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Technical information on Solar Panels?

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  • Technical information on Solar Panels?

    When load is switched on to solar panels, does it's terminal voltage fall? To put it another way, how susceptible to internal voltage-drop are the solar panels?

    Thanks,
    Jeff

  • #2
    Hi Jeff,

    The are very susceptible. They have a relatively high internal resistance, and it varies with the amount of sunlight.

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    • #3
      With regard to voltage drop in PV design, voltage drop needs be be considered both on the DC and the AC side, with AC voltage drop being much more critical. I am not sure that I have ever considered the voltage drop within the modules themselves, as I would consider them to be the voltage source on the DC side. I would consider any design consideration for the internal voltage drop to be the responsiblity of the manufacturer.

      For DC runs longer than about 50-60 feet we will check the voltage drop and try to limit to 1-1.5%. This is not critical to the operation of the system, however it ensures efficient operation. Usually remedying a DC voltage drop higher than 1.5% only takes bumping the wire size from 10awg to 8awg at most.

      On the AC side, the voltage drop is extremely important. The NEC limits voltage drop to 3%, however for efficient operation of the inverter, the voltage drop from inverter to main service panel should be no more than 1-1.5%. SMA recommends no more than 1%. If the voltage drop is too high the AC voltage seen by the inverter will higher than the nominal utilty voltage and potentially outside of the inverter's operating range.

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      • #4
        i'm a little late on replying but I just wanted to say thanks guys. Solar_GEoff your answre was helpful thanks man

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        • #5
          Originally posted by Jeff_the_electrician View Post
          When load is switched on to solar panels, does it's terminal voltage fall? To put it another way, how susceptible to internal voltage-drop are the solar panels?
          Originally posted by solar_geoff View Post
          ...voltage drop in PV design, ... needs be be considered both on the DC and the AC side, with AC voltage drop being much more critical. ...
          remedying a DC voltage drop higher than 1.5% only takes bumping the wire size from 10awg to 8awg at most. ...
          On the AC side, the voltage drop is extremely important. The NEC limits voltage drop to 3%, ...

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          • #6
            Jeff, If the DC voltage draw is greater than the solar panel's combined voltage the voltage will fall. If the device draws 12 volts and the solar panel puts out 41 volts the voltage should not fall at all.

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            • #7
              He is right.

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              • #8
                panels do sag, according to load. The specs:
                Max Power Voltage - Vmp
                Open Circuit Voltage - Voc
                tell you the max, and the best voltage points to allow for. That's why MPPT charge controllers work, by playing with the load on the PV, and downconverting the output voltage.
                Powerfab top of pole PV mount (2) | 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

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                • #9
                  Charge controller managing ...

                  Right. Though, i prefer to say Charge controller managing in other word of controlling. But playing also can handle.
                  In extrim case burn can happen?

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