Cell Protection

[GeorgeR]

I have been thinking and figured id ask here. Would it damage a cell to coat the back with clear acylic paint to protect it from oxidation, etc. After all soldering has been done.

George

[hobot]

I sprayed my bolted and slodered connections on a 24 V battery

bank back in '99 used clear coat of some sort and it looks like

new yet. I don't think it matters much what paint or cear coat

you use as long as its dry inside and not boiling hot with solvent

exposure for it to endure, just needs to seal air/moisture off

the conact surfaces, heck even grease works but collects a mess.

Enamel probalely easy cheapest long lastig to find.

hobot

[Jeff7]

The back? I don't think it'd damage the cell, though the high temps of the cell in the sun might cause the paint to peel in time.

Why just the back? What about protecting the front then? I don't know that the acrylic would do good then - the constant sunlight will likely cause the clear-coat to turn yellow. And the front needs to be protected from weathering.

[GeorgeR]

Thank you! I think im going to try it. Also I have a bunch of O2 absorbers I swiped out of old hard drives. I also get the neo magnets . I wonder if putting one of these inside if you were going to seal them up would help?

George

[GeorgeR]

Yeah, im encasing them as well, the clear was more of an idea to prevent oxidation,

as opposed to filling them with inert gas, etc.

[crag]

Okay, this is what I've been wondering -- with all the problems people have with moisture, breaking glass, expanding plexiglas, why couldn't a person just epoxy over the cells or paint over them with a helping of polycarbonate, like you can imbed relics in from the hobby store?

I'm thinking of tiling my RV roof in some of these broken or flawed cells, and am wondering why I shouldn't lay it out, stick it down with some silicon, and then maybe fiberglass the connections and glass over the cells? I mean, it doesn't have to be really thick, and if a section or cell went dead I could bust it out in about the effort it would take to take apart a panel. Maybe tester leads could be left exposed somehow so I could pinpoint the offending cell? I don't know, what do you think?

Or what if I, after securing the leads (either for a section or for each cell), suspended it in a shallow bath of polycarbonate (which probably has better light and lasting properties then epoxy), and then epoxied these on as tiles? Wouldn't this be the quickest, most cost effective route for making something that wouldn't oxidize or be damaged by anything but extraordinary damage? I've seen pieces of that polycarbonate that must be from the 50's or 60's that is in full light and still looks like glass. Now epoxy would probably yellow too fast to be worth it.

[Jeff7]

Can't be all that old - polycarbonate was only developed in 1953. You sure that stuff is in fact polycarbonate?

As for suspending the cells in something, either epoxy or polycarbonate - there is expansion and contraction to worry about. And then there's the problem of impacts, like from hail. The solid embedding material would still need protection, otherwise the impact force would be easily transferred into the cells, cracking them.


I've heard that epoxy will contract as it hardens - this would also crack the cells.





Evergreen's site says that they use ethyl vinyl acetate and Tedlar. EVA is some kind of soft, flexible stuff, as best as I can tell. That's probably the encapsulant. It would absorb impact forces, as well as pressure from the contraction of the glass in cold weather.




Tedlar is a DuPont product...it appears that it is used as the backing material.

Yes, I can tell you that epoxy, unless specially made to remain clear in UV light, will yellow, and quickly - maybe in only a day or two.

[ghurd]

Spray-On / Sherma Williams makes a 'non yellowing' coating for electronics.

I have used it on PCBs. Didn't yellow, but not much exposure to UV either.

G-

[crag]

Well, then late fifties, early sixties maybe. If that is polycarbonate. My family has had a used car lot since the forties, and there are this match book they dropped in that stuff that has been sitting in the window since then and it looks perfectly clear, and to me it looks like the fifties, maybe it is the late fifties.

Yeah, I'm not sure what the impact rating is for that stuff, or what thickness would be required to make it strong enough to use, or if it would be cost effective to use in hobby store quantities. But it would seem that some plug-in play resin solution might allow one to expand their array gradually over time and possibly gain from the use of these less expensive blemished or factory second cells.

From what I've read on the net the people listing these cells on ebay have raised their prices quite a bit, is that correct? Has anyone looked into where they are buying them from? Like maybe contacting the factory and asking about buying them directly? Or since it seems they have them from various makers, maybe there is a wholesale source for larger quantities? I asked one of them for what they'd be willing to give for bulk quantities and they said they wouldn't do it because of what they could sell them for, and yet they didn't seem to have over 300 watts worth, so they obviously bought a bulk amount from someone. Maybe I should start this last part as a new thread. . .

[Jeff7]

The company is Evergreen Solar. Word from the guy on eBay is that they are lowering their reject rate and raising prices. A lot of the world's production of solar cells are going to Europe now, as a few countries there are building huge solar power plants.


And on top of that, there's a shortage of pure silicon now. The computer industry uses a lot less silicon for their products - a CPU die can easily be less than 0.25 square inches, whereas these solar cells are 18 square inches. So the computer industry can afford to pay more for the pure silicon that's available, leaving little for the solar cell industry.



Best bet to get solar cells, according to the eBay seller, is to get them by the ton. A lot of this is paraphrased from what I can remember being told. The cells are basically lost money as soon as they are labeled "rejected" - the companies don't want to spend any more money on them anymore. So you're probably going to have to arrange pickup of the things, possibly by the pallet full, so it might help to have a truck. And live near the factory, because you're probably not going to want to drive unprotected cells all over the place before you can sort them and sell them. And you'll need to talk to the right person at the place, to get clearance to do this kind of thing.



These various obstacles are probably the reason you don't see people everywhere selling second-rate solar cells.

[crag]

Is there a thread that deals directly with buying these cells from the company, because I couldn't find one and someone deleted the thread I started on it?

Well, besides myself, I actually am looking for larger quantities for use in a large community project, so tons or the truck wouldn't be a problem.

Are the moderators of this forum the people selling the cells on ebay, is that why it was deleted?

[crag]

Nudge-nudge-wink-wink

[pyrocasto]

No I'd have to say they arent. At least not all of them. If they were, they wouldnt delete the post either.

Everyone selling cells on ebay(evergreen's at least) got them from cusdn(our ebay supplier) and are just reselling them for more.

I've emailed a few companies and most say they sell their rejects off, but they are sold out at the time  so I cant purchase any. I would be more than willing to purchase a few tons of them(for the right price) and start selling like it used to be. Since now the prices are too high for anyone to make it worth their while, except for school projects and such. :-|

[ghurd]

I know of one company that is remelting all the rejects to reuse.

The cost is that high.

[crag]

Yeah, I can see it. Resource commodities are interesting. One day the landfill, the next people are selling objects strictly for their metallurgy content.

[orochi8]

Did you ever find anywhere to purchase EVA? Im looking arround, and so far I havent realy found any retail source for it.

-Orochi

[Jeff7]

I hadn't really been looking. I'm just going on the assumption that if we try to buy EVA (and even Tedlar) as individuals, it might wind up making for panels that are as expensive as the store-bought ones.

However, one flaw I realize with that is that I don't know how much of the cost of the panel the cells themselves make up.

[Jeff7]

Ok, just did a quick search on Google. Seems that EVA would be tough to work with, since it's solid at room temperature, and it looks like it needs to be melted in order to be liquid - not something like epoxy that can be mixed. One site says that it's a mixture of vinyl and polyethylene. This site says, "...Ethyl Vinyl Acetate, just like the cushioning on your training shoes."

One site I found indicates that the stuff is sold in powder form. So if that's true, you'd need a way of melting it first, and then handling it without encapsulating yourself. But hey, at least you'd be safe, and well cushioned for many decades to come.