Fuse on series/parallel connected panels?

rgk1
rgk1 Solar Expert Posts: 134 ✭✭✭
I am sure this has probably been covered, but can not find quite what I am looking for.  I have 4 panels that are installed on a storage building roof - lets call them 1,2,3, and 4.  I have 1 and 2 connected together in series with the + - wires for the string brought down.  I also have 3 and 4 connected the same way.  That leaves me with  2 positive leads and 2 negative leads to contend with.

From what I understand, no fusing is required between the series connections.  The question is, do I need fuse/breaker on each of the strings when combining?  The answers I can find do not make this clear.  The general consensus is 3 or more strings put together in parallel for sure need fusing. But what about just 2?  Some say yes, some say no.  I do and always have had a breaker to disconnect the entire array, but does not address the issue of fusing parallel strings. 

Panel specs. are:  Voc 45.7V and Isc 9.15A each.
4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.

Comments

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    I like to fuse each string. ( circuit breakers actually ) then  you can test each against the other to see if there is a weak string, even with just 2 strings.
    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 ||
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  • rgk1
    rgk1 Solar Expert Posts: 134 ✭✭✭
    Thanks mike95490.  I will go ahead and use a combiner box with breakers.  Just didn't know if it was a must for safety reasons.
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,036 ✭✭✭✭✭
    A solar panel can be safely short circuited by itself. Short circuit current is even listed as a spec on panels. The problem arises when the potential current of 3 or more panels, or strings,  gets shorted. Code requires strings of 3 or more to be individually fused

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

  • rgk1
    rgk1 Solar Expert Posts: 134 ✭✭✭
    So, if 2 panels are connected in series, does that appear as 1 large panel?  If so, is it safe to a second "large" panel to it in parallel?
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,036 ✭✭✭✭✭
    It appears as one panel current wise. The voltage will be double. The current of a series string remains the same as the current of a single panel, The voltage is multiplied. You can safely parallel two panels, or panel strings without overcurrent protection. Many people prefer to use DC rated breakers on the individual strings but it is not required.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.