Best way to connect grid tie panels to off grid system

wingnutter
wingnutter Registered Users Posts: 12 ✭
in Advanced Solar Electric Technical Forum #1
Hi Folks,

I am wondering if anyone has any suggestions as to how to connect these 4 "24" volt panels to a 24V off gid system?

The panels are rated as follows:


Peak watts: 180 W
Peak volts 23 V
Max amps 7.5 A
Open circuit amps 8.3 A
Open circuit volts 29.3 V


I am assuming that these panels are intended for grid tie, I intend to connect them to charge a 24V lead acid battery bank. My reading into this is that I could never get enough volts out of the to equalise the battery bank if I were to wire them in parallel as per normal off grid panels that are rated over 30 volts.

Would the best route be to wire them in series and to a mppt controller such as the Outback FM60 or could I get away with wiring them to a normal PWM controller such as the Xantrex C60 and use another source such as battery charger and electric generator to equalise my batteries?

Any suggestions would be welcome. especially those that do no involve the purchase of a mppt controller. (money issue).

Thanks

Wingnutter
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Comments

  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    #2
    Re: Best way to connect grid tie panels to off grid system
    wingnutter wrote: »
    ...Would the best route be to wire them in series and to a mppt controller such as the Outback FM60...

    This is the best and the only way you can efficiently connect those panels to 24V system. Connect each pair in series, then parallel those two pairs. You will end up with approx. 46V 15A solar array. You will need MPPT controller. Rogue 30A MPPT controller may work for you, but your array Voc is right at 60V input limit of that CC. The manual says 75V is the magic smoke limit, and your array may reach that on very cold, sunny day. So, in your case, Morning Star 45A MPPT controller with it's 150V limit and $133 extra cost, will work best.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #3
    Re: Best way to connect grid tie panels to off grid system

    And I believe that if you do choose the morningstar unit then you don't need to worry about keeping the array voltage close to the bat voltage, so you can simply put all 4 panels in series to reduce wiring size/voltage drop.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: Best way to connect grid tie panels to off grid system

    stephen,
    yes he could reduce the wire size by going straight series for all of the pvs, but at a cost of efficiency in the controller. you would lose a bit more than you'd gain with an all series arrangement and placing 2 in series and then paralleling with similar strings of 2 would be the best arrangement.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #5
    Re: Best way to connect grid tie panels to off grid system

    I thought that was only the case for some controllers and not an issue for Morningstar or outback controllers since they use synchronous rectification: http://forum.solar-electric.com/showthread.php?t=8475&highlight=xantrex+efficiency
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
    Re: Best way to connect grid tie panels to off grid system

    they still are a bit less efficient when the in/out is spread more widely.
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  • wingnutter
    wingnutter Registered Users Posts: 12 ✭
    #7
    Re: Best way to connect grid tie panels to off grid system

    Hi,

    Many thanks for the help and the links

    I have one queston, you say my solar array would be "46V 15A", is this not 46V and 30A with the 2 pairs of 7.5A panels?

    Don´t mean to be picky, just want to get my install correct, as this does not seem like a lot of amps out of 4 * 180W panels.

    Thanks.

    Wingnutter
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #8
    Re: Best way to connect grid tie panels to off grid system

    15 amps/46 volts.

    Take a 7.5 amp 23 volt panel, double the panel (parallel) and you get 15 amps/ 23 volts
    Double the panel (series) and you get 46 volts/7.5 amps

    Now series/parallel these two together, you get 15 amps/46 volts.


    Tony
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