A virtual impactor aerosol concentrator with a circumferential inlet slot has been built and tested. Circumferential slot virtual impactors (CSVIs) have low pressure losses, similar to linear slot impactors, but without particle losses due to end effects. The CSVI was designed using the results from a computational fluid dynamics study. The device has a total sampling flow rate of 10 to 30 L/min and a concentration factor of 10:1. CSVIs were built based on the CFD study design and tested with oleic acid droplets and polystyrene latex beads. The test results found a cutpoint Stokes number of 0.75 and 90% particle transmission at least 52X the Stokes cutpoint. At a flow rate of 10 L/min the cutpoint is 2.0 µm aerodynamic diameter (AD) and >90% transmission efficiency was found between 4 mm AD, and 22 µm AD. At the flow rate of 30 L/min the cutpoint is 1.2 mm AD and a >90% transmission efficiency was found between 2 and 10 mm AD. Performance and pressure drop curves were found for a variety of flow rates. The pressure drop across the CSVI at 10 L/min was 270 Pa (1.1 in H2O) with an ideal power consumption of 0.045 watts. At 30 L/min the pressure drop was 970 Pa (3.9 in H2O) with an ideal power consumption of 0.44 watts.

A two -stage circumferential slot virtual impactor aerosol concentrator system has been developed that is designed for nominal operational conditions of a 2 μm AD cutpoint, an aerosol inflow to the first stage of 100 L/min and a minor flow rate from the second stage of 1 L/min. Each unit was tested separately before being combined in the system. However, because of high inter-stage losses, a sheath air system was inserted between the two stages, wherein a small amount of air was injected into the apex of a cone placed on top of the second stage. The sheath air displaced the stagnation point at the apex of the cone and redirected particles into the sampling zone of the second stage unit. The cutpoint particle size of the system was 2.5 μm AD at the nominal flow rate. The dynamic range (ratio of upper limit to the lower limit of aerodynamic particle diameter associated with transmission efficiencies of 50%) was 5.4, and the largest particle size for which the transmission was at least 50% is 13.6 μm AD. When run at 67 L/min, the cutpoint is 4 μm AD and the dynamic range is 3.75; at 150 L/min the cutpoint is 2.05 μm AD and the dynamic range is not less than 4.74. The pressure drop across the system is 685 Pa (2.75 in. H2O). This yields an ideal power consumption of 0.77 watts.

A two -stage circumferential slot virtual impactor aerosol concentrator system has been developed that is designed for nominal operational conditions of a 2 μm AD cutpoint, an aerosol inflow to the first stage of 100 L/min and a minor flow rate from the second stage of 1 L/min. Each unit was tested separately before being combined in the system. However, because of high inter-stage losses, a sheath air system was inserted between the two stages, wherein a small amount of air was injected into the apex of a cone placed on top of the second stage. The sheath air displaced the stagnation point at the apex of the cone and redirected particles into the sampling zone of the second stage unit. The cutpoint particle size of the system was 2.5 μm AD at the nominal flow rate. The dynamic range (ratio of upper limit to the lower limit of aerodynamic particle diameter associated with transmission efficiencies of 50%) was 5.4, and the largest particle size for which the transmission was at least 50% is 13.6 μm AD. When run at 67 L/min, the cutpoint is 4 μm AD and the dynamic range is 3.75; at 150 L/min the cutpoint is 2.05 μm AD and the dynamic range is not less than 4.74. The pressure drop across the system is 685 Pa (2.75 in. H2O). This yields an ideal power consumption of 0.77 watts.

The energy issue has been gaining a lot of attention in many countries in recent years. Among the kinds of energies, the solar energy is one of the most interesting topics of them. In addition to the fabrication process and raw material, another focal point aims at solar concentrator. This paper shows a new and easy way to increase the solar energy efficiency. We utilize the micro-optics principle to design and fabricate a microlens array of the solar concentrator. With this concentrator, it can enhance the optical absorption on the solar cell. The microlens array concentrator (MLA-concentrator) is different from the conventional concentrator. The MLA-concentrator does not need any electric equipment to follow the sunlight, and it is easy to manufacture. The size is smaller than conventional concentrator, especially. The MLA-concentrator can decrease the reflection of light at oblique angles and increases the second reflection at the interface between concentrator and solar cell, which makes the sunlight uniform. It also has an interesting characteristic which is the pantoscopic incidence. This new-type MLA-concentrator is fabricated by using LIGA-like process, and then it is integrated to the solar cell for electricity generation. Most important, this kind of structure can be combined with all kinds of solar cell. The solar cell with the MLA- concentrator adds the total watt 3.96% in all angle.

archives@tulane.edu / As global energy consumption continues to grow, new paths towards renewable energy generation are needed to reduce environmental impact and allow for more zero-net energy development. This includes not only electricity generation but also energy required for thermal applications. This dissertation explores three different technologies to generate electricity and high temperature heat simultaneously by using an actively tracked parabolic dish concentrator (2.72 m2) and an all-in-one hybrid receiver. This hybrid receiver usually consists of two key components, a PV module assembled with multijunction solar cells based on III-V materials, and a thermal receiver that transfers absorbed solar energy into a working fluid for a variety of commercial and industrial process heating applications. A key goal of this work is to use spectrum splitting and other design innovations to operate PV cells at much lower temperatures than the thermal receiver output temperatures. PV cooling is critical for PV modules to sustain high energy conversion efficiencies and to work for longer duration under concentrated light. A key distinction in different designs reported here is how the PV cells are cooled, either “transmissive microfluidic cooling”, “transmissive direct fluid cooling”, and “non-transmissive microfluidic cooling”. All three technologies show good performance for both efficient PV cooling (< 120°C) and high system energy conversion efficiency (> 80%). This dissertation is divided into four key chapters. Chapter 2 discusses spectrum splitting CPV with transmissive microfluidic cooling, focusing on the optical performance of the PV modules. By applying a transfer matrix-style approach, the cumulative transmission through the entire PV module is calculated: these results are verified experimentally. By doing so, the power collected by the PV cells and thermal receiver can be predicted. Chapter 3 explores a spectrum splitting hybrid receiver design using a cheaper and more straightforward cooling method that flows silicone oil across PV cells to extract their waste heat and to eliminate the use of sapphire for cost reduction. The cooling performance is verified by outdoor tests and the system efficiencies are discussed under different solar concentration. Chapter 4 investigates another hybrid receiver design that utilizes waste heat from high efficiency PV cells to preheat the working fluid in the thermal receiver instead of dumping the energy to surroundings as in the previous two methods. This design allows both the cells and the thermal receiver to be illuminated with concentrated sunlight simultaneously without the need for spectrum splitting. The electrical and thermal performance are tested both in the lab and outdoors. Chapter 5 discusses a proposed way to enhance the transmission of the spectrum splitting III-V solar cells used in Chapters 2 and 3. Epitaxial lift-off is used to remove the III-V cell substrate and to fabricate highly infrared-transmissive, spectrum-splitting thin-film solar cells. In summary, we explore the power collection performance, including optical, electrical, and thermal aspects, for these hybrid solar receiver technologies, enabling their use in a number of promising applications. / 1 / Yaping Ji

This work shows a laboratory based demonstration that elastic scattering from a layer of wavelength-sized particles can be used to concentrate sunlight for use in photovoltaic power production. The concentrator design consists of a layer of particles dispersed across a mirrored glass plate. Photovoltaic cells line the edges of the plate, which receive light that is coupled into the plate via scattering by the particles and confined thereafter by total internal reflection. All materials used to construct the concentrator are low-cost off-the-shelf items typically available at hardware stores. The net power produced is compared to a single, bare cell that is directly illuminated by the same light source. This comparison shows a promising trend in terms of overall concentrator size that may eventually yield a concentrator capable of producing more power than that produced by the same amount of cell material under direct illumination.

This thesis discusses aspects of a novel solar concentrating photovoltaic / thermal (PV/T) collector that has been designed to produce both electricity and hot water. The motivation for the development of the Combined Heat and Power Solar (CHAPS) collector is twofold: in the short term, to produce photovoltaic power and solar hot water at a cost which is competitive with other renewable energy technologies, and in the longer term, at a cost which is lower than possible with current technologies. To the author’s knowledge, the CHAPS collector is the first PV/T system using a reflective linear concentrator with a concentration ratio in the range 20-40x. The work contained in this thesis is a thorough study of all facets of the CHAPS collector, through a combination of theoretical and experimental investigation. A theoretical discussion of the concept of ‘energy value’ is presented, with the aim of developing methodologies that could be used in optimisation studies to compare the value of electrical and thermal energy. Three approaches are discussed; thermodynamic methods, using second law concepts of energy usefulness; economic valuation of the hot water and electricity through levelised energy costs; and environmental valuation, based on the greenhouse gas emissions associated with the generation of hot water and electricity. It is proposed that the value of electrical energy and thermal energy is best compared using a simple ratio. Experimental measurement of the thermal and electrical efficiency of a CHAPS receiver was carried out for a range of operating temperatures and fluid flow rates. The effectiveness of internal fins incorporated to augment heat transfer was examined. The glass surface temperature was measured using an infrared camera, to assist in the calculation of thermal losses, and to help determine the extent of radiation absorbed in the cover materials. FEA analysis, using the software package Strand7, examines the conductive heat transfer within the receiver body to obtain a temperature profile under operating conditions. Electrical efficiency is not only affected by temperature, but by non-uniformities in the radiation flux profile. Highly non-uniform illumination across the cells was found to reduce the efficiency by about 10% relative. The radiation flux profile longitudinal to the receivers was measured by a custom-built flux scanning device. The results show significant fluctuations in the flux profile and, at worst, the minimum flux intensity is as much as 27% lower than the median. A single cell with low flux intensity limits the current and performance of all cells in series, causing a significant drop in overall output. Therefore, a detailed understanding of the causes of flux non-uniformities is essential for the design of a single-axis tracking PV trough concentrator. Simulation of the flux profile was carried out using the ray tracing software Opticad, and good agreement was achieved between the simulated and measured results. The ray tracing allows the effect of the receiver supports, the gap between mirrors and the mirror shape imperfections to be examined individually. A detailed analytical model simulating the CHAPS collector was developed in the TRNSYS simulation environment. The accuracy of the new component was tested against measured data, with acceptable results. A system model was created to demonstrate how sub components of the collector, such as the insulation thickness and the conductivity of the tape bonding the cells to the receiver, can be examined as part of a long term simulation.

Two experimental configurations of linear slot nozzle virtual impactors were constructed and experimentally investigated for use as bioaerosol concentrators. In one configuration, the Linear Slot Virtual Impactor (LSVI), the nozzle was a straight slot having a length of 89 mm (3.5"). In the second configuration, the Circumferential Slot Virtual Impactor (CSVI), the nozzle was curvilinear following a circular path having a diameter of 152.4 mm (6.0") and the resulting total slot length was 479 mm (18.8"). Multiple prototypes of the two configurations were constructed having nozzle widths that varied from 0.508 mm (0.015") to 0.203 mm (0.008"). Optical and physical measurements were made of the nozzle dimensions in the critical region of the virtual impactor units. For the LSVI units the misalignment between the acceleration nozzle and the receiver nozzle was measured between 6 µm (0.00025") and 29 µm (0.00114"). This represented a range of 2% to 10% misalignment relative to the acceleration nozzle width. The CSVI Unit 1 and 2 misalignments were measured to be 15 µm (0.00061") and 9 µm (0.00036"), or 10% and 1.8% relative misalignment, respectively. The virtual impactors were tested with liquid and solid monodisperse aerosol particles. For operation at flow rate conditions predicted from the literature to produce a cutpoint of 0.8 µm AD, an acoustic resonance was observed, corresponding to significant nozzle wall losses of particles and an absence of normal particle separation in the virtual impactor. The onset of the resonance phenomenon was observed to begin at a nozzle Reynolds number of approximately 500 for the LSVI configuration, and 300 for the CSVI configuration. For flow rates just below the onset of resonance, normal virtual impactor behavior was observed. The value of Stk50 was 0.58 for both devices, corresponding to a particle cutpoint size of 1.1 µm AD for the LSVI configuration and 2.2 µm AD for the CSVI. The collection efficiency was greater than 72% for all particle sizes larger than twice the cutpoint up to the largest particle size tested (≈ 10 µm AD). The peak collection efficiency for both concentrators was greater than 95%.

The aim of the work was to create an automatic positioning system, with optics for radiation concentration and a body for its collection, by monitoring the sun across the sky using a camera. At the beginning are introduced the concentrator systems and the movement of the sun from the perspective of the observer. Follows description of the various potential components which requires a functional system. The last part deal with the implementation of selected components for operation as a whole system, verification of functionality by accurate tracking of the sun across the sky and measuring the performance of the concentrator system with automatic positioning.

Hydrogen is a valuable and versatile energy currency; it may be produced by harvesting solar energy and later used as a fuel to generate electricity any time of the day. This energy transaction of solar energy to hydrogen is evaluated in this work by employing a one-to-one multi-junction solar cell to proton exchange membrane combined system in a laboratory setting. Both components of the system were commercially available. The energy conversion efficiency of each isolated system was first evaluated to determine the ideal operation conditions of each respective system. For input currents in the range of 60 mA to 440 mA, the proton exchange membrane converted electrical energy to chemical potential energy with an efficiency greater than 90%. The multi-junction solar cell reached efficiencies of up to 33% while under a solar concentration of 30 Suns. The current and voltage characteristics, which resulted in the optimal operation of the isolated systems did not align and therefore, both systems were not operating at their ideal operation conditions when in the combined system. The overall energy conversion efficiency of the system was measured to be at most 19.1% under 25 Suns, an efficiency higher than systems employing traditional silicon solar cells. It was theorized that if the two system were operating under ideal conditions, the overall energy conversion efficiency would be 30.3% between 10 and 15 Suns. Methods to align the ideal operation conditions of the two systems are presented.