Solar panels configuration dilemma.




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  1. #1
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    Default Solar panels configuration dilemma.

    ave 250 w 24v x4 and 150w 12v x6. I have a 48 v battery bank of 800ah and mppt 60A 150v limit and a 48v kv inverter. zI need help with the pairing of the panels ad the voltage of the 12v panels in seried doed noy match the voltage of the 24 string
    and i wanted to connect the 2 strings in parallel

  2. #2
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    Default Re: Solar panels configuration dilemma.

    Quote Originally Posted by Mbu View Post
    ave 250 w 24v x4 and 150w 12v x6. I have a 48 v battery bank of 800ah and mppt 60A 150v limit and a 48v kv inverter. zI need help with the pairing of the panels ad the voltage of the 12v panels in seried doed noy match the voltage of the 24 string
    and i wanted to connect the 2 strings in parallel
    No real way to do it. Buy another MPPT charger and connect the 24V panels to one charger and the 12V panels to the other charger.

    24V panels - two strings of two panels in series, connected in parallel.

    12V panels - two strings of three panels in series, connected in parallel.
    Cheers

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  3. #3
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    Default Re: Solar panels configuration dilemma.

    Quote Originally Posted by Fluffy View Post
    No real way to do it. Buy another MPPT charger and connect the 24V panels to one charger and the 12V panels to the other charger.

    24V panels - two strings of two panels in series, connected in parallel.

    12V panels - two strings of three panels in series, connected in parallel.
    Thanks. What about the battery bank?Do I need to split it or can both mppt's charge the same battery bank at the same time

  4. #4
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    Default Re: Solar panels configuration dilemma.

    What about adding 2 more 12V panels to make all 48V

    Thus
    - 24V panels - 2 strings of 2 panels
    - 12V panels - 2 strings of 4 panels
    - then only one controller

    2 panels cheaper than another controller
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  5. #5
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    Default Re: Solar panels configuration dilemma.

    Quote Originally Posted by Mbu View Post
    Thanks. What about the battery bank?Do I need to split it or can both mppt's charge the same battery bank at the same time
    Both chargers can charge one battery, with most chargers anyway. You need to check the specs.
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  6. #6
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    Default Re: Solar panels configuration dilemma.

    Quote Originally Posted by Dungbeetle View Post
    What about adding 2 more 12V panels to make all 48V

    Thus
    - 24V panels - 2 strings of 2 panels
    - 12V panels - 2 strings of 4 panels
    - then only one controller

    2 panels cheaper than another controller
    Not a good idea, especially with an mppt charger. You get multiple mppt points, only one of which is the true Mppt. This can confuse the hell out of a mpg chargers tracking system.
    Cheers

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  8. #7
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    Default Re: Solar panels configuration dilemma.

    Quote Originally Posted by Mbu View Post
    ave 250 w 24v x4 and 150w 12v x6. I have a 48 v battery bank of 800ah and mppt 60A 150v limit and a 48v kv inverter. zI need help with the pairing of the panels ad the voltage of the 12v panels in seried doed noy match the voltage of the 24 string
    and i wanted to connect the 2 strings in parallel
    BTW - You don’t need to configure them to get 48V. That’s what the solar charger is there for. The mppt spec will tell you what panel voltages will work. In your case the max PV voltage must just be <150V

    PLEASE NOTE - THIS IS THE PV PANELS Voc MAX, not 24V or 12V
    Cheers

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  9. #8
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    Default Re: Solar panels configuration dilemma.

    Quote Originally Posted by Fluffy View Post
    Not a good idea, especially with an mppt charger. You get multiple mppt points, only one of which is the true Mppt. This can confuse the hell out of a mpg chargers tracking system.
    Thanks for the advice Ill just get a second mppt controller. Currently only the 12v pv are connected to the mppt and I lined all six of them in series and they give me an Voc of around 117 v. and +- 8.3 A . Reason being I wanted a high voltage system to reduce voltage loss on the 6 gauge wiring to the.charge controller. With your setup of two strings of 3 x12v panels in parallel will supply twice the current at about 16.6A which I assume will charge the battery bank in a shorter time.

  10. #9
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    Default Re: Solar panels configuration dilemma.

    Does that mean you can connect the 4 24V panels and 4 of the 12V panels all in series ?

    4x24 + 4x12 = 144 V
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  11. #10
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    Default Re: Solar panels configuration dilemma.

    Quote Originally Posted by Mbu View Post
    Thanks for the advice Ill just get a second mppt controller. Currently only the 12v pv are connected to the mppt and I lined all six of them in series and they give me an Voc of around 117 v. and +- 8.3 A . Reason being I wanted a high voltage system to reduce voltage loss on the 6 gauge wiring to the.charge controller. With your setup of two strings of 3 x12v panels in parallel will supply twice the current at about 16.6A which I assume will charge the battery bank in a shorter time.
    Actually no. I suggested the configuration to be safe. If all in series is safe then that is good, go for it, unless there is a chance of shading.

    It actually doesn’t matter what the currents are from the PV array. In a mppt Charger it performs a power conversion not a current or voltage conversion, so either way the net current into the battery will be the same no matter what the PV current is.
    Cheers

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  12. #11
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    Default Re: Solar panels configuration dilemma.

    Quote Originally Posted by Fluffy View Post
    BTW - You don’t need to configure them to get 48V. That’s what the solar charger is there for. The mppt spec will tell you what panel voltages will work. In your case the max PV voltage must just be <150V

    PLEASE NOTE - THIS IS THE PV PANELS Voc MAX, not 24V or 12V
    Does that mean you can connect the 4 24V panels and 4 of the 12V panels all in series ?

    4x24 + 4x12 = 144 V
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  13. #12
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    Default Re: Solar panels configuration dilemma.

    Quote Originally Posted by Dungbeetle View Post
    Does that mean you can connect the 4 24V panels and 4 of the 12V panels all in series ?

    4x24 + 4x12 = 144 V
    Absolutely no way, ever. Please read the last sentence in post #7 carefully.

    I also urge people to be aware when playing with larger systems and panels in series.

    We are getting into lethal voltages territory. PASOP.
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  15. #13
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    Default Re: Solar panels configuration dilemma.

    I hear what you say about dangerous Voltage, but in post 7 you said it must just be smaller than 150V

    Now I am asking if you can string to create 144V - that is < 150V

    Slightly confusing me...
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  16. #14
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    Default Re: Solar panels configuration dilemma.

    Quote Originally Posted by Dungbeetle View Post
    I hear what you say about dangerous Voltage, but in post 7 you said it must just be smaller than 150V

    Now I am asking if you can string to create 144V - that is < 150V

    Slightly confusing me...
    Read post #7.

    A panel has two main voltages. Basically the “working” voltage and the “disconnected” voltage.

    So typical voltages for your “12V” Panel are 17V and about 23-26V, basically twice you’re string voltage. Your 144V string is going to have an open circuit voltage of around 260-300V DC.
    Cheers

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  18. #15
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    Default Re: Solar panels configuration dilemma.

    And it is now considered a low voltage electrical installation with legal considerations

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  20. #16
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    Default Re: Solar panels configuration dilemma.

    as you can see 4 x36.8 is 147v which is too close to the limit 150v
    initially i thought that if I can match the 12 v string to the 24v string in parrallell with no more than 5% difference in the voltange of the strings then it may work
    but I would rather be safe and not confuse the mppt.Click image for larger version. 

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  22. #17
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    Thumbs up Re: Solar panels configuration dilemma.

    Many things can be learned by reading this forum...
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  24. #18
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    Default Re: Solar panels configuration dilemma.

    Rather get a 2nd MPPT controller.
    Have the 24V panels on one MPPT and the 12V panels on the 2nd MPPT.
    You can now have each set also facing different directions, so now you can have morning and afternoon covered.


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  26. #19
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    Default Re: Solar panels configuration dilemma.

    Buy a second MPPT charge controller and rig the strings as @Fluffy said. Locate the two sets of panels as @Wetkit said. One set facing True North and the other True West to True North West.

    If I may quote: "MPPT checks output of PV module, compares it to battery voltage then fixes what is the best power that PV module can produce to charge the battery and converts it to the best voltage to get maximum current into battery."
    Last edited by mygoggie; 2018/04/30 at 09:35 PM.

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