This PDF file contains the front matter associated with SPIE Proceedings Volume 10758, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

As the cost of electricity from photovoltaics drops rapidly, some have begun to ask whether solar concentration has any place at all in our energy future. Nevertheless, even in Dubai, where record-low costs for PV electricity has recently been achieved, the state utility DEWA, a combined power and water provider, recently ordered the construction of a 700MW CSP plant which will sell electricity at 7.3 c/kWh, more than double the cost of energy from PV! This premium is associated to the intrinsic energy storage ability of CSP systems as PV energy production profile does not fully match electricity demand curve. Clearly, CSP provides an added value that points a way forward for solar concentration technologies. While the capacity for energy storage is the critical factor in this situation, concentration-based approaches can be advantageous in other aspects of the energy-water nexus, especially where desalination is the dominant pathway to satisfy water demand. We will discuss several areas where solar concentration can provide benefits for electricity and water production, including solar-driven water desalination; integration of solar electricity, daylighting and heating capacity in buildings; and boosting capacity factors and LCOE of unconventional photovoltaic power systems.

The long-term goal of the project is to create and justify a reliable mathematical model that expresses the efficiency of geometrical shapes of non-tracking flexible solar panels. However, the amount of solar energy absorbed by a non-tracking flexible solar panel depends on many parameters: the direction of the sun beam, reflected light, and temperature, etc., which would make a complete model mathematically complicated. In the current model, we limit our consideration to the direction of the sunbeam. In order to simulate the exposure of the panel, we describe the trajectory of the Sun and base the model on the mathematical flux that uses the sun rays as the vector field. To be precise, the efficiency of a geometrical panel is defined as the flux density, which is the ratio of the mathematical flux and the surface area. Our current model was evaluated for the latitude of New York City and we determined the efficiency of the optimized at panels, cylindrical panels, and conical panels. The analysis was largely done through geometrical studies and numerical integration with software programs Python, Maple, Mathematica, and MATLAB.

Conventional tracking solar concentrators track sunlight by rotating the concentrator optics to face the sun, which adds to the cost and bulk of the system. Beam-steering lens arrays, in contrast, allow solar tracking without bulk rotation of the optics. It consists of lens arrays stacked in an afocal configuration, and tracking is implemented by relative translation between these lens arrays. In this work, we present a phase-space methodology for analyzing and optimizing the performance of the beam-steering, and for revealing optical aberrations in the system. Using this methodology, we develop a beam-steering lens array with simulated ≈70% efficiency across a two-axis ±40° tracking range, and a divergence of the outgoing beam of less than ±0.65°. We also present a functional small-scale prototype and demonstrate the feasibility of the concept for solar tracking. Beam-steering lens arrays can be placed in front of conventional concentrator optics and operated with little or no external tracking. This may enable low-cost robust concentrated solar power systems, and could also find other applications such as solar lighting and steerable illumination.

Experimental performance of a two-stage 50X spectral beam splitting (SBS) parabolic trough collector (PTC) - incorporating double-junction epitaxial lift-off (ELO) InGaP/GaAs solar cells and using a suspended alumina particulate heat transfer media tested to 600°C - is presented.

A novel glazing system consisting of a polymer layer with embedded micro compound parabolic concentrators (CPCs), which is attached to a glass pane of glazing, is proposed. It aims to reduce the energy consumption due to cooling in buildings, provide daylighting, and maintain the transparent view. In the present work, the daylighting system is modelled for ray-tracing simulation, and the angular-dependent transmittance at the azimuth angle of 0° is calculated. Structural characterization is conducted using optical microscope for the microstructures which serve as support for the reflective thin films of a micro CPC. Based on self-shading effect of a microstructure, facet-selective deposition of Aluminum with various thickness has been achieved by physical vapor deposition. Spectral measurement has been used to characterize the optical properties of the Aluminum thin films. Diffraction effect with respect to the thin film thickness on the transmission of linear micro-CPCs arrays is investigated by a monochromatic laser beam and visual observation. The results of the present work provides the reference for the optimization of the transmittance of the deposited thin film for a micro CPC, in order to achieve the desired optical property.

The Compound parabolic concentrator used in the solar collector discussed in this paper is of the novel design, glass encased with 23% truncated reflectors and all glass receiver. Optical modeling was done in Light tools illumination design software to determine the optimum optical efficiency within a range of half acceptance angle and the heat transfer modeling and simulation was done in COMSOL Multiphysics simulation software. The Collector was built, tested and performance characterization was done. The experimental tests performed are stagnation test, water test for optical efficiency at low temperatures and closed loop oil test for thermal efficiency at high temperatures as high as 200°C. For the water and oil test, Flow rate method and Calorimetry method were used. The light tools optical modeling gave the optical efficiency of 64%. The stagnation temperature recorded at the absorber at 0% efficiency was 350°C. The water test at the temperature of 30-40°C gave the efficiency of 59%.

Conventional silicon Photovoltaic (PV) modules often have a significant surface obstruction that reduces the collection of incident solar illumination and energy conversion efficiency. In this paper, light management methods that combine low cost holographic optical elements and diffusers into conventional PV modules are evaluated to capture unused illumination. It is found that by using reflection volume holograms (RVHs) with 300 nm spectral bandwidth in combination with a diffuser on a PV module with 12% of its surface area not covered with active PV cell regions that an improvement in power collection efficiency of 9.36% is possible.

Mask-aligner lithography is a technology used to transfer patterns with critical dimensions in the micrometer range from below 1 micron for contact printing to a dozen of microns in proximity printing. This technology is widely used in the fabrication of MEMS, micro-optical components, and similar fields. Traditionally, the light sources used for mask-aligners are high-pressure mercury arc lamps, which emit in the UV rang of the spectrum with peaks at 365 nm, 405 nm and 435 nm, respectively the g-, h- and i- lines. These lamps suffer from several disadvantages (inefficient, bulky, dangerous), which makes alternatives interesting. In recent years, high power UV LEDs at the same wavelengths appeared on the market, opening the door to new illumination systems for mask-aligners. We have developed a modular 250 W LED-based illumination system, which can advantageously replace a 1 kW mercury arc lamp illumination. LEDs, arranged in a 7×7 grid array, are placed in the entrance apertures of individual reflectors, which collimate the individual irradiation to an output angle of 10°. A subsequent fly’s eye integrator homogenizes the illumination in the mask plane. It is followed by a Fourier lens, superimposing the individual channels in the mask plane, and a field lens to ensure telecentric illumination. This multisource approach allows the shaping of the source by switching individual illumination channels, determining the illumination angles and the spatial coherence in the mask plane. This concept can be used, for example, to do source-mask optimization. Compared to mercury arc lamp illumination, our system is simultaneously more efficient, compact, versatile, economic and sustainable. In our contribution, we present the design of the system as well as lithographic test prints done with different illumination patterns.

It has been well established that nonimaging optics is the ideal way to concentrate or funnel light for applications ranging from solar energy to illumination. One industry where lighting is critical is the theater in which stage performers must be illuminated effectively. Historically theater lighting has been done using filament bulbs, which produce a lot of heat and provide discomfort to the actors and patrons. With the advent of LED lighting, many theaters are starting to replace the old filament bulbs with LED fixtures to provide the same effect. However, the last holdout for transition to LEDs has been the spotlight, because of the high standards of theater experts. Typical spotlights use a halogen-tungsten bulb coupled with an ellipsoid reflector to provide illumination of 10,000 lumens with a power input of 1000 watts. In this paper we present the work on the development of a nonimaging optics reflector coupled with a 100-watt LED fixture that can match the 10,000 lumens required by theaters for spotlighting, at a fraction of the power requirement and heat generation.

The flowline design has been shown to be a powerful tool for nonimaging optics, utilizing a vector field analogy to describe the reasoning behind the various designing method. However, as a set of tools the vector analysis has not been fully explored, especially it vector potential, A, which has found its usage in modern physics. In this talk we will try to link the vector potential with the fundamental understanding of thermodynamics.

The rotationally symmetric flow line is one of the few examples of the closed form solutions for flow lines in 3D configurations. In this paper we give its analytical form.

Spectral management and diffusive light transport enables plants to both survive on extremely low irradiance and also to survive long enough under extreme temperature and pressure to leave imprints in super-heated impact glasses. These properties are related to structures wherein a low density of light absorbent particles are embedded in a light scattering and spectral selective reflective matrix. This marvelous diffusive light engineering has wide-ranging applications based on bio-mimicry. Where, environmentally sensitive radiative-to-non-radiative lifetime ratios increase the photon flux to the chlorophyll molecules best positioned for favorable photochemistry and for preservation under extreme conditions. The embedding of absorptive particles within a transparent scattering matrix has far reaching intriguing applications. Included is the extreme heating of light absorbent particles within a relatively cold matrix. Interestingly, the hot absorbent particle-cold matrix condition is critical for the efficient extreme heating of small particles. Here the potential of non-equilibrium passive diffusive light collection will consider be explored using one of the most challenging application extreme particle heating for controlled nuclear fusion.

Nonimaging optics is focused on the study of techniques to design concentrators or illuminators systems. The flowline optical design method, based on the definition of the geometrical flux vector J, is one of these techniques. The main property of flowline method is, its ability to estimate how radiant energy is transferred by the optical systems using the concepts of vector field theory, like field line or flux tube, overcoming traditional raytrace methods. This method has been developed only at an academic level, where characteristic optical parameters are ideal and the studied geometries are simple. The main objective of the present paper is the extension of the flowline method to the analysis and design of real 3D concentration and illumination systems by means of simulation. Using the concept of vector potential we can generalize flowline computations to real 3D systems. This new computation methodology provides, traditional simulations results like irradiance maps with higher precision and lower computation time, and new information as vector field maps produced by the system.

Redistribution of light from a given source in order to create a prescribed intensity pattern on a given set in 3D space is a task arising in numerous applications. Designing optical systems with capabilities to perform such tasks reliably in a wide variety of applications is the overall goal of much of research in optics. An important practical case is the “laser beam shaping problem” which requires transformation of a Gaussian beam from a laser into a beam with “flat top” intensity profile. It has been shown by John A. Hoffnagle and C. Michael Jefferson that a pair of plano-aspheric lenses can be used to transform a collimated, radially symmetric, Gaussian beam to a radially symmetric, collimated beam with “flat-top” intensity profile. Here we discuss this design problem when a priori requirement of radial symmetry is not imposed neither on the input/output radiances nor on the geometry of the input/output beams. The solution in this case is sought among “freeform” optical surfaces.

To approach the Shockley-Queisser limit, a solar cell must embody the principles of efficient light-emitting diode (LED) design. Here we describe how ultra-high luminescence efficiency, both internal and external, is the basis for the present efficiency records in solar energy conversion. These developments have provided an impetus for new energy technologies, which rely on the same design strategies to reach their theoretical limits. Thermophotovoltaics, the conversion of terrestrially produced thermal radiation to electricity, can now approach >50% efficiency. Ultra-efficient photovoltaics and LEDs also enable optoelectronic refrigerators with the potential to surpass other methods of solid-state cooling in energy efficiency.

The need to cool people in a warming world has led to renewed interest in radiative cooling in recent years. Most recent research has focused on the development of spectrum-selective materials designed to radiate in the atmospheric window while suppressing absorption of radiation outside of this window. However the alternative approach of using angular selectivity, via the inclusion of nonimaging optical components to restrict the cooling element’s field of view, has been neglected. Here we argue for the value of nonimaging optics in the design of practical radiative cooling systems.

Described are the prospects for broadband optical refrigeration based on Raman scattering of incoherent light. Laser pumped rare earth fluorescence has been demonstrated and commercial applications are sure to follow. Broadband refrigeration requires strong Raman scattering and large Raman shift. Also required are spectral management and photonic patterning to offset the unfavorable anti-Stoke’s to Stoke’s shift ratio. Materials such as diamond, silicon, and a number of molecular systems are ideal and have low absorption. Optics splits the broadband spectrum into light and dark bands with width corresponding to the Raman shift. Broadband spectrums where photon flux decreases with increasing photon energy are ideal. By tailoring the incoming spectrum, by utilizing extremely transparent strong Raman shift materials and by photonic inhibition of Stoke’s shifted light the prospect become feasible. The Raman optical cross- section increases with decreasing particle size (until the particle become too small to support the Raman-phonons). Where conservation of phonon states in these truncated Brillioun-zone particles requires an increased density (number/cm³) of the allowed-states to compensate for states lost to particle size. Nonetheless, the anti-Stokes to Stokes ratio is approximately one-to-two at laboratory temperature. Thin film deposited diamond is an excellent candidate for refrigeration applications due to its high transparency small grain size and its large Raman magnitude and large shift. Simple one-dimensional photonic structures selectively inhibit the Stoke’s shifted light making refrigeration possible.

We introduce flowlines as an analytical tool to optimize solar concentrator designing based on non-imaging optics. Comparisons were performed for multiple concentrator configurations from the same flowlines group to understand the final flux on low-cost heat pipes or minichannel absorbers for a small scale residential hybrid system. With the optical simulation results, we assemble and test a novel optical design for new low-cost, high-efficiency solar CHP collector to analyze both thermal and electric performances. By combining photovoltaic (PV) cells with heat pipes and mini channels, we further thermal energy capture while simultaneously enhance the solar cell performance.

We present a computational framework for optimizing nonimaging solar concentrators. Our approach is to represent the concentrator’s shape as a polygon, use ray tracing to compute the flux at the receiver, and employ Generalized Pattern Search (GPS) on the polygon’s vertices. Many shape optimization techniques use gradients to seek a direction of steepest ascent or descent. For solar concentrators, these approaches can easily get trapped in local minima. In contrast, GPS is a derivative-free method that seeks a global optimum on suitable meshes, without computing gradients. This helps to avoid getting trapped in local minima. Results for 2D concentrators show that our algorithm can converge to the ideal concentrator's shape as the number of polygon vertices increases. We also show that when the number of vertices is small and fixed, the optimal polygon can differ significantly from the polygon that would be obtained using a uniform collocation of the ideal shape. This approach could lead to a simple, accurate, and fast design method, and improve the performance and lower the fabrication costs of nonimaging concentrators for solar and thermal applications.

The demand for high brightness, stable, long-life and broadband light sources has been rising continuously in advanced applications for semiconductor metrology, sensor calibrations, and life sciences imaging. Laser-Driven Light Sources (LDLS™) are capable of delivering super-high brightness and stable radiation over long lifetimes. LDLS sources use high power diode lasers to energize high-intensity xenon (Xe) plasma which produces broadband radiation from 170nm to 2400nm. The LDLS spectrum has several spectral peaks located near 826nm, 885nm, and 920nm, similar to regular Xe short arc lamps. Those peaks, when compared with lower emission wavelengths, can reduce the dynamic range of broadband spectral measurements. In this paper, the application of a spectral flattening filter for LDLS sources is presented. With optimized coupling optical design, the output power and spectral performance for the LDLS under different fiber coupling conditions have been compared and analyzed. Measurement results show the coupled flux could reach 83mW with a 600μm diameter fiber, and the high Xe peaks near 826nm, 885nm, and 920nm have been suppressed successfully.

The most expensive electrical energy occurs during early morning and late afternoon time periods. This poses a problem for fixed latitude mounted photovoltaic (PV) systems since the sun is low in the sky. One potential solution is to use vertically mounted bifacial PV modules to increase the East-West collection area and solar energy production during high energy usage time periods. However, vertically mounted PV modules have reduced conversion efficiency during mid-day time periods. In this paper the use of a horizontally mounted collector with holographic elements is examined as a way of increasing the energy yield of vertically mounted bifacial PV (VMBP) modules during mid-day time periods. The design of a holographic `cap’ collector is evaluated that considers dimensional constraints, holographic diffraction efficiency characteristics, and system solar collection efficiency properties. The irradiance illuminating the vertical mount is modeled with and without the cap. The design process also includes the optimization of separation between rows of vertically mounted modules and the use of directional diffusers in the proximity of the modules to maximize system energy yield.

In solar applications, traditional crystalline silicon photovoltaic (PV) cells are the most commonly used technology to harvest solar energy. The efficiency of Si PV is fundamentally limited to around 33% and in practice, these cells have an outdoor efficiency of less than 22%. Concentrated PV technology uses multi-junction PV cells that collect a broader spectrum of the sun with high efficiency (>40% has been reported). However, due to the different semiconductors used, multi-junction cell costs are higher than traditional PV cells. Increasing the solar concentration not only reduces the cost of electricity produced by multi-junction cells, by reducing the required area, but can also maximize the IV efficiency of the cells. There exist different methods to concentrate solar energy such as large parabolic mirrors, which have tracking challenges due their size and weight; or spherical lens arrays, which have limited optical geometrical concentration ratios. In this respect, freeform optical devices can be used to enhance the optical throughput for multi-junction cells and reduce the space required to achieve large concentration ratios. In this work, we discuss a novel optical design combining aspherical lens arrays and arrays of optical waveguides, which constitute broadband, freeform non-imaging optical devices. We compare different waveguide designs which have been optimized using non-sequential ray tracing software. The relationship between the optical surface quality and the optical efficiency is also investigated. Finally, we present the results of the experimental characterization of these waveguides under laboratory conditions using different techniques to measure optical throughput and stray light losses.