Numerical analysis of lateral illumination lightpipes using elliptical groovesSánchez-Guerrero, Guillermo E.; Viera-González, Perla M.; Martínez-Guerra, Edgar; Ceballos-Herrera, Daniel E.
doi: 10.1117/12.2273096pmid: N/A
Lightpipes are used for illumination in applications such as back-lighting or solar cell concentrators due to the high irradiance uniformity, but its optimal design requires several parameters. This work presents a procedure to design a square lightpipe to control the light-extraction on its lateral face using commercial LEDs placed symmetrically in the lightpipe frontal face. We propose the use of grooves using total internal reflection placed successively in the same face of extraction to control the area of emission. The LED area of emission is small compared with the illuminated area, and, as expected, the lateral face total power is attenuated. These grooves reduce the optical elements in the system and can control areas of illumination. A mathematical and numerical analysis are presented to determine the dependencies on the light-extraction.
The characteristics of luminescent solar concentrators (LSCs) using inorganic phosphorsYing, Shang-Ping; Chen, Bing-Mau; Li, An-Ting
doi: 10.1117/12.2272907pmid: N/A
The Luminescent Solar Concentrator (LSC) consists of a transparent plate with solar cells on one or more sides. The incoming sunlight is absorbed by the luminescent dyes or particles, which are embedded in the transparent plate or applied in a film on the top or bottom of the transparent plate. The absorbed light is re-emitted at a longer wavelength, and part of the re-emitting light is trapped in the transparent plate by total internal reflection (TIR). Then the solar cells attached to the edges of the transparent plate would collect the light and convert it to electricity. However, the luminescent dyes or particles used in the conventional LSC still suffer from reduced efficiencies and lifetimes, then the inorganic phosphors with relatively high quantum yields, good absorption properties and longer lifetime could be alternative materials used in the structure. In this study, the ray-tracing simulation is used to investigate the optical characteristics of the LSC with the inorganic phosphors embedded film on the top or bottom of the transparent plate. The simulation results will also be used to study the loss mechanisms in the LSC with inorganic phosphors embedded film.
Thermodynamic investigation of the segmented CPCWidyolar, Bennett; Jiang, Lun; Winston, Roland
doi: 10.1117/12.2276711pmid: N/A
We investigate the relationship between the number of segments and the optical transmission of a CPC approximated by equal length segments whose start and end points lie along the CPC profile. We also investigate a separate method for generating CPC-like profiles by adjusting the angle of each segment to satisfy the edge-ray principle. Three variations of this method are examined where the edge-ray condition is taken from the start, mid, and end points of each segment. A flux efficiency (FE) to compare concentrators, which combines the concentration ratio and optical efficiency, is introduced and directly relates to the maximum achievable flux on the absorber. We demonstrate that the FE defined is another way to look at the compromises one makes for a geometric concentrator designed under real-world constraints.
Design and optimization of cascaded DCG based holographic elements for spectrum-splitting PV systemsWu, Yuechen; Chrysler, Benjamin; Pelaez, Silvana Ayala; Kostuk, Raymond K.
doi: 10.1117/12.2273229pmid: N/A
In this work, the technique of designing and optimizing broadband volume transmission holograms using dichromate gelatin (DCG) is summarized for solar spectrum-splitting application. Spectrum splitting photovoltaic system uses a series of single bandgap PV cells that have different spectral conversion efficiency properties to more fully utilize the solar spectrum. In such a system, one or more high performance optical filters are usually required to split the solar spectrum and efficiently send them to the corresponding PV cells. An ideal spectral filter should have a rectangular shape with sharp transition wavelengths. DCG is a near ideal holographic material for solar applications as it can achieve high refractive index modulation, low absorption and scattering properties and long-term stability to solar exposure after sealing. In this research, a methodology of designing and modeling a transmission DCG hologram using coupled wave analysis for different PV bandgap combinations is described. To achieve a broad diffraction bandwidth and sharp cut-off wavelength, a cascaded structure of multiple thick holograms is described. A search algorithm is also developed to optimize both single and two-layer cascaded holographic spectrum splitters for the best bandgap combinations of two- and three-junction SSPV systems illuminated under the AM1.5 solar spectrum. The power conversion efficiencies of the optimized systems under the AM1.5 solar spectrum are then calculated using the detailed balance method, and shows an improvement compared with tandem structure.
Enhancing the light conversion efficiency in a luminescent solar concentrator by using a prism filmYang, Pao-Keng; Tseng, Hua-Yu; Lin, Chia-Wei; Chung, Min-Hsiu; Huang, Tsung-Wei
doi: 10.1117/12.2272964pmid: N/A
We present a method for enhancing the light conversion efficiency of a luminescent solar concentrator by putting a prism film on the upper surface for receiving the incoming light. The luminescent solar concentrator under study was composed of a thick glass with a luminescent film deposited on the top surface and a solar cell attached to the lateral surface. The prism film will deflect the incident light into two different directions. Dependence of the conversion efficiency on the incident angle of the sunlight and influence of the rotation of the prism film on the conversion efficiency were also investigated. Experimental results show that the prism film will increase the light falling on the solar cell in our luminescent solar concentrator.
Compact collimators designed with a modified point approximation for light-emitting diodesLuo, Tao; Wang, Gang
doi: 10.1117/12.2273526pmid: N/A
We present a novel freeform lens design method for an application to LED collimating illumination. The method is derived from a basic geometric-optics analysis and construction approach. By using this method, a compact collimated lenses with Aspect Ratio = 0.219 is presented. Moreover, the utility efficiency (UE) inside the angle defined by ideal concentrator hypothesis with different lens-to-LED size ratios for both this lens and TIR lens are presented. A prototype of the collimator lens is also made to verify the practical performance of the lens, which has light distribution very compatible with the simulation results.
Real time 3D photometryFernandez-Balbuena, A. A.; Vazquez-Molini, D.; García-Botella, A.; Romo, J.; Serrano, Ana
doi: 10.1117/12.2281850pmid: N/A
The photometry and radiometry measurement is a well-developed field. The necessity of measuring optical systems performance involves the use of several techniques like Gonio-photometry. The Gonio photometers are a precise measurement tool that is used in the lighting area like office, luminaire head car lighting, concentrator /collimator measurement and all the designed and fabricated optical systems that works with light. There is one disadvantage in this kind of measurements that obtain the intensity polar curves and the total flux of the optical system. In the industry, there are good Gonio photometers that are precise and reliable but they are very expensive and the measurement time is long. In industry the cost can be of minor importance but measuring time that is around 30 minutes is of major importance due to trained staff cost. We have designed a system to measure photometry in real time; it consists in a curved screen to get a huge measurement angle and a CCD. The system to be measured projects light onto the screen and the CCD records a video of the screen obtaining an image of the projected profile. A complex calibration permits to trace screen data (x,y,z) to intensity polar curve (I,). This intensity is obtained in candels (cd) with an image + processing time below one second.
Tracking and shape errors measurement of concentrating heliostatsCoquand, Mathieu; Caliot, Cyril; Hénault, François
doi: 10.1117/12.2272791pmid: N/A
In solar tower power plants, factors such as tracking accuracy, facets misalignment and surface shape errors of concentrating heliostats are of prime importance on the efficiency of the system. At industrial scale, one critical issue is the time and effort required to adjust the different mirrors of the faceted heliostats, which could take several months using current techniques. Thus, methods enabling quick adjustment of a field with a huge number of heliostats are essential for the rise of solar tower technology. In this communication is described a new method for heliostat characterization that makes use of four cameras located near the solar receiver and simultaneously recording images of the sun reflected by the optical surfaces. From knowledge of a measured sun profile, data processing of the acquired images allows reconstructing the slope and shape errors of the heliostats, including tracking and canting errors. The mathematical basis of this shape reconstruction process is explained comprehensively. Numerical simulations demonstrate that the measurement accuracy of this “backward-gazing method” is compliant with the requirements of solar concentrating optics. Finally, we present our first experimental results obtained at the THEMIS experimental solar tower plant in Targasonne, France.
Advances on geometric flux optical design methodGarcía-Botella, Ángel; Fernández-Balbuena, Antonio Álvarez; Vázquez, Daniel
doi: 10.1117/12.2281481pmid: N/A
Nonimaging optics is focused on the study of methods to design concentrators or illuminators systems. It can be included in the area of photometry and radiometry and it is governed by the laws of geometrical optics. The field vector method, which starts with the definition of the irradiance vector E, is one of the techniques used in nonimaging optics. Called “Geometrical flux vector” it has provide ideal designs. The main property of this model is, its ability to estimate how radiant energy is transferred by the optical system, from the concepts of field line, flux tube and pseudopotential surface, overcoming traditional raytrace methods. Nevertheless this model has been developed only at an academic level, where characteristic optical parameters are ideal not real and the studied geometries are simple. The main objective of the present paper is the application of the vector field method to the analysis and design of real concentration and illumination systems. We propose the development of a calculation tool for optical simulations by vector field, using algorithms based on Fermat`s principle, as an alternative to traditional tools for optical simulations by raytrace, based on reflection and refraction law. This new tool provides, first, traditional simulations results: efficiency, illuminance/irradiance calculations, angular distribution of light- with lower computation time, photometrical information needs about a few tens of field lines, in comparison with million rays needed nowadays. On the other hand the tool will provides new information as vector field maps produced by the system, composed by field lines and quasipotential surfaces. We show our first results with the vector field simulation tool.
Optical coatings for luminescent solar concentratorsJaing, Cheng-Chung; Lu, Po-Chun; Chen, Jian-Wei; Yu, Wei-Gwo; Xie, Jing-Han; Yang, Pao-Keng; Chen, Bing-Mau
doi: 10.1117/12.2273512pmid: N/A
In this paper, the luminescent solar concentrator comprises a thick glass with a spectrally-selective optical coating deposited on the bottom surface and an inorganic phosphor layer contacted on the coating surface. A solar cell is contacted to the lateral surface of the thick glass. Spectrally-selective coatings are applied to reflect and redirect the invisible solar radiation to the edges of luminescent solar concentrators. These coatings also transmit the visible solar light and the emission light of the inorganic phosphor. The short-circuit current of the solar cell is measured in a flashing-mode solar simulator with metal-dielectric heat mirrors and dielectric edge filters coated on the thick glass of the luminescent solar concentrators respectively. Experimental results show that the dielectric edge filter will increase the short-circuit current of the solar cell and the invisible light falling on the solar cell in our luminescent solar concentrator. The metal-dielectric coatings, silver-based transparent heat mirrors, will not increase the short-circuit current of the solar cell in our luminescent solar concentrator due to absorption of metal films.