This PDF file contains the front matter associated with SPIE Proceedings Volume 7043, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

A lot lies ahead. The reality is that CPV today shows a lot of promise - but it is yet to be established as a part of the solar market place never mind the energy market. This paper does not focus on the particular CPV technology being commercialized today but rather on the process of commercialization. My presentation will rely on my experience with Solar Systems' CPV technology. It is not just that there is a lot ahead, much is to be done... There are three key phases involved in bringing technology to market with each phase an identifiable and measurable process. Technology and its development are inextricably linked to the organisation in which it exists. Technology cannot be commercialized in a vacuum; it needs to exist in an organisation that is capable of, and intentional in, supporting the delivery of the technology to market. Commercial operation is of course not the end of the journey, but just another weigh point - the process forms a continuum of activity that is constantly taking new developments through the various stages. For now, lets just look at the three phases in a line and consider what has to happen in order to get along the path. We will come back to the continuum thought later.

Commercial buildings represent a near term market for cost competitive solar electric power provided installation costs and solar photovoltaic module costs can be reduced. JX Crystals has developed a carousel sun tracker that is prefabricated and can easily be deployed on building flat roof tops without roof penetration. JX Crystals is also developing 3-sun PV mirror modules where less expensive mirrors are substituted for two-thirds of the expensive single crystal silicon solar cell surface area. Carousels each with four 3-sun modules have been set up at two sites, specifically at Oak Ridge National Lab and at the University of Nevada in Las Vegas. The test results for these systems are presented.

The Luminescent Solar Concentrator (LSC) consists of a transparent polymer plate containing luminescent particles. Solar cells are connected to one or more sides of the polymer plate. Part of the light emitted by the luminescent particles is guided towards the solar cells by total internal reflection. About 25% of the dye emission is typically emitted within the optical escape cone of the matrix material and is lost due to emission from the top. We study the application of selectively-reflective cholesteric layers to reduce these losses. We have implemented these mirrors in the ray-tracing model for the LSC. The simulations show that an optimum in performance can be obtained by selecting an appropriate centre wavelength of the cholesteric mirror. External Quantum Efficiency measurements were performed on LSC devices with a mc-Si, GaAs or InGaP cell and a dichroic mirror. This mirror shows a similar behavior as the cholesteric mirror. The results show that for a 5x5 cm² LSC the mirror does improve the EQE in the absorption range of the dye.

Rooftop high concentration photovoltaic system is an attractive alternative to silicon panels in applications where high efficiency is imperative for limited roof space. Due to the in-panel integrated 2-axis tracking structure, limited heat dissipation makes it a significant challenge to keep solar cells cool. Finite element analysis modeling is carried out by taking into consideration of conductive, convective, and radiative mechanisms. Dominant thermal path is identified. We will show that, with improved designs, solar cell temperature can be reduced by more than 20C. Experimental results are used to verify the model and to improve thermal design.

SolFocus has designed and built a flexible and adaptable solar flash tester capable of reaching in excess of 2500x suns flux using a commercially available Xenon flash and power supply. Using calibrated isotype cells and photodetectors, the intensity and color balance of the flash are controlled through software algorithms that compensate for tube aging and thermal drift. The data acquisition system dynamically normalizes each of the 1600 I-V data pairs to the lamp intensity during each flash. Up to 32 cells can be measured simultaneously, with a flash re-cycle time of 3 seconds. The dynamic current range is 100μA to 10A over 0 to 5V. Test ranges are limited by user input through a modern GUI screen. The system is mated to a commercially available probe station tester which allows automated testing of up to 150mm diameter wafers, and is capable of testing a 4000 cell wafer in less than 8 minutes. The core software and optical components are easily adaptable to receiver and full panel testing as well. Data on the calibration and performance of the flash tester, the dynamic range achieved in test, and throughputs obtained during operation are presented.

In this work, based on the advanced drift and diffusion theory with improved tunneling junction model, two-dimensional modeling for the GaInP/GaAs/Ge and the inverted-grown metamorphic GaInP/GaAs/GaInAs triple-junction solar cells are performed by using a commercial software, the Crosslight APSYS. Basic physical quantities like band diagram, optical absorption and generation are obtained and characteristic results such as I-V curves, current matching, fill factor, efficiency etc under one-sun and multi-sun illumination are presented. Some of the modeling results generally agree with the published experimental results for both TJ cells. Comparative analyses are made with these two TJ cells and optimization approaches are discussed with respect to minority carrier lifetime, front anti-reflection coating, and top contact grid size and spacing.

Some current high-concentration photovoltaic designs are based on folded mirror optics, i.e., the optical path is reversed via reflection in order to achieve minimal aspect ratio. One apparently overlooked class of aplanats is the unfolded dualmirror aplanat explored in this presentation. The confluence of practical constraints presented by many highconcentration photovoltaic systems creates a niche for unfolded aplanatic optics that permit the elimination of optical bonds between dielectric elements and solar cells while achieving an angular tolerance near the fundamental limit. The long-term material integrity of the optical bonds - especially at high irradiance - remains to be established and has been viewed as potentially precarious. Furthermore, the unfolded optic and the target can be decoupled. The disadvantage of unfolded optics is depth: concentrator aspect ratios far larger than the fundamental compactness bound realizable with folded optics. However, with high-concentration photovoltaics evolving to millimeter-scale cells, the corresponding depth of the concentrator would be only a few centimeters: compatible with precision large-volume fabrication techniques. We also show how a lens at the center of the aplanat's glazing permits a noticeable reduction in concentrator depth. A fringe benefit is the paucity of hot spots on the optical elements, creating the option of coated polymeric reflectors, which reduces mass and cost.

A novel photovoltaic concentrator is presented. The goal is to achieve high concentration design with high efficiency and high acceptance angle that in the same time is compact and convenient for thermal and mechanical management. This photovoltaic system is based on 1 cm² multi-junction tandem solar cells and an XR concentrator. The XR concentrator in this system is an SMS 3D design formed by one reflective (X) and one refractive (R) free-form surfaces (i.e., without rotational or linear symmetry) and has been chosen for its excellent aspect ratio and for its ability to perform near the thermodynamic limit. It is a mirror-lens device that has no shadowing elements and has square entry aperture (the whole system aperture area is used for collecting light). This large acceptance angle relaxes the manufacturing tolerances of all the optical and mechanical components of the system included the concentrator itself and is one of the keys to get a cost competitive photovoltaic generator. For the geometrical concentration of 1000x the simulation results show the acceptance angle of ±1.8 deg. The irradiance distribution on the cell is achieved with ultra-short homogenizing prism, whose size is optimised to keep the maximum values under the ones that the cell can accept. The application of the XR optics to high-concentration is being developed in a consortium leaded by The Boeing Company, which has been awarded a project by US DOE in the framework of the Solar America Initiative.

Significant efficiency increases in photovoltaic power conversion are due to improved absorption over the broad spectrum of the sun. Semiconductors have an efficiency peak at a specific wavelength associated with the material band gap. The current trend towards high-efficiency photovoltaics involves multi-junction cells where several semiconductors are grown on top of one another creating a layered device with a broad spectral response. Fabrication is a difficult and expensive process that results in small area solar cells. An alternative approach uses dielectric mirrors to optically separate the incident light by reflecting one spectral band while transmitting another. Spectral splitting is simulated within a 10x non-imaging concentrator. The optical system may be concatenated into large arrays and incorporates two separated ray paths exiting at a common plane. Optimized photovoltaic cells can be interleaved on a single circuit board, improving packaging and thermal management compared to orthogonal arrangements. The entire concentrator can be molded from glass or acrylic and requires a dichroic coating as the only reflector. Average collection efficiencies above 84% are realized within 40°x16° angular acceptance.

Purpose: Cost reduction is a major focus of the solar industry. Thin film technologies and concentration systems are viable ways to reducing cost, with unique strengths and weakness for both. Most of the concentrating PV work focuses on high concentration systems for reducing energy cost. Meanwhile, many believe that low concentrators provide significant cost reduction potential while addressing the mainstream PV market with a product that acts as a flat panel replacement. This paper analyzes the relative benefit of asymmetric vs. symmetric optics for low-concentrators in light of specific PV applications. Approach: Symmetric and asymmetric concentrating PV module performance is evaluated using computer simulation to determine potential value across various geographic locations and applications. The selected optic design is modeled against standard cSi flat panels and thin film to determine application fit, system level energy density and economic value. Results: While symmetric designs may seem ideal, asymmetric designs have an advantage in energy density. Both designs are assessed for aperture, optimum concentration ratio, and ideal system array configuration. Analysis of performance across climate specific effects (diffuse, direct and circumsolar) and location specific effects (sunpath) are also presented. The energy density and energy production of low concentrators provide a compelling value proposition. More significantly, the choice of optics for a low concentrating design can affect real world performance. With the goal of maximizing energy density and return on investment, this paper presents the advantages of asymmetric optic concentration and illustrates the value of this design within specific PV applications.

We present performance and cost data on a distributed concentrated photovoltaic (CPV) system that is commercially available in 2008 and will break the long pursued $2/W price barrier. This technology was developed from an existing product platform used originally for solar fiber optic lighting applications and includes a novel segmented plastic mirror that concentrates sunlight into a dense-array CPV module at 600 suns. The design's segmented plastic mirror and high-precision, low-cost tracking unit are presented as a flexible hardware platform evolved in response to market pressure over the past two years and suitable for multiple applications being developed in the concentrating solar field. To illustrate the economic benefits of this solar collection platform, the specific costs related to COGS and installation activities associated with a commercial CPV product available in 2008 are presented.

The diffraction and the dispersion properties of holographic optical elements are examined for use as solar concentrators for photovoltaic and hybrid photovoltaic/thermal energy conversion systems. The diffraction angle and efficiency are computed for folded optical geometries that are potentially useful for low concentration ratio systems that can reduce the cost of residential solar energy systems. An investigation of the collection efficiency of a holographic planar concentrator and a spectrum splitting concentrator are analyzed with different construction parameters. It is found that collection angles of 40^o and spectral bandwidth of 70 nm result with folded optical geometries for single volume holograms.

This paper describes the design and experimental characterization of two optimized thermal actuators devised to operate by means of scavenging heat from the environment. Different from the traditional MEMS thermal actuator that relies on electric current to generate heat by Joule effect, the devices herein presented have been optimized to absorb external heat and convert it into mechanical displacement and force. The behavior of vertical and horizontal microactuators fabricated in a standard surface micro-machining process (PolyMUMPs) demonstrates the viability of exploiting heat from the surrounding medium to realize batteryless microsystems. Analytical and finite element models are provided in support of the design. Results show that fairly large and useful displacements can be achieved at commonly available operating temperatures.

In this work, we present the basic considerations of a solar follower, realized with a control module based on a Dspic 30F40011. The Dspic was programmed considering the basic equations to track the apparent sun position. The Dspic programming was realized considering three fundamental blocks: Real time clock, the movement determined by the hour angle, and the movement determined by the declination angle (based on a CD motor). The mechanical design was realized considering a parabolic antenna used as concentrator, with a diameter of 60 cm, a depth of 6 cm, weight of approximately 1.5 kg, made of glass fiber. The control module is easy to use due to the LCD implementation, which indicates all necessaries entries to the correct operation of each block. The LCD is also used to display the date, hour, and the temperature obtained by the sensor temperature located at the antenna focus. As a proof of the correct system calibration and operation, the shadow of the sensor temperature circuit was located at the antenna center, during all realized probes. Due to the antenna characteristics, which were made by hands, the amount of thermal energy is relatively small but for example, enough to heating water. The obtained temperature can be increased by replace the antenna, without to redesign the mechanical and electronic systems because they can be used for antennas weight until 15 kg.

The aim of this work concerns the study of the silicone carbide fluidized bed in order to release a fluidized bed solar receiver with direct absorption of the concentrated solar radiation and to optimize the quantity of collected energy. For that, we tested several geometries in order to optimise the distribution of the particles during fluidization. For that, we built and tested several transparent columns with different geometries and dimensions and analyse several cold experiments. An analysis of test results and images enabled us to determine the height and the porosity of different layers in the fluidized bed, to optimise the geometry of the column and its dimensions.