• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1159
  • 270
  • 103
  • 74
  • 68
  • 58
  • 47
  • 40
  • 25
  • 14
  • 13
  • 11
  • 10
  • 9
  • 9
  • Tagged with
  • 2295
  • 2295
  • 733
  • 577
  • 461
  • 326
  • 284
  • 264
  • 255
  • 250
  • 240
  • 211
  • 199
  • 177
  • 173
  • 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.
581

Optimisation of the applications of sustainable energy systems

Mitchell, Keith Owen, University of Western Sydney, College of Science, Technology and Environment, School of Engineering and Industrial Design January 2005 (has links)
This work examines issues that are restricting the wider adaptation of sustainable (‘renewable’) energy systems in Australia and elsewhere. Several new innovative areas of opportunity for improving the application of wind and solar PV based systems have been explored and developed. A number of financial and regulatory obstructions to wind and solar systems and grid connection are examined and a number of regulatory changes to the regulatory electricity codes are suggested. / Doctor of Philosophy (PhD)
582

Defect chemistry and charge transport in niobium-doped titanium dioxide

Sheppard, Leigh Russell, Materials Science & Engineering, Faculty of Science, UNSW January 2007 (has links)
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.
583

台灣的住戶太陽能市場: 障礙, 解決辦法與發展遠景 / Taiwan’s residential solar photovoltaic (PV) market: barriers, solutions and developmental prospects

哈溫海, Karl Wendell Haby Unknown Date (has links)
雖然台灣在太陽能PV科技製造業上位居於領先位置,也採取了FIT來推廣太陽能PV及其他再生能源,但是市場的吸收(以及新計畫的完成)至今仍是進展緩慢;因此再生能源在台灣明顯且矛盾的狀況成了本論文的研究動機 為了理解為什麼有這種狀況,本論文採用了兩個廣泛的觀點: (一)市場障礙觀點:這個觀點提供了一個簡明的總結;在經濟學上國內太陽能PV的安裝,特別是家用投資者在FIT計劃下考慮電網連接。 (二)市場轉型觀點:這個觀點確定了影響並降低台灣再生能源市場的因素或是參與者(政府機關或其他相關團體的人員)。 本論文最後一個章節中提出了可能有助於提高台灣太陽能PV或是其他再生能源的接受度的實用步驟及政策措施。 本研究結果指向複雜且費時的申請手續,反覆修改的相關法令,及設定太低的FIT為至今台灣太陽能PV市場開發成功有限的主要原因。低電價、政府與台電間所發展出的相互依賴狀況以及極力避免破壞現況的密集產業為造成這些狀況的難題。 為了解決這些缺陷,本論文建議立即將FIT上修(至少每千瓦新台幣12.6元)並恢復補貼中小型投資者的資本。削除行政與程序上的障礙是促進在地太陽能PV市場和建立信心的整體方案上非常重要的的一環。論文中的最後一章節提到一個發展框架,並且描述了 一些針對於更棘手並減緩台灣的多元化能源供應問題的可能解決方案。 / The motivation for this research stems from an obvious contradiction in Taiwan’s approach to renewable energy – that while Taiwan remains a leading manufacturer of solar photovoltaics (PV) technology, and has adopted a feed-in-tariff (FIT) to promote solar PV and other renewable energies, market uptake (and completion of new projects) has so far been slow. In order to understand why, this thesis adopts two broad-based perspectives first identified by the International Energy Agency (IEA): (i) the Market Barriers Perspective provides a concise summary of the economics of domestic solar PV installation in Taiwan, specifically for the small scale (residential) investor contemplating grid connection under the FIT scheme; (ii) the Market Transformation Perspective identifies those factors (or actors) contributing to inertia in the renewable energy market in Taiwan. A final section in this thesis is given over to describing practical steps and policy approaches which may help boost solar PV (and other renewable) capacity in Taiwan. The results of this research point to a complicated and time-consuming applications process, repeated changes to relevant legislation, and a FIT which is set too low, as the primary reasons for the limited success to date in developing Taiwan’s small-scale (distributed) solar PV market. These difficulties are compounded by low electricity prices and a mutual dependency that has developed between the government, Taiwan Power, and large energy-intensive industries to avoid any upset to the status quo. In order to address these problem areas this thesis recommends immediately revising the FIT upwards (to at least NT$12.6 per kWh) in conjunction with the reinstatement of capital subsidies for small to medium investors. Removing administrative and procedural barriers is likewise deemed essential to fostering growth in the local solar PV market and establishing confidence in overall program. A Developmental Framework in the final section of this thesis describes some potential solutions to the more intractable problems slowing the diversification of Taiwan’s energy supply.
584

Sustainable Power Production in Chile

Björnfot, Karl January 2007 (has links)
<p>Summary</p><p>This report is about how Chile can find its way towards a sustainable power production. The two major Chilean electric systems are modeled and optimized by a special optimization program for energy systems called MODEST. The model is then altered so that new sustainable energy sources can be put into the system. If these new energy sources are more economically beneficial they will enter the system. The time period that is modeled is the years 2006 to 2010 and the demand for electricity is rising between these years. 7 different scenarios where the terms for fossil fuels and renewable energies are changed in different ways is tested to see what can be done to introduce more sustainable energy into the system. The different changes include tax on carbon dioxide emissions, subsidies for new sustainable energy sources and limits in carbon dioxide emissions. The results show that:</p><p>• Taxes are an ineffective way to get more sustainable energy but can work to reduce emissions. The tax could be used to fund subsidies for cleaner energies.</p><p>• Subsidies can work to bring in more sustainable energy and if there is a possibility to use the clean development mechanisms available within the Kyoto protocol. Then it does not have to be subsidies but investments from companies in countries that have signed the Kyoto protocol.</p><p>• Waste to energy is the most cost effective new energy source, although it is questionable however this is really a renewable energy source. The author thinks that although it might not be renewable it is certainly sustainable within a foreseeable future.</p><p>• A natural gas shortage will have serious effects on the system and should be avoided at least until there are enough alternative fuels available. It is therefore important to continue encourage the development of sustainable power sources.</p><p>• Carbon dioxide limits could be used in Chile. If they are at reasonable levels they do not need to cost that much and could really help the sustainable energy sources to become more interesting for investors.</p>
585

Electric Energy Conversion Systems: Wave Energy and Hydropower

Thorburn, Karin January 2006 (has links)
<p>Electric energy conversion is an important issue in today's society as our daily lives largely depend on the supplies of energy. Two energy sources are studied for conversion in the present thesis, ocean waves and hydropower. The work focuses on the generator and the transmission of its output to the electric grid.</p><p>Different approaches have been used, over the years, to convert the energy in ocean waves, and the method presently used is based on a point absorber (buoy) directly coupled to a linear generator on the seabed. A varying alternating voltage is induced with such configuration, where both the amplitude and the frequency changes continuously. The target is to connect several units in a farm, and thereby decrease the fluctuations in power production. This is shown to be possible to accomplish with a rectifier connected to each generator. Transmission systems can be designed with converters and transformers to connect the farm to the electric grid onshore. Several aspects of the concept are considered as well as interconnection issues. Analytical calculations verified by finite element simulations and measured data are used to model the behaviour of a linear generator. A series expanded expression for the ideal no-load flux and EMF (electromotive force) is derived, which can be developed into an analytical transmission design tool.</p><p>Hydropower has been used for more than a century. Today many of the stations from the mid 1900's are up for refurbishment. Studies with finite element calculations show that a higher electric efficiency can be obtained with a high voltage cable wound generator.</p>
586

Robust decisions and deep uncertainty an application of real options to public and private investment in hydrogen and fuel cell technologies /

Mahnovski, Sergej. January 2007 (has links)
Thesis (Ph.D.)--RAND Graduate School, 2007. / Includes bibliographical references.
587

Modeling a drip irrigation system powered by a renewable energy source

Al-zoheiry, Ahmed M. January 2006 (has links)
Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references.
588

Clean Development Mechanism - Key to the future? : A minor field study of organizations working in rural areas in Vietnam with renewable energy sources.

Ewerton, Maria, Åkerblom, Linus January 2010 (has links)
A scholarship from the Swedish International Development Cooperation Agency (SIDA) made it possible for the authors to collect primary data on location in Vietnam. Through a study of three organizations we aimed to create an understanding of the Clean Development Mechanism. Despite all the natural resources and the potential of renewable energy in Vietnam, a large percent of the electricity production comes from coal and other sources that contribute to carbon dioxide emissions. However, there are organizations working nationwide with implementing renewable energy projects and educating the Vietnamese. Since the birth of carbon market in connection with the Kyoto Protocol new possibilities have emerged as e.g the Clean Development Mechanism. For example high quality carbon offsetting companies are working on projects that reduce greenhouse gas emissions. The purpose of this thesis is to study and describe how three organizations are working with renewable energy in rural areas in Vietnam and their connection to Clean Development Mechanism. We have carried out an explorative study with an inductive approach. Our three semi-structured interviews were conducted as personal interviews at location in Vietnam. We also had two informative meetings, also in Vietnam. Beyond, we had e-mail correspondents with a number of professionals in their field. Due to the heavy bureaucracy the Governmental process rate is slow, which are making projects such as in the area of renewable energy difficult to initiate. Also the Governmental interest in renewable energy as a source of generating electricity is limited. However, new policies are on the agenda which might increase the support for organisations working towards a sustainable development.
589

The process of technology commercialization : A case study of project CHRISGAS

Holmgren, Annie, Karlsson, Simon January 2007 (has links)
This thesis investigates, describes and understands the extensive process of technology commercialization. What stages there are, important aspects and implications. It is structured as a case analysis of project CHRISGAS development. CHRISGAS is a Swedish project, based in Värnamo, developing the technique of direct gasification of biomass to fuels. The work has its origin in the debate of the imminent climate changes, where society needs to reduce its reliance on fossil fuels. The automotive sector (particularly transport) is significantly reliant. However, current attempts to transition to biofuels have not completely succeeded. New, efficient technologies must be commercialized, and the technology of wood gasification is said to be particularly promising for launching the next generation of biofuels.
590

Quantification Of Thermoelectric Energy Scavenging Opportunity In Notebook Computers

Denker, Reha 01 September 2012 (has links) (PDF)
Thermoelectric (TE) module integration into a notebook computer is experimentally investigated in this thesis for its energy harvesting opportunities. A detailed Finite Element (FE) model was constructed first for thermal simulations. The model outputs were then correlated with the thermal validation results of the selected system. In parallel, a commercial TE micro-module was experimentally characterized to quantify maximum power generation opportunity from the combined system and component data set. Next, suitable &ldquo / warm spots&rdquo / were identified within the mobile computer to extract TE power with minimum or no notable impact to system performance, as measured by thermal changes in the system, in order to avoid unacceptable performance degradation. The prediction was validated by integrating a TE micro-module to the mobile system under test. Measured TE power generation power density in the carefully selected vicinity of the heat pipe was around 1.26 mW/cm3 with high CPU load. The generated power scales down with lower CPU activity and scales up in proportion to the utilized opportunistic space within the system. The technical feasibility of TE energy harvesting in mobile computers was hence experimentally shown for the first time in this thesis.

Page generated in 0.3142 seconds