This PDF file contains the front matter associated with SPIE Proceedings Volume 10379, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Nonimaging Optics has been shown to achieve the theoretical limits constrained only by thermodynamic principles. The designing principles of nonimaging optics allow a non-conventional way of thinking about and generating new optical devices. Compared to conventional imaging optics which rarely utilizes the framework of thermodynamic arguments, nonimaging optics chooses to map etendue instead of rays. This fundamental shift of design paradigm frees the optics design from ray based designs which heavily relies on error tolerance analysis. Instead, the underlying thermodynamic principles guide the nonimaging design to be naturally constructed for extended light source for illumination, non-tracking concentrators and sensors that require sharp cut-off angles. We argue in this article that such optical devices which has enabled a multitude of applications depends on probabilities, geometric flux field and radiative heat transfer while “optics” in the conventional sense recedes into the background.

While the use of the asymmetric compound parabolic concentrator (ACPC) for solar concentration has been addressed, documentation regarding the étendue and angular acceptance of the ACPC is absent from the literature. This paper delves into the 2D design of the ACPC and discusses its étendue and angular acceptance, offering a new design tool regarding such instances when symmetry is broken. It is found that unlike the compound parabolic concentrator (CPC) whose angular acceptance fills a symmetric ellipse, the ACPC’s angular acceptance fills an asymmetric ellipse in some cases, and a folded ellipse in others. Both cases are dependent on the maximum acceptance angles of the design. Ray tracing is utilized to confirm both the angular acceptance ellipses and étendue, as well as to offer a visual representation of the intensity distribution for asymmetric designs in both angular and phase space.

With PV module prices low and flat-plate technology dominating the market, the solar industry has taken a hard turn away from concentrator PV systems, which has faced high cost barriers. Despite this, there may still be space for CPV products and concepts to contribute, but these advantages are best realized by aggressively rethinking the way we design PV concentrators.

The use of non-imaging optics in the application of high temperature solar thermal collectors can be extremely advantageous in eliminating the need to track the sun. The stationary nature of non-imaging optics collectors, commonly called compound parabolic concentrators (CPC’s), present a unique design challenge when orienting them to collect sunlight. Many facilities throughout the world that adopt CPCs are not situated to orient the collectors in the ideal angle facing the sun. This East-West misalignment can adversely affect the optical and power performance of the CPC collector. To characterize how this misalignment effects CPCs, reverse raytracing simulations are conducted for varying offset angles of the collectors from solar South. Optical performance is analyzed for an ideal East-West oriented CPC with a 40-degree acceptance angle. Direction cosine plots are used to develop a ratio of annual solar collection by the CPC over the total annual solar input. From these simulations, average annual collector performance is given for offset angles ranging from 0 to 90 degrees for different Earth Latitudes in 10 degree increments.

Conventional solar trackers use information of the sun’s position, either by direct sensing or by GPS. Our method uses the shading of the receiver. This, coupled with nonimaging optics design allows us to achieve ultra-high concentration. Incorporating a sensor based shadow tracking method with a two stage concentration solar hybrid parabolic trough allows the system to maintain high concentration with acute accuracy.

In designing solar concentrator optics there are many parameters that must be optimized in order to create a useful system, such as compactness, number of elements or interfaces, and acceptance angle, among others. Using geometric optics, tradeoffs between these parameters become inevitable. For example, a lens, trough or dish may be compact but has low tolerance of angular misalignment; angular tolerance can be improved by adding secondary and tertiary optics, but this increases complexity and reduces optical throughput; nonimaging optics such as the CPC offer wide acceptance angles from as single element, but are too long to be practical, in most applications, above low concentrations. These tradeoffs can be avoided by using angle-selective photonic materials to exploit the equivalence between angular restriction and concentration. Recently, broadband angular selectivity in optical films has been demonstrated by the Soljacic group in MIT. In this collaborative work we use this material to experimentally demonstrate two visible-spectrum optical concentrators. We demonstrate that these concentrators are thermodynamically ideal when the material properties are ideal, and describe the material improvements most essential for improving device performance, and discuss how commercial solar concentrator systems could be improved by the use of angular-selective optics

With more than 30 Medium-Size Telescopes (MST) located in both North and South hemispheres, the Cherenkov Telescope Array (CTA) shall be the largest cosmic gamma ray detector ever built. Each MST focal plane consists in an array of some 1800 photomultipliers equipped with their own light concentrating optics in order to maximizing the amount of Cherenkov radiation collected by the telescope and to block stray light originating from ground environment. Within the CTA Consortium, the Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) is in charge of designing, subcontracting the realization to industry, and testing the MST light concentrators. Two different optical solutions were pre-selected, respectively based on CPCs (Winston cones) and non-imaging concentrating lenses. Prototypes were manufactured by different industrial companies and tested in our laboratory on a test bench specifically built for the project. After shortly describing both optical designs, this communication is essentially focused at experimental results. Each type of concentrator has been submitted to extensive performance measurements, including radiometric efficiency at different wavelengths, rejection curves, and qualitative shape error test. The final selected concentrator is the CPC, although non-imaging lenses exhibit interesting properties in terms of radiometric performance.

Optical freeform surfaces are very popular today in such fields as lighting systems, sensors, photovoltaic concentrators, and others. The application of such surfaces allows to obtain systems with a new quality with a reduced number of optical components to ensure high consumer characteristics: small size, weight, high optical transmittance. This article presents the methods of synthesis of refractive surface for a given source and the radiation pattern of various shapes using a computer simulation cubic spline interpolation.

The purpose of this study is to analyze various surfaces of flexible solar panels and compare them to the traditional at panels mathematically. We evaluated the efficiency based on the integral formulas that involve flux. We performed calculations for flat panels with different positions, a cylindrical panel, conical panels with various opening angles and segments of a spherical panel. Our results indicate that the best efficiency per unit area belongs to particular segments of spherically-shaped panels. In addition, we calculated the optimal opening angle of a cone-shaped panel that maximizes the annual accumulation of the sun radiation per unit area. The considered shapes are presented below with a suggestion for connections of the cells.

Shaping of LED white light is of increasing interest for several industrial applications. There are several known design concepts available. However these concepts suffer from high uniformity errors, low efficiencies, chromatic aberrations and/or high tolerance sensitivity. To overcome these limitations we present a novel design concept which is based on the design of aperiodic scattering cell arrays. In a first design step, a unit scattering cell is designed. Afterwards this cell is periodically replicated. Finally the periodicity of the array is broken using parametric optimization. Obtained design results are compared with experimental data.

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.

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.

Use of new of light sources based on LED technology should allow the develop of systems that combine conservation and exhibition requirements and allow to make these art goods available to the next generations according to sustainability principles. The goal of this work is to develop light systems and sources with an optimized spectral distribution for each specific point of the art piece. This optimization process implies to maximize the color fidelity reproduction and the same time to minimize the photochemical damage. Perceived color under these sources will be similar (metameric) to technical requirements given by the restoration team uncharged of the conservation and exhibition of the goods of art. Depending of the fragility of the exposed art objects (i.e. spectral responsivity of the material) the irradiance must be kept under a critical level. Therefore, it is necessary to develop a mathematical model that simulates with enough accuracy both the visual effect of the illumination and the photochemical impact of the radiation. Spectral reflectance of a reference painting The mathematical model is based on a merit function that optimized the individual intensity of the LED-light sources taking into account the damage function of the material and color space coordinates. Moreover the algorithm used weights for damage and color fidelity in order to adapt the model to a specific museal application. In this work we show a sample of this technology applied to a picture of Sorolla (1863-1923) an important Spanish painter title “woman walking at the beach”.

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.

In real world applications the nonimaging optics has the advantage of high error tolerance compared to conventional imaging optics. In this paper we present the result of a solar collector constructed with the nonimaging optics principles and the effect of off-positioning its absorbers on its optical efficiency. Thermal analysis of such effects are also presented.

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.

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.

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.

The efficiency in Fresnel lenses is affected by three principal sources: energy loss by absorption, chromatic dispersion and reflectance losses at refracting surfaces. On this subject, the design of nonimaging Fresnel lenses integrated by refractive and total internal reflection prisms is presented. This design method uses iterative calculations for design every prism and it selects the best option for avoid reflectance losses. A design and characterization of a Fresnel lens that takes chromatic aberration into account is shown, including a comparison with a nonimaging Fresnel lens composed only by refraction prisms is performed and with other integrated by only total internal reflection prisms. In addition, the study about how acceptance angle and the number of prisms affects the final transmittance of the lens is included.

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.

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.

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.

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,αγ). This intensity is obtained in candels (cd) with an image + processing time below one second.