Solar Cookers World Network

Changes: Reflective material


Back to page

(See also)
m (Replaced text with link to article in 'See also')
Line 3: Line 3:
[[Image:Aluminum_foil.jpg|thumb|Standard kitchen aluminum foil works very well for solar cooking reflectors.]]The most common reflective material used in homemade solar cookers is plain aluminum foil. This can be glued very well with white [[glue]] or [[wheat paste]].
[[Image:Aluminum_foil.jpg|thumb|Standard kitchen aluminum foil works very well for solar cooking reflectors.]]The most common reflective material used in homemade solar cookers is plain aluminum foil. This can be glued very well with white [[glue]] or [[wheat paste]].
==Advanced optical materials evaluation==
<p class="MsoNormal" style="margin-bottom:13.0pt;mso-pagination:none;mso-layout-grid-align: none;text-autospace:none">'''<span style="mso-bidi-font-size:13.0pt;font-family: Helvetica;mso-bidi-font-family:Helvetica;color:#2C2C2C">Cherly Kennedy, </span><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">Senior Scientist, Concentrating Solar Power, Advanced Optical Materials Project Leader</span>'''<span style="mso-bidi-font-size:13.0pt; font-family:Helvetica;mso-bidi-font-family:Helvetica;color:#2C2C2C">''' at the Department of Energy's National Renewable Energy Laboratory '''has provided the following detailed information on reflective materials used in solar thermal arrays:   </span></p>
<p class="MsoNormal" style="margin-bottom:13.0pt;mso-pagination:none;mso-layout-grid-align: none;text-autospace:none"><span style="mso-bidi-font-size:15.0pt;font-family: Helvetica;mso-bidi-font-family:Calibri">"As part of our DOE task mission we work to develop  advanced solar mirrors and absorber coatings and test the optical properties and durability of solar materials (i.e., mirrors, glazings, Fresnel lenses, and solar selective coatings) provided by industry as a service to the solar industry. In most cases, the number of samples is limited, we do not charge for these services, and neither party signs a Nondisclosure Agreement (NDA).  Typically, the industry contact tells me what is considered proprietary and that information is just not disclosed.  If the work becomes more extensive, than an NDA or one of the technical agreements described at<span style="color:#2A4A82"> [ <span style="color:rgb(42,74,130);"></span>] </span>are more appropriate.</span><span style="font-family:Helvetica;text-align:justify;">  The reflectors that are commercially available for solar applications are thick and thin glass mirrors, silvered polymer mirrors from ReflecTech and 3M, and an enhanced aluminized reflector from Alanod. All have their positive and negative points.</span></p>
<p class="MsoNormal" style="text-align:justify;mso-pagination:none;mso-layout-grid-align: none;text-autospace:none"><span style="mso-bidi-font-size:15.0pt;font-family: Helvetica;mso-bidi-font-family:Calibri">"The SEGS trough plants and the new 64-MWe Nevada Solar One trough plant in Nevada use silvered low-iron thick (4-mm) slumped glass mirrors from Flabeg because of their historical durability. Hemispherical reflectance of 4-mm low-iron glass silvered mirrors is ~94.5%, the specular reflectance at 25-mradian full-cone angle (mrad) is ~94.5% and at 7-mrad is ~94.2%. The mirrors currently cost $43.2–$64.8/m</span><sup><span style="mso-bidi-font-size:11.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">2</span></sup><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri"> ($4–$6/ft</span><sup><span style="mso-bidi-font-size:11.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">2</span></sup><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">) for large volume purchases. For trough applications, it is desirable for the mirror costs to be reduced to $21.6–$27/m</span><sup><span style="mso-bidi-font-size:11.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">2</span></sup><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri"> ($2–$2.5/ft</span><sup><span style="mso-bidi-font-size:11.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">2</span></sup><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">). Recently, AFG [now owned by Asahi Glass Company (AGC)], Guardian Glass, PPG, Saint-Gobain, and Rio Glass companies have developed thick glass mirrors for CSP applications. Rio mirrors are tempered and Guardian are laminated (1-mm silvered glass laminated to 3-mm glass) glass mirrors for CSP parabolic troughs. Pilkington (now owned by Nippon Sheet Glass), Virginia, and Gardner mirror companies have expressed interest in providing thick glass mirrors for solar applications. </span></p>
<p class="MsoNormal" style="text-align:justify;mso-pagination:none;mso-layout-grid-align: none;text-autospace:none"><span style="font-family:Helvetica;">"Several parabolic dish manufacturers use silvered thin (1-mm) flat glass mirrors from Naugatuck and Glaverbel (now AGC). Hemispherical reflectance of 1-mm low-iron glass mirrors is ~96.4%, the specular reflectance  at 25-mrad is ~95.6% and at 7-mrad is ~94.6%; cost depends on purchase volume and ranges from ~$16.1/m</span><sup><span style="mso-bidi-font-size:11.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">2</span></sup><span style="font-family:Helvetica;"> to $43.0/m</span><sup><span style="mso-bidi-font-size:11.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">2</span></sup><span style="font-family:Helvetica;"> (~$1.5/ft</span><sup><span style="mso-bidi-font-size:11.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">2</span></sup><span style="font-family:Helvetica;"> to $4.0/ft</span><sup><span style="mso-bidi-font-size:11.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">2</span></sup><span style="font-family:Helvetica;">). The flat glass is applied to a substrate and during final assembly the entire stack is slightly curved. These segments are assembled to form a parabolic dish, for a CSP dish-Stirling or a Concentrating Photovoltaic (CPV) designs; but a similar architecture could be used in a trough, heliostat, or solar oven.</span></p>
<p class="MsoNormal" style="text-align:justify;mso-pagination:none;mso-layout-grid-align: none;text-autospace:none"><span style="font-family:Helvetica;">"A silvered polymer mirror jointly developed by NREL and ReflecTech is available through Sky Fuels has been used in some trough and CPV designs. Hemispherical reflectance is ~94.%1, the specular reflectance at 25-mrad is  ~93.7% and at 7-mrad is~ 72.1%. Cost depends on purchase volume and ranges from ~$14.0/m</span><sup><span style="mso-bidi-font-size:11.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">2</span></sup><span style="font-family:Helvetica;"> to $32.3/m</span><sup><span style="mso-bidi-font-size:11.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">2</span></sup><span style="font-family:Helvetica;"> (~$1.30-$3/ft</span><sup><span style="mso-bidi-font-size:11.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">2</span></sup><span style="font-family:Helvetica;">). The material is sold in rolls or applied to the substrate. It is recommended for 1-axis curvatures but could be used in dishes and heliostats if the material is cut in gores (i.e., clothing darts). ReflecTech will soon be available with an Abrasion Resistant Coating (ARC) to prevent scratching of the polymer surface with contact mechanical cleaning.</span></p>
<p class="MsoNormal" style="text-align:justify;mso-pagination:none;mso-layout-grid-align: none;text-autospace:none"><span style="mso-bidi-font-size:15.0pt;font-family: Helvetica;mso-bidi-font-family:Calibri">"Recently, 3M decided to reintroduce a new Solar Material Film (SMF) 1100 which is an improved version of the ECP-305+ polymer solar reflector jointly developed by 3M and NREL. 3M took the ECP-305+ off the market more than 15 years ago because of a corporate restructuring and a delamination issue.  The hemispherical reflectance of the ECP-305+ was ~95.4% and the specular reflectance was ~95.3% at 25-mrad and ~94.4% at 7-mrad, 3M said they could sell ECP-305+ for $2.25 back in 1992 ($1.35 when accounted for in, I think, the 1985 dollar).  We have samples of ECP-305+ that have been in exposure testing for more than 14 years in CO, AZ, and FL that are still in test. The new SMF 1100 has adhesion layers to prevent delamination and will be available with an abrasion resistant, anti-soiling coating.  I received the first versions for the new SMF 1100 in December 2010..</span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">"Alanod markets an enhanced aluminum mirror that is of interest to some CSP and CPV manufacturers. NREL and Alanod worked together to develop an enhanced (with ¼ λ’s to boost reflectivity) anodized aluminum mirror with a polymer protective overcoat. A couple of years ago, NREL identified a problem with a loss of specularity after long-term outdoor exposure and at the same time  Alanod was receiving word of delamination of the overcoat occurring in the field.  Alanod stopped selling their Miro/4270kk for outdoor use because of this delamination problem and associated specularity decrease. The company worked hard to find a solution and to improve the abrasion resistance of the reflector. They reintroduced and began marketing an improved Miro-Sun aluminized reflector with a sol-gel nanocomposite protective overcoat. Hemispherical reflectance is ~91.6%, specular reflectance at 25-mrad is ~85.0% and at 7-mrad is ~77.3%. The cost is ~$21.5/m</span><sup><span style="mso-bidi-font-size:11.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">2</span></sup><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri"> (~$2/ft</span><sup><span style="mso-bidi-font-size: 11.0pt;font-family:Helvetica;mso-bidi-font-family:Calibri">2</span></sup><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">). Alanod began producing the nanocomposite sol-gel protective  overcoat in-house on the Miro-Sun in November 2009 with a harder, smoother, and clearer top surface; resulting in improved specular reflectance and durability.  They have developed versions where the reflectance is maximized for use with Si photovoltaic solar cells.  Recently, Aluminum Coil Anodizing (ACA), Alucobond , Alcoa and Alcan have expressed interest in providing aluminum mirrors for solar applications. </span></p>
<p class="MsoNormal" style="text-align:justify;mso-pagination:none;mso-layout-grid-align: none;text-autospace:none"><span style="font-family:Helvetica;">"There are no commercial solar front surface mirrors.  The front surface mirror closest to commercial deployment was developed by NREL and Science Applications International Corporation (SAIC).  It is a low-cost advanced solar reflective material (ASRM) combining the best of both thin-glass and silvered-polymer reflectors. The alumina (Al</span><sub><span style="mso-bidi-font-size:11.0pt;font-family: Helvetica;mso-bidi-font-family:Calibri">2</span></sub><span style="font-family:Helvetica;">O</span><sub><span style="mso-bidi-font-size:11.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">3</span></sub><span style="font-family:Helvetica;">) coating is deposited by ion-beam-assisted physical vapor deposition (IBAD).  Hemispherical reflectance is ~96.7%, the specular reflectance at 25-mrad is ~96.1% and at 7-mrad is ~91.2%.  Materials undergoing testing demonstrate excellent durability under accelerated and outdoor weathering.  Samples have been outdoors in Arizona for more than  11 years without degrading. From an NREL cost analysis, a commercial roll-coating company can produce the ASRM, including purchasing the roll coater, for less than $10.76/m</span><sup><span style="mso-bidi-font-size:11.0pt; font-family:Helvetica;mso-bidi-font-family:Calibri">2</span></sup><span style="font-family:Helvetica;"> ($1/ft</span><sup><span style="mso-bidi-font-size:11.0pt; font-family:Helvetica;mso-bidi-font-family:Calibri">2</span></sup><span style="font-family:Helvetica;">) by limiting the alumina thickness to 1.4 mm with high-purity alumina, if purchased in bulk quantities, and by depositing the alumina at deposition rates higher than 50 nm/s with multiple zones on a wide PET web.  The ASRM could also be deposited in a batch process.  Further development of the ASRM has been transitioned to a commercial company, Abengoa Solar, below. </span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">"I am serving as NREL’s technical advisor for the Concentrating Solar Power (CSP) projects selected by DOE for awards developing advanced solar mirrors to reduce the cost of solar power to less than $0.10/kWh by 2015. All of the contracts have successfully moved into Phase II and III of their proposals. Specifically:</span></p>
<p class="MsoNormal">'''<span style="mso-bidi-font-size:15.0pt;font-family: Helvetica;mso-bidi-font-family:Calibri">3M (St. Paul, MN)</span>'''<span style="mso-bidi-font-size:15.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri"> </span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">3M will develop abrasion-resistant, anti-soiling protective acrylic front surfaces on silvered polymeric mirrors <span style="color:blue">(i.e., SMF 1100)</span> as low-cost replacements for thick glass mirrors in parabolic trough CSP installations.  The project objective aims to reduce the installed system cost and levelized cost of energy for CSP trough installations.  </span></p>
<p class="MsoNormal">'''<span style="mso-bidi-font-size:15.0pt;font-family: Helvetica;mso-bidi-font-family:Calibri">Alcoa (Alcoa Center, PA)</span>'''<span style="mso-bidi-font-size:15.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri"> </span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">Alcoa will develop an aluminum intensive collector (supporting structure and [<span style="color:blue">i.e., protected aluminum-based)</span> reflector] to reduce the installed system cost and levelized cost of energy for CSP trough installations.  </span></p>
<p class="MsoNormal">'''<span style="mso-bidi-font-size:15.0pt;font-family: Helvetica;mso-bidi-font-family:Calibri">PPG Industries (Pittsburgh, PA)</span>'''<span style="mso-bidi-font-size:15.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri"> </span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">PPG Industries will develop and commercialize large-area, low-cost, high performance <span style="color:blue">(i.e., glass-based)</span> mirrors, through alternate materials, structures, and fabrication processes for reflector components, to enable lower cost CSP parabolic trough technology.</span></p>
<p class="MsoNormal">'''<span style="mso-bidi-font-size:15.0pt;font-family: Helvetica;mso-bidi-font-family:Calibri">Abengoa Solar </span>'''<span style="mso-bidi-font-size:15.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri;color:blue">(formerly Solucar)</span>'''<span style="mso-bidi-font-size: 15.0pt;font-family:Helvetica;mso-bidi-font-family:Calibri"> (Lakewood, CO)</span>'''<span style="mso-bidi-font-size:15.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri"> </span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">Abengoa Solar was also selected to develop a low-cost, advanced polymeric reflector <span style="color:blue">(i.e., the SAIC IBAD alumina front surface reflector) </span>for CSP applications to lower the cost of CSP parabolic trough power plants.</span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">"We have also been working to develop new, more-efficient advanced solar  selective coatings for receivers with high solar absorptance (''a'' > 0.96), low thermal emittance (''e'' < 0.07;  >450ºC), thermally stable >550ºC, ideally in air, with improved durability and manufacturability and reduced cost and potentially can encourage development of US &/or 3</span><sup><span style="mso-bidi-font-size: 11.0pt;font-family:Helvetica;mso-bidi-font-family:Calibri">rd</span></sup><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri"> receiver manufacturer.</span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">"Carl Bingham from NREL said he typically uses stainless or aluminum at the solar furnace, but is sure stainless is likely too expensive for this application and aluminum will not handle the temperature.  The other materials he can think of are pretty exotic and likely expensive, but he is checking  with Roland Pitts at NREL and someone at CRES more familiar with solar cookers.  My substrate experience is from high-temperature (T>400°C) receiver tubes so likewise the materials are pretty expensive.  Absorber coatings  may be deposited on stainless steel grade 316, Ti (321), Nb (347), and alloys (Monel 400) for high-temperature molten salt applications.  Absorber coatings may also be deposited on stainless steel (304), glass, copper, or aluminum tubular or flat substrates for mid-temperature </span><span style="mso-bidi-font-size: 15.0pt;font-family:Helvetica;mso-bidi-font-family:Arial">(100ºC < T<400ºC)</span><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri"> applications. Some formed black polymer materials are used for low-temperature (<100°C) hot water heaters.   We do have a the Granta Design CES Selector 2009 Aero & Polymer Edition that can help select materials depending on a variety of material, thermal, and cost parameters and plot them in a succinct Ashby Diagram, that may be of assistance.</span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">"NREL tests the reflectivity and durability of solar mirrors, glazings, and absorber coating.  Typically, we measure the hemispherical reflectance of the samples from 250 to 2500 nm using a Perkin-Elmer Lambda 9 and 900 UV-VIS-NIR spectrophotometer with a 60-mm, integrating-sphere attachment relative to National Institute of Science and Technology (NIST) traceable standards (the standard is chosen based on the reflective surface).  The direct normal air-mass 1.5 (DIRNOR15) solar-weighted hemispherical reflectance is calculated from data collected in the 250-2500-nm range. The transmittance of the samples can be measured from 200 to 2600 nm using a sphere and from 190 to 3200 nm without the sphere.  We have a Perkin-Elmer Lambda 1050 spectrophotometer with Universal Reflectance Attachment (URA) and 150-mm sphere.  The URA allows us to make high-sensitivity, absolute reflectance measurements from 190 to 3300, and can automatically and reproducibly change the angle of the sample.</span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">"Developing spectrally selective or absorber materials also depends on reliable characterization of their composition, morphology, and physical and optical properties. The key for high-temperature usage is low ε.  NREL has been developing the protocols and building the capability for accurate, precise measurements of the thermal/optic properties of the selective coating. We can measure the hemispherical reflectance of the samples from 250 to 2500 nm the PE λ-9 , 900, and 1050 UV-VIS-NIR spectrophotometer with the integrating-sphere in the 250-2500-nm range or with the  URA attachments. The reflectance of the samples from 2.5 to 50 μm can be measured using a PE IR 883 IR spectrophotometer with a reflectance attachment and NIST traceable gold reflectance standard.  Recently, new National Institute of Standards and Technology (NIST) traceable gold IR standards were purchased and instead of the V reflectance attachment previously used a 3X Beam Condenser Specular Reflectance accessory was purchased to more accurately measure the samples with the 883. We purchased a Surface Optics Corporation (SOC) 100 HDR Hemispherical Reflectometer (Nicolet FTIR) under the American and Recovery Act (ARRA) that can measure the IR reflectance of absorber coatings at the receivers operating temperatures (up to 650°C) that should be delivered in February or March.</span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">"The specular reflectance is measured at 7-, 15-, 25-, and 46-mrad cone angle with two Device and Services (D&S) Field Portable Specular Reflectometer at 660 nm.  We also have a SOC 410-Vis Directional Hemispherical Reflectometer and ET100 Emissometer.  The SOC instruments are handheld reflectometers that allow precise, reproducible measurements in the lab or in the field of specular reflectance in the visible spectral region and thermal emittance in the infrared spectral region. The SOC 410-VIS measures the specular reflectance in four bands between 400-540 nm, 590-720 nm, 480-600 nm, 900-1100 nm.  The signal intensity is normalized against an internal standard. Total, diffuse, and specular reflectance is reported for the data at 20° incidence. The SOC ET100 measures directional thermal emittance at two incidence angles, 20° and 60° and predicts Hemispherical Total Emittance. Emittance measurements can be measured with a Gier-Dunkle DB 100 Infrared Reflectometer at room temperature.  A filter is used to simulate a 100°C measurement, i.e., by weighting the measurement by a 100°C blackbody curve. </span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">"We perform outdoor exposure testing at Golden, Colorado; Miami, Fl, and Phoenix, AZ.  NREL has the capability to perform accelerated aging of materials using natural sunlight.  We purchased an Atlas EMMAQUA under the ARRA that can accelerate natural sunlight in Golden, CO, concentrated 7 to 8 times with a Fresnel reflector while samples are cooled with a fan to near-ambient conditions and sprayed with deionized water 8 min per natural sun hour that should be installed this spring. NREL has two Ultra-Accelerated Weathering Systems (UAWS). The original dish has been operating for 10 years at 100X < 500 nm and  the new UV dish includes an environmental chamber; the same 100X < 500 nm, but 4 times the sample testing area.  The UAWS is a recharge system so the cost of the testing would need to be covered by the company requesting testing or the appropriate DOE program.</span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">"Accelerated exposure testing is performed in Atlas Ci5000 Weather-Ometers (WOM).  The WOM’s use a xenon-arc light source with filters designed to closely match the terrestrial air-mass 1.5 solar spectrum and allow control of exposure temperature and ambient humidity.  The WOMs operate continuously at 60°C and 60% relative humidity (RH).  The Ci5000 uses light levels about twice outdoor exposure.  A single day of testing (24 hours) is roughly equivalent to six times for the Ci5000 in terms of light intensity.  We also have a Ci5000 with extended temperature capability for cyclic testing with light, a Ci 5000 that simulates a rain cycle, a Tenney cyclic tester (dark), and a humidity/salt spray tester. We also perform accelerated testing in a BlueM that operates continuously at 80°C and 80% RH, but the samples are not exposed to the light. The BlueM does not have the same acceleration factor as the WOM, but from other experiments we believe the acceleration factor is at least 25X the outdoor exposure at NREL for glass mirrors. We can use a Q-Panel QUV with 340A fluorescent bulbs that match the UVA solar spectrum from 290 to 340 nm. The QUV operates continuously in 4 hour cycles; 4 h of light exposure with 40ºC, followed by 4 h of 100% RH.  A single day of testing is roughly equivalent to 1.5 times the outdoor exposure.   We have a 1.4kW solar simulator (1.4kW-SS ) that uses a filtered xenon-arc light source and can achieve intensities of about five times the outdoor exposure in a wavelength band between 300 and 500 nm. The 1.4 kW-SS sample chamber is divided into four quadrants allowing samples to be exposed at two different RH and temperatures.  The chamber allows four 25.4 mm x 25.4 mm or eight 12.7 mm x 25.4 mm samples to be exposed per quadrant.  Within each quadrant, samples can be either exposed or shielded from the light (but exposed to temperature and humidity). We purchased two new solar simulators under the ARRA that should be delivered in March or April that will need to be installed.</span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">"We perform accelerated stability testing of absorber coatings in the BlueM damp heat oven and a Blue M Inert Gas Oven (IGS).  The IGS can operate up to 600°C in an inert gas (i.e., air, N</span><sub><span style="mso-bidi-font-size:11.0pt;font-family:Helvetica;mso-bidi-font-family: Calibri">2</span></sub><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">).   We purchased a High-Temperature (650°C) Vacuum Oven under the ARRA and a High Temperature (1500˚C) Box Furnace that should be delivered in February; both will need to be installed.</span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">"NREL's sample size is typically 1¾” x 2</span><span style="mso-bidi-font-size:15.0pt;font-family:Calibri;mso-ascii-font-family: Helvetica;mso-bidi-font-family:Calibri">⅝</span><span style="mso-bidi-font-size: 15.0pt;font-family:Helvetica;mso-bidi-font-family:Calibri">” (45 mm x 65 mm), although we can measure larger or odd shaped samples or cut samples down to size.  We typically like to measure triplicates of samples for each site and chamber (depending on chamber space availability).  Samples are measured initially and after exposure testing at periodic intervals of approximately 1, 3, 6, 9, 12, 15, 18, 21, 24. ...months except in Florida and Arizona where the samples are measured annually. We test samples until they drop 10% of their initial value or fail catastrophically.  </span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">"We typically characterize >1000 samples/mo, Currently, we have roughly >10,000 advanced reflector, glazings, polymers, and  solar selective samples under test for CSP (& CPV) industry.  We have a database of solar materials that contains: >1500 experiments, >25,000 samples, >350,000 measurements, >23 yr. Over the last 18 months we have been restoring and  upgrading our capabilities, which includes hiring new staff, installing new equipment, upgrading our database to be web accessible and secured (hopefully completed March-May), and developing the capability to measure 2-mrad specular reflectance. In addition, we can test the mechanical, thermal, permeation properties of most materials.  In addition, NREL has the capabilities to test the surface analytical properties of materials which is described on [ <span style="color:blue"></span>].  This testing is also a recharge center. </span></p>
<p class="MsoNormal"><span style="font-family:Helvetica;">"The steady-state off-sun thermal losses of receivers used in solar parabolic trough power plants can be analyzed in NREL's parabolic trough receiver test stand.  Electric heaters and thermocouples are placed inside the receiver being tested and the heater power use is recorded at a desired absorber temperature. This routine is repeated for several different absorber temperatures, generating heat loss curves for a receiver.  NREL can survey the receiver temperature by using a vehicle with an infrared (IR) camera and Global Positioning System (GPS) receiver that is driven down each solar field row while the solar plant operates normally. A data acquisition system uses the IR camera to photograph the receiver glass temperatures and processes them automatically. The glass temperature indicates how efficiently the receiver is working. The cooler the receiver glass temperature for a given air temperature, wind speed, and internal heat-transfer fluid (HTF) temperature, the less the heat lost to the environment — leaving more heat to increase the temperature of the heat transfer fluid. Receiver’s that have lost their vacuum or have hydrogen in their annuli show significantly increased glass temperatures (~300°F) and heat losses relative to evacuated receiver’s.  The glass temperatures of about 6000 receiver’s can be determined in one day. </span></p>
<p class="MsoNormal"><span style="mso-bidi-font-size:15.0pt;font-family:Helvetica; mso-bidi-font-family:Calibri">"NREL has the Optical Efficiency Test Loop (OETL) facility.  The test loop supplies coolant to the receiver tubes of parabolic trough units.  The coolant, a water-glycol solution, will be at near ambient conditions.  The trough is put on sun and the heat input to the coolant is compared to the direct normal insolation, as measured at NREL’s Solar Radiation Research Laboratory (SRRL).  The ratio of the two will give the efficiency at the limit of no thermal losses, i.e., the optical efficiency.  The system operates as a closed loop.  The heat input to the coolant will be transferred to the environment by a 28 ton chiller system.  Fine control of the coolant temperature will be maintained with the chiller and a 20 kW electric circulation heater.  The tracker is two-axis and can accommodate troughs 20 m long by 5 m wide.  Different manufacturers will supply prototype troughs for testing.  </span><span style="font-family:Helvetica;">Check the technology transfer page of the </span>[ <span style="color:blue"></span>]<span style="font-family:Helvetica;"> site."  </span></p>
<p class="MsoNormal" style="text-align:center;">'''<span style="font-family:Helvetica;">End of information from Cheryl Kennedy, NREL.</span>'''</p>
<p style="text-align:center;">
Mylar is a brand name used by the DuPont corporation to identify thin polyester plastic films that it makes. Actually, DuPont and a Japanese company have created a joint company called DuPont Teijin Films to handle the polyester film business.
Mylar is a brand name used by the DuPont corporation to identify thin polyester plastic films that it makes. Actually, DuPont and a Japanese company have created a joint company called DuPont Teijin Films to handle the polyester film business.

Revision as of 18:18, March 19, 2013

Aluminum foil
Standard kitchen aluminum foil works very well for solar cooking reflectors.
Tom SponheimAdded by Tom Sponheim
The most common reflective material used in homemade solar cookers is plain aluminum foil. This can be glued very well with white glue or wheat paste.

Mylar is a brand name used by the DuPont corporation to identify thin polyester plastic films that it makes. Actually, DuPont and a Japanese company have created a joint company called DuPont Teijin Films to handle the polyester film business.

Windshield shade
A simple windshield shade can be used as a reflector.
Beth OgilvieAdded by Beth Ogilvie
It also appears that many large companies in different parts of the world produce similar products. It also appears that some companies may buy the polyester film from companies such as DuPont and then add the aluminum coating themselves, before distributing to consumers. In other words, there may be dozens, scores or hundreds of companies that sell polyester films with aluminum coating. This may make it very impractical to trace a supplier for you in Port Harcourt through the manufacturers, which is what I tried to do in my email to DuPont Teijin.

Solar cooker experimenters in Kenya, Ethiopia, Tanzania, Peru and Bolivia have all found that gift wrap can be found easily that can be used for making reflective surfaces for solar cookers. Glues made from flour and water or "wheat paste" work well enough to hold the gift wrap onto the CooKit. The gift wrap is like a mirror on one side (the aluminum) and a color on the other side. So, if I can't find better information through DuPont Teijin, you might find that just shopping for shiny gift wrap is the most practical solution.

Aluminum can reflector1
A funnel cooker made out of wood, using old beer and drink cans (cut open, flattened and then stapled to the wood) as reflectors
Tom SponheimAdded by Tom Sponheim

From the information I currently have, it seems that these polyester products are not suitable for lining the inside of a solar box cooker, because of the danger that at the temperatures inside the box-type cooker, the polyester would melt or at least give off foul smelling foods. I am told that this problem does not necessarily show up the first time one uses a cooker made with these materials--that it may show up after five or ten or twenty uses.

Therefore, I would suggest that the polyester or gift wrap material only be used for CooKits or for the reflectors on box cookers that are outside the box.

Ravindra Pardeshi writes:

Also note that most metals cannot be polished enough to be reflective enough for solar cooking. One exception is anodized aluminum. Metallic paints usually do NOT reflect well enough. We polish the assembled cooker of sheets. We do the polishing in two ways:

  1. Professional buffing service
  2. On our own. This is very crude way but works. First we polish the surface with fine cloth and fine tooth powder and then with one localy found polishing liquid. Results are quite satisfying. For repolishing we use liquid polish only.

Reflective material possibilities

Here is a comprehensive list of various inexpensive reflective materials that are available for solar cooker construction. Table of Reflector Materials

Stephen and Sheila Harrigan of Solar Clutch, report from Addis Ababa, Ethiopia, where they promote solar cooking, that common solar panel cooker construction materials have always been difficult to obatin. The widely used CooKit has traditionally been made from cardboard, though recent versions are being made from fluteboard, such as the Poly Furnace CooKit variation. These updated cookers last far longer than the cardboard versions, which are considered to be successful if they last six months. For them however, the major problem with providing inexpensive yet durable cookers is the availability of construction materials. Cardboard is scarce, and when it is commercially available, the quality if often poor, or the product arrives torn. Tinfoil and glue can also be difficult to find. Stephen began looking more closely at what was available locally, and hit upon a product referred to as 'cool roofing'.

Cool roofing is a zinc galvanized metal material, which is fairly reflective. Besides shedding water, it is also intended to reflect the hot sun from the roofs of local homes. And because of its availability, the material cost for cookers is competitive with cardboard. A CooKit can be constructed for about $6USD worth of the metal roofing. It can be cut with tin snips, and bends are made by folding the metal around a straight board. The metal CooKit has performed well, if not quite as well as the mylar covered fluteboard version, and its weight would help in windy conditions. Because the material is easily available, and can be made with existing worker skills, local manufacturing of solar cookers offers the possibility for a community business enterprise. Disadvantages include the inability to fold the cooker for storage, and transporting completed cookers will take considerable space and will be relatively heavy. The cooker edges need to be dulled or protected, as the cut metal edge is quite sharp. As solar cookers are more widely promoted and accepted, the durability of inexpensive solar cookers becomes a significant issue to be addressed. The question raised will be, is it better to offer a cooker that can be made locally, or find a way to finance the availability of cookers that are made at a more sophisticated facility, losing the empowering aspect of neighborhood manufacturing?

Use the foil from cigarette packages

Most cigarette packages have a inner foil liner. Collect these and use them in a patchwork fashion to create a reflective surface.

Mirrors made from decal/stickers

Chrome mirror sign vinyl is excellent for most solar cooking applications where the material itself is not touch the hottest part. It is made to be used on business signs and is designed to stand up to many trips to the car wash. This material can turn nearly anything into a powerful mirror. You can find it on the internet. You must use phrases like "Chrome mirror sign vinyl", or, ""Mirror sign vinyl, or Gold sign vinyl. This material is available in a self-adhesive roll. You can find short rolls or long and wide rolls. The rolls start at inchers in width to feet in width. Apply it with soapy water in the same way as window tint. After some exposure to warmth, the soap vanishes and your mirrors will stick for years. Keep them shiny with wax, oil, Scott's liquid gold, experiment with it.

A flexible cutting board could make a good mirror. When finished cutting the underside of the cutting board may have a mirror on it to help cook the food you cut up.

Think of the many shapes we have availble. Now you can turn junk into ovens and dish cookers. Here are some things I know would make terrific ovens and parabolic, and parabolic hybrids. A thermal parabolic hybrid oven will acheive temperatures hotter than needed for normal cooking, when combine with thermal cookware it is nearly dangerous.

It is dangerous. Be careful. It will take some time to adapt to your new abilities. A thermal griddle may be a griddle with ceramic tile in a sandwich of steel or aluminum. ALUMINUM COOKWARE WARNING: See: Aluminum Oxide poisoning. Aluminum loses heat so quickly too. I want my food cooked with glass and ceramic and steel. Matt West

Rescue blankets (Mylar)

Rescue blankets (or space blankets) consist of a thin plastic foil (often polyethylene terephthalate, PET) and a thin layer of aluminium (cf. The silver side is the aluminium side, while the gold color on the reverse side comes from a translucent yellow tint of the plastic in combination with the front aluminium layer.

Such material is similar in cost as aluminium foil or self-adhesive vinyl stickers, large formats are common (e.g. 160 by 210 cm), and the material is indended for outdoor use. Relflective accuracy is mirror-like, in contrast to aluminium foil which has fine directional grooves in the surface from production and thus reflection artefacts. Although as with self-adhesive mirror foil, the material should not be used for the hottest part of the oven, i.e. where in contact with pot or glazing. Melting point of PET is around 260°C (500°F).

Using the foil on the inside of Tetra Pak juice boxes


Solar Cookers International East Africa Office recycles waste from Tetra Pak materials. This is a packaging making industry and sometimes they have waste which they have already prepared, this then we use as our foil. When this is not available they buy from another packaging industry called Pressmasters Ltd. Here are their coordinates: Pressmasters Ltd.
P.O. Box 17560 - 00500
Kenya Fax: +254 20 823044
Tel: +254 20 820253,820254
Mobile +254 722514623 / 733743783


Solar Health and Education Project (SHEP) has developed a relationship with Tetra Pak International — manufacturer of aseptic drink containers — whereby SHEP uses Tetra Pak’s excess foil-lined paper for solar cooker construction. (The foil-lined paper is printed in wide rolls, sometimes resulting in excess material begin generated.) According to SHEP, Tetra Pak is willing to accept proposals from other nongovernmental organizations that may want to use the reflective material as long as the material will be used for workshop participants to construct solar cookers.

Parabolic disk foiled with reflective tape

This photo shows how to use a Direct TV antenna as a solar cooker using reflective tape applied in strips. Photo sent by Ranyere Bezerra.
Tom SponheimAdded by Tom Sponheim
IMG 3405
Reflective tape can be used to foil parabolic reflectors.
Tom SponheimAdded by Tom Sponheim

Lithograph printing plates

Looking for inexpensive, recycled reflective material for solar cookers? Here’s a tip from the SunStove Organization of South Africa: "Lithograph printing plates are available in every country at the government printing office, the local printer or the local newspaper. Used printing plates are sold as scrap." This scrap may be sold for the equivalent of US $1.25 per kilogram. Before using the plates in solar cookers, clean with paint thinner and water.


See also

Using a white color instead of reflective sheet

Kyoto box
The updated Kyoto Box cooker uses a white surface instead of a reflective surface.
Abigail FayAdded by Abigail Fay

See Topic needing research

External links

Around Wikia's network

Random Wiki