Adding two more panels...

alyaz
alyaz Solar Expert Posts: 114 ✭✭✭
in Off Grid Solar & Battery Systems #1
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Initially we had anticipated using tempered glass on the upper deck patio structure. However, as fate would have it we are considering adding two more Helios clear backed panels, both to keep the look similar to the lower deck build and it can never hurt to have more solar, can it?

Anyway, in theory, just want to run the addition of two more panels past you guys.

The main patio cover has six Helios 250 watt panels. The six panels are wired in three series runs (two panels in series) to a Midnite Classic 150. I ran the specs through the Midnite Classic string sizing tool and the 150 will handle two more panels in series (so we would have four series runs with two panels in each series). The two panels to be added will be the same specs as the six already in place. The orientation is the same and the location is within 20 feet or so with almost exactly the same exposure etc.

The six panels (already in place and hooked up) are wired to a combiner box at the panels and one 6 gauge wire runs from the panel combiner box to the Midnite Classic 150. Is it okay to run a sufficiently sized (yet to be determined) wire from the two new panels (after wired in series) to maybe just before the controller where the the current 6 gauge wire and the new wire can be combined?

Is that how it's done?
3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Adding two more panels...
    alyaz wrote: »
    The six panels (already in place and hooked up) are wired to a combiner box at the panels and one 6 gauge wire runs from the panel combiner box to the Midnite Classic 150. Is it okay to run a sufficiently sized (yet to be determined) wire from the two new panels (after wired in series) to maybe just before the controller where the the current 6 gauge wire and the new wire can be combined?

    Is that how it's done?

    This is getting a bit dicey... Distributed power systems become quite complex to keep safe... Each wire should be protected against excessive current flow--So you might be looking at a "combiner box" type setup at the proposed connection just before the controller's PV Array input... The fuse/breaker needing to be sized to protect the wire run back to the original array (probably not an issue with just one added array string) and a fuse/breaker to protect the wire run back to the new string, and also rated for the series protection fuse of the panel (protect both the wire from the controller to the new string, and to protect the string if it gets shorted somehow).

    So--It does seem that you could do this--Will you ever be adding more panels/strings to this controller? If so, it might be easier/better to upgrade the original combiner box to add a the extra panel string(s) there, and upgrade the 6 awg to the controller (if needed).

    Another option (if it makes sense for your home) would be to wire the panels up into 3 panels per string. That will increase the Vmp-array and reduce Imp-array--allowing you to (possibly) use the existing 6AWG wire with the new panels (and the existing combiner box).

    So, instead of 2 series panels * 3 strings, you could have 3 series panels * 3 parallel strings (9 panels total) at the cost of a bit of extra rewiring of the array.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • alyaz
    alyaz Solar Expert Posts: 114 ✭✭✭
    #3
    Re: Adding two more panels...

    Thanks Bill. Appreciate the thoroughness of your reply.

    Thinking of leaving well enough alone after that. Haha...

    It would be difficult, running the wire back to the original array; and the new build would not fit three panels... so, at this point I'm leaning towards just returning to the original idea of putting tempered glass on the new build. Guess we'll see what happens after a good nights sleep :confused:
    3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    Re: Adding two more panels...

    Sorry Alyaz,

    Many of my responses seem to gather those types of replies.

    -Bill :blush:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • alyaz
    alyaz Solar Expert Posts: 114 ✭✭✭
    #5
    Re: Adding two more panels...
    BB. wrote: »
    Sorry Alyaz,

    Many of my responses seem to gather those types of replies.

    -Bill :blush:

    hahahahaha.... we are fortunate to have someone like you here on the forum. it's much better to be able to make informed decisions than to just forge ahead with bad ideas...

    thanks Bill!
    3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #6
    Re: Adding two more panels...

    Other options, might be to add one panel and switch to strings of three panels to use your current combiner box.

    Or if it's one of the newer combiner boxes with MC4 connectors and no combined breaker, you could use an inline MC4 fuse and connect it in behind the combiner box. Though if you have long runs, likely you have a standard combiner box with heavier wire...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #7
    Re: Adding two more panels...

    I would install Baby Box just before the controller and would use it to combine wires coming from the existing combiner box with wires from new panels, using appropriate breakers or fuses. It would have room for more breakers in case you need to add more panels in the future. They have a slightly bigger version too.
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  • alyaz
    alyaz Solar Expert Posts: 114 ✭✭✭
    #8
    Re: Adding two more panels...

    thanks for all the information gang... i'm really back and forth on this right now...
    3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9
    Re: Adding two more panels...

    If your current system setup works OK--Then Photowhit's suggestion of wring the two new panels into the existing string to get a 3 series x 2 parallel array would seem to be ideal (if you can get the wiring to work out OK for your home).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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