System design after the fact

Desert Rat
Desert Rat Solar Expert Posts: 147 ✭✭✭
in Off Grid Solar & Battery Systems #1
I saw a new off-grid installation last week that I've been thinking about. Let me first say that I had nothing to do with the design or installation of this system; I'm just an interested observer. The array consists of 82 250W panels. Not a typo--yes, a 20,500 watt array. They are charging a 48V battery bank of big Surrettes. In the short time I had to check out the system I was not able to get the specs of the batteries. There are many problems with the system, one of the big ones being that they are running the array through only two charge controllers--an Outback FM80 and an FM60. I have my own ideas about how to set this all up properly, but would also like to hear from folks here--how would you deal with an array of this size, assuming that you really needed 20.5 KW?

Panel specs
Pmax 250W
Imp 8.57A
Vmp 29.47V
Voc 37.09V
Isc 9.07A
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: System design after the fact

    20,500 Watt array @ 48 Volts: 328 Amps. No chance on two controllers.

    That would feed a 3,280 Amp hour 48 Volt battery bank: 78 kW hours of stored power. Lunacy.

    First thing I would do is revisit the loads. As an all-in-one system this sizing makes no sense. Divided up into several sub systems gives you an added measure of redundant power supply and an extra degree of safety and sanity.

    But you'd still need at least four 80 Amp controllers.

    If they've really got that much PV on one 60 and one 80 they have wasted about $12,000 on PV that will be doing nothing.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #3
    Re: System design after the fact
    Cariboocoot wrote: »
    If they've really got that much PV on one 60 and one 80 they have wasted about $12,000 on PV that will be doing nothing.
    Except maybe extending the useful charging time farther from solar noon. That may be a significant benefit is winter with few solar hours in the day. It would still be a waste, but not a total waste.
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: System design after the fact
    inetdog wrote: »
    Except maybe extending the useful charging time farther from solar noon. That may be a significant benefit is winter with few solar hours in the day. It would still be a waste, but not a total waste.

    Not at that level of over-paneling!
    I factored the typical loss sizing in to my original equation. Even making allowances for low-light conditions ... well an extra 12 kW of panel is silly, even up here.
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,166 ✭✭✭✭
    #5
    Re: System design after the fact

    It depends upon the buyers perception of the value of money.
    I always have more questions than answers. That's the nature of life.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: System design after the fact
    Marc Kurth wrote: »
    It depends upon the buyers perception of the value of money.

    You're kidding right?

    We're not looking about 30% or even 50% over-paneling here; we're looking at 134% greater current potential than the charge controllers can handle. I doubt even Outback controllers could clip that much.

    Either there is something missing from the design (such as AC coupled GTI's) or else this is the stupidest waste of PV ever.
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #7
    Re: System design after the fact

    would be interesting to know the string voltage per inverter... something has to give... lots of magic smoke???
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #8
    Re: System design after the fact

    I suspect the batteries will be well charged and not accepting much more, by 9am on a sunny day, so the MPPT's won't smoke. But in winter/cloudy weather, I suspect the owner will not have much of a standby generator fuel bill either.
    now if at noon, the 2 Ton air conditioners kick on, then the MPPT's are going to vaporize !
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #9
    Re: System design after the fact
    mike95490 wrote: »
    ...
    now if at noon, the 2 Ton air conditioners kick on, then the MPPT's are going to vaporize !
    Not if they have output current limiting, which I am sure they do (except maybe for cheap no-name models)
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: System design after the fact
    inetdog wrote: »
    Not if they have output current limiting, which I am sure they do (except maybe for cheap no-name models)

    Even the good ones will have limits to how much current they can clip.
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