Looking for design feedback

This system will consist of:
1 OB FlexPower1 vfx3524 (FM80)
7 Suniva 270 modules in parallel (temp comp Voc=46V, Array Imp=60A)
6 Concorde 12V / 285Ah - 2 series / 3 parallel for 855Ah

My plan is to run a homerun from each module to a combiner (probably OB 12 banger for future expansion) w/7 CB's, and the appropriate wire size to the controller.

Looking for feedback, or suggestions. Thanks.

Comments

  • AuricTechAuricTech Solar Expert Posts: 140 ✭✭
    Re: Looking for design feedback

    Why did you decide to go with a 24V battery bank over a 48V battery bank?
  • BB.BB. Super Moderators, Administrators Posts: 30,642 admin
    Re: Looking for design feedback

    Do you have your power (Watts, Watt*Hours per day, seasonal usage, etc.) defined?

    I am not a big fan of parrallel battery strings. Also, if you aim for 10% rate of charge, you are already at 85.5 amps--That is pretty close to the 80 amp maximum for a single FM 80 controller. Are you going bigger in the future?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Looking for design feedback

    Well let's see how the basic math plays out for balance.

    Seven 270 Watt panels all in parallel. Not good. Imp about 8.5 each? You don't really want to run that much current to a charge controller: requires large (8 AWG or better) wire for what is likely the longest run. The odd number of panels makes other configurations impossible though.

    1890 Watt array on a 24 Volt system = 60 Amps output current. Six 12 Volt 285 Amp hour batteries configured for 855 Amp hours. Not good to have three parallel strings of batteries even on 24 Volts, but can be done. Array isn't large enough for that much battery though: 7% peak charge rate is definitely on the low side.

    Suggestions:
    1). Loads are how much? Do you need 855 Amp hours @ 24 Volts? That's up to 10 kW hours. If you really need that kind of stored power go up to a 48 Volt system.
    2). Array needs to be expanded for the given bank. On 24 Volts an FM80 would be maxed out (another reason to go 48) for 855 Amp hours and you'd need 2500 Watts to do so. Of course adding even one more panel will help with configuration, current, and charging. But really it would need three more.
    3). 48 Volt system requires re-think of battery choice to get equivalent stored power. You will end up going larger or smaller. Eight of those batteries would give you 570 Amp hours @ 48 Volts (13 kW hours). The FM80 could handle that. You'd need an array of 3500+ Watts to supply the current though. Ten of those panels (2700 Watts) minimum, twelve would be better. In strings of two.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Looking for design feedback
    NuWind wrote: »
    7 Suniva 270 modules in parallel (temp comp Voc=46V, Array Imp=60A)

    What is "temp comp Voc"? I think the Vmp of those panels is 31.2 volts
    48 Volt system <snip> Ten of those panels (2700 Watts) minimum, twelve would be better. In strings of two.

    If I'm correct about the Vmp, he would need strings of 3 in a 48 volt system.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • NuWindNuWind Registered Users Posts: 14
    Re: Looking for design feedback

    This is another "I bought it online, can you hook it up" situation...regarding the VFX3524. Coot, if I decreased this to 2 strings of the 285's for 570 Ah's, would that be a reasonable option? I was already planning on #2 from the combiner to the CC.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Looking for design feedback
    vtmaps wrote: »

    If I'm correct about the Vmp, he would need strings of 3 in a 48 volt system.

    --vtMaps

    Yes, he would. Which makes array configuration different. Twelve panels as four strings of three, for example.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Looking for design feedback
    NuWind wrote: »
    This is another "I bought it online, can you hook it up" situation...regarding the VFX3524. Coot, if I decreased this to 2 strings of the 285's for 570 Ah's, would that be a reasonable option? I was already planning on #2 from the combiner to the CC.

    570 Amp hours @ 24 Volts ideally would have an array around 1750-1800 Watts. Yes, seven of those 270's would do it but ...

    Did you see vtMaps warning about Vmp? If it's 31.2 then that's low for a 24 Volt system: you may have too much V-drop between array and controller due to temperature effect and wire loss even with 2 AWG. And who wants to run 2 AWG that far? It won't fit the terminals of the controller, btw.

    Six of those panels (three parallel strings of two in series) will give you about 52 Amps output. That's a 9% peak charge rate on 570 Amp hours so that would work fine, and reduce the wire size demands.
  • NuWindNuWind Registered Users Posts: 14
    Re: Looking for design feedback
    570 Amp hours @ 24 Volts ideally would have an array around 1750-1800 Watts. Yes, seven of those 270's would do it but ...

    Did you see vtMaps warning about Vmp? If it's 31.2 then that's low for a 24 Volt system: you may have too much V-drop between array and controller due to temperature effect and wire loss even with 2 AWG. And who wants to run 2 AWG that far? It won't fit the terminals of the controller, btw.

    Six of those panels (three parallel strings of two in series) will give you about 52 Amps output. That's a 9% peak charge rate on 570 Amp hours so that would work fine, and reduce the wire size demands.

    #2 is listed as the max wire size for the controller. 3x2 would only give me 26A, correct?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Looking for design feedback
    NuWind wrote: »
    #2 is listed as the max wire size for the controller. 3x2 would only give me 26A, correct?

    Good luck getting #2 in there.

    Input current will be Imp of panels * the number of parallel connections. If the Imp is 8.5 and there's three strings in parallel the result is 25.5. In other word the current could be handled by 10 AWG, but you'd want to use larger to reduce the V-drop over any distance greater than about 14 feet.
  • NuWindNuWind Registered Users Posts: 14
    Re: Looking for design feedback

    Yes, they are 31.2 Vmp...the OB string sizer uses the temp adjusted Voc, which is 46V. Suniva specs are 38.5 Voc.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Looking for design feedback
    NuWind wrote: »
    Yes, they are 31.2 Vmp...the OB string sizer uses the temp adjusted Voc, which is 46V. Suniva specs are 38.5 Voc.

    Voc is used on string sizers to make sure the panels' maximum cold temp output doesn't exceed the V-max in of the controller. For power output and wire V-drop calculations you need to use Vmp.

    To that end I just realized I did those quick calcs @ 24 Volts and in using two panels in series 48 Volts is more accurate. So 10 AWG would actually handle the 25 Amps for about 24 feet, not 14. You still will probably want to go to 8 AWG between combiner and controller. And if you are planning on expansion, wire for it now; no sense having to take out a long run of one gauge to replace it all!
  • NuWindNuWind Registered Users Posts: 14
    Re: Looking for design feedback
    Good luck getting #2 in there.

    Input current will be Imp of panels * the number of parallel connections. If the Imp is 8.5 and there's three strings in parallel the result is 25.5. In other word the current could be handled by 10 AWG, but you'd want to use larger to reduce the V-drop over any distance greater than about 14 feet.

    The Imp is 8.68...x3 would be just over 26A. 3x2 sounds like a good solution if it would adequately charge the 570 Ah battery bank.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Looking for design feedback
    NuWind wrote: »
    The Imp is 8.68...x3 would be just over 26A. 3x2 sounds like a good solution if it would adequately charge the 570 Ah battery bank.

    Six panels @ 270 Watts each = 1620 Watts. 77% efficiency and 24 Volts nominal = 52 Amps current. On 570 Amp hours that's 9% peak charge current. Close enough to the 10% target that it should not be a problem at all.
  • NuWindNuWind Registered Users Posts: 14
    Re: Looking for design feedback

    Thanks to everybody!
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