as part of a project "Competence Center – Intelligent Mechatronic, Eco, and Energy Saving Systems and Technologies". Three different PV modules types have been used: monocrystalline silicon (mono-Si), cadmium telluride (CdTe), and copper indium gallium selenide (CIGS). New three power plants, together with the existing amorphous silicon and poly-crystalline silicon photovoltaic power plants at the TU-Gabrovo enhanced simultaneous testing of five different photovoltaic materials. A small 500 Wp mono-Si photovoltaic thermal hybrid solar collectors (PVT) PV system has also been constructed. The power plants feature a monitoring system for the meteorological and electrical operating parameters, which measures, displays, and stores data on solar radiation, temperature, wind speed, currents, voltages, and electrical power of each power plant. PV plants components' technical characteristics are given in the paper. The schemes describing the basic wiring diagram, disposition of the three PV subsystems on the roof of the building at the technology center have also been presented. The initial comparative software data for monitoring of meteorological and electrical operating characteristics of the three different types of PV subsystems are shown as well. According to the specific ecological equivalent of energy resources and energy for the region of Bulgaria, the data are presented on the saved CO2 emissions from the avoided production and transmission of electricity owing to the operation of photovoltaic power plants.

SUSTAINABLE TRANSBOUNDARY HYDROPOWER SYSTEM ON DRINA RIVER AS SYNERGY OF WATER -FOOD-ENERGY-CLIMATE NEXUS

The Drina River has always been a source of drinking water and irrigation for food production, with all its tributaries and branching catchment area across the territories of Bosnia and Herzegovina, Montenegro and Serbia. It has connected peoples and cultures for centuries with its bridges. At the same time, with its great head, the Drina has always represented a significant hydropower potential. Throughout history, numerous watermills have been built on it. Currently, there are several constructed hydro-technical facilities on the Drina and in its catchment area. Among them, the most important are dams, with roads over them, associated hydroelectric power plants and belonging structures for flood control, water intakes for drinking water or irrigation. Due to multiple possible, almost always conflicting purposes, as well as several states, entities and other stakeholders, the management of Drina River water resources from the angle of the water-food-energy and climate nexus is an extremely complex problem. In addition to the impact on hydropower, agriculture, forestry, transport, irrigation and drainage, tourism and socio-cultural events, the construction of such strategic structures has also an impact on the climate of the Western Balkans. The issue of optimization within the nexus of the water-food-energy-climate requires holistic research to find synergistic solutions. These solutions are certainly a compromise. But inevitably, they must meet the criteria of sustainable development and the requirements of reducing global warming, according to the set conditions of the adopted European Green Plan for the Western Balkans. This paper proposes a methodology for finding optimal/compromise hydropower solutions, which synergistically include all parameters of influence. Holistic research of sustainable hydropower systems on the Drina River, from the angle of the water-food-energyclimate nexus, is presented. Particularly detailed analyses of the course of the river between the towns of Foča and Goražde, as well as the downstream part between Zvornik and mouth, known as the Lower Drina. In these sections, the most pronounced conflict is whether water will be used for drinking and/or food production and/or energy production and what impact possible solutions have on the climate of the region.

TOWARD LOW-ENERGY SPARK PLASMA SINTERING OF HOT-DEFORMED Nd-Fe-B MAGNETS

In this work, we present a newly developed, economically efficient method for processing rare-earth Nd-Fe-B magnets based on spark plasma sintering. It makes us possible to retain the technologically essential properties of the produced magnet by consuming about 30% of the energy as compared to the conventional SPS process. A magnet with anisotropic microstructure was fabricated from MQU F commercial ribbons by low energy consumption (0.37 MJ) during the deformation process and compared to the conventionally prepared hot-deformed magnet, which consumed 3-times more energy (1.2 MJ). Both magnets were post-annealed at 650 °C for 120 min in a vacuum. After the postannealing process, the low-energy processing (LEP) hot-deformed magnet showed a coercivity of 1327 kAm-1, and remanent magnetization of 1.27 T. In comparison, the highenergy processing (HEP) hot-deformed magnet had a coercivity of 1337 kAm-1 and a remanent magnetization of 1.31 T. Complete microstructural characterization and detailed statistical analyses revealed a better texture orientation for the HEP hot-deformed magnet processed by high energy consumption, which is the main reason for the difference in remanent magnetization between the two hot-deformed magnets. The results show that, although the LEP hot-deformed magnet was processed by three times lower energy consumption than in a typical hot-deformation process, the maximum energy product is only 8 % lower than the maximum energy product of a HEP hot-deformed magnet.

ENERGY PROSPECTS IN WESTERN BALKAN REGION ‒ MONTENEGRO CASE

To meet new energy demands and climate targets for 2030, the EU member states and West Balkans countries are requested to introduce the National Energy and Climate Plans (NECP) for the period from 2021 to 2030. That implies implementing clean, affordable and renewable energies to reach a climate-neutral economy by 2050. This will require moving towards the long-term goals set by Power agreements, which means to perform economic transformations to reach broader sustainable development goals. To achieve those goals national long-term strategies in Western Balkan countries jointly with EU strategies have to cover, at least, the following in the coming 30 years: total greenhouse emission reduction, even elimination, to extend feasible socio-economic effects of the decarburization measures, to enable links to other national long-term objectives, to make progress on a low greenhouse gas emission economy by encouraging the use of renewable energy sources to approach the European green plan. All those measures will lead the energy sector in the Western Balkans (WB6) to be organized to function with diversified sources of energy, secure fully functional integrated energy market, the free flow of energy, improve efficiency by reducing needs for energy imports; move to low carbon economy by promoting research and innovations in low carbon and clean energy technologies, which will all lead to extensive implantation of renewable energy sources and control of climate change in the region.

LEGAL REGULATIONS FOR THE USE OF RENEWABLE SOURCES OF ENERGY IN SERBIA AND THE REPUBLIC OF SRPSKA

The paper provides information on renewable energy sources (RES) and legislation related to the RES generated electricity in Serbia and the Republic of Srpska. In Serbia, hydropower, wind energy, solar energy, biomass and biogas are used for the RES generated electricity, whereas hydropower, solar energy, biomass and biogas are utilized in the Republic of Srpska. The paper gives an overview of the power of RES power plants and the percentage share of the thermal power plants and RES power plants in electricity production and the guaranteed (incentive) prices for RES generated electricity in Serbia and the Republic of Srpska. Furthermore, legal regulations related to the production of electricity from RES in Serbia and the Republic of Srpska are given. In the conclusion, it is pointed out that RES is increasingly used in Serbia and the Republic of Srpska for the production of electricity, that there are appropriate legal regulations and guarantees (incentive prices) for electricity generated by RES power plants.

ARTIFICIAL INTELLIGENCE AND NATURE-INSPIRED OPTIMIZATION ON INTEGRATIVE CAPACITY OF RENEWABLE ENERGY IN THE WESTERN BALKAN

Two artificial intelligence models for the integration of renewable energy sources are developed within this research to contribute to the European Green Plan realization. The review of renewable energy natural potential, on one hand, and installed capacity, on the other hand, in the Western Balkans and twenty-eight European countries is done within this research, as well as emissions. The analyses show that the European countries, sometimes even with lower natural potential in renewables, have installed much more renewable capacities than the Balkans countries with much higher natural potential. According to this, the first artificial intelligence model is developed based on multi-criteria linear regression analysis. This model relies on the correlation between the relevant regressors, i.e. relevant input variables for twenty-eight European countries and the same regressors for a particular Balkans country. Its goal is to find the maximum possible integrative renewable capacity in a Balkans’s country within the real socio-economic environment. The second artificial intelligence model is developed based on multi-criteria evolution genetic algorithms. Its goal is to find the maximum possible integrative renewable capacity within a real electric power system. Nature-inspired optimization is applied. From the framework of a given large number of generations, technical combinations of the degree of renewable energy sources integration, the best populations, i.e. combinations are selected. As nature selects from many generations and allows the best to survive and punishes the „weakˮ, in our case, „weak” combinations are those failing to meet the given conditions and limitations of the real electric power system. A new methodology is offered. Theoretical general formulas are given for both models. Developed models are tested on a numerical experiment of solar energy integration in the Serbia case study. Analyses of sensitivity prove that both models are applicable for all renewable energy sources and countries or regions.

THE USE OF SOLAR ENERGY IN CROATIA

The Europeans are still facing extraordinary challenges and uncertainties in their daily lives to the extent that all efforts will still focus on protecting citizens and overcoming the crisis. The COVID-19 poses a challenge to Europe on a historical scale. At the request of Heads of State or Governments, the European Commission has presented a comprehensive package combining the future Multiannual Financial Framework (MFF) and specific recovery efforts within the next generation EU (NGEU). The EU's Next Generation Fund (NGEU) represents the European Union's recovery package to support Member States affected by the COVID-19 pandemic. The fund was approved by the European Council on July 21, 2020, and is worth €750 billion. The NGEU fund covers the period 2021 – 2023 and will be linked to the regular EU budget (MFF) from 2021 to 2027. The comprehensive NGEU and VFO packages are projected to reach €1,824.3 billion. Most of the investment relates to the reforms and investments regarding green and digital transition. To achieve the European Green Plan and the next generation EU plan, policies related to clean energy supply in the economy, industry, general production and consumption, infrastructure, transport, agriculture, construction, etc., need to be reconsidered. In the light of all the above mentioned, and to achieve the green and digital transition, one of the significant areas in Croatia is the use of renewable energy sources, especially solar energy, which will be discussed in more detail in this paper.

THE EFFECT OF METHYL METHACRYLATE ON THE PROPERTIES OF SYNTHESIZED ACRYLATE EMULSIONS

The effect of methyl methacrylate (MMA) addition on the properties of synthesized acrylate emulsions based on butyl acrylate (BA) and 2-ethylhexyl acrylate (EHA) was investigated. The samples were synthesized by addition of MMA in copolymer structure, ranging from 10 to 50 wt% of the total mass of BA and EHA. Fourier transformation infrared (FTIR) spectroscopy was used to analyze the molecular structure of synthesized acrylate emulsions and the results confirmed that a quantitative polymerization reaction occurred. The analysis of thermal properties showed that the addition of methyl methacrylate increases the glass transition temperature of the acrylate films obtained by drying the synthesized emulsions. The tensile strength and elongation at break increased proportionally with the increase of the content of MMA in the synthesized samples. Since the obtained acrylate materials can be used to improve the water impermeability of paper and other materials, the obtained emulsion was applied in a thin layer on a sheet of paper and the resistance of the paper to water and oil was investigated. The results showed that all emulsions were impermeable both to water and oil.