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Thread: Solar Panels in series with different Voltages? What problems does this cause?

  1. #1
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    Default Solar Panels in series with different Voltages? What problems does this cause?

    Dear forum

    I am new to this forum, so I hope I am posting in the correct section.

    I have been studying PV installations in my region (most of which are excellent examples of bad practice )

    I have just studied an 8yr old installation. There are 16 Kyocera solar panels of 120W, connected in 4 paralell series for a 48V system. However many of the panels are only operating at half their Open Circuit Voltage- ie some panels give 16V or so and others only 8V.

    My question is- what effects will this have on the system? Can you have panels connected in series with such different voltages?

    The total Open Circuit Voltage of the system is about 60V- but with the batteries connected no current seems to be getting to the batteries (possibly a failed charge controller)

    Thanks very much for any information

    Larry

  2. #2
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    Larry to sum it up quickly here is the run down.

    For series panels the Imp ratings need to be matched because the lowest Imp rating in a series string will be limited to the lowest value. So let's say you have 3 panels rated at 10 amps @ 18 volts where each panels produces 180 watts. However you have a 4th panel rated at 5 amps at 18 volts @ 90 watts. When all 4 are connected in series you would have a string that produce 72 volts @ 5 amps for a total of 360 watts, when you think you should have 180 + 180 + 180 + 90 = 630 watts. So for series voltage adds, and current is limited to the lowest value in the series string.

    In parallel circuits current adds, and voltage is limited to the lowest value. So you need the Vmp and Voc to be matched. IF you put a 18 volt panel in parallel with a 16 volt panel, you get a 16 volt block of panels.
    MSEE, PE

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    Thanks for your reply SunKing

    That's what i thought. A strange thing though. I measured the voltage (in open circuit) over each of the bypass diodes in the panel. In the correctly functioning panels it read 8V and 8V over each bypass diode... summing to 16V (total for the panel). However in the failing panels, it read 8V for one string and almost 0V for the other string (hence 8V for the entire panel).

    Can someone enlighten me on why this would be?

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    Default parallel circuits

    Sunking, I have a similar question. I have 10 panels of the same type joined in series to give a v of 450v and another 4 panels of another brand joined in series to give 272.2v.(all the 14 panels orientate west) The installers have run both the series circuits and joined them in parallel before it joins the inverter. There are now 2 outputs with different voltages? I wonder if this is the normal way of putting them together. I have a growatt 4.2kw inverter. The other mppt is running another 8 panels orientated north.thanks for helping

  5. #5
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    Quote Originally Posted by newsolar View Post
    Sunking, I have a similar question. I have 10 panels of the same type joined in series to give a v of 450v and another 4 panels of another brand joined in series to give 272.2v.(all the 14 panels orientate west) The installers have run both the series circuits and joined them in parallel before it joins the inverter. There are now 2 outputs with different voltages? I wonder if this is the normal way of putting them together. I have a growatt 4.2kw inverter. The other mppt is running another 8 panels orientated north.thanks for helping
    This seems wrong, if I understand the description. This would bring the entire array down to 272.2 v (the 4 panel string)

    > The other mppt is running another 8 panels
    does this mean you have a 2nd inverter that is grid tie too ?

  6. #6
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    Quote Originally Posted by newsolar View Post
    Sunking, I have a similar question. I have 10 panels of the same type joined in series to give a v of 450v and another 4 panels of another brand joined in series to give 272.2v.(all the 14 panels orientate west) The installers have run both the series circuits and joined them in parallel before it joins the inverter. There are now 2 outputs with different voltages? I wonder if this is the normal way of putting them together. I have a growatt 4.2kw inverter. The other mppt is running another 8 panels orientated north.thanks for helping
    Huh? If I understand you correctly you have one hell of a problem or problems. If they are in fact in parallel, you are dragging down the system voltage down roughly 50% which means you lost 50% of your power.
    MSEE, PE

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    Thanks, guys you all r right. The installers are back to fix it keep you guys posted. Cheers

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    Default connecting two 12v PVs wired in series and one 24 PV to get 24V

    Hi

    I am currently running a DIY solar power system with two nos of 12V 100W Im 6.1A and VoC 22.4) panels in series, 30A PWM charge controller (Max PV Voltage <48V), 4 nos of 40AH 12v batteries in series-parallel (24V) and 800VA 230V Sine wave Digital Inverter.

    I am planning to increase the PV size. But I am not able to locate similar panels.

    Recently I saw 200W 24V (Im 6.2A) and 250W 24V (Im 7.1A) panels in a store nearby. (VoC 43V)

    Is it possible to use any of these panels in parallel with my existing PV array?
    Thanks

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    Quote Originally Posted by portman View Post
    Hi

    I am currently running a DIY solar power system with two nos of 12V 100W Im 6.1A and VoC 22.4) panels in series, 30A PWM charge controller (Max PV Voltage <48V), 4 nos of 40AH 12v batteries in series-parallel (24V) and 800VA 230V Sine wave Digital Inverter.

    I am planning to increase the PV size. But I am not able to locate similar panels.

    Recently I saw 200W 24V (Im 6.2A) and 250W 24V (Im 7.1A) panels in a store nearby. (VoC 43V)

    Is it possible to use any of these panels in parallel with my existing PV array?
    Thanks
    Yes. The 200w 6.2a panel would be very similar to your 2 100w panels and can be wired in parallel with them. While I believe having less than 3 sets of panels wired in parallel does not require any fuse protection I would build a combiner box and fuse the + wire from the 200w and the 2 series 100w panels before going to your charge controller. Having the fuses will make your system safer than not having them.

  10. #10
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    Quote Originally Posted by SunEagle View Post
    Having the fuses will make your system safer than not having them.
    Not by much really, as long as you have a single combined fuse to protect the panels against a failed CC, but I would consider putting in individual string fuses anyway to make it easier to add additional panel(s) later.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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