Results 1 - 10 of 29
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[en] Light concentrators to be used by the camera of a telescope to view gamma-ray-induced Cherenkov light, are analyzed from the point of view of optical efficiency, background rejection capability and manufacturability. A small decrease in the optical efficiency due to multiple reflections undergone by rays incident at small angles in a compound parabolic concentrator is observed. The influence of the angle of incidence on the reflectivity of the wall is analyzed and found to be inconsequential. A closed-packed matrix of concentrators with hexagonal entrance apertures is considered and the light spread in the adjacent pixels introduced by the removal of portions of the surface of concentrators is evaluated
[en] Highlights: • A novel CPC was experimentally tested in East-West and North-South orientation. • E-W orientation has an optical efficiency of 6% greater than N-S. • The heat losses to the environment are lower in the N-S orientation. • The mathematical model presents a difference of ±0.15 °C for the N-S and ± 0.21 °C for the E-W. - Abstract: In this paper, we present a comparative study of two compound parabolic concentrators with a concentric tube as absorber positioned longitudinally in the North-South and East-West directions. The analysis includes the design, modeling, construction, experimentation and validation of the concentrators. It was defined as an object of study a CPC with 24.3° of acceptance and 2.22 of geometric concentration, with a length of 2 m. The absorber tube has an outside diameter of 0.04 m. Later a mathematical model and a simulator for the thermal analysis of the CPC were elaborated. In order to carry out the experimentation, two pieces of equipment were formed by 4 CPC cavities implementing the same construction method. It was necessary to set up a test bench to position both collectors respectively in the N-S and E-W direction. Based on the experimental results it was possible to adjust the simulator to obtain an average difference of ±0.15 °C for N-S and ±0.21 °C for E-W. The results show that on average, the CPC with an E-W orientation has an optical efficiency of 57.5%, while the N-S position reaches 51.3%. The coefficient of heat losses is higher for the CPC E-W than the N-S position, with −21.54 and −10.44 respectively.
[en] Highlights: • A novel hybrid concentrating photovoltaic thermal (PV/T) collector is developed. • Thermal component achieves 60× concentration using nonimaging optics. • GaAs solar cells used as spectrally selective mirrors for low energy photons. • Thermal efficiencies of 37% at 365 °C and electrical efficiencies of 8% achieved. • Combined electric efficiency reaches 25% of DNI for system cost of $283.10/m"2". - Abstract: A novel double stage high-concentration hybrid solar photovoltaic thermal (PV/T) collector using nonimaging optics and world record thin film single-junction gallium arsenide (GaAs) solar cells has been developed. We present a detailed design and simulation of the system, experimental setup, prototype, system performance, and economic analysis. The system uses a parabolic trough (primary concentrator) to focus sunlight towards a secondary nonimaging compound parabolic concentrator (CPC) to simultaneously generate electricity from single junction GaAs solar cells, as well as high temperature dispatchable heat. This study is novel in that (a) the solar cells inside the vacuum tube act as spectrally selective mirrors for lower energy photons to maximize the system exergy, and (b) secondary concentrator allows the thermal component to reach a concentration ratio ∼60×, which is significantly higher than conventional PV/T concentration ratios. The maximum outlet temperature reached was 365 °C, and on average the thermal efficiency of the experiment was around 37%. The maximum electrical efficiency was around 8%. The total system electricity generation is around 25% of incoming DNI, by assuming the high temperature stream is used to power a steam turbine. The installed system cost per unit of parabolic trough aperture area is $283.10 per m"2.
[en] A method for summarising annual or seasonal solar irradiation data in irradiation distribution diagrams, including both direct and diffuse irradiation, is outlined. The practical use of irradiation distribution diagrams is discussed in the paper. Examples are given for the calculation of collectable irradiation on flat plate collectors or trough-like concentrators like the compound parabolic concentrator (CPC), and for the calculation of overhang geometries for windows to prevent overheating of buildings. (author)
[en] In this work, the performances of two optimized reflective secondary optics elements a CPC (Compound Parabolic Concentrator) and a Cone for use in a CPV concentrator system are studied using ray-tracing simulation for the same primary optical element: a Fresnel lens. These optical elements are compared in terms of concentration, acceptance angle, exit angle and output light distribution. Our results show that the power distribution at the end of the concentrator is more uniform in the case of the cone. The optical efficiency is higher when the secondary element is placed at a distance with f the focal length; R the input radius of the secondary optical element and θ the acceptance angle of the secondary optical element. Also, we found that the length and the input radius of each optical element decrease when the Fresnel lens diameter increases but the input radius of the CPC stills the larger. Finally, our calculation show that the CPC is longer than the cone while the Fresnel lens diameter is less than 200 mm and beyond this value both the cone and the CPC mostly present the same length. (paper)
[en] This work presents a developed field-test scaled asymmetrical compound parabolic concentrator (ACPC) and an investigation of its performance with a single flow system of water on Escherichia coli inactivation. As a function of water flow rate, ability to produce hot water of the ACPC and hence inhibit the growth of bacterial in water is focused to study; the flow rates varied are 0.2, 0.4, and 0.6 l min−1. With a design and choice of material, the constructed ACPC unit with 0.2 l min−1 could produce hot water with maximum temperature of 76.4 °C, with lower flow rates resulting in the lower outlet water temperature and consequently the reduced kinetics of bacteria inactivation. Thermal performance parameters have been described in a correlative view with the particular operation condition and flow rate variables through mathematic calculation. The effect of inlet driving temperature, believed to play a significant role controlling the outlet temperature, on E. coli inactivation has been investigated. (paper)
[en] With the increasing population and industrialization, there is need to cut down the load of fossil fuels and to reduce environmental pollution. A large part of industrial process heat lies from low to medium temperature range which can be supplied by solar energy. Scheffler fixed focus concentrators are successfully used for medium temperature applications in different parts of the world. These concentrators are taken as lateral sections of paraboloids and provide fixed focus away from the path of incident beam radiations throughout the year. The paper presents description and experimental results of medicinal and fruit processing using an 8 m/sup 2/ surface area Scheffler solar concentrator installed at solar campus, university of Kassel, Witzenhausen Germany. The research was focused to promote solar renewable energy in rural and remote locations. The solar system was equipped with Pyranometer and thermocouples to evaluate real time data which was used for performance evaluation of the solar system during processing of different products. In the first phase of the research, several trials were made to evaluate the performance of the system. Within the solar radiations range of 700- 800 W m-2, the receiver temperatures were recorded between 300 - 400 deg. C. The average power was found to be 1.55 kW and system efficiency was found to be 32.34%. Different medicinal plants like Melissa, Peppermint, Rosemary, Cumin, and Cloves buds were successfully processed by using solar energy. Different fruit and vegetables like Apples, Plums, cherries, tomatoes were also processed by using solar energy. Research results have showed that solar energy can be successfully used for the post harvest and fruit processing at rural location. (author)
[en] We examine the possibility of improving the performance of solar concentrator photoelectric devices (SCPDs) using optical media. It is shown that the area of a photocell can be decreased by a factor of 1.5-1.7 with the same SCPD power when using optical media. (author)