Solar selective coating surface
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RFQ: I need to have metal sheet plated (or perhaps treated) to yield a reasonable performance solar collecting surface that would remain stable for a few years if the surface is periodically heated to 300 C in air. Probably the black chrome platings described in the literature are more than adequate. I don't believe any of the spray-on paint type coatings are stable enough. My effort is investigative (applications: heat sterilization, solar cooking, others), and an initial order would be small.
What is specifically needed: Quantity: 4 Single sided coating with above described surface on: Sheets of metal 24 in. X 24 in. X .030 in. (approx. dimensions) Material: steel, copper, or aluminum (choice of metal is not very important, although if my effort results in production, the cost of copper would probably be to great. One additional specification: The sheet metal is to be rolled into a cylindrical/conical shape, thus putting the coating under tension. The coating has to be able to survive such a forming process. Possibly this means that the metal has to be first formed to its (nearly) final shape, and then coated.
Martin G
inventing solar collector - Dearborn, Michigan, USA
A. Hi, Martin. I agree that black chrome plating would be the first choice. But chrome plating is brittle, the parts would have to be plated after forming. Good luck.
Regards,
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 Ted Mooney, P.E. RET finishing.com Brick, New Jersey |
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Q. I am fabricating flat plate solar water heaters. I need a selective coating to apply to the plate, to absorb as much energy and emit as little energy as possible, and to withstand temps up to 220° F. Need a black matte selective coating. I know Thurmalox was a brand to use but I don't find any more info specific to this application. Please help with your info in this.
Thank you,
Jesus BermudezVarnier - San Diego, California, USA
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A. Hi Jesus.
I browsed a library on this topic some years ago and recall that there were three good coatings: best was black chrome plating, then black oxided copper, then regular nickel chrome plating. At that time the author found no black paint that was worthwhile, not just because of optical properties for the coating itself, but because outgassing from the paint clouded the glass cover of the enclosing box. The situation may have changed since then, but if the collector is enclosed don't forget to investigate the possibility of gassing from the coating obscuring the cover glass.
Regards,
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Ted Mooney, P.E. RET finishing.com Brick, New Jersey |
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In approximately 1980, a friend and I built a flat roof mounted water solar system on a roof 30'(N/S) x 60'(E/W) consisting of 14 - 4'x 8' copper "selective surface" collectors purchased from Phelps Dodge Copper Co. This building was a laundromat, and had a 3,000 gal insulated storage tank in the building. It was a total drain back system, thus no anti-freeze was ever needed even in cold temperature extremes (-30 F). An efficient heat exchanger allowed us to heat all incoming city water to above 120° for up to 4 weeks at a time in the summer without using any additional heat source, and pre-heated water in winter to between 70° and 90°, even on cold sunny days in January. The whole array (14) collector insulated boxes were built as one unit and faced south, in summer at a 35 degree angle with the roof, and in winter were raised to a 65 degree angle. We were located 17 miles north of the 45th parallel in Northeastern Wisconsin.
RFQ: I now live in New Ulm MN, and have a laundromat which I would like to do the same thing with, but cannot seem to find the same type of collector panels to build a similar system. My thanks in advance for any help in locating a solar supply company that I can buy individual components and build my own system once again.
Norman ELaundromat Owner - New Ulm, Minnesota, USA
