Control of Moisture Ingress into Solar Panels

[russ]

the thermal expansion between 77 and 120 degrees f (25 to 50C) is not that much for many materials.....and I wouldnt' worry about it. much worse when things freeze up in the north.

there is a post in the forum from a guy that made his own panels in ecuador sucessfully with out encapsulants at all.

the thermal expansion is not that much for many materials? A meaningless statement. The comparison to colder areas is accurate though.

ecusolar (Joe) in Ecuador is in a very dry area - not quite the same as a tropical island. Joe has pointed this out quite carefully.

The affect of salt depends on your proximity to the water. I am about 1 km from the bay and on a hillside (70 meters elevation) - there I see zero corrosion on aluminum window frames or balcony hand rails.

Russ

[Alan]

obvioulsy we are talking about glass since that is what the cells are bonded too a quick google search reveals little change at those temperatures.

http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html

gives coefficients
Calculating Linear Expansion

below from http://www.answers.com/topic/thermal-expansion
The linear expansion of a given solid can be calculated according to the formula δL = aLOΔT. The Greek letter delta (d) means "a change in"; hence, the first figure represents change in length, while the last figure in the equation stands for change in temperature. The letter a is the coefficient of linear expansion, and LO is the original length.

Suppose a bar of lead 5 meters long experiences a temperature change of 10

[russ]

I meant the way you stated it - for most materials - I know how to calculate the rate of thermal expansion quite well.

Your comparison of the cold north countries temperature difference was apt.

Russ

[sbkenn]

I wonder if the marine caulking compounds, usually polyurethane, would work to seal around the edges of a laminated panel. The cells would need to be bonded (EVA ?) to the front glass for heat dissipation first , or maybe bond them to an aluminium oxide or other thermally conductive substrate behind. AlClad is a term used for an alloy with a layer of pure aluminium which oxidises to protect the alloy
.

[Mike90250]

I wonder if the marine caulking compounds, usually polyurethane, would work to seal around the edges of a laminated panel........

Not likely. Very few caulk, paints, or epoxies can seal tight against water vapor. Water vapor only needs a day to penetrate 1/2 inch of silicone caulk, that's what cures it. Generally, a "ring" of EVA is used to seal the edges in the lamination process, keeps the chemistry simpler. The metal rails may be "glued" on with silicone or epoxy, but it's used as glue, not vapor barrier. EVA was designed to be vapor proof (and Tedlar backsheet too).

[wilco]

Certainly an interesting read - thanks for posting Jason. And a big thanks of course to everyone else who has contributed to this thread and others on this site - I've certainly learnt a hell of a lot.

What actually bought me to researching panel construction etc and then this thread was the problem of water ingress into my existing panels. They're actually commercially made panels (about 4 years old) and mounted on my campervan. They're supposedly warrantied for 10 years but the supplier is unfortunately not coming to the party as far as replacing them is concerned, stating that campervans are a lot harder on them (constant movement, occasional tree branch etc) than when they're sitting on a house roof.

Anyway, with the possibility of getting warranty replacement panels looking slimmer by the day, I'm considering what I can do with my existing panels. I've currently come up with two options:

1. One was along the lines of what dsnuffer and mike90250 (posts 3 and 4 above) were suggesting - i.e. cut one or several holes in the backing sheet and bottom layer of EVA of each panel (obviously in the "cell-free diamond" areas - i.e. not under the actual PV cells ), gluing a small box around each of these holes and filling these boxes with a silica gel bag or other desiccant. For this to work, all the PV cells would obviously have to share the same air space and herein lies my question. After the top/bottom layers of EVA are cured during panel construction, does each individual PV cell end up residing in it's own pocket of air (i.e. effectively surrounded/wrapped by EVA) or do the two EVA layers effectively become a big plastic bag, containing all the PV cells and allowing the air between the PV cells to move about?

Also, has anyone actually tried this idea and witnessed a big success/fail?

2. If the above idea is a total dud, would it be worthwhile stripping down the panel completely and rebuilding it or would it be pretty much impossible to break the EVA down and get the panel to pieces somehow without lots of breaking glass, PV cell shrapnel etc exploding around me in a fiery blaze of silicone doom (maybe a bit overdone but you get the idea...).

Anyway, thanks for taking the time to read this and any comments, ideas etc on the above would be greatly appreciated!

[Mike90250]

The EVA is applied like a sheet of plastic wrap, between the glass and cells, and is vacuum heat bonded, to remove any airspace in there. There is often another sheet of EVA used to attache the Tedlar backsheet, again with vacuum heat bonding at the same time the front side is done. So taking a panel apart, is not going to be easy and not likely successful unless you find a solvent that dissolves EVA

[wilco]

Thanks for your post Mike90250 - much appreciated!

Mmmm... Having done further research, it appears that the EVA is only about 0.5mm thick and provides an extremely good bond once cured, so as you say, there obviously wouldn't be much of a chance of disassembling a panel successfully without a really good solvent. Bummer....

I suppose the question still remains as to whether the top and bottom layers of EVA would have enough stretch in them to also vacuum seal each of the PV cells individually during the vacuum heat bonding stage? Or would the bonding process simply create a vacuum "chamber" in which the bulk or all the PV cells reside? Looking at the panel directly, it doesn't look like each of the PV cells is individually vacuum isolated but I suppose the EVA is so thin and clear that you wouldn't see it visually anyway.

If the cells ARE individually vacuum isolated, I could probably still create numerous holes in the backing sheet/bottom EVA layer to expose each of the individual PV cell chambers that have moisture in them. Then create a a new backing sheet with a good size hole in the middle, glue my desiccant box to this hole, place the new backing sheet in the frame but only seal around the edges of the backing sheet, rather than gluing the whole sheet down. Hopefully over time, that would dry out the PV cell areas affected by moisture...?

[Mike90250]

Thanks for your post Mike90250 - much appreciated!

Mmmm... Having done further research, it appears that the EVA is only about 0.5mm thick and provides an extremely good bond once cured, so as you say, there obviously wouldn't be much of a chance of disassembling a panel successfully without a really good solvent. Bummer....

I suppose the question still remains as to whether the top and bottom layers of EVA would have enough stretch in them to also vacuum seal each of the PV cells individually during the vacuum heat bonding stage? Or would the bonding process simply create a vacuum "chamber" in which the bulk or all the PV cells reside? Looking at the panel directly, it doesn't look like each of the PV cells is individually vacuum isolated but I suppose the EVA is so thin and clear that you wouldn't see it visually anyway.

If the cells ARE individually vacuum isolated, I could probably still create numerous holes in the backing sheet/bottom EVA layer to expose each of the individual PV cell chambers that have moisture in them. Then create a a new backing sheet with a good size hole in the middle, glue my desiccant box to this hole, place the new backing sheet in the frame but only seal around the edges of the backing sheet, rather than gluing the whole sheet down. Hopefully over time, that would dry out the PV cell areas affected by moisture...?

It is likely simpler to get new panels. Once you touch a knife to the used panels, the warranty is void. The dealer may be feeding you a line of BS about mobile use, contact the next higher up - the Distributor or Mfg to try to get that resolved.

The bonding agent you attach the desiccant box with will have to be a low water vapor transmitter, otherwise, you are simply drying the air behind the panels.

[JSchnee21]

Port all of the panels and sparge with dry nitrogen or argon to a slight positive pressure (-: Guaranteed to cost more than replacing the panels every 10 or 20 years. Or use higher quality interconnects that won't corrode.

[J.P.M.]

Port all of the panels and sparge with dry nitrogen or argon to a slight positive pressure (-: Guaranteed to cost more than replacing the panels every 10 or 20 years. Or use higher quality interconnects that won't corrode.

And probably won't be as vapor impervious as new panels either.

[JSchnee21]

Impervious no, but by keeping the panels under slight positive pressure with a dry, inert gas (continuously, not like sealed windows) any moisture that does ingress will be quickly dried and displaced by incoming dry gas. Now I just need a large LN2 dewar and Airgas to refill it once a month (-: Obviously just kidding. Totally not cost effective.

[wilco]

Hi Mike90250 - thanks again for your response.

Unfortunately, I can't go higher up the food chain as that would be China - the crowd I bought them off are a distributor/retailer in this country. I'm suspecting that they're feeding me a load of BS too but without taking it to a small claims tribunal and trying to "prove" some sort of case under the Consumer Guarantees act in this country, I'm a bit screwed. So really, cutting up the backing wouldn't be voiding a warranty anymore as they've pretty much already said that the warranty is void anyway...

As you say, it's probably easier and cheaper in the long run just to buy some new panels but it just seemed such a waste to throw away $500 worth of panels that are currently still working (but probably won't be soon) without trying to remove the moisture in some way.

Or maybe (as suggested by JSchnee21) I'll just strip the backing/EVA off the back of both panels, glue a new backing panel on each panel with a 2-3cm gap between the new backing panel and PV cells (to create a gas chamber) and connect each panel to a portable Argon dewer which I could tow around with me on a trailer. Problem solved!

[Mike90250]

The LN2 Dewar is both common and cheap. The boil off gas will be more than enough to keep the panels purged. No need for expensive argon

[wilco]

Hi - thanks again, Mike 90250!

Was thinking that helium might be another good option. Any party place will sell you a tank of gas and I'd probably even get better mileage due to my "balloon panels". Could even sell party balloons as an extra income earner while I'm on the road!