Access to sustainable energy in the developing world has become a fundamental challenge in development and environmental policy in the 21st Century, and rural electrification in developing countries constitutes a central element of access to energy goals. However, traditional ways of providing electricity to dispersed rural populations (i.e. through centralised electricity infrastructure or fuel-based on-site generation) is proving to be ineffective, inefficient and less sustainable than the use of renewable energy technologies (RETs) in off-grid settings. Such ‘system innovations' for sustainable electricity services in rural areas are the focus of this study, which seeks to understand the reasons underlying success or failure in the diffusion of radical innovations. Embracing evolutionary and constructivist theories of socio-technical change and sustainability transitions, the thesis attempts to explain the use and diffusion of PV (photovoltaic) and wind technology in off-grid rural electrification over the last 20 years in Chile, a country where access to rural electricity has increased from 53% to 95%. RETs have contributed to nearly 10% of that increment. By using a framework that combines Strategic Niche Management (SNM), systemic intermediation and power, agency and conflicts in decision making, the thesis analyses the dynamics between the development and adaptation of new technologies and their influence in regime shift through replication, scaling up and translation of new socio-technical practices. The thesis attempts to shed light on processes affecting niche construction and it concludes that internal niche processes are relevant to understanding how radical innovations are structured and stabilised from the aggregation of projects. However, those processes are not only a managerial activity that can be steered but a politically underpinned (and iterative) process between specific (socio-political) settings. The study also highlights the role of systemic intermediaries, government and incumbent actors in the dynamic interaction between emergent niche dynamics and traditional ways of improving electricity access.

The aim of this thesis is the project for biomass cogeneration units using ORC cycle and subsequent use of thermal energy for drying wood biomass for a briquetting line. The introducing sections describe the principle of cogeneration, organic Rankine cycle (primarily the indication of potential applications and their use in practice) and the selection of the proper working fluid. The following sections provide a technical description of the selected plants for cogeneration unit, total circulation scheme and calculation of the evaporator working fluid. The last section is devoted to the economic evaluation of three variants according to the investor's task to design a better option for implementation.

Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2018-06-13T19:12:48Z No. of bitstreams: 1 2017 - Lidiane Benites de Campos.pdf: 4991873 bytes, checksum: b8396eff5b6aec80b0657e9e4c07eb15 (MD5) / Made available in DSpace on 2018-06-13T19:12:48Z (GMT). No. of bitstreams: 1 2017 - Lidiane Benites de Campos.pdf: 4991873 bytes, checksum: b8396eff5b6aec80b0657e9e4c07eb15 (MD5) Previous issue date: 2017-04-03 / This work aimed to develop a thematic approach within a CTS (Science-Technology-Society) focus to physics teaching, dealing with the issue of "Electric Energy Production". The CTS focused teaching approaches scientific knowledge in the technological and social context of the learner and relates it to their everyday experiences, leading them to reflect on historical, ethical, political and socioeconomic aspects, and thus providing skills and values that help them to take responsible decisions and attitudes. In our case, the proposal was applied in a public school in the city of Angra dos Reis, in the State of Rio de Janeiro, to be evaluated and reworked according to the needs verified. The theme was chosen to be worked in this place, because the city houses the only nuclear power plant in Brazil, being a subject of extreme importance for the population and that allows the CTS approach with emphasis on the reality of the students. However, the approach was not restricted to the nuclear power plant, but involved all means of producing electric energy, such as hydroelectric, thermoelectric, with its variations of fuels, wave power plant, solar power plants and wind power plants, so that the general theme Production Of Electric Energy was divided into three sub-themes: Hydroelectric Plants, Other Modes of Energy Production and Nuclear Plants. The objective of this approach, besides teaching physical concepts involved in the processes of electric energy production, is also to make students aware of the risks, consequences and benefits of each mode of production, to have them reflect and evaluate the most to be able to actively participate in decision-making processes involving such issues. The final product of this work is a didactic sequence with varied didactic methods and resources, to serve as a guide for other teachers who wish to adopt the proposal. The text presents a brief history of science education in Brazil, its peculiarities and needs that justify the proposal and also presents the CTS movement and its main characteristics, that guide this work. The methodology adopted was the Action-research, which allowed the readjustment of the proposal throughout its application. The results were very promising and showed that the teaching of physics with a CTS approach, practiced through a thematic approach focused on students' reality, can be a means to promote a quality scientific education and to train citizens able to understand the world and the Society in which they live. / Este trabalho teve como objetivo desenvolver uma proposta de abordagem tem?tica com enfoque CTS (Ci?ncia-Tecnologia-Sociedade) para o ensino de f?sica, abordando o tema ?Produ??o de Energia El?trica?. O ensino com enfoque CTS aborda os conhecimentos cient?ficos no contexto tecnol?gico e social do educando e o relaciona com suas experi?ncias cotidianas, levando-o a refletir sobre aspectos hist?ricos, ?ticos, pol?ticos e socioecon?micos, fornecendo assim habilidades e valores que o auxiliem na tomada de decis?es respons?veis e atitudes. No nosso caso, a proposta foi aplicada em uma escola p?blica da cidade de Angra dos Reis, no Rio de Janeiro, para que fosse avaliada e reelaborada de acordo com as necessidades verificadas. O tema foi escolhido para ser trabalhado neste local, pois a cidade abriga a ?nica usina nuclear do Brasil, sendo um assunto de extrema import?ncia para a popula??o e que possibilita o enfoque CTS com ?nfase na realidade dos alunos. Por?m, a abordagem n?o ficou restrita ? usina nuclear, mas envolveu todos os meios de produ??o de energia el?trica, tais como hidrel?tricas, termoel?tricas e suas varia??es de combust?veis, usina de ondas, usinas solares e usinas e?licas, de modo que o tema geral Produ??o de Energia El?trica foi dividido em tr?s subtemas: Usinas Hidrel?tricas, Outros Modos de Produ??o de Energia e Usinas Nucleares. O objetivo desta abordagem, al?m de ensinar conceitos f?sicos que envolvem os processos de produ??o de energia el?trica, ?, tamb?m, conscientizar os alunos dos riscos, consequ?ncias e benef?cios de cada modo de produ??o, lev?-los a refletir e avaliar quais os modos mais vantajosos, para que estejam aptos a opinar e participar ativamente de processos decis?rios envolvendo tais quest?es. O produto final deste trabalho ? uma sequ?ncia did?tica com m?todos e recursos did?ticos variados, para servir como guia para outros professores que desejem adotar a proposta. O texto apresenta um breve hist?rico do ensino de ci?ncias no Brasil, suas peculiaridades e necessidades que justificam a proposta e apresenta tamb?m o movimento CTS e suas principais caracter?sticas, que norteiam este trabalho. A metodologia adotada foi a pesquisa-a??o, o que permitiu a readequa??o da proposta ao longo de sua aplica??o. Os resultados foram muito promissores e mostraram que o ensino de f?sica com enfoque CTS, praticado atrav?s de uma abordagem tem?tica voltada para a realidade dos alunos, pode ser um meio de promover uma educa??o cient?fica de qualidade e formar cidad?os aptos a compreender o mundo e a sociedade em que vivem.

In this study, we investigated the effect of electrolyte composition, photoanode thickness, and the additions of GuSCN (guanidinium thiocyanate), NMB (N-methylbenimidazole), and SiO2 on the photovoltaic performance of DSSCs (dye sensitized solar cells). A bifacial DSSC is realized and irradiated from front and rear sides. The devices give maximum photovoltaic efficiencies for 70% PMII (1-propyl 3-ethylimidazoliumiodide)/30%(EMIB(CN)4)(1-ethyl-3-methyl-imidazolium tetracyano borate) electrolyte composition and 10 &mu / m thick photoanode coating which is considered to be the ideal coating thickness for the diffusion length of electrolyte and dye absorption. A significant increase in the photocurrent for DSSCs with optimum molarity of 0.1 M GuSCN was observed due to decreased recombination which is believed to be surface passivation effect at photoanode electrolyte interface suppressing recombination rate. Moreover, optimum NMB molarity was found to be 0.4 for maximum efficiency. Addition of SiO2 to the electrolyte both as an overlayer and dispersed particles enhanced rear side illuminated cells where dispersed particles are found to be more efficient for the front side illuminated cells due to additional electron transport properties. Best rear side illuminated cell efficiency was 3.2% compared to front side illuminated cell efficiency of 4.2% which is a promising result for future rear side dye sensitized solar cell applications where front side illumination is not possible like tandem structures and for cells working from both front and rear side illuminations.

In this thesis an educational test bench for studying the power quality attributes of the commonly used single-phase full-bridge diode rectifiers with power factor correction (PFC) circuits is designed and tested. This thesis covers the active and passive power factor correction methods for single-phase bridge rectifier. Passive filtering approach with dc side inductor and tuned filter along with active filtering approach via singleswitch boost converter is considered. Analysis, simulation, and design of a single phase rectifier and PFC circuits is followed by hardware implementation and tests. In the active PFC approach, various control methods is applied and compared. The educational bench is aimed to useful for undergraduate and graduate power electronics course, power quality related laboratory studies.

This thesis study presents the design, simulation, and fabrication of a low frequency electromagnetic micro power generator. This power generator can effectively harvest energy from low frequency external vibrations (1-100 Hz). The main objective of the study is to increase the efficiency of the previously proposed structure in METU-MEMS Center, which uses the frequency up-conversion technique to harvest energy from low frequency vibration. The proposed structure has been demonstrated by constructing several macro scale prototypes. In one of the constucted prototypes, the diaphragms are connected to a fixed frame via metal springs. The upper diaphragm having lower resonance frequency carries a magnet, and the lower diaphragm carries a hand wound coil and a magnetic piece for converting 6 Hz external vibrations up to 85 Hz, resulting a maximum voltage and power levels of 11.1 mV and 5.1 &micro / W, respectively. In an improved prototype, the metal springs are replaced with rubber ones, providing higher energy conversion efficiency and flexibility to tune the resonance frequency of both diaphragms to desired values. This prototype provides 104 &micro / W maximum power and 37.7 mV maximum voltage in response to vibration levels of 30 Hz. The proposed structure is also suitable to be realized by using microfabrication techniques. Hence, the structure to be microfabricated is studied and optimized for this purpose. When scaled to microelectromechanical dimensions, the expected maximum power and voltage from the 10 x 8.5 x 2.5 mm3 generator is 119 nW and 15.2 mV, respectively. A microfabrication process has also been designed for the proposed generator structure. According to this process, the structure consists of a stack of two pieces, each carrying different diaphragms. The diaphragms are made of parylene, and the coil and the magnetic piece are electroplated copper and nickel, respectively. As a result of this study, a new topology is proposed for harvesting energy at low frequency vibrations by the frequency up-conversion technique, and an efficiency improvement is expected with more than three orders of magnitude (119 nanoWatts output for the same size) compared to the study realized in our laboratory in converting low frequency (70-150 Hz) environmental vibrations to electrical energy.

In order to inject solar power to the utility grid, among various types of inverters, Grid Connected Transformerless Solar Inverters (GCTSI) are mostly preferred for residential or commercial applications. This preference is because of the high energy efficiency and low cost due to the absence of a line frequency or a high frequency transformer. Peak value of the efficiency characteristics of GCTSIs can reach 98%, which are selected topology, component optimization, switching strategy and operating condition dependent. In spite of the attractive energy efficiency characteristics of GCTSIs, due to the lack of galvanic isolation, these inverters are vulnerable to leakage currents, which are prohibitive for the safety and the maintenance reasons. The purpose of this research is to analyze GCTSIs in terms of their leakage current and energy efficiency characteristics. In the research, the leakage current mechanisms of GCTSIs are identified and grid connected solar inverters are classified in terms of their leakage current characteristics including the GCTSIs. In addition to the existing ones, several novel topologies are proposed enriching the family of GCTSIs. The leakage current and the inductor current ripple performances of GCTSI topologies are analyzed and evaluated by detailed simulations for 3 kVA and 10 kVA single-phase systems. In addition, the energy efficiency characteristics of GCTSIs are investigated in these power levels by making use of Calculated Average Power Per Switching Cycle (CAPPSC) method. The efficiency studies with CAPPSC method provide design guidelines and comparison of the GCTSI topologies in terms of their energy efficiency characteristics.

This thesis deals with the topic of nuclear energy. The Czech Republic is currently a net electricity exporter however this status will probably change in next few years because of growing electricity consumption and decommissioning of obsolete coal-fired power plants. Moreover, contemporary government declared that it won't approve any construction of new reactors stressing the importance of renewable sources of energy (in spite of their limited potential in the Czech Republic). The goal of this thesis is to answer the question whether nuclear energy can compete with other sources of energy and whether is it possible to satisfy growing electricity consumption under the conditions of the Czech Republic by any other source of electricity besides nuclear energy taking into account environmental aspects.

In this thesis, the conventional pulse-width modulated (PWM) and zero-voltage switching (ZVS) quasi-resonant buck converters are analyzed and a variable-frequency control technique is proposed to regulate the output voltage due to the immediate input line and load changes. The quasi-resonant technique provides favorable switching conditions for active switch to reduce switching losses and electromagnetic interference (EMI). The method is based on shaping the voltage across the active switch in quasisinusoidal fashion and the switching action occurs with nearly zero voltage across the active switch. This requires only two additional components to the conventional PWM buck converter. The proposed quasi-resonant converter is capable of operating in megahertz range with a significant improvement in performance and power density. Detailed analytic and small-signal models of the ZVS quasi-resonant buck converter are established and the switching behavior is investigated in order to provide nearly zerovoltage turn-on. The performance of the ZVS quasi-resonant technique is verified with the computer simulations. The results are compared with the experiments in the laboratory involving both the open-loop and closed-loop operations. The detailed experiment procedure is added to use this converter for educational purposes.

In this thesis design, optimization, fabrication and performance characterization of MEMS thermoelectric (TE) energy harvesters for harnessing waste heat in mobile systems are presented. As a proof of concept, chromium and nickel are used as the thermoelectric material in the proposed design. The feasibility of the state of the art thermoelectric materials is also discussed. MEMS TE energy harvesters proposed in this study are designed to generate power at relatively lower &Delta / T values. The performance of the MEMS TE energy harvesters was optimized using analytical and 3-D finite element models. An analytical code was used for profiling the electrical power output with varying geometry. The design points with maximum generated power were selected, and the microfabricated thermoelectric energy harvesters were designed accordingly. The fabricated devices are formed on a silicon wafer and composed of Nickel and Chromium thermocouples on SiO2/Si3N4 diaphragms, and Titanium heater and monitor resistors for testing purposes. Microfabrication was followed by the performance characterization of MEMS TE energy harvesters with the conducted tests. For 10 &deg / C temperature difference between the hot and cold junctions (a heat source at 35 &deg / C), the proposed TE energy harvesters are capable of providing 1.1 &micro / W/cm2 power density and 1.71 V voltage. The performance of the thermoelectric generators in general is limited by Carnot cycle efficiency. Nevertheless, the validated practical performance of MEMS TE energy harvesters proposed in this thesis is comparable to other examples in literature. It is anticipated by the calculations that this design will be able to provide the highest thermoelectric efficiency factor (4.04 &micro / W/K2cm2) among the lateral TE energy harvesters if thermoelectric materials having high Seebeck coefficient values (such as p-Si, n-Si, polysilicon, Bi2Te3 etc.) are used. According to the performance results, the MEMS TE energy harvesters can be implemented in mobile systems to convert waste heat into electricity. The fabrication process can be adapted to CMOS with some modifications if needed. The lateral MEMS thermoelectric energy harvesters can also be combined with vibration energy harvesters to realize multi-mode energy scavenging. For prospective study, vertical thermoelectric generator configurations are also discussed in order to further increase the power density generated. The finite element simulations for proposed vertical configurations with air and water convection were completed. The vertical TE generators proposed can supply up to 4.2 mW/cm2 with a heat source at a temperature of 310 K.