Adding larger panels to a small setup

oglethorp
oglethorp Solar Expert Posts: 30 ✭✭
in Solar Beginners Corner #1
I have 4 / 164watt Solar World (discontinued) 4.72lmp,, 35.2Vmp
tied to Apollo T80 to keep up two strings of 8 235AH 6v Gulf Cart Batts (48 v)
Started with these batts 5yrs old, 3years ago, now 8years old.. Lost one whole strinds worth one by one. Hope to replace this string with Trogen 105s, 225AH,.
Can I add 4 more larger panels like 220 watt more or less( as the pricing has come down a bit), put them through a separate charge controler (MPPT) then through a battery switch to charge the 105s normally and if the other array needs help switch them together . The batt switch is a make then break type.
; Please recommend panels, and charge controller, and of coarse weather or not this is a good idea. And this is a small off grid life style with little cash flow.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Adding larger panels to a small setup

    I'm not surprised you lost batteries. Your system as it stands is "under-paneled". Since you want to add more, you must be aware of this. Good!

    What you've got now:
    (4)*164W = 656 @80% = 524 / 57 Volts charging = roughly 9 Amps. That doesn't even meet the 5% minimum for 235 Amp hours (11.75 Amps), let alone two strings (23.5 Amps).

    The Trojan T105's are a comparable replacement. But you're going to need 10% of their rating for recharge - 22.5 Amps.

    That is for one string of 225 Amp hours @ 48 Volts nominal. Two strings would require double the current.

    Now, do you want to spend all that $ for all new panels? Probably not. You can add new ones to up your over-all array capacity through a second charge controller. You do not need to switch between arrays; both can feed and charge the bank at the same time, no problem.

    So you'd probably want about 1600 Watts of array. Subtract the existing 656 and you get around 950 more. Whether or not you'll need a larger array or can get away with a smaller one would depend on your exact circumstances. If it's hot where you are you'll want more. If the wiring is long-ish you'll want more. But it looks like a need for at least four 200 Watt panels.
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  • oglethorp
    oglethorp Solar Expert Posts: 30 ✭✭
    #3
    Re: Adding larger panels to a small setup

    Can anyone recommend 4/ 200 + W panels for a 48V system and a MPPT charge controller without spending a lot of wasted money
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #4
    Re: Adding larger panels to a small setup

    One thing to worry about with a 48 volt battery bank a running panel in the Vmp~50-70 volt range with the current crop of MPPT charge controllers.

    The Vmp is not high enough the charge a 48 volt battery bank (Vbatt-charging > 60 VDC). And Voc is too high (in cold weather) which will exceed the typically 150 VDC maximum of most high end charge controllers.

    If you are planning on continuing using your Vmp=35 volt solar panels, you could add these Solar World 245 watt panels with Vmp=37.7 volts in parallel with your existing panels on the same controller (your Apollo controller should be large enough to hand the second panel string). In general, if you solar panels are within 10% on the Vmp (for parallel connections) or 10% of Imp of the existing panels, then there is not very much power loss because of the voltage/current miss-matches.

    If you are looking for a new controller--the Morning Star TS MPPT 45/60 Amp units are pretty nice right now. The 60 amp includes a web server. As always, we recommend the Remote Battery Temperature Sensor. The TS's also have a remote battery voltage sense lead connection--Very nice as it corrects for any (small) voltage drop from the controller to the battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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