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sdeering
10-27-2006, 05:54 PM
Hi folks I have a shell 75watt panel that is shattered. It looks like just the exterior glass covering is shattered. It still makes juice. Have any of you played around with them? I am thinking of dissolving the glue that binds the glass to the modals. It may be silicone I'm not sure. Anyone know of a good solvent for silicone?
Thanks for any help.
Stephen

Evan
10-27-2006, 06:19 PM
Anyone know of a good solvent for silicone?

Sure, same stuff they use for PTFE. :D

I don't think that stuff is easy to remove other than by scraping.

sdeering
10-27-2006, 06:34 PM
I know gas and silicone don't get along. Sorry Evan what is PTFE solvent?
I am also thinking of paint stripper. Do you know if the monochristaline silicon wafers are reactive with chemicals? I am thinking they are quite stable.

I haven't done anything with it yet. It was bought on ebay and mailed. I did pay for insurance but after reading the fine print Canada Post doesn't pay for glass damage and most of the time don't pay for any damage atoll. I’m kind of battling with the seller at this point but I don't think it will go anywhere.
He is mad at me for even thinking it is his problem for not packaging them correctly. One layer of cardboard and one layer of thin bubble rap don't protect crap.
Stephen

jesse557
10-27-2006, 06:59 PM
Many adhesives can be dissolved with acetone and it won't damage the AR coating of the cells. Whatever you do, don't use anything acidic, it will eat the AR coating and the efficiency of the cells will drop significantly.

Also, test a tiny area before you use anything. Better safe than really annoyed.

Todd Tolhurst
10-27-2006, 07:04 PM
I know gas and silicone don't get along. Sorry Evan what is PTFE solvent?

Supercritical CO2, of course.

This stuff (http://www.prosoco.com/Product.asp?ID=43) might work. However, it does appear to contain sulfonic acid, so if acidity is a Bad Thing, it might not be appropriate.

Evan
10-27-2006, 07:38 PM
The cells are subject to contamination. The properties are determined by trace amounts of dopants diffused in a very thin layer near the surface. The junction is less than a micron deep. The cell is overcoated with an antireflection layer but it is somewhat porous. This means that contaminants can get through to the junction layer and alter the properties as well as reduce the effectiveness of the antireflection layer. They shouldn't be cleaned or even touched.

BTW, the most ironic thing about solar cells is that they eventually become useless if you leave them in the sun...

sdeering
10-27-2006, 08:05 PM
Well maybe I will just bag it to keep the water out of it and use it till it craps out.
Stephen

Mad Scientist
10-27-2006, 10:23 PM
If just the glass is broken and the cells were not damaged rather trying to remove the broken glass and maybe do more damage, how about just covering the whole thing with a new piece of glass?
Leaving the original broken glass in place should little effect on its output.

Evan
10-27-2006, 10:55 PM
Leaving the broken bits in place isn't a good idea. The cells are very thin and very fragile. Also, the front collector traces can be easily damaged. The best bet is to carefully pick away any loose pieces from the front and then vacuum up any remaining small bits without touching the cells. Very carefully examine the cells for cracks. If any cell has been damaged it will reduce the output current of the entire panel. If you do find a damaged cell the best is to short around it with a wire.

Then cover it with another piece of glass.

If you do find any cracked cells and it looks like they can be removed from the panel don't throw them out. You can cut up large cells into smaller ones and make small panels that way. All you need is a diamond scriber used for cutting glass. I have done a lot of experimenting making solar panels in small sizes this way.

[edit]

If I had a smashed panel like that and the cells weren't glued down I would be tempted to remove them all very carefully. I would then build a concentrator panel to double the output. The cells need to be mounted on a heat sink with insulators and silicon grease, perhaps a sheet of anodized aluminum and some sort of backside cooling. Then use a simple set of mirrors to give them about three suns and you can easily get double the wattage from them. You can even recover the waste heat by using it to heat water by adding collector loops to the back of the panel. Most of the energy that falls on the cells is wasted as heat. The cooler the cells are kept in use the more efficient they are.

J Tiers
10-27-2006, 11:47 PM
I have the same exact problem.....

4 old Carrizo power plant panels that did duty for 12 years on the shed.... until the big St Louis storm this summer got 'em. A 25 foot branch fell on them and bent 3 out of 4 of them.

I also have not gotten very far getting the busted up temperd glass off the front of them. I estimate that about 3/4 of the cells can be salvaged if I can get to them.

The problem is not knowing what the adhesive is. It is fairly weatherproof, although the back was covered with a sheet of what seems like mylar.

It appears the glass was covered with some adhesive, which they wewre carefully laid down on w/o bubbles, and then a goodly amount more poured over them. They are stuck down well, but now only to small "cubes"

sdeering
10-28-2006, 12:43 AM
They may use a vacume process to pull all the air out. I will keep you informed if I find out anything you do the same.
Thanks for all the replys.
Stephen

Evan
10-28-2006, 12:50 AM
As a wild guess JT I would say water clear acrylic. It has about the same transmission properties as glass and is resistant to UV degradation.

If that's the case then acrylic solvent should dissolve it without damaging the cells. Just looked it up, the solvent is dichloromethane.

sdeering
10-28-2006, 12:18 PM
Sounds interesting Evan. Now if I could find a on the shelf product in a small quantity to try. I will do some searching.
Thanks again Evan
Stephen

Evan
10-28-2006, 12:37 PM
Acrylic solvent should be available at any good plastics supplier.

Shaidorsai
10-29-2006, 12:06 AM
Assuming you are correct that it is sealed with silicone adhesive sealant (and that would have been a good choice from a manufacturing standpoint), then go to any large hardware store and obtain a tube of silicone caulk remover. It will be in the same section as all the caulking products. It is cheap, safe, and it works. It is also usually available at large paint stores. The other thing you will need is a very thin putty knife to lift the edge of the glass off. Do yourself a favor and coat the broken glass with some sticky tape to hold the broken glass together and away from the solar cells as you remove the panel. Another hint. If possible, turn the whole assembly upside down for the removal process so the glass falls away from the solar cells as it comes off. Exercise some care here to make sure the solar cells are firmly bonded to their backing. Sometimes only the glass is holding them down

I have seen these assembled with thin double-sided foam tape. If you think this is the case, and you can get to the edges of the panel and the bond line between substrate and glass cover, then use a thin razor blade to cut through the foam tape. Remove the residue with Goo-Gone or other similar product. It also helps to clean / wet the blade with this stuff during the cut. Be careful to limit your depth of cut into the bond line to avoid damaging solar cells or connecting wires.

Hope this helps, Good Luck!

Evan
10-29-2006, 07:07 AM
Silicone is the likely material for sealing the edges of the panel.

As for sealing the individual cells to the glass I did some more research and it is almost certainly EVA (Etheylene Vinyl Acetate copolymer). The solvent for that is also dichlormethane, aka methylene chloride. The backsheet that JT mentions is PVF (Poly Vinyl Fluoride, aka Tedlar by Dupont).

tryp
10-30-2006, 04:36 PM
Just note that DCM (dichloromethane) is carcinogenic and quite expensive at a plastics supplier, it shouldn't be but it is when I have looked. Just don't breathe the profuse fumes (low bp high vapor pressure) and for the love of all things dispose of it at a facility that takes chlorinated hydrocarbons.

Sorry I can't help with the panel problem.

RobDee
10-31-2006, 08:50 AM
Why guess??

Call the company that makes the panels and ask them! Shell is still in the business.

Evan
10-31-2006, 09:13 AM
It isn't a guess. I looked up the specs from the major manufacturers of panels and they all use EVA as the potting compound for the cells when the panel is made that way. The main advantage it has over acrylic is that it is flexible so that temperature changes won't be a problem.

RobDee
10-31-2006, 05:49 PM
Evan,

My statement simply expessed the best solution is to ask the manufacturer how to remove the glass and repair the panel and not that you specifically were guessing.

Evan
10-31-2006, 05:53 PM
Fair enough.