Is it worth it to change from 48v strings to 36v strings?

Planning the best efficiency/ lowest loss possible:

Using two Outback MPPT FM80 controllers to a 24v battery bank, I'm planning the best layout and size design for my ground array. Would it be worth wiring 3,200 watts of panel power in strings of 36v instead of strings of 48v to make the solar controller more efficient?

Comparing "apples to apples" as in wire size, if the 48v strings go to a combiner box are the same length as would be the 36 volt strings to same combiner box, would the lower 36 voltage cause more loss or could I plan to use the same size wire used for 48v strings? The longest solar panel string combiner box would 30 feet or less to the FM80 controllers and batteries. Wire from solar panels to combiner box is multi-strand #10. Wire from combiner boxes to controller is #6 copper.

Thanks,
Bill
Bill

Comments

  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Is it worth it to change from 48v strings to 36v strings?
    Using two Outback MPPT FM80 controllers to a 24v battery bank, I'm planning the best layout and size design for my ground array. Would it be worth wiring 3,200 watts of panel power in strings of 36v instead of strings of 48v to make the solar controller more efficient?

    What are the specs on the panels? When you refer to 36 and 48 volt strings, you are referring to nominal voltages, to answer your question I need to know the Vmp of the panels.
    Comparing "apples to apples" as in wire size, if the 48v strings go to a combiner box are the same length as would be the 36 volt strings to same combiner box, would the lower 36 voltage cause more loss or could I plan to use the same size wire used for 48v strings? The longest solar panel string combiner box would 30 feet or less to the FM80 controllers and batteries. Wire from solar panels to combiner box is multi-strand #10. Wire from combiner boxes to controller is #6 copper.

    The current in the wires to the combiner will be the same in either case, so the loss will be the same in either case.

    The 30 ft cable between combiner and controller will have greater loss with 36 volt strings because the current will be higher at the lower voltage.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BilljustBill
    BilljustBill Solar Expert Posts: 219 ✭✭✭
    Re: Is it worth it to change from 48v strings to 36v strings?
    vtmaps wrote: »
    What are the specs on the panels? When you refer to 36 and 48 volt strings, you are referring to nominal voltages, to answer your question I need to know the Vmp of the panels.



    The current in the wires to the combiner will be the same in either case, so the loss will be the same in either case.

    The 30 ft cable between combiner and controller will have greater loss with 36 volt strings because the current will be higher at the lower voltage.

    --vtMaps

    The Vmp is 17.7
    Bill
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Is it worth it to change from 48v strings to 36v strings?
    The Vmp is 17.7

    Two in series will have a Vmp of 35.4 volts. On hot days the Vmp drops and may not be high enough to charge a 24 volt battery. It's really close. I would leave them 3 in series (Vmp= 53.1 volts).

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i