This thesis work demonstrates the feasibility to fabricate high-efficiency crystalline silicon solar cells by using metal stencil printing technique to replace screen printing or electroless plating techniques for implementing crystalline silicon solar cell front metallization. The developed laser-cut stainless steel stencils successfully challenge two of the cell performance limitations associated with commercial screen printing technology: the wide and non-uniform front gridline fingers and low height-to-width aspect ratio of the fingers. These limitations lower the short circuit current density, the fill factor and, in turn, the efficiency of a screen printed solar cell. Metal stencils are capable of printing fine, high and continuous features on the cell front that have a high aspect ratio. Both single-level and double-level structured stainless steel stencils for solar cell front metallization have been developed, with laser-cut double-level stainless steel stencils being demonstrated for the first time worldwide. Both of them are able to print fine, high and continuous gridline pattern to the front surfaces of solar cells in one step, with a certain number of special short bridges being put at the places where fingers meet busbar and along fingers and busbar. The deformation issue of the very thin stainless steel foils due to its thermal expansion in the process of laser cutting is solved by increasing the energy content in each laser pulse that impinges upon the stainless steel foil with changed Q-switch frequencies, while maintaining the laser average output energy in unit time to an optimum value. A chemical etching process has been developed to etch the dross that results from laser cutting, resulting in well formed metal stencils suitable for printing. By a comparison between the metal stencil printed and conventional mesh screen printed silicon solar cells, which are fabricated on similar Cz silicon wafers with a almost identical cell processing sequence except for using different front contact printing masks, the following conclusions are reached: Fired Ag finger lines with 75-??m width on finished solar cells, using a doublelevel stainless steel stencil can be achieved. In contrast, the fired Ag finger line on finished solar cells using a traditional mesh screen is 121-??m wide. The stencil printed finger is smoother and more uniform than by screen printing and the former has a 25-??m fired finger height with a 0.33 height-to-width aspect ratio, compared to a 10-??m fired finger height with a 0.08 height-to-width aspect ratio for the later. With these advantages, the 4-cm2 stencil-printed silicon solar cells has an averaged 1.28 mA/cm2 higher short circuit current and an averaged 5.9% higher efficiency than the 4-cm2 screen printed silicon solar cell, which identifies one of the key advantages of solar cell metallization schemes by using metal stencil printing in place of screen printing. Using a ???feedback alignment??? method for registration of the laser-formed metal stencil printed pattern and the laser-formed groove pattern, Ag paste can be printed and filled into wafer grooves by using a hand-operated without an optical vision system. The fired finger profile is 50-??m wide and 22-??m high. The best metal stencil printed, selective emitter silicon solar cell demonstrates a 34.2 mA/cm2 short circuit current density, 625 mV open circuit voltage, 0.77 fill factor and 16.4% efficiency, with an excellent spectral response at short wavelengths due to its selective emitter cell structure. It is believed that the performance of this type of solar cell can be enhanced with a screen printer that has an optical vision system and an automatic alignment device. The successful development of metal stencil printed silicon solar cells demonstrates the feasibility of the metal stencil printing as a beneficial technology for the PV industry.

Photovoltaics is currently the fastest growing energy source in the world. Increasing the conversion efficiency towards the thermodynamic limits is the trend in research development. ???Third generation??? photovoltaics involves the investigation of ideas that may achieve this goal. Among the third generation concepts, the tandem cell structure has experimentally proven to have conversion efficiencies higher than a standard p-n junction solar cell. The alternative hot carrier solar cell design is one of the most elegant approaches. Energy selective contacts are crucial elements for the operation of hot carrier solar cells. Besides the carrier cooling problem within the absorber, carrier extraction has to be done through a narrow range of energy to minimise the interaction between the hot carriers in the absorber and the cooler carriers in the contacts. Resonant tunnelling through localised states, such as associated with atomic defects or with quantum dots in a dielectric matrix, may provide the required energy selectivity. A new model in studying the properties of resonant tunnelling through defects in an insulator is proposed and investigated. The resulting calculations are simple and useful in obtaining physical insight into the underlying tunneling processes. It is found that defects having a normal distribution along the tunnelling direction do not reduce the transmission coefficient dramatically, which increases the engineering prospects for fabrication. Silicon quantum dots embedded in an oxide provide the required deep energy confinement for room temperature resonant tunnelling operation. A single layer of silicon quantum dots in the centre of an oxide matrix are prepared by RF magnetron sputtering. The method has the advantage of controlling the dot size and the dot spatial position along the tunnelling direction. The presence of these crystalline silicon dots in the oxide is confirmed by high resolution transmission electron microscopy (HRTEM). A negative-differential resistance characteristic has been measured at room temperature on such structures fabricated on an N-type degenerated silicon wafer, a feature that can be explained by the desired resonant tunnelling process. A silicon quantum dot superlattice can be made by stacking multiple layers of silicon quantum dots. A model is proposed for calculating the band structure of such a silicon quantum dot superlattice, with the anisotropic silicon effective mass being taken into account. It suggests a high density of silicon quantum dots in a carbide matrix may provide the bandgap and required mobility for the top cell in the stacks for the recently proposed all-silicon tandem solar cell. The resonant tunnelling modeling and silicon quantum dot experiments developed have demonstrated new results relevant to energy selective contacts for hot carrier solar cells. Building on this work, the modeling study on silicon quantum dots may provide the theoretical basis for bandgap engineering of all-silicon tandem cells.

The Compact Linear Fresnel Reflector is a solar thermal energy system currently at prototype stage in Australia. The system uses parallel rows of mirrors lined up underneath a long, elevated thermal absorber. The mirrors move so as to focus solar radiation onto the absorber; the absorber contains a bank of high-pressure water pipes through which water is pumped and gradually boils. The process of ??direct steam generation?? in very long pipes, up to 300 m in a straight run, has not previously been performed at this scale; other systems use shorter pipe runs, or use other fluids such as non-boiling oil. This thesis addresses a broad range of design issues relating to the CLFR prototype and its components. Beam solar radiation at the prototype site is estimated from available data including satellite-derived and ground-based measurements. Existing correlations for the beam component of global radiation do not apply well to Australian conditions so a new correlation is proposed. Computational fluid dynamics simulations establish radiative heat-loss as the dominant mode for the thermal absorber. Results are gathered for a range of sizes and shapes, and heat-loss correlations are derived for use in subsequent simulation. Two-phase flow in the absorber direct-steam-generation process is examined, and a detailed model including, pipe-friction pressure drops, flow-boiling heat transfer and cavity heat loss is presented, with validation against the experimental results of other workers. A series of ??performance maps?? give the predicted outlet flow regime for varied inlet conditions, allowing selection of desired operating points. A full system model is given that integrates this absorber model with ancillary components including the pump and connecting pipework; the model is used to evaluate pumping requirements and to establish expected operating conditions. The inherent pressure instability arising from the two phase flow is examined and orifice plates are sizes to stabilise this effect. A dynamic model for the absorber pipe flow using fully implicit finite difference techniques and accurate IAPWS-IF97 steam properties gives the predicted behaviour during solar transients at both long and short time-scales.

This thesis work demonstrates the feasibility to fabricate high-efficiency crystalline silicon solar cells by using metal stencil printing technique to replace screen printing or electroless plating techniques for implementing crystalline silicon solar cell front metallization. The developed laser-cut stainless steel stencils successfully challenge two of the cell performance limitations associated with commercial screen printing technology: the wide and non-uniform front gridline fingers and low height-to-width aspect ratio of the fingers. These limitations lower the short circuit current density, the fill factor and, in turn, the efficiency of a screen printed solar cell. Metal stencils are capable of printing fine, high and continuous features on the cell front that have a high aspect ratio. Both single-level and double-level structured stainless steel stencils for solar cell front metallization have been developed, with laser-cut double-level stainless steel stencils being demonstrated for the first time worldwide. Both of them are able to print fine, high and continuous gridline pattern to the front surfaces of solar cells in one step, with a certain number of special short bridges being put at the places where fingers meet busbar and along fingers and busbar. The deformation issue of the very thin stainless steel foils due to its thermal expansion in the process of laser cutting is solved by increasing the energy content in each laser pulse that impinges upon the stainless steel foil with changed Q-switch frequencies, while maintaining the laser average output energy in unit time to an optimum value. A chemical etching process has been developed to etch the dross that results from laser cutting, resulting in well formed metal stencils suitable for printing. By a comparison between the metal stencil printed and conventional mesh screen printed silicon solar cells, which are fabricated on similar Cz silicon wafers with a almost identical cell processing sequence except for using different front contact printing masks, the following conclusions are reached: Fired Ag finger lines with 75-??m width on finished solar cells, using a doublelevel stainless steel stencil can be achieved. In contrast, the fired Ag finger line on finished solar cells using a traditional mesh screen is 121-??m wide. The stencil printed finger is smoother and more uniform than by screen printing and the former has a 25-??m fired finger height with a 0.33 height-to-width aspect ratio, compared to a 10-??m fired finger height with a 0.08 height-to-width aspect ratio for the later. With these advantages, the 4-cm2 stencil-printed silicon solar cells has an averaged 1.28 mA/cm2 higher short circuit current and an averaged 5.9% higher efficiency than the 4-cm2 screen printed silicon solar cell, which identifies one of the key advantages of solar cell metallization schemes by using metal stencil printing in place of screen printing. Using a ???feedback alignment??? method for registration of the laser-formed metal stencil printed pattern and the laser-formed groove pattern, Ag paste can be printed and filled into wafer grooves by using a hand-operated without an optical vision system. The fired finger profile is 50-??m wide and 22-??m high. The best metal stencil printed, selective emitter silicon solar cell demonstrates a 34.2 mA/cm2 short circuit current density, 625 mV open circuit voltage, 0.77 fill factor and 16.4% efficiency, with an excellent spectral response at short wavelengths due to its selective emitter cell structure. It is believed that the performance of this type of solar cell can be enhanced with a screen printer that has an optical vision system and an automatic alignment device. The successful development of metal stencil printed silicon solar cells demonstrates the feasibility of the metal stencil printing as a beneficial technology for the PV industry.

This thesis work demonstrates the feasibility to fabricate high-efficiency crystalline silicon solar cells by using metal stencil printing technique to replace screen printing or electroless plating techniques for implementing crystalline silicon solar cell front metallization. The developed laser-cut stainless steel stencils successfully challenge two of the cell performance limitations associated with commercial screen printing technology: the wide and non-uniform front gridline fingers and low height-to-width aspect ratio of the fingers. These limitations lower the short circuit current density, the fill factor and, in turn, the efficiency of a screen printed solar cell. Metal stencils are capable of printing fine, high and continuous features on the cell front that have a high aspect ratio. Both single-level and double-level structured stainless steel stencils for solar cell front metallization have been developed, with laser-cut double-level stainless steel stencils being demonstrated for the first time worldwide. Both of them are able to print fine, high and continuous gridline pattern to the front surfaces of solar cells in one step, with a certain number of special short bridges being put at the places where fingers meet busbar and along fingers and busbar. The deformation issue of the very thin stainless steel foils due to its thermal expansion in the process of laser cutting is solved by increasing the energy content in each laser pulse that impinges upon the stainless steel foil with changed Q-switch frequencies, while maintaining the laser average output energy in unit time to an optimum value. A chemical etching process has been developed to etch the dross that results from laser cutting, resulting in well formed metal stencils suitable for printing. By a comparison between the metal stencil printed and conventional mesh screen printed silicon solar cells, which are fabricated on similar Cz silicon wafers with a almost identical cell processing sequence except for using different front contact printing masks, the following conclusions are reached: Fired Ag finger lines with 75-??m width on finished solar cells, using a doublelevel stainless steel stencil can be achieved. In contrast, the fired Ag finger line on finished solar cells using a traditional mesh screen is 121-??m wide. The stencil printed finger is smoother and more uniform than by screen printing and the former has a 25-??m fired finger height with a 0.33 height-to-width aspect ratio, compared to a 10-??m fired finger height with a 0.08 height-to-width aspect ratio for the later. With these advantages, the 4-cm2 stencil-printed silicon solar cells has an averaged 1.28 mA/cm2 higher short circuit current and an averaged 5.9% higher efficiency than the 4-cm2 screen printed silicon solar cell, which identifies one of the key advantages of solar cell metallization schemes by using metal stencil printing in place of screen printing. Using a ???feedback alignment??? method for registration of the laser-formed metal stencil printed pattern and the laser-formed groove pattern, Ag paste can be printed and filled into wafer grooves by using a hand-operated without an optical vision system. The fired finger profile is 50-??m wide and 22-??m high. The best metal stencil printed, selective emitter silicon solar cell demonstrates a 34.2 mA/cm2 short circuit current density, 625 mV open circuit voltage, 0.77 fill factor and 16.4% efficiency, with an excellent spectral response at short wavelengths due to its selective emitter cell structure. It is believed that the performance of this type of solar cell can be enhanced with a screen printer that has an optical vision system and an automatic alignment device. The successful development of metal stencil printed silicon solar cells demonstrates the feasibility of the metal stencil printing as a beneficial technology for the PV industry.

<p>Project Solaris is a student research project with the goal to build a solar powered Unmanned Aerial Vehicle. This study is one in a set of studies that make up the initial phase of project Solaris. The main objective of this report is to investigate earlier solar powered airplanes as well as evaluate (or explore) potential future niche markets where solar powered UAVs could excel.A presentation of earlier solar powered airplanes will give an overall understanding of how solar powered airplanes have evolved and also provide information about the goals and ambitions behind the projects.Potential applications such as power line inspection and algal bloom observation will be described and a list of specifications for each application will be presented.</p> / Solaris

<p>Almost all the domestic water in Brazil is heated with an electrical heater directly by the end consumer. A typical heater has an effect of 5 400 W and when the whole population takes a shower in the evening it causes big peaks in the electrical grid. This consumption peaks could be reduced by simple and cheap solar collector system. </p><p>Different system technologies and the most important parts of a solar collector system are described in the technical background. In Lajeado almost every system is a self-circulated system because of the simplicity and the lower costs. </p><p>Solar cooling as an alternative to the vapor compressor chillers has been studied. The cooling demand is biggest when the sun shines; this makes the sun perfect as a source to cooling. The ab- and adsorption chillers as a method in the future have been discussed in this paper; however it has only been studied briefly because small scale chillers using the technology can not be found on the market yet. </p><p>A number of different systems have been dimensioned after the existing conditions of Lajeado, the town where the project has been carried out in. Prizes and costs for both installation and materials come from the local solar collector supplier. With this as a background; several systems for various hot water demands has been dimensioned and costs and repayment time been calculated. A study of all the systems shows that, if the hot water demand increases and the systems get bigger, the profitability grows and the repayment time becomes shorter, down to three years. In almost every case the repayment time was under eight years, which makes solar heating attractive and the profit is good for the southern Brazil.</p>

Graduation date: 2000

Third-generation optoelectronics, which utilize nanoscale materials, have received a considerable amount of attention in the chemical sciences and are poised to make a large impact in both fundamental research and real-world application. In order to make a contribution to the field, this thesis describes a route towards highly stable, water-soluble semiconductor nanorods and their incorporation into nanoparticle/polymer composite thin films. To characterize the photoelectrical properties of these multilayers, and to provide a proof-of-concept for a functional optoelectronic device, the films were integrated into an excitonic solar cell. To gain further insight into the physical properties of the thin films, computational modeling of the carrier transport in thiophenes was conducted, and the limits to device performance were described in the context of their charge transport characteristics. Electrostatic layer-by-layer (ELBL) assembly was used for the synthesis of multilayer nanorod/polymer composite films. CdSe nanorods (NRs) were synthesized and made cationic and water-soluble using ligand exchange chemistry. The NRs were partnered with anionic polymers including poly(sodium 4-styrenesulfonate) (PSS) and the two polythiophene-based photoactive polymers, sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate (PTEBS) and poly[3-(potassium-6-hexanoate)thiophene-2,5-diyl] (P3KHT). Multilayer growth, with nanoscale control, is shown through UV-vis spectroscopy, cross-sectional scanning electron microscopy (SEM) and surface analytical techniques including atomic force microscopy (AFM). The formation of an intimate nanorod/conducting polymer bulk heterojunction is confirmed through cross-sectional SEM, transmission electron microscopy (TEM), and scanning Auger analysis. A series of photovoltaic devices was fabricated on ITO electrodes using CdSe NRs in combination with PTEBS or P3KHT. A thorough device analysis showed that performance was limited by carrier transport throughout the films. Computational modeling of the thiophene component in polymer-based third-generation devices was done using density functional theory (DFT) with core potentials added to account for long range dispersion interactions inherent to optoelectronic thin films. Binding energies and orbital splittings in dimers composed of monomers up to six rings were investigated. The combination of experimental and computational studies elucidates some of the underlying mechanisms behind the production of third-generation solar energy.

Project Solaris is a student research project with the goal to build a solar powered Unmanned Aerial Vehicle. This study is one in a set of studies that make up the initial phase of project Solaris. The main objective of this report is to investigate earlier solar powered airplanes as well as evaluate (or explore) potential future niche markets where solar powered UAVs could excel.A presentation of earlier solar powered airplanes will give an overall understanding of how solar powered airplanes have evolved and also provide information about the goals and ambitions behind the projects.Potential applications such as power line inspection and algal bloom observation will be described and a list of specifications for each application will be presented. / Solaris