A little help on new system???

volleypc
volleypc Registered Users Posts: 2
in Solar Beginners Corner #1
I have a little cabin on a few acres that I try to get out to when I can. I had 2 Ramsond 100 watt panels and a generic charge controller I purchased off ebay.. Those items plus two GC2 batteries from Sams Club has worked great for providing a little light and satellite radio this past year. I just purchased 6 145 Watt DM Solar Panels and 6 GC2 batteries (6 Volt) from Sams. I also purchased a Tristar MPPT 60 A. I was planning on using the Square D QO disconnect which is rated at 48 Max VDC.. My plan was to wire the panels so that I had 2x100 and 3 - 2x145.. Would that be 4 disconnects needed since I can max out at 48VDC? Would I be better off buying another 100 watt and wiring at 3 x 100, 2 - 3 x 145? My understanding with the MPPT is I can input at 36 volt and still run a 12 volt system?? (I would prefer a 12 volt system). The panels are about 24 feet from the controller.. the batteries are roughly 8 feet from the controller. I am not sure how to include the 100 watt panels without hurting the efficiency of the system. What would you do? I have to admit I do not really understand GFI. I know the Square D QO disconnect is offered with GFI but would that work with DC? If it helps I am in Northeast MS

Specs on Ramsond 100 Watt
Make: Ramsond
Model No.: SP100 125x125x36
Product: Photovoltaic Solar Panel
Solar Cell Type: Mono-Crystalline
Solar Cell Grade (A, B, C): A
Condition: Brand New
Availability: IN STOCK
Output Power: 100 Watts
Nominal Voltage: 12 Volts
Maximum/Peak Voltage (Vmp): 18.5 Volts
Open Circuit Voltage (Voc): 22.7 Volts
Maximum/Peak Current (Imp): 5.41 Amp
Short Circuit Current (Isc): 5.55 Amp
Warranty: 25 Years Limited Power Warranty

Specs on DM Solar
* 36pcs of 6" poly-crystalline solar cells
* Cell Efficiency: 17%
* Max Voltage: 1000V
* Pmax: 145W
* Vmp: 18.7V
* Imp: 7.75A
* Voc: 22.3V
* Isc: 8.37A
* Size: 58.27"x26.58"x1.38"
* Weight: 26.4lbs
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: A little help on new system???

    Welcome to the forum.

    Okay, let's sort things out a little.
    First of all, you want to run a 12 Volt system. For that you want to use six 6 Volt batteries (three parallel strings of two in series). Three parallel strings isn't a good idea, really. But let's see what you'd get from that:

    3 * 220 Amp hours = 660 Amp hours @ 12 Volts.
    Panels needed for fully recharging: about 1028 Watts.
    Peak current from same: 66 Amps (more than the 60 Amp controller can pass).
    Proposed panels: six 145 Watt units, 870 Watts total. Peak expected current: 55 Amps (8.5% charge rate on 660 Amp hours - this would work).
    Vmp of these panels is about 17 to 18 Volts, running three in series would be 54 Volts - beyond the rating of the QO breakers.
    But you could run three parallel strings of two, but then you'd need one fuse per string and 8 AWG wire to keep the V-drop to a minimum.

    The Ramsond panels can be in parallel with the DM this way as the Vmp of the two is very close. However this ups the array current to nearly 30 Amps, worsening the V-drop problem.

    Now, which of these problems do you want to address first?

    Me, I'd re-estimate the power usage demands and see about re-sizing the battery bank. Then I'd re-visit the idea of a 24 Volt system instead of a 12 Volt one.
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  • volleypc
    volleypc Registered Users Posts: 2
    #3
    Re: A little help on new system???

    I am going to dig deeper into this tonight after work.. my only issue with 12 volt vs 24 volt is that I do already have some 12 volt DC lights which are not rated for 24 volt. We arent talking many lights so I guess that isnt really much of an issue. Oh.. and it's 8 6 volt batteries.. 2 existing and 6 new.. all the GC2 battery from Sams Club.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: A little help on new system???

    Please note that mixing old and new batteries isn't a good idea, and that four parallel strings of batteries is even worse than three.

    Here's a bit about choosing system Voltage: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power
    And another reference on basic array configuration for MPPT controllers: http://forum.solar-electric.com/showthread.php?16241-Different-Panel-Configurations-on-an-MPPT-Controller
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #5
    Re: A little help on new system???

    We recently helped a guy named Al (aka 'ywhic') He is working on a system using the same panels and has many of the same questions. Here's a thread where he went back and forth about 24 or 12 volt system.

    You might use/abuse your current batteries, expand what your willing to draw them down to (DOD - depth of discharge) and replace them and go to a 24 volt system at a later date. I'm not a fan of adding new to old batteries either.
    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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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #6
    Re: A little help on new system???

    Welcome tot he forum.

    Keep this in mind,, and design and hardware considerations stem, ultimately,from the load calcs. If you have a GOOD estimate of your loads, that will dictate the battery config, which in turn will dictate the charge regimen (and hardware) and will dictate the use hardware (inverter, wiring, etc.)

    Tony
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