59 resultados para Materials degradation


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In the framework of the biorefinery concept researchers aspire to optimize the utilization of plant materials, such as agricultural wastes and wood. For most of the known processes, the first steps in the valorisation of biomass are the extraction and purification of the individual components. The obtained raw products by means of a controlled separation can consecutively be modified to result in biofuels or biogas for energy production, but also in value-added products such as additives and important building blocks for the chemical and material industries. Considerable efforts are undertaken in order to substitute the use of oil-based starting materials or at least minimize their processing for the production of everyday goods. Wood is one of the raw materials, which have gained large attention in the last decades and its composition has been studied in detail. Nowadays, the extraction of water-soluble hemicelluloses from wood is well known and so for example xylan can be obtained from hardwoods and O-acetyl galactoglucomannans (GGMs) from softwoods. The aim of this work was to develop water-soluble amphiphilic materials of GGM and to assess their potential use as additives. Furthermore, GGM was also applied as a crosslinker in the synthesis of functional hydrogels for the removal of toxic metals and metalloid ions from aqueous solutions. The distinguished products were obtained by several chemical approaches and analysed by nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR), size exclusion chromatography (SEC), thermal gravimetric analysis (TGA), scanning electron microscope SEM, among others. Bio-based surfactants were produced by applying GGM and different fatty acids as starting materials. On one hand, GGM-grafted-fatty acids were prepared by esterification and on the other hand, well-defined GGM-block-fatty acid derivatives were obtained by linking amino-functional fatty acids to the reducing end of GGM. The reaction conditions for the syntheses were optimized and the resultant amphiphilic GGM derivatives were evaluated concerning their ability to reduce the surface tension of water as surfactants. Furthermore, the block-structured derivatives were tested in respect to their applicability as additives for the surface modification of cellulosic materials. Besides the GGM surfactants with a bio-based hydrophilic and a bio-based hydrophobic part, also GGM block-structured derivatives with a synthetic hydrophobic tail, consisting of a polydimethylsiloxane chain, were prepared and assessed for the hydrophobization of surface of nanofibrillated cellulose films. In order to generate GGM block-structured derivatives containing a synthetic tail with distinguished physical and chemical properties, as well as a tailored chain length, a controlled polymerization method was used. Therefore, firstly an initiator group was introduced at the reducing end of the GGM and consecutively single electron transfer-living radical polymerization (SET-LRP) was performed by applying three different monomers in individual reactions. For the accomplishment of the synthesis and the analysis of the products, challenges related to the solubility of the reactants had to be overcome. Overall, a synthesis route for the production of GGM block-copolymers bearing different synthetic polymer chains was developed and several derivatives were obtained. Moreover, GGM with different molar masses were, after modification, used as a crosslinker in the synthesis of functional hydrogels. Hereby, a cationic monomer was used during the free radical polymerization and the resultant hydrogels were successfully tested for the removal of chromium and arsenic ions from aqueous solutions. The hydrogel synthesis was tailored and materials with distinguished physical properties, such as the swelling rate, were obtained after purification. The results generated in this work underline the potential of bio-based products and the urge to continue carrying out research in order to be able to use more green chemicals for the manufacturing of biorenewable and biodegradable daily products.

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Biofuels for transport are a renewable source of energy that were once heralded as a solution to multiple problems associated with poor urban air quality, the overproduction of agricultural commodities, the energy security of the European Union (EU) and climate change. It was only after the Union had implemented an incentivizing framework of legal and political instruments for the production, trade and consumption of biofuels that the problems of weakening food security, environmental degradation and increasing greenhouse gases through land-use changes began to unfold. In other words, the difference between political aims for why biofuels are promoted and their consequences has grown – which is also recognized by the EU policy-makers. Therefore, the global networks of producing, trading and consuming biofuels may face a complete restructure if the European Commission accomplishes its pursuit to sideline crop-based biofuels after 2020. My aim with this dissertation is not only to trace the manifold evolutions of the instruments used by the Union to govern biofuels but also to reveal how this evolution has influenced the dynamics of biofuel development. Therefore, I study the ways the EU’s legal and political instruments of steering biofuels are coconstitutive with the globalized spaces of biofuel development. My analytical strategy can be outlined through three concepts. I use the term ‘assemblage’ to approach the operations of the loose entity of actors and non-human elements that are the constituents of multi-scalar and -sectorial biofuel development. ‘Topology’ refers to the spatiality of this European biofuel assemblage and its parts whose evolving relations are treated as the active constituents of space, instead of simply being located in space. I apply the concept of ‘nomosphere’ to characterize the framework of policies, laws and other instruments that the EU applies and construes while attempting to govern biofuels. Even though both the materials and methods vary in the independent articles, these three concepts characterize my analytical strategy that allows me to study law, policy and space associated with each other. The results of my examinations underscore the importance of the instruments of governance of the EU constituting and stabilizing the spaces of producing and, on the other hand, how topological ruptures in biofuel development have enforced the need to reform policies. This analysis maps the vast scope of actors that are influenced by the mechanism of EU biofuel governance and, what is more, shows how they are actively engaging in the Union’s institutional policy formulation. By examining the consequences of fast biofuel development that are spatially dislocated from the established spaces of producing, trading and consuming biofuels such as indirect land use changes, I unfold the processes not tackled by the instruments of the EU. Indeed, it is these spatially dislocated processes that have pushed the Commission construing a new type of governing biofuels: transferring the instruments of climate change mitigation to land-use policies. Although efficient in mitigating these dislocated consequences, these instruments have also created peculiar ontological scaffolding for governing biofuels. According to this mode of governance, the spatiality of biofuel development appears to be already determined and the agency that could dampen the negative consequences originating from land-use practices is treated as irrelevant.

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In recent decades, industrial activity growth and increasing water usage worldwide have led to the release of various pollutants, such as toxic heavy metals and nutrients, into the aquatic environment. Modified nanocellulose and microcellulose-based adsorption materials have the potential to remove these contaminants from aqueous solutions. The present research consisted of the preparation of five different nano/microcellulose-based adsorbents, their characterization, the study of adsorption kinetics and isotherms, the determination of adsorption mechanisms, and an evaluation of adsorbents’ regeneration properties. The same well known reactions and modification methods that were used for modifying conventional cellulose also worked for microfibrillated cellulose (MFC). The use of succinic anhydride modified mercerized nanocellulose, and aminosilane and hydroxyapatite modified nanostructured MFC for the removal of heavy metals from aqueous solutions exhibited promising results. Aminosilane, epoxy and hydroxyapatite modified MFC could be used as a promising alternative for H2S removal from aqueous solutions. In addition, new knowledge about the adsorption properties of carbonated hydroxyapatite modified MFC as multifunctional adsorbent for the removal of both cations and anions ions from water was obtained. The maghemite nanoparticles (Fe3O4) modified MFC was found to be a highly promising adsorbent for the removal of As(V) from aqueous solutions due to its magnetic properties, high surface area, and high adsorption capacity . The maximum removal efficiencies of each adsorbent were studied in batch mode. The results of adsorption kinetics indicated very fast removal rates for all the studied pollutants. Modeling of adsorption isotherms and adsorption kinetics using various theoretical models provided information about the adsorbent’s surface properties and the adsorption mechanisms. This knowledge is important for instance, in designing water treatment units/plants. Furthermore, the correspondence between the theory behind the model and properties of the adsorbent as well as adsorption mechanisms were also discussed. On the whole, both the experimental results and theoretical considerations supported the potential applicability of the studied nano/microcellulose-based adsorbents in water treatment applications.

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Presentation at "Soome-ugri keelte andmebaasid ja e-leksikograafia" at Eesti Keele Instituut (Institution of Estonian Languages) in Tallnn on the 18th of November 2014.

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Electrospraying or electrostatic atomisation is a process of liquid disruption by electrostatic forces. When liquid is brought into an electric field, charge is induced to its surface. Once the repulsive electrostatic force exceeds the liquid surface tension, the liquid disrupts into small highly charged droplets. The size of the electrosprayed droplets can range from hundreds of micrometers down to a few tens of nanometers. Electrospraying can be used not only to produce droplets, but also solid particles. The research presented in this thesis concentrates on producing drug particles by this method. In the experiments, a drug powder was dissolved in a convenient solvent and the solution was atomised. The solvent was then evaporated from the formed droplets in a drying medium and inside each droplet, a dense cluster of the dissolved drug remained. From the pharmaceutical point of view, the most important characteristics of the produced particles are size distribution, porosity, crystal form and degree of crystallinity. These properties affect the dissolution behaviour and ultimately the drug bioavailability in the body. The effects of electrostatic atomization on the aforementioned characteristics are generally not well understood. The research focused on studying these particle properties and finding possible correlations with the spraying parameters. The produced droplets were dried either under atmospheric or reduced pressure, the latter in order to improve the drying process. Special emphasis was put on implementing the spraying under reduced pressure, and the effects of the drying pressure on particle properties. Based on the results, the possibilities to enhance the dissolution of poorly soluble drugs by this method were estimated. In the course of experiments, it was also discovered that electrospraying may have a profound effect on the polymorphic form of the produced drug particles. In the light of the obtained results, it was concluded that electrospraying may offer a valuable tool to overcome some of the challenges met in modern drug development and formulation.

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Defects in semiconductor crystals and at their interfaces usually impair the properties and the performance of devices. These defects include, for example, vacancies (i.e., missing crystal atoms), interstitials (i.e., extra atoms between the host crystal sites), and impurities such as oxygen atoms. The defects can decrease (i) the rate of the radiative electron transition from the conduction band to the valence band, (ii) the amount of charge carriers, and (iii) the mobility of the electrons in the conduction band. It is a common situation that the presence of crystal defects can be readily concluded as a decrease in the luminescence intensity or in the current flow for example. However, the identification of the harmful defects is not straightforward at all because it is challenging to characterize local defects with atomic resolution and identification. Such atomic-scale knowledge is however essential to find methods for reducing the amount of defects in energy-efficient semiconductor devices. The defects formed in thin interface layers of semiconductors are particularly difficult to characterize due to their buried and amorphous structures. Characterization methods which are sensitive to defects often require well-defined samples with long range order. Photoelectron spectroscopy (PES) combined with photoluminescence (PL) or electrical measurements is a potential approach to elucidate the structure and defects of the interface. It is essential to combine the PES with complementary measurements of similar samples to relate the PES changes to changes in the interface defect density. Understanding of the nature of defects related to III-V materials is relevant to developing for example field-effect transistors which include a III-V channel, but research is still far from complete. In this thesis, PES measurements are utilized in studies of various III-V compound semiconductor materials. PES is combined with photoluminescence measurements to study the SiO2/GaAs, SiNx/GaAs and BaO/GaAs interfaces. Also the formation of novel materials InN and photoluminescent GaAs nanoparticles are studied. Finally, the formation of Ga interstitial defects in GaAsN is elucidated by combining calculational results with PES measurements.

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The Baltic Sea is unique by its biological, geochemical and physical features. The number of species of larger organisms is small and the species composition is distinctive. On the contrary microbial communities are diverse. Because of the low salinity levels, bacterial communities differ from the ones in the oceans. Knowing the structure of these communities better and how they response to different environmental conditions helps us to estimate how different factors affect the balance and function of the Baltic Sea ecosystem. Bacteria are the key players when it comes to natural biogeochemical processes and human-induced phenomena like eutrophication, oil spills or disposal of other harmful substances to the sea ecosystem. In this thesis, bacterial community structure in the sea surface microlayer and subsurface water of the Archipelago Sea were compared. In addition, the effect of diatom derived polyunsaturated aldehydes on bacterial community structure was studied by a mesocosm experiment. Diesel, crude oil and polycyclic aromatic hydrocarbon degradation capacity of the Baltic Sea bacteria was studied in smaller scale microcosm experiments. In diesel oil experiments bacteria from water phase of the Archipelago Sea was studied. Sediment and iron manganese concretions collected from the Gulf of Finland were used in the crude oil and polycyclic aromatic hydrocarbon experiments. The amount of polycyclic aromatic hydrocarbon degradation genes was measured in all of the oil degradation experiments. The results show how differences in bacterial community structure can be seen in the sea surface when compared to the subsurface waters. The mesocosm experiment demonstrated how diatom-bacteria interactions depend on other factors than diatom derived polyunsaturated aldehydes, which do not seem to have an effect on the bacterial community structure as has been suggested in earlier studies. The dominant bacterial groups in the diesel microcosms differed in samples taken from a pristine site when compared to a site with previous oil exposure in the Archipelago Sea area. Results of the study with sediment and iron-manganese concretions indicate that there are diverse bacterial communities, typical to each bottom type, inhabiting the bottoms of the Gulf of Finland capable to degrade oil and polycyclic aromatic hydrocarbon compounds.  

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The need for industries to remain competitive in the welding business, has created necessity to develop innovative processes that can exceed customer’s demand. Significant development in improving weld efficiency, during the past decades, still have their drawbacks, specifically in the weld strength properties. The recent innovative technologies have created smallest possible solid material known as nanomaterial and their introduction in welding production has improved the weld strength properties and to overcome unstable microstructures in the weld. This study utilizes a qualitative research method, to elaborate the methods of introducing nanomaterial to the weldments and the characteristic of the welds produced by different welding processes. The study mainly focuses on changes in the microstructural formation and strength properties on the welded joint and also discusses those factors influencing such improvements, due to the addition of nanomaterials. The effect of nanomaterial addition in welding process modifies the physics of joining region, thereby, resulting in significant improvement in the strength properties, with stable microstructure in the weld. The addition of nanomaterials in the welding processes are, through coating on base metal, addition in filler metal and utilizing nanostructured base metal. However, due to its insignificant size, the addition of nanomaterials directly to the weld, would poses complications. The factors having major influence on the joint integrity are dispersion of nanomaterials, characteristics of the nanomaterials, quantity of nanomaterials and selection of nanomaterials. The addition of nanomaterials does not affect the fundamental properties and characteristics of base metals and the filler metal. However, in some cases, the addition of nanomaterials lead to the deterioration of the joint properties by unstable microstructural formations. Still research are ongoing to achieve high joint integrity, in various materials through different welding processes and also on other factors that influence the joint strength.

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Increasing demand and shortage of energy resources and clean water due to the rapid development of industry, population growth and long term droughts have become an issue worldwide. As a result, global warming, long term droughts and pollution-related diseases are becoming more and more serious. The traditional technologies, such as precipitation, neutralization, sedimentation, filtration and waste immobilization, cannot prevent the pollution but restrict the waste chemicals only after the pollution emission. Meanwhile, most of these treatments cannot thoroughly degrade the contaminants and may generate toxic secondary pollutants into ecosystem. Heterogeneous photocatalysis as the innovative wastewater technology attracts many attention, because it is able to generate highly reactive transitory species for total degradation of organic compounds, water pathogens and disinfection by-products. Semiconductor as photocatalysts have demonstrated their efficiency in degrading a wide range of organics into readily biodegradable compounds, and eventually mineralized them to innocuous carbon dioxide and water. But, the efficiency of photocatalysis is limited, and hence, it is crucial issue to modify photocatalyst to enhance photocatalytic activity. In this thesis, first of all, two literature views are conducted. A survey of materials for photocatalysis has been carried out in order to summarize the properties and the applications of photocatalysts that have been developed in this field. Meanwhile, the strategy for the improvement of photocatalytic activity have been explicit discussed. Furthermore, all the raw material and chemicals used in this work have been listed as well as a specific experimental process and characterization method has been described. The synthesize methods of different photocatalysts have been depicted step by step. Among these cases, different modification strategies have been used to enhance the efficiency of photocatalyst on degradation of organic compounds (Methylene Blue or Phenol). For each case, photocatalytic experiments have been done to exhibit their photocatalytic activity.The photocatalytic experiments have been designed and its process have been explained and illustrated in detailed. Moreover, the experimental results have been shown and discussion. All the findings have been demonstrated in detail and discussed case by case. Eventually, the mechanisms on the improvement of photocatalytic activities have been clarified by characterization of samples and analysis of results. As a conclusion, the photocatalytic activities of selected semiconductors have been successfully enhanced via choosing appropriate strategy for the modification of photocatalysts.

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Fiber-reinforced composite fixed dental prostheses – Studies of the materials used as pontics University of Turku, Faculty of Medicine, Institute of Dentistry, Department of Biomaterials Science, Finnish Doctoral Program in Oral Sciences – FINDOS, Annales Universitatis Turkuensis, Turku, Finland 2015 Fiber-reinforced composites (FRC), a non-metallic biomaterial, represent a suitable alternative in prosthetic dentistry when used as a component of fixed dental prostheses (FDPs). Some drawbacks have been identified in the clinical performance of FRC restorations, such as delamination of the veneering material and fracture of the pontic. Therefore, the current series of studies were performed to investigate the possibilities of enhancing the mechanical and physical properties of FRC FDPs by improving the materials used as pontics, to then heighten their longevity. Four experiments showed the importance of the pontic design and surface treatment in the performance of FRC FDPs. In the first, the load-bearing capacities of inlay-retained FRC FDPs with pontics of various materials and thicknesses were evaluated. Three different pontic materials were assessed with different FRC framework vertical positioning. Thicker pontics showed increased load-bearing capacities, especially ceramic pontics. A second study was completed investigating the influence of the chemical conditioning of the ridge-lap surface of acrylic resin denture teeth on their bonding to a composite resin. Increased shear bond strength demonstrated the positive influence of the pretreatment of the acrylic surfaces, indicating dissolution of the denture surfaces, and suggesting potential penetration of the monomer systems into the surface of denture teeth. A third study analyzed the penetration depth of different monomer systems on the acrylic resin denture teeth surfaces. The possibility of establishing a durable bond between acrylic pontics and FRC frameworks was demonstrated by the ability of monomers to penetrate the surface of acrylic resin denture teeth, measured by a confocal scanning type microscope. A fourth study was designed to evaluate the load-bearing capacities of FRC FDPs using the findings of the previous three studies. In this case, the performance of pre-shaped acrylic resin denture teeth used as pontics with different composite resins as filling materials was evaluated. The filling material influenced the load-bearing capacities, providing more durable FRC FDPs. It can be concluded that the mechanical and physical properties of FRC FDPs can be improved as has been shown in the development of this thesis. The improvements reported then might provide long lasting prosthetic solutions of this kind, positioning them as potentially permanent rehabilitation treatments. Key words: fiber-reinforced composite, fixed dental prostheses, inlay-retained bridges, adhesion, acrylic resin denture teeth, dental material.

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Torrefaction is moderate thermal treatment (~200-300 °C) of biomass in an inert atmosphere. The torrefied fuel offers advantages to traditional biomass, such as higher heating value, reduced hydrophilic nature, increased its resistance to biological decay, and improved grindability. These factors could, for instance, lead to better handling and storage of biomass and increased use of biomass in pulverized combustors. In this work, we look at several aspects of changes in the biomass during torrefaction. We investigate the fate of carboxylic groups during torrefaction and its dependency to equilibrium moisture content. The changes in the wood components including carbohydrates, lignin, extractable materials and ashforming matters are also studied. And at last, the effect of K on torrefaction is investigated and then modeled. In biomass, carboxylic sites are partially responsible for its hydrophilic characteristic. These sites are degraded to varying extents during torrefaction. In this work, methylene blue sorption and potentiometric titration were applied to measure the concentration of carboxylic groups in torrefied spruce wood. The results from both methods were applicable and the values agreed well. A decrease in the equilibrium moisture content at different humidity was also measured for the torrefied wood samples, which is in good agreement with the decrease in carboxylic group contents. Thus, both methods offer a means of directly measuring the decomposition of carboxylic groups in biomass during torrefaction as a valuable parameter in evaluating the extent of torrefaction. This provides new information to the chemical changes occurring during torrefaction. The effect of torrefaction temperature on the chemistry of birch wood was investigated. The samples were from a pilot plant at Energy research Center of the Netherlands (ECN). And in that way they were representative of industrially produced samples. Sugar analysis was applied to analyze the hemicellulose and cellulose content during torrefaction. The results show a significant degradation of hemicellulose already at 240 °C, while cellulose degradation becomes significant above 270 °C torrefaction. Several methods including Klason lignin method, solid state NMR and Py-GC-MS analyses were applied to measure the changes in lignin during torrefaction. The changes in the ratio of phenyl, guaiacyl and syringyl units show that lignin degrades already at 240 °C to a small extent. To investigate the changes in the extractives from acetone extraction during torrefaction, gravimetric method, HP-SEC and GC-FID followed by GC-MS analysis were performed. The content of acetone-extractable material increases already at 240 °C torrefaction through the degradation of carbohydrate and lignin. The molecular weight of the acetone-extractable material decreases with increasing the torrefaction temperature. The formation of some valuable materials like syringaresinol or vanillin is also observed which is important from biorefinery perspective. To investigate the change in the chemical association of ash-forming elements in birch wood during torrefaction, chemical fractionation was performed on the original and torrefied birch samples. These results give a first understanding of the changes in the association of ashforming elements during torrefaction. The most significant changes can be seen in the distribution of calcium, magnesium and manganese, with some change in water solubility seen in potassium. These changes may in part be due to the destruction of carboxylic groups. In addition to some changes in water and acid solubility of phosphorous, a clear decrease in the concentration of both chlorine and sulfur was observed. This would be a significant additional benefit for the combustion of torrefied biomass. Another objective of this work is studying the impact of organically bound K, Na, Ca and Mn on mass loss of biomass during torrefaction. These elements were of interest because they have been shown to be catalytically active in solid fuels during pyrolysis and/or gasification. The biomasses were first acid washed to remove the ash-forming matters and then organic sites were doped with K, Na, Ca or Mn. The results show that K and Na bound to organic sites can significantly increase the mass loss during torrefaction. It is also seen that Mn bound to organic sites increases the mass loss and Ca addition does not influence the mass loss rate on torrefaction. This increase in mass loss during torrefaction with alkali addition is unlike what has been found in the case of pyrolysis where alkali addition resulted in a reduced mass loss. These results are important for the future operation of torrefaction plants, which will likely be designed to handle various biomasses with significantly different contents of K. The results imply that shorter retention times are possible for high K-containing biomasses. The mass loss of spruce wood with different content of K was modeled using a two-step reaction model based on four kinetic rate constants. The results show that it is possible to model the mass loss of spruce wood doped with different levels of K using the same activation energies but different pre-exponential factors for the rate constants. Three of the pre-exponential factors increased linearly with increasing K content, while one of the preexponential factors decreased with increasing K content. Therefore, a new torrefaction model was formulated using the hemicellulose and cellulose content and K content. The new torrefaction model was validated against the mass loss during the torrefaction of aspen, miscanthus, straw and bark. There is good agreement between the model and the experimental data for the other biomasses, except bark. For bark, the mass loss of acetone extractable material is also needed to be taken into account. The new model can describe the kinetics of mass loss during torrefaction of different types of biomass. This is important for considering fuel flexibility in torrefaction plants.

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Transmission system operators and distribution system operators are experiencing new challenges in terms of reliability, power quality, and cost efficiency. Although the potential of energy storages to face those challenges is recognized, the economic implications are still obscure, which introduce the risk into the business models. This thesis aims to investigate the technical and economic value indicators of lithium-ion battery energy storage systems (BESS) in grid-scale applications. In order to do that, a comprehensive performance lithium-ion BESS model with degradation effects estimation is developed. The model development process implies literature review on lifetime modelling, use, and modification of previous study progress, building the additional system parts and integrating it into a complete tool. The constructed model is capable of describing the dynamic behavior of the BESS voltage, state of charge, temperature and capacity loss. Five control strategies for BESS unit providing primary frequency regulation are implemented, in addition to the model. The questions related to BESS dimensioning and the end of life (EoL) criterion are addressed. Simulations are performed with one-month real frequency data acquired from Fingrid. The lifetime and cost-benefit analysis of the simulation results allow to compare and determine the preferable control strategy. Finally, the study performs the sensitivity analysis of economic profitability with variable size, EoL and system price. The research reports that BESS can be profitable in certain cases and presents the recommendations.