• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 261
  • 100
  • 57
  • 35
  • 33
  • 27
  • 9
  • 6
  • 6
  • 6
  • 6
  • 6
  • 5
  • 5
  • 4
  • Tagged with
  • 644
  • 644
  • 644
  • 194
  • 95
  • 94
  • 85
  • 84
  • 82
  • 81
  • 71
  • 68
  • 63
  • 62
  • 62
  • 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.
161

Building capacity for green, just and sustainable futures – a new knowledge field requiring transformative research methodology

Rosenberg, Eureta, Ramsarup, Presha, Gumede, Sibusisiwe, Lotz-Sisitka, Heila 1965- January 2016 (has links)
Education has contributed to a society-wide awareness of environmental issues, and we are increasingly confronted with the need for new ways to generate energy, save water and reduce pollution. Thus new forms of work are emerging and government, employers and educators need to know what ‘green’ skills South Africa needs and has. This creates a new demand for ‘green skills’ research. We propose that this new knowledge field – like some other educational fields – requires a transformative approach to research methodology. In conducting reviews of existing research, we found that a transformative approach requires a reframing of key concepts commonly used in researching work and learning; multi-layered, mixed method studies; researching within and across diverse knowledge fields including non-traditional fields; and both newly configured national platforms and new conceptual frameworks to help us integrate coherently across these. Critical realism is presented as a helpful underpinning for such conceptual frameworks, and implications for how universities prepare educational researchers are flagged.
162

Bio-Energy with Carbon Capture and Storage (BECCS)- Production of H2 with Suppressed CO2 Formation via Alkaline Thermal Treatment

Stonor, Maxim Richard Alphonse January 2017 (has links)
The demand for energy continues to grow but concerns over climate change means that conventional fossil fuels will eventually need to be replaced. The solution to the energy crisis will require a combination of both conventional energy sources with CO2 capture and renewable technologies. While many renewable technologies exist, it is not common that CO2 capture is incorporated into the process. Biomass is an ideal feed-stock for bio-energy production as it is CO2 neutral. Many thermochemical conversion technologies exist, but the Alkaline Thermal Treatment (ATT) reaction is particularly interesting because it combines conventional thermochemical conversion with CO2 capture in order to create a process that is potentially CO2 negative. By reacting biomass with a metal hydroxide, high purity H2 can be produced while simultaneously locking the carbon as a stable carbonate, which is a form of Bio-energy with Carbon Capture & Storage (BECCS). The H2 can then be used for applications ranging from Fischer-Tropsch synthesis to PEM fuel cells. Group I & II hydroxides were investigated for their ability to react with cellulose (a biomass model compound) in the ATT reaction scheme. Comparison between both groups indicated that NaOH and Ca(OH)2 were the best hydroxides from groups I & II respectively. However, the amount of H2 produced during the ATT of cellulose with Ca(OH)2 is considerably lower than with NaOH. A 10% Ni/ZrO2 catalyst was then added to increase the yield of H2 from the reaction between cellulose and Ca(OH)2. It was found that at 20% catalyst loading, the amount of H2 produced and the suppressed level of CO2 was similar to the ATT with NaOH. Several other catalytic metals were also investigated and found to have the following H2 production activity: Ni > Pt≈Pd > Co > Fe, Cu. Since Ni was the most active and has a considerably lower cost than noble metals it was chosen for additional studies. The ATT reaction in the presence of Ni has two distinct steps in the formation of H2 from cellulose. The presence of Ca(OH)2 enhances the formation of linear oxygenates from cellulose. These oxygenates are then reformed over the Ni-based catalyst to H2 and CO2, the latter of which is captured by Ca(OH)2 to form CaCO3. If either Ca(OH)2 or Ni was removed from the reaction, the yield H2 fell significantly. Although the reactants and the catalyst are all solid materials, they do not need to be physically mixed. The Ni-based catalyst produced H2 primarily through the reforming of gaseous species and therefore could be placed ex-situ of the cellulose and Ca(OH)2 mixture. However, placing the catalyst away from Ca(OH)2 prevented CO2 capture. In order to remedy this Ca(OH)2 was mixed with the Ni-based catalyst and mixture was placed ex-situ of pure cellulose. This created a process whereby cellulose could be decomposed thermally followed by a single gas-phase Alkaline Thermal Treatment (GATT) reforming step of the pyrolysis vapors to H2 with suppressed CO2.
163

Análise da intensidade energética: um estudo de caso para o Estado de São Paulo / Energy Intensity Analysis: A Case Study for the Sao Paulo State

André Hideki Furukawa Oshiro 20 March 2015 (has links)
O sistema energético pode ser visto não apenas como uma restrição, mas também como uma oportunidade para o desenvolvimento produtivo de uma sociedade. Pela segunda ótica, o objetivo principal a ser perseguido é a da garantia do suprimento energético e da adequação das formas e fontes de energia aos usos finais demandados. Ao mesmo tempo, dentro do contexto global de preocupação com as mudanças climáticas, faz-se necessário conceber uma nova trajetória de desenvolvimento para o estado de São Paulo, mais moderna, com maior participação de fontes renováveis de energia, focada na diminuição da ntensidade energética, e mais voltada ao desenvolvimento tecnológico. Este trabalho procurou, então, mostrar que o estado de São Paulo já promoveu uma verdadeira transformação de sua matriz energética em termos da participação de energias renováveis, no entanto, que os paulistas ainda devem encarar outros desafios maiores como saber lidar com a tendência não declinante de sua intensidade energética nos últimos anos. Enfim, ao decompor o indicador de intensidade energética para o estado de São Paulo, buscou-se explicitar as possíveis causas de forma a observar se há um tradeoff aparente entre o uso de fontes energéticas renováveis e a estagnação dos valores da intensidade energética estadual. / The energy system can be understood not only as a constraint, but also as an opportunity for a society productive development. Taking the second approach, the main objective to be pursued is that of securing energy supply and adequacy of forms and sources of energy to the demanded end uses. At the same time, within the context of global concern about climate change, it is necessary to devise a new development path for the state of São Paulo, more modern, with a higher share of renewable energy sources, focused on reduction of energy intensity and more focused on technological development. This study sought to show, therefore, that the state of São Paulo has promoted a true transformation of its energy matrix in terms of the share of renewable energies. However, the state must still face other major challenges such as how to deal with its non-downward energy intensity trend in recent years. Finally, by decomposing the energy intensity indicator for the state of São Paulo, we sought to clarify the possible causes in order to observe whether there is an apparent tradeoff between the use of renewable energy sources and the stagnation of the state energy intensity values.
164

An analysis of the environmental impacts of biomass application in hybrid microgrids in South Africa

Gesha, Hlonela January 2018 (has links)
Thesis (Master of Engineering in Electrical Engineering)--Cape Peninsula University of Technology, 2018. / In Sub-Saharan Africa (SSA), there are several challenges that hinder development. One of these challenges is access to electricity. There are numerous benefits to having access to reliable electricity. These include less time spent fetching water from rivers and dams, as water purification systems for households could be used in villages; children in villages would be able to spend more time doing their schoolwork and not fetching wood for fire; and automated irrigation systems could be used for villagers to farm and make an income. Finding alternative ways to generate electricity would enable access to electricity for regions that currently do not have the electricity. This means that large organisations need to find alternative ways of generating electricity, as they have the means to do so. With the current renewable energy technologies available, there are now more ways in which electricity could be generated. The use of biomass is no exception to this. With constant developments in the renewable energy sector, waste-to-energy (WtE) is proving to be a viable method to generate electricity. The main aim of this research was to determine if a commercial food retailing organisation could use their food waste for generating electricity for their own use to reduce their demand from the central grid. A way of determining the viability of this type of technology is using a software that simulates renewable energy projects. In this research, an organisation was contacted for waste data. Systems for two of the stores will be simulated and results will be discussed. The organisation will remain anonymous. The software used in this research is System Advisor Model (SAM), which was developed by the National Renewable Energy Laboratory (NREL) in the United States. In the results, three results were discussed. These are the monthly energy, monthly heat rate and the monthly boiler efficiency for each of the stores for Store 1, the annual energy simulated was 138,509 kWh and 131,677 kWh for Store 2. Monthly energy averages for each store were 11,542 kWh for Store 1 and 10,973 kWh for Store 2, respectively. There are several opportunities for research based on the findings. These include researching other food sectors in the study; conducting a financial analysis of small-scale WtE systems; constructing a prototype of the system; and using three different softwares to simulate a system for the same project.
165

Electric Water Heater Modeling for Distributed Energy Resource Aggregation and Control

Clarke, Anne E. 13 June 2018 (has links)
Today's utilities face new challenges due to the continually increasing penetration of residential solar and other distributed, stochastic generation sources. In order to maintain balance and stability in the grid without building costly, large-scale generation plants, utilities are turning to distributed energy resources for use in demand response programs. Demand response is a cost-efficient way to balance grid load/generation without the need for increased capital investment in traditional generation resources. Demand response programs are excellent exploiters of end-user devices that otherwise further accentuate the daily load curve and thus, add to the difficulties created by daily load peaks. Electric water heaters are excellent candidates for use in demand response programs for a variety of reason. One, electric water heaters represent a large portion of daily household loads due to their high nominal power ratings (1.5 kW - 5.5kW), and frequent use estimated to account for approximately one third of all daily residential power demand. Two, they are composed of strictly resistive elements, which greatly simplifies modeling, aggregation and control. And third, they can be used for load "shedding" during periods of high electrical demand as well as load "absorbing" during periods of excess generation due to their thermal storage capabilities. With improved access and control, electric water heaters could become a major distributed energy resource for utilities. In order to properly control and use a distributed energy resource, it is important to know how these resources operate and their patterns of behavior in different environments. This thesis presents a single-element, single mass electric water heater model for analyzing the effectiveness of using electric water heaters as distributed energy resources and for participation in demand response programs. The CTA-2045 communication protocol was used for testing demand response signals. The electric water heater is modeled in Python and the communication pathway was built in C++ and Python.
166

Comparison of Heat Output and Microchemical Changes of Palladium Cathodes under Electrolysis in Acidified Light and Heavy Water

Salas Cano, Conrado 01 July 2002 (has links)
Two experiments have been conducted to ascertain if a cell with a palladium cathode, a platinum anode, and a solution of H2SO4 in D2O can produce excess heat under electrolysis compared to a similar cell with H2O. In each experiment, two cells were connected in series with constant current. The two cells were identical except for the fact that the heavy water cell used D2O instead of H2O in the electrolyte. Both cells in each experiment employed Pd cathodes, Pt anodes, and H2SO4 in the solution. On a piece of Pd foil that had been cold-rolled and cleaned like the cathodes but had not been electrolyzed, scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) failed to find any traces of unexpected elements. In the first experiment the indication was that the light water cell was slightly warmer despite receiving slightly less power. Small amounts of silver were found on both cathodes after electrolysis. In the second experiment, the D2O cell produced an excess heat relative to the H2O cell that was too large by at least an order of magnitude to be explainable by chemical reactions or mechanical artifacts. After electrolysis, it was found that Cd was present on the surface of the H2O cathode at levels of concentration that were variable but generally no less than 4% relative to Pd (above 3σ). The H2O cathode of this second experiment finished electrolysis very straight. The D2O cell cathode finished severely arched (~30o), with its convex side facing the anode, and covered in a deposit of powdery black substance which was most likely PdS formed accidentally on the first day of this experiment when the D2O cell had been run with the wrong polarity. On this D2O cell cathode, no statistically significant traces of Cd were detected but Ag was present in 2-5% concentration relative to Pd. In some spots, the Ag abundance surpassed 20% that of Pd. The most likely explanation is neutron-induced nuclear transmutation of some of the Pd nuclides with direct release of heat into the solid-state lattice.
167

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)
168

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.
169

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.
170

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.

Page generated in 0.0501 seconds