Search

Concentrating photovoltaic technology harnesses solar energy by increasing the solar density upon solar cells using optical concentrators. Ongoing research on concentrating photovoltaic systems aim to improve the achievable energy harnessing and utilisation potential. Increasing the concentration ratio for high energy generation raises many advances and limitations in the concentrating photovoltaic design. However, the field of concentrating photovoltaic research is still in progress where new configurations, methods and materials are fabricated to reach a competitive cost by enhancing the efficiencies of the system to standard silicon photovoltaic systems. The work presented in this thesis focuses on developing and demonstrating an ultrahigh concentrated photovoltaic system beyond 3000×. This system is based on a Silicon-on-Glass Fresnel lens resulting in a geometrical design of 5831×. The Fresnel lens as a primary optical interface was investigated theoretically, numerically, and experimentally to understand the operating limits in terms of power output, optical performance (optical efficiency and concentration ratio), and working temperature. The discrepancy between a Fresnel lens's theoretical and experimental optical characterisation results was studied. All the equations were elaborated for single- and multi-junction solar cells, emphasising the performance when the focal spot area is larger or lesser than the solar cell area. The prediction approach of optical characterisation has shown a strong agreement between the theoretical and experimental results of the multi-junction solar cells with a discrepancy of 2% at 7.7 W (77 suns) and 6% on the average cross a solar irradiance on the cell from 3.1 W - 7.7 W corresponding to 31 suns - 77 suns in concentration ratio. The numerical model using COMSOL Multiphysics software was established to study the Fresnel lens optically and thermally. The developed optical model was validated theoretically and experimentally to show a firm agreement with a discrepancy of ≤1%. Also, the developed thermal model was validated experimentally to show a difference of only 2.18%. Further, optical and electrical characterisations of the flawed glass have been conducted. The optical characterisation has shown a drop of 3.2% in optical efficiency. I-V and power curves of cracked and non-cracked Fresnel lenses were also compared to show a drop of 3.2% in short circuit current and power. A theoretical analysis of the optical performance for a ¼ of the ultrahigh concentrated photovoltaic system design grouping three optical interfaces is performed to estimate the optical loss and its influence on the optical efficiency and concentration ratio. Also, a numerical model was established using COMSOL Multiphysics software to simultaneously evaluate the thermal and optical performance of a ¼ of the ultrahigh concentrated photovoltaic system. The system was analysed under direct normal irradiance ranging from 400 W/m^2 to 1000 W/m^2 in an interval of 100 W/m^2 , showing a simulative optical efficiency of ~93% and a simulative concentration ratio of 1361 suns at 1000 W/m^2 . The thermal model was interlinked with the optical model to generate the results accordingly. The final stage receiver shows a maximum temperature ranging between 157.4 ℃ and 78.5 ℃. Moving toward a ultrahigh concentrated photovoltaic design raises the importance of a cooling management system due to thermal excitation. Although the thermal performance and thermal management for the ultrahigh concentrated photovoltaic system are beyond this thesis's scope, the cooling mechanism arrangement based on either pre- or post-illumination techniques was explored. The post-cooling mechanism study was established using COMSOL Multiphysics software for numerical analysis. A flat-plate and micro fin heatsink studied the effect of concentration ratio up to 2000 suns to determine their limits as a passive cooling system and establish when an active cooling system is needed based on the recommended operating temperature of the solar cell of 80 °C. On the other hand, Graphene was experimentally exploited as a pre-illumination cooling technique for a solar cell with different graphene coating thicknesses. The concept of utilising graphene as a neutral density filter for focal spot concentrating photovoltaic (Fresnel lens primary optic) reduces the solar cell temperature significantly and maintains the cell temperature for a more extended period. The graphene coating orientation further influenced the temperature gradient behaviour of the focal spot and incident temperature. The Fresnel lens working parameters (focal length and the focal spot) were defined to establish the mechanical structural design accordingly. The system was mechanically designed based on three optical interfaces, built in-house, and incorporated with a sun tracker. Different aspects were examined initially before the outdoor testing, the sun tracker alignment accuracy and payload capacity, windage load, and counterbalance weight and moments effects using SOLIDWORKS software. The ultrahigh concentrated photovoltaic system was tested outdoor with three types of secondary mirrors, resulting in an effective concentration ratio of 984 suns, 1220 suns, and 1291 suns and an average optical efficiency of 18.5%, 20.25%, and 22% for Aluminium reflective film, Pilkington Optimirror, and ReflecTech® Polymer secondary optic types, respectively. The fabricated ultrahigh concentrated photovoltaic system and tested experimentally outdoor is the highest in both geometrical and effective concentration ratios so far. It would not be possible to design and perform the ultrahigh concentrated photovoltaic system without fully characterising its primary optic, which helps set the performance basis and associated losses. Although the experimented system showed the highest value in terms of both geometrical and effective concentration ratios, the subsequent optics to the Fresnel lens were standard optics. The attained outcomes are practical in progressing concentrating photovoltaic technologies to a higher concentration ratio.

This thesis project investigates the configuration of an enclosed evaporation chamber with the intention of converting seawater into potable freshwater. The evaporation chamber's sole heat source is provided by a Fresnel lens, located above the chamber, which concentrates sunlight onto a 3-inch diameter focal plate built into the core of the chamber. The design of the evaporation chamber is modeled after a solar still and is coupled with a heat exchanger to boost efficiency of the system. The chamber was designed with the objectives of being portable, lightweight, low cost, corrosion resistant, interchangeable, and size convenient with the goal of producing 1 Liter of freshwater per hour of operation. The evaporation chamber consists of two primary components, a core and an attached arrangement of fins, all of which are heated via the Fresnel lens. A consistent intake of 2 grams/second of saltwater enters from the top of the chamber and is then gravity fed across the fins. Fin orientation has been designed to inhibit the flow rate of water within the chamber, maximizing the surface area of contact with the heated fins. The evaporation chamber was modeled through SOLIDWORKS and underwent a physical optimization study to reduce material usage while maximizing potential for heat transfer and minimizing fluid flow rate. A symmetric profile of one quarter of the chamber was then simulated in COMSOL Multiphysics. Concentrated solar heat flux through a Fresnel lens was applied to the receiver on the top of the core. The simulation was split into a preheating and an evaporation phase. A profile approximation for the fluid flow was modeled by the CFD module. Following computer simulations, the evaporation chamber was constructed and tested.

This thesis project investigates, analyzes, designs, simulates, constructs and tests a dual-axis solar tracker system to track the sun and concentrates the heat of the sunlight, using a Fresnel lens, into a small area, which is above of an evaporator, to increase the temperature of the seawater to convert it into freshwater. The dual-axis solar tracker was designed with the main objectives that the structure was portable, dismountable, lightweight, low cost, corrosion resistant, wires inside pipes, accurate, small size, follow the sun automatically, off-grid (electrical), use green energy (solar powered), and has an empty area right below of the lens. First, a 500 mm diameter flat Fresnel lens was selected and simulated based on an algorithmic method achieved by a previous PhD student at UNT using MATLAB®, to give the optimization lens dimensions. The lens profile was drawn with AutoCAD®, then output profile lens was simulated in COMSOL Multiphysics®. The objective was to provide the high efficiency, optimum and high precision of the focal rays and heat to the receiver of the evaporator. A novel dual-axis solar tracker system was then designed that is portable, dismountable, lightweight and corrosion resistant. The solar tracker tracks the sun in two axis of rotation automatically during the day time, maximizing the angles of inclination on each axis. After testing computer simulations, the dual-axis solar tracker system was constructed and tested. Last, a detailed cost analysis was performed of the entire project. The outcome of this work can be applied for desalination seawater purposes or other any Fresnel lens application that require a focal high temperature directed by dual-axis solar tracker system.

This work investigates the Fresnel-lens-based solar concentrator-receiver system in a multi-perspective manner to design, test and fabricate this concentrator with high-efficiency photon and heat outputs and a minimized effect of chromatic aberrations. First, a MATLAB®-incorporated algorithm optimizes both the flat-spot and the curved lens designs via a statistical ray-tracing methodology of the incident light, considering all of its incidence parameters. The target is to maximize the solar ray intensity on the receiver's aperture, and therefore, achieve the highest possible focal flux. The algorithm outputs prismatic and dimensional geometries of the Fresnel-lens concentrator, which are simulated by COMSOL® Multiphysics to validate the design. For the second part, a novel genetically-themed hierarchical algorithm (GTHA) has been investigated to design Fresnel-lens solar concentrators that match with the distinct energy input and spatial geometry of various thermal applications. Basic heat transfer analysis of each application decides its solar energy requirement. The GTHA incorporated in MATLAB® optimizes the concentrator characteristics to secure this energy demand, balancing a minimized geometry and a maximized efficiency. Two experimental applications were selected from literature to validate the optimization process, a solar welding system for H13 steel plates and a solar Stirling engine with an aluminum-cavity receiver attached to the heater section. In each case, a flat Fresnel-lens with a spot focus was algorithmically designed to supply the desired solar heat, and then a computer simulation of the optimized lens was conducted showing great comparability to the original experimental results. Thirdly, the prismatic geometry of the Fresnel lens was further optimized through a statistical approach that incorporates laws of light refraction and trigonometry. The proposed design produces high focal irradiance that is more suitable for thermal applications. The motivation was to enhance the tolerability of a flat Fresnel-lens concentrator to tracking errors, without the use of secondary optics or sophisticated, and normally costly, meticulous tracking equipment. A comparative simulation analysis was conducted for two case studies from literature, each with a different design method. Fresnel lenses optimized by this work enhanced the concentration acceptance product (CAP) significantly, compared to that in literature. Then, this work introduced an innovative code-based, detailed, and deterministic geometrical approach, which couples the optimization of the Fresnel lens primary optical element (POE) and the dome-shaped secondary optical element (SOE). The objective was to maximize the concentration acceptance product, while using the minimum SOE and receiver geometries at a given f-number and incidence angle (also referred to as the tracking error angle). The laws of polychromatic light refraction along with trigonometry and spherical geometry were utilized to optimize the POE grooves, SOE radius, receiver size, and SOE–receiver spacing. Two literature case studies were analyzed to verify this work's optimization, and the equivalent POEs designed by this work, with optimized SOEs, showed a significant enhancement in the CAP values compared to that of literature. Lastly, four methods for prototyping the Fresnel lens were discussed and experimentally tested; 3D printing, acrylic resin casting, direct CNC machining in acrylic and hot embossing. Once tested, the methods of CNC machining and hot embossing of acrylic proved to be the most promising in terms of cost, fabrication time, and concentration effectiveness. Future work will focus on enhancing the algorithmic design and improving the quality of lens fabrication.

The thesis describes the use of a high numerical aperture phase Fresnel lens for high resolution ion imaging and scalable fluorescence collection. We have demonstrated the first step towards fabricating and integrating a scalable collection optic with an ion trap with applications towards large scale ion trap quantum computers. I outline the use of the lens for capturing high resolution images of trapped ions. Using these high resolution images we have demonstrated spatial thermometry, a thermometry technique which relies on imaging the small changes in the ion spot size as the ion temperature changes. By adding a beam propagating along the optic axis of the imaging system we have also been able to use the high resolution imaging system to observe the absorption image from a single atom. We have verified that the contrast of the absorption images was the maximum achievable with our imaging system according to theory. Finally, using the absorption images we have been able to observe the phase shift of the light scattered by the atom with respect to the illumination field. The observed phase shift was found to be the maximum allowed by theory.