Reflective Material for Solar Thermal

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

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 airscan@cscoms.com
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 the
solar thermal dish Stirling engine system for a 10 kW power plant with lead acid battery
storage, named “Siam Solar Dish I” research project. It shows a comparison on technical
characteristics between general photovoltaic systems and a small solar thermal dish Stirling
Engine System, on condition that both systems maintain the same output and storage capacity
at 10 kW with lead acid battery.
The dish in this paper is a parabolic design and equipped with a solar tracker. The Stirling
engine is a 10 kWe four– cylinder, swash- plate design and features a moving tube type heat
exchanger, low offset space, and double acting pistons. The 10 kWe photovoltaic system is
polycrystalline based without solar tracker and for this study both systems are assumed to
maintain the same 250 kWe battery storage.
The researcher in this research project believes that Thailand as a developing country is
still 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. In
particular, the solar insolation capacity in a very moist climate like Thailand, is also very far
below in comparison to dry country weather. Therefore, it looks quite impossible to design
the above mentioned system in the manner like as being done in other advanced technological
and well developed countries. Inevitably, “Siam Solar Dish I” will not reach high efficiency
level in general performance, but the researcher believes that “Siam Solar Dish I”
manufacturing cost, operating cost, together with her durability capacity would be well
accepted 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 insolation
value, which is the international standard design value referred to in Advanced Dish
Development System 9 kWe (ADDS) [1]
One purpose of this research project is to establish the advantages and disadvantages of
reflector materials as a guide for the end users to select the right material among, Anodized
Aluminium, Mirror Polished Stainless, Acrylic and Glass etc, where the best suited for using
in Thailand as well as other global markets in terms of Price, Maintenance Cost, Operating
Cost, Economy, Performance, Reliability, and Efficiency will then be selected for further
implementation. The comparison in this paper will be presented in descriptive format, with
relevance tables being displayed under the discussion section in this paper. This research
project has utilized a variety of information resources, including the data solar from library,
web search engines, solar industrial

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* The Engineering Institute of Thailand Under H.M. The King’s Patronage

catalogues and directories, personal contacts, aluminium industry sources, solar cooker
discussion groups, and a wealth of other investigative resources. A great deal of time has been
spent 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, very
economical.

INTRODUCTION
Concentrating solar power systems use large solar reflectors to concentrate sunlight to
generate electricity. The widespread application of concentrating solar power generation
depends in part on developing a durable, lower cost reflector. The purpose of this research
project activities is to select reflectors which are suitable for Concentrating Solar Power in
Thailand. The ultimate goals are to obtain specula reflectance above 90% for at least 10 years
under outdoor service conditions and a large- volume manufacturing cost of less than 500
B/m2. Currently, the best candidate materials for solar reflectors can be classified in four
categories (These materials may meet the current reflector goal, but it is uncertain whether
they 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 relatively
high cost, fragility in shipping and handling, and the availability manufacturer to manufacture
it.
Anodized coated thin aluminium, such as MIRO- SUN should fit for Thailand
environment and conditions. It is durable, reasonable price, not fragility in shipping and
handling, 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 as
decorative material.
Silvered polymer films reflectors are lighter in weight, offer greater system design
flexibility, and have the potential for lower cost than glass reflectors. However, silvered
polymer 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 be
both suitable for this application as well as economical. This research project activities have
conducted an extensive search for available reflective materials including contacting
reflective materials manufacturers as well as national laboratories in U.S.A and other

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countries that are currently working with private industry in developing reflectors that can be
used primarily on large concentrating solar energy devices. [5]

PRODUCTS AVAILABLE ON THE MARKET [8]

3M VM2000 radiant mirror film
This material is a multilayered polymeric film. The outside layer is polyethylene. It is
metal free, therefore non corrosive and non-conducting. It is thermally stable to a temperature
of 125C. The manufacturer claims that the material has low-shrinkage. Unfortunately the
material is not ultra-violet ray resistant. 3M can add ultra-violet ray protection materials at
additional cost. (This special coating can only be applied at two facilities in Tennessee.) The
material can also be coated with a 3M adhesive (#M 467MP) or can be purchased without the
adhesive. The reflective (optical luminosity is greater than 98%) reflects more than 98 % of
visible light. The drop off if reflectance at 700 nm is unfortunate, but is not detrimental for
this application. It is a film like product that is flexible, lightweight and highly reflective. It is
commonly 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 minimum
purchase). To that would be added $0.30 per square foot for the ultra violet ray inhibiting
coating. 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 that
developed solar films in the past have retired and 3M seems to have retired their interests in
such products along with him. Nevertheless, 3M has stated that they would provide samples
with improved screening layers for future testing. FSEC staff came upon an National
Renewable 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 at
a fraction of the cost of glass mirrors and have excellent optical and wear-resistant
properties." 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 an
outdoor weathering acrylic coating over the aluminium. (Per John Roche, the developer of the
film.) The former manager of the 3M section that manufactured solar films developed this
film in the 1980s. There are several companies and individuals that use this material on their
current solar reflectors. Contact with 3M revealed that 3M would no longer be manufacturing
this material and once the current supply in the field runs out, none would be available in the
future.
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 is
no longer being manufactured by 3M.

3M Silver Flux material
This material is marketed by 3M for existing luminaries or as interior surfaces for
luminaries. It maintains a specula reflectance of 85% and an overall reflectance of 90%. It is
bonded to 0.7 mm treated aluminium and is ideal for producing rigid precision quality specula

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reflectors. It does not contain ultra violet ray protection and is unsuitable for outdoor use
following is the product specification:
3M Silver flux reflectors for fluorescent light fixtures, 2.5 mil polyester film with a
specula metallized layer on front surface treated with an acrylic coating to suitable for
protecting metallized layer from oxidation, corrosion and polyester film from ultra violet,
degradation, covered with a removable pre-mask and a pressure sensitive adhesive backing
and low release liner and meeting or exceeding the requirements of EPA Green Lights
Program 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 Services
Specula 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 1000
hours 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 the
company uses on solar concentrators. (Solar Laser Mirror) They have the material in 48-inch
wide rolls. The material has an adhesive backing. Cost of the material from Acrosolar is $2
per 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 an
optically perfect acrylic sheet that is vacuum metalized in a vacuum chamber. The sheets
themselves are protected on the back by a durable scratch resistant coating and on the front
surface be either a clear polyethylene film or a paper masking. The material can also be made
with pressure sensitive backing. The manufacturing of this product is very complex. The cost
of this material is also very high, which makes it unfeasible for this project. Close to $5 per
square foot. This material for indoor used.

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Alanod Aluminium
This is a German company that manufactures a variety of aluminium grades. It does
market one product specifically for solar applications. That is MIROSUN Extra bright. This
material reflects super intensive spectral areas. The materials curve of the spectral reflectance
follows the spectrum of the sun and it guarantees reduced diffusion together with high
reflection values. Alanod states that their tests have proved the weather durability of the
additional lacquer used to provide external protection in demanding conditions. They also
state 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 thin
yellow film applied to protect the mirror surface during shipping. This material is quite
suitable for solar reflectors. The cost is somewhat higher than others, but the material would
be indestructible. The material cost for information. MIROSUN - 4270 KK (MIRO 27 with
clear varnish on the front and reverse side), C1 natural tone with protective film on the front
side 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 at
US$ 7.37/ lb. These cost comes out to $2.15 per square foot.
Cheryl Kennedy provided information on the latest NREL tested reflectors. This
information is based on Cheryl's report, “Summary of Status of Most Promising Candidate
Advanced Solar Mirrors (Testing and Development Activities), 30 Sep 2001”.
Alanod Front Surface Aluminized Reflector product (Note: This is the Alanod product
reviewed in this report) Front surface aluminized reflectors using a polished aluminium
substrate, an enhanced aluminium reflective layer, and the formation of a protective oxidized
topcoat (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 PACES
project. Has a polymeric overcoat to protect the aluminium. The acrylic over coated material
failed in accelerated testing and was replaced by Fluro Polymer overcoat. The new
formulation 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 for
solar applications and is still being evaluated by NREL. Base commercial silvered polymer
92% hemispherical reflectance cost about $1.50/ ft2. Reflec Tech product not commercially
available 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 proved
fruitless in finding a product that could be used in the solar reflector. This company produces
aluminium products for industrial and commercial use competes with Reynolds aluminium in

5

the household aluminium foil market. Other than standard aluminium foil, they do not have
any special materials suitable for this project.

All Foils
This is a distributor and service centre for thin-gauge metal foils, strips, or sheets. Their
inventory includes aluminium in gauges of 0.00025 to 0.125 inches. The material they have
available unfortunately is not designed for outdoor use.

Aluminium, polished
Pure aluminium (99%+) develops a protective coating of aluminium oxide immediately
on exposure to air (oxygen). This actually protects the aluminium from further oxidation by
oxygen in the air (unlike iron which will continue to oxidize until there is nothing left but iron
oxide rust.) However, pure aluminium has poor structural properties. Therefore, aluminium
that 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 to
fairly rapid atmospheric corrosion. One will often see white chalky pitting on unprotected
structural aluminium products. Pure aluminium is also subject to severe corrosion from strong
acids and bases like cement “lime” products will destroy it in very short order. Thus
aluminium products that are expected to last for extended periods of time must be coated with
a protective coating.

Aluminium foil emergency blankets
There are numerous products of this nature in the marketplace. Basically they are all
offshoots of NASA research that initially developed this “blanket” technology for space
application. A search of various web sites and solar reflector discussion groups revealed that
this product had been used in solar reflector application in the past. Several individuals had
tried the product as a dish reflector and were unsuccessful in long term application since, as
they stated, “the material eventually falls apart.”

Aluminium foil, heavy duty
This is common everyday kitchen application aluminium foil. Here are some facts about
standard kitchen aluminium foil provided by Reynolds Aluminium. Reynolds Wrap®
Aluminium Foil is the most versatile of all food wrapping materials. It can withstand both
heat and cold. Reynolds Wrap® Aluminium Foil was first introduced in 1947. Since that time
it has become one of the most immediately identifiable brands on the market. Reynolds
Wrap® Aluminium Foil is 98.5% aluminium. The balance is primarily iron and silicon. These
are added to give the strength and puncture resistance obtained only in the alloy used in
Reynolds household foil. Reynolds Wrap® Aluminium Foil contains no recycled material and
complies 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 locations
Louisville, Kentucky and Richmond, Virginia. Aluminium for Reynolds Wrap® Aluminium
Foil is placed into alloying furnaces at the continuous cast plant in Hot Springs, Arkansas and
heated until molten. It is then modified to the correct alloy chemistry and fed into a machine
known as a "continuous caster." The continuous caster converts molten aluminium to a coil of
metal by forcing it between large, water cooled chill rollers at several feet per minute. The
aluminium is formed as a long sheet with a thickness of .045". It's rolled into large coils that
measure 74 inches in diameter and weigh over 30,000 pounds! These coils are shipped in

6

Reynolds' specially designed rail cars to Richmond and Louisville, where they are converted
into the Reynolds Wrap® Aluminium Foil.
In addition, here are some little known application facts about aluminium foil that could
have an impact on its use in solar reflector.
The difference in appearance between dull and shiny is due to the foil manufacturing
process. In the final rolling step, two layers of aluminium foil are passed through the rolling
mill at the same time. The side coming in contact with the mill's highly polished steel rollers
becomes shiny. The other side, not coming in contact with the heavy rollers, comes out with a
dull or matte finish.
The darkening of foil may be caused by moisture. This results in a build up of aluminium
oxide. 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 aluminium
foil in standard ovens and kitchens, bit will have, in the long term, a negative impact when
used as a reflector in solar reflectors.)
Occasionally when aluminium foil comes in contact with a different metal or a food that is
highly salted or acidic, small pinholes are formed in the foil. This is a harmless reaction that
does not affect the safety of the food. It is difficult to predict, but may occur under the
following conditions:
When aluminium and a dissimilar metal are in contact in the presence of moisture, an
electrolytic reaction may occur causing a breakdown of the aluminium. To avoid this use
aluminium, glass, ceramic, plastic or paper containers. Do not cover sterling silver, silver
plate, stainless steel or iron utensils with aluminium foil.
A similar reaction may occur when salt, vinegar, highly acidic foods or highly spiced
foods come in contact with aluminium foil. The result of these reactions is a harmless
aluminium salt. Some aluminium salts are used in medicines to treat stomach disorders. The
food can be safely eaten; however, the aluminium salt particles can be removed from the food
to improve the appearance of the food.
Although these situations are questionably applicable to solar reflectors the above facts
indicate 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 without
creating wrinkles. Special 3M adhesive had to be procured to affix the material to insulation
board. Standard white glue did not adhere very well. The material is so thin that it quite easy
to damage.

Aluminized polyester
This material discoloured and faded after a year or two. Therefore, it appears that the
material 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 Anocoil
grade 710.33 which was 86 % reflective and exhibited a mirror quality. Anacoil is the largest
independent manufacturer of lithographic plates in North America and supplies high quality
plates to many leading publishers in North and Central America, Europe, and Asia. This
product is not protected from oxidation.

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Astro-Foil
Foil based reflective insulation material that is sold as an insulator. Bubble wrap type
material is incorporated in the product and therefore would not be suitable for this
application. Also, the manufacturer cannot provide optical property specifications. The
specification that they did provide, indicate that Astro-Foil is 5/16” thick, has a temperature
range of –60 to 180 F, and has a reflectivity of 95- 97%. The manufacturer states that the
material can withstand solar radiation and environmental conditions and that it is available
throughout 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 the
manufacturer’s inability to provide specifications; it does not appear as a suitable reflective
material for this application.

Clear Dome Solar– Solar Flex material
This product is Triple laminated, tear resistant metallic fabric. Clear Dome states that this
product 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, glass
mirrors, Mylar, etc. by 18-20% in heat generation. This is stated as being due to the excellent
IR reflection properties that the other surfaces do not seem to reflect as well. The
manufacturer also states that since their material reflects most of the IR, and because it has a
metallic surface and not a plastic surface, there is little or no effect from IR exposure. In
regards to degradation, the manufacturer has had samples outdoors for the past year in all
types of weather, and except for a very slight loss in visible reflection, there have been no
changes in the products heating capabilities. The manufacturer states that water has no effect
on 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 knives
and scissors easily cut the material. The material can be scrunched into a ball and easily
reconfigured 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 tests
indicated no change in shape until the material reaches approximately 200 F. Above that
temperature, the centre plastic thermal barrier starts to shrink, causing a small ripple effect to
the 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. The
centre is flexible and reinforced plastic provides excellent strength.
Clear Dome has found the best adhesive to be 3M contact cement. As long as the two
surfaces 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 feet
wide. 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. Once
affixed, it is very easy to remove wrinkles. Unlike standard heavy duty aluminium foil, the
material is very sturdy. It cannot be ripped by hand; instead, it requires a knife or scissors to
cut the material. This makes it ideal for rough handling and long term use.

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Heat shield (R + Heat shield I)
This material is manufactured for use as radiant barrier. It contains 99% pure aluminium
on both sides. Also contains a layer of polyethylene film for puncture resistance as well as
polyolefin 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 flame
and smoke rating, 12 lb/square inch tensile strength, and is 1.4 mil. thick. The manufacturer
claims that ultra violet rays will not affect the material. Costs have been requested from the
manufacturer and should be received the first of the year. Note that this material looks very
much 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% pure
aluminium on one side. On the reverse side incorporates aluminized polyethylene (MPET). It
exhibits superior tear and puncture resistance. The manufacturer also states that it can
withstand repeated pressure washing and is also available in a solid or perforated
configuration. 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 A
flame 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 been
requested from the manufacturer and should be received the first of the year. Note that this
material 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 radiant
barrier 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 to
application 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 to
that employed as radiation barrier on the Apollo Command and Lunar Modules.
4. Decorative Papers - MPI's line of non-laminated holographic papers, boards and films
provide excitement to gift wrap, cosmetic and security markets.
5. Mirrorbrite - Mirrorbrite is a high gloss, metallic paper or board with a mirror-like
surface. Mirrorbrite is used in both packaging and printing applications.
6. Prismabrite: A holographic paper available in standard or customized patterns used in
both packaging and printing applications.

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Mirrorbrite was investigating. It appeared to be the only possible product from this
manufacturer that would be applicable to this project, but it does not have UV inhibiting
characteristics and is therefore unsuitable.

Mirrored Plexiglas
The Standard Plexiglas with mirror coating. It can be used for ray testing only. Not
outdoors durable and very expensive. Comes in 4 foot by 8 foot sheets - $136 (Includes 15%
discount for not cutting) 1/ 8" thick. It's $5 per square foot without cut.

Mirroflex
Mirroflex is a composition of rigid high impact plastics, vacuum metalized and bonded
together to create highly reflective, unbreakable mirror-like sheets. Mirroflex is a reflective,
impact resistant plastic with unusual surface treatments including silver, gold, brass, brushed
metallic, wood grains and granites. This material is very easy to fabricate. Mirroflex is
available in sheets or rolls (depending on the thickness). Mirroflex thermo plastic sheet and
roll programs are also available as metallic trim. In roll form, it has a pressure sensitive
adhesive 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 in
2' x 8' and 4' x 8' sheets, varying in thickness from .020" to .025". Also available in a large
selection of wood grains, granites, solid colours and specialty finishes suitable for interior and
exterior application. Mirrotiles are fabricated in Mirroflex to fit standard suspension ceilings
where an easy to use, easy to fabricate very low-cost mirrored ceiling tile (chrome or gold) is
desired.
Mirroflex materials are primarily manufactured and marketed for interior decorative
purposes. Without investigating the optical, solar, and durability properties of this
manufacturer’s products, it was determined that the cost is too prohibitive for this solar
reflectors.

Mylar
Dr. Steven F. Jones, Professor of Physics at Brigham Young University, reports in his
paper “The Solar Funnel Cooker,” Solar Cooker International archives, that aluminized Mylar
was used in the development of the funnel solar cooker. Dr. Jones reported that aluminized
Mylar was a good reflective material but was “relatively expensive and rather hard to come
by in large sheets.” (Therefore, the funnel cooker used standard aluminium foil instead.) It
has been noted previously that Mylar does not have long term weathering characteristics
required 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 on
a parabolic solar concentrator. The material was inadequate as “it yellowed along the edges
and peeled after only two months. The film used was metallized Mylar and it was bonded to
several 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 booming
commodity.

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Metallized Products, Inc. (MPI), Winchester, Massachusetts, was one of the companies
that worked with NASA on the original space materials. MPI continues to supply metallized
materials for space use and has developed lines of industrial and consumer oriented
metallized film, fabric, paper, and foam. One of the most successful MPI products is TXG
laminate, once employed by NASA as a reflective canopy for visual and radar detection of
the rafts in which returning Apollo astronaut’s awaited pickup by ships or helicopters. TXG
not only is super reflective, but nonporous, waterproof, and rot proof. Subsequently, Winslow
Company Marine Products, osprey, Florida, obtained a license for commercial production of
the survival raft. In cooperation with MPI, Winslow improved the strength and thermal
characteristics of TXG so that its survival rafts would provide maximum protection from
heat, 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 Signal
Kite can be flown as high as 2OO feet to enhance radar and visual delectability. It provides
campers, hikers, and mountain climbers with a lightweight, easily portable emergency
signalling device, and boaters with a convenient substitute for bulky dish devices. Made of
metallized nylon, the kite spans six feet but weight only six ounces.
Connecticut Advanced Products, Glastonbury, Connecticut, has adopted TXG for its
Thermo guard heat shields, custom-tailored reflective curtains that cover the windshield and
windows of parked aircraft to protect avionics equipment from heat build up and ultraviolet
radiation. In a similar application, the Star shade ~ from Star Technology Corporation,
Carbondale, Colorado, is a multilayered automatic shade system for large windows in
commercial or residential buildings. (See: http://vesuvius.jsc.nasa.gov/er/she/spinoff.html)
Among MPI's own products are various protective fabrics that retain up to 8O percent of
the user's body heat, helping to keep a person warm for hours in cold weather crises or to
prevent post-accident shock. All are remarkably compact. The Space* Emergency Bag, for
instance, 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 radar
detection. Material is super reflective, nonporous, waterproof, and rot proof which used in
boating 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- polymer
reflectors, which cause the material lower- cost. The reflector consists of a polymer substrate
coated with a copper layer, followed by a layer of silver, and finally by a protective optically
transparent alumina top coating. Earlier, this basic design was recognized as having high
potential, but the difficulty has been to find a durable top coating. The alumina top coating is
essential to sustain high reflectance in outdoor service. This high performance solar reflective
material can be produced in a roll format using vacuum deposition techniques. The material
consists of a multilayer thin film stack on a substrate. The essential feature of the film stack is
an alumina film several microns thick deposited over a silver film. The alumina film is
deposited under high vacuum using a physical vapour deposition technique called ion beam
assisted deposition (IBAD). The alumina film is optically transparent, scratch resistant, and
durable. Its purpose is to protect the silver film and maintain high optical reflectance. Work
on this reflective material began five years ago. Samples were produced on polyester
substrates by batch coating. Those samples showed excellent durability in accelerated testing
at the National Renewable Energy Laboratory (NREL) in Golden Colorado. The principal

11

limitation to commercialization of the process was a low alumina deposition rate. Over the
past three years the alumina deposition rate has been increased from 1 nm/ s to 20 nm/ s. The
next 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 finish
will be used as the web material. The advantage of this material compared to polyester is that
it withstands a higher process temperature and lowers final product installation costs. A major
technical challenge will be to reproduce high reflector durability in a continuous, high rate
process.
The description below is from this report. 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 electric production by solar thermal energy systems.
The reflector materials must be low in cost and maintain high specula 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-mated 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. Silvered PET protected by IBAD deposited
alumina represents an advance in solar reflector durability. Preliminary results have shown an
initial solar-weighted hemispherical reflectance of 95% and excellent optical durability in
both accelerated and outdoor (Colorado) exposure testing. Additional issues to address
include determining the minimum coating thickness needed to ensure optical durability,
increasing the deposition rate, testing the long-term Mechanical stability of the material under
biaxial stress, and field testing the material. Research into a better stainless steel levelling
layer is being pursued. The alumina-coated reflector material under development offers
promise as a commercially viable solar reflector material. The deposition system at SAIC is
large enough and has sufficient capability to support a range of reproduction scale coatings
work and the new state-of-the- art deposition system at NREL will allow the development of
additional innovative coatings to be prototyped. This is in the realm of national laboratory
research and development into products that can be used on large parabolic and dish type
concentrating solar collectors. Mass production is not available. (From "Progress Toward
Achieving a Commercially Viable Solar Reflective Material” by C. (Cheryl) E. Kennedy and
R.V. Smilgys, NREL/ CP510- 24058.)

Metallizing Polymer Mirrors
The following is from an information report developed by NREL "Durable Metallized
Polymer Mirrors". NREL researchers have made several modifications in the construction of
Silvered Polymer solar mirrors which improves their optical durability and resistance to
delaminate failure. One innovation is to interpose an oxide layer between the polymer film
and the silver reflecting layer. The oxide layer impedes the initiation of delaminate and also
impedes the propagation of delaminate if initiation occurs. The oxide layer also provides
protection to the silver and slows corrosion. In a preferred construction, there is a copper
layer between the silver and the adhesive, which significantly helps to slow corrosion of the
use silver. Silvered polymer solar reflectors are finding increasing use in parabolic trough and

12

dish concentrator applications. At present the 3M Company of Minnesota is the major
supplier of these polymer mirrors. Their commercial product, ECP-305+, developed in
collaboration with NREL, incorporates the protective black layer of copper along with a
delaminate resisting alternative adhesive. A number of industrial partners, including
Industrial Solar Technology and Cummins Power Generation, are field testing these mirrors
at the present time. In a follow-up to this report, Mr. Ken May at Solar Technology and was
told that the 3M silver film (ECP- 305) never made it and that they now use the 3M SA-85
aluminized acrylic film on their reflectors. Unfortunately, 3M has discontinued using this
material 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 site
archives that she also uses the SA85 since it is very durable and UV resistant. It is also
scratch 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 well
known authority in the use of solar cookers internationally.
Tested report from NREL- Cheryl Kennedy Cheryl. “Optical Durability Testing of
Candidate Solar Mirrors, March 2000.” Report states that the following were excellent tested
materials (durability wise); thin glass, thick glass, SA-85 and ECP-305+ Glass is of no use to
the application for this solar reflector. The SA-85 and ECP-305+ were made by 3M and will
no longer be manufactured once current stock in the filed is consumed. The report states that
these materials can be characterized as intermediate and require further improvement
1. All polymeric construction
2. Alanod's 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 for
solar 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 layer

Polyester 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 a
radiant barrier material. Reflectance characteristics have not been obtained from the
manufacturer. The material is .0003/30 lb aluminized foil and at $ 0.04 per square foot is
economically attractive. This product has affixed this material to one of the Roger 7.7 cookers
and tested. It is easy to adhere to a backing when using 3M adhesive spray material. The
material came in a large roll. Creases were evident in the material which undoubtedly resulted
from the rolling process. It was not able to remove the creases during the application to the
cooker backing. Interestingly, the Kraft backing more than likely was a positive feature, as it
tended to allow better adhesion to the backing material.

13

Roche, John
Mr. Roche is the former 3M scientist that developed numerous 3M solar firms during the
1980s. He is currently retired and is associated with the Solar Oven Society. Currently he uses
the 3M SA-85 solar reflective film on his Solar Reflectors, but acknowledged that 3M is no
longer 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 solar
films and related products with the retirement of John Roche from 3M. Actually the current
3M films division representative suggested contacting Mr. Roche to obtain information on
solar films. 3M did not seem very enthusiastic about solar films. This is probably in large part
due to the very small demand and use of this material.

United Aluminium
Manufactures custom rolled aluminium coils. Darwin Curtis’ son, John, obtained
aluminium from this company for a solar cooker that he designed. Determination will have to
be 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% reflected
value. 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 for
solar thermal energy conversion have been exposed to real outdoor conditions at 8 test sites in
the U.S. as well as in Spain and in Germany under various climatic conditions. Further tests
have been performed in a simulating weather chamber. Weather and air pollution data have
been 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 reflectance
as a function of exposure time with a dual beam UV- VIS- IR spectrometer equipped with an
integrating sphere. Microscopic investigations have been performed additionally to
characterize material degradation [7].
In general the cooperation within the Solar PACES program foresees that any participant
may 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 distributed
to all test sites. Besides these "close to the market" materials, those types being in
developmental states are previously tested in a weather simulator or at one outdoor site.

14

The reflective materials investigated in this research can be classified into the following
groups:

Anodized Aluminium
These materials, fabricated in the CIEMAT labs in Madrid consist of different kinds of
substrate materials (glass, aluminium), a reflective film (aluminium, silver) and an oxidation
protective layer processed via the sol-gel route.

Coated Aluminium
The 3 sheet aluminium materials employed in their study consist of an aluminium
substrate (0.8 mm) carrying a reflective layer of pure aluminium and an oxidation protective
thin ceramic coating. SOLAR direct provides an anodized and Alanod and Anofol/
Metalloxid a PVD coated surface. Metal/ Polymer: ECP305 Plus is a silvered weather able
acrylic 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 acrylic
protective overcoat. Float glass and stainless steel were tested as substrates. Sun flex consists
of an aluminized Hostaflon film with a protective film on the back side. Samples have been
exposed without any substrate.

Stretched-membrane
Stretched- membrane designs incorporating membranes of plastic or steel stretched over
both 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. Examples
include LaJet and Cummins facets, the SAIC USJVP dish and several heliostat designs.
(Bean and Diver, 1995 and, Beninga, et al., 1989 and 1997) Stretched-membrane
concentrators with plastically deformed metal membranes, for short focal length to diameter
ratios, 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 substrate
silvered from the backside and sealed with an oxidation protective layer. A low iron content
float glass is used with optimized transmission properties in the UV VIS-IR range. The
materials 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 in
order to be used in concentrating solar thermal systems. In collaboration with the Cummins
dish/ Stirling development program, we started investigating sandwich construction as a way
to 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 a
sandwich). For solar optical elements, a glass mirror is bonded to one of the membranes. This
type of construction has the advantages of a high strength- to- weight ratio, and reasonable
material and manufacturing cost. The inherent stiffness of sandwich construction mirror
panels also facilitates large panels. This can have cost advantages for both the amount of
hardware required as well as reduced installation and alignment costs. In addition, by

15

incorporating the panels into the support structure reductions in the amount of structural
support required are potentially possible.
Glass- foam core mirrors were developed by the Jet Propulsion Laboratory (JPL) in the
1970s and 1980s [2]. With this construction, glass mirrors are mechanically deformed and
bonded to a foamed glass support, which has been ground to the specified contour. The foam
glass 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 are
supported by a stretch-formed or stamped steel backup structure (like a car hood). This type
of support was used in the McDonnell Douglas dish concentrator. (Stone, et al., 1993) Similar
approaches, but with rib supports stretch-formed or stamped to the desired curvature, were
used by Acurex in their Innovative Concentrator design and by Solar Kinetics, Inc. (SKI) on
the 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 recently
by Kansas Structural (Gill and Plunkett, 1997) and McDonnell Douglas (NREL, 1998) [3].

DISCUSSION
The solar weighted hemispherical reflectance values RS of selected weathered samples
are resumed in Table 1, the reflectance values of the accelerated weathering tests are listed in
Table 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 after
accelerated weathering. Furthermore no visible damage occurred due to corrosion from the
edges or from the surface.
The polymer/ silver materials exhibit good results in the outdoor test (which is of course
too short to draw final conclusions), but a slight decrease of the solar reflectance after
accelerated 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 and
1850- 1950 nm.
The results from the accelerated weathering tests in combination with the preliminary
outdoor exposure tests provide information on possible lifetime limiting environmental
factors. Oxidation attack of the reflective layer by means of surface flaws in the protective
coating is a limiting factor for all materials except silver/ glass. In contrast to polymer
surfaces, which predominantly suffer from radiation in the UV range, PVD coated aluminium
materials are attacked by corrosion, which is accelerated by means of moisture probably in
combination with atmospheric and rain pollutants. The applicability of those materials is not
yet proven and results from all test sites have to be compared to clarify the degradation
process and to perform reliable lifetime predictions. The investigated glass/ silver materials
confirm their known good weather ability and reflectance properties.

16

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 93.8
Glass/ Silver 1 mm Steinmuller (D) 94.0 93.5
Glass/ Silver 1 mm Glaverbel (B)/ Hirtz(F) 94.6 94.6
Miro 2 - 95 Alanod (D) 88.6 85.4
Miro 2 – 95 Alano (D) 91.1
Anod. Aluminium Solar Direct (D) 86.8 84.8
1000.90 Anofol (E)/ Metalloxid (D) 89.8 83.0
ECP305+/ Aluminum 3M (US) 95.6 95.7
ECP305+/ Glass 3M (US) 96.1 95.8
Sunflex (Polymer/ Aluminium) HTC Solar (D) 86.9 <80
SA 85/Glass 3M (US) 88.1 88.1
SA85/ 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 94.5
Miro 2 – 95 88.6 88.1 88.2
ECP305+/ Glass 96.1 95.4 94.8
Sunflex (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 in
developing a new type of solar reflective material. This material has the potential to deliver
high performance at a manufacturing cost lower than thin glass. A significant advantage
should lie in lowering system weight and installation costs.
Concentrating solar power systems use large solar reflectors to concentrate sunlight to
generate electricity. The widespread application of concentrating solar power generation
depends in part on developing a durable, lower cost reflector. The purpose of this research is
to select reflectors which are suitable for Thailand of Energy Concentrating Solar Power
Program. The goals are specula reflectance above 90% for at least 10 years under outdoor
service 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 in
regards to those products currently being used on solar dishes. The materials currently being
used range from common kitchen aluminium foil to complex films developed by major. The
only valid 3M product that could be used as a solar dish reflector is currently manufactured
for other applications and would have to be coated (for ultra violet ray protection) for use on
solar dishes. The other products described in this report that researcher has been investigating

17

are cutting edge technology materials and still have a ways to go before they are ready for
market.
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. For
Thailand the anodized coated thin aluminium such as MIRO-SUN should fit for Thailand
environment and conditions. It cost should lower than 500 B/m2, easy to find in Thailand, life
time more than 10 years, specula reflectance above 90%, easy to maintenance, and durable.

ACKNOWLEDGEMENTS
This research was prepared by Mr. Suravut SNIDVONGS, Vice President, Asian
Renewable Energy Development and Promotion Foundation, EIT member, a PhD Student,
School of Renewable Energy Technology, Naraesuan University, Pitsanulok, Thailand. The
author would like to acknowledge the assistance and guidance of Asian Renewable Energy
Development and Promotion Foundation Dr. Sub.Lt. Prapas Limpabandhu Deputy Minister
of Foreign Affair, Mr. Sutas AROONPAIROJ and staffs, the Engineering Institute of
Thailand members who provided a critical review of this research through its various stages,
including Dr. Chavalit THISAYAKORN IEEE Valued Senior Member, and EIT Fellow
member and her EE Chief Director, and the Naraesuan University Staffs, especially the Don
Bosco 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 this
research.

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

Reflective Material for Solar Thermal

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