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Thread: Encapsulating with EVA

  1. #1
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    Default Encapsulating with EVA

    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

  2. #2
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    Default

    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 ?
    Since the dawn of time it has been mankind's dream to blot out the sun.
    Montgomery Burns

    "Always listen to experts. They'll tell you what can't be done and why. Then do it."

    spreadsheet based voltage drop calculator:
    http://www.solar-guppy.com/download/...calculator.zip
    http://www.solarpaneltalk.com/showth...oss-calculator

    http://www.mike-burgess.org/PVinfo_2.html

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
    battery lugs http://tinyurl.com/LMR-BigLug
    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV || || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

  3. #3
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    Default

    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.

  4. #4
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    Default 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

  5. #5
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    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.
    Since the dawn of time it has been mankind's dream to blot out the sun.
    Montgomery Burns

    "Always listen to experts. They'll tell you what can't be done and why. Then do it."

    spreadsheet based voltage drop calculator:
    http://www.solar-guppy.com/download/...calculator.zip
    http://www.solarpaneltalk.com/showth...oss-calculator

    http://www.mike-burgess.org/PVinfo_2.html

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
    battery lugs http://tinyurl.com/LMR-BigLug
    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV || || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

  6. #6
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    Default

    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.

  7. #7
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    In the process I used a vacuum pump sucks all the air out of the bag and forces eva and cells against the glass. The difference between inside the bag and outside air preasure creates this force. When I put the laminate into an autoclave and increase the pressure outside the bag the force on the laminate increases because the differential between inside and out increases. At 15psi I shut off the vaccum pump and open the inside of the bag to outside the autoclave. The 15psi presure creates sufficient laminating forces and "venting" the bag ensures that if there are any small leaks in the bag the preasure inside and out won't equalize causing the bag to stop pressing down on the laminate. This is a common technique for building composite laminates. Preasure is preferable to vacuum because any air bubles in epoxy resin will enlarge under vacuum and shrink under pressure.

    I used to work as a boat builder and have access to a large autoclave that is used to create carbon fiber hulls, masts, and components. When they fire up the autoclave they don't mind me putting a pannel in with a boat parts.

  8. #8
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    Default New question

    Can this be done without the autoclave? I have the Tedlar (TCP) but no info on how to apply it.

  9. #9
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    The Teddar is bonded to the backs of the solar cells with a sheet of EVA. The EVA bonds when it is heated. Commercially this is done with a vacuum press. If you don't have access to a press you might apply pressure with two aluminum sheets clamped together and heated in an oven. You would have to be careful to get even preasure and not to break the glass. The tough part will be to ensure you get no air bubbles without a vacuum.

  10. #10
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    Default Thanks

    Thanks for the reply. I guess I am out of luck. My panel is 52" x 96".
    Do you think the liquid encapsulating might work with enough pressure evenly applied as it dries?
    I have made several panels of increasing level of professional look. This one has an aluminum frame with the liquid encapsulation (took 4 jars). So far cost about $350 CAD so I figure it's a good deal if I can get it to last.

    Is it possible to buy a vacuum bag of that size?
    Cheers

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