Benny
Member
Does anyone know of a local supplier of highly reflective film for making flexible mirrors ? There are several in the US and germany but they only supply big quantities or don't ship to Australia - like this one http://www.reflectechsolar.com/pricing.html
I'm looking for a few square metres to coat my parabolic trough water heater. I used a space/survival blanket to show it works OK but that degraded pretty quickly.
Some time ago I was looking for a lightweight reflective material to line a lightshaft. It was just a concept and so far hasn't been persued.
I found Rosco Shrink Mirror which is used in theatres instead of glass mirrors, and is simply heat-shrinked?? onto a timber frame. The chap I spoke to was very helpful, though he wasn't sure how long the material would last with UV exposure. Therefore I wouldn't know if it would be suited to your exterior application. roscoaus@rosco.com.au
Another possibility is polished stainless steel. In 'Making Your Home Sustainable' Derek Wrigley mentions Vincenc & Bridgford in Queanbeyan as suppliers.
Using Derek's inspiration, I attempted to source something similarly shiny for a reflective pergola outside a Southern window. The local Taree Onesteel yard had a 0.7mm thick 304 stainless steel sheet in '2B Polished' finish for a reasonable $180 for a 2400 x 1200mm sheet. It wasn't a full mirror finish but I suspect it could be easily upgraded with a couple of hours of buffing. It's another project on the back burner at the moment.
Hopefully some of these suppliers may be able to help out.
Benny
Member
Thanks John. I've found someone in WA - a manufacturer of solar light tubes - that will supply me with 98% reflective sheet. 1.5 x 1.2m, with sticky back, but expensive at $207!
Also Lance from ATA found a cheaper source http://cgi.ebay.com/ws/?ViewItem&item=380065194730 but only 3yr life outside. Also as usual it costs 5 times as much to ship from US as it costs to buy it!
Stainless steel, even polished is a bad reflector.
If the precision of reflection is not so relevant (which is most likely the case with a parabolic trough water heater) the reflective foil used underneath roofs is unbeatable. About $1 per m2 and according to data sheet 97% reflection and UV resistant.
Most foils are not flexible. The work around is to cut and glue only narrow strips, one at the time.
I don't understand why polished stainless steel would be a bad reflector - perhaps sun2steam can clarify. Derek Wrigley has many years experience using polished stainless steel in his various successful projects.
The scattered reflections off the dappled surface of sarking is interesting for lightshelf type uses, though more directional than just white paint. When standing in the shade on the receiving end of sarking reflections (done intentionally), there is no doubt at all about it reflecting heat.
The 'Rosco Shrink Mirror' film that I mentioned above is cheaper now than it was, due to currency parity, and I have made a flat mirror and a flexible mirror with it as prototypes for a current project.
For the relatively low cost of about $18 per sq m it is quite close to a 'normal' glass mirror in appearance, not as shiny as stainless but a lot easier to keep flat because it's shrunk onto a frame.
Next thing I'll try is to make some exterior mirrors and see what happens to the material in the elements.
Sorry, it is difficult to find good data on the web. This is what I could find in a quick search:
http://www.214m.com/html/Heat%20Transfer%20Thermodynamics%20engineering/20080416/27419.html
"With a solar absorptance of 0.42, stainless steel is not a great material to use as a collector"
In other words, polished stainless steel reflects just 58% of solar energy.
That's literature. You can also take a practical test. Put a piece of stainless steel and a glass mirror out in the sun on a sunny day. After a while check the temperature by touching it with your hand. The glass mirror will feel cool to the touch and the stainless steel mirror will be worm or even hot.
S2s "ut a piece of stainless steel and a glass mirror out in the sun on a sunny day. After a while check the temperature by touching it with your hand"
That is true. I remember when setup my first solar water heater with vacuum tubes, the cylinder was made of stainless steel, and quite insulated inside.
So there was may surprise when water was boiling inside I touched cylinder and almost burn my hand - it was so hot.
Not because of escaping heat from boiling water but from direct sun.
Minutes later when sun was covered by clouds , surface was cold enough to touch but water was still boiling.
So stainless steel is not maybe the best material for reflector but when covered with chrome or nickel as sheets on my old photographic paper dryer properties are much better. From all materials silver is the best for reflector but only when protected from air.
PS. Mylar is material used by hydroponic growers as very good reflector.
shem
Member
hi
not sure on the application you need, but mirror window tint in cheap. http://www.protinting.com.au
it needs not get wet though.
Johnnojack
Member
What is the shiny foil the florists use? Must be fairly cheap.
Metallized Mylar film is quite cost effective. http://cgi.ebay.com.au/NEW-MYLAR-1-32M-X-3M-LONG-ROLL-2MIL-REFLECTIVE-FILM-/120673584139?pt=AU_Seed_Starting_Hydroponics&hash=item1c18b4c40b
However clear reflectors can be very dangerous for the eyes if you get near the focal point. Most simple solar thermal applications don't need such a precise focus. So in applications where sarking foil works, it is cheaper and safer.
That's very interesting about the 0.42 absorptance of the polished stainless steel - down the bottom of S2's link buffed aluminium is suggested with a value of 0.16.
As a comparison, Bluescope's website lists Zincalume steel's absorptance as <0.35. http://www.colorbondcolours.com/home/commercial-and-industrial/information/technical-information-and-advice/thermal-performance/classification-of-colorbond-steel-colours-for-bca-and-basix
It seems hard to imagine that Zincalume is more reflective than a ss mirror.
dymonite69
Member
I have seen Galv quoted around the 50% reflectance/50% absorbance figure.
I just googled this old ATA forum thread, because I am thinking again about using outdoor mirrors to warm the south of the house in winter.
I had thought of simply buying fairly cheap wardrobe door mirrors. The local glass agent says they will not stand the weather. He said why not try stainless steel. This thread puts paid to that idea: stainless steel has high solar absorbtance (say 0.4).
It seems that using the foil intended for roof sarking may be practical.
However, unlike stainless steel, it is not strong or durable. To use any sort of foil, you must attach it securely to a rigid sheet that is durable.
Can anyone add advice from their experience?
[Do you know how to search this forum? Enter the topic in the "Search" box at the top. Ignore the nonsensical results, but click "google" in the bottom corner. Magic!]
Hoping someone will respond, I can give some project details.
I have enclosed the area around my south side back door with a courtyard. The courtyard walls are white-painted "Slimwall" panels 2 metres high and 50 mm thick, with fibre cement skins on an expanded polystyrene core.
The project is to hang mirrors on the courtyard wall in winter-time only, to reflect sunshine on the the south wall of the house. Not all of the courtyard wall receives winter sun, and not all the time. I estimate that 4 to 5 square metres of mirror would be best.
Given that wardrobe mirrors are not durable, and that stainless steel reflects far less radiation than the existing white painted surface, it seems that aluminium foil could be the most suitable solar reflector.
I then need a practical and cheap means of mounting the foil on the courtyard wall.
Lance
Key Master
Not sure what stainless steel you are using, but SS is available with a mirror finish, either 1P (hot rolled) or 2P (cold rolled), which reflects just like a glass mirror, with a slightly less bright image. It's what is used for safety mirrors on road corners etc. These guys have it, any SS supplier should: http://stirlingsaustralia.com.au/stainless-performance-steels/products/sheet-and-plate/13-products/sheet/26-standard-sheet.html
Lance, I think that polished stainless steel, being a specular (literally "mirror-like') reflector will re-direct a lot of solar radiation in a precise direction. It does not re-direct it all. As you say, the image is "slightly less bright". I have seen reports that it is only 60%, with the remaining 40% absorbed to heat the metal.
In my courtyard I am not very concerned to direct the reflected sunlight precisely to particular places. (Perhaps the "heliostats" that Greg mentions would be required for that.) My white-painted courtyard walls make solar radiation bounce around within the courtyard, without reflecting like a mirror.
I would like to experiment with a few surfaces of reflectivity higher than that of stainless steel (as reported) to see if some areas of concrete and brick in contact with the cold south wall of the house can be warmed by reflected sunlight.
I can report some progress in my project to hang reflecting surfaces on my courtyard wall.
My very recent posts in this thread refer.
I am now using "Alfoil" that is, cooking foil made of aluminium. I bought a 30-metre roll 300mm wide (on special) at $6.00. That is about 70c per square metre.
As a first trial, I have simply stuck 600mm lengths of foil next to each other along the upper part of my courtyard wall. I used Scotch "permanent" double-sided tape. These have survived several days in the weather. One tape patch came loose but I stuck it back again.
The reflection is basically specular (mirror-like) but, due to ripples and scores in the surface, the reflected light is spread to about twice the area. The warmth is very noticeable.
I think the problem of a suitable mounting material will be solved by using "Corflute". I didn't know what this was, but I found I even have some myself. It is a sheet plastic material 3 mm thick, that is rigid, smooth, light, and weatherproof. It is the material now generally used for making Real Estate "For Sale" placards. Hardware retailers have it for less than $10.00 per square metre.
I need to choose a suitable adhesive, and a way of securing the panels to the wall for each winter season.
It seems that I may be able to get 5 square metres of serviceable sunlight-reflector for rather less than $100.00.
Thanks, Annette.
On my starkly-white courtyard wall, the Velcro would have to be white, not black. I feel that perhaps the hook sections would be a bit obtrusive in the summer season when the mirrors are stowed away.
There is another product that is much stronger (for tornadoes). It looks a bit like Velcro, but the hooks are several millimetres long and each hook is easily seen. Does anyone know what that product is called, and where to get it? I have seen it used for the surface-mounting of extra navigation instruments in gliders.
I am unsure how to stick the alfoil to the corflute surface. Perhaps a sheet adhesive would give the most planar reflective surface. But it must be weather-proof.
I'll check out spray adhesives.
Bushwalker
Member
I suggest some masonry plugs in the wall, and just screw the corfute to the wall. You can paint over them, they will be less noticeable than velcro once the corfute is removed. They won't fall off either. 
Thanks for the suggestion, Bushwalker.
In building and in furniture making there are various tricks to conceal "fixings".
It seems to be a matter of either making the fixing point, such as a screw hole, practically invisible, or of adding some kind of concealing cover, to make it look "neat".
Johnnojack
Member
Corflute you will find shuns most glues according to DIY forums where peeps have built their own Heat Recovery Ventilators. You could staple it? Good project, good luck with it.
johnmath
Member
Catopsilia said:
I think the problem of a suitable mounting material will be solved by using "Corflute". I didn't know what this was, but I found I even have some myself. It is a sheet plastic material 3 mm thick, that is rigid, smooth, light, and weatherproof. It is the material now generally used for making Real Estate "For Sale" placards. Hardware retailers have it for less than $10.00 per square metre.
Corflute is the material of choice for political electioneering. There will be millions of square meters of Corflute available free of charge in the next few weeks. I get a certain (unhealthy) pleasure from scissoring up images of my (un)favourite politicians when making something useful out of rescued plastic landfill material.
Thanks, johnmath and Johnnojack, for information about Corflute.
It is a real worry that Corflute "shuns most glues". I really need the alfoil to attach very smoothly to the Corflute surface. Are there some types of adhesive that work? What kind of a plastic is it?
Johnnojack, do you have a link to the DIY forums that discuss it?
Signage companies attach permanent signs on the Corflute surface perfectly smoothly, so there must be a way to do it.
As often happens, I eventually hit on the right search terms to get the answers.
Corflute is in the Wikipedia article "Corrugated plastic". It is made of polypropylene.
[Corrugated plastic is made using the techniques of corrugated fibreboard patented in 1856.]
There is comparison of adhesives for polypropylene here:
http://info.craftechind.com/blog/bid/323475/Stick-to-it-A-Guide-to-the-Best-Glue-for-Plastic
The testers tried gluing polypropylene to stainless steel, which seems relevant.
