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Thread: 12 volt or 24 volt battery bank?

  1. #1
    jawss250 Guest

    Default 12 volt or 24 volt battery bank?

    Is it better to have a 12 volt or 24 volt battery bank for a 3000 watt PV system? What combination of batteries is most efficient / cost effective?

  2. #2

    Default Re: 12 volt or 24 volt battery bank?

    Quote Originally Posted by jawss250 View Post
    Is it better to have a 12 volt or 24 volt battery bank for a 3000 watt PV system?
    A popular question!
    Your system Voltage should not be based on the array size. The whole thing should be designed around the loads. How many Watts do you need to supply at any given time? If it is less than 2kW, you can use a 12 Volt system. The higher it goes, the higher the system Voltage should be in order to reduce the Amps drawn for a given Wattage, enabling smaller DC wiring and less heat generation.

    Size the Inverter according to the maximum Wattage drawn at any one time. The battery bank needs to have enough capacity to supply the daily Watt hour needs (to a maximum 50% DOD). The array & charge controller should be suitable to recharge the battery bank in the (typically) "equivalent 4 hours of good sun". Designing it otherwise leads to disappointments.

    What combination of batteries is most efficient / cost effective?
    That would depend on what batteries you can get for what price. Sometimes you can buy "golf cart" deep cycles from Sam's Club or Costco for quite cheap, and many here have reported quite acceptable service from them. A good "starting out" battery, as they don't cost much per $ and the FLA-type batteries are more tolerant of "mistakes" in charging & discharging.
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  3. #3
    Join Date
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    Default Re: 12 volt or 24 volt battery bank?

    For a 3kW PV Array--I would suggest that 24 volt is a minimum (that is around 100 amps charging your battery bank @ 24 volts and would require around 2 MPPT charge controllers; at 12 volts that would be >200 amps and require 3-4 MPPT charge controllers)...

    If you did this at 48 volts, you would only need 1x MPPT charge controllers (around $600 a piece)--That can save you a lot of money (to put into the battery bank and inverter(s)).

    But as Marc says--You also need to look at your peak loads...

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

  4. #4
    Join Date
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    Telford,Pa
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    Default Re: 12 volt or 24 volt battery bank?

    I vote for looking at 48 volts.

    I have a 960 watt array. If I had to do it again, I would be going 24 volts.


    3000 watts @ 12 volts = 250 amps = 5 Charge controllers
    3000 watts @ 24 volts = 125 amps = 2 charge controllers
    3000 watts @ 48 volts = 63 amps = 1 charge controller
    Ken
    Telford,Pa
    Old Homepage: http://home.comcast.net/~n3qik
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  5. #5

    Default Re: 12 volt or 24 volt battery bank?

    Quote Originally Posted by bobdog View Post
    ...what's the deal with the charge controllers?
    They can only output 60 Amps regardless of output voltage. Power = Volts times Amps, therefore 12V x 60A = 720 Watts maximum of panels per controller and 48V x 60A = 2880 Watts of panels (roughly). Most popular ones anyway: Outback FM-60, Xantrex XW-60 and Morning Star MPPT-60.

  6. #6
    Join Date
    Feb 2008
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    Gila Wilderness, NM
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    Default Re: 12 volt or 24 volt battery bank?

    Quote Originally Posted by AntronX View Post
    They can only output 60 Amps regardless of output voltage. Power = Volts times Amps, therefore 12V x 60A = 720 Watts maximum of panels per controller and 48V x 60A = 2880 Watts of panels (roughly). Most popular ones anyway: Outback FM-60, Xantrex XW-60 and Morning Star MPPT-60.
    Thanks. I felt embarrassed to ask. This stuff is like math in that you have to practice it. And unfortunately I don't keep very good notes or "practice" enough.
    2 Kyocera 130, 2 Kyocera 135, Tristar MPPT 45, SureSine 300, Iota 30r TS, 420 amps battery juice, 5000 watt and 2500 watt gen, lots of wire...

  7. #7

    Default Re: 12 volt or 24 volt battery bank?

    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

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