best way to mix solar panels

henrehenre Registered Users Posts: 5 ✭
in Off Grid Solar & Battery Systems #1
I have 7, 100 Watt, 18 Volt, 5.5 Amp Panels, a 100 Amp MPPT Charge Controller and a 12 Volt Battery System.

I connected 2 of the panels in parallel so I had 1 at 200W 18V and 5 at 100W 18V. Then I connected everything in 2 serial pairs so I had 2 at 100W 36V and 1 at (I'm totally guessing 150W) 36V. I then ran those 3 sets in parallel to the charge controller.

Is there a better way to do this?

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  • TecnodaveTecnodave Registered Users Posts: 437 ✭✭✭✭
    edited June 2019 #2
    henre,

    Best result with what you have is to configure 3 strings of 2 panels each. Any attempt at using the 7th panel will not produce more power when using this 6 panel array with a MPPT type of controller. 

    If if this installation is on an RV you might consider an additional controller of the PWM type to charge the house lighting battery or the engine starting battery.
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Exeltech XP-1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or LiFePO4,
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  • HorseflyHorsefly Registered Users Posts: 451 ✭✭✭✭
    #3
    There isn't really a good way to connect an odd number of panels. If you put panels in series, you want them to all be rated the same Amps (within 5%).  If you put panels in parallel, you want them to be rated the same Volts (within 5%).

    If you put two panels in parallel, that creates effectively one virtual panel with the Amps added of both. So those two in parallel now makes an 18V 11A panel.  If you put two panels in series, the resulting virtual panel will have a voltage rating of the sum of the two panels. 

    If you put two panels in series that are not the same Amps, the resultant virtual panel will be limited to the lower of the two Amps.  If you put two panels in parallel that are not the same voltage, the resultant virtual panel will be limited to the lower of the two Voltages.     

    In your case, you can create combinations of three parallel strings of two panels, or two parallel strings of three panels. There isn't anyplace to put the seventh panel that doesn't drag down the total combined power.

    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 8S (25.6V), 230Ah Eve LiFePO4 battery in a custom insulated and heated case.
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  • BB.BB. Super Moderators, Administrators Posts: 32,999 admin
    #4
    Also, look at the specs for your MPPT charge controller.

    Vmp and Imp requirements for the MPPT input puts hard limits on your array configuration. And local min/max temperatures also need to be taken into account.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • henrehenre Registered Users Posts: 5 ✭
    #5
    Thanks for the info. I think I will buy an 8th panel to even it out.

    Is the 7th panel actually reducing the over all power or just adding less than the others?

    End goal is to power a 12V battery. What is best running 2 panels in serial so the input is 36V or all in parallel so the input is 18V?
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  • TecnodaveTecnodave Registered Users Posts: 437 ✭✭✭✭
    #6
    henre 

    an MPPT controller needs some headroom so a all parallel connection will not work for you, you need two in series to get enough voltage for the MPPT controller to do its job. 

    A 7 panel will produce nothing when connected in parallel with banks of 2 in series, do buy an another panel to keep system balanced.
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Exeltech XP-1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or LiFePO4,
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  • littleharbor2littleharbor2 Solar Expert Posts: 1,823 ✭✭✭✭✭
    #7
    This proposed 8 panel set up has the potential to produce in the neighborhood of 65 amps. What size battery bank do you have? What batteries and configuration are you using?

    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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  • henrehenre Registered Users Posts: 5 ✭
    #8
    I have 2, 12V 100 AH lithium batteries in parallel.

    I just realized my controller is 60W not 100. So I guess the 8th panel will put me over the limit? They are all flat on an RV roof. Since they are flat would they perform under 60 amps?
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  • BB.BB. Super Moderators, Administrators Posts: 32,999 admin
    #9
    Can you give us a link to your controller?

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • littleharbor2littleharbor2 Solar Expert Posts: 1,823 ✭✭✭✭✭
    #10
    henre said:
    I have 2, 12V 100 AH lithium batteries in parallel.

    I just realized my controller is 60W not 100. So I guess the 8th panel will put me over the limit? They are all flat on an RV roof. Since they are flat would they perform under 60 amps?
    I'm not  very familiar with lithium battery charging characteristics. You will have the potential to charge at 30% of your bank's capacity though. 

    Flat mounted on an RV roof isn't the ideal arrangement although you could still have high output if, say you were camping up in the mountains on a cool summer day.

    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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  • henrehenre Registered Users Posts: 5 ✭
    #11

    I purchased 100A but the manual says 60A. Not sure if it is 60 or 100. Any way to tell for sure?

    I will be camping in the mountains on cool summer days.

    Thanks for all the help


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  • littleharbor2littleharbor2 Solar Expert Posts: 1,823 ✭✭✭✭✭
    #12
    Two things,   That isn't a real MPPT controller and I'd be very leery of putting 60 amps into one of those cheap controllers.

    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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  • henrehenre Registered Users Posts: 5 ✭
    #13
    Does that mean it's a PWM or something different?
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  • TecnodaveTecnodave Registered Users Posts: 437 ✭✭✭✭
    #14
    Henry,

    At $16 it's Chinese junk, there is no law against using the term MPPT in your product name it does not mean it's an MPPT controller. Even a decent PWM controller will cost more than that! Go look at something decent, maybe a Victron Smart solar for a less expensive full featured controller. Or maybe MidNite Brat in a less expensive PWM type controller...about $90 at solar-electric.com
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Exeltech XP-1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or LiFePO4,
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  • TecnodaveTecnodave Registered Users Posts: 437 ✭✭✭✭
    #15
    There is one other seller selling that same controller on eBay for $1.99..........pure junk
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Exeltech XP-1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or LiFePO4,
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  • Raj174Raj174 Solar Expert Posts: 795 ✭✭✭✭
    #16
    littleharbor2 said:
    henre said:
    I have 2, 12V 100 AH lithium batteries in parallel.

    I just realized my controller is 60W not 100. So I guess the 8th panel will put me over the limit? They are all flat on an RV roof. Since they are flat would they perform under 60 amps?
    I'm not  very familiar with lithium battery charging characteristics. You will have the potential to charge at 30% of your bank's capacity though. 

    Flat mounted on an RV roof isn't the ideal arrangement although you could still have high output if, say you were camping up in the mountains on a cool summer day.
    Lithium drop-ins can generally be charged at 50% of capacity, up to 100 amps in this case.
    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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