Has anyone experience with expired EVA?

[nickskethisnikske]

Hi,

Has anyone experience with expired EVA? will it be useful or useless?

thanks

[dnix71]

How much heat did you use? I think the original specs were 265 to 270 F (about 130 C). It has to be vacuumed down, heated and held until it cools. One of the other guys here I sent some to can explain it better. Only the dull side is coated.

Heating to 130 C is the catch. If you have a heavy solid object like solar panels in a frame under the film it will conduct away the heat pretty well. Using a hair dryer or heat gun may be the trick, instead of building a vacuum oven.

[nickskethisnikske]

no your laminate is working, I did a small test

But I'm talking about real EVA, the shelf date was feb 2011, will it still work?
I could get it very low cost.

[Larsmartinxt]

I think it depends on how it's been stored. Tested some expired eva from work. and it did stick to the glass but not as good as the fresh EVA. The force required to peal off the eva from the glass was much less with the expired eva. I would still use it if I could get it at a very low cost/free

[dnix71]

If you use them on a solar panel it should get better with age as long as you vacuum them down first. Solar panels get plenty hot enough to cure EVA in full sun. I saved those rolls of one-sided because it's getting hard to get the stuff. It's used as a screen protector on cell phones and portable music players and web devices, so the competition has bid up the price and made the supply tight.

2011 isn't that far out of date as long as it's still on the roll and was kept indoors cool and dry.

[nickskethisnikske]

I will post results soon!

Today I picked up the eva foil, I did a small test and so far it seems promising. Tomorrow  we will see if it still sticks to glass.

keep you posted!

[nickskethisnikske]

Hi all,

I did some testing, but the 1,6 x 1m panels needed to much power to heat so I did a 0,5*0.35m  panel.

Not the best result, it needs longer heating and a bit faster vacuum for less air bubbles.

I will open a new topic in the "user diaries if I have time so you can follow my adventures  :p


( the eva I have only starts curing @ 80°C, the oven is reaching 100-120°C @ this moment. The datasheets says 15 minutes @ 150°C.

This was the result: (after 40minutes above 100°C, it is possible that I also had to many blankets/sheets around my glas for the vacuum)











Uploaded with ImageShack.us

[gww]

I did mine half at a time in an oven with no vacume.  My air bubbles were much smaller but I will say I have plenty of moisture in mine in the whether and don't believe they will hold up well.  Some have been out for over a year and they still work but ozz's in ghurds post at the top of the page are the way to go.  Good vacuming to go with the heat almost seems a must.
I like watching, thanks for posting.
gww

[nickskethisnikske]

hi gww, yes its all about  "fine tuning"

Today I was very bussy (again)...

I did some improvements here and there so here we go:

-I use backsheet material (mine has also aluminum foil inside) to make my vacume bag, it holds well around 300-330°C, above this the white layer inside will become sticky.
-I improved the isolation for quick heat up and holding its temperature.

I reheated the testpanel again in my oven today but I couldn't remove the bubbles.




I also have found a better solution to connect the air hose to my vacume bag: ( the picture will speak for itself I think) I made it myself, not to diffucult if you have the equipment and materials.
Now my vacume holds steady around 0.85 bar below atm pressure





Here you see the back of a panel, you can see the impact of the blanket


My second test panel, 99% perfect because of two air bubbles with a diameter of 1mm 




My 2 panels :



Nickskethisnikske

[gww]

Looks improved to me now you need to make it bigger and rock and roll.
Cheers
gww

[nickskethisnikske]

Hi what is the biggest cause for air bubbles?

Because this morning I had a good one again, but after that I had a bad one with bubbles.
My vacume is good so that couldn't be the problem.

With the first panel today I put on the pump after 16 minutes, and with the second one I did after 13 minutes, the first time the oven was not that hot (60°C) when I put in the bag, the second time it was about 82°C.


Is the problem to soon vacuming or to late vacuming? I guess to late vacuming ?


I hope I have my temperature sensors next week, then I can test different settings.....
Maybe my panel is not heating up evenly, I noticed that the bubbles are always on one side of the panel ...

[gww]

Can you vacume and cook at the same time?  It would make me want to try it in the sun under vacume and then if it wasnt clear, finish it off in the oven.  I am just throwing things out there if you are in an expermenting mood. 
good luck and please post your fixes.
gww

[nickskethisnikske]

Hi,

this is how I do it:

1) start heating the oven a few minutes
2) put in the vacume bag and connect the vacume hose
3) closing the oven
4) after a few minutes I start the vacume pump, the heating stays on
5) after 2hours the proces is finished

Today I did 2 panels again, but the problem stays the same, so tommorow I will get a few NTC resistors to monitor the heating proces inside the bag, I will stick them on the solar glass, and maybe a few on the backsheet.

I have another 40pcs small glass and broken cells to test, and since I have EVA and backsheet good for about 150m² for less then 200€ I can spend hours and hours and hours to optimize the laminating proces.

I won't start working the big panels before the small panels are perfect.

[gww]

I really think you need the vacume on before any heat is aplied.  I did mine with kithen oven or a hot blower.  The eva starts sticking with very little heat and once the bubbles are traped your job has gotten harder.  I think.
gww

[fabricator]

According to the method OZ uses you are doing it wrong, he puts the whole thing in the oven and does 15 minutes at room temp at full vacuum before any heat is applied.

[oztules]

Fab, thats true for summer and smaller cells.
In winter and for 6x6 cells, I found i needed to pull the temp up to 45 degrees C or more ( but less than 60C) and pull a full vacuum for 15 mins or so.

At cooler temps (winter etc) the EVA has little flex, and you may crack the cell with full vacuum and no temp.

When we heat it up to less than melt, but warmer than 45C, it is soft enough so that when the vac pulls down at zero, the buss bars sink into the EVA, and so don't encourage the cells to crack or fracture around the bus bars. (cells dont bend too well at all)

This way we get to pull all the bubbles of air out of the cell eva glass interface, any voids are left as voids without air, and so fill in with EVA  when the EVA actually melts.

If we don't get rid of the bubbles at pre melt, we will likely not get them to migrate out through the viscous molten EVA.

Thats also why it is very useful to get a perfect vacuum. We use the vacuum as pressure to keep it all bonded flat and together... yes, but also to get all the air to expel before the EVA melts.... after melt is likely too late...... but I have never actually seen this as it is inside the oven and wrapping at this point..... so anyone else with other ideas can chime in...... so this is really only guess work by me.... but it seems to work well.




................oztules

[fabricator]

Professional vacuum baggers just use two sheets of plastic and caulking tape to make the bag, they also use a piece of perforated plastic tube around the perimeter of the bag.

[nickskethisnikske]

Hi again,

Unlike you I'm not using the EVA from aliexpress.com, but I'm using a product from dnp solar, it's not that flexibel. And not as soft as the Chinese stuff. So my problem is that the solar cells don't sink in the EVA, the outer side of the panel is heated faster then the inside of the panel so bubbles get traped in the panel.

So:
On first side I was thinking my temperature was to high before I put on the vacuum but it's the opposite, my temperature is to low!  BUT, my panel is also not heated evenly! So, some area is perfect and some area is verry bad.

I did a temperature analyse and took some pictures of my setup: (I put 4 NTC resistors on my glass), because I wanted a simple temperature monitor I just made a box with 4 switches, the sensors are numbered so are the switches. On the meter comes the resistance of one sensor selected by the switches, in a table I can find the temperature that is related with the resistance.



So I took a guess, first I heated my oven untill my panel was reaching 30-35°C, I put on the heatguns with intervals so my glass was heated evenly. Then I did the vacume pump on for a minute and then I heated at full power. The result was a better panel then before.

Then I heated A NEW panel evenly untill it reached 50°C, then again vacume and then full power heating. The result was perfect! You can see the pictures.

[fabricator]

I think you need a good hard vacuum before you apply any heat, and you also need something on top that will withstand the vacuum long enough to get all the air out before it collapses.

[nickskethisnikske]

I think you need a good hard vacuum before you apply any heat, and you also need something on top that will withstand the vacuum long enough to get all the air out before it collapses.

I went that way before, but it will destroy all your solar cells, you really need to soften your EVA first otherwise it will crack your solar cells along the tabbingwire.

My last method is actually the same as oztules uses so I think this method is proven now!

I don't think you have expierence with laminating solar cells?

btw:  I use backsheet material for the vacume bag, I did already 8 panels with it, I just need to reseal it everytime with tape if I put in a new panel. My vacume holds untill the end of the proces. 

[nickskethisnikske]

Time for an update:

made some changes is my system:
I now heat the panels with Isachrome 60 wire on 24V about 25Amps on low 80 to 100 Amps on high power, depending on the voltage drop in the cable ( 25meters 10, 20 or 30mm²).
But I use 1h on 12V ( 600w) to 80°C for preheating and then 1h with vacume and 24V ( 17V and 80A) to reach 150°C.


some pictures:

7 with bubbles and now 14 with no bubbles:

















 

[gww]

nicksk
You seem to be coming along.  I didn't understand you wire heeting in the last post.  I thought I would throw something out while you are in an expermenting mood.  Might be crazy.  You know how some have said to feed power back into a panel as a way to clean snow off them.  I wonder if you did this just prior to starting the vacume if it would heat the solar cells hot enough to soften the eva and keep the cells from being broke when you start the vacume, before you put it in your oven?  What you are doing is probly much simpler and I don't even know if it would work.  just throwing it out there.
cheers
gww

[nickskethisnikske]

nicksk
You seem to be coming along.  I didn't understand you wire heeting in the last post.  I thought I would throw something out while you are in an expermenting mood.  Might be crazy.  You know how some have said to feed power back into a panel as a way to clean snow off them.  I wonder if you did this just prior to starting the vacume if it would heat the solar cells hot enough to soften the eva and keep the cells from being broke when you start the vacume, before you put it in your oven?  What you are doing is probly much simpler and I don't even know if it would work.  just throwing it out there.
cheers
gww

Yes everything is falling together now, I can't follow you, but you can see in my first pictures that I was using heatguns for the heating part.  Now I use the the wire heating, you can see it in the last picture of my previous post, but you have to look very good then you see all the wires from the left to the right .
It never came to my mind to use the solar cells as heating elements, I won't try that because I don't want to destroy them or melt the tabbing wire (desolder), but I think if you do that carefully it might work. My system is working properly now, so I keep walking this path. I'm past the experiment fase now, I have spent lots of hours to optimize the proces, so I just want to make solar panels now an seeing results


Here a few pictures:

[bart]

   Not doing any panel building, but I like to see what others are doing.
Looking good. Skimmed though this post but did not see how big that panel is.
Impressive.

[oztules]

Very nice Nick.

It is comforting to see that your final procedure is similar to mine. Looking at your product, you have it down to a  fine art.

Well done...... what size solar farm to you intend to build?....... I stopped after about 5kw. The chinese ones are just too cheap now to compete with (thankfully).


I like the pattern too



...................oztules

[fabricator]

OZ, what Brand Chinese panels do you use? This outfit has a good deal on Chinese panels but how could a guy order a skid of panels without knowing if they are any good? http://www.sunelec.com/

[oztules]

If they have UL or  TUV ,CE etc and ISO your good to go.

Just ask for the spec sheet.

Over here if they get CEC approval,  you need not look at the rest of the certs.... I suspect the UL certification does it there. Once attained, it assures the production and quality.
I doubt the home grown (american) is any better, and I could not see how they could be worse for that matter. The Australian ones can be no better / worse either...

It really is a simple process to get decent panels.

We bought 40 of these :
http://www.sunhopeaustralia.com.au/dloads/prd/proddload8.pdf

I got 24, Jamie the rest..... the 190 watts ones.

$1.00/watt delivered to a remote island (inc insurance), could have gotten cheaper, but happy at that price point. No need to screw em to the wall.



...................oztules

[fabricator]

Nice, that sounds reasonable, those panels are UL approved and several other things, so they ought to be good to go.

[nickskethisnikske]

Very nice Nick.

It is comforting to see that your final procedure is similar to mine. Looking at your product, you have it down to a  fine art.

Well done...... what size solar farm to you intend to build?....... I stopped after about 5kw. The chinese ones are just too cheap now to compete with (thankfully).


I like the pattern too



...................oztules

At this moment I'm planning to make another 5 with the 120pcs 3*6 inch cells, 2 with 135pcs 4*4 inch cells and 5 with 60 6*6 inch cells, this is what I have laying around. And another 6 small panels with perfect cells.

So it will be
6*180-200W
2*150W
5*240W
= +/- 2580W

small panels
21*15W
6* 21W
=+/-440W

I have already 800W of selfmade panels mounted on a roof, those were done with an ecapsulant (plastosil M-2000) between 2 glass sheets.

The plan is to build more if I can buy european solar cells (German) at about 0.25€/W. 
I spend about 500€ (incl transport) on total for:
- 182m² solar glass (110pcs),
- 300m² back sheet
- 300m² encapsulant
- 20liter silicone
- black frames for 13 panels
- silver frames  around 130pcs of 1 meter.

115€ for 1200meters tabbingwire
300€ for 1kw solar cells 3*6inch  (inclusive 1kg buswire and 10junction boxes, 20pcs mc4 pairs)
75€ for 50pairs mc4 connectors with 1meter cable
the rest of the solar cells I bought for about 0.3€/W

So let's say if I build 10 panels the cost would be:
-50€(frame, glass, eva,...)
-2€ cable
-60€ solar cells

=112€ for a 200w panel not bad I think


if I build 20 panels the price would drop to:

25+2+60=87€

ok there will be more costs so maybe add another 10-15€ per panel, ( I didnt count the heat wiring( 35€), and soldering iron, soldering wire, heatguns, and other tools/material because I already have them)

Of course I had the luck to buy most of the parts like framing and glass from a bankrupt company in an auction, otherwise It would cost me more than a new factory panel!!

[gww]

I bought 3000 watts worth of evergreen cells and when I was done I made about 2300 watts worth of homade panels.  I cut all kind of corners.  I didn't use junction boxes.  No frames.  Used three kinds of encapsulant.  liquid, eva and contact paper.  got them all in the weather.  The incapsulant and two of the contact paper ones are the only ones that dont have some condensed moisture in them.  I wish I would have read ozz's post on vacuming before I would have did mine.  Even with free glass and cheep prosses it cost me 50 bucks for 60 watts.  I just bought 2800 watts mx panels for 92 cents per watt delivered.  I wasn't impressed with the qualitie of the first 1400 watts I bought but the second 1400 watts were good.  All 2800 watts will probly outlast my home made except for maby the ones I used liquid incapsulant on.  I don't have big bubbles in my eva ones but I still see lines of moisture in the right weather.  I can't make crappy panels for what I can buy them for now.  I did have fun over the winter though.  If I ever get bored enough to do it again I'm glad I have a couple of threads to refer back to
Thanks
gww

[tecker]

I've been trying to get back to all my projects but too busy on the make money while the work is there . Winter slows things and I have spent time in the shop getting all the benches cleared . And projects ramped up I'll use the same thread I think .
 I like the small panels for a lot of reasons . Your work looks good No moister . Nice . I have gotten a supply of Silicon encapsulation  to finish 500 watts  the EV encapsulation has been proven good and the 25 yr life is UL approved.