What if we connect string with different voltage in parallel ?

JAYMINJAYMIN Registered Users Posts: 22 ✭✭
dear forum users i have a question what will be the Vmp and Imp if we connect string with different current in series or If we connect string with different voltages in parallel?


Comments

  • BB.BB. Super Moderators, Administrators Posts: 28,141 admin
    More or less, the generic recommendation is that series connections match Imp within 10% (i.e., 7 amp + 7.7 amp panels in series).

    For parallel connections, Vmp within 10% (18 volt plus 19.8 volt panels in parallel).

    If the values are farther apart, you will lose significant panel efficiency. Some folks suggest to match panels within 5% of Vmp/Imp.

    If you exceed matching current--You can overheat/damage the lower rated panel. Too much voltage difference can damage a panel too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,123 ✭✭✭✭
    I had to do this once as a client lost a CC do to lightning.  I placed a 2kw 300vdc array in parallel with a 2kw 360vdc array. They were about 10% less power than when they had their own cc. They did have some issues with picking the mpv in winter when there were clouds on a single cc.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
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  • GreenPowerManiacGreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    They seem to balance out whether it's panels or batteries.   You'll get the average V/A, unless it's over 10%, then problems could arise. 

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  • MarkCMarkC Solar Expert Posts: 175 ✭✭✭
    edited September 2016 #5
    I will soon have two PV grid tied systems;
    ~4000 watts - 14 Sunmodule Plus - SW275 monos (exisiting)
    ~ 2700 watts - 8 Sunmodule - SW 340 XL monos (soon to be on-line).  Filling out the existing roof area.

    I may want to reconfigure in the future to use as many panels as possible to provide a minimum of 450 VDC operating voltage.  The Imp is essentially the same for all panels ~ 9 amps.   The Vmp/Voc is ~31/40 for the SW280's and ~38/48 for the 340's.  

    Is there a effective combination of the panels to achieve this goal?   Appears the only "paper" combination is to put as many in series as the downstream equipment can take at Voc?  DC breakers from "solar" suppliers seem to be limited to 600 VDC.   This is "theoretical" (NOT heretical) only and has to do with DC "quick charging" my EV off-grid.  



    3850 watts - 14 - 275SW SolarWorld Panels, 4000 TL-US SMA Sunny Boy Grid tied inverter.  2760 Watts - 8 - 345XL Solar World Panels, 3000 TL-US SMA Sunny Boy GT inverter.   3000 watts SMA/SPS power.  PV "switchable" to MidNite Classic 250ks based charging of Golf cart + spare battery array of 8 - 155 AH 12V Trojans with an  APC SMT3000 - 48 volt DC=>120 Volt AC inverter for emergency off-grid.   Also, "PriUPS" backup generator with APC SURT6000/SURT003  => 192 volt DC/240 volt split phase AC inverter.  
  • mike95490mike95490 Solar Expert Posts: 8,009 ✭✭✭✭
    MarkC said:....  Appears the only "paper" combination is to put as many in series as the downstream equipment can take at Voc?  DC breakers from "solar" suppliers seem to be limited to 600 VDC.   ......
    You have to calculate the Voc on the 50 year coldest day history for your area.   A 580Voc @ 70F could be 650V @ -5F  Most gear has a "string calculator" where you enter your low temps and PV info.
    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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