A geração de eletricidade fundamentada na complementariedade pelas fontes renováveis como a solar fotovoltaica distribuída, tem se tornado relevante e essencial para o fornecimento de energia elétrica no modelo atual das redes elétricas em ambientes urbanos. Porém, tendem a ser impactadas por diversos fatores, tais como sujidade, temperatura, degradação, ângulo de orientação e inclinação, bem como topografia do terreno e qualidade de fabricação do módulo. Somasse o sombreamento parcial de elementos do entorno, o qual é o principal fator que afeta a produtividade do sistema fotovoltaico. Esta tese tem como objetivo propor um método para posicionar módulos fotovoltaicos de maiores potências nominais nas regiões com maiores índices de irradiação da planta, para formar associações de módulos que iram operar em semelhantes condições de irradiação durante todo o ano e quantificar a influência da incompatibilidade elétrica devido as diferenças de fabricação dos módulos. Métodos tradicionais de simulação da estimativa de produção anual consideram módulos idênticos e não permitem importar arquivos flash test de cada módulo utilizado na planta fotovoltaica. O método proposto incluiu a análise de irradiação (sombreamento) global média diária anual de cada módulo e desenvolvimento de algoritmo em MATLAB para estudo da incompatibilidade elétrica e posicionamento. O método foi desenvolvido para um estudo de caso teórico de um estacionamento fotovoltaico com sombreamento parcial na cidade São Paulo, no qual o catálogo do módulo e os flash tests foram disponibilizados pelo fabricante. Os resultados do estudo mostram para uma associação série da planta, variação entre -1,4 e +1,2 Wp entre os valores máximos e mínimos da PMPP, indicando um desvio em relação ao valor médio de 0,57% e 0,48%, resultando uma queda da tolerância relativa à qualidade do módulo em comparação com os valores praticado nas simulações. Sendo obtida uma potência total média teórica de 5,922 kWp, enquanto que em uma ordenação aleatório teríamos uma potência total média teórica de 5,880 kWp, ou seja, -40,49 Wp (0,7%) inferior em comparação com a associação série na qual foi aplicado o algoritmo de ordenação. / The energy generation based on the complementary renewable sources as distributed photovoltaic solar energy, has become relevant and essential for current model of energy supply in the urban environment. However, tend to be impacted for several conditions whereby soiling, temperature, degradation, ground topology, orientation and tilt angle, manufacturing tolerances of photovoltaic module. In addition, the partial shading due to the surrounding elements, which is the main factor that decrease the yield of photovoltaic systems. The objective of this thesis is to propose a method to positioning the higher nominal power photovoltaic modules in the regions with higher homogeneous solar irradiance of the plant, to form a string of photovoltaic modules that will operate in a similar ambient condition during the whole year and quantify the influence of electrical mismatch due to small manufacturing differences. Traditional solar simulation tools not allow flash test dataset inputs, often modeled them as an identical devices to estimate the annual energy production. The method consists in identifying and quantifying the reduction of electrical mismatch tolerance, relating the irradiance (shading) on each photovoltaic module and propose a Matlab algorithm to study the electrical mismatch. The method was developed through a theoretical study case of a parking-integrated photovoltaic with partial shading simulated in São Paulo city for which module datasheets as well as flash test data are available. The results show that the percentage deviation of mismatch tolerance for a string of 24 modules when applied the sorting algorithm was reduced among 0.57% (1.4 Wp) and 0.48% (1.2 Wp), between the lowest and highest value of the average nominal maximum power of 245 Wp, when compared with randomly ordered of ± 2.5% (± 6 Wp). In terms of energy production for the string, these values represents an average theoretical nominal power of 5.922 kWp for sorting algorithm and 5.880 kWp considering the random ordered, which represents a PV string energy production of -40.49 Wp (0.7%) lower without the method proposed.

Esta dissertação tem por objetivo determinar a contribuição de uma unidade habitacional unifamiliar, que utiliza o sol como fonte principal de energia, e adota premissas e estratégias de uma Casa Solar, para a conservação e geração de energia, e redução de emissões de GEE. O Sistema Interligado Nacional (SIN) de eletricidade é analisado considerando as fontes de geração, emissões de GEE associadas e as previsões de expansão. São estudados o potencial e as limitações para a inserção da fonte solar fotovoltaica na matriz de energia elétrica brasileira. O consumo de eletricidade do setor residencial é caracterizado, considerando as previsões de aumento da demanda por eletricidade. São elencadas e estudadas as premissas e estratégias de uma Casa Solar, com foco no aproveitamento do sol na arquitetura e no uso de sistema de aquecimento solar (SAS) e sistema fotovoltaico (SFV). Estas premissas e estratégias são demonstradas de forma aplicada por meio do protótipo Ekó House, um modelo de residência de energia zero (REZ) que incorpora as premissas e estratégias de uma Casa Solar. As estratégias bioclimáticas e os sistemas solares são analisados considerando sua aplicação na cidade de São Paulo. A análise qualitativa de estratégias passivas e de baixo consumo para o condicionamento térmico demonstram um potencial de se aumentar em até 70% as horas de conforto no ano. Dentro dos parâmetros definidos e considerando um valor médio de consumo residencial, a adoção de tecnologias mais eficientes para iluminação demonstra um potencial de reduzir o consumo de eletricidade em até 12,5%, e o uso de SAS apresenta um potencial para conservar até 16,3% da eletricidade consumida. A geração de energia elétrica por SFV, associada à adoção medidas de eficiência energética, demonstra potencial para atingir um balanço energético próximo a zero ou positivo. Com isso, estima-se um potencial de se evitar até 1,66 t CO2 de emissões ao ano por unidade habitacional. / This dissertation aims to determine the contribution of a single-family dwelling unit that harnesses the sun as a main energy source, and adopts guidelines and strategies of a Solar House, aiming energy conservation and generation, and GHG emissions reduction. The Brazilian interconnected electricity system is analyzed regarding energy sources, associated GHG emissions and expansion projection. The electricity consumption in residential sector is characterized, considering the projections of increase in electricity demand. The guidelines and strategies for a Solar House are studied, focusing on the harnessing of sun in architecture and solar systems for domestic hot water (DHW) and electricity generation by photovoltaic (PV) systems. The practical application of these guidelines and strategies is exemplified by the Ekó House prototype, a zero energy dwelling housing model that incorporates Solar House guidelines and strategies in its design. Bioclimatic strategies and solar systems are analyzed considering their application in São Paulo city. The qualitative analysis of passive and low consumption strategies points out a potential of increasing 70% of comfort hours in a year. Within the parameters defined and considering the Brazilian average consumption for dwellings, it is shown that the adoption of efficient technologies for lighting can save up to 12.5%, and solar systems for DHW can save up to 16.3% of electricity consumption. The PV electricity generation associated to energy efficiency measures can reach a near zero energy balance or even a positive energy balance. Thus, it is estimated a potential of avoiding up to 1.66 t CO2/year for each dwelling.

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.

Made available in DSpace on 2017-07-10T15:14:41Z (GMT). No. of bitstreams: 1 Willian_Rottava.pdf: 1085103 bytes, checksum: 2e8e2f0008a606c2c158e781ccd9907b (MD5) Previous issue date: 2016-04-06 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work aimed to develop and evaluate an electrolytic reactor system for the production of hydrogen gas by applying an electromotive force from solar energy. Solar energy is converted into electrical energy through photovoltaic panels and the method of electrolysis was generated hydrogen gas. To carry out the work, different electrodes and electrolytes were tested to determine the best combination to be applied in the reactor on a pilot scale. Developed an electrolytic reactor with unipolar electrodes and graphite using formic acid electrolyte with added glycerol. After a series of tests, the graphite electrode was chosen primarily for its ease of acquisition and use, and also due to the good performance. The electrolyte with higher hydrogen production using graphite was added formic acid with glycerol at 40 °C, with the addition of 0,1% glycerol at 25 °C gave a 313,2% increase in hydrogen production compared to using only formic acid / Este trabalho desenvolveu e avaliou um sistema de reator eletrolítico para a produção de gás hidrogênio aplicando uma força eletromotriz proveniente de energia solar. A energia solar foi convertida em energia elétrica por meio de painéis fotovoltaicos e, pelo método da eletrólise, gerou-se o gás hidrogênio. Para a realização do trabalho, foram testados diferentes eletrodos e eletrólitos para determinar a melhor combinação a ser aplicado no reator em escala piloto. Desenvolveu-se um reator eletrolítico do tipo unipolar com eletrodos de grafite e utilizando-se de eletrólitos de ácido fórmico com adição de glicerol. Após uma série de testes, o eletrodo de grafite foi escolhido, principalmente pela facilidade de aquisição e utilização e também devido ao bom desempenho. O eletrólito com maior produção de hidrogênio utilizando o grafite foi o ácido fórmico com adição de glicerol a 40° C, sendo que a adição de 0,1% de glicerol a 25° C proporcionou um aumento de 313,2% na produção de hidrogênio em relação à utilização de somente ácido fórmico.

The ever-increasing challenges that we face with our consumption of resources on Earth are factors which have prompted researchers to show interest in studying the possibilities of human habitat on other celestial bodies. Mars is a stone planet and is at such distance from the sun that it could be feasible for future settlements with the right technology and solutions. Future missions to Mars rely on solar panels as their primary power system. Utilizing solar architecture is a solution that reduces both a building’s energy consumption and the extent of environmental damage fossil fuels are causing the Earth. This leads to extensive opportunities to explore how we can increase the use of renewable energy using new technologies developed for use on Earth but also for use in the space industry.   This study used a qualitative method through literature studies and semi-structured interviews as well as a quantitative method through calculations. The literature study was meant to act as a theoretical base for this study and for the interviews by creating an understanding of the world’s usage of renewable and non-renewable energy sources and how solar power works by the means of photovoltaic cells. The interviews were held to identify the opportunities and obstacles regarding a solar power system on Mars as well as the usage of BIPV (building-integrated photovoltaics) in extreme environments. Mathematical calculations were based on the fundamental geometric shape of a cylinder where the walls were set to be the varying parameter. Six locations on Mars with different coordinates and underlying matters were selected to the study based on the knowledge collected from the literature study and the interviews.   Aspects that needs to be considered for building-integrated photovoltaics placed on a building’s envelope on Mars are several. Some of the most crucial are: dust deposition and dust in the atmosphere, a climate with major temperature extremes, the habitats location on the planet and the amount of output energy provided by BIPV partly affected by the Mars-Sun distance. If the fundamental geometric shape of the building is a cylinder, the building’s shape would to form as a truncated cone with smaller wall slopes the closer the equator the habitat is located. If the habitat is placed far away from the equator the walls’ slope, the optimal tilt angle of the photovoltaic module, would be steeper and increase with the higher latitude. The maximized power by using BIPV on a building on Mars is provided as close to the equator as possible due to the big amount of sunlight reaching the surface. If BIPV could be used on the Martian surface is still a relatively extensive hypothesis. Studies about Mars and other planets tend to result in this kind of approach because of the many insecurities that cannot be proven before humans get to the planet or detailed tests have been accomplished and analyzed. A solar power system shows great opportunities for future human missions to Mars but BIPV is not considered an option in the near future without further research and development verifying the option.

After the Second World War, there was an expression of interest in the study of the future. In order to achieve reliable objectives, several methods of scenario planning were invented. These methods comprise of qualitative and quantitative approaches inherited from their own school of origin. Each approach has advantages and limitations that can be observed by the study of each method in progress. However, mixed approaches often show a weak connection between qualitative and quantitative methods. The use of fuzzy cognitive maps (FCMs), among scenario planning approaches, can overcoming the limitations of qualitative and quantitative techniques. This study focused on the problem of the lack of proper planning of scenarios based on FCMs in the alternative energy sectors, raising the question of whether this situation comes from a shortage of information or limitations of the FCMs. To resolve this problem, this study investigated benefits and limitations of FCM-based scenario planning through the application in the Brazilian photovoltaic sector. The following specific objectives were established: identify the strong and weak points of FCMs; analyze the expansion of these to different areas; identification of the main stakeholders used to develop FCM-based scenarios; application of the method in the Brazilian solar energy sector. We identified an increasing number of studies on FCMs in several new areas not considered in previous studies. This suggests that experts are expanding frontiers and recognizing the interdisciplinary potential of FCMs and their robustness of solving diverse kinds of problems. The main contribution of the research is to present the benefits and limitations of FCM-based scenario planning. For that, a scenario planning method was presented and the empirical evidence of its effectiveness was presented in the context of the Brazilian photovoltaic solar energy sector. / Após a Segunda Guerra Mundial, houve um crescente de interesse no estudo do futuro. Para alcançar objetivos confiáveis, foram inventados vários métodos de planejamento de cenários. Esses métodos possuem abordagens qualitativas e quantitativas herdadas de sua própria escola de origem. Cada abordagem possui vantagens e limitações que podem ser observadas pelo estudo de cada método. No entanto, abordagens mistas muitas vezes mostram uma conexão fraca entre métodos qualitativos e quantitativos. O uso de fuzzycognitivemaps (FCMs), no planejamento de cenários, pode superar as limitações das técnicas qualitativas e quantitativas. Este estudo centrou-se no problema da falta de planejamento adequado de cenários baseados em FCMs nos setores de energia alternativa, levantando a questão de saber se esta situação vem da escassez de informações ou das limitações dos FCMs no planejamento estratégico. Para resolver este problema, este estudo investigou os benefícios e as limitações do planejamento de cenários baseado em FCM através da aplicação no setor fotovoltaico brasileiro. Foram estabelecidos os seguintes objetivos específicos: identificar os pontos fortes e fracos dos FCMs; analisar a expansão destes para diferentes áreas; identificar os principais stakeholders utilizados para desenvolver cenários baseados em FCMs; aplicar o método no setor de energia solar brasileira. Identificamos um número crescente de estudos sobre FCMs em várias novas áreas não consideradas em estudos anteriores. Isso sugere que os especialistas estão expandindo as fronteiras e reconhecendo o potencial interdisciplinar dos FCMs e sua robustez na resolução de diversos tipos de problemas. A principal contribuição desta pesquisa é apresentar os benefícios e as limitações do planejamento de cenário baseado em FCM. Para isso, foi apresentado um método de planejamento de cenários e a evidência empírica de sua eficácia foi apresentada no contexto do setor de energia solar fotovoltaica brasileira.

<p>There is an increased discharge of produced water in the USA, which is causing decrease in the amount of usable water and is being rendered useless by refinery and extraction operations. Produced water that is obtained from these activities is usually not feasible to be used in any form. So, it becomes necessary to get the water to a quality standard, as per the US EPA, which will make this water suitable for both commercial as well as household purposes.</p><p> </p><p>There have been a number of studies on Au, Ag and Carbon Nanotubes solar enabled steam generation with potential applications in water purification, distillation and sterilization of medical equipment. The key challenge with these nanoparticles is cost of production, hence limiting its wide application for clean water production. This work, for the first time, reports on activated carbon enabled steam generation hence addressing the cost limitations of metallic nanoparticles. Activated carbon has high solar absorptivity at various wavelengths of visible light.</p><p> </p>This work uses Activated Carbon coated Polyurethane foam to simultaneously adsorb oil from the produced water and also yield surface vapors under application of solar light to get a clean distillate which can be used in various ways be it commercial or household. The given fabricated system will be an inexpensive and simple method to get clean water. The temporal evolution of the distillate has been measured as well as the temperature characteristics. Experiments were carried out using activated carbon and CNT nanofluids and polyurethane membrane with immobilized activated carbon and CNT. A simulated solar light of 1 KW ~1 Sun was used. The rate of evaporation, temporal and spatial evolution of bulk temperature in the water were monitored automatically and recorded for further data reductions. Parametric studies of the effect of nanoparticle concentration, water quality and salinity were performed. Experimental evidence showed that activated carbon has potential. Previous work reported for the first time that optimal activated carbon concentration for maximum steam generation is 60 % vol. There was a 160 % increase in steam production rate at 60 % concentration of activated carbon when compared with D.I. water.Different atmospheric conditions were varied and the concentration of the sun to see the effects on the production of water. The recovery capacity of the foam was also tested so as to determine the waste oil that can be obtained from the foam and if the foam can be reused without being disposed of. More than 95% oil can be recovered The quality analysis has been performed and is an integral focus of the work as the comparison with the USA EPA (Environmental Protection Agency) will make it more robust and real world ready. The inclusion of Polyurethane foam, which is a major accumulating waste in the environment because of its use in packaging industry, and solar light as the energy source, to drive the distillation process, makes this a very clean and green process to treat produced water.

Methods of generating renewable energy such as through solar photovoltaic (PV) cells and wind turbines offer great promise in terms of a reduced carbon footprint and overall impact on the environment. However, these methods also share the attribute of being highly stochastic, meaning they are variable in such a way that is difficult to forecast with sufficient accuracy. While solar power currently constitutes a small amount of generating potential in most regions, the cost of photovoltaics continues to decline and a trend has emerged to build larger PV plants than was once feasible. This has brought the matter of increased variability to the forefront of research in the industry. Energy storage has been proposed as a means of mitigating this increased variability -- and thus reducing the need to utilize traditional spinning reserves -- as well as offering auxiliary grid services such as peak-shifting and frequency control. This thesis addresses the feasibility of using electrochemical storage methods (i.e. batteries) to decrease the ramp rates of PV power plants. By building a simulation of a grid-connected PV array and a typical Battery Energy Storage System (BESS) in the NetLogo simulation environment, I have created a parameterized tool that can be tailored to describe almost any potential PV setup. This thesis describes the design and function of this model, and makes a case for the accuracy of its measurements by comparing its simulated output to that of well-documented real world sites. Finally, a set of recommendations for the design and operational parameters of such a system are then put forth based on the results of several experiments performed using this model.

A Metal-Insulator-Metal (MIM) diode is a high frequency device used for energy harvesting purpose in the RECTENNA. The main objective of this thesis work is to design, fabricate and characterize a thin-film MIM diode. A key issue associated in this research work is the development MIM diode with nanometer thin insulator region. The reason for the development of MIM diode is to rectify a wide spectrum of AC signal to usable DC power. In this thesis work, a planar MIM diode with Aluminum/Aluminum-Oxide/Gold has been fabricated. The thickness of the insulator region obtained was about 3nm. The Metal and insulator depositions were done by sputtering and plasma oxidation, respectively. I-V Characteristics of the diode was measured by making use of in-house set-up and 70% of the devices on a single wafer yielded with better result. Most of the I-V curves obtained were highly non-linear and asymmetric. Based on the I-V measurement, the logarithmic derivative of I vs. V was plotted and the tunneling behavior was also observed.

The present project has made a comprehensive assessment of the effect of Nb doping on various charge-transfer related properties of TiO2. Of particular focus, the electrical properties of Nb-doped TiO2 (0.65 at %) have been investigated using the simultaneous measurement of electrical conductivity and thermoelectric power. This investigation was undertaken at elevated temperatures (1073 K -- 1298 K) in equilibrium with a gas phase of controlled oxygen activity (10-10 Pa < p(O2) < 75 kPa). In addition, the effect of segregation on the surface versus bulk composition of Nb-doped TiO2 was also investigated at a function of temperature and oxygen activity. Specifically, the following determinations were undertaken: The effect of oxygen activity, p(O2) and temperature on both electrical conductivity and thermoelectric power The effect of Nb on the defect disorder and related electrical properties of TiO2 The determination of equilibration kinetics and the associated chemical diffusion data for Nb-doped TiO2 The determination of Nb bulk diffusion in TiO2 The effect of p(O2), temperature and dopant content on Nb segregation and the related surface composition of Nb-doped TiO2 The obtained electrical properties enable the determination of a defect disorder model for Nb-doped TiO2, which may be considered within the following p(O2) regimes: Strongly Reduced Regime. In this regime, the predominant ionic defect was anticipated to be oxygen vacancies compensated electronically by electrons. While the transition to this regime (from higher p(O2)) was clearly observed, the predominant defect disorder existing beyond this transition was not confirmed due to an inability to obtain sufficiently low oxygen activity. Metallic-type conductivity behaviour was observed within this transition region. Reduced Regime I. In this regime, the predominate defect disorder defined by the electronic compensation of incorporated Nb ions by electrons was clearly observed. Reduced Regime II. In this regime, the predominate defect disorder defined by the ionic compensation of incorporated Nb ions by quadruply-charged titanium vacancies, was clearly observed. The present project included the determination of diffusion data which included: Temperature dependence of 93Nb tracer diffusion in single crystal TiO2 over the temperature range 1073 K -- 1573 K Chemical diffusion coefficient over the temperature range 1073 K -- 1298 K and oxygen activity range, 10-10 Pa < p(O2) < 75 kPa These pioneering studies are significant as they enable the prediction of the processing conditions required to reliably 1) incorporate Nb into the TiO2 lattice, and 2) achieve equilibrium with the gas phase. Finally, the present project included investigations on the effect of Nb segregation on the surface composition of Nb-doped TiO2, with the following outcomes: Due to segregation, the surface can be significantly enriched in Nb compared to the bulk The extent of enrichment increases as the bulk Nb content or the oxygen activity is decreased Following enrichment, the surface Nb concentration could be sufficiently high to assume a unique surface phase The outcomes of the present project are significant as they can enable the processing of TiO2 with enhanced charge transport and controlled surface properties.