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netttech

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Posts: 720
Reply with quote  #1 
Reflectors has been debated for some time. A few weeks ago I built a reflector from scrap of foam & Mylar for my 10' x 3' panel, that's located on my roofed over front porch. Being under the porch roof I lose sunlight as we approach spring. The idea was to see if the reflector does help with the panel performance, plus extend the use of the panel.

I haven't evaluated the temp difference yet (if any) of the panel since installing the reflector. I noticed yesterday where the shadow is located on the panel. Below are the pictures & I have marked where my snap switch is located. The panel is still producing a sustained (fan running constantly) amount of heat with the maximum temp of 105 degrees. I could play with the reflector position to try extending the panel use.

Jeff
Central IL
Solar air & water

P2272661.JPG  P2272662.JPG 

gbwillson

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Reply with quote  #2 
Jeff-

Of course if it's winter and you have snow around you can simply not shovel the snow in front of the collector. But for early and late season performance, this looks promising. I can't tell from the photos, but I suggest smaller reflective panels instead of large ones; Easier to store and place. Kinda crazy idea, any chance you could easily remove the railings during winter?

Greg in MN
KevinH

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Reply with quote  #3 
Looks like the top foot or so of the collector is already shaded.  Later you would probably need a wider reflector, but what you have now will definitely keep it going longer than it did in the past without the reflector.  Being under the porch there are probably fewer times when snow has to be cleared off the reflector.

Reflectors give better gains than the snow by itself, but to maintain that gain you need to clear off the snow.  I made most of my reflectors on 2' x 4'  1/4" panels with a 1x2 stiffener on the back.  At one time Menards had very inexpensive panels (a few bucks) with a smooth laminated surface on both sides.  Now they are more expensive, but once in a while there is a slightly damaged one in the discount bin.

Kevin H

netttech

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Reply with quote  #4 
Funny you ask that Greg....yes I can remove the railings. [smile]

The contractor had installed the railing too high. When I sat on the porch, the top of the railings were eye-ball high. You couldn't see anything unless you ducked under or stood up. So, I removed the retaining screws, lowered the railings 3-4" so it was easier to see. Instead of screwing it in, I drilled it out the ends & it now has a 3/8" bolt just pushed into it.

I can easily remove the bolt & remove the railing.

However, I'm getting good heat with them in place, so why bother.

I do get a dusting of snow on the reflector, but usually it isn't much though. I can easily store a larger reflector the same size as the panel.

If I build a larger reflector, I was thinking of placing clear acrylic on the mylar. The heat-shrink plastic was ok for this reflector, but the acrylic would be more durable. I squeeggeed off puddled melted snow one day & it ripped a corner of the plastic.

Jeff
Central IL
Solar air & water
netttech

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Posts: 720
Reply with quote  #5 
I thought I would add 1 last post on the this subject. Yesterday (10ish am) I was unloading groceries & noticed the fan was running on my 10'x3' panel. It surprised me since the sun has gotten higher in the spring sky & no longer directly shining on the panel.

I went inside, opened the vent doors & was getting 90 degree hot air. The panel didn't sustain that amount of heat, but cycled the fan every 5 minutes. I had forgotten about the reflector & haven't open the vents doors for a week.

Apparently, it does make a difference. The picture shows the shadow line of the porch roof. Perhaps I will make the reflector bigger for next winter. [smile]

Jeff
Central IL
Solar air & water

P3192673.JPG 

stmbtwle

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Reply with quote  #6 
Does the mylar tarnish after time like ordinary aluminum or does it stay bright?
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Willie, Tampa Bay
KevinH

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Posts: 547
Reply with quote  #7 
As long as the clear layer is facing the sun and the aluminized layer is protected, it holds up well.  I have been using my reflectors since 2013 (search "reflectors" to see the topic on it).  There are some small spots where the aluminized layer has tarnished, but more the 90% of the reflective area is still OK.  The clear layer can get light scratches from brushing off snow.  On one reflector I just wrapped it over a board.  The clear layer got brittle and started cracking this year.  I may try using Armor All to protect it next time.  The others were glued to the board using spray glue and sealed at the edges with exterior duct tape.

Kevin H
MN
stmbtwle

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Reply with quote  #8 
Curious. So I should put the aluminized side down.    As the reflectors seem to be so effective, I was wondering how well they held up.  My next collector is going to be mounted vertically on the roof (which is already white).  My feeling was that when the sun is low in the winter I would get more reflected heat, but in the summer the reflection striking the collector would be minimal.  Snow is not a problem but UV and salt air could be.  Sealing it would protect it from the salt but the sun here is brutal.


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Willie, Tampa Bay
gbwillson

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Reply with quote  #9 
Willie-

I think the clear plastic is not for protection, but to be a surface for the ultra thin reflective coating. All of the mylar I've seen is pretty lightweight and likely not UV treated. By placing the clear plastic coating up you help protect the delicate, reflective surface. Most tarnish would start in little pinholes amor cracks in the plastic coating, exposing the reflective coating to the elements. I bet you could wipe a coating of Armour All on the surface to extend the life expectancy. But you can pick up a bundle of emergency blankets for about $5, and 4'x25' rolls are about the same price. So treat them like disposables and expect to replace them every couple of years or less if needed, so shop around for the best price. You could also look for heavy duty mylar that is UV treated and designed to be used repeatedly and outdoors. But you have to weigh the cost against the ultra cheap mylar sources. However you mount or attach them should have an easy, quick change feature, especially up on a roof. Using spray adhesive is probably the "best" way to attach mylar, but not up on a roof.

Greg in MN
stmbtwle

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Reply with quote  #10 
Well the mylar could be glued to a sheet of polyiso, which could be removed, resurfaced, and replaced. But it would still entail climbing up on the roof, not something I'm fond of. I think I would be better served to let the white roof do the work and accept the loss in reflectivity.
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Willie, Tampa Bay
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