Solar Panel

Discussion in 'The Projects Forum' started by Dalaran, Jun 13, 2011.

  1. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    I purchased some solar cells off ebay the other week and created a solar panel out of them this weekend. I put 36 in series to create an 18V panel. They are cells with chipped corners and such, more of just a practice vehicle for my first time. The specs are below:
    These 3"X6" SOLAR CELLS rated at:
    0.5V
    3.6 Amps
    1.8 Watts each.



    After I put together the panel I measure in direct sunlight
    Voc = 19.5V
    Isc = 1.85A

    It seems voltage is good but the current is not as much as I would expect. Since the voltage is correct is seems that all of my connections must be fine… Can someone suggest why I am getting only ½ the expected current?
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Firstly, the panels have not stabilized yet. This will take about a week of exposure to the sun. Secondly, how did you 'short circuit' the panel output?

    Also, what did you use to interconnect the cells? What gauge was it, and are you SURE there is not a resistive connection somewhere due to insufficient heat when soldering?

    You can isolate the two series strings and investigate their output seperately, thereby confirming a correct hookup if both strings have identical current outputs.
     
  3. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    Thanks for the thoughts. Would a resistive short not also show me a drop in voltage not just current? I used the tabbing wire provided with the solar cells. On the backs of the cells there are 6 spots for the tabbing wire to attached... I did solder all 6 of these but what if one had a poor connection? Would the other 5 still be enough?


    The panel is made of 4 rows of 9 cells. I checked each row individually for current before putting them together. However now they are glued in place and cannot be pulled back up. I guess I should have checked them for current as well as voltage before putting them down.

    To short circuit them I simply connected an ammeter between the positive and negative terminals of the array.

    Does the Isc of the panel actually increase once the cells have ‘stablized’?

    Thanks!
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Did you check the cells before assembly? The wattage of the cells will be closer to 1.25 W each, not 1.8W, if the specs are correct. As they stabilize, the power out will fall a bit.
     
  5. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    I checked the voltage of each row before assembling, but not each cell individually or the current. I will try to measure the current in each row when I get home today to determine if it is consistent or just one bad cell causing the drop.

    Thanks.
     
  6. gerty

    AAC Fanatic!

    Aug 30, 2007
    1,153
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    The solar cells I've seen are grossly overrated and never put out the avertised current. I have one at my desk now, rated at 13.5 v@ 1.19a and a 1 amp load will draw the voltage down to a few volts.
    It might work great on the Equator at high noon...
     
    Last edited: Jun 13, 2011
  7. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    Right... figured it was possible that the rated current may never happen... I also thought that 50% of the rated was a little low. I guess the true test will come when I can isolate the cells and measure the current for each to see if they are all around this level.

    Thanks all for the quick replies.
     
  8. russpatterson

    Member

    Feb 1, 2010
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    I've never seen a panel or cell that needed a "break in period" they always just put out at or above the rated power. I would guess that one of the cells got cracked when you soldered the tabs on and is limiting current. It's a weakest link kind of thing with the current.

    As not fun as this sounds. Try to unsolder or cut the tabbing so you have two sets of cells and test those. I expect one will perform as expected and the other much lower, then you can continue to hunt for the bad apple.

    You may be able to just connect your test probes at different nodes (tab between cells) to locate the issue.
     
  9. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    Will do. Hopefully I'm home tonight before the sun falls!

    I don't think that I should need to cut any of the tabs yet... Just shorting the cells neg/pos with an ammeter should give me the current measurement I am after. Thanks!
     
  10. debe

    Well-Known Member

    Sep 21, 2010
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    With the current pricing of solar pannels one wonders if its worth while trying to make one as the cells are quite fragile. Have never seen cells that need to be broken in, they either work properly or they dont. Also suspect cells sold individualy very cheep may be rejects that are not up to specs.
     
  11. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    There is not a break-in period. the first10-20 hours of operation the cells simply show much wider variations than they do after the cells have been exposed to solar flux for a time.

    The point being that the current may become a bit better after this time has passed. As someone else stated, the usual scenario is for the current and voltage to drop some after this initial time period.

    Most likely one of the cells in your series has a problem that was not visible to the naked eye. You really should have checked each individual cell before connecting them since they are factory 'seconds'. Now you will have to do some troubleshooting(time waster) to find where the problem lies.

    Great job on building your own though. More people should try it.
     
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