Help wanted string design???

Stone Mason
Stone Mason Registered Users Posts: 16 ✭
in Advanced Solar Electric Technical Forum #1
Hi, im doing my 4th install for a mate in off grid application
My other installs have been small 12v & 24v systems with small controllers and need some advice on this one.

So its a 48v battery bank with 8x crown 6v
FM60 controller

There is 16x 190w panels,

Electrical characteristics
Application: DC 24 volt
Max. Power as per STC: 190 Pmax(W)
Power Tolerance: 3 %
Max. Power Voltage: 36.96 Vm(V)
Max. Power Current: 5.14 Im(A)
Open Circuit Voltage: 44.15 Voc(V)

So do i run 2 in series and join at combiner box? so that would be 8 strings at 48v?

Have been reading and it seems that you can run strings of 4 panels in series giving 96v.

So is it fine to do the 4 strings at 96v and the controller will sort it to charge the 48v battery bank?

Cheers
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Comments

  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #2
    Re: Help wanted string design???

    Hi Stone Mason,

    First, strings of four PVs is simply too much voltage into the FM-60, unless there is a typo in the Vmp of the PVs. Strings of three should be OK, but as photowhit mentioned, Voc at the coldest recorded temperature for the site should be considered. Yes, this would probably mean 15 PVs total, unless two more of these PVs can be found. Perhaps strings of two PVs might work, but need to think about high temperature of PVs and cool batteries.

    What is the battery bank AH? Are the batteries Flooded?

    Guess that you and the "mate" have considered just what are the loads on the system, when they occur, max power at any given time, and the need for storage capacity of the battery ?

    EDIT: Looks like photowhit's post has disappeared ... ??!

    FWIW, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #3
    Re: Help wanted string design???

    And, Stone ..,

    Have looked for an " Outback Power String Sizing Tool ". But, it requires Java, which I no longer use. If you use a search engine on the term in quotes, but without the quotes, you will probably find a sizer for the FM-60. This will probably help in determining that with the max and min times of the site that the string configuration that you are considering will work with the FM-60 CC. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Help wanted string design???

    With a panel Vmp of 36 you only need two panels in series to accommodate a 48 Volt system. More would increase array Vmp & Voc decreasing the controller's efficiency possibly exceeding it's input maximum.

    Four in series, for example, would give a string Voc of over 176 Volts which is well above the FM60's 150 limit.

    Three in series gives a string Voc of 132 and likewise can exceed that maximum in cold temps (which increase Voltage).

    You will need to run eight parallel strings of two in series to utilize sixteen of those panels on a 48 Volt system.
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