12 volt or 24 volt

schwy
schwy Registered Users Posts: 9 ✭✭
edited April 2016 in Solar Beginners Corner #1
Hi.  I have a small off the grid system in northern Wisconsin.  It consists of 2 315 watt Kyocera panels wired in parallel to a 60 Outback Flexmax charge controller.  The parallel connection is made inside the charge controller.  So there are 4 wires coming into the charge controller.  It is charging 4 Interstate golf cart batteries.  My wire runs are 50 feet from the panels to the charge controller.  Wire size is 10 awg solar panel wiring.    I am putting on a new roof this summer and have to take the system down.  My question is should I continue to run this system as is or should I wire my panels in series.  Thanks a lot for helping.

Comments

  • WaterWheel
    WaterWheel Registered Users Posts: 375 ✭✭✭
    edited April 2016 #2
    While there are much more knowledgeable people on this site than me but...
    With the Flexmax 60 you can have input voltage as high as 150v so I would definatly wire the panels on series ( 2, even 3 panels if you want to add one) and you will have a slightly more efficient system with less wire.      Your current 10 ga wire is more than sufficient size.

    Conext XW6848 with PDP, SCP, 80/600 controller, 60/150 controller and Conext battery monitor

    21 SW280 panels on Schletter ground mount

    48v Rolls 6CS 27P

  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭

    Since you have already made 'home run' connections from your panels, I'd leave it unless you are running a 24volt system.

    Your title would indicate you are choosing between system voltages? MPPT charge controllers tend to run most efficiently at 2 times the system voltage. If you are choosing, no 12 volt loads and no inverter purchased yet, I would go with a 24 volt system. Combine the panels at the array and pull (or cap) the extra lines for future expansion.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • schwy
    schwy Registered Users Posts: 9 ✭✭
    edited April 2016 #4
    We currently have a 12 volt 1000 watt inverter.  If I ran the panels in series would I have to change my inverter or rewire my battery bank?  Thanks for your help.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    No, your CC will reduce the incoming PV voltage to the battery voltage, nominal 12 Volt. As you indicated you have 4 golf cart batteries, I assume they are 6 volt and you have 2 parallel sets of 2 -  6 volt cells...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    schwy said:
    We currently have a 12 volt 1000 watt inverter.  If I ran the panels in series would I have to change my inverter or rewire my battery bank?  Thanks for your help.


    Okay, I'll stick with my original statement;

    Since you have already made 'home run' connections from your panels, I'd leave it unless you are running a 24volt system. MPPT charge controllers work more efficiently at about 2 times the system voltage. Changing it now to run near 4 times the system voltage won't save you anything and create more waste heat at the charge controller and shorten it's life as well as reducing it's efficiency.

    If you had NOT run your wiring already, there might be an argument that you can save some voltage loss as well as wiring by running a single the higher voltage line. Since you have 2 sets in place it mitigates any advantage.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • schwy
    schwy Registered Users Posts: 9 ✭✭
    Thanks for all the input.  From what I gather it may not be worth the hassle of changing my wiring.  Thanks again.
  • fauss
    fauss Registered Users Posts: 26 ✭✭
    So since schwy has already ran his wiring it's not ideal for him. I'm still building my system and don't a inverter or batteries yet. Nothing is wired. So is 24v always the better option?
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    fauss said:
    So since schwy has already ran his wiring it's not ideal for him. I'm still building my system and don't a inverter or batteries yet. Nothing is wired. So is 24v always the better option?
    No.  It depends on the size of the system.  If your peak and sustained loads are only a few hundred watts, a 12 volt system is superior because you have fewer battery cells (6 cells, rather than 12 cells).   This assumes a single string of batteries.

    Batteries also have a role in making the choice...  For example, suppose you determine that four 6-volt golf cart batteries is the amount of storage that you need.  Those four batteries will have the same storage capacity whether you configure them at 24 volts or 12 volts.  The 24 volt configuration is superior because there are no parallel batteries. 

    On the other hand, you could get about the same capacity with two L-16 batteries in series for 12 volts, and if your loads are small enough, that would be a superior choice because you have fewer cells.

    If the distance between your panels and your controller is long, that argues for a higher system voltage.

    --vtMaps

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