Solar Panels and Condensation

[BCborn]

Hi!

I've recently purchased a couple of Trojan 6v 220 amp/hr batteries to give me LED lighting in my Yurt, which is off the grid. I have been messing around with the ins and outs of soldering solar cells together and have been trying to decide how to build a frame/casing for home-made panels. I noticed www.siliconsolar.com offer cells (seconds) as low as $1.60 a watt, seems like the best deal anywhere. I've also seen that on ebay they are sold by the pound, but several ads said they just ship in a big box, with some foam chips on top, so you know breakage WILL occur beyond what is already broken - which you have no idea. I don't know the translation between pounds and watts either LOL. Anyhow, here's my real question:

Condensation and panels.

Are commercially made panels actually made so that the airspace is a vacuum? Or do they breathe? We get a LOT of morning dew here, so condensation is a REAL factor. Some days small plants are literally bent over from the weight and stress of condensation alone, and temperatures can easily vary over 50F throughout the day.

Is it better to make a panel that breathes, or try and make it 100% sealed, and pull a vacuum afterwards?

Thanks for any critique!

[pyrocasto]

Well, everyone has different opinions about that. I say go sealed, but it will be harder to build that way. You will keep your cells a lot longer sealed though.

BTW, I've experienced about 68watts(50 cells) per lb. so far.

I think all my panels from now on will be sealed in siding vinyl which is garranteed 5 years outside, and just replace the the laminate whenever needed. I'm also contemplating sticking the vinyl on the back of the cells and just sticking the whole thing to a sheet of glass. That way it's protected against foreign objects and easy to clean.

[richhagen]

I made a panel and tried to seal it up with silicone.  It didn't work out so well and within a few months condensation and the resulting electrolysis destroyed the panel (or at least some of the cells inside)  For commercial panels, ther is no air inside.  The Cells are usually completely encapsulated in EVA, which is a polymer which is somewhat resistant to yellowing.  Some of the other folks here have made sealed panels with Butyl calk and had I think somewhat better results, and one fellow was going to fill the panel with oil, although I do not know how that worked out as there was some concern expressed about thermal expansion differences.   Rich

[georgeodjungle]

how about silica gel?

just a thought.

[John II]

I have seen and owned several different commercial brands of PV panels. They each appear to have been manufactured by laying the glass down and putting a layer of some sort of UV resistant liquid gel, then laying the pv cells on top of that, then pouring one or more thick layers over the backs of them, Then adding a plastic or glass panel to the back of them and encasing them in an aluminum frame.

This might be a terrible idea, and I have not yet built a PV panel, but what I think I might try, is to put the cells against the glass just as close as I can get them to lay.. make sure the glass and cells are warm and dry, then pour a UV resistant clear plastic epoxy over the whole thing. You would want to use "clear" because if it is a different color, it probably would seep in under the cells and cover the front of them.

The good thing about this, is it should really seal away the moisture. The bad thing is if your glass should break, so will your cells. Tempered glass would be better for this. On commercial panels, you can crack the glass and because of the soft silicon gel inside, they often keep functioning.

One other tip that might really help. The most vicious sealant I can find... and it is good stuff is Urethane Caulk which usually come in metal caulking gun tubes for about $12.00 per tube. I can only find it locally in the color of black. It's good stuff. Ever look in the bed of a new pickup and see they seamed all the metal with some sort of ultra durable material ? This is what they use. It can be found at most window repair centers.

John II

[Jeff7]

Problem is, silica gel won't absorb water indefinitely - once it's "full", you'll get condensation anyway. And if the sun manages to heat the silica gel enough, it'll release its stored water too, and there'll just be that much more in the air inside the panel.

[DanG]

John II has good info - but there is a good chance the epoxy will move as it sets up. When the Axial Flux wind generator folks use expoxy for stator coils they adjust the mix to prevent cracking, a slow cure avoids major cracking. Instead of a 4 or 8 hour cure allow it to extend to 24+ hours, etc. For cosmetique and waterproofing purposes epoxy can work but there are underlying problems.

Solar cells are more delicate then eggshells, if the epoxy heaves or shrinks it can  propagate flaws that pre-exist in the silicon wafer into into micro-cracks or whole splits of the wafer glass. Then the solar heating cycles will keep pulling and twisting the epoxy as sure as ocean tides and reduce power w/ cracking or snap off solder points on the back, or even open the circut completely.

Epoxy bedding was used succesfully when the PC cells were physically thicker then they are now, advances in the foundry processes make for thinner cells. I am tempted to try a thick (> 3/16") fiberglass circut board material as foundation (backer board) and encapsulating PV strings on top w/o using any cover glass - but it would be a utility panel for camping or field use, not to be used for permanent installation ...

[steak2k1]

Well.  First of and since this is my first post (not sure how to start a new thread..hlp needed there please..?), gotta say this is an extremely informative forum on a subject now becomming very dear to me. Just need to look at my power/nat gas bills to know why.

Just built first panel 40W.  Needed for Tent Trailer such that I am not stuck in one of those RV parks with everyone 10' from one another. And I like doing things for myself.

Aluminum frame (welded), cardboard covered closed cell foam backing, and silicone sealed.

problem is condensation as well. Am thinking of simply drilling a couple of holes in bottom and top ends of panel to allow natural ventilation (while adding a rain cover to the holed areas.  thinking that it should work...heat rises..??

I have been doing plenty of reading and some searchin ... some awesome panels I have seen.  Next set of panels will be made with Aluminum frame...am thinking that picture frames are the ticket. With glass both sides.

comments greatly appreciated.

thanx and gald to be here.

stk

[Jeff7]

Welded aluminum frame? How'd you manage to weld aluminum? My reading indicated that the stuff is damn near impossible to weld to.

[steak2k1]

Well...I am a journeyman Welder/Welding Eng Tech (30 yrs),and work for ESAB as a Sales Mgr for S. Alberta Canada. Most aluminum alloys are readily weldable. There are some that are not because they artificially age and become harder as time passes..in particular those types used in aircraft..see a weld on an aircraft in the wing, ...run..!!

Aluminum can be welded with most of the most common processes including Stick (not very good), Oxy-Fuel - tricky, and most commonly these days with the TIG or MIG process.

Most common filler metals are:

4043. :  An alloy of 5% Si (silicon) Remainder Al.
      
5356. :  An alloy of 5% Mg (Magnesium)w/ .12-.15 of Mn, Cr, Ti with the Remainder Al
      
      

Now that is all fine and dandy..but I have seen some panels made with extruded/anodized frames that are typically used in picture frames...and I'll tell ya, they look and seem to work great.!  With a lot less hassle than welding one together. Likely cheaper and much easier to put together.  One can buy 12'- 20' lengths of this product, use a carbide tipped - closely spaced blade and cut it with a mitre saw quite handily to get your 45 deg corners. Blades are around $100.00 CAD but well worth it.

rgds,

stk