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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Absorber and Window Study – CdSexTe1-x/CdTe Thin Film Solar Cells

Hsu, Chih-An 17 January 2019 (has links)
CdTe an II-VI semiconductor has been a leading thin film photovoltaic material due to its near ideal bandgap and high absorption coefficient [1]. The typical thin film CdTe solar cells have been of the superstrate configuration with CdS (Eg-2.42eV) as the n-type heterojunction partner. Due to the relatively narrow bandgap of CdS, a wider bandgap n-type window layer has recently emerged as a promising substitute: alloys of MgyZn1-yO have been successfully used as the emitter or window layer. The benefits in the usage of MgyZn1-yO (MZO) are its tunable bandgap and wide optical spectrum on optoelectronic devices. Due to an increasing bandgap of the window layer, the carrier collection can be improved in the short wavelength range (<500 nm). In addition alloys of CdSexTe1-x (CST) have also been used in the absorber layer (i.e., CST/CdTe) for the fabrication of CdTe devices to improve the carrier collection and lifetime [2]. The lower bandgap of the CST alloy can lead to higher short-circuit current (JSC), but it can also result in lower open circuit voltage (VOC). Another critical aspect of the CdTe solar cell is the use of copper as a p-type dopant, which is typically incorporated in the cell during the fabrication of the back contact. The most challenging issue related to further advancing the CdTe solar cell efficiency is the relatively low level of p-type doping, which limits the VOC. Efforts to dope CdTe with group V dopants are yet to produce the desired results. ZnO has been used as an effective high resistivity transparent. When CdTe is deposited directly on sputtered ZnO, VOC of typically 500-600 mV is produced. Band alignment measurements indicate that a negative conduction band offset with CdS exists; alloying with MgO to produce MgyZn1-yO with a composition of y = 0.15 can produce a flat conduction band alignment with CdS. This material has an additional benefit for improving the energy bandgap of the MZO for better UV light transmission in the short wavelengths. By changing the magnesium content from y = 0 to 0.30 allowed researchers to make the tunable conduction band offset from a “cliff” to a “spike,” with both increased open-circuit voltage and fill factor as increasing magnesium compositions [3] — the bandgap gains as expected with increased magnesium composition. The large compositions (y > 0.30) of MgyZn1-yO cause the enormous spike result in S-kink in the IV measurement so that the FF decreases. Besides, due to the instability of MZO material, the fabrication process has to proceed carefully. The properties of CST films and cells were investigated as a function of Se composition (x), substrate temperature (TSUB), and ambient used during the CSS deposition. The higher ratio of Se in CST alloy causes the smaller grain structures and lower bandgap, which profoundly detrimental to the device performance (VOC). However, the CST can be deposited in various substrate temperatures and different inert ambient gas to improve the grain structure by utilizing the especial Close Space Sublimation (CSS) deposition system. Therefore, despite the fact that the CST (25% Se) has the optical bandgap (1.37eV), the improvement of grain structure can slightly increase the doping concentration and decrease the grain boundary (GBs) due to increased alloys grain size 3X larger, which is contributed to improving the VOC [4]. The study of higher ratio Se of CST alloy is significant to achieve the high efficiency polycrystalline CST/CdTe photovoltaic devices. The effect of Cu doping back contact in CdSexTe1-x (CST)/CdTe solar cells with varying amounts of Se (x) has been investigated. The Cu-based back contact was annealed at different thermal temperatures in order to vary the amount of Cu in-diffusion. Net p-type doping was found to increase as the back-contact annealing temperature increased. All cells exhibited a decrease in VOC with increased annealing temperature (i.e., higher Cu concertation), presumably due to a degradation of the lifetime with increased amounts of Cu [5]. However, cells with the highest Se composition appeared to exhibit a higher degree of tolerance to the amount of Cu – i.e., they exhibited a smaller loss in VOC with the increased amount of Cu. Extrinsic p-type doping of CdSeTe can be fabricated using two different experimental processes. Firstly, by using group I elements such as, Cu to substitute Cd, which is promising during the back contact process. Secondly, using group V (P, As, Sb) elements to substitute Te, and this is suitable for Cd-rich of intrinsic CdTe. Intrinsic CST alloy has lower hole density concentration as higher Se composition with limitation of the VOC. Thus, in order to increase the p-type net doping up to 1016 cm-3 the extrinsic P or As doping have been widely investigated recently. The research studies show the CST/CdTe devices lead to improve VOC up to 850 mV with higher hole density in higher Se compositions of As doped CST alloys. Nevertheless, the group V doped CdTe still cause the formation of compensating defects limits the upper boundary of dupability on the CdTe thin film solar cells. Even if a high hole density concentration is achieved for intrinsically-doped p-type CST/CdTe, it is believed the poor carrier lifetime in the CdTe side would still limit the VOC.
42

Design and Testing of a Reciprocating Wind Harvester

Topcuoglu, Ahmet 24 June 2019 (has links)
Renewable energy sources are vital to reduce dependence on fossil fuels that are harmful for the environment and release greenhouse gases causing global warming. Wind energy is a natural source of energy that is abundant in the environment. While wind turbines are most popular, convenient, and used to harvest energy at large scales, there have been recent studies focusing on harvesting energy from the wind for microdevices. Such micro wind energy harvesters can decrease dependence on batteries. In this study, a novel, framed flag micro wind harvester was designed and tested, and its behavior at three different wind speeds was experimentally examined in a wind tunnel. The main purpose of this study is to determine the geometric and wind speed conditions under which regular flapping occurs in the flag material. A high-speed camera was used to visualize the motion of the harvester at different wind speeds and at various parametric ratios of the flag material length to the frame length. The movies taken by the camera are analyzed using Image J software to find the flapping frequency, flapping angle, and the amplitude. Nondimensional parameters such as the Re number and St number also are calculated. This study finds that parametric ratios of 1.1 and 1.2 with the medium wind speed condition of 5 m/s are optimal flapping conditions. These optimal conditions would conveniently allow the use of piezoelectric material as the flag material in order to harvest energy. Further, an advantage of this novel design over previous designs is that the wind harvester naturally aligns with the wind direction and is thus omnidirectional.
43

Phenomenological Study on Female Engineering Leaders in the New York Utility Industry

Gonsalves, Shelanda 01 January 2018 (has links)
This qualitative phenomenological study explored the development of women with an engineering background who became leaders. The purpose of this study was to explore the lived experiences of female engineering leaders in the New York utility sector. The research problem was why few women with engineering degrees obtain leadership positions. Women comprise half the total working population, yet few hold leadership positions, especially in the utility sector. In this study, 28 women in the New York utility sector shared experiences on their progression from engineer to leadership. The conceptual framework was the Moustakas phenomenological approach, investigating the humanistic properties of female leaders with backgrounds in engineering and Bandura's social cognitive theory on the role of self-efficacy for women. Through the phenomenological approach, in-depth interviews captured the challenges and successes each woman has faced and identified themes that emerged from those experiences. The modified van Kaam method of phenomenology was used for data analysis to capture the experiences and perceptions of female engineers in leadership positions. Key findings from this study indicated how working in teams helped build the self-efficacy of women during their undergraduate studies and fostered effective teamwork in their work environment. Work-life balance encouraged female engineering leaders to go further in their career because it allowed them stability and the ability to advance. Through this study, positive social change may occur for women seeking to pursue engineering degrees who are striving for leadership roles in traditionally male fields.
44

Preliminary investigation for underground storage of pipeline gas in the Bruer and Flora pools, Mist gas field, Columbia County, Oregon

Townley, Paul Joseph 01 January 1985 (has links)
Northwest Natural Gas Canpany has proposed to convert the Bruer and Flora pools of the Mist Gas Field in west-central Columbia County, Northwestern Oregon, to pipeline gas storage reservoirs. Conversion to underground storage of pipeline gas in these depleted gas reservoirs would be the first in the Pacific Northwest. The Bruer and Flora Pools are fault trapped within the Cowlitz Formation. The shales overlying the Cowlitz Formation create a local seal for these gas reservoirs. X-ray diffraction and density log measurements suggest that the clay in these shales is primarily composed of smectite, which provides an excellent caprock seal. The reservoir rock of the Bruer and Flora Pools is the arkosic Cl ark and Wilson Sand. An average weighted grain density for the sand is 2.65 g/cm3. The abundance of potassium feldspar in the sand, hence K40, creates a background gamma radiation for the sand roughly equal to that of the shale, making the sand and shale virtually indistinguishable on the gamma ray log. Bottan Hole Temperatures (BHT), which were recorded on open hole logs, indicate the Bruer Pool is 7°C (20°F) wanner than the Flora Pool, even though the Flora Pool is deeper. This temperature anomaly may be the result of equipment variation. A calibrated temperature survey would remove any discrepancies. A comparison of the thermal gradient determined in a previous study of the Oregon Coast Range and a gradient determined using BHT, suggest that BHT provide a good approximation of formation temperature. Utilizing the formation water analysis determined from four different wells in the Mist Gas Field, average total dissolved solids was found to be 24, 444 mg/l. Of the four analyses, the sample from Well CC#6 R/D2 is considered to be the most representative of the Bruer and Flora fools formation waters. Analysis of the four samples using the Palmer System suggests that the formation water of the Cowlitz Formation is in the early stages of sea water diagenasis. Formation water resistivity (Rw) was determined using a chemical and spontaneous potential analysis. Rw derived using chemical analysis averaged 0.175 ohm-meters and is considered the ITDst precise. Water saturation determined using the Archie saturation equation averaged 47.5% and ranged from 26.4 to 80.0% for the zone 814-836 meters (2670-2742 feet) in CC#10. These results are similar to those determined by the Thermal Time Decay (TDT) log.
45

Ecosystem Enriching and Efficient Solar Energy: Exploring the Effects of Pollinator-Friendly Solar Facilities on Ecosystem Function and Solar Panel Efficiency

Martin, Jordan 01 January 2022 (has links)
As the solar energy industry grows, many hundreds of thousands of acres of land will be transformed into solar panel facilities. With this large change in land use, there is the opportunity to promote biodiversity and support pollinators by using pollinator-friendly management practices at the solar facilities. This paper explores the ecological and economic effects of a pollinator-friendly solar facility compared to a turfgrass solar facility. I hypothesized that a pollinator-friendly solar facility would be functionally equivalent in pollinator support and overall insect diversity to a pollinator-friendly non-solar field and that both sites would have far greater pollinator support and insect diversity than a turfgrass solar field. To test this hypothesis, vegetation and insect sampling were conducted and the resulting data were analyzed for differences in vegetative and insect diversity and pollinator abundance at a pollinator-friendly solar facility, a turfgrass solar facility, and a reference non-solar pollinator-friendly field. The diversity analysis revealed that the pollinator-friendly solar site was overall functionally equivalent to the non-solar pollinator-friendly site and the turfgrass solar site had low insect and vegetative diversity, but high insect abundance. Photovoltaic solar panel energy production is negatively affected by high temperatures. Therefore, to maximize energy production and promote biodiversity native forbs may be incorporated into a solar facility landscape to cool the solar panels by the cooling effect of transpiration and produce more energy than a traditional turfgrass landscaped solar facility throughout the growing season. This study tested that hypothesis by analyzing environmental and vegetation data from two solar facilities, one with a turfgrass landscape and one with a pollinator-friendly forb-dominated landscape. Irradiance, ambient temperature, panel temperature, and percent forb ground cover were recorded for a section of solar panels at each site throughout the 2021 growing season. This data was used to create generalized linear models (GLMs) for predicting panel temperature and humidity based on irradiance, ambient temperature, site, and the interactions between each of them. The predictions made by the panel temperature predicting model supported the hypothesis that the pollinator-friendly landscape had a greater cooling effect than the turfgrass landscape under high and medium irradiance conditions. But this cooling effect was not seen under low irradiance conditions. This suggests that the negative effect of high temperatures on energy output is only significant under high irradiance conditions. Overall, this study supports the idea that pollinator-friendly landscapes could be more economically viable, as pertaining to energy output, and more ecologically beneficial compared to turfgrass. More research is necessary to further investigate and test the patterns seen at only these two solar sites, but these results are encouraging for the future widespread implementation of pollinator-friendly management practices in solar facilities across the Mid-Atlantic.
46

Renewable Energy Investment Planning and Policy Design

Ghalebani, Alireza 08 April 2016 (has links)
In this dissertation, we leverage predictive and prescriptive analytics to develop decision support systems to promote the use of renewable energy in society. Since electricity from renewable energy sources is still relatively expensive, there are variety of financial incentive programs available in different regions. Our research focuses on financial incentive programs and tackles two main problem: 1) how to optimally design and control hybrid renewable energy systems for residential and commercial buildings given the capacity based and performance based incentives, and 2) how to develop a model-based system for policy makers for designing optimal financial incentive programs to promote investment in net zero energy (NZE) buildings. In order to customize optimal investment and operational plans for buildings, we developed a mixed integer program (MIP). The optimization model considers the load profile and specifications of the buildings, local weather data, technology specifications and pricing, electricity tariff, and most importantly, the available financial incentives to assess the financial viability of investment in renewable energy. It is shown how the MIP model can be used in developing customized incentive policy designs and controls for renewable energy system.
47

An Investigation Into the Origin, Composition, and Commercial Significance of a Sedimentary Subsalt Formation: Keathley Canyon, Gulf of Mexico

Brassieur, David Aaron 16 December 2016 (has links)
Sub-salt oil and gas formations in deep-water northern Gulf of Mexico are high priority targets. Advances in seismic processing allow for high-resolution, below-salt imaging. Understanding the modes of salt emplacement provide insight into sub-salt traps and potential drilling hazards. A sub-salt sedimentary unit lies in the Keathley Canyon protraction. Autosutures created the transport-parallel lineaments of the upper surface of the unit. In addition, highly variable sediment aggradation rates created ramps, flats, and basal cutoffs along the base of the allochthon as salt and sediment competed for space. Seismic models identify modes of salt emplacement, salt/sediment interactions, and mechanisms responsible for the morphology. Petrophysical assessments highlight an abnormally pressured, dirty salt environment transitioning into a gouge zone. Dirty salt adds an element of difficulty to managing borehole pressures requiring a unique mud-weight plan designed to resist formation pressures without fracturing lithology.
48

Submarine Channel Evolution Linked to Rising Salt Dome, Mississippi Canyon, Gulf of Mexico

Carter, Rachel C 18 December 2015 (has links)
By examining halokinetics and channel evolution in a deep-water system, we investigate how submarine channel morphology is affected by changing seascape linked to diapirism. The study area is located in Mississippi Canyon, Gulf of Mexico (GOM), situated directly off the continental slope in a prominent salt dome region. Interactions of salt domes with submarine channels in the GOM are poorly documented. Utilizing 3D seismic data and seismic geomorphology techniques, a long-lived Plio-Pleistocene submarine channel system has been investigated to develop a relationship between variable phases of salt movement and plan-form morphology of preserved channels. We suggest that halokinetics acts as a driver for topographic-channel evolution in the study area. We show how submarine channel morphology can be directly controlled by halokinetics, where salt movement can act as a structural control on both location and morphology of meandering channel complexes. Channels are able to move towards an equilibrium state only when holokinetics decreases.
49

Electrodeposition of Hydrogen Molybdenum Bronze Films and Electrochemical Reduction of Carbon Dioxide at Low Over Potentials

Alharbi, Sami 01 August 2019 (has links)
Hydrogen molybdenum oxide, known has molybdenum bronze, is a material of interest due to catalyzing electron transfer reactions. Specifically, molybdenum bronze is an electrocatalyst toward carbon dioxide reduction. Electrochemical deposition from a peroxymolybdic acid solution is a method for preparing molybdenum bronze films. This work demonstrates reproducible electrodeposition on indium tin oxide substrates and conductive carbon paper. Film thickness depends on concentration, time and pH. After characterization by film thickness, resistance, XRD and XPS, the as deposited films served as the working electrode for electrochemical reduction of carbon dioxide in 0.1 M NaHCO3. Ion chromatography determined formate resulting in 8% faradaic efficiency at an applied potential of -0.4 V. Interestingly, this potential is similar to use of formate dehydrogenase as an electrocatalyst. Carbon monoxide levels were attempted to be determined by GC in the headspace of an H type electrochemical cell. Results show that these films are applicable towards electrochemical CO2 reduction to formate when supported on carbon.
50

Dynamically Hedging Oil and Currency Futures Using Receding Horizontal Control and Stochastic Programming

Cottrell, Paul Edward 01 January 2015 (has links)
There is a lack of research in the area of hedging future contracts, especially in illiquid or very volatile market conditions. It is important to understand the volatility of the oil and currency markets because reduced fluctuations in these markets could lead to better hedging performance. This study compared different hedging methods by using a hedging error metric, supplementing the Receding Horizontal Control and Stochastic Programming (RHCSP) method by utilizing the London Interbank Offered Rate with the Levy process. The RHCSP hedging method was investigated to determine if improved hedging error was accomplished compared to the Black-Scholes, Leland, and Whalley and Wilmott methods when applied on simulated, oil, and currency futures markets. A modified RHCSP method was also investigated to determine if this method could significantly reduce hedging error under extreme market illiquidity conditions when applied on simulated, oil, and currency futures markets. This quantitative study used chaos theory and emergence for its theoretical foundation. An experimental research method was utilized for this study with a sample size of 506 hedging errors pertaining to historical and simulation data. The historical data were from January 1, 2005 through December 31, 2012. The modified RHCSP method was found to significantly reduce hedging error for the oil and currency market futures by the use of a 2-way ANOVA with a t test and post hoc Tukey test. This study promotes positive social change by identifying better risk controls for investment portfolios and illustrating how to benefit from high volatility in markets. Economists, professional investment managers, and independent investors could benefit from the findings of this study.

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