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Heliostat Manufacturing for Near-Term Markets: Phase II Final Report

Description: This report describes a project by Science Applications International Corporation and its subcontractors Boeing/Rocketdyne and Bechtel Corp. to develop manufacturing technology for production of SAIC stretched membrane heliostats. The project consists of three phases, of which two are complete. This first phase had as its goals to identify and complete a detailed evaluation of manufacturing technology, process changes, and design enhancements to be pursued for near-term heliostat markets. In the second phase, the design of the SAIC stretched membrane heliostat was refined, manufacturing tooling for mirror facet and structural component fabrication was implemented, and four proof-of-concept/test heliostats were produced and installed in three locations. The proposed plan for Phase III calls for improvements in production tooling to enhance product quality and prepare increased production capacity. This project is part of the U.S. Department of Energy's Solar Manufacturing Technology Program (SolMaT).
Date: December 21, 1998
Creator: Energy Products Division: Science Applications International Corporation: Golden, Colorado
Partner: UNT Libraries Government Documents Department

Advanced reflector materials for solar concentrators

Description: This paper describes the research and development program at the U.S. National Renewable Energy Laboratory (NREL) in advanced reflector materials for solar concentrators. NREL's research thrust is to develop solar reflector materials that maintain high specular reflectance for extended lifetimes under outdoor service conditions and whose cost is significantly lower than existing products. Much of this work has been in collaboration with private-sector companies that have extensive expertise in vacuum-coating and polymer-film technologies. Significant progress and other promising developments will be discussed. These are expected to lead to additional improvements needed to commercialize solar thermal concentration systems and make them economically attractive to the solar manufacturing industry. To explicitly demonstrate the optical durability of candidate reflector materials in real-world service conditions, a network of instrumented outdoor exposure sites has been activated.
Date: October 1, 1994
Creator: Jorgensen, G.; Williams, T. & Wendelin, T.
Partner: UNT Libraries Government Documents Department

Development of a Prototype Reflectrometer for PDIL, of a System for Commercial Sale: Cooperative Research and Development Final Report, CRADA Number CRD-08-272

Description: The first commercial unit of GT-FabScan was fabricated by GT Solar and delivered to NREL. The system is located in the Process Development and Integration Laboratory (PDIL) and is fully functional.
Date: February 1, 2011
Creator: Sopori, B.
Partner: UNT Libraries Government Documents Department

State-of-the-art low-cost solar reflector materials

Description: Solar thermal technologies generate power by concentrating sunlight with large mirrors. The National Renewable Energy Laboratory (NREL) is working with industrial partners to develop the optical reflector materials needed for the successful deployment of this technology. The reflector materials must be low in cost and maintain high specular reflectance for extended lifetimes in severe outdoor environments. Currently, the best candidate materials for solar mirrors are silver-coated low-iron glass and silvered polymer films. Polymer reflectors are lighter in weight, offer greater flexibility in system design, and have the potential for lower cost than glass mirrors. In parallel with collaborative activities, several innovative candidate reflector-material constructions were investigated at NREL. The low-cost material requirement necessitates manufacturing compatible with mass-production techniques. Future cooperative efforts with the web-coating industry offers the promise of exciting new alternative materials and the potential for dramatic cost savings in developing advanced solar reflector materials.
Date: November 1, 1994
Creator: Kennedy, C & Jorgensen, G
Partner: UNT Libraries Government Documents Department

Progress toward achieving a commercially viable solar reflective material

Description: Solar thermal technologies use large mirrors to concentrate sunlight for renewable power generation. The development of advanced reflector materials is important to the viability of electricity production by solar thermal energy systems. The reflector materials must be low in cost and maintain high specular reflectance for extended lifetimes under severe outdoor environments. Production processes associated with candidate materials must be scalable to mass production techniques. A promising low-cost construction uses a stainless steel foil substrate with a silver reflective layer protected by an optically transparent oxide topcoat. Thick (2 to 4 micron), dense alumina coatings provide durable protective layers. The excellent performance of alumina-coated reflector materials in outdoor and accelerated testing suggests that a larger field trial of the material is warranted. The key to producing a greater quantity of material for field deployment and testing without incurring substantial capital is the use of a chilled drum coater. An existing chamber is being modified, and the deposition rate will be increased prior to the installation of a drum coater to produce 1-ft wide by 10-ft long strips of solar reflector material. The production and performance of these materials are discussed.
Date: June 1, 1998
Creator: Kennedy, C.E. & Smilgys, R.V.
Partner: UNT Libraries Government Documents Department

Solar reflector soiling pattern distributions and reflectance measurement requirements

Description: Short-term specular reflectance losses from optical surfaces used in the collection or concentration of solar energy results in significant reduction of these systems' output. Losses range from 0.1% to 1.0% per day, approaching asymptotes of 25% to 60% for periods greater than one year, depending onsite and season. To appropriately assess the value of a particular location for the production of power, consideration of the rates of soiling and strategies to minimize losses resulting from soiling must be considered. Strategies for measuring the optical performance of reflector materials to a specified degree of accuracy have been developed, according to the types of soiling patterns observed. It was found most soiling occurs with the accumulation of particulates in spots of different sizes, and the spot sizes follow a lognormal distribution. For most practical situations, it was determined that 10 measurements with a 1-cm-diameter beam are enough to place the average value within 3% of the true value, with a confidence level of 95%.
Date: October 1, 1990
Creator: Kidney, K. (Colorado Univ., Denver, CO (USA))
Partner: UNT Libraries Government Documents Department

Standardization of Solar Mirror Reflectance Measurements - Round Robin Test: Preprint

Description: Within the SolarPaces Task III standardization activities, DLR, CIEMAT, and NREL have concentrated on optimizing the procedure to measure the reflectance of solar mirrors. From this work, the laboratories have developed a clear definition of the method and requirements needed of commercial instruments for reliable reflectance results. A round robin test was performed between the three laboratories with samples that represent all of the commercial solar mirrors currently available for concentrating solar power (CSP) applications. The results show surprisingly large differences in hemispherical reflectance (sh) of 0.007 and specular reflectance (ss) of 0.004 between the laboratories. These differences indicate the importance of minimum instrument requirements and standardized procedures. Based on these results, the optimal procedure will be formulated and validated with a new round robin test in which a better accuracy is expected. Improved instruments and reference standards are needed to reach the necessary accuracy for cost and efficiency calculations.
Date: October 1, 2010
Creator: Meyen, S.; Lupfert, E.; Fernandez-Garcia, A. & Kennedy, C.
Partner: UNT Libraries Government Documents Department

The optical materials update. Volume 1, No. 1, Winter 1995

Description: This update presents SunLab`s current efforts to develop low-cost, high-performance advanced optical materials for solar thermal applications. The SunLab team conducts basic research and analysis on the fundamental properties that influence material performance;tests, characterizes and evaluates candidate materials; and collaborates with the solar and materials industries to develop, and test optical materials.
Date: December 1, 1995
Partner: UNT Libraries Government Documents Department

Finite element strategies for the efficient analysis and evaluation of solar collector structures

Description: Concentrating or reflecting structures for solar energy systems must be evaluated as to their structural integrity and optical performance. Computer studies can be used as an integral part of these evaluations. The computer studies make use of finite element structural codes coupled with post-processors that calculate optical data. If the analysis of a solar structure is to be carried out in an efficient manner, these computer codes must have certain capabilities. A number of solar energy projects at Sandia National Laboratories have made extensive use of finite element analyses. The analyses have been useful in evaluating design concepts which hold promise for large scale use in solar energy projects. Analysis procedures have been developed for some structures so that evaluations can be carried out in a straightforward manner.
Date: January 1, 1980
Creator: Koteras, J. R.
Partner: UNT Libraries Government Documents Department

Solar reflector materials. [Overview of state-of-art]

Description: A brief overview is given of the current state-of-the-art in solar reflector materials. Its purpose is to outline the uses of reflectors in the solar industry and present some insights into the operational and materials considerations that must be incorporated into the solar reflector design. Current problem areas and research goals will be emphasized.
Date: January 1, 1979
Creator: Lind, M. A.
Partner: UNT Libraries Government Documents Department

Image collapsing concentrators. Interim scientific report No. 2

Description: A cylindrical Fresnel-type lens has been designed and ray traced that focuses approximately to lines over a 60/sup 0/ elevation angle interval. Forty stepped prism facets are configured on the inside surface of the lens, and the lens outer surface can be well approximated by a smooth circular arc. Especially contoured cylindrical subreflectors are described for concentrating the broad image fields of the lens onto a narrow fixed shelf. These image collapsing subreflectors also compensate for focal shortening with azimuth angle incidence variations over nearly a +-60/sup 0/ sector. Ray tracing on the lens and subreflector provide approximate energy distributions on the absorber shelf over the large acceptance angle intervals. The expected performance characteristics of a solar concentrator using the curved lens with facets on the inside surface are compared with a concentrator employing a straight stepped prism lens with facets cut on the outer lens surface.
Date: January 20, 1980
Creator: Sletten, C.J.
Partner: UNT Libraries Government Documents Department

Survey mirrors and lenses and their required surface accuracy. Semiannual technical progress report, September 15, 1978-April 15, 1979

Description: Since the beginning of widespread research and development for solar energy, a major concern has been the effect of optical and surface quality of collector materials on collector performance and the changes in these properties due to environmental conditions. In many instances, this type of data has not been compiled. When data is available on surface quality, mirror or lens optical characteristics, surface deformations due to stress and other errors, it is difficult to quantify the effect these have on a particular concentrator design performance. To further investigate these errors, Honeywell is performing a study of concentrator designs and mirror and lens surfaces. There are two taks within this program. The first task involves investigation and evaluation of concentrator performance. Within this task, Honeywell has conducted a survey of the literature, solar manufacturers and government information to obtain data on existing concentrator designs (i.e., V-troughs, parabolic mirror concentrators) and lens and mirror materials. Ten collector configurations have been selected to be mathematically modeled. These models will be incorporated into existing ray trace software and will be used to evaluate concentrator performance. Optical quality properties, structural deformations due to loading and stress, tracking errors and material property changes due to the environment will be included in this assessment of performance. The second task involves the expansion of an existing data base on mirror degradation due to environmental exposure and the collection of similar information on lenses. Status of the program is reported. (WHK)
Date: May 1, 1979
Partner: UNT Libraries Government Documents Department

High efficiency epitaxial optical reflector solar cells. Final subcontract report, 1 January 1990--31 October 1992

Description: This report describes work to test the feasibility of a new solar cell concept -- the epitaxial optical reflector (EOR) solar cell. This cell concept alters current designs for high efficiency cells by changing the optical absorption efficiency of single cells. The change is introduced by the use an epitaxial multilayer reflector as an integral part of the cell to increase the optical path length of certain wavelengths of light in the cell. These changes are expected to increase the open circuit voltage at which power is extracted from the cell. The program is designed to test the feasibility of the use of a broad band epitaxial multilayer reflector grown as an integral part of the device structure to reflect the near-band-edge light back through the device for a second absorption pass. This second pass allows the design of a solar cell with a thinner base, and the use of the epitaxial reflector as a heterojunction carrier-reflecting barrier at the rear of the device. The thinner cell design and altered carrier profile that results from the light- and carrier-reflecting barrier will decrease the carrier concentration gradient and increase the open circuit voltage. The program is structured to have three tasks: (1) Solar Cell and Reflector Modeling, (2) Materials Growth and Optimization, and (3) Solar Cell Fabrication and Characterization.
Date: August 1, 1993
Creator: Dapkus, P. D. & Hummel, S. G.
Partner: UNT Libraries Government Documents Department

Step-Stress Accelerated Degradation Testing for Solar Reflectors: Preprint

Description: To meet the challenge to reduce the cost of electricity generated with concentrating solar power (CSP) new low-cost reflector materials are being developed including metalized polymer reflectors and must be tested and validated against appropriate failure mechanisms. We explore the application of testing methods and statistical inference techniques for quantifying estimates and improving lifetimes of concentrating solar power (CSP) reflectors associated with failure mechanisms initiated by exposure to the ultraviolet (UV) part of the solar spectrum. In general, a suite of durability and reliability tests are available for testing a variety of failure mechanisms where the results of a set are required to understand overall lifetime of a CSP reflector. We will focus on the use of the Ultra-Accelerated Weathering System (UAWS) as a testing device for assessing various degradation patterns attributable to accelerated UV exposure. Depending on number of samples, test conditions, degradation and failure patterns, test results may be used to derive insight into failure mechanisms, associated physical parameters, lifetimes and uncertainties. In the most complicated case warranting advanced planning and statistical inference, step-stress accelerated degradation (SSADT) methods may be applied.
Date: September 1, 2011
Creator: Jones, W.; Elmore, R.; Lee, J. & Kennedy, C.
Partner: UNT Libraries Government Documents Department

Comparison of indoor-outdoor thermal performance for the Sunpak evacuated tube liquid collector

Description: Performance data is provided for current Sunpak production collectors. The effects of an improved manifold are seen from the test results. The test results show excellent correlation between the solar simulator derived test results and outdoor test results. Also, because of different incident angle modifiers, the all-day efficiency of this collector with a diffuse reflector is found to be comparable to the performance with the standard shaped specular reflector.
Date: March 1, 1980
Partner: UNT Libraries Government Documents Department

Development of surfaces optically suitable for flat solar panels. Final report

Description: This final report contains three principal items. The first describes a simple and novel reflectometer which can separately evaluate the spectral and diffuse reflectivities of surfaces. A phase locked detection system for the reflectometer is also described. The second item is a selective coating on aluminium potentially useful for flat-plate solar collector applications. The coating is composed of strongly bound copper oxide (divalent) and is formed by an etching process performed on an aluminium alloy with high copper content. Because of this one step fabrication process, fabrication costs are expected to be small. Process parameters, however, need further definition. The third item contains conclusions gleaned from the literature as to the required optical properties of flat plate solar collectors.
Date: August 1, 1979
Partner: UNT Libraries Government Documents Department

The formation of optical membrane reflector surfaces using uniform pressure loading

Description: Potentially high quality optical reflector surfaces are attainable with the use of pressure formed membranes. Such reflector surfaces offer the prospect of very low weight and low cost. The formation of such surfaces, using initially flat circular membranes with uniform pressure loading, is studied in this paper. Finite axisymmetric deformations, along with both linear and nonlinear material response is considered. A wide range of focal-length-to-diameter ratios (above 0.6) are addressed and the structural/optical response mechanisms that lead to optical distortions relative to ideal parabolic reflector shapes are also considered. Results show that elastic material response can often lead to a significantly larger deviation from the ideal shape than will inelastic material response. This results primarily from the ability to limit stress nonuniformities when inelastic material response is operative. Furthermore, when under pressure loading the membrane focal length decreases monotonically with increasing radius for both linear and nonlinear material response. Further, the predicted focal length variation is increasingly nonlinear near the membrane support.
Date: August 1, 1987
Creator: Murphy, L.M. & Tuan, C.
Partner: UNT Libraries Government Documents Department

Evaluation of cellular glasses for solar mirror panel applications

Description: An analytic technique is developed to compare the structural and environmental performance of various materials considered for backing of second surface glass solar mirrors. Metals, ceramics, dense molded plastics, foamed plastics, forest products and plastic laminates are surveyed. Cellular glass is determined to be a prime candidate due to its low cost, high stiffness-to-weight ratio, thermal expansion match to mirror glass, evident minimal environmental impact and chemical and dimensional stability under conditions of use. While applications could employ this material as a foam core or compressive member of a composite material system, the present analysis addresses the bulk material only, allowing a basis for simple extrapolations. The current state of the art and anticipated developments in cellular glass technology are discussed. Material properties are correlated to design requirements using a Weibull weakest link statistical method appropriate for describing the behavior of such brittle materials. A mathematical model is presented which suggests a design approach which allows minimization of life cycle cost; given adequate information for a specific aplication, this would permit high confidence estimates of the cost/performance factor. A mechanical and environmental testing program is outlined, designed to providea material property basis for development of cellular glass hardware, together with methodology for collecting lifetime predictive data required by the mathematical treatment provided herein. Preliminary material property data from measurements is given.
Date: June 15, 1979
Creator: Giovan, M. & Adams, M.
Partner: UNT Libraries Government Documents Department

Development, testing, and certification of Owens--Illinois Model SEC-601 Solar Energy Collector System. Final report

Description: The final results of Owens-Illinois, Toledo, Ohio, for the additional development work on their existing air-cooled solar energy collector subsystem for use with solar heating and cooling systems are summarized. The intended use of the final report is discussed, the deliverable end items are described, program objectives and how they were accomplished are listed, problems encountered during fabrication and testing are mentioned, and a certification statement of performance are included. It is shown that the products developed are marketable and suitable for public use.
Date: January 1, 1979
Creator: Parker, J.C.
Partner: UNT Libraries Government Documents Department

Optical performance and durability of solar reflectors protected by an alumina coating

Description: Solar thermal electric power systems use large solar reflectors to concentrate sunlight to generate electricity. The economic viability of these systems depends on developing a durable, low-cost reflector. The goals for such a reflector are specular reflectance above 90% for at least 10 years under outdoor service conditions and a large-volume manufacturing cost of less than $10.8/m{sup 2} ($1.00/ft{sup 2}). Currently, the best candidate materials for solar reflectors are silver-coated, low-iron glass and silvered polymer films. Polymer reflectors are lighter in weight, offer greater system design flexibility, and have the potential for lower cost than glass reflectors. A promising low-cost reflector consists of a silvered polymer protected by an optically transparent alumina coating. The coating is deposited by an ion-beam-assisted physical vapor deposition (IBAD) technique. Samples of this reflector have maintained high optical performance in accelerated testing at the National Renewable Energy Laboratory for more than 3000 hours. Solar reflectors produced using this technique may represent an opportunity to bring solar power generation to reality.
Date: July 1, 1996
Creator: Kennedy, C.E.; Smilgys, R.V.; Kirkpatrick, D.A. & Ross, J.S.
Partner: UNT Libraries Government Documents Department

Development of high, stable-efficiency triple-junction a-Si alloy solar cells. Annual technical progress report, October 1995--October 1996

Description: The overall objective of this amorphous silicon research program is to develop high efficiency a-Si solar cells and to develop and improve processes for large area deposition of a-Si solar cells and modules. The knowledge obtained and technologies demonstrated in this program will be incorporated into ECD`s continuous roll-to-roll deposition process to further enhance its photovoltaic manufacturing technology.
Date: April 1, 1997
Creator: Deng, X.; Izu, M.; Jones, S.J. & Kopf, R.
Partner: UNT Libraries Government Documents Department

Optical durability testing of candidate solar mirrors

Description: Durability testing of a variety of candidate solar reflector materials at outdoor test sites and in laboratory accelerated weathering chambers is the main activity within the Advanced Materials task of the Concentrated Solar Power (CSP) Program. Outdoor exposure testing (OET) at up to eight outdoor, worldwide exposure sites has been underway for several years. This includes collaboration under the auspices of the International Energy Agency (IEA) Solar Power and Chemical Energy Systems (SolarPACES) agreement. Outdoor sites are fully instrumented in terms of monitoring meteorological conditions and solar irradiance. Candidate materials are optically characterized prior to being subjected to exposure in real and simulated weathering environments. Optical durability is quantified by periodically re-measuring hemispherical and specular reflectance as a function of exposure time. By closely monitoring the site- and time-dependent environmental stress conditions experienced by the material samples, site-dependent loss of performance may be quantified. In addition, accelerated exposure testing (AET) of these materials in parallel under laboratory-controlled conditions may permit correlating the outdoor results with AET, and subsequently predicting service lifetimes. Test results to date for a large number of candidate solar reflector materials are presented in this report. Acronyms are defined. Based upon OET and AET results to date, conclusions can be drawn about the optical durability of the candidate reflector materials. The optical durability of thin glass, thick glass, and two metallized polymers can be characterized as excellent. The all-polymeric construction, several of the aluminized reflectors, and a metallized polymer can be characterized as having intermediate durability and require further improvement, testing and evaluation, or both.
Date: March 24, 2000
Creator: Jorgensen, G.; Kennedy, C.; King, D. & Terwilliger, K.
Partner: UNT Libraries Government Documents Department