Control of Moisture Ingress into Solar Panels

[Jason]

Found this link, and thought it may be of interest to some. It's research done by the National Renewable Energy Laboratory.

"During long-term exposure of photovoltaic modules to environmental stress, the ingress of water into the module is correlated with decreased performance. By using diffusivity measurements for water through encapsulants such as ethylene vinyl acetate (EVA), we have modeled moisture ingress using a finite-element analysis with atmospheric data from various locations such as Miami, Florida. This analysis shows that because of the high diffusivity of EVA, even an impermeable glass back-sheet alone is in-capable of preventing significant moisture ingress from the edges for a 20-year lifecycle. This result has led us to investigate ways to protect module from the moisture through the use of different encapsulating chemistries and materials."

http://docs.google.com/viewer?a=v&q=cache:LSjqorTw3U0J:www.nrel.gov/docs/fy05osti/37390.pdf+sylgard+184&hl=en&gl=us&pid=bl&srcid=ADGEESjmlFJNS1O-9aAxW03LQhpIzKJ6lwtXSibUY7CxgJBsUkiRaTk4bHsAUgO_B6xY7Rt16t08rLaud2m7EYKTK6MUtP0hvBu03fbxUVb431RZMEDaEHM4AZuCB-6iYGls40U30CWZ&sig=AHIEtbRxWLSo0IFmKgP-ammJHakkUZk9tA

[Mike90250]

Well, that tells a sad story. The good stuff is too rigid, and cracks/de-laminates. The flexy stuff lets moisture zoom right through. I guess the secret is to use a conductive grid that won't corrode/electro-migrate.

[dsnuffer]

Moisture

This is how I think I can control moisture. Drill a weep hole in the bottom center of the panel. Attached a PVC coupling with a screw cap and filled it with Silica. When I see moisture forming I discard the spent Silica , replace with fresh and I am good to go. What do you think? I live in Arkansas.

[Mike90250]

This is how I think I can control moisture. Drill a weep hole in the bottom center of the panel. Attached a PVC coupling with a screw cap and filled it with Silica. When I see moisture forming I discard the spent Silica , replace with fresh and I am good to go. What do you think? I live in Arkansas.

Maybe use a 3" access port, like they have in boats, to replace the silica . You can re-dry the silica in a 200F oven.

[netttech]

Too bad I didn't think fast enough. I could have strapped my panel to the deck to see how my ventilated panel handled the extreme fog we just had.

We were shrouded with fog for several days & it would have been a good opportunity to see how it handled the moisture.

I did place the panel outside to see what it would produce even in a pretty heavy fog. Surprisedly it did produce 30 volts. That's 3/4 of what it normally does on a sunny day.

Of course the panel isn't connected to anything...just a toy-project.

Jeff

[photovoltaik]

Nice post... interesting !

Thank you very much for your efforts!!

[rollandelliott]

confused.

I just glanced at the article,. read first and last paragraphs,

Seems that EVA is not good? but from what I've read so far that is how "real" solar panels are made?!?

Is Slyguard 184 the best solution then?

[Mike90250]

Is Slyguard 184 the best solution then?

After reading the date sheet for it yesterday, I'll say no. it is water resistant. that means water vapor will blow right thru it, just like any other silicone. maybe good for a couple years, but the moisture will build up in it to match the ambient. If you live in the desert <20% you will fare a bit better.

[rollandelliott]

all bad!

Thanks Mike, you seem to know a lot about solar so I appreciate your experience.
I know you recommend people buy premanufactured, but I'll ask anyways cause I love DIY projects.
There seems to be 3 popular ways of encapsulating Solar cells:
1. Glass-Cell-Slyguard 184-TPE
2. Glass-EVA-Cell-EVA-TPE
3. Glass-Cell-Silicone-glass
4. ???perhaps there are others I've only been researching for around 20 hours on this forum and the net. so I'm open to ideas.

This article seems to suggest that method#2 EVA is bad, you are saying method #1 is no good either and the article seems to say method #3 is bad as well. Yet there are many members saying methods 1 and 3 work great, at least after a year or so, maybe after 20 years they are all junk.

So there are no good ways of doing this??!?

What is the least "bad" then?

[Mike90250]

I just am saying the silicones are not insurance against water vapor. Maybe there is another coating that goes over it. If you can't stop water vapor, the panel is doomed.

[russ]

DuPont makes some stuff too - may have the same quantity problem though.

http://www2.dupont.com/Photovoltaics/en_US/products_services/encapsulant/index.html

Russ

[crusty]

In the end we are all doomed.

Hello Mike: I've been reading entries all morning and find it interesting and informative.
I live on a tropical island close to the equator - 30 degC every day, dry half the year and
wet the other half. Salt air corrosion is a real problem for any non-stainless steels. While
air temperature cycling is not much of an issue, I worry about panel temperatures cycling
between 25 degC at night and 50 degC at noon. None of the posts I've read make mention
of problems or experience with thermal expansion/contraction and how it affects the
edge joint/encapsulation issue. Do you or other commenters have any knowledge of same?

[russ]

Hi crusty - Welcome to Solar Panel Talk!

Interesting point - unfortunately I haven't the foggiest notion.

Russ

[Alan]

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.

[Mike90250]

The thermal activity pumps air in and out of the panel innards, and moisture gets trapped inside, usually. A bag of desiccant would need changing several times a year.