Vacuum sealed solar panels?

[Jeff7]

I've searched for this, without finding anything substantial, so here goes.

I have read about homemade panels developing moisture problems. This is sometimes solved by sealing the panel, however, this can lead to the buildup of high pressures when the panel is heated, possibly damaging various components.

So I'm wondering about adapting something like this to a panel, to suck some of the air out (not all, as this might crush some slightly curved solar cells), thus allowing room for the air in the panel to both expand and contract. With less air, in winter, the panel could still contract, without causing anything harm, and in summer, it could expand without causing explosive pressure.

Thoughts on this? Has this method been attempted before?

[Jeff7]

Wanted to add too, yes, I'm another buyer of those fine EvergreenSolar solar cells from eBay. My sister's in college in that area; maybe one time when she's making a trip between here and there, I'll do the driving, and make a stop off at Foxboro, and pick up some cells in person, and hopefully avoid breakage.

I just got a pound of the things, and here's the breakdown:

286. grams good (30 cells)
     
180. grams cracked
     
     

That's close to a 40% breakage rate. A lot of them had hairline cracks, which I found by lightly twisting each cell, listening for the high-pitched grinding of silicon on silicon. Most of the breaks were the bad vertical ones, across all the crossconnects. However, I did still wind up with a lot of sizable scrap pieces, which means that I have plenty for experimentation. I intend to make a small prototype with a few of these cells. Then I can also decide if it's worth a drive up to Boston from east-central Pennsylvania, plus the monetary investment of a few hundred dollars for more solar cells.

[tecker]

Removing all the air will work but the vacumm process pulls in on the Glass so this has to be a acounted for. If you try this post your results . I think that bringing the panel up 250 F with one end open and sealing then this will remove 90% of the moisture from the air that remains inside a a slight vaccum will exist after and the sealent will dry quickly  but you have to keep the temp above 200. Alittle silica gell packet at one corner can remove the rest .

[Ungrounded Lightning Rod]

Sucking out the air reduces the heat transfer, and losing heat is the big issue for solar cells.  Their output drops when hot.

I understand the main issue with deterioration is moisture.  If I were doing them I'd think about this:

 - Stick 'em to a metallic backing with an insulating barrier and two layers of heatsink compound.

 - Throw a little freshly-charged silica jell into the panel before sealing it.

 - Seal it in a hot dry environment (easy for me, with the desert house).

 - If I'm feeling fancy, purge it with dry nitrogen or canned dry air just before sealing it.

[pyrocasto]

I never thought of any of that.

I was going to let my panel get hot, open it up, and close it. But are there any other gasses that would not expand so much?

Also, instead of silicone I was going to use a rumber gasket around the edge. Would that now work?

[iFred]

Seems silica is all the rave, but is it? Nope I don't thing so. The problem is that the silica will indeed pull in moisture, but ask yourself where that then goes? Unfortunately the moisture ends up in a single place now, in the silica, which as soon as the temp rises or falls or the humidity changes or what ever the silica will release the moistures  and thereby causing the problem again. The idea of silica is actually a good one if it could eat the moisture or something, but it does not, it stores it, and that can only lead to more problems.

 

[tcrenshaw]

I'm using helium and it seems to work well. After mounting the glass against the panel using insulation seal AKA: weather stripping, I punch two small holes in the bottom of the seal with a hot soldering iron. I insert the tube for the helium into one hole, tilt the panel up and open the valve allowing the helium to enter the panel slowly. Since helium is lighter than air it goes to the top of the panel, pushing the air out the bottom. Hold a match, candle, lighter..etc near the open hole at the bottom where the air is coming out. When you see the flame go out, helium is escaping. I only had to do this a few times and learned how long it takes to fill a panel. Close the valve, remove the gas tube and plug the two holes. I use wooden dowels to plug the holes with. Since I'm sure I don't have a solid or perfect seal around the glass eventually the helium will escape. Using the plugs in the holes allows me to do this procedure at a later date if moisture becomes a problem again. Also since it's not a perfect seal, there's no worry about pressure build up when the helium expands in the sun light. Unfortunate part is of course that when it contracts it will pull in regular air and moisture, but that'll all be at the bottom of the panel.

The problem? Helium isn't that cheap. Well the helium is cheap, it's the disposable bottle that it comes in that costs. I don't know if I'll continue with this process. I have two panels that are open air with four vent holes. They do see some condensation but it doesn't seem to be a major issue, yet. One has the silica pack in it mentioned above, the other does not - no visible difference. I'm no longer putting the silica packs in.

I have modified my design since my first panel. My first panel worked great for a few days and then needed to be dis-assembled because of an over heating problem. It was a nightmare to pull apart (was completely silicon sealed). Now I can pull my panels apart if need be.

[RatOmeter]

Just pondering it and I'd think it would be better than nothing.  Best to dry the silica packet in low heat for an hour or so, to be sure it's as dry as possible before installation.

Another thought for those with Mig or Tig rigs (sorry for the alliteration), how about using welding gas (argon/argon mix) to purge the panel (I'm assuming it's quite dry)?

[Jeff7]

I wasn't looking to use glass for this - I was looking at polycarbonate. Glass...for one, I don't know that there are many good places around here to get sheets of it, and second, it's not easy to cut accurately. PC can be cut with a bandsaw.

I'm also hoping to use two sheets of PC per cell - the one extra sheet will be on standoffs, away from the main panel, as a shield against hail and other flying objects. It would also be removable and replacable, should it suffer serious damage. Granted, I might get slightly lower output from two sheets of PC, but it should be worth it if I don't have to replace an array from impact damage. I'll test just how much output I do lose, when and if the sun ever shines here again; it seems like it's been cloudy non-stop since sometime in November.

And I am not going to remove all of the air - I said I only wanted to remove some of the air, and just make it low pressure, not a vacuum. Maybe I should have put "Low pressure sealed" in the title instead of vacuum.

But if only some of the air is removed, then there's not enough outside pressure to crush the cells, while at the same time, allowing for the air inside to heat and expand, without popping the entire assembly apart.

I would also like to use a metallic backing on these cells, to serve as a heatsink. I'm thinking maybe a sheet of steel (that'd be pretty heavy though) or aluminum, with cross supports for rigidity. Maybe I could use a dab of thermal adhesive on the back of each cell, or maybe something like this, maybe 5 of them per cell - 4 corners, and the center. Or a combination of both adhesive (center dab) and 4 thermal pads.

[picmacmillan]

here is something i just came up with about moisture and condensation......when we go moose hunting in the north we build a shack out of plastic......if you used just one layer of plastic the tent will drop condensation all over the place when you turn on the wood stove  but we use 2 sheets of plasic and the condensation runs between the two and we have no problem with it on the other side where we are living.....i am going to take one of my homebuilt panels and try using an extra layer of clear plastic or glass just to see what may occur...i beleive from past practice the moisture can be diverted in this fashion....pickster

[ghurd]

Someone here not long ago took their panels to a glass shop and had them filled with gas and sealed.  Just like a thermopane window. Cost effective. He was happy.

Sounds like a winner of an idea to me.

Six or eight weeks ago? Wish I could remember who it was.

G-

[iFred]

I think the vacuum out and insert inert gas into space is a good one. The problem is keeping a vacuum and leaking of the gas. Plastics for fact do not do this well, they vent semi rapidly, the molecular structure is not designed for this. The second problem is bending. As the vacuum begins the plastic or glass will bend inward with the high probability of breaking the cells. I use 3/16 " spacers in my panels which are made of the tempered glass to avoid bends or other problems. If you visited my web site you will note the spacers placed evenly. Hope this helps.

[pyrocasto]

So what about two piece of glass(like yours), with some kinda seal on the outside, and spacers everywhere. Could you just take it to the glass shop and have it turned into a thermopane window like ghurd said?

[Jeff7]

This is probably the page you mean.

Wonder what kind of "glass place" he means?

That does sound like a good idea though; it'd be professional grade sealing then, and with inert, dry gas.

If I knew of a place like that nearby (I did inquire in that thread there as to the name/type of place it is), and a source of cheap glass, that sounds like a good way to go.

When everyone says "auto glass place" or something along those lines, what do you mean specifically? What are some store names I can look up? I'm afraid I really don't know the first thing about acquiring materials outside of conventional channels like retail stores.

[picmacmillan]

i just called a window factory and they didn't seem to enthusiastic or knowledgeable about gases either inert or not....i actually had to let him know that krypton and argon are group 7 gases on the periodic table which means they are not explosive like group 8.....anyhow,i would be interested to see where we could get such gases as individuals and i would have to refresh my memory or go back to my physics and engineering books to see what properties we are especially looking for in  this gas...one more note is the saleman said they use krypton gas...maybe this is cheaper to use than argon, or radon but that is just my assumption....pickster