Repairing solar panels

Hi Folks,

I have a problem with some solar panels that I have recently aquired. They are factory reject 24 180W.

The problem is the j boxes at the rear of the panels have been "ripped off" with only the tabs or what is left of the tabs remaining. My guess is that the j boxes have been placed on the panles prior to visual and electrical testing and the J box has been ben removed as the only useful part of the panel, that the factory can use.

I have soldered new tabs onto the back of the panels but can not figure out how to connect them so that they give me useful current.

The panels have four tabs on the rear, between which should be connected 3 diodes.

As I do not have the diodes (in the post) I am trying to connect the 4 tabs together in various fashiones in order to get a useful 24V.

I have connected 2 of the inside tabs together (middle two) hoping that the outside two tabs would then give the rated 7 amps at 24V. This is not the case I get various voltages (could be light conditions around 12V / 14V with 14 amps, Great if you need a 12 panel. Some other panels that I have connected together in the same fashion give me 18V and 7 amps! where is the extra 9V hiding?

The truth is I am now more confused than I was before I started.

My big question is:

Do the bypass diodes in the back of solar panels serve any other purpose than the shading and hot spot thing?

How should I be wiring these four tabs together?

I have worked quite a bit on solar project but have never had to rebuild a hastely deconstructed panel.

Any help would be appreciated



David, solar panel rich several volts short of a picnic

Comments

  • wingnutter
    wingnutter Registered Users Posts: 12
    Re: Repairing solar panels

    Hi,
    Furhter to my above rantings.

    Forgot to mention something, that has just come to me. I am testing the solar panels on a 12V battery without a charge controller just an amp meter and voltmeter

    Is it the test procedure that is wrong? Tomorrow I shall use a 24V battery and a charge controller.

    David
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Repairing solar panels

    First, they are defective panels, and may never put out much, or only one set may work.

    Before you add diodes, you have to figure out which tab is what, there's likely several strings of cells, and you have to "reverse engineer" it's configuration.

    Put the panel in light and start probing with a meter, that's the only way, unless you can find a working panel, and see what the wire layout is.

    no batteries or charge controller needed, just a multi meter. Check for volts first.
    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 ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • wingnutter
    wingnutter Registered Users Posts: 12
    Re: Repairing solar panels

    Thanks for the quick reply, I have been trying to figure out where the tabs go, but it is not easy as the Tedlar hides them. I have broken a couple of panels in transport so maybe I will cut into them and do the de engineering you suggested. It is not easy half an hour of hacking with a stanley knife gets you nowhere. It is not untill you do some cutting of solar panels that you realise how wel they are put together. You are correct about the posibility of them being shorted or open circuit and otherwise broken, "reject" but hey 200 panels for the asking I have to give it a try! Free charging
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Repairing solar panels

    NO NO don't cut into the panels

    Just use the meter to probe the 4 tabs.

    Visually look at the front, how many rows, how are the cell-cell ribbons run......... figure it out from there. No cutting till you find out the bad sectors.
    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 ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • wingnutter
    wingnutter Registered Users Posts: 12
    Re: Repairing solar panels

    Thanks for your comments

    I was going to cut into the broken ones for some exploration work. However, I am not too worried about cutting into the panels as some of the tabs have been ripped back to the ribbons and the backing has been destroyed in the process. Breaking these panels any further would be quite difficult.

    It is quite hard to figure out where the ribbons run from looking at the front of the panel, harder to unsterstand the why bit. Once I understand the why I can find the soulution.

    In your opinion what should the voltage readings be between the four tabs?

    According to the manufactures spec sheet the panels have 48 cells in series. Why four tabs then and not just 2? :confused:

    The open circuit voltage is 30V and the closed circuit is 23,7V (from spec sheet)

    Any feedback at all is more than apreciated
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Repairing solar panels

    Four tabs: A, B, C, D
    Systematically measure Voltage between tabs: A to B, A to C, A to D et cetera.
    Various combinations will read +V, -V, or 0V
    Within any panel some cells are connected in series to boost Voltage. These series strings are then connected in parallel to boost Amperage.
    It is simple, basic, straightforward wiring - that requires tedious diagnostic work to figure out. :roll:

    Edit to add; since these panels are known defective, don't expect the readings to be better than zero or sufficient to be of any use. There's a good reason they went to scrap. Can't really fix broken panels (although everyone keeps asking about it).
  • NEOH
    NEOH Solar Expert Posts: 74 ✭✭
    Re: Repairing solar panels

    I suspect 3 Series Strings ...

    A-to-B will be the 1st 10 Volt string with a Bypass diode
    B-to-C will be the 2nd 10 Volt string with a Bypass diode
    C-to-D will be the 3nd 10 Volt string with a Bypass diode

    Finally, A-to-D will be the overall output = 30 Voc.

    Do all of your initial testing Open Circuit (no loads, no batteries, no inverters, etc).

    Normally, you do not connect any of the leads together, they are present for conection to the bypass diodes.

    If you have one bad string (AB, BC or CD) you could short that pair of leads together to allow the rest of the panel to operate at 20 Voc.

    Two bad strings and you have a 10 Volt Panel.

    Three bad strings and you have "Modern Art".


    {A} + String #1 - {B} + String #2 - {C} + String #3 - {D}
  • wingnutter
    wingnutter Registered Users Posts: 12
    Re: Repairing solar panels

    Many thanks Neoh / Cariboocoot
    http://forum.solar-electric.com/images/smilies/teeth_smile.gif
    That answer / reply is perfect, just what I was looking for. I have tested lots of the panels, 50% have only 20V the rest test ok. I have fitted diodes to them and they are performing great. For how long only time wil tell. I never found any Modern Art, but I might just make one of the 20V panels into a coffee table!


    Wingnutter