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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.
1

Design and synthesis of multi-component molecular architectures for intramolecular energy transfer

Pariani, Consuelo January 2007 (has links)
No description available.
2

Design and analysis of a novel 3-D elliptical hyperboloid static solar concentrator for process heat applications

Ali, Imhamed M. Saleh January 2013 (has links)
In the present thesis, performance characterisation of a novel non-imaging concentrator, a 3-D elliptical hyperboloid concentrator (EHC) for process heat applications (medium temperature) is investigated. In this investigation, optical and thermal characterisations are extensively carried out for the novel 3-D static concentrator. In the optical study, a 2-D ray tracing simulation was carried out in MATLAB® to predict the optical efficiency of the EHC. The 3-D ray tracing was also carried out in OptisTM software to obtain the optical efficiency. Detailed flux distributions on the receiver are also analysed. Ray tracing and flux distributions were investigated for different solar incidence angle by varying the system parameters such as concentrator height, receiver diameters and concentration ratio. A parametric analysis of four different system configurations, (I) Elliptical Hyperboloid Concentrator (EHC), (ii) Circular Hyperboloid Concentrator (CHC), (iii) Elliptical Parabolic Concentrator (ECPC) and (IV) Circular Parabolic Concentrator (CCPC) were performed. Based on the parametric analysis it was found that the EHC gives better optical performance compared to other configurations. It was found that the EHC gives better optical performance than others. It was also found that for a wide range of acceptance angles (±30) the optimised concentration ratio of 20× resulted in an optimised optical efficiency of 28%. For thermal performance, separate indoor and outdoor characterisations were conducted to predict the receiver stagnation and fluid temperatures. In the indoor test, the performances of three different hyperboloid solar concentrators (EHC1, EHC2 and CHC) were investigated. The outdoor performance test was also carried out for a scaled-up version of the developed prototype of the 3-D static elliptical hyperboloid concentrator system (EHC) of 20× concentration ratio. The tests were carried out at Chennai, INDIA to obtain the maximum stagnation temperature and daily performance of the EHC system. It was observed that a maximum temperature of 150°C is obtained as the stagnation temperature. In the daily performance test, the maximum fluid temperature of 90°C was observed. Thus, the developed 3-D static elliptical hyperboloid concentrator system can be effectively used for medium temperature applications.
3

Sunwater Project : an innovative water desalination system operated with solar thermal energy

Buschert, Daniel January 2014 (has links)
The present document is in the field of renewable energies in combination with an innovative water desalination unit (WDU). During this project a future proof and environmentally friendly solar desalination demonstration plant was planned, modelled and simulated in Germany and finally installed in Egypt. This includes a model of the solar thermal system and a model of the innovative water desalination unit, which works with evaporation. Additionally a few measurement and simulation results are presented and discussed. A connection is also given between both aspects. Furthermore a few future prospects are added, which can be used to improve later installations. During this project it was shown, that it is possible to produce freshwater with state of the art technologies by using a solar desalination system. Solar energy can be tapped in a lot of areas to produce enough thermal heat to operate an evaporation desalination unit, which produces high-quality freshwater. The quality is high enough for the daily life in private homes and for the agriculture. If it should be used as drinking water it has to be accumulated with trace elements. During this project different difficult problems were found and solved, which should be taken into account during a later realisation and for a commercial use. One bigger problem is that the sun does not shine the whole day and therefore the produced thermal energy must be stored for a later usage, if the desalination unit should be operated 24 h/d. Another problem is the storage of the heat source itself, because the working temperature of the WDU is up to 95 °C and therefore the long-time storage is very difficult due to heat losses during the night and convection of hot and cold water. Additionally it is very difficult to adjust the output temperature of a huge solar thermal field to the desired operation temperature. Finally the present document shows an innovative way for a worldwide future-proof freshwater supply, but the complete system is still optimisable and it could be very interesting to add new aspects in future projects.
4

Form measurement and durability of mirror surfaces for concentrating solar power applications

King, Peter January 2014 (has links)
Concentrating solar power systems currently have a high capital cost when compared with other energy generating systems. The solar energy is captured in the form of thermal energy rather than directly electrical, which is attractive as thermal energy is easier and currently cheaper to store in large amounts. It is also used directly as processing heat including desalination and water purification. For the technology to compete against other generating systems it is important to reduce the electrical energy cost to the $0.05 per kilowatt-hour level. One of the significant capital costs is the solar field, which contains the concentrators. To reduce the cost of this field, novel constructions and improvements to the durability and lifetime of the concentrators are required. Techniques for characterising the shape, durability and optical properties of such novel mirrors are the focus of this thesis. The thesis describes the development and validation of an inexpensive, highly portable photogrammetry technique, which has been used to measure the shape of large mirror facets for solar collectors. Photogrammetry has demonstrated its versatility and portability by successful measurements across concentrating solar power sites globally. The accuracy of the technique has been validated to show a measurement capability of better than 100 µm using a large coordinate measuring machine. Measurements performed on novel thin glass mirrors and their comparison with conventional thick glass mirrors are presented, showing that the increased flexibility of thin mirrors is an important consideration during installation, but that it is possible for such novel mirrors to perform to the same level.
5

Novel applications of luminescence for solar energy

Videira, Jose Joao Henriques January 2016 (has links)
Luminescent solar concentrators (LSCs) provide indirect light concentration by absorbing both direct and indirect incident light, and have applications in building-integrated photovoltaics (BIPV). Fibre LSCs were found to have a linear relationship between photon concentration and fibre lengths in scales suitable for LSC modules. Using raytrace modelling, cylindrical LSC arrays were found to exhibit light trapping properties at certain angles of incidence, which can pave the way for more efficient BIPV applications. Novel optics for a double-illuminated water splitting reactor were introduced, for the objective of solar hydrogen for energy storage and sustainable transport fuels. A reflective cone embedded in a waveguide reflects incident concentrated light into the waveguide. Raytrace modelling and practical high concentration measurements demonstrate the viability of the optical system as well as necessity for a perfectly smooth reflective cone. It was also shown that replaced the reflective cone with a quantum well solar cell (QWSC) in order to harness the photoluminescence (PL) is not a viable concept with current QWSC structures. Another form of sustainable transport fuels is to use biofuels produced by algae. Algae have evolved to absorb excess amounts of energy, even when it is detrimental to their own growth and survival. This causes inefficiencies when growing algae in raceway ponds. The luminescent solar diffuser (LSD) is an optical funnel, optimisable by use of a genetic algorithm, that can be retrofitted into an algae raceway pond in order to better distribute incident light into the pond depths. This was calculated to increase algae growth rates in the pond, thereby increasing the yield of an algae farm.
6

An experimental and theoretical investigation of novel configurations of solar ponds for use in Iraq

Sayer, Asaad Hameed January 2017 (has links)
Solar energy is likely to be the energy of the future; solar ponds, especially salinity gradient solar ponds (SGSPs), facilitate simple and cost-effective thermal energy storage. Research on maximising their potential is of particular relevance to developing countries, which often have an abundance of solar energy and a critical need for increased power supplies. For this research, a theoretical model for heat transfer in a SGSP was developed to study the energy balance in the three separate zones: the upper convective zone (UCZ), lower convective zone or storage zone (LCZ) and non-convective zone (NCZ). The model showed that the LCZ temperature could reach more than 90 °C in summer and more than 50 °C in winter, in a pond in the Middle East. It was also concluded that surface heat loss occurred mainly by evaporation. The new model was also used to examine the feasibility of a second type of solar pond, the gel pond; this offers solutions to some of the SGSP’s challenges, but presents other difficulties relating to cost and labour. To verify the theoretical results of the SGSP, a small experimental pond was constructed and operated for 71 days in Nasiriyah, Iraq. It was observed that adding a thin surface layer (0.5 cm) of paraffin eliminated the significant evaporation seen in the uncovered pond. Further analysis of the evaporation rate showed a significant correlation with temperature, solar radiation and humidity. Crucially, it was also noted that while the salinity gradient in the NCZ remained substantially intact, the temperature profile became approximately uniform throughout the pond after about 50 days. Analytical formulae to describe the concentrations and temperatures of the UCZ and LCZ were derived. The results achieved and comparisons with the experimental data showed that these equations can be used to compute both concentrations and temperatures.
7

Transient natural convection induced by the absorption of concentrated solar radiation in high temperature molten salts

Amber, Ityona January 2016 (has links)
Solar-thermal energy systems that involve the deposition of radiation in absorbing high temperature molten salts to harness the entire solar spectrum and achieve high efficiencies and low Levelised Cost Of Energy (LCOE) are of considerable interest for power generation. From a design stand point, to achieve a competitive solar power generation devices, it is imperative to have an accurate knowledge of the inherent physical processes of such a fluid system. Thus under high temperature conditions, detailed understanding of the heat transfer and fluid flow characteristics in an irradiated fluid is considered. The work investigates the spectral dependent heat transfer and fluid dynamics in a thermal storage concept which uniquely combines a volumetric receiver and a single tank thermal store. The Thermal Energy Storage (TES) is protypical of a small scale concept concentrated solar plant. Advances in computing power, has seen Computational Fluid Dynamics(CFD) consolidated as a powerful tool employed by researchers and engineers to simulate real world behaviour and complex phenomena to a certain degree of accuracy with low effort in time, personnel and resources. This thesis is focused on the development of a realistic numerical model capable of predicting the local volumetric absorption of solar radiation in a fluid layer which provides an improved understanding of the hydrodynamic and thermal conditions in an enclosed fluid layer. Computational Fluid Dynamics is used to simulate the transient heat transfer and fluid flow determined by a combined influence of volumetric absorption and natural convection in a high temperature fluid filled enclosure. The enclosure is studied for the specific case in which a high temperature salt is first heated by direct volumetric absorption of the incident solar radiation and secondly by natural convection from a absorber plate located at the bottom of the enclosure whose sole purpose is to absorb all non-absorbed radiation reaching the lower surface. The current models considers the depth dependence absorption of solar radiation based on (i) a solar weighted absorption coe cient (assumed constant over all wavelengths) and (ii) spectral absorption coe cient characterised by wavelength band based on a standard solar spectrum reference. A commercially available CFD Package based on Finite Element Method (FEM), COMSOL Multiphysics is used to discretise and solve the Navier Stokes and energy equation under transients heating conditions for a non Boussinesq condition by accounting for the temperature variable properties of molten salts. A time-dependent and Backward Differentiation Formula (BDF) solver using implicit time-stepping methods is combined with refined mesh to solve the non-linear PDE. Validity of the numerical tool has been conducted, by comparing results from published results found in literature with corresponding numerical results. The mesh element optimum sizes and time steps used conform to those obtained in validation models. Simulations have been conducted for a daily charging period of three hours as used in conjunction with a solar system. The effects of bottom absorber plate, flux Rayleigh number, aspect ratio, variable Air Mass and inclination angle have also been investigated. Numerical results are presented in terms of surface plots, temperature contours, and velocity contours and streamlines which show the thermal field distribution and flow structures, for volumetric absorption of thermal radiation coupled with natural convection. Performance criteria are based on quantification of the level of thermal stratification using the MIX number, the dimensionless exergy and capture efficiency. Three dimensionality effects were studied by considering three dimensional simulation for the same problem. The results show that the present method and models are capable of capturing the main features of the flow and the overall performance of these turbulence models in terms of predicting time-averaged quantities. Results obtained indicate a nonlinear temperature profile consisting of two distinct layers: a surface layer and a bottom layer. The numerical results reveal natural convection in the cavity follows an initial stage, a transitional stage and a quasi-steady stage. Results indicate that volumetric absorption of solar radiation, when coupled to natural convection has a direct influence on the thermal field through the disparities in absorption and emission phenomena. The isotherms and streamlines show that the natural convective heat transfer and flow are quite different from those obtained in differentially heat enclosures. Thus the heat transfer mechanism destroys a symmetry of the system that relates clockwise and counter clockwise flows. Temperature and flow field are found to be greatly influenced by the aspect ratio (H/D) of the store and the flux Rayleigh number. It is found that the predicted heat transfer from the lower surface in the cavity is increased when the simulation is extended from two to three dimensional. Results obtained indicated that increasing the aspect ratio, Air Mass and inclination angle all result in increasing levels of thermal stratification. Natural convection from the lower absorber surface is found to increase with increasing flux Rayleigh number.
8

Computational methods for assessment of solar energy potential in present and future climates

Smith, Christopher James January 2015 (has links)
Climate change has motivated the need to produce energy from non-fossil sources such as solar photovoltaics (PV) and concentrating solar power (CSP). As solar power output depends on both the incident irradiance and the ambient temperature, climate change could affect solar energy production. In the last few years, a handful of studies have investigated the interactions between global climate and solar energy output. The aims of this thesis are to build on this previous work by both introducing a tilted solar collector alignment, such as would be seen in the real world, and also to include the spectral response of different PV semiconductor materials. A method to mitigate the effects of global temperature increase on solar PV is also explored. These simulations are performed with a number of radiative transfer, heat transfer and energy balance models. It is shown that the solar resource at the end of the 21st Century is expected to differ by more than ±5% compared to today in many regions of the world, and in some places up to ±20%. PV semiconductors with bandgaps in the range of 1.4–1.7 eV perform relatively better in a future climate scenario compared to the commonly-used crystalline silicon (1.1 eV), due to changes in atmospheric absorption characteristics. A further extension to a geoengineering scenario, in which humans deliberately inject aerosols into the atmosphere to lower global temperatures, shows that tracking PV and CSP energy outputs could decline by up to 15% compared to present-day values. Solar PV output can be increased by up to 6% by passive cooling of solar modules with phase change materials. As solar energy investment decisions are often made on the long-term annual mean energy output being known to within a few percent, changes in solar resource estimates of this magnitude are of importance.
9

Advanced reconfigurable photovoltaic arrays

Storey, Jonathan P. January 2015 (has links)
This thesis describes works relating to advancements in the field of dynamic photovoltaic arrays (DPVA). This subject is becoming extremely active with a flurry of new papers appearing in recent times, all detailing ideas and developments regarding a range of engineering issues. One of the biggest problems with any photovoltaic system is the non-linear reduction in power output caused by the partial shading of the array surface. This is the main focal point of the developments discussed where new techniques regarding the reconfiguration of photovoltaic devices within a topology are identified and used to reduce the negative effects of non uniform insolation. In particular, the most successful type of dynamic array has been modified (the Irradiance Equalized Dynamic Photovoltaic Array) such that it now exhibits it's maximum flexibility and is able to show complete resilience to partial shading allowing for maximum power extraction. Furthermore, the operational speed of the device has been increased so that it can operate in real time with minimal computational effort and we have investigated the future of the device as source of electricity in a wide range of applications. On top of that, a second completely new type of dynamic array (the Optimise String Dynamic Photovoltaic Array) that demonstrates unique behaviour is presented and tested via a custom made simulator programmed into MATLAB. Both of these developments have included conceiving new sorting algorithms that are particularly rapid in their execution while obtaining a high level of optimisation. Three other classes of arrays found in literature are discussed and their characteristics are identified while concerns with their implementation are cross is examined. A new classification framework used in identifying all types of dynamic array has been introduced. This is very useful when discussing the main attributes associated with the various contributions made by authors of the literature. Not only this but it also allows for a comparative study between matrix architecture and device flexibility for arrays within the same class. A simulator that uses standard mathematical models to virtually realise irradiated solar cells and then perform the operations dictated by the sorting algorithms is presented. It reveals in detail the behaviour of featured DPVAs under a complete range of environments. Working with that, a new comprehensive test procedure has been developed that exercises the simulated arrays and documents their expected output under precisely controlled conditions. The resulting graphs are extremely useful in highlighting to the researcher the proficiency's and failings of the arrays under said conditions. This simulation environment interfaces to a real 16 section prototype array so that predictions can be verified by experimentation. The device can be used in such a way that it mimics the simulated dynamic array, while also providing a convenient terminal where more bespoke tests can be conducted. As will be discussed, all market bound DPVA research must be conducted with both a virtual and physical devices because each environment provides an incite that is of great importance to the designer. A later discussion introduces some abstract but potentially significant ideas about synthesising AC electricity using the switching mechanism. An argument suggesting why an industrially accepted synthesis method is not suitable for photovoltaic use is given and a more suitable solution is hypothesized. To finish there is a discussion about the remaining unexplored topics in the field which highlights how and why further research is required. The aim of this is to acknowledge that more work is needed but also to show the way to developing a completely new state of the art source of electricity which may one day help society effectively exploit the abundance of power being delivered to us by the Sun.
10

A thermo-economic model and a simulation analysis of a solar hydrogen system using IPSEpro

El-Sharif, Abdulhamid January 2013 (has links)
The high growth of world population and modern lifestyle are increasing the world’s energy consumption and fossil fuel depletion, as well as increasing environmental and economic adverse impacts. This concern is encouraging scientists and governments to create more reliable, long-lasting and environmentally benign energy sources. Renewable energy sources, particularly solar energy, are nowadays suggested as being one of the main alternative and future sources of energy to traditional fossil fuel sources. Nevertheless, the main challenge in utilizing solar energy is its high utilization cost and variability, when a storage or backup system is required. To overcome this problem, many researchers have introduced hydrogen because it is the cleanest, most abundant and safest fuel that can be used as an energy carrier or a backup system in place of batteries and fossil fuel generators. Solar hydrogen system (SHS) technologies are still immature and a few experimental projects have been installed around the world, inspiring more studies to improve these technologies towards a hydrogen-economy objective. Very little software is commercially available to use for simulation and optimization of a solar hydrogen system and no effective software has been developed for thermo-economic analysis. However, in this study a thermo-economic model library component for solar hydrogen system units such as photovoltaic (PV), photovoltaic thermal (PV/T), fuel cell and electrolyzer have been developed and validated using the commercially available software package IPSEpro. The developed models, along with the existing IPSEpro model libraries have been used to; design, optimize and simulate the entire system to meet the energy demands of a small community in three different sites. The sites considered were Sabha and Misurata in Libya, a hot region as well as Newcastle in United Kingdom in a cold region, using yearly average and a typical summer and winter actual weather data for each site. A parametric study was carried out to investigate the effects of the environmental, main operation and economic parameters on the performance and outputs of each component and the entire system. A thermo-economic analysis of the SHS showed that the PV unit has the highest factors for; (exergy destruction (exdf), destruction cost (CD), investment and destruction summation (ZTCD), and the lowest exergoeconomic (fk), followed by the fuel cell and the electrolyzer. However, the low (fk) factor of the PV and the fuel cell units indicated that a high level of attention has to be focused on increasing the unit’s exergy efficiency. Moreover, the high (fk) factor of the electrolyzer indicates that the reduction of the unit investment cost (ZT) has the priority for unit performance improvement and production cost reduction. It has also been established that, for a SHS at base condition, A. A. El-sharif iii Newcastle University the system’s exergy efficiency was 5.07% with a daily average output electricity cost of 0.23$/kWh. However, for Sabha and Newcastle, the yearly average electricity cost was 0.40$/kWh and 0.77 $/kWh respectively. This is still uncompetitive compared with (+- 0.15 $/kWh) typical current electricity market prices. In addition, the study clarified that SHS will be economically reasonable if the costs of the CO2 emission and fossil fuels consumed are considered in the analysis, particularly in Sabha and Misurata regions. Nevertheless, in these regions the photovoltaic electricity is competitive to the traditional power plant current prices. The analysis also shows that the variation in the environmental, economic and operation parameters have a significant effect on the system and its units’ performance and output costs. The parametric study mainly considered the variation of; ambient temperature (Ta), solar intensity (Sirr), module surface temperature (PV/Tc), interest rate (ir), capacity factor (CF), capital cost (CFC), lifetime (ny), price of output hot water (cwh), cell voltage (Vc), stoichiometric ratio (StH2), hot water temperature and mass flow rate. The parametric study results revealed that the optimum SHS operation conditions will achieve at the smallest ambient temperature and the highest solar intensity. It is also found that recycling the output streams, particularly the hydrogen and utilizing the output hot water of the unit’s cooling system will significantly enhance its performance and reduce the production costs. The study proves that increasing the output hot water of the PV/T system to utilize it in a low thermal energy system using an electric heater is unfeasible. More investigation is recommended to build an integrated IPSEpro thermo-economic model to utilize the SHS output hot water in a low thermal energy system using a solar collector.

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