The Comparison of Different type reflector materials using with SmallSolar Thermal Dish Stirling 10 kW Power Plant for Tha...
*      The Engineering Institute of Thailand Under H.M. The King’s Patronagecatalogues and directories, personal contacts,...
countries that are currently working with private industry in developing reflectors that can beused primarily on large con...
reflectors. It does not contain ultra violet ray protection and is unsuitable for outdoor usefollowing is the product spec...
Alanod Aluminium    This is a German company that manufactures a variety of aluminium grades. It doesmarket one product sp...
the household aluminium foil market. Other than standard aluminium foil, they do not haveany special materials suitable fo...
Reynolds specially designed rail cars to Richmond and Louisville, where they are convertedinto the Reynolds Wrap® Aluminiu...
Astro-Foil    Foil based reflective insulation material that is sold as an insulator. Bubble wrap typematerial is incorpor...
Heat shield (R + Heat shield I)    This material is manufactured for use as radiant barrier. It contains 99% pure aluminiu...
Mirrorbrite was investigating. It appeared to be the only possible product from thismanufacturer that would be applicable ...
Metallized Products, Inc. (MPI), Winchester, Massachusetts, was one of the companiesthat worked with NASA on the original ...
limitation to commercialization of the process was a low alumina deposition rate. Over thepast three years the alumina dep...
dish concentrator applications. At present the 3M Company of Minnesota is the majorsupplier of these polymer mirrors. Thei...
Roche, John    Mr. Roche is the former 3M scientist that developed numerous 3M solar firms during the1980s. He is currentl...
The reflective materials investigated in this research can be classified into the followinggroups:Anodized Aluminium   The...
incorporating the panels into the support structure reductions in the amount of structuralsupport required are potentially...
Table 1. Solar Weighted hemispherical reflectance Rs value of selected weathered samples                               (Ou...
are cutting edge technology materials and still have a ways to go before they are ready formarket.   The best candidate ma...
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Reflective Material for Solar Thermal


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The Comparison of Different type reflector materials using with Small Solar Thermal Dish Stirling 10 kW Power Plant for Thailand Soft-land and Poor Insolation Nature

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Reflective Material for Solar Thermal

  1. 1. The Comparison of Different type reflector materials using with SmallSolar Thermal Dish Stirling 10 kW Power Plant for Thailand Soft-land and Poor Insolation Nature Suravut SNIDVONGS, EIT member* Vice President, Asian Renewable Energy Development and Promotion Foundation (AREF) 211/2 V.S.S Bldg, Ratchadaphisek Rd., Din-Daeng, Bangkok, 10400, Thailand Tel 662 276 7908-0 Fax 662 276 7913 email PhD Student, School of Renewable Energy Technology, Naresuan University, Pitsanulok, Thailand. ABSTRACT The detail in this paper is one part of the dissertation development research project on thesolar thermal dish Stirling engine system for a 10 kW power plant with lead acid batterystorage, named “Siam Solar Dish I” research project. It shows a comparison on technicalcharacteristics between general photovoltaic systems and a small solar thermal dish StirlingEngine System, on condition that both systems maintain the same output and storage capacityat 10 kW with lead acid battery. The dish in this paper is a parabolic design and equipped with a solar tracker. The Stirlingengine is a 10 kWe four– cylinder, swash- plate design and features a moving tube type heatexchanger, low offset space, and double acting pistons. The 10 kWe photovoltaic system ispolycrystalline based without solar tracker and for this study both systems are assumed tomaintain the same 250 kWe battery storage. The researcher in this research project believes that Thailand as a developing country isstill far behind on the know how of high technology in related areas of metallurgy, reflector,solar tracking, high efficiency and high sensitivity motor, high temperature seal, etc. Inparticular, the solar insolation capacity in a very moist climate like Thailand, is also very farbelow in comparison to dry country weather. Therefore, it looks quite impossible to designthe above mentioned system in the manner like as being done in other advanced technologicaland well developed countries. Inevitably, “Siam Solar Dish I” will not reach high efficiencylevel in general performance, but the researcher believes that “Siam Solar Dish I”manufacturing cost, operating cost, together with her durability capacity would be wellaccepted in Thailand’s market including many other under developed countries. However,“Siam Solar Dish I” design and calculation have been based on 1,000 W/ m2 solar insolationvalue, which is the international standard design value referred to in Advanced DishDevelopment System 9 kWe (ADDS) [1] One purpose of this research project is to establish the advantages and disadvantages ofreflector materials as a guide for the end users to select the right material among, AnodizedAluminium, Mirror Polished Stainless, Acrylic and Glass etc, where the best suited for usingin Thailand as well as other global markets in terms of Price, Maintenance Cost, OperatingCost, Economy, Performance, Reliability, and Efficiency will then be selected for furtherimplementation. The comparison in this paper will be presented in descriptive format, withrelevance tables being displayed under the discussion section in this paper. This researchproject has utilized a variety of information resources, including the data solar from library,web search engines, solar industrial 1
  2. 2. * The Engineering Institute of Thailand Under H.M. The King’s Patronagecatalogues and directories, personal contacts, aluminium industry sources, solar cookerdiscussion groups, and a wealth of other investigative resources. A great deal of time has beenspent on this searching activities for the best quality material available at low cost possibility.The selected material would, of course, provide higher characteristics in optical reflectance,ultra violet ray resistant, durability in a variety of environmental and abusive conditions,pliable, and easily attached to a substrate, available internationally, last but not least, veryeconomical.INTRODUCTION Concentrating solar power systems use large solar reflectors to concentrate sunlight togenerate electricity. The widespread application of concentrating solar power generationdepends in part on developing a durable, lower cost reflector. The purpose of this researchproject activities is to select reflectors which are suitable for Concentrating Solar Power inThailand. The ultimate goals are to obtain specula reflectance above 90% for at least 10 yearsunder outdoor service conditions and a large- volume manufacturing cost of less than 500B/m2. Currently, the best candidate materials for solar reflectors can be classified in fourcategories (These materials may meet the current reflector goal, but it is uncertain whetherthey can meet a longer lifetime goal of 30 years of outdoor service. [6]):- Silver coated thin and ultra- thin glass; (1.0 mm thick) glass is durable but has relativelyhigh cost, fragility in shipping and handling, and the availability manufacturer to manufactureit. Anodized coated thin aluminium, such as MIRO- SUN should fit for Thailandenvironment and conditions. It is durable, reasonable price, not fragility in shipping andhandling, and very easy to find in Thailand as the source of lighting fixture reflector. Silver coated thin acrylic is not durable for 30 years but at least 10 years in operation,reasonable price, not fragility in shipping and handling, and very easy to find in Thailand asdecorative material. Silvered polymer films reflectors are lighter in weight, offer greater system designflexibility, and have the potential for lower cost than glass reflectors. However, silveredpolymer has several limitations, including relatively high cost, a lifetime less than 30 years,and poor adhesion between the silver and the polymer on exposure to water (Schissel, 1995). The good solar reflectors must have the following characteristics:- 1. Light weight 2. Durable for wind, moisture, deflection, high and low temperature 3. Flexible 4. Low cost, less than 500 Baht/ m2or 12.5 $/ m2 (1 US $ = 40 Baht March, 2005) 5. Low reflection loss 6. Reflect more than 90% in wavelength 700 to 1000 nm 7. Easy to clean 8. High impact not easy to break 9. Life more than 30 years. 10. Ultra violet resists A critical task in developing a solar dish is to identify reflector materials that would beboth suitable for this application as well as economical. This research project activities haveconducted an extensive search for available reflective materials including contactingreflective materials manufacturers as well as national laboratories in U.S.A and other 2
  3. 3. countries that are currently working with private industry in developing reflectors that can beused primarily on large concentrating solar energy devices. [5]PRODUCTS AVAILABLE ON THE MARKET [8]3M VM2000 radiant mirror film This material is a multi- layered polymeric film. The outside layer is polyethylene. It ismetal free, therefore non corrosive and non-conducting. It is thermally stable to a temperatureof 125C. The manufacturer claims that the material has low-shrinkage. Unfortunately thematerial is not ultra-violet ray resistant. 3M can add ultra-violet ray protection materials atadditional cost. (This special coating can only be applied at two facilities in Tennessee.) Thematerial can also be coated with a 3M adhesive (#M 467MP) or can be purchased without theadhesive. The reflective (optical luminosity is greater than 98%) reflects more than 98 % ofvisible light. The drop off if reflectance at 700 nm is unfortunate, but is not detrimental forthis application. It is a film like product that is flexible, lightweight and highly reflective. It iscommonly used as an indoor reflective material for sun tubes and other. 3M has verbally quoted a price of $1.25 per square foot (1,000 square foot minimumpurchase). To that would be added $0.30 per square foot for the ultra violet ray inhibitingcoating. The product is still in the development and testing stage. 3M does not seem to be interested in solar products. The manager of the section thatdeveloped solar films in the past have retired and 3M seems to have retired their interests insuch products along with him. Nevertheless, 3M has stated that they would provide sampleswith improved screening layers for future testing. FSEC staff came upon an NationalRenewable Energy Laboratory (NREL) [9] that mentioned that the Sun Lab researchers are"developing new reflective materials, such as advanced polymer films that can be produced ata fraction of the cost of glass mirrors and have excellent optical and wear-resistantproperties." Contact Gary Jorgensen at NREL regarding this matter.M SA- 85 solar film SA- 85 is aluminized acrylic, aluminium vapour coated on 2-mil polyester film with anoutdoor weathering acrylic coating over the aluminium. (Per John Roche, the developer of thefilm.) The former manager of the 3M section that manufactured solar films developed thisfilm in the 1980s. There are several companies and individuals that use this material on theircurrent solar reflectors. Contact with 3M revealed that 3M would no longer be manufacturingthis material and once the current supply in the field runs out, none would be available in thefuture. The 3M SA-85 film appears to be an ideal reflective material for use with solar reflectors.Numerous solar reflectors have used it successfully in the past. Unfortunately, the material isno longer being manufactured by 3M.3M Silver Flux material This material is marketed by 3M for existing luminaries or as interior surfaces forluminaries. It maintains a specula reflectance of 85% and an overall reflectance of 90%. It isbonded to 0.7 mm treated aluminium and is ideal for producing rigid precision quality specula 3
  4. 4. reflectors. It does not contain ultra violet ray protection and is unsuitable for outdoor usefollowing is the product specification: 3M Silver flux reflectors for fluorescent light fixtures, 2.5 mil polyester film with aspecula metallized layer on front surface treated with an acrylic coating to suitable forprotecting metallized layer from oxidation, corrosion and polyester film from ultra violet,degradation, covered with a removable pre-mask and a pressure sensitive adhesive backingand low release liner and meeting or exceeding the requirements of EPA Green LightsProgram and following requirements: 1. Tensile Strength: 45 lbs. per inch of width 2. Elongation at Break: 100% 3. Specula Silver Reflectors a. Specula Reflectivity: 95% at 1.5 degrees field angle using Devices and ServicesSpecula Reflectometer: 92% at 0.5 degrees field angle (ASTM E 430) b. Diffuse Reflectivity: 2% c. Total Reflectivity: 97% d. Total Solar Reflectivity 95% integrated over air mass 2 solar spectrum. e. Reflective Life (ASTM G 53): 3% maximum loss of original Reflectivity after 1000hours accelerator aging 4. Specula Aluminium Reflectors a. Specula Reflectivity: 85% b. Diffuse Reflectivity: 2% c. Total Reflectivity: 87% This product appears to be similar to the VM2000 film.Acrosolar Acrosolar is the name of the company that used 3M SA-85 on their owned trade name.This company uses and has a large supply of the 3M SA-85 reflective material that thecompany uses on solar concentrators. (Solar Laser Mirror) They have the material in 48-inchwide rolls. The material has an adhesive backing. Cost of the material from Acrosolar is $2per square foot. Todate, it is not certain that Acrosolar product is still available to buyers,since the original 3M SA- 85 material has been terminated from 3M production.Acrylic Mirror This material is half the weight of glass. It is shatter resistant and highly reflective. It is anoptically perfect acrylic sheet that is vacuum metalized in a vacuum chamber. The sheetsthemselves are protected on the back by a durable scratch resistant coating and on the frontsurface be either a clear polyethylene film or a paper masking. The material can also be madewith pressure sensitive backing. The manufacturing of this product is very complex. The costof this material is also very high, which makes it unfeasible for this project. Close to $5 persquare foot. This material for indoor used. 4
  5. 5. Alanod Aluminium This is a German company that manufactures a variety of aluminium grades. It doesmarket one product specifically for solar applications. That is MIROSUN Extra bright. Thismaterial reflects super intensive spectral areas. The materials curve of the spectral reflectancefollows the spectrum of the sun and it guarantees reduced diffusion together with highreflection values. Alanod states that their tests have proved the weather durability of theadditional lacquer used to provide external protection in demanding conditions. They alsostate that the lacquer does not reduce the optical properties of the material. The 4270 KK(being MIRO 27 with clear varnish on the front and reverse side) is ultra violet ray resistant,but the protective film coated is not ultra violet ray resistant, referred to be actually a thinyellow film applied to protect the mirror surface during shipping. This material is quitesuitable for solar reflectors. The cost is somewhat higher than others, but the material wouldbe indestructible. The material cost for information. MIROSUN - 4270 KK (MIRO 27 withclear varnish on the front and reverse side), C1 natural tone with protective film on the frontside 0.020" x 49.212" coils. 2,000 lbs at US$ 7.71/lb, 10,000 lbs at US$ 7.62/lb, 40,000 lbs atUS$ 7.37/ lb. These cost comes out to $2.15 per square foot. Cheryl Kennedy provided information on the latest NREL tested reflectors. Thisinformation is based on Cheryls report, “Summary of Status of Most Promising CandidateAdvanced Solar Mirrors (Testing and Development Activities), 30 Sep 2001”. Alanod Front Surface Aluminized Reflector product (Note: This is the Alanod productreviewed in this report) Front surface aluminized reflectors using a polished aluminiumsubstrate, an enhanced aluminium reflective layer, and the formation of a protective oxidizedtopcoat (alumina) were shown to have inadequate durability in industrial environments.Samples with a polymeric overcoat to protect the alumina layer have improved durability.Samples have survived >3 years outdoor exposure in Koln, Germany under the Solar PACESproject. Has a polymeric overcoat to protect the aluminium. The acrylic over coated materialfailed in accelerated testing and was replaced by Fluro Polymer overcoat. The newformulation is still being evaluated consists of: a. Protective Polymeric Overcoat b. Alumina c. Aluminium reflective layer d. Polished aluminium substrate e. Price $ 2.15 per square foot.Reflec Tech Reflec Tech is a commercial product of Alanod Aluminium that has been untested forsolar applications and is still being evaluated by NREL. Base commercial silvered polymer92% hemispherical reflectance cost about $1.50/ ft2. Reflec Tech product not commerciallyavailable yet but developer will contact FSEC when the product is commercially available.Alcan Aluminium Alcan is a major aluminium manufacturer. Contacts with this company have provedfruitless in finding a product that could be used in the solar reflector. This company producesaluminium products for industrial and commercial use competes with Reynolds aluminium in 5
  6. 6. the household aluminium foil market. Other than standard aluminium foil, they do not haveany special materials suitable for this project.All Foils This is a distributor and service centre for thin-gauge metal foils, strips, or sheets. Theirinventory includes aluminium in gauges of 0.00025 to 0.125 inches. The material they haveavailable unfortunately is not designed for outdoor use.Aluminium, polished Pure aluminium (99%+) develops a protective coating of aluminium oxide immediatelyon exposure to air (oxygen). This actually protects the aluminium from further oxidation byoxygen in the air (unlike iron which will continue to oxidize until there is nothing left but ironoxide rust.) However, pure aluminium has poor structural properties. Therefore, aluminiumthat is used for anything structural is actually an alloy of aluminium. These alloys can be“polished” however, without some kind of protection (anodized or coated) they are subject tofairly rapid atmospheric corrosion. One will often see white chalky pitting on unprotectedstructural aluminium products. Pure aluminium is also subject to severe corrosion from strongacids and bases like cement “lime” products will destroy it in very short order. Thusaluminium products that are expected to last for extended periods of time must be coated witha protective coating.Aluminium foil emergency blankets There are numerous products of this nature in the marketplace. Basically they are alloffshoots of NASA research that initially developed this “blanket” technology for spaceapplication. A search of various web sites and solar reflector discussion groups revealed thatthis product had been used in solar reflector application in the past. Several individuals hadtried the product as a dish reflector and were unsuccessful in long term application since, asthey stated, “the material eventually falls apart.”Aluminium foil, heavy duty This is common everyday kitchen application aluminium foil. Here are some facts aboutstandard kitchen aluminium foil provided by Reynolds Aluminium. Reynolds Wrap®Aluminium Foil is the most versatile of all food wrapping materials. It can withstand bothheat and cold. Reynolds Wrap® Aluminium Foil was first introduced in 1947. Since that timeit has become one of the most immediately identifiable brands on the market. ReynoldsWrap® Aluminium Foil is 98.5% aluminium. The balance is primarily iron and silicon. Theseare added to give the strength and puncture resistance obtained only in the alloy used inReynolds household foil. Reynolds Wrap® Aluminium Foil contains no recycled material andcomplies with U.S. Food and Drug Administration requirements for direct contact with food. The brand that is known and sold all over the world is manufactured in two locationsLouisville, Kentucky and Richmond, Virginia. Aluminium for Reynolds Wrap® AluminiumFoil is placed into alloying furnaces at the continuous cast plant in Hot Springs, Arkansas andheated until molten. It is then modified to the correct alloy chemistry and fed into a machineknown as a "continuous caster." The continuous caster converts molten aluminium to a coil ofmetal by forcing it between large, water cooled chill rollers at several feet per minute. Thealuminium is formed as a long sheet with a thickness of .045". Its rolled into large coils thatmeasure 74 inches in diameter and weigh over 30,000 pounds! These coils are shipped in 6
  7. 7. Reynolds specially designed rail cars to Richmond and Louisville, where they are convertedinto the Reynolds Wrap® Aluminium Foil. In addition, here are some little known application facts about aluminium foil that couldhave an impact on its use in solar reflector. The difference in appearance between dull and shiny is due to the foil manufacturingprocess. In the final rolling step, two layers of aluminium foil are passed through the rollingmill at the same time. The side coming in contact with the mills highly polished steel rollersbecomes shiny. The other side, not coming in contact with the heavy rollers, comes out with adull or matte finish. The darkening of foil may be caused by moisture. This results in a build up of aluminiumoxide. This is a totally harmless substance that is naturally present on the surface of foil.Moisture tends to accelerate this build up. (This is acceptable for standard use of aluminiumfoil in standard ovens and kitchens, bit will have, in the long term, a negative impact whenused as a reflector in solar reflectors.) Occasionally when aluminium foil comes in contact with a different metal or a food that ishighly salted or acidic, small pinholes are formed in the foil. This is a harmless reaction thatdoes not affect the safety of the food. It is difficult to predict, but may occur under thefollowing conditions: When aluminium and a dissimilar metal are in contact in the presence of moisture, anelectrolytic reaction may occur causing a breakdown of the aluminium. To avoid this usealuminium, glass, ceramic, plastic or paper containers. Do not cover sterling silver, silverplate, stainless steel or iron utensils with aluminium foil. A similar reaction may occur when salt, vinegar, highly acidic foods or highly spicedfoods come in contact with aluminium foil. The result of these reactions is a harmlessaluminium salt. Some aluminium salts are used in medicines to treat stomach disorders. Thefood can be safely eaten; however, the aluminium salt particles can be removed from the foodto improve the appearance of the food. Although these situations are questionably applicable to solar reflectors the above factsindicate that standard aluminium foil is not as resistant and all purpose as many assume. In addition, the material, although pliable, was not easy to handle and apply withoutcreating wrinkles. Special 3M adhesive had to be procured to affix the material to insulationboard. Standard white glue did not adhere very well. The material is so thin that it quite easyto damage.Aluminized polyester This material discoloured and faded after a year or two. Therefore, it appears that thematerial does not contain ultra violet ray inhibiting coatings or properties.Anocoil aluminium sheet, 0.3mm thick This material is used in the Peru Children’s Trust solar stove. They used 0.3 mm Anocoilgrade 710.33 which was 86 % reflective and exhibited a mirror quality. Anacoil is the largestindependent manufacturer of lithographic plates in North America and supplies high qualityplates to many leading publishers in North and Central America, Europe, and Asia. Thisproduct is not protected from oxidation. 7
  8. 8. Astro-Foil Foil based reflective insulation material that is sold as an insulator. Bubble wrap typematerial is incorporated in the product and therefore would not be suitable for thisapplication. Also, the manufacturer cannot provide optical property specifications. Thespecification that they did provide, indicate that Astro-Foil is 5/16” thick, has a temperaturerange of –60 to 180 F, and has a reflectivity of 95- 97%. The manufacturer states that thematerial can withstand solar radiation and environmental conditions and that it is availablethroughout the United States as well as in the Middle East and South East Asia. This material is easily available but does to the bubble wrap appearance and themanufacturer’s inability to provide specifications; it does not appear as a suitable reflectivematerial for this application.Clear Dome Solar– Solar Flex material This product is Triple laminated, tear resistant metallic fabric. Clear Dome states that thisproduct is an offshoot of NASA research. Manufacturer states that in comparison heat tests,their reflective material continuously beat any other material such as aluminium foil, glassmirrors, Mylar, etc. by 18-20% in heat generation. This is stated as being due to the excellentIR reflection properties that the other surfaces do not seem to reflect as well. Themanufacturer also states that since their material reflects most of the IR, and because it has ametallic surface and not a plastic surface, there is little or no effect from IR exposure. Inregards to degradation, the manufacturer has had samples outdoors for the past year in alltypes of weather, and except for a very slight loss in visible reflection, there have been nochanges in the products heating capabilities. The manufacturer states that water has no effecton it. Food can be easily wiped off. Normal soap and water are recommended for cleaning.The product is also very scratch resistant and almost impossible to tear by hand. Yet knivesand scissors easily cut the material. The material can be scrunched into a ball and easilyreconfigured into a flat position without creases, etc. remaining. It is rated by the manufacturer to over 400 F and to –60 F. Clear Dome outdoor testsindicated no change in shape until the material reaches approximately 200 F. Above thattemperature, the centre plastic thermal barrier starts to shrink, causing a small ripple effect tothe exterior metal surface. The shape changes slightly, but the material stays together. The manufacture states that the material will take many bends before showing any wear.The material is thick, and feels like 8-10 layers of aluminium foil laminated together. Thecentre is flexible and reinforced plastic provides excellent strength. Clear Dome has found the best adhesive to be 3M contact cement. As long as the twosurfaces are clean when the glue is applied, the two surfaces will remain bonded. Unfortunately, Clear Dome could not provide any specification sheets on the product.Undoubtedly, Clear Dome is purchasing this material from a unknown manufacturer name. For 51- 125 feet, the cost is $4 per square foot, which equals to $204 for 51 feet by 4 feetwide. The standard size is 2 feet by 4 feet. A 51-foot roll cost comes to $1 per square foot. 3M spray adhesive was used. The material is very pliable and quite easy to handle. Onceaffixed, it is very easy to remove wrinkles. Unlike standard heavy duty aluminium foil, thematerial is very sturdy. It cannot be ripped by hand; instead, it requires a knife or scissors tocut the material. This makes it ideal for rough handling and long term use. 8
  9. 9. Heat shield (R + Heat shield I) This material is manufactured for use as radiant barrier. It contains 99% pure aluminiumon both sides. Also contains a layer of polyethylene film for puncture resistance as well aspolyolefin scrim for tear resistance. The material is available in solid or perforated structure.The material has the following specifications: 97% reflectivity, 3% emissive, Class A flameand smoke rating, 12 lb/square inch tensile strength, and is 1.4 mil. thick. The manufacturerclaims that ultra violet rays will not affect the material. Costs have been requested from themanufacturer and should be received the first of the year. Note that this material looks verymuch like the previously mentioned Clear Dome solar material.Heat shield (R + Heat shield II) This material is also manufactured for use a radiant barrier. It contains 99% purealuminium on one side. On the reverse side incorporates aluminized polyethylene (MPET). Itexhibits superior tear and puncture resistance. The manufacturer also states that it canwithstand repeated pressure washing and is also available in a solid or perforatedconfiguration. The material has the following specifications, 97% reflectivity on the foil side,76% on the MPERT side, 3% emissivity on the foil side, 24% on the MPET side, Class Aflame and smoke rating, 78 lb/square inch tensile strength, 1.4 mil. thick. The manufacturer claims that ultra violet rays will not affect the material. Costs have beenrequested from the manufacturer and should be received the first of the year. Note that thismaterial looks very much like the previously mentioned Clear Dome solar material.Low Met This is a silicon based spray on material that is used (and marketed) primarily as a radiantbarrier material FSEC comments: This material would not be suitable to this project due to its“diffuse reflectance” properties.Metalized Products, Inc. Metalized Products, Inc. is a leader in developing and manufacturing protective,reflective, decorative, and functional and performance coated products using plastic films,paper, and textiles as well as producing laminates for these products. The following materials are sold: 1. Astrolon – A family of super-light radiant barrier materials perfectly suited toapplication ranging from emergency medical care to outdoor recreation. 2. NRC-2 – A family of high-performance thermal insulating materials 3. Heat Shield - Vacuum aluminized film used as a thermal/vapour barrier similar tothat employed as radiation barrier on the Apollo Command and Lunar Modules. 4. Decorative Papers - MPIs line of non-laminated holographic papers, boards and filmsprovide excitement to gift wrap, cosmetic and security markets. 5. Mirrorbrite - Mirrorbrite is a high gloss, metallic paper or board with a mirror-likesurface. Mirrorbrite is used in both packaging and printing applications. 6. Prismabrite: A holographic paper available in standard or customized patterns used inboth packaging and printing applications. 9
  10. 10. Mirrorbrite was investigating. It appeared to be the only possible product from thismanufacturer that would be applicable to this project, but it does not have UV inhibitingcharacteristics and is therefore unsuitable.Mirrored Plexiglas The Standard Plexiglas with mirror coating. It can be used for ray testing only. Notoutdoors durable and very expensive. Comes in 4 foot by 8 foot sheets - $136 (Includes 15%discount for not cutting) 1/ 8" thick. Its $5 per square foot without cut.Mirroflex Mirroflex is a composition of rigid high impact plastics, vacuum metalized and bondedtogether to create highly reflective, unbreakable mirror-like sheets. Mirroflex is a reflective,impact resistant plastic with unusual surface treatments including silver, gold, brass, brushedmetallic, wood grains and granites. This material is very easy to fabricate. Mirroflex isavailable in sheets or rolls (depending on the thickness). Mirroflex thermo plastic sheet androll programs are also available as metallic trim. In roll form, it has a pressure sensitiveadhesive backing for use in decorative metallic trim applications from 1/4" and up in 1/8"increments. Miroflex are available in polished aluminium, brass & gold, brushed aluminium& brass, black and more. Mirroflex sheets are available in all metallic colours listed above in2 x 8 and 4 x 8 sheets, varying in thickness from .020" to .025". Also available in a largeselection of wood grains, granites, solid colours and specialty finishes suitable for interior andexterior application. Mirrotiles are fabricated in Mirroflex to fit standard suspension ceilingswhere an easy to use, easy to fabricate very low-cost mirrored ceiling tile (chrome or gold) isdesired. Mirroflex materials are primarily manufactured and marketed for interior decorativepurposes. Without investigating the optical, solar, and durability properties of thismanufacturer’s products, it was determined that the cost is too prohibitive for this solarreflectors.Mylar Dr. Steven F. Jones, Professor of Physics at Brigham Young University, reports in hispaper “The Solar Funnel Cooker,” Solar Cooker International archives, that aluminized Mylarwas used in the development of the funnel solar cooker. Dr. Jones reported that aluminizedMylar was a good reflective material but was “relatively expensive and rather hard to comeby in large sheets.” (Therefore, the funnel cooker used standard aluminium foil instead.) Ithas been noted previously that Mylar does not have long term weathering characteristicsrequired for this solar cooker product and will not hold up to outdoor use. Metalized Mylar was used at the University of Texas, Pan American, Edinburg, Texas ona parabolic solar concentrator. The material was inadequate as “it yellowed along the edgesand peeled after only two months. The film used was metallized Mylar and it was bonded toseveral layers of soft woven and heavy woven fibreglass using amine epoxy.”Spin Offs NASA’s product Through space use, a once commercially obscure product has become a boomingcommodity. 10
  11. 11. Metallized Products, Inc. (MPI), Winchester, Massachusetts, was one of the companiesthat worked with NASA on the original space materials. MPI continues to supply metallizedmaterials for space use and has developed lines of industrial and consumer orientedmetallized film, fabric, paper, and foam. One of the most successful MPI products is TXGlaminate, once employed by NASA as a reflective canopy for visual and radar detection ofthe rafts in which returning Apollo astronaut’s awaited pickup by ships or helicopters. TXGnot only is super reflective, but nonporous, waterproof, and rot proof. Subsequently, WinslowCompany Marine Products, osprey, Florida, obtained a license for commercial production ofthe survival raft. In cooperation with MPI, Winslow improved the strength and thermalcharacteristics of TXG so that its survival rafts would provide maximum protection fromheat, cold, wind, and rain. A reflective kite of gold TXG produced by Solar Reflections, Inc., Fort Lauderdale,Florida, serves as a highly conspicuous distress indicator in an emergency. The SOS SignalKite can be flown as high as 2OO feet to enhance radar and visual delectability. It providescampers, hikers, and mountain climbers with a lightweight, easily portable emergencysignalling device, and boaters with a convenient substitute for bulky dish devices. Made ofmetallized nylon, the kite spans six feet but weight only six ounces. Connecticut Advanced Products, Glastonbury, Connecticut, has adopted TXG for itsThermo guard heat shields, custom-tailored reflective curtains that cover the windshield andwindows of parked aircraft to protect avionics equipment from heat build up and ultravioletradiation. In a similar application, the Star shade ~ from Star Technology Corporation,Carbondale, Colorado, is a multilayered automatic shade system for large windows incommercial or residential buildings. (See: Among MPIs own products are various protective fabrics that retain up to 8O percent ofthe users body heat, helping to keep a person warm for hours in cold weather crises or toprevent post-accident shock. All are remarkably compact. The Space* Emergency Bag, forinstance, opens into a three-by-seven-foot personal tent/blanket and then folds into a three-ounce package the side of a deck of playing cards. One of the most successful materials developed reflector canopy for visual and radardetection. Material is super reflective, nonporous, waterproof, and rot proof which used inboating life rafts. Similar to the Clear dome product listed above.IBAD Ultra- thin glass reflector is combining the best of both thin-glass and silvered- polymerreflectors, which cause the material lower- cost. The reflector consists of a polymer substratecoated with a copper layer, followed by a layer of silver, and finally by a protective opticallytransparent alumina top coating. Earlier, this basic design was recognized as having highpotential, but the difficulty has been to find a durable top coating. The alumina top coating isessential to sustain high reflectance in outdoor service. This high performance solar reflectivematerial can be produced in a roll format using vacuum deposition techniques. The materialconsists of a multilayer thin film stack on a substrate. The essential feature of the film stack isan alumina film several microns thick deposited over a silver film. The alumina film isdeposited under high vacuum using a physical vapour deposition technique called ion beamassisted deposition (IBAD). The alumina film is optically transparent, scratch resistant, anddurable. Its purpose is to protect the silver film and maintain high optical reflectance. Workon this reflective material began five years ago. Samples were produced on polyestersubstrates by batch coating. Those samples showed excellent durability in accelerated testingat the National Renewable Energy Laboratory (NREL) in Golden Colorado. The principal 11
  12. 12. limitation to commercialization of the process was a low alumina deposition rate. Over thepast three years the alumina deposition rate has been increased from 1 nm/ s to 20 nm/ s. Thenext step is to produce material in a roll format. A roll coater has been built to process 30.48-cm wide rolls of solar reflective material. A steel strip with a highly specula surface finishwill be used as the web material. The advantage of this material compared to polyester is thatit withstands a higher process temperature and lowers final product installation costs. A majortechnical challenge will be to reproduce high reflector durability in a continuous, high rateprocess. The description below is from this report. Solar thermal technologies use large mirrors toconcentrate sunlight for renewable power generation. The development of advanced reflectormaterials is important to the viability of electric production by solar thermal energy systems.The reflector materials must be low in cost and maintain high specula reflectance forextended lifetimes under severe outdoor environments. Production processes associated withcandidate materials must be scalable to mass production techniques. A promising low-costconstruction uses a stainless steel foil substrate with a silver reflective layer protected by anoptically transparent oxide topcoat. Thick (2 to 4 micron), dense alumina coatings providedurable protective layers. The excellent performance of alumina-mated reflector materials inoutdoor 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 withoutincurring substantial capital is the use of a chilled drum coater. An existing chamber is beingmodified, and the deposition rate will be increased prior to the installation of a drum coater toproduce-1 ft wide by 10-ft long strips of solar reflector material. The production andperformance of these materials are discussed. Silvered PET protected by IBAD depositedalumina represents an advance in solar reflector durability. Preliminary results have shown aninitial solar-weighted hemispherical reflectance of 95% and excellent optical durability inboth accelerated and outdoor (Colorado) exposure testing. Additional issues to addressinclude determining the minimum coating thickness needed to ensure optical durability,increasing the deposition rate, testing the long-term Mechanical stability of the material underbiaxial stress, and field testing the material. Research into a better stainless steel levellinglayer is being pursued. The alumina-coated reflector material under development offerspromise as a commercially viable solar reflector material. The deposition system at SAIC islarge enough and has sufficient capability to support a range of reproduction scale coatingswork and the new state-of-the- art deposition system at NREL will allow the development ofadditional innovative coatings to be prototyped. This is in the realm of national laboratoryresearch and development into products that can be used on large parabolic and dish typeconcentrating solar collectors. Mass production is not available. (From "Progress TowardAchieving a Commercially Viable Solar Reflective Material” by C. (Cheryl) E. Kennedy andR.V. Smilgys, NREL/ CP510- 24058.)Metallizing Polymer Mirrors The following is from an information report developed by NREL "Durable MetallizedPolymer Mirrors". NREL researchers have made several modifications in the construction ofSilvered Polymer solar mirrors which improves their optical durability and resistance todelaminate failure. One innovation is to interpose an oxide layer between the polymer filmand the silver reflecting layer. The oxide layer impedes the initiation of delaminate and alsoimpedes the propagation of delaminate if initiation occurs. The oxide layer also providesprotection to the silver and slows corrosion. In a preferred construction, there is a copperlayer between the silver and the adhesive, which significantly helps to slow corrosion of theuse silver. Silvered polymer solar reflectors are finding increasing use in parabolic trough and 12
  13. 13. dish concentrator applications. At present the 3M Company of Minnesota is the majorsupplier of these polymer mirrors. Their commercial product, ECP-305+, developed incollaboration with NREL, incorporates the protective black layer of copper along with adelaminate resisting alternative adhesive. A number of industrial partners, includingIndustrial Solar Technology and Cummins Power Generation, are field testing these mirrorsat the present time. In a follow-up to this report, Mr. Ken May at Solar Technology and wastold that the 3M silver film (ECP- 305) never made it and that they now use the 3M SA-85aluminized acrylic film on their reflectors. Unfortunately, 3M has discontinued using thismaterial and it will no longer be available once existing stock is used up. Mrs. Barbara Kerr states in an e-mail posted on the Solar Cookers International web sitearchives that she also uses the SA85 since it is very durable and UV resistant. It is alsoscratch resistant. Barbara is associated with Solar Cookers International and is the author of“Spreading Solar Cooking, A Field Guide. Second Expanded Edition, 1997,” and is a wellknown authority in the use of solar cookers internationally. Tested report from NREL- Cheryl Kennedy Cheryl. “Optical Durability Testing ofCandidate Solar Mirrors, March 2000.” Report states that the following were excellent testedmaterials (durability wise); thin glass, thick glass, SA-85 and ECP-305+ Glass is of no use tothe application for this solar reflector. The SA-85 and ECP-305+ were made by 3M and willno longer be manufactured once current stock in the filed is consumed. The report states thatthese materials can be characterized as intermediate and require further improvement 1. All polymeric construction 2. Alanods aluminized reflector 3. A metallized polymer (ECP- 305)Note that NREL continues it’s evaluation of this material and is also evaluated in 2001. The report also states that the following were characterized as poor and unsuitable forsolar reflector applications: 1. Metallized polymer (SS- 95) 2. Metallized Fluro Polymers (until secularity can be sufficiently improved) 3. Constructions in which adhesives are in direct contact with a silver reflective layerPolyester based reflective materials Comments discovered in the Solar Cookers International archives attest to the fact that"this material does not stand sun-radiation for very long."Ra Bar Products Inc Aluminized foil material that incorporates Kraft paper backing. It was marketed as aradiant barrier material. Reflectance characteristics have not been obtained from themanufacturer. The material is .0003/30 lb aluminized foil and at $ 0.04 per square foot iseconomically attractive. This product has affixed this material to one of the Roger 7.7 cookersand tested. It is easy to adhere to a backing when using 3M adhesive spray material. Thematerial came in a large roll. Creases were evident in the material which undoubtedly resultedfrom the rolling process. It was not able to remove the creases during the application to thecooker backing. Interestingly, the Kraft backing more than likely was a positive feature, as ittended to allow better adhesion to the backing material. 13
  14. 14. Roche, John Mr. Roche is the former 3M scientist that developed numerous 3M solar firms during the1980s. He is currently retired and is associated with the Solar Oven Society. Currently he usesthe 3M SA-85 solar reflective film on his Solar Reflectors, but acknowledged that 3M is nolonger manufacturing this product and once it is used up, it will no longer be available. 3M,and the solar industry at large, have lost a great advocate (and developer) within 3M of solarfilms and related products with the retirement of John Roche from 3M. Actually the current3M films division representative suggested contacting Mr. Roche to obtain information onsolar films. 3M did not seem very enthusiastic about solar films. This is probably in large partdue to the very small demand and use of this material.United Aluminium Manufactures custom rolled aluminium coils. Darwin Curtis’ son, John, obtainedaluminium from this company for a solar cooker that he designed. Determination will have tobe made whether this aluminium has a protective coating to prevent long term oxidation. Or,if that coating is ultra violet ray resistant.Mirror Polished Stainless The Mirror Polished Stainless can be used for solar reflector but it had 50% reflectedvalue. It strength is very good. It can used very perfect for outdoor. The prices are reasonable.It easy to work but it more weight when compared to aluminium or film type.TESTING METHOD From the report of some researchers a number of promising new reflective materials forsolar thermal energy conversion have been exposed to real outdoor conditions at 8 test sites inthe U.S. as well as in Spain and in Germany under various climatic conditions. Further testshave been performed in a simulating weather chamber. Weather and air pollution data havebeen monitored to reveal possible lifetime limiting environmental factors. Materials investigated were:- 1. Anodized aluminium, Sao 2 coated silver and Sao 2 coated aluminium processed via the sol gel technique. 2. Silvered polymer 3. Aluminized polymer mirrors 4. Silvered coated thin and ultra-thin glass. Theoretical performance has been determined by measuring the hemispherical reflectanceas a function of exposure time with a dual beam UV- VIS- IR spectrometer equipped with anintegrating sphere. Microscopic investigations have been performed additionally tocharacterize material degradation [7]. In general the cooperation within the Solar PACES program foresees that any participantmay distribute reflector samples to test sites of the partners on a "request to be weathered"status. However, only those materials promising to meet the performance goals are distributedto all test sites. Besides these "close to the market" materials, those types being indevelopmental states are previously tested in a weather simulator or at one outdoor site. 14
  15. 15. The reflective materials investigated in this research can be classified into the followinggroups:Anodized Aluminium These materials, fabricated in the CIEMAT labs in Madrid consist of different kinds ofsubstrate materials (glass, aluminium), a reflective film (aluminium, silver) and an oxidationprotective layer processed via the sol-gel route.Coated Aluminium The 3 sheet aluminium materials employed in their study consist of an aluminiumsubstrate (0.8 mm) carrying a reflective layer of pure aluminium and an oxidation protectivethin ceramic coating. SOLAR direct provides an anodized and Alanod and Anofol/Metalloxid a PVD coated surface. Metal/ Polymer: ECP305 Plus is a silvered weather ableacrylic film with an adhesive layer on the back side. Two kinds of substrate materials(aluminium, float glass) are tested. SA85 is an aluminized polymer material with an acrylicprotective overcoat. Float glass and stainless steel were tested as substrates. Sun flex consistsof an aluminized Hostaflon film with a protective film on the back side. Samples have beenexposed without any substrate.Stretched-membrane Stretched- membrane designs incorporating membranes of plastic or steel stretched overboth sides of a ring have received a lot of attention. In the stretched membrane design,vacuum in the plenum between the membranes is drawn to create curvature. Examplesinclude LaJet and Cummins facets, the SAIC USJVP dish and several heliostat designs.(Bean and Diver, 1995 and, Beninga, et al., 1989 and 1997) Stretched-membraneconcentrators with plastically deformed metal membranes, for short focal length to diameterratios, have been developed by Solar Kinetics, Inc. (Schertz et al., 1991) and Schlaich,Bergermann, und Partner. (Schlaich et al., 1994). [4]Silvered coated thin and ultra-thin glass The 3 types of silvered glass materials used in their study consist of a glass substratesilvered from the backside and sealed with an oxidation protective layer. A low iron contentfloat glass is used with optimized transmission properties in the UV VIS-IR range. Thematerials have been applied successfully in the LUZ- LS3 collectors (Flatbed 4 mm glass/silver) as well as in a stretched membrane heliostat project (Glaverbel/Hirtz 1 mm glass/silver) and in dish/ Stirling systems (Steinmuller 1 mm glass/ silver). Silver/ glass mirrors have excellent optical properties but need a method of support inorder to be used in concentrating solar thermal systems. In collaboration with the Cumminsdish/ Stirling development program, we started investigating sandwich construction as a wayto integrate silver/ glass mirrors into solar optical elements. In sandwich construction,membranes such as sheet metal or plastic are bonded to the front and back of a core (like asandwich). For solar optical elements, a glass mirror is bonded to one of the membranes. Thistype of construction has the advantages of a high strength- to- weight ratio, and reasonablematerial and manufacturing cost. The inherent stiffness of sandwich construction mirrorpanels also facilitates large panels. This can have cost advantages for both the amount ofhardware required as well as reduced installation and alignment costs. In addition, by 15
  16. 16. incorporating the panels into the support structure reductions in the amount of structuralsupport required are potentially possible. Glass- foam core mirrors were developed by the Jet Propulsion Laboratory (JPL) in the1970s and 1980s [2]. With this construction, glass mirrors are mechanically deformed andbonded to a foamed glass support, which has been ground to the specified contour. The foamglass is intended to match the thermal expansion coefficient of the glass mirror. (Argoud,1980) Steel-substrate support entails glass mirrors bonded to a steel sheet, which in turn aresupported by a stretch-formed or stamped steel backup structure (like a car hood). This typeof support was used in the McDonnell Douglas dish concentrator. (Stone, et al., 1993) Similarapproaches, but with rib supports stretch-formed or stamped to the desired curvature, wereused by Acurex in their Innovative Concentrator design and by Solar Kinetics, Inc. (SKI) onthe Shenandoah dishes. Both of these concentrators used reflective film. (Overly, et al., 1985,and Saydah, 1983) Fibreglass supports formed over a mandrel have been investigated recentlyby Kansas Structural (Gill and Plunkett, 1997) and McDonnell Douglas (NREL, 1998) [3].DISCUSSION The solar weighted hemispherical reflectance values RS of selected weathered samplesare resumed in Table 1, the reflectance values of the accelerated weathering tests are listed inTable 2. In general, it can be stated that glass/ silver materials exhibit good weather ability.They do exhibit markedly losses in solar reflectance neither after outdoor exposure nor afteraccelerated weathering. Furthermore no visible damage occurred due to corrosion from theedges or from the surface. The polymer/ silver materials exhibit good results in the outdoor test (which is of coursetoo short to draw final conclusions), but a slight decrease of the solar reflectance afteraccelerated weathering. The hemispherical reflectance is plotted as a function of wavelength.It shows that the loss in reflectance is restricted to the wavelength intervals 400- 700 nm and1850- 1950 nm. The results from the accelerated weathering tests in combination with the preliminaryoutdoor exposure tests provide information on possible lifetime limiting environmentalfactors. Oxidation attack of the reflective layer by means of surface flaws in the protectivecoating is a limiting factor for all materials except silver/ glass. In contrast to polymersurfaces, which predominantly suffer from radiation in the UV range, PVD coated aluminiummaterials are attacked by corrosion, which is accelerated by means of moisture probably incombination with atmospheric and rain pollutants. The applicability of those materials is notyet proven and results from all test sites have to be compared to clarify the degradationprocess and to perform reliable lifetime predictions. The investigated glass/ silver materialsconfirm their known good weather ability and reflectance properties. 16
  17. 17. Table 1. Solar Weighted hemispherical reflectance Rs value of selected weathered samples (Outdoor exposure Koln) Material Manufacture/ Supplier Rs (t=0) % Rs (t=0.5y) %Glass/ Silver 4 mm Falbeg (D) 93.8 93.8Glass/ Silver 1 mm Steinmuller (D) 94.0 93.5Glass/ Silver 1 mm Glaverbel (B)/ Hirtz(F) 94.6 94.6Miro 2 - 95 Alanod (D) 88.6 85.4Miro 2 – 95 Alano (D) 91.1Anod. Aluminium Solar Direct (D) 86.8 84.81000.90 Anofol (E)/ Metalloxid (D) 89.8 83.0ECP305+/ Aluminum 3M (US) 95.6 95.7ECP305+/ Glass 3M (US) 96.1 95.8Sunflex (Polymer/ Aluminium) HTC Solar (D) 86.9 <80SA 85/Glass 3M (US) 88.1 88.1SA85/ Steel 3M (US) 88.2 88.1 Table 2. Solar Weighted hemispherical reflectance Rs values of selected samples after accelerated weathering in OUV weather simulation (* reflective aluminium film totally removed) Material Rs (t=0) Rs (t=2000 h QUV) Rs (t=4000 h QUV) % % %Glass/Silver 1 mm 94.6 94.7 94.5Miro 2 – 95 88.6 88.1 88.2ECP305+/ Glass 96.1 95.4 94.8Sunflex (Polymer/ Aluminium) 86.9 <50* -Sol-Gel coated Silver 95.5 94.0* -Sol-Gel coated Aluminium 91.0 - -SUMMARY AND CONCLUSIONS Over the past five years, solar reflector material has made significant progress indeveloping a new type of solar reflective material. This material has the potential to deliverhigh performance at a manufacturing cost lower than thin glass. A significant advantageshould lie in lowering system weight and installation costs. Concentrating solar power systems use large solar reflectors to concentrate sunlight togenerate electricity. The widespread application of concentrating solar power generationdepends in part on developing a durable, lower cost reflector. The purpose of this research isto select reflectors which are suitable for Thailand of Energy Concentrating Solar PowerProgram. The goals are specula reflectance above 90% for at least 10 years under outdoorservice conditions and a large volume manufacturing cost of less than 500 B/ m2. Basically, this research could find a product that would be considered a breakthrough inregards to those products currently being used on solar dishes. The materials currently beingused range from common kitchen aluminium foil to complex films developed by major. Theonly valid 3M product that could be used as a solar dish reflector is currently manufacturedfor other applications and would have to be coated (for ultra violet ray protection) for use onsolar dishes. The other products described in this report that researcher has been investigating 17
  18. 18. are cutting edge technology materials and still have a ways to go before they are ready formarket. The best candidate materials for solar reflectors are silver coated thin and ultra-thin glass,anodized coated thin aluminium, silver coated thin acrylic, and silvered polymer films. ForThailand the anodized coated thin aluminium such as MIRO-SUN should fit for Thailandenvironment and conditions. It cost should lower than 500 B/m2, easy to find in Thailand, lifetime more than 10 years, specula reflectance above 90%, easy to maintenance, and durable.ACKNOWLEDGEMENTS This research was prepared by Mr. Suravut SNIDVONGS, Vice President, AsianRenewable Energy Development and Promotion Foundation, EIT member, a PhD Student,School of Renewable Energy Technology, Naraesuan University, Pitsanulok, Thailand. Theauthor would like to acknowledge the assistance and guidance of Asian Renewable EnergyDevelopment and Promotion Foundation Dr. Sub.Lt. Prapas Limpabandhu Deputy Ministerof Foreign Affair, Mr. Sutas AROONPAIROJ and staffs, the Engineering Institute ofThailand members who provided a critical review of this research through its various stages,including Dr. Chavalit THISAYAKORN IEEE Valued Senior Member, and EIT Fellowmember and her EE Chief Director, and the Naraesuan University Staffs, especially the DonBosco Technical School staffs for their fabrication and construction work on the prototype.Finally, the author would like to thank the numerous industries to provide information for thisresearch.REFERENCES[1] Richard B. Diver The Advanced Dish Development System Project, Proceeding of Solar Forum 2001, Solar Energy, April 21-25, 2001, Washington, DC. Page 2.[2] Argoud, M.J., 1980, "Test Bed Concentrator Mirrors," Proceedings of the First Semiannual Distributed Receiver Systems Program Review, DOE/JPL-1060-33, Pasadena, CA.[3] Bean, J.R., Diver, R.B., 1995, “Technical Status of the Dish/Stirling Joint Venture Program,” Proceedings of the 30th Intersociety Energy Conversion Engineering Conference, Paper Number 95-202, Orlando, FL.[4] Beninga, K., Butler, B., Sandubrae, J., Walcott, K., 1989, “An Improved Design for Stretched-Membrane Heliostats,” SAND89- 7027, Albuquerque, NM.[5] Richard B. Diver, James W. Grossman, 1995, “Sanwich Construction Solar Structural Facets” SAND95-1931, Sandia National Laboratories, Albuquerque, NM.[6] Russell V. Smilgys Process Toward Roll Processing of Solar Reflective Material, Proceeding of Solar Forum 2001, Solar Energy, April 21-25, Washington, DC Page 1.[7] Kennedy, C., “Durability of Solar Reflective Materials with an Alumina Hard Coat Produced by Ion-Beam-Assisted Deposition”, National Renewable Energy Laboratory, Golden, CO, March 21, 1997.[8] John Harrison, “Investigation of Reflective Materials for the Solar Cooker”, Florida Solar Energy Center, December 24, 2001.[9] National Renewable Energy Laboratory (NREL) FACT Sheet titled "Concentrating Solar Power Research” by Gary Jorgensen (12/ 98, FS24863) 18