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Thread: Can I Use 24v Panels on a 12v System

  1. #1

    Default Can I Use 24v Panels on a 12v System

    I would like to use a couple (2) 240w panels (~33v and 7a for each panel) to charge a 12v battery bank (2 - 6v 220ah batteries in series) using a MPPT charge controller... will I have any problems with this? Also, I plan to connect the panels in series and the CC is rated for 150voc and 45a. Thanks for any input!

  2. #2
    Join Date
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    Near Phoenix
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    Default Re: Can I Use 24v Panels on a 12v System

    Quote Originally Posted by Caneman View Post
    I would like to use a couple (2) 240w panels (~33v and 7a for each panel) to charge a 12v battery bank (2 - 6v 220ah batteries in series) using a MPPT charge controller... will I have any problems with this? Also, I plan to connect the panels in series and the CC is rated for 150voc and 45a. Thanks for any input!
    Yes that will work, given all the rest of the components are sized. OK.
    My TED 5000 system
    Sticking it to the power company one watt at a time!
    60 Ningbo Electric 175 watt panels and 12 Canadian Solar 180 watt panels with 2 PVP 5200 Inverters

  3. #3
    Join Date
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    Default Re: Can I Use 24v Panels on a 12v System

    Yes, assuming you're using a MPPT controller. what is your controller?

    Tony
    Please note, being a moderator does not add any weight to my opinions 300 watts Siemens/BP panels,plus a Sun 90,, making ~400. ~30 amps into Rogue MPT-3024, 450 ah of Trojan T-105, Morningstar ts300 inverter, a Tri-Metric meter.a collection of antique generators, plus 2 Honda eu-1000i's (also a BS2512 IX controller) and assorted other stuff!

  4. #4

    Default Re: Can I Use 24v Panels on a 12v System

    I am planning on using this CC:


  5. #5
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    pittsburgh, pa
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    Default Re: Can I Use 24v Panels on a 12v System

    this will be capable of a higher than normal charge rate so you may need to watch your maintenance of the batteries more often. otherwise it is fine.
    NIEL

  6. #6
    Join Date
    Oct 2010
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    Nova Scotia canada
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    Default Re: Can I Use 24v Panels on a 12v System

    My cousin has similar at his camp. Two 37 volt panels, and since they are roughly 200 feet from the camp, wired them in series, doubling the voltage to his TS-MPPT-60 which then dumps into his two L-16 batteries. (12 volt system)
    Works very well for him.
    By the way, I highly recommend the optional meter for this controller. Really shows you what's going on.
    1900 watts PV, (1000 watts PV feeding MidNite Classic 150; 900 watts PV + 160 watts micro hydro both feeding into a single shared Morningstar TS-MPPT-60) ; Xantrex Pure Sine 1800/12 for heavy loads; Xantrex Pure Sine 1000/12 on 24/7 for everything else; six Rolls Surrette 2 volt L16 @ 12 volts.
    Domestic hot water totally provided by the sun 8 months out of every year via thermal panel.

  7. #7

    Default Re: Can I Use 24v Panels on a 12v System

    Quote Originally Posted by waynefromnscanada View Post
    By the way, I highly recommend the optional meter for this controller. Really shows you what's going on.
    I was thinking about that meter as well... will it give me the same information that a Trimetric battery monitor would?

  8. #8
    Join Date
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    Default Re: Can I Use 24v Panels on a 12v System

    No--Not really.

    The charge controller display only shows what the charge controller is outputting (voltage, current, other parameters). Not bad and probably useful if you need to access charge controller parameters without plugging in an adapter and PC. It cannot tell the difference between loads and charging current to the battery.

    A Battery Monitor logs the current into and out of the battery bank (which is very important to the health of your batteries). Most battery monitors can give you an estimated State of Charge (XX% SOC) at anytime (very nice for spouse, kids, guests to help them not drain your bank because of too much loading). As well as showing you the present current into/out of the battery bank.--You don't need to use a hydrometer or measure the resting voltage. And for sealed batteries, you cannot even measure the specific gravity.

    Of course, Battery Monitors are not perfect and can drift overtime. Usually they reset back to 100% based on >XX volts charging for longer than Y hours. And, they cannot account for sulfation/aging of the battery (loss of capacity)--Of course, you can always program the charge controller for less capacity if needed.

    Although, there are many people that have used a hydrometer and voltmeter to monitor their batteries over the years with great success too.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  9. #9

    Default Re: Can I Use 24v Panels on a 12v System

    thanks everyone you have been really helpful!

    Can I expand this 150v 45a CC with 2 strings of panels in parallel, each string is (3) 240w panels in series, to charge the 12v battery bank?


    edit: I think it just dawned on me that the max solar array I can use with a 45a CC and 12v battery bank is 45 x 12 = 540w. and any incoming panel watts over this will not be used, is this correct?
    Last edited by Caneman; March 15th, 2012 at 15:55 PDT. Reason: doh

  10. #10
    Join Date
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    Default Re: Can I Use 24v Panels on a 12v System

    Depending on how cold it gets in your area--Around Vmp-array of ~100 VDC maximum (higher Vmp can make Voc-cold>150 VDC max controller input voltage). MPPT charge controllers can manage very large arrays as the (good quality) MPPT controllers will limit their output current to a safe level (no damage)... So, normally, the maximum cost effective array size would be:
    • 45 amps * 14.5 volts batt charge * 1/0.77 panel+controller derating = ~847 watt maximum "cost effective" array


    You can go over this value, but on clear/cool days, your charge controller will bump up against the 45 amp limit for a greater percentage of the day.

    Again, just a rough number, going >>847 watts is not going to hurt anything--but the controller will simply not output any more than 45 amps.

    So 2 strings * 3 panels * 240 watts per panel = 1,440 watts ... Your controller will spend a fair amount of time (several hours a day) at 45 amp output maximum.

    If you think you will have 1,440 watts of solar panels, you have too (major) options.

    Option 1 is to get a larger charge controller (or two smaller controllers in parallel at the battery bank--each handling 1/2 the string):
    • 1,440 watts * 0.77 derating * 1/14.5 volts = 76.5 amps


    So, either two 45 amp controllers or one 80 amp controller.

    Option 2 is to pick a 24 or 48 volt battery bank... That will cost you a new inverter (and other possible direct DC load issues), but, for example a 24 volt battery bank controller (your 45 amp MPPT controller is 12/24/48 volt) will manage:
    • 1,440 watts * 0.77 derating * 1/29.0 volts = 38.2 amps (your planned 45 amp MPPT controller will be fine)


    And a 48 volt battery bank will be 1/2 the output again:
    • 1,440 watts * 0.77 derating * 1/58.0 volts = 19.1 amps (you can add even more panels/strings to your 45 amp MPPT controller)


    Your choice... Figure out what your ultimate planned loads/battery bank/array size will be... And what voltage(s) make sense for your loads (inverter, 12/24 volt DC loads are more common than 48 VDC). And remember if you are sending the power any distance--12 volts is a bear to send very much power any distance without spending a ton on copper wiring.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

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