Encapsulating with EVA

[nayubis]

Would clarify, please, when you said "the bag was vented"
...when the pressure got to 15psi the bag was vented and the pressure was increased to 20psi ...
How do you vent the vacuum bag when it is inside the autoclave @ 15psi?

Thanks for the great thread!! You're a big help.

[Mike90250]

Sorry, I didn't see any units in your temps, so I thought they were C. I'd figured panels toasting on a roof would easily see 180F in the summer, so I figured you had to bond them together hotter than that.
Rosin core, tin/lead has 80 years of solid history.

[Sandman57]

EVA manufacture cure specs

This is the info that the vendor who sold me the EVA gave me for a cure cycle. They were not clear on the timing but did give me some temp guidence.

"The press cycle should start when the sandwich has deaerated
to 1 Torr or less, and the encapsulant has
softened (encapsulant temperature of 130-150

[Sandman57]

Oops

I meant 0.5v 1.7W 3"x6" cells

I used a rosin flux, type RMA pen to solder the tabing wire and a small amount of rosin - core solder on each bus wire.
Should I be using a different flux/solder?


I gently cleaned the cells and glass with alcohol prior to bonding with EVA.

do you really mean 95c as my temps were degrees F

I was origionally thinking that the EVA might need 250-350F but what little I find seemed to indicate lower temps.

[Mike90250]

Thanks for the update, and the excellent walk thru.

I think I would let cool till 95c, and then remove, my concern is thermal shock to the tempered glass from the "cool" air, and most plastic sets up/softens right at 100c.

Did you solder with lead free solder, or standard tin/lead? Rosin flux, water base flux, cleaned or uncleaned?

I've never heard of a 1.5V cell, are they 3 cells factory stacked ?

[Sandman57]

I encapsulated my first panel today with EVA and Tedlar. I soldered up 36 1.5v 3x6 cells to get a 60watt panel. I have access to a vacuum pump and autoclave so I wanted to see if I could do a profesional grade encapsulation. The laminate was stacked as follows:

1. Glass
2. EVA sheet
3. Solar cells
4. EVA sheet
5. Tedlar Backing

The laminate was placed in a vacuum bag and the pump drew a 27hg vacuum. This sucks all the air out of the bag and squeezes the laminate together.

The bag was placed in an autoclave and heated to 175 deg and pressurized. When the pressure got to 15psi the bag was vented and the preasure was increased to 20psi (i.e. 20psi outside the bag, one atmosphere inside the bag) and was left for 20 min. Pressure is preferable to vacuum becasue any air inside the bag is compressed though the vacuum pump should remove 99.9% of the air.

I wasn't sure what the correct pressure should have been but I was nervous about the glass cracking or the cells splitting so I didn't increase it any further. I let autoclave cool to 135 and then removed the laminate.

This process seemed to work well. The cells are flat against the glass with no air bubles. The EVA seems to cure clear and bonds the cells to the glass and the Tedlar to the back. Tedlar is an opaque smooth plastic sheet that should keep moisture from migrating through the EVA and into the panel.

The only thing I will do different next time is to let the pannel fully cool before removing the panel and possibly leaving the panel in longer at the max temp. I think taking the panel out at 135 degrees the EVA isn't fully cured and might be susceptible to delaminating.

Anyone out there know what temp/preasure/time the factories use with their laminating tables?

Regards,

Jack