Voltage concern

alcatel99
alcatel99 Registered Users Posts: 31 ✭✭
my system has 4 Trina pv panels wired 2 strings of 2 panels series parallel and its wired to my batteries through a Morningstar Tristar 60 amp 150 volt mppt charge controller to give 24 volt on my 8 battery bank all is working great 
my question is can i add another 2  similar panels without over voltage problems my  neighbour is leaving AZ
so has some equipment for sale.

Here are the panels i have
max power                 290 watt
open circuit voltage    44.9
Volts @ Pmax            36.4
Short circuit current    8.47
Pmax current              7.97

Panels i am thinking of adding
max power                 270 watt
open circuit voltage    44.4
Volts @ Pmax            35.5
Short circuit current    8.25
Pmax current              7.60
I apologise for the long worded question but would rather ask the more knowlegable people here than just blunder in and ruin a good working system 
As always thank you for any help you can offer







Comments

  • 706jim
    706jim Solar Expert Posts: 514 ✭✭✭✭
    It looks like you could add one panel to each string and still be within the 150 volt limit of your controller.

    Or add a third string of two in series and you would still be within the 60 amp limit.

    The lower voltage option would be best if you have a problem with shading.
    Island cottage solar system with 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 30th year.
  • alcatel99
    alcatel99 Registered Users Posts: 31 ✭✭
    Thanks for your reply i am also considering mounting them south west to catch the late afternoon activity
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Morningstar does have a string sizing tool, it's here;

    String Calculator » Morningstar Corporation

    The match isn't too bad, I might worry a bit about the upper limit, can't recall if it's okay to 'over panel' a Morningstar MPPT 60. You would have 1700 watt array with the potential of 70 amps at 24 volts, but your batteries would have to be severely discharged and the weather very cold and clear to have the potential to produce more than 60 amps.
    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.
  • alcatel99
    alcatel99 Registered Users Posts: 31 ✭✭
    edited May 2021 #5
    Thanks for your reply
  • UpNorthMan
    UpNorthMan Registered Users Posts: 21 ✭✭
    I would be cautious about running 3 series. At 20F you are at about 148 voc. Your cc will run cooler with 2S 3P.

    Just food for thought.
    Ed
    1000W panels Kid CC 184 ah battery bank @ 48v
    Weekend cabin, 250w inverter.
    Looking to upgrade inverter!
  • alcatel99
    alcatel99 Registered Users Posts: 31 ✭✭
    thanks for reply
  • alcatel99
    alcatel99 Registered Users Posts: 31 ✭✭
    I am considering building on to my solar panel frame to accomadate the additional panels and have them facing 
    west 0r south west and also make 3 strings as mentioned i really appreciate the help on this forum