Various panels- Opinions requested.

andyrud
andyrud Solar Expert Posts: 70 ✭✭
in Off Grid Solar & Battery Systems #1

As you can see in the photo, I have 3 different kinds of panels that make up my 24 volt array.  The blue ones are 24 volt panels, the four gray panels are 12 volt panels that I have connected in series to make 24 volts.  My knowledge and off grid solar system has been a work in progress.  It produces ample current for all my needs.  My controller is a Midnight Solar 150, my batteries are 12 volt totaling 600 amp hours, and my invertor is a 12 volt 2800 watt Magnum .

My question is,  by using various panels this way what are the ramifications by doing this?  Just curious.

Thanks in advance,

Andy


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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Need to know the exact Vmp and Imp of the panels.

    I would suggest the largest useful ac inverter for your battery bank would be about 1,500 watts.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • andyrud
    andyrud Solar Expert Posts: 70 ✭✭
    #3
    BB. said:
    Need to know the exact Vmp and Imp of the panels.

    I would suggest the largest useful ac inverter for your battery bank would be about 1,500 watts.

    -Bill
    Thanks for the reply Bill.  I don't have this information, some of the labels are gone.  But I think the 24 volt panels are 230 watt, 30 VDC, 7.67 amps,  and the 12 volt panels are 100 watt, 17 VDC, 5.88 amps.  
    Andy R
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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    edited January 2017 #4
    Hi Andy,

    Sorry, this advice is in error. Panel amperage needs to match to within 5 percent in series strings. Rick

    Your 24 volt panels are not really 24 volt panels. They are called grid tie panels and have 60 cells. True 24 volt panels will have 72 cells and a voltage of about 36 volts. However, you have a very good MPPT charge controller and it will allow you to to string 1 grid tie panel, 230 watts, in series with 1 12 volt panel, 100 watts, to make a 330 watt string at 47 volts and about 13 amps. Connect these strings in parallel for 1320 watts. That is about the max wattage for the classic 150 at 12 volts. Of course you should have a DC circuit breaker on each string in a combiner box. 

    If you have flooded lead acid batteries you will need to set the max charging amps in the classic 150 to 78 amps. If the batteries are AGM then you will not need to set the amps limit.

    Rick
    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,102 ✭✭✭✭✭
    edited January 2017 #5
    Raj174 said:However, you have a very good MPPT charge controller and it will allow you to to string 1 grid tie panel, 230 watts, in series with 1 12 volt panel, 100 watts, to make a 330 watt string at 47 volts and about 13 amps. Connect these strings in parallel for 1320 watts. That is about the max wattage for the classic 150 at 12 volts. Of course you should have a DC circuit breaker on each string in a combiner box. 

      Absolutely wrong.  Series wiring such dissimilar panels will result in an amperage output in the 5.8 amp range, not "about 13".  There isn't a sensible way to combine these very different modules without considerable losses. IF the larger ones were 72 cell panels you would be able to series wire the 12 volt panels to get similar voltage to the 72 cell panels.
     Your picture , at least on my monitor, makes it impossible to count the cells. The 12 volt modules must be something other than typical 36 cell 12 volt modules. The larger ones look to be other than 60 cell modules. Can you give cell count?

    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.

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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    edited January 2017 #6
    Thanks for the correction littleharbor2. Should have had my coffee before getting on the forum.
    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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  • andyrud
    andyrud Solar Expert Posts: 70 ✭✭
    #7
    littleharbor2 said:
    Raj174 said:However, you have a very good MPPT charge controller and it will allow you to to string 1 grid tie panel, 230 watts, in series with 1 12 volt panel, 100 watts, to make a 330 watt string at 47 volts and about 13 amps. Connect these strings in parallel for 1320 watts. That is about the max wattage for the classic 150 at 12 volts. Of course you should have a DC circuit breaker on each string in a combiner box. 

      Absolutely wrong.  Series wiring such dissimilar panels will result in an amperage output in the 5.8 amp range, not "about 13".  There isn't a sensible way to combine these very different modules without considerable losses. IF the larger ones were 72 cell panels you would be able to series wire the 12 volt panels to get similar voltage to the 72 cell panels.
     Your picture , at least on my monitor, makes it impossible to count the cells. The 12 volt modules must be something other than typical 36 cell 12 volt modules. The larger ones look to be other than 60 cell modules. Can you give cell count?
    The 24 volt panels have 72 cells and the 12 volt panels have 36 cells.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,102 ✭✭✭✭✭
    edited January 2017 #8
    You mentioned you thought the 24 volt panels were 30 volts DC. The 72 cell panels should be around 36 volts  and around 44 volts open circuit. And the 36 cell panels should be around 18 Vmp and 21-22 Voc.
    You should be able to series wire the12 volt panels 2 at a time to create a 24 volt nominal voltage similar to your 24 volt panels.

     Being that you are running a 12 volt system I would parallel all 24 volt strings and single 24 volt panels in a fused combiner box and send that to your charge controller. If you were to series the 24 volt panels your voltage would be unnecessarily high unless you are sending this a long distance to the charge controller. How far is the array from the CC and what size wire are you using for that run?

    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.

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  • andyrud
    andyrud Solar Expert Posts: 70 ✭✭
    #9
    littleharbor2 said:
    You mentioned you thought the 24 volt panels were 30 volts DC. The 72 cell panels should be around 36 volts  and around 44 volts open circuit. And the 36 cell panels should be around 18 Vmp and 21-22 Voc.
    You should be able to series wire the12 volt panels 2 at a time to create a 24 volt nominal voltage similar to your 24 volt panels.

     Being that you are running a 12 volt system I would parallel all 24 volt strings and single 24 volt panels in a fused combiner box and send that to your charge controller. If you were to series the 24 volt panels your voltage would be unnecessarily high unless you are sending this a long distance to the charge controller. How far is the array from the CC and what size wire are you using for that run?
    About 60 feet.  I don't recall the wire size BUT the wire was sized for a 12 volt system, and since then I changed it to a 24 volt array so the wiring is oversized now.

    Andy R
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