Optical Durability of Candidate Solar Reflectors

2005 ◽  
Vol 127 (2) ◽  
pp. 262-269 ◽  
Author(s):  
C. E. Kennedy ◽  
K. Terwilliger
Keyword(s):  
Cone Angle ◽  
Front Surface ◽  
Advanced Materials ◽  
Accelerated Weathering ◽  
Thin Glass ◽  
Specular Reflectance ◽  
Outdoor Environments ◽  
Exposure Testing ◽  
Durability Testing ◽  
Main Activity

Concentrating solar power (CSP) technologies use large mirrors to collect sunlight to convert thermal energy to electricity. The viability of CSP systems requires the development of advanced reflector materials that are low in cost and maintain high specular reflectance for extended lifetimes under severe outdoor environments. The long-standing goals for a solar reflector are specular reflectance above 90% into a 4 mrad half-cone angle for at least 10 years outdoors with a cost of less than $13.8/m2 (the 1992 $10.8/m2 goal corrected for inflation to 2002 dollars) when manufactured in large volumes. 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 CSP Program at the National Renewable Energy Laboratory (NREL) in Golden, Colorado. Test results to date for several candidate solar reflector materials will be presented. These include the optical durability of thin glass, thick glass, aluminized reflectors, front-surface mirrors, and silvered polymer mirrors. The development, performance, and durability of these materials will be discussed. Based on accelerated exposure testing the glass, silvered polymer, and front-surface mirrors may meet the 10 year lifetime goals, but at this time because of significant process changes none of the commercially available solar reflectors and advanced solar reflectors have demonstrated the 10 year or more aggressive 20 year lifetime goal.

Optical Durability of Candidate Solar Reflectors

Solar Energy ◽  
2004 ◽  
Author(s):  
C. E. Kennedy ◽  
K. Terwilliger
Keyword(s):  
Cone Angle ◽  
Front Surface ◽  
Advanced Materials ◽  
Accelerated Weathering ◽  
Thin Glass ◽  
Specular Reflectance ◽  
Outdoor Environments ◽  
Exposure Testing ◽  
Durability Testing ◽  
Main Activity

Concentrating solar power (CSP) technologies use large mirrors to collect sunlight to convert thermal energy to electricity. The viability of CSP systems requires the development of advanced reflector materials that are low in cost and maintain high specular reflectance for extended lifetimes under severe outdoor environments. The long-standing goals for a solar reflector are specular reflectance above 90% into a 4-mrad half-cone angle for at least 10 years outdoors with a cost of less than $13.8/m2 (the 1992 $10.8/m2 goal corrected for inflation to 2002 dollars) when manufactured in large volumes. 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 CSP Program at the National Renewable Energy Laboratory (NREL) in Golden, Colorado. Test results to date for several candidate solar reflector materials will be presented. These include the optical durability of thin glass, thick glass, aluminized reflectors, frontsurface mirrors, and silvered polymer mirrors. The development, performance, and durability of these materials will be discussed. Based on accelerated exposure testing the glass, silvered polymer, and front-surface mirrors may meet the 10-year lifetime goals, but at this time because of significant process changes none of the commercially available solar reflectors and advanced solar reflectors have demonstrated the 10-year or more aggressive 20-year lifetime goal.

Furthur Analysis of Accelerated Exposure Testing of Thin-Glass Mirror Matrix

2007 ◽  
Author(s):  
C. E. Kennedy ◽  
K. Terwilliger ◽  
G. J. Jorgensen
Keyword(s):  
Lead Free ◽  
Advanced Materials ◽  
Thin Glass ◽  
Metal Substrates ◽  
Solar Systems ◽  
Free Process ◽  
Hemispherical Reflectance ◽  
Designed Experiment ◽  
Exposure Testing ◽  
The Cost

Concentrating solar power (CSP) companies have deployed thin-glass mirrors produced by wet-silver processes on ∼1-mm-thick, relatively lightweight glass. These mirrors are bonded to metal substrates in commercial installations and have the confidence of the CSP industry. Initial hemispherical reflectance is ∼93%–96%, and the cost is ∼$16.1/m2–$43.0/m2. However, corrosion was observed in mirror elements of operational solar systems deployed outdoors for 2 years. National Renewable Energy Laboratory (NREL) Advanced Materials Team has been investigating this problem. First, it was noted that this corrosion is very similar to the corrosion bands and spots observed on small (45 mm × 67 mm) thin-glass mirrors laminated to metal substrates with several different types of adhesives and subjected to accelerated exposure testing (AET) at NREL. The corrosion appears as dark splotches in the center of the mirror, with a corresponding 5%–20% loss in reflectivity. Secondly, two significant changes in mirror manufacture have occurred in the wet-chemistry process because of environmental concerns. The first is the method of forming a copper-free reflective mirror, and the second is the use of lead-free paints. However, the copper-free process requires stringent quality control and the lead-free paints were developed for interior applications. A test matrix of 84 combinations of sample constructions (mirror type/back-protective paint/adhesive/substrate) was devised for AET as a designed experiment to identify the most-promising mirrors, paints, and adhesives for use with concentrator designs. Two types of accelerated exposure were used: an Atlas Ci5000 WeatherOmeter (CI5000) and a BlueM damp-heat chamber. Based on an analysis of variance (ANOVA), the various factors and interactions were modeled. These samples now have more than 36 months of accelerated exposure, and most samples have completed their test cycle. We will discuss the results of the final exposure testing of these mirror samples. Glass mirrors with copper back-layers and heavily leaded paints have been considered robust for outdoor use. However, the basic mirror composition of the new mirrors is radically different from that of historically durable solar mirrors, and the outdoor durability must be determined.

Sol-Gel Protective Films for Metal Solar Mirrors

1988 ◽  
Vol 121 ◽  
Author(s):  
Scott Reed ◽  
Carol Ashley
Keyword(s):  
Protective Coatings ◽  
Sol Gel ◽  
Protective Layer ◽  
Front Surface ◽  
Optical Measurements ◽  
Preliminary Evaluation ◽  
Environmental Testing ◽  
Specular Reflectance ◽  
Outdoor Environments ◽  
Sputter Deposited

ABSTRACTFront-surface metal mirrors were coated with a variety of sol-gel derived glass films for preliminary evaluation as protective coatings for silver. Optical measurements (hemispherical, diffuse and specular reflectance) were used to characterize changes in the mirror resulting from the application of the sol, subsequent processing, or environmental testing. The abrasion resistance of the films was determined on sol-gel coated silicon wafers per ASTM procedures. The mirrors were exposed to outdoor environments in Albuquerque, N.M., as well as accelerated testing in H2SO4, with periodic monitoring of optical properties. A two layer coating scheme, consisting of a thin primary protective layer of sputter deposited SiO2 followed by a thicker sol-gel overcoat, was also evaluated.

Exposure of Polymeric Glazing Materials Using NREL’s Ultra-Accelerated Weathering System (UAWs)

2010 ◽  
Author(s):  
Carl Bingham ◽  
Gary Jorgensen ◽  
Amy Wylie
Keyword(s):  
Light Intensity ◽  
Thermal Effects ◽  
Outdoor Exposure ◽  
Exposure Chamber ◽  
Accelerated Weathering ◽  
Intensity Level ◽  
Design And Implementation ◽  
Different Temperatures ◽  
Exposure Testing ◽  
Ultraviolet Irradiance

NREL’s Ultra-Accelerated Weathering System (UAWS) selectively reflects and concentrates natural sunlight ultraviolet irradiance below 475 nm onto exposed samples to provide accelerated weathering of materials while keeping samples within realistic temperature limits. This paper will explain the design and implementation of the UAWS which allow it to simulate the effect of years of weathering in weeks of exposure. Exposure chamber design and instrumentation will be discussed for both a prototype UAWS used to test glazing samples as well as a commercial version of UAWS. Candidate polymeric glazing materials have been subjected to accelerated exposure testing at a light intensity level of up to 50 UV suns for an equivalent outdoor exposure in Miami, FL exceeding 15 years. Samples include an impact modified acrylic, fiberglass, and polycarbonate having several thin UV-screening coatings. Concurrent exposure is carried out for identical sample sets at two different temperatures to allow thermal effects to be quantified along with resistance to UV.

scholarly journals The Environmental Impact of Advanced Material Concepts for Luminescent Solar Concentrators

2011 ◽  
Vol 68 (2) ◽  
Author(s):  
Mihai ANGHEL ◽  
Violeta NICULESCU ◽  
Ioan STEFANESCU
Keyword(s):  
Solar Spectrum ◽  
Front Surface ◽  
Thermal Conversion ◽  
Advanced Materials ◽  
Large Area ◽  
Potential Cost ◽  
Diffuse Solar Radiation ◽  
Building Integrated Photovoltaics ◽  
Luminescent Solar Concentrators ◽  
Pv Panel

Sunlight that is incident on the front surface of a luminescent solar concentrator (LSC) is absorbed and subsequently re-emitted by luminescent materials. The resulting luminescence is transported to the edge of the LSC sheet and concentrated onto photovoltaic devices. This paper outlines the loss mechanisms that limit conversion efficiency of the LSC and highlights the role that advanced materials can play. Losses include nonunity fluorescence quantum yield (FQY), reabsorption losses, incomplete utilization of the solar spectrum, and escape cone losses. Long-term photostability is also discussed as it is essential for commercial feasibility of any solar technology. The main motivation for implementing an LSC is to replace the large area of expensive solar cells required in a standard flat-plate PV panel, with an inexpensive polymeric collector, thereby, reducing the cost of the module (in dollars per watt) and also of the solar power (in dollars per kilowatthour). A key advantage of LSC technology compared to other concentrating systems is that it can collect both direct and diffuse solar radiation. This means that tracking of the sun is not required—enhancing further potential cost reductions and making LSCs excellent candidates for building integrated photovoltaics (BIPV)—as well as making them the ideal PV technology for cloudier northern European climates. Similarly to electricity conversion, LSCs also have applications in daylighting (Hiramoto et al., 1991), thermal conversion, and hybrid thermal–photovoltaic systems that could generate electricity and extract the heat generated by the LSC plate (Xue et al., 2005).

Analysis of Accelerated Exposure Testing of Thin-Glass Mirror Matrix

Solar Energy ◽  
2005 ◽  
Author(s):  
C. E. Kennedy ◽  
K. Terwilliger ◽  
G. J. Jorgensen
Keyword(s):  
Lead Free ◽  
Thin Glass ◽  
Metal Substrates ◽  
Solar Systems ◽  
Paint Systems ◽  
Heat Chamber ◽  
Hemispherical Reflectance ◽  
Designed Experiment ◽  
Exposure Testing ◽  
The Cost

Concentrating solar power (CSP) companies have deployed thin-glass mirrors produced by wet silver processes on ∼1-mm-thick, relatively lightweight glass. These mirrors have been bonded to metal substrates in commercial installations. Initial hemispherical reflectance is ∼93% to 96%, and the cost is ∼$16.1/m2 to $43.0/m2. These mirrors have the confidence of the CSP industry. However, corrosion was observed in mirror elements of operational solar systems deployed outdoors for 2 years. NREL’s advanced optical materials team was assigned to investigate the problem. First, it was noted that this corrosion is very similar to the corrosion bands and spots observed on small (45 mm × 67 mm) thin-glass mirrors laminated to metal substrates with several different types of adhesives and subjected to accelerated exposure testing (AET) at NREL. These samples exhibited corrosion at the unprotected edges and along cracks, and the choice of adhesive affected the performance of weathered thin-glass mirrors. Secondly, two significant changes in mirror manufacture have occurred in the wet-chemistry process because of environmental concerns. The first is the method of forming a copper-free reflective mirror, and the second is the use of lead-free paints. A test matrix of 84 combinations of sample constructions (mirror type / back protective paint / adhesive / substrate) was devised for AET as a designed experiment to identify the most promising mirrors, paints, and adhesives for use with concentrator designs. Two types of accelerated exposure were used: an Atlas Ci5000 WeatherOmeter (WOM) and a damp-heat chamber. Based on an analysis of variance (ANOVA), the various factors and interactions were modeled. These samples now have almost 24 months of accelerated exposure. Analysis of the thin-glass mirror matrix indicated that the Glaverbel mirror with a copperless formulation demonstrates slightly better performance compared to the Naugatuck standard copper-containing mirror and new copperless constructions although most results are within experimental uncertainty. Analysis of the thin-glass mirror matrix indicates commercial (non-mirror) back-protective paint applied after mirror manufacturing is not beneficial. Degradation of the samples exposed to date in the damp-heat chamber is similar, but at a rate 10 times faster than observed for samples in the WOM. We will discuss the results of the continued exposure testing of these mirror samples. Although glass mirrors with copper back-layers and heavily leaded paints have been considered robust for outdoor use, the new copperless back-layer and lead-free paint systems were designed for interior mirror applications and the outdoor durability must be determined.

ReflecTech® Polymer Mirror Film Advancements in Technology and Durability Testing

2011 ◽  
Author(s):  
Michael J. DiGrazia ◽  
Gary Jorgensen ◽  
Randy Gee ◽  
Carl Bingham ◽  
Christa Loux
Keyword(s):  
Uv Light ◽  
Water Immersion ◽  
Accelerated Weathering ◽  
Production Environment ◽  
Cooperative Research ◽  
Curved Glass ◽  
Durability Testing ◽  
Cleaning Methods ◽  
The Cost ◽  
Utility Scale

One of the most promising developments for lowering the cost of utility scale concentrating solar power (CSP) is the emergence of durable reflective polymer films as an alternative to conventional curved glass mirrors. The broad adoption of wide web polymer film reflectors has been slowed by the lack of long-term weathering data. With the advent of the Ultra Accelerated Weathering System (UAWS), testing and development can proceed at a faster pace, and ReflecTech® Mirror Film has recently exceeded the equivalent terrestrial UV cumulative dosage of 25 years. ReflecTech® Mirror Film was developed through earlier collaborations between ReflecTech, Inc. (a subsidiary of SkyFuel, Inc.) and the National Renewable Energy Laboratory (NREL). More recently, through a Cooperative Research and Development Agreement (CRADA), ReflecTech, Inc. and NREL have developed an abrasion resistant coating (ARC) appropriate for application to polymer based mirror film. This hardcoat was developed to address the need for reflectors that are low in cost, high in performance and durable to mechanical cleaning methods sometimes used in the CSP environment. The combined impact of these two developments has the potential to significantly change the preferred supply choice for solar reflectors in new utility scale CSP projects. ReflecTech® Mirror Film samples prepared with and without the ARC hardcoat were subjected to accelerated exposure conditions more extreme than actual conditions. Both the uncoated and ARC films exhibit excellent weatherability with no loss in reflectance after highly accelerated exposure of over 25 years equivalent terrestrial UV. The ARC coated samples also exhibited outstanding initial abrasion resistance and adhesion to ReflecTech® Mirror Film, properties that were retained after exposure to various accelerated stress conditions including condensation cycling, thermal cycling, water immersion, and accelerated exposure to UV light. ReflecTech® Mirror Film is a commercially available product. The ARC-coated ReflecTech® Mirror Film has been successfully manufactured as a 1.5 m (5 ft) wide roll-to-roll construction in a commercial production environment and after further testing is expected to be commercially available in late 2011.

XG40—Advanced Combat Engine Technology Demonstrator Program

1989 ◽  
Vol 111 (2) ◽  
pp. 193-199 ◽  
Author(s):  
A. F. Jarvis
Keyword(s):  
Fuel Consumption ◽  
Operating Cost ◽  
Weight Ratio ◽  
Advanced Technology ◽  
Advanced Materials ◽  
Demonstration Program ◽  
Performance Requirements ◽  
Time Requirements ◽  
Durability Testing ◽  
Technology Demonstrator

Commenced in 1982, the XG40 program is central to the demonstration of Rolls-Royce technology appropriate to the requirements of the advanced combat engine for mid-1990s operation. At the same time, the technology in scaled form is viewed as having wider application than for the advanced combat engine alone. This program is jointly funded by UK MoD and Rolls-Royce. In the paper the concepts and scope of the program are described. Associations with previous research programs and other advanced technology demonstrator programs of Rolls-Royce are stated. To meet the multirole capabilities of the advanced fighter and taking the European requirements in particular, the combat engine must be designed to give enhanced dry thrust, retain good dry specific fuel consumption, and reduce reheated fuel consumption compared with current fighter engines. A thrust/weight ratio of 10:1 is targeted and at the same time, requirements for operating cost, reliability, and durability are stringent. As a demonstrator, XG40 has been designed to meet the foregoing performance requirements. At the same time, advanced materials, manufacturing technology, and design of structures have been incorporated to enable the required levels of reliability, durability, component cost, and weight to be demonstrated. Although a demonstrator, XG40 was designed at a scale judged to be appropriate to the likely next generation European fighter requirement. Thus, the engine is in the 90/95 kN nominal Sea Level Static Combat thrust class. Configuration and design are discussed. XG40 is a total technology demonstration program. Principal modules each have a full-scale aerothermal rig program and appropriate structure rig programs. Apart from rigs, the program, including durability testing, utilizes a number of cores and engines plus spares. Achievements and progress toward milestones are reviewed.

Sign in / Sign up

Export Citation Format

Share Document