Newbie solar system voltage question and sizing

learaviatorlearaviator Posts: 6Registered Users ✭✭
edited March 29 in Solar Beginners Corner #1
Hello, new guy here. I am building my system for a home 24 miles SW of Seligman, Az. I have 8 JA Solar panels, 280 watts, 36 volt max power voltage. Originally I was thinking of a 24 volt system but now I am not sure.  I already have a Magnum 4000 watt, 24 volt inverter and a Flexmax 80 charge controller. It appears judging by Outbacks sizing tool on their website that at 24 volts I can only run 7 panels because of the wattage rating of the controller, or add another charge controller and run 4 batteries on each. Or I could sell my 24 volt inverter and buy  a 48 volt inverter and have a lot more options as far as panel array. I figure my daily usage at 5200 watt hours per day at the highest.  I am planning on 8 Fullriver  DC400-6 batteries.  I also have a 17 kw generator for backup. Any advice or  thoughts would be greatly appreciated!! Also is this system sized correctly for my needs?

Comments

  • EstragonEstragon Posts: 2,925Registered Users ✭✭✭✭✭
    edited March 29 #2
    IMHO, you could get away with using 8 panels on the single controller. Although the 8 are STC rated for ~2.2kw, realistically they'll usually produce less with warm panels. For example, maybe 1.7kw / 28v charging = ~60a or a bit more at your altitude. Within reason, having "excess" pv makes sense, as you're able to charge better on light overcast days. Most controllers can limit output (within reason), so moderate overpanelling isn't such a bad idea.

    That said, with ~5kwh/day load, 48v likely makes more sense long term. On the short term, if you have any large wattage loads (eg pumps), a 24v system will need heavier wire to handle surges, and battery voltage sag may be worse. Longer term, you may find the 5kwh load wants more pv to both charge batteries and support loads. At 48v you would have expansion room with the one controller, but at 24v, not really. Running a controller at close to full current also means more heat and a likely shorter lifespan. It may also need altitude derating.

    If you did add a controller at 24v, you wouldn't run 4 batteries on each. You would have two strings (4x6v batteries x 2 strings in parallel), with 2 controllers in parallel charging the 2 parallel battery strings. You wouldn't normally want controllers charging battery strings separately. Each controller would have it's own pv array though, and this has advantages in some applications (eg different array orientations).

    Going to 48v initially would also give you some flexibility with storage. If you find a single string at 48v isn't enough, you could add a second (although you would want to do this while the first string is newish). At 24v, adding more strings beyond 2 could be problematic.

    If the inverter is new in the box, I would probably sell it and go to 48v initially. At 5kwh/day, there's a decent chance I'd want more pv, more storage, or both, and adding either/both would be easier at 48v. If the inverter is used already, I might install it in a 24v system and see how it goes for a bit.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mcgivormcgivor Posts: 2,302Solar Expert ✭✭✭✭✭
    edited March 29 #3
    Going 48V is by far the best if expansion are in the plans, all ballance of system equipment controller, conductors, circuit breakers  ( assuming breaker voltage compatibility ) could be utilized and if this is a new system then everything would be less expensive. Expansion on 24V would possibly meen another controller, if 48V a new inverter, if the latter is chosen, an inverter charger would be a wise choice to incorporate the generator.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • HorseflyHorsefly Posts: 313Registered Users ✭✭✭✭
    ... It appears judging by Outbacks sizing tool on their website that at 24 volts I can only run 7 panels because of the wattage rating of the controller, or add another charge controller and run 4 batteries on each. ...
    Just to be clear: If you do have run with two charge controllers, you would put both on the entire battery bank. What you would split is between two sets of panels, one feeding each charge controller.
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 4 x Vmax XTR12-155 12V, 155AH batteries in a 2x2 24V 310AH bank.
  • learaviatorlearaviator Posts: 6Registered Users ✭✭
    Horsefly said:
    ... It appears judging by Outbacks sizing tool on their website that at 24 volts I can only run 7 panels because of the wattage rating of the controller, or add another charge controller and run 4 batteries on each. ...
    Just to be clear: If you do have run with two charge controllers, you would put both on the entire battery bank. What you would split is between two sets of panels, one feeding each charge controller.

    Thank you for your reply and input! I actually did mean panels instead of batteries  LOL

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