This PDF file contains the front matter associated with SPIE Proceedings Volume 7769, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

Abstract In this presentation we evaluate the energy collection efficiency and energy yield of different holographic planar concentrator designs. The holographic planar concentrator replaces expensive photovoltaic cell material with holographic collectors that cost approximately 1% of the photovoltaic material. An analysis is performed using a combination of raytracing and coupled wave theory. Other loss factors such as Fresnel reflection and polarization are also incorporated. The performance of single gratings is optimized to maximize the spectral and angular bandwidth that matches the spectral responsivity of different photovoltaic devices. Multiple grating collectors are also modeled to maximize energy collection over the course of a year accommodating the movement of the sun. The results show that approximately half of the light illuminating the hologram can directly be collected by diffraction and directed to the photovoltaic cell. A test system is evaluated and the experimental results compare well with the analysis.

The paper describes a new system architecture optimized for utility-scale generation with concentrating photovoltaic cells (CPV) at fossil fuel price. We report on-sun tests of the architecture and development at the University of Arizona of the manufacturing processes adapted for high volume production. The new system takes advantage of triple-junction cells to convert concentrated sunlight into electricity. These commercially available cells have twice the conversion efficiency of silicon panels (40%) and one-tenth the cost per watt, when used at 1000x concentration. Telescope technology is adapted to deliver concentrated light to the cells at minimum cost. The architecture combines three novel elements: large (3.1 m x 3.1 m square) dish reflectors made as back-silvered glass monoliths; 2.5 kW receivers at each dish focus, each one incorporating a spherical field lens to deliver uniform illumination to multiple cells; and a lightweight steel spaceframe structure to hold multiple dish/receiver units in coalignment and oriented to the sun. Development of the process for replicating single-piece reflector dishes is well advanced at the Steward Observatory Mirror Lab. End-to-end system tests have been completed with single cells. A lightweight steel spaceframe to hold and track eight dish/receiver units to generate 20 kW has been completed. A single 2.5 kW receiver is presently under construction, and is expected to be operated in an end-to-end on-sun test with a monolithic dish before the end of 2010. The University of Arizona has granted an exclusive license to REhnu, LLC to commercialize this technology.

High-concentration photo-voltaic systems focus incident sunlight by hundreds of times by combining focusing lenses with accurate, dual-axis solar tracking. Conventional systems mount large optical arrays on expensive tracking pedestals to maintain normal incidence throughout the day. A recently proposed micro-optic solar concentrator utilizes a twodimensional lens array focusing into a planar slab waveguide. Localized mirrors fabricated on the waveguide surface reflect focused sunlight into guided modes which propagate towards an edge-mounted photovoltaic cell. This geometry enables a new method of solar tracking by laterally translating the waveguide with respect to the lens array to capture off-axis illumination. Using short focal length lenses, translations on the order of millimeters can efficiently collect 70° full-angle incident fields. This allows for either one or two-axis tracking systems where the small physical motion is contained within the physical footprint of a fixed solar panel. Here, we experimentally demonstrate lateral micro tracking for off-axis light collection using table-mounted components. We also present a novel tracking frame based on de-centered cams and describe a lens configuration optimized for off-axis coupling.

Recently identified fundamental classes of dual-mirror double-tailored nonimaging optics have the potential to satisfy the pragmatic exigencies of concentrator photovoltaics. Via a comprehensive survey of their parameter space, including raytrace verification, we identify champion high-concentration high-efficiency designs that offer unprecedented optical tolerance (i.e., sensitivity to off-axis orientation) - a pivotal figure-of-merit with a basic bound that depends on concentration, exit angle and effective solar angular radius. For comparison, results for the best corresponding dualmirror aplanatic concentrators are also presented.

Tin monosulfide (SnS) was grown by atomic layer deposition (ALD) using sequential exposures of tin(II) 2,4- pentanedionate (Sn(acac)²) and hydrogen sulfide (H2S). In situ quartz crystal microbalance (QCM) studies showed that the SnS ALD mass gain per cycle was 11-12 ng/cm² at 175°C on a gold-covered QCM sensor. Using a film density of 5.07 g/cm3 determined by X-ray reflectivity measurements, these mass gains are equivalent to SnS ALD growth rates of 0.22-0.24 Å/cycle. The ratio of the mass loss and mass gain ratio |▵m²/▵m1| from the H2S and Sn(acac)₂ reactions was |▵m²/▵m1| ~0.32 at 175 °C. This measured ratio is close to the predicted ratio from the proposed surface chemistry for SnS ALD. The SnS ALD was self-limiting versus the Sn(acac)2 and H2S exposures. The SnS ALD growth rate was also independent of substrate temperature from 125-225 °C. X-ray fluorescence studies confirmed a Sn/S atomic ratio of ~1.0 for the SnS ALD films. X-ray photoelectron spectroscopy measurements revealed that the SnS ALD films contained oxygen impurities at 15-20 at% after air exposure. These oxygen-containing SnS ALD films displayed a bandgap of ~1.87 eV that is higher than the SnS bulk value of ~1.3 eV.

A number of methods to reduce the cost of solar power generation have been developed over the last few decades. Recently, research and development in the area of Luminescent Solar Concentrators (LSCs) have shown that these devices are capable of significantly reducing the price of solar energy. We propose using near infra-red (NIR) quantum dots (QDs) as luminescent media in the LSC. Our results demonstrate that LSCs designed with NIR QDs can generate over twice the energy as the ones using their visible counterparts.

Spire Semiconductor has demonstrated a new bi-facial epigrowth manufacturing process for InGaP/GaAs/InGaAs N/P tandem concentrator cells. NREL has verified 5.5 mm cells as 41.4% at 334 suns, AM1.5D, 25°C, matching within measurement error the world record efficiency. A lattice-mismatched 0.94 eV InGaAs cell is epitaxially grown on the backside of a lightly doped, N-type GaAs wafer, the epiwafer is flipped, and 1.42 eV GaAs and 1.89 eV InGaP cells are grown lattice matched on the opposite wafer surface. Cells are then made using only standard III-V process steps. The bi-facial process is an alternative to the inverted metamorphic (IMM) process. It does not use epitaxial liftoff and wafer bonding as in the IMM approach, but does require breaking the growth into two parts and flipping the epiwafer, which we believe is an easier task.

A high irradiance solar furnace geared toward elucidating the distinctive physics of concentrator photovoltaics and driving high-temperature reactors for the generation of novel nanostructures is described, with a target irradiance up to 12 W/mm². The opto-mechanical design permits real-sun flash illumination at a millisecond time scale so that solar cells can be characterized with only insubstantial increases in cell temperature even at irradiance levels of thousands of suns.

Amonix has installed over 300 kW of systems using III-V multijunction cells. The Amonix 7500 Solar Power Generator, rated at 38 kWAC, generated over 90 MW-hr during its first twelve months of operation. A model of system performance using a meteorological database and applying the effects of losses in the optical and power paths predicted field performance to within 1% after twelve months of operation. The energy yield of power plants employing Amonix systems is expected to exceed 2700 kW-hr/kW. Systems installed in 2010 are expected to deliver a 10% increase in performance.

The DoE funded Solar Energy Technology Program (SETP) within the Research and Technology division of The Boeing Company has been operating successfully since March 2007. June 2010 marks the close of the partnership with production and installation completion of a 100kW power plant at California State University at Northridge (CSUN). The XR700 Proof of Manufacturing (POM) design, fully automated manufacturing operation and power plant installation are discussed and evaluated. The completion of the CSUN power plant represents a critical milestone in the commercial development and deployment of the XR optics-based CPV power solution.

Dual aperture holographic planar concentrator (DA-HPC) technology consists of bifacial cells separated by strips of holographic film that diffract the light from the spacing into the cells for direct incident, diffuse, roof-reflected and albedo irradiance. The holographic film is angularly dependent of the seasonal sun angle. DA-HPC modules are compared to single aperture conventional modules for clear and cloudy days as well as for a seasonal period of eight months. Direct-current IV and alternating-current power curves are used to compare modules with comparable silicon active area and cell efficiency.

Concentrating photovoltaic (CPV) companies are constantly making gains in efficiency and a lower levelized cost of energy, but continue to face questions of reliability and efficiency at scale remain. New technologies such as highly efficient aluminum mirrors help CPV companies fulfill both of these demands by allowing for performance and reliability gains, while also enabling high volume production for scaled deployment. In testing, metal mirrors have shown to be good matches for concentrating applications while performing at the same level as glass mirrors in accelerated weather tests. When combined with the inherent lighter weight and formability of aluminum, these new mirrors provide CPV solutions with a compelling advantage in the field.

Thermal management is a critical issue for photovoltaics (PVs), especially concentrator photovoltaic systems. Thermal management problems are similar for all semiconductors, including those used in microelectronics and other optoelectronic applications, such as lasers, light-emitting diodes (LEDs), detectors and displays. We divide the thermal management problem into two parts: heat dissipation and thermal stresses. Heat dissipation affects efficiency and lifetime. Thermal stresses affect manufacturing yield and lifetime. Traditional thermal management materials all have serious deficiencies. Copper and aluminum have high coefficients of thermal expansion (CTEs), which can cause severe thermal stresses during manufacturing and in service. Compliant attach materials, used to minimize thermal stresses, all have major drawbacks. Traditional low-CTE thermal management materials have relatively low thermal conductivities and are hard to machine. In response to these deficiencies, new thermal management materials have been, and are continuing to be developed, which have low CTEs and thermal conductivities up to four times that of copper. Some are reportedly are cheaper than copper. In this paper, we survey the six categories of advanced thermal materials, including properties, state of maturity and cost. We also review a CPV application in which an advanced metal matrix composite with a tailored CTE eliminated solder joint failure and provided other benefits.

Introducing a new solar photovoltaic architecture requires an accurate method of performance testing and energy rating that is accepted for cross technology comparison. Standard testing methods are well defined for mature technologies but their use is ambiguous when applied to one-axis Concentrated Photovoltaic (CPV) systems. We present a methodology to better capture the performance of a one-axis tracked system with an energy harvesting model to evaluate the yearly output. A simple irradiance sensor is used to measure the effective irradiance on the system for performance ratio metrics and identification of any operational issues of installed systems.

As the amount of solar generated energy usage increases worldwide, researches are turning to more advanced methods to increase collection efficiencies and drive down system costs. In this paper, four different optical system designs for solar concentrator applications are discussed. Each of the designs studied utilizes a parabolic trough optical element. The use of the parabolic trough in conjunction with a secondary optical component eliminates the need for expensive complicated 2-axis tracking, whilst still allowing the precise point focus normally only possible with more complex paraboloid systems. The result is an optical system, which offers all the advantages of a linear focus geometry combined with the possibility to utilize point focus concentration. The results were obtained using photometric geometrical ray tracing methods. Ideal surface simulations were initially used to separate surface from geometrical loss contributions. Later, more realistic simulations, including surface and reflectivity data of typical manufacturing methods and materials, were used to compare optical output power densities and system losses. For the systems studied, the minimum and maximum optical efficiencies obtained were 76.73% and 81% respectively. The AM 1.5 solar spectrum power densities in the absorption plane ranged from 50 to 195.8Wm^-2.

We present the results of combining copper indium gallium (di)selenide (CIGS) photovoltaic cells with holographic planar concentrating film over a broad range of illumination levels. The film, originally designed for silicon bifacial solar applications worked well with the CIGS cells. The Voc, cell efficiency and fill factor reached full operating values at lower light levels; with a significant boost in performance being recorded. The holographic regions of the concentrator act as extended heat transfer surfaces, allowing the CIGS cells to operate at lower operational temperatures than they normally would in a traditional PV application.

The recent focus on renewable energy has lead to an increased awareness of solar energy. Concentrating photovoltaic systems have seen a resurgence in research interest since their earlier pilot plant origins in the 1970s and 1980s. The use of concentration reduces the amount of expensive photovoltaic materials while maintaining a high level of incident solar radiation. This research combines the advantage of concentrating solar energy with high efficiency multijunction cells and an active cooling system to create a system that efficiently produces both electricity and heat. A linear concentrating photovoltaic system model was developed in order to simulate the system under actual solar and climatic conditions, where a number of different system variables can be adjusted. This simulation was used to evaluate the effects of domestic hot water use on a 6.2 kWp system. The results show the changes in solar cell efficiency, electricity produced, thermal energy produced, dollar value displaced, and global warming potential displaced as the domestic hot water use of the system is varied. This simulation can be used to find an optimal system for given input conditions and can be used to find optimal operating conditions for a given system size.