Solar Cells - A simple Question, I think?

Discussion in 'The Projects Forum' started by iONic, Apr 10, 2009.

  1. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
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    In the circuits below I connected some solar cells both in series and in parallel.
    1) Are my numbers correct?
    2) Is there any drawback to circuit 2, except for the reduced voltage?

    Thanks
     
  2. pilko

    Senior Member

    Dec 8, 2008
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    Your left circuit should produce slightly over 24V,and the right circuit produce slightly under 24V.The actual voltages and currents will depend on panel type,panel efficiency,and panel internal resistance.
     
  3. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
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    OK, I didn't expect precise outputs. I think I was looking for any negative outcomes as a result of such hookups. In other words are they generally acceptable means of configuring solar cells? Should diode be used in any of these configurations? The end game is to use as many small solar panels as available to 1) Keep the voltage at or above 13.8V and the current as high as possible for the charging of 12V Lead acid batteries. I am aware that it would not be the optimal charging scenario, but am looking to maintain and use some older batteries.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    The diagram on the left is OK, but the one on the right isn't so good. You'll have the two 24v solar panels on the left "fighting" the 18v panel on the right. This will cause heating, and solar panels lose efficiency as they get warmer.

    If they are SLA batteries, don't charge them faster than 1/10 of their AH rating. 1/20 of their rating would be much better. Charging ANY lead/acid batteries too fast will cause them to heat, reducing their lifespan. Charging gel-cells too fast will cause pockets to form in the gel, permanently reducing battery capacity. Overcharging lead/acid batteries for a short period of time is occasionally performed as an "equalization charge", but overcharging a gel cell battery will quickly kill it due to the formation of gas pockets.

    You also need a mechanism to prevent the battery/batteries from discharging through the solar panels when their voltage drops lower than the battery voltage.

    You'll also need something to either maintain the batteries at float voltage or disconnect the solar cells when the batteries are fully charged.
     
  5. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
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    Sgt.
    Not mentioned previously is the fact that I would be using a Solar Charge Controller SCC3 from cirkits.com thus taking care of much of the battery harming properties inherent in using no controlling mechanism whatsoever.

    I have another solar panel that produces about 7V that I could place in series with the 18V solar panel to approximate 24V. All these panels combined will not equal 1/10 of the batteries AH rating and may get to 1/20.

    I really need one larger solar panel, but not in these difficult times.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    The circuit on the left shouldn't pose a problem, as long as you're using a charge controller.
     
  7. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
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    I had the circuit on the right (circuit 2) connected via the Charge controller in the sun much of the day and did not notice any warm or hot parts at all. Perhaps given the time of year, early spring, and with a breeze everything was cooled. I will stay shy of this circuit, especially with any larger solar panel construction.

    Thanks
     
  8. thingmaker3

    Retired Moderator

    May 16, 2005
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    PV cells of different voltage in parallel will average.

    PV cells of different current in series will be limited to the lower source current.
     
  9. italo

    New Member

    Nov 20, 2005
    205
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    solar cells are like batteries and they are not created equal therefore one can source the other can sink current into each other. either add a diode in series or a very small resistor in series to equalize them.
     
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