The huge environmental awareness emerging last years by reason of global warming and greenhouse effect, on one hand, and the need of finding other sources of energy production and conversion due to the declining of fossil resources and the increasing cost of this kind of energy resource, on the other hand, both have led position renewable energies as a powerful alternative on the energy production and conversion. PV-systems have emerged at an exponential rate in recent year as the main candidate and a satisfactory possibility with respect to environmental and economic sustainability. Nowadays, the large volume on photovoltaic market is currently dominated by four types of solar cells, divided by the semiconductor material used to absorb light and convert the energy into electricity: (1) crystalline silicon (monocrystalline and polycrystalline), (2) amorphous silicon, (3) CIGS and (4) cadmium telluride; and among them, monocrystalline silicon and CIGS technologies are installed on the building 45 of the University of Gävle, at the south face of the laboratory. In this context and with the motivation to contribute knowledge on PV field, a comparison between single crystal solar technology and thin film CIGS technology has carried out through f ratio and performance ratio procedures in order to perform an assessment of the energy conversion of each one under field conditions. A logger monitors the power conversion from the PV modules since June 2014 while two pyranometers monitor global and diffuse solar radiation since March 2016. It must take into account that only clear sunny days have been considered during a period from 8:00 to 14:00 in order to avoid shadows effect on the PV systems. The results come to conclude that single crystal silicon modules present a better behavior with respect to energy conversion under no shadows effect conditions by two reason: (1) f ratio, relationship of PV conversion per kW (PV yield) between CIGS and single crystal silicon, is about 87.25% with some variations along a day due to ambient temperature, cell temperature and incidence angle; (2) PV module's performance ratio of monocrystalline silicon modules is higher than thin film CIGS ones during a sunny day about 87.56% and 76.38%, respectively; and they are consistent with usual performance ratio values between 80% and 90% since 2010 onwards. In light of the outcome and in order to confirm these conclusions, it intends to launch a project with the objective of evaluating the data collected and compare the performance of the module after a year of measurements outdoors by the PV module's performance ratio procedure. Along the same lines, the next step of the University of Gävle will be to launch a project with the objective of evaluating the potential to be self-sufficient.

Achieving the reductions in carbon dioxide emissions which are necessary will require improvements in the way in which domestic space heating is supplied. Air Source Heat Pumps and micro-Combined Heat and Power units both have the potential to reduce emissions while using primary energy resources more efficiently. The performance which these technologies can achieve is fundamental to fulfilling this potential and yet it is still subject to some uncertainty. This thesis analyses the performance of Air Source Heat Pumps and micro-Combined Heat and Power units in terms of their energy and exergy requirements and in terms of the carbon dioxide emissions associated with their operation. A review of the literature identified that it was appropriate to develop a novel modelling approach. Models of many components currently exist and these are adopted and extended wherever possible within this modelling approach. However, it is the unique way in which this research combines these models and adds additional components which delivers performance data relating to a wider range of conditions at a greater level of detail than that which was previously available. The model which was developed can dynamically simulate the heating and power demands in many dwellings simultaneously, facilitating meaningful study of effects which are dependent upon the sum of their power flows. Consideration of the effect of operating conditions includes permutations of climate, control systems (including those which engage with demand side management), grid generation mixes and building properties. Efficient Air Source Heat Pumps units have the potential to make energy and carbon emissions savings at present but their performance is sensitive to the conditions studied. In particular, appropriate control of the units can yield energy savings of around 25%. Additionally, the carbon emissions intensity of the grid is an important consideration which is explored in depth. Currently, energy requirements and carbon emissions can be reduced by the use of micro-Combined Heat and Power units. Their potential to further reduce carbon emissions diminishes if the grid is predominantly decarbonised but units with high electrical efficiencies can still save energy. The effect of the control approach which is adopted is also significant and has different effects on fuel-cell based units compared to combustion-based units. The key contribution of this work is the analysis of performance data for a selection of units operating under a range of conditions, calculated with a consistent, accurate methodology. Comparison is made between the technologies and between the effects of different operating conditions. A second significant contribution of this work is the development of the model which was used to generate the performance results. These advances allow more detailed comparative analysis of performance data in a wider range of conditions than previously possible.

Submitted by admin tede (tede@pucgoias.edu.br) on 2018-08-23T10:49:49Z No. of bitstreams: 1 FELIPE RABELO RODRIGUES ALVES.pdf: 2420637 bytes, checksum: 29b86a56944a6b8d8dd2f04052fb7420 (MD5) / Made available in DSpace on 2018-08-23T10:49:49Z (GMT). No. of bitstreams: 1 FELIPE RABELO RODRIGUES ALVES.pdf: 2420637 bytes, checksum: 29b86a56944a6b8d8dd2f04052fb7420 (MD5) Previous issue date: 2018-06-06 / The dependence on nonrenewable sources and concern about high levels of pollutant emissions encourage the use of systems that are derived from renewable resources. In this way, photovoltaic systems are seen as promising because they depend on a clean and abundant source, especially in areas of tropical climate, the solar radiation. However, the accumulation of soiling on the surfaces of photovoltaic modules is one of the main environmental factors that cause of the loss of efficiency of these systems, together with irradiance, temperature and shading. In this sense, the present work seeks to verify the soiling effects on the efficiency of photovoltaic modules, through data collection, measurement of specific parameters, statistical analysis and comparisons of scenarios of dirty and clean modules. For the verification and quantification of soiling interference in the efficiency of photovoltaic modules, the electrical and environmental parameters capable of characterizing them are obtained: Isc - Short circuit current (A); Voc - Open circuit voltage (V); G - Solar irradiance (W/m²); T - Module temperature (°C). From the results it can be observed that the intensity of the solar radiation has greater influence on the current of the module, while the temperature directly affects the voltage. This work showed that, in the universe studied, soiling has reduced the power generation efficiency of modules by 3,2% for accumulated soiling in periods of 45 days, and by 18% for accumulated soiling in a longer period of 3,5 years. The characterization of the soiling showed that in addition to mineral particles, there is also organic matter derived from biofilms, which makes it difficult to clean the modules by natural methods (rains and winds). Based on the bibliography and the tests realized, it is estimated that the periodicity of the hygiene should not exceed 60 days, with that, the effects of the soiling are reduced significantly. / A dependência por fontes não renováveis e a preocupação com os elevados níveis de emissões de poluentes estimulam o uso de sistemas que são provenientes de recursos renováveis. Com isso, são vistos como promissores os sistemas fotovoltaicos, por dependerem de uma fonte limpa e abundante, em especial em áreas de clima tropical, a radiação solar. Porém, o acúmulo de sujeira nas superfícies de módulos fotovoltaicos é um dos principais fatores ambientais que causam perda de eficiência desses sistemas, juntamente com irradiância, temperatura e sombreamento. Neste sentido, o presente trabalho busca verificar os efeitos da sujidade na eficiência dos módulos fotovoltaicos, por meio de coletas de dados, medições de parâmetros específicos, análise estatística e comparações de cenários de módulos sujos e limpos. Para a comprovação e quantificação da interferência da sujidade na eficiência de módulos fotovoltaicos são obtidos os parâmetros elétricos e ambientais capazes de caracterizá-los, são eles: Isc - Corrente de curto-circuito (A); Voc - Tensão de circuito aberto (V); G - Irradiância solar (W/m²); T - Temperatura do módulo (°C). A partir dos resultados pode-se observar que a intensidade da radiação solar tem maior influência sobre a corrente do módulo, enquanto que a temperatura afeta diretamente a tensão. Este trabalho comprovou que, no universo estudado, a sujidade diminuiu a eficiência dos módulos em até 3,2% para sujeira acumulada em períodos de 45 dias, e em até 18% para sujidades acumuladas por um período mais longo, de 3,5 anos. A caracterização da sujidade demonstrou que além de partículas minerais, há também matéria orgânica derivada de biofilmes, que dificulta a limpeza dos módulos pelos métodos naturais (chuvas e ventos). Com base na bibliografia e nos ensaios realizados, estima-se que a periodicidade de higienização não deva exceder 60 dias, assim os efeitos da sujidade são reduzidos significativamente.

Today, energy has become one of the most indispensable necessities in the world. Most of the wars and the disputes between the countries have been arising because of the increasing scarcity of energy resources. Therefore, like most country, Turkey has also started to develop new energy policies for more efficient production and utilization of energy. In order to help the understanding of more efficient energy utilization, so far there have been some researches made about energy and exergy (available energy) utilization efficiencies of Turkey with the viewpoint of the quality of energy. In this study, it is aimed to examine energy system of Turkey by computing energy and exergy utilization efficiencies between 1990 and 2006 using the first and the second laws of thermodynamics. The utility sector energy efficiencies are found to range from 41% to 47% and the exergy efficiencies to range from 42% and 48% between 1990 and 2006. The energy efficiencies of the end use sectors of Turkey , namely Industrial, Transportation, Agricultural and Residential-Commercial sectors, are respectively 62%, 22%, 27% and 55% on the average with respect to years. On the other hand, their average exergy efficiencies are 33%, 23%, 27% and 7% between the examined years. The total end use energy and exergy efficiencies are 49% and 21% on the average. Overall energy efficiencies of Turkey range between 37% and 41%, whereas overall exergy efficiencies range between 16% and 17%. Within all the sectors, Residential&ndash / Commercial sector is found as the sector having the highest exergetic improvement potential.

This project examines the efficiency of a biochar-producing stove in meeting the needs of households in rural of Kenya. The stove has been tested and evaluated by five household in Embu, Kenya and compared with two other common cooking methods. The main parameters were time consumption, fuel consumption and emissions of carbon monoxide and particulate matter. Usability and energy use efficiency have also been evaluated. Three potential feedstocks have been examined for use in the biochar-producing stove; Grevillea prunings, maize cobs and coconut husks. The biochar-producing stove was well received by the households. It has potential of saving time, it saves fuel and it has a significantly lower level of emissions than other examined stoves. Despite some challenges related to the usability and the handling of the stove, an implementation of the biochar-producing stove can contribute to an alleviation of the women’s burdens, save fuel and contribute to a healthier indoor air climate.

Dieser Beitrag untersucht die Verluste elektrischer Maschinen in Abhängigkeit von der verwendeten Stromrichtertopologie und bei verschiedenen Pulsfrequenz. Beispielhaft wird eine permanentmagneterregte Synchronmaschine (PMSM) mit einer Bemessungsleistung von 18 kW behandelt. Zum Betrieb der Maschine wird der Prototyp des 3-Level-Stromrichters LT300-ML von M&P Motion Control and Power Electronics GmbH (M&P) verwendet. Beim 3-Level-Stromrichter werden mehr Spannungsebenen geschaltet als beim 2-Level-Stromrichter. Dies führt zu einer geringeren Stromwelligkeit und u. a. zu geringeren Verlusten in der Maschine. Die Messergebnisse zeigen, dass die Maschinenverluste im Vergleich zum Einsatz eines 2-Level-Stromrichters um 20 ... 30 % reduziert werden können. Für die Untersuchung wird der M&P-Maschinen-Prüfstand verwendet. / This paper deals with the losses of electrical machines depending on the converter topology used and with different switching frequency’s. A permanent magnet synchronous machine (PMSM) with a rated output power of 18 kW is investigated. As power converter the LT300-ML (3-level converter) from M&P Motion Control and Power Electronics GmbH (M&P) is used. By using a 3-level topology, more voltage levels are switched than with a 2-level topology. This, among other things, results in a lower current ripple and lower losses in the machine. The measurement results show that the machine losses can be reduced by 20 ... 30 % compared to the use of a 2-level converter. The M&P machine test bench is used for the investigation.

Commercial mobile communication systems are mainly based on licensed frequency spectrum, and the license is very expensive as the spectrum is a sparse wireless resource. Therefore, sharing this wireless resource is an essential requirement not only at the present but also in the future considering trends like connectivity for everybody and everything. In this thesis, we study the sharing of wireless resources with different approaches for realizing fair, efficient, and predictable sharing solutions in a controlled manner. The efficient use of wireless channel resources is an important target to reduce the costs of network operation and deployment. To achieve this, we need practical scheduling algorithms for wireless resources, out of which several of them will be presented and analyzed in this work. Different optimization frameworks for the spectral efficiency utility are presented, with an individual focus on guaranteeing resource or rate fairness among the operators in a network with shared radio resources. Thus, the presented proposals will help the mobile network operators to overcome the issues of losing network control and traceability of used wireless resources in a shared environment. Besides this, emerging vertical industries, such as automotive, healthcare, industry 4.0, internet of things (IoT) industries will put a certain burden on the wireless networks asking for guaranteed service level requirement from the mobile network operators. In this regard, this thesis provides the necessary methods addressing these challenges with the help of scheduling methods which are based on the joint optimization of spectral and energy efficiency. Thus, wireless networks will be enabled as a service function in a controlled and scalable way for new emerging markets. Furthermore, the presented solutions t well with the requirements of fifth generation (5G) network slicing.

Yes / This study aims to evaluate the impacts of using thermally enhanced concrete on the thermal performance of geoenergy structures and interaction between the thermo-active-structures and adjacent dry and partly saturated soils. Experiments using a fully instrumented testing rig were carried out on prototypes of energy pile and diaphragm wall made from normal concrete and thermally enhanced concrete by the addition of graphTHERM powder. Results illustrated that adding 36% of graphTHERM powder to the concrete by weight of cement was found to double the thermal conductivity of concrete and improve the stiffness by 15% without detrimental effects on the compressive strength. The heat transfer efficiency of energy pile and energy diaphragm wall made from thermally enhanced concrete was significantly improved by 50% and 66% respectively, in comparison with the efficiency of the same type of energy structure that was made from a typical normal concrete.

Nearly half of Britain’s carbon dioxide emissions result from the activity of households, both within the home and from personal transport. This research examines how the carbon dioxide emissions of households can be reduced, particularly through the calculation of carbon footprints and testing the public’s reaction to the concept of personal carbon allowances (PCAs). Two data collection stages were used - a postal survey providing quantitative data, followed by semi-structured interviews producing mainly qualitative data. The research was carried out in a largely rural district which is run by a council noted for its work on sustainable energy, Newark and Sherwood. The survey looked at PCAs as well as a variety of contemporary issues that might influence household footprints such as energy efficiency grants and information, as well as relationships with gas and electricity suppliers. Each interview involved the calculation of a household carbon footprint, the identification of measures to reduce it, and the gathering of attitudes about personal carbon allowances, in order to identify challenges and opportunities with respect to reducing household carbon emissions. Support for PCAs was higher than anticipated, and tended to be associated with those who were prepared to use public transport or cycle more, or were supportive of renewable energy in homes. Interviewees had much to say about individual carbon reducing measures. Opposition was associated with those who envisaged that they would be unlikely to sell carbon units. Regarding personal transport, long commutes were common, and the cost of public transport was of concern. Specific findings were made about domestic heating, insulation, lighting, refrigeration, water use, commuting, public transport, and rail as an alternative to short-haul flights. There was more interest in monetary savings than carbon savings. Recommendations about policy and regarding further research are made.

Le développement de lubrifiants à haute valeur ajoutée subissant des conditions opératoires de plus en plus draconiennes, économes en carburant et performants pendant une longue durée reste un défi considérable pour les fabricants d’huiles. Cette thèse concerne l’étude du rôle et des actions des améliorants d’indice de viscosité (ou Viscosity Index Improvers (VII)) dans les lubrifiants moteurs. Le premier objectif visé dans ce travail est la caractérisation des comportements rhéologiques et la modélisation de la viscosité en fonction de conditions réelles de température, pression et contrainte de cisaillement pour des solutions d’huile de base et de polymère sans additifs fonctionnels. Plusieurs polymères (PAMA, OCP et PISH) de masses moléculaires et conformations (peigne, linéaire et étoile) différentes sont utilisés à 1,2% en masse dans une huile de base minérale hydrocraquée. L’originalité de la thèse réside dans l’utilisation de rhéomètres non-commerciaux à haute pression (jusqu’à 800 MPa). Un deuxième défi réside dans la compréhension de la relation entre la réponse rhéologique des lubrifiants automobiles simplifiés et les mécanismes présents à l’échelle moléculaire en explorant les notions de conformation, de solubilité et de rayon hydrodynamique grâce à l’extension de la loi d’Einstein à haute pression. Enfin, l’étude se concentre sur le lien entre rhéologie et tribologie et par extension, entre la composition chimique du lubrifiant et la tribologie. Les épaisseurs de film sont mesurées et comparées avec les prédictions analytiques de Hamrock-Dowson et avec les simulations numériques basées sur l’équation de Reynolds généralisée en incluant les modèles rhéologiques. Les données expérimentales et numériques sont en adéquation. / The development of high value-added lubricants overcoming more and more drastic operating conditions, fuel-efficient and providing excellent performance during a long time remains a huge challenge for oil makers. This thesis is dedicated to the study of the role and the actions of Viscosity Index Improvers (VII) in engine lubricants. The first objective targeted in this work is the characterization of the rheological behaviors and the modeling of viscosity in function of realistic conditions of temperature, pressure and shear stress for polymer-thickened base oil solutions without functional additives. Several polymers (PAMA, OCP and PISH) with different molecular weights and conformations (comb, linear and star) are used with a concentration of 1.2% (w/w) in a hydrocracked mineral base oil. The originality of the thesis lies in the use of non-commercial rheometers under high pressure (up to 800 MPa). A second challenge is the understanding of the relationship between the rheological response of simplified engine lubricants and the mechanisms occurring at the molecular scale by exploring the notions of conformation, solubility and hydrodynamic radius by the extension of the Einstein’s law at high pressure. Finally, the study focuses on the link between rheology and tribology and by extrapolation, between the chemical composition of the lubricant and tribology. The film thickness is measured and compared with the Hamrock-Dowson analytical predictions and with the numerical simulations based on the generalized Reynolds’ equation including the rheological models. Both experimental and numerical data are in good agreement.