This PDF file contains the front matter associated with SPIE Proceedings Volume 11120, including the title page, copyright information, table of contents, and author and conference committee lists.

A highly reflective rear mirror can increase the efficiency of thermophotovoltaics through regeneration of unused photons. Based on this concept, we recently demonstrated a record 29.1% thermophotovoltaic device efficiency. We have also identified the challenges as we aim towards 50% thermophotovoltaic efficiency.

This work reports progress towards demonstrated Raman-based optical refrigeration. Previously [1] we introduced Raman refrigeration and its required photonic structures. Building on the previous, the mechanisms and photonic structures are detailed and simplified proof-of-concept devices described. Three wavelength bands, two illuminated and one dark, are considered. The width of each of these bands is predicated upon the magnitude of the Raman shift of the active layer. Optimally, the first illuminated band is approximately one Raman shift (wavelength) in width. This illuminated band is capped above (at shorter wavelengths) by a dark band. At longer wavelengths a second illuminated band again one Raman shift in width is reflected by photonic structuring that forbids light propagation. The dark bands provide an exhaust through which up energy (anti-Stokes) shifted light can be emitted thereby carrying away heat. The Photonic structure prohibits the propagation of a band of long wavelength light thereby both blocking Stoke’s shifted illuminated band light and reflecting incident light having these wavelengths. The naturally occurring solar spectrum with its light and dark bands caused by atmospheric absorption is a good match to diamond-based Raman refrigeration. Diamond also has extremely low absorption and large Raman cross-section especially in small grain form. Proof-of-concept devices employing simple one-dimensional photonic structures are the focus of present experimental effort. The prospect of broadband refrigeration remains a delicate balance requiring limited absorption and increased Raman cross section through phonon engineering of the Raman active layer.

In this research work, the performance of novel secondary concentrator in the vacuum receiver of the parabolic trough collector is investigated. The secondary concentrator is designed, the optical and thermal performance analysis is done analytically and validated numerically by using Finite Element Analysis based computational software. From the initial optical and thermal modeling, it is found that the use of secondary reflector gives the concentration of 53X against the concentration in 20’s X of conventional trough collectors, the optical efficiency of 75% and the thermal efficiency of 60% at 650oC. After the design and analysis, the secondary concentrator is formed to the shape and photogrammetry technique is adopted to validate the optical simulations. In future work, the secondary concentrator and selective coated absorber will be produced and will be packaged inside the vacuum receiver. The installation, testing and commissioning of the full system two-stage concentration parabolic trough collector with novel secondary concentrator will be performed at University of California Merced in 2020.

A method to design Ronchi-Hartmann screens for testing a fast plano-convex aspherical Fresnel lens is presented. We design null screens that produce either aligned straight fringes or quasi-angular spots arrays for observed patterns. The designs of these null screens are based on knowledge of the caustic by refraction through arbitrary curves. A qualitative test for a Fresnel lens is presented.

We will discuss the design & development of a low cost vacuum solar thermal collector with thermal storage for small scale desalination systems. The design consists of a novel low cost non-tracking solar thermal collector, called the Integrated Compound Parabolic Concentrator (ICPC), with 64% solar-to-thermal efficiency at 150°C, which is paired with a low-cost phase-change thermal energy storage system. Together, they will significantly reduce the levelized cost of heat (LCOH) to below $0.015 per kWhth over 20 years, while also incorporating features of dispatchability and portability

Freeform optics has great potential for delivering highly effective solar concentrators and lighting systems, but in some cases it can be challenging to implement. A numerical method is described for calculating 3D flowline concentrator shapes in a way that provides complete freedom over the specification of arbitrary source and receiver objects. This lends the approach to a range of practical design problems involving asymmetric systems, non-lambertian and extended light sources. The method reproduces the hyperbolic and hyperparabolic concentrator geometries identified in the literature, operating close to the thermodynamic limit of concentration. A practical example is given in the optimisation of a secondary concentrator for a concentrator photovoltaic array receiving light from a field of heliostats. The secondary improves the overall capture efficiency of the photovoltaic receiver at noon, and is expected to deliver further improvement at other times of day.

An essential part of a concentrated solar power system is the solar tracker. Tracking is usually implemented by rotating the entire optical system to follow the sun, adding to the bulk and complexity of the system. Beam-steering lens arrays, on the other hand, enable solar tracking using millimeter-scale relative translation between a set of lens arrays stacked in an afocal configuration. We present an approach for designing and comparing beam-steering lens arrays based on multi-objective optimization, where the objective is to maximize efficiency, minimize divergence, and minimize cost/complexity. We then use this approach to develop new configurations with improved performance compared to previously reported results. As an example of a design suitable for high-concentration applications, we present a system consisting of four single-sided lens arrays that can track the sun with a yearly average efficiency of 74.4% into an exit-cone with divergence half-angle less than ±1◦. We also present a simplified system consisting of three single-sided lens arrays, which can be implemented with less mechanical complexity and potentially lower cost. This simplified system achieves 74.6% efficiency and a divergence half-angle of less than ±2.2◦, and might be relevant for low or medium concentration applications. We believe that these results demonstrate the previously untapped potential of beam-steering lens arrays. If such designs are successfully manufactured, they may become an attractive alternative to conventional external solar trackers for a range of solar energy applications.

Nonimaging optics is focused on the study of techniques to design optical systems for the purpose of energy transfer instead of image forming. The flowline optical design method, based on the definition of the geometrical flux vector J, is one of these techniques. The main advantage of flowline method is its capability to visualize and estimate how radiant energy is transferred by the optical systems using the concepts of vector field theory, like field line or flux tube, which overcomes traditional raytrace methods. The main objective this paper is to extend the flowline method to analyze and design real 3D concentration and illumination systems by the development of new simulation techniques. In this paper we will analyzed real 3D refractive and reflective systems using flowline vector potential method. A new constant term of Optical Path Length has been introduced, similar and comparable to the gauge invariant, which produces a correction to enable the agreement between raytrace and flowline based computations. Finally an introduction to Flowline computations for non-Lambertian sources has been carry out. This new optical simulation methodology provides traditional raytrace results, like irradiance maps, but opens new perspectives to obtaining higher precision, lower computation time.

U.S. energy consumption is reviewed from a top-down approach with special emphasis on thermal energy consumption in the residential, commercial, and industrial sectors. The solar thermal R&D efforts of the past 10 years at UC Merced are then presented which detail (i) a low cost combined heat and power collector (PV/T) for space heating, hot water, and electricity (ii) a nonimaging integrated compound parabolic concentrator (ICPC) with phase change thermal energy storage (TES) for low cost (< $0.015 / kWh_th) dispatchable (24/7) solar for 120 °C process heating (iii) a mediumtemperature external compound parabolic concentrator (XCPC) for 100-250 °C process heat which has been used to demonstrate efficient solar cooling and solar driven wastewater evaporation for brine management, and (iv) a two-stage high concentration parabolic trough collector with a nonimaging secondary to achieve < 650 °C operation.

The pragmatic virtues of ground-level receivers in solar towers have long been recognized, but the associated beam-down optics reduce concentration, resulting in higher heat loss and cost, or the need for an actively-cooled tertiary concentrator that incurs additional optical losses. Here, we describe the concept of an aplanatic beam-down solar tower, where concentration can be increased without the need for a tertiary concentrator, while retaining a ground-level receiver. The basis for satisfying aplanatism constitutes tailoring the contour of a stationary secondary mirror atop the tower with a distinct heliostat tracking strategy. Conflating the aplanatic solar tower with the option of multiple towers, where a heliostat can be aimed at different targets depending on solar geometry, can markedly reduce shading, blocking and cosine losses. Also, a system of many mini-towers each of which is only a few meters in height could enable systems that are more modular, efficient and easily-maintained.

As electricity from both photovoltaics and concentrating solar power has become dramatically more affordable in the last several years, the prospect of converting entire national electrical grids to run almost entirely on renewable energy has become feasible in any location with a strong solar resource. However, focusing only on the electric grid neglects the large portion of our energy usage which is thermal rather than electrical. One frequently proposed solution has been to simply electrify all thermal processes, for example in heavy industry, space and water heating. We suggest that the direct use of solar heat for thermal processes enables savings in terms of energy loss, land usage and dollar cost. Focusing on the requirements of heavy industry, desalination and long-distance heat transport, we identify the current and future potential of efficient collection, use and distribution of solar heat to extend the ongoing renewable revolution beyond the grid.

One can display an image by scanning a laser light on a fluorescent waveguide. Solar cells attached to its edge surface harvest the photoluminescent photons. Its optical efficiency is defined as the ratio of the number of the photoluminescent photons collected by the solar cells over the number of incident photons. There are models reported on this topic for a luminescent solar concentrator and most of them are based on either numerical integration or Monte Carlo simulation. In our model, an isotropic emitter is placed at a single spot in a square waveguide. First, we ignore optical losses during propagation for simplicity and calculate the efficiency as the product of three factors: the trapping probability in the waveguide, the ratio of the angle subtended by one edge from the single spot over 2π, and the probability of exiting from the edge. The other three edges are assumed to be absorbing. This simple calculation gives the efficiency as a function of the coordinates of the excitation spot. Next, we introduce an attenuation coefficient to account for optical losses. Adding contribution from each wavelength of a photoluminescent spectrum would give the overall efficiency. In experiment, we can measure this efficiency by coupling a photodiode array to one edge of a fluorescent waveguide and exciting a single spot by a laser beam. Our preliminary result indicates that the model roughly reproduces the value of the efficiency and its dependency on the position of the excitation spot.

Classical nonimaging optical designs often use elliptical and hyperbolic flow lines. The transition can be understood by introducing change of gauge in the vector potential.

Nonimaging optics is based on the thermodynamic understanding of optical design. Using Stokes' law one can find the energy throughput represented by the flow line is also the line integral of its vector potential. A detailed examination reveals that nonimaging optics is closely related with equal vector potential lines. We explore the possibility to further extend this into a more fundamental understanding of what nonimaging optical design represents.

Traditional silicon photovoltaic modules have some inactive module surface area (IMSA) that are not covered by the solar cells due to the shading of bus bars, finger contacts, and the unused space between the octagonal solar cells. Collecting the solar power falling onto the IMSA will increase the overall energy yield and potentially decrease the $/kW-hr rating for the PV system. Therefore, we proposed a low-cost holographic light management technique which combines the holographic optical elements (HOEs) and a white Lambertian scatter surface. Simulation and comparison are performed for three different light collection systems. The results show that 6.40% more light collection efficiency can be achieved by using HOEs combined with a white scatter surface.

Evolutionary optimization algorithms have been recently introduced as nonimaging optics design techniques. Unlike optimization of imaging systems, non sequential ray tracing simulations and complex non centred systems design must be considered, adding complexity to the problem. The Merit Function (MF) is a key element in the automatic optimization algorithm, nevertheless the selection of each objective's weight, {w_i}, inside merit function needs a previous trial and error process for each optimization. The problem then is to determine appropriate weights value for each objective. In this paper we propose a new Dynamic Merit Function, DMF, with variable weight factors {w_i(n)}. The proposed algorithm, automatically adapts weight factors, during the evolution of the optimization process. This dynamic merit function avoids the previous trial and error procedure selecting the right merit function and provides better results than conventional merit functions (CMF). Also we analyse the Multistart optimization algorithm applied in the flowline nonimaging design technique.

For those patients with degenerated photoreceptors such that fail to transfer visual information to other retinal cells in the retinal network, a 16x16 pixel self-powered implantable subretinal device has been developed trying to restore their vision. The device contains sensing pixels that collect environmental signal, and electrodes that serve neurostimulation. A photovoltaic cell was designed aside of the sensing pixels and electrodes for power supplying. IR LED was selected to radiate on the photovoltaic cells for energy input such that proper optical layout shall be designed. Several extraocular optical layouts for IR LED illumination are studied to evaluate the perfect efficiency of each layout. Suitable design is to be selected through the evaluation process. Some experiments are performed to study the feasibility of optical layout. Images of IR LED are taken by a CMOS sensor. Irradiance on the calibrated CMOS sensor is calculated for comparison.

The electric lighting is responsible for 15% of the electricity consumption, the efficiency in this sector has a good progress in recent years, it can still improve more. Conventional energy sources are polluting and limited, so it is essential to use less aggressive energies with the environment. In lighting, this premise is being implemented in a cross-cutting manner, but in response to varied and sometimes contradictory interests. The development of lighting devices based on solar radiation is an inalienable objective, as is the use of artificial lighting sources that are clean with the environment. To achieve these two objectives, it is essential to know and study the design techniques of non-image optics. In the present work we present new systems design techniques and lighting elements: ray tracing optimization technique, light vector field technique. As well as its implementation and application in various areas of lighting: lighting in office buildings, libraries museums. We show that renewable energy strategy in the field of lighting not only produce energy save, also produce good effects in other aspects of human life like well-being, productivity and heritage conservation.

Prismatic film offer advantages such as the possibility of transmit light effectively in lighting applications with the benefit of reducing energy consumption. This paper presents several developments based on their characteristics which allow direct light suitably in several fields as architecture, road and automotive lighting and signaling. A mathematical model is presented to provide a quantitative estimation of the influence of numerous factors that affect the transport of light in order to easily predict light extraction while avoiding heavy software calculations. The deformation produced in a prismatic film induced by changes in the curvature of the cylindrical guide is characterized by image analysis. This method shows the relationship between the curvature of the film, the deformation and the flux of transmitted light.

We design Fresnel mirrors by using an exact ray tracing considering an incident plane wavefront propagating along the optical axis, impinging at arbitrary reflective surfaces, in order to efficiently redirect the light at a predefined area where will be placed the absorber. The solar concentrator consists of a set of planar mirrors, each one has its own slope in such a way that all the rays impinging on it will be focused at a predefined area as a CPC does. Finally, we provide a qualitative test for a commercial FM based on the null screen method.