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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.
11

Glass melting using concentrated solar heat

Ahmad, Syed Qasid Safeer January 2017 (has links)
Glass production is an energy intensive process, primarily requiring high temperature (≈1500oC) heat, usually provided by combustion of fossil fuels. Concerns about the future depletion of fossil fuels and the emissions due to their combustion have driven a shift towards the use of alternative energy sources. Concentrated solar radiation is the only form of renewable energy which could directly provide the high temperature process heat required for glass production, without the otherwise necessary intermediate conversion to electricity and thereby avoiding the associated efficiency and capital costs. The technology for concentrating solar radiation using fields of heliostat mirrors to collectively generate a high intensity beam at a central focal point, is already well developed. However, the ability to use of such a solar beam to effect a viable glass making process involves significant challenges associated with the fact that glass furnaces typically require continuous and consistent process heat smoothly distributed, over large areas while concentrated solar radiation is only intermittently available and provides heat over relatively small areas with steep intensity gradients. In this project, experiments were conducted to incrementally develop and investigate the feasibility of an efficient and scalable process for manufacturing useful glasses with the primary process heat demand provided by a realistic concentrated solar beam. A High Flux Solar Simulator (HFSS) consisting of an array of xenon arc lamps, each coupled with an ellipsoidal reflector, was used to generate an artificial, controllable ‘solar’ beam. First, the HFSS beam was used to directly irradiate pure silica and soda-lime-silica glass forming batches contained inside insulated, refractory crucibles and directly irradiated by a realistic solar beam (intensity < 2000 kW/m2). All silicate batches generated complete melt pools with full conversion from crystalline raw materials, to x-ray amorphous glasses but only soda-lime-silica batches would generate melts with sufficient fluidity to homogenise and remove entrained gases (fining) and thereby produce transparent glasses. Next, a series of experiments were conducted to investigate factors affecting the continuity of the process. Glass forming batch, directly irradiated by a vertical HFSS beam, was contained inside a modified apparatus which enabled the melt produced to sustain a continuous flow . A specially made batch feeder enabled additional raw materials to be intermittently fed into the melting zone while the beam was still on. It was demonstrated that a semi-continuous glass melting process could be realised using primarily concentrated solar heat. However, secondary heating was necessary to sustain the flow beyond the focal spot of the beam while avoiding fracture of the crucible due to thermal gradients induced by the beam. Also, the efficiency of this process was very poor (3-4%) and the throughput was very low. This was mainly due small size of the melt limited by the area of focal spot (~6 cm dia) of the beam and the radiative heat losses from the exposed surface of the glass forming melt. Finally, a scaled-up solar-heated glass furnace was designed, built and tested, to address the remaining issues of efficiency, throughput, secondary heating demands, intermittent solar radiation availability and glass quality. The furnace was essentially an insulated box, containing the glass forming melt with an aperture in the roof for the vertical HFSS beam and raw material inlet. Integrated electrical resistance heating elements provided the secondary heating required to sustain continuity of the process by minimising thermal gradients during periods were solar radiation was unavailable. The HFSS beam converged at the inlet aperture and then diverged inside the insulated cavity to irradiate the surface of the glass forming melt. This provided a much larger surface area for glass melting relative to the focal spot of the beam. This resulted in both greatly reducing re-radiation heat losses and increasing the productivity compared to the previous experiments in which the beam was directly focussed at the glass melting surface. Also, a specially made flow control system was developed, enabling the glass melt to accumulate in the crucible until fully melted and fined before and then extracted to demonstrated production of pressed glassware. With 5.26 kW of radiation from the HFSS beam entering the beam inlet aperture of this solar-heated glass furnace, 300 g of soda-lime-silica glass forming batch was periodically fed, requiring 16 minutes between consecutive feeding cycles required to fully melt the batch and recover the glass melt temperature to 1460oC, which corresponded to a thermal efficiency of 16 %. It was shown that complete melting and fining of melt pools with surface areas an order of magnitude larger than the focal point of a solar beam could be sustained without any secondary heating. Also, beam power was switched off intermittently during melting and overnight which simulated realistic operation as per natural solar radiation availability and during these periods, the secondary electrical heating automatically provided sufficient power to avoid thermal shock. Analysis of the performance of the scaled-up solar-heated glass furnace suggested that it could not directly compete with conventional large scale (~300 tonnes/day), continuous glass tank furnaces. However, in markets where conventional glass manufacturing is infeasible due to insufficient local demand, a solar-heated glass furnace appears more commercially attractive to meet smaller local demands. For example, it is estimated, that with realistically achievable improvements expected on commercial scale up (30% glass melting efficiency), a 4 tonnes/day solar-heated glass furnace, requiring a total initial capital investment of $13M and a land area of 2 hectares, would have a payback period of 6 years for oil at 50-60 $/barrel.
12

Demonstration and evaluation of a nanocrystal-nanowire solar cell

Jacques, David Andrew January 2015 (has links)
Climate change is likely to have a major impact on future civilisation. To combat the worst effects of this, progress in renewable energy is necessary. With a plentiful resource, solar photovoltaics is one such renewable technology that holds promise. However, the incumbent photovoltaic technology currently suffers from high costs, a carbon intensive manufacturing process and a limited potential for efficiency improvement. The aims of this research was to address these three issues through the fabrication of a novel solar cell architecture and identification of further areas that have the potential to improve device performance. This architecture utilises nanomaterials and therefore reduces material use and allows for less energy intensive fabrication processes while also allowing for a higher theoretical efficiency limit than that of silicon. Upon proof-of concept and despite efforts to improve cell efficiency, the output was still exceedingly low (External quantum efficiency circa 0.3 %). It was also deemed impractical to perform a life cycle analysis on such a prototypal device. However, analysis of a standard silicon device resulted in carbon intensities greater than 100 g/kWh CO2e, reaffirming the need to replace silicon. Through development of both a solar resource assessment methodology and a policy mechanism, avenues for carbon reduction were identified and quantified. For example, a reduction in the carbon intensity of the Chinese national grid could save over 500,000 tonnes CO2e in UK Feed-in tariff installations alone. Upon maturing of the demonstrated device, all chapters can be combined to maximise electrical output, minimise cost and reduce the levels of carbon intensity.
13

A conceptual electrical energy storage (EES) receiver for solar parabolic trough collector (PTC) power plants

Nation, Deju Denton January 2013 (has links)
This work outlines the conceptualization, modelling and design of a novel electrical energy storage (EES) receiver for use in solar parabolic trough collector (PTC) power plants. A hybridization of sodium sulphur (NaS) battery and parabolic trough collector (PTC) Technologies, the EES receiver concept could one day enable PTC power plants to operate 24 hrs using solar energy only, while simultaneously providing them significant ancillary power benefits. Modelling of the EES receiver operation is achieved using of a system of ten steady state (algebraic) equations and two transient (partial differential) temperature dependent equations. The method of solving the system consisted of precedence ordering and back substituting of the steady state equations to develop a single complex and highly non-linear algebraic equation, in terms of the main process heat flux ݍ′̇ ௖௢௡ௗ,௔௧,. This equation was solved with the assistance of the Microsoft Excel goalseek tool. For the partial differential equations, a one dimensional finite difference approximation, consisting of a forward difference predictor, and a modified central difference corrector was used in discretization. Visual Basic code was then written to solve the system at each increment, each time utilizing the solution obtained for the complex non-linear algebraic equation in ݍ′̇ ௖௢௡ௗ,௔௧. This allowed investigation of the initial heat-up and charge/discharge function of the conceptual solar field. Results of simulations indicate the concept is both promising and implementable and that the slightly higher heat losses in the order of 400 – 600 W/m (a direct result of the unavoidably larger size of the conceptual receiver), are seen to be insignificant when compared to the possible energy storage and power support benefits. Though NaS batteries are currently expensive, this condition is thought to be ephemeral, since cells are made from low cost and widely available materials. Thus falling battery prices (with future mass production) could make this novel energy storage concept worthy of evaluation in a prototype PTC power plant.
14

Electrochemical deposition of Cu-Zn-Sn-S films

Tay, En January 2015 (has links)
CZTS (Cu2ZnSnS4) solar cells offer an earth-abundant and non-toxic alternative to CIGS (CuIn1 xGaxSe2) and CdTe technologies. In a one-bath electrodeposition approach for CZTS, the wide deposition potential difference between Cu and Zn would result in dendritic morphology with poor adhesion to the substrate. This challenge was explored in Chapter 4 with three different additives (citric acid, thiosulfate, and thiourea) in pH 1.5 - 2.0, where Sn2+ is stable. Cyclic voltammetry was used to study reduction and oxidation peaks in electrolyte baths containing the metal ion and additive. Citric acid did not show significant complexing effect while thiosulfate and thiourea exhibited a negative shift in Cu deposition potential such that the deposition window is defined by Sn and Zn instead of Cu and Zn. In the pH range investigated, thiourea was found to be much more stable than thiosulfate, which decomposed to sulfur particles. With a suitable additive (thiourea) identified, a one-bath deposition of Cu-Zn-Sn was explored in Chapter 5. Electrolyte baths with Cu2+, Zn2+, Sn2+, and an additive was used for electrodeposition of films at -0.2 V, -0.5 V, -0.8 V, -1.1 V, and -1.3 V. Films deposited using thiosulfate showed weak adhesion to the substrate, and flaked off easily. Nanostructures obtained from citric acid and no additive exhibited were similar, highlighting an inactivation of citric acid at low pH values as suggested in literature. Nanostructures obtained from thiourea were different. In terms of film homogeneity, electrodeposition with thiourea resulted in films with improved surface coverage and less pinholes than the case with no additive and citric acid. The composition of the films exhibited a Sn incorporation from -0.5 V and below, and Zn incorporation from -1.1 V and below for citric acid and thiourea. Once films of Cu-Zn-Sn were obtained, sulfur was incorporated using co-deposition of metal ions and sulfur particles in Chapter 6. A comparison of continuous and pulsed co-deposition was explored and films obtained from pulsed co-deposition were found to exhibit significantly better film homogeneity, hence pulsed co-deposition was used for subsequent studies. Sulfur loading was increased from 0 g/L to 0.32 g/L and 0.64 g/L. The morphologies obtained from these films were similar, with sulfur incorporation increasing from 0 g/L to 0.32 g/L, with a slight increase from 0.32 g/L to 0.64 g/L. The results obtained from this work will be advantageous towards an economical one-bath electrodeposition approach for earth-abundant and non-toxic CZTS solar cells. In addition, this study is helpful for future possibilities of a multi-metal electrodeposition in a one-bath approach.
15

Assemblages of solar electricity : enacting power, time and weather at home in the United Kingdom and Sri Lanka

Turner, Britta Rosenlund January 2016 (has links)
This thesis explores what happens to the social enquiry of the powers of energy, if energy technologies and electricity are taken seriously as actants. It questions how photovoltaic solar panels and solar electricity act in everyday lives in domestic homes and how a more material enquiry of them can help shed light on the ways in which photovoltaic technology is made to matter in different places. It proposes to contribute to the social enquiry of energy by providing an example of how the power of electricity can be investigated and analyzed as a contingent achievement of particular assemblages rather than a neutral resource and affordance. Photovoltaic solar panels are enrolled in global discourses of environmental governance and sustainable development, and are employed not merely to generate electricity but also to have particular social powers: they generate electricity in different quantities and for different socio-political purposes in different places. As solar photovoltaic technology has gained momentum as a renewable energy technology that can be scaled and adjusted to fit different local and global matters of concern, it has also increasingly become part of different domestic homes, where it provides small portions of power for individual householders to use. This thesis considers two empirical settings where micro-generation solar is at work: in efforts to provide electricity to rural households in Sri Lanka and in efforts to reduce carbon emissions from households in the United Kingdom. The thesis argues that a tendency to focus on diffusion and social acceptance of solar in both policy and research has left gaps in our understanding of how solar works as a material force in everyday life after installation. The thesis engages with theories of assemblage and material agency and argues that the sustainability or green-ness of domestic solar power should not be considered an attribute of the technology, but rather seen as the achievement of a particular socio-material assemblage. It offers insights into how domestic solar is assembled and illustrates how solar electricity acts not as a neutral resource, which is handled and interpreted by human beings but rather as a spatially and temporally diverse force with properties and propensities, which encourage particular orderings of meaning and matter.
16

A data logging and processing system for solar energy studies : instrumentation for the measuring and logging of total and spectral solar radiation and the evaluation of solar thermal and electric systems

Munroe, Milton Marlborough January 1978 (has links)
No description available.
17

Characterisation and optimisation of hybrid polymer/metal oxide photovoltaic devices

Ravirajan, Punniamoorthy January 2005 (has links)
No description available.
18

Numerical and experimental study of dynamic solar cooling system with a liquid piston converter

Hashem, Gamal January 2016 (has links)
Solar energy has been actively used to drive cooling cycles for domestic and industrial applications, especially in remote areas with a lack of electricity supply for running conventional refrigeration or air-conditioning systems. A number of solar cooling technologies exists but their market penetration level is relatively low due to the high capital costs involved and a long pay-back period. Extensive R & D activities are underway at Universities and industrial companies across many countries to improve performance and reduce capital and running costs of solar cooling systems. Systems based on application of a liquid piston converter for solar water pumping and dynamic water desalination have been developed at Northumbria University. Some preliminary work has been completed on the development of a new solar cooling system built around the above fluid piston converter. In this work, the task is to experimentally and numerically investigate performance of the solar cooling system with the fluid piston converter. The developed theoretical model then can be used for determination of its rational design parameters. Experimental tests were conducted in the Energy Laboratory of the Faculty. The test rig consisted of a solar simulator and evacuated tube solar collector, coupled to the liquid piston converters, equipped with a heat exchanger. Three different configurations of the solar cooling unit were tested and a data acquisition system with pressure, temperature and liquid piston displacement sensors was used to evaluate the experimental performance on the cooling capacity. In the theoretical part of the study, the thermodynamic model of the solar cooling system was developed. In the calculation scheme, the system was split into a number of control volumes and ordinary differential equations of energy and mass conservation were used to describe mass and heat transfer in each such volume. The system of ordinary equations then was solved numerically in MATLAB/Simulink environment and information on the variations of pressure and temperatures in the control volumes of the system over the cycle were obtained. Calibration of the mathematical model with the use of experimental data demonstrated that the model predicts the performance of the system with accuracy acceptable for engineering purposes. Experimental investigations showed that laboratory prototypes of the system demonstrate a stable operation during the tests with an amplitude and frequency of liquid piston oscillations being about 4- 6 cm and 3 Hz, respectively. The reduction in the air temperature in the cooling space was about 1 and 2 K, compared to the ambient temperature. The cooling effect increases with the raise in the heat input into the solar collector and in the flow rate of cooling water. The developed mathematical model of the system describes the pressure variation in the cycle, amplitude and frequency of oscillation of pistons with a level accuracy sufficient for performing engineering design calculations. Overall, both experimental and theoretical investigations confirm that the system demonstrates a capacity to produce a cooling effect with utilisation of solar energy. However, further R & D is required to enhance its performance.
19

Active layer control for high efficiency perovskite solar cells

Eperon, Giles E. January 2015 (has links)
The work documented in this thesis concerns the control and modification of semiconducting perovskite thin films for their use in perovksite solar cells (PSCs). PSCs are a promising new thin-film technology, offering both high solar to electricity conversion efficiencies and cheap fabrication costs. Herein, the boundaries of perovskite solar cell research are pushed further by tackling several challenges important to the field. Initially, this work focuses on understanding why the best PSCs made so far have been mesostructured devices, with the perovskite infiltrated into a scaffold. It is shown that this can be seen as simply a fabrication aid; without the scaffold, thin films easily dewet from the substrate. By understanding the crucial parameters important in carefully controlling this dewetting, it is minimised, and it is shown that scaffold-free planar heterojunction devices with high efficiencies can be fabricated. This work leads on to the next section; the development of semi-transparent perovskite solar cells. In their present state, PSCs cannot compete with silicon as stand-alone modules. Here, the morphological control has been leveraged to realise a different embodiment – semi-transparent perovskite devices for use in building-integrated photovoltaics. Competitive efficiency and transparency are demonstrated. Moreover, a hybrid self-tinting power-generating window concept is fabricated, by combining the photovoltaic and electrochromic technologies. In the third section of the thesis, the limitations of the most studied perovskite material, methylammonium lead halide, are addressed: its overly wide bandgap and thermal instability. To address these, the chemical constituents of the perovksite are altered, and the development of more efficient and more stable materials are reported. These are likely to be important for perovskite modules to pass international certification requirements for commercialisation. Finally, an in-depth study on the effect of ambient moisture, relevant for considering scale-up and the fabrication environment needed, is carried out. It is shown that the presence of some moisture during film fabrication allows a reduction of defect states in the perovskite material, enhancing device performance and film quality.
20

Comparative study of dilute nitride and bismide sub-junctions for tandem solar cells

Ketlhwaafetse, Richard January 2016 (has links)
Theoretical models show that tandem solar cells can reach efficiency of more than 50 %. To achieve efficiencies closer to the projected outputs in a quad tandem solar cell, a 1.0 eV sub-junction with good optical and electrical properties is sought. The observed bandgap reduction when small amounts of Nitrogen or Bismuth is incorporated into GaAs makes these alloys (dilute nitrides and bismides) possible candidates for the tandem solar cells. In this work, the performance of dilute nitride and bismide solar cells of different designs which include p-i-n bulk and p-i-n multiple quantum wells (MQWs), and n-i-p-i structures are studied comparatively. Performance in this context refers to: the magnitude and quality of the dark current generated by the devices, the spectral response of the solar cells especially in the dilute nitride and bismide absorption regions, and efficiency responsivity to temperature and to elevated radiation. To achieve the latter objectives, dark and under the AM1.5G and spectral response measurements were performed on the solar cells. The results reveal that, in the dilute bulk or MQWs p-i-n and n-i-p-i solar the total dark current is nearly the dark current generated by dilute nitride or bismide material alone. The applicability of Sah-Noyce-Shockley model to bulk p-i-n dilute nitride solar cells dark current is demonstrated. The dilute nitride solar cells exhibit temperature coefficients of efficiency that are lower than that of the conventional GaAs p-n junction solar cell. MQWs solar cells show lowest sensitivity to temperature changes. The dilute nitride and bismide materials show similar diode characteristics with dark currents that are dominated by non-radiative recombination mechanisms.

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