String guidance - higher voltage or more panels and strings?

autoxsteveautoxsteve Solar Expert Posts: 114 ✭✭✭✭
I'm VERY close to ordering a grid tie system for my south facing socal home.

I'm torn between a 3 strings of 7 panels each (21 panels) system and a 2 string of 10 panels each (20 panels) system.

I'm planning on using Evergreen Solar's 190W-SL panels with a Fronius 4000 inverter.

The engineer in me says to get the 7 X 3 sys (3900W) and size the wiring to minimize IR drop....

With the higher rebate available, I essentially get the 21st panel for ~50% off.

Thoughts?

Comments

  • mike95490mike95490 Solar Expert Posts: 8,652 ✭✭✭✭✭
    Re: String guidance - higher voltage or more panels and strings?

    I'm prone to go the higher voltage, less copper loss route. (if your winter low temps don't kick the upper voltage limits)

    Not being familiar with Fronius quirks, I think there may be a point of diminishing returns as DC voltages get to the upper limits of the inverter, the losses in the FET's increase, where at lower voltages, the losses are not as bad. ( maybe goes from 95% to 90% )
    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
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  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: String guidance - higher voltage or more panels and strings?

    i'd probably go with neither. 3 strings of 8 would most likely do best as 3 strings of 7 put the vmp on hot days too close to the minimum voltage of operation and losses increase with the higher voltages. if i had to pick one given the choice of the 2 i'd pick the 2 strings of 10. max voltage of the 2x10 pv system won't be exceeding the inverter's 450v max even on the coldest days.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: String guidance - higher voltage or more panels and strings?

    I'd say use another inverter manufacture and go 2x11,2x12,2x13 ect

    the Xantrex GT4.0 is lower cost, more features and a better operational range
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