Battery Bank

With54With54 Registered Users Posts: 21
We have 600 watts of pv at the cottage and needs to instal a battery bank without breaking the bank. How do I calculate the number of batteries I will need? What type of battery should I purchase?



  • RCinFLARCinFLA Solar Expert Posts: 1,353 ✭✭✭
    Re: Battery Bank

    You are doing things backwards.

    What is your consumption?

    What is DC input voltage of inverter?

    What charge controller do you have or intending to buy?

    General rule of thumb is 12vdc for every 1200 watts of needed peak power.

    1000 watt -> okay with 12v
    2000 watts -> 24 v or higher
    3000 watts -> 48 v system.
  • mike95490mike95490 Solar Expert Posts: 9,320 ✭✭✭✭✭
    Re: Battery Bank

    You have to look at your loads. Watts of each, x hours you run them. are they 12V gadgets, or 240V well pumps. 120V vacuum cleaner ? You size the batteries to the loads, and then size the PV to charge the battery bank.

    600W of PV could charge a 12V 400A bank (2, 6V 200A in series)
    or a 24V 200A bank (2, 12V 100A in series)

    Useing AGM batteries, you could go 10% higher in bank capacity (less losses in the batteries)
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Bank

    No slur on you, With54, but here we are designing in reverse again! :p

    Normally you size the PV to recharge the batteries you need to handle the loads you've got to run. In other words: calculate loads first, get the right inverter & batteries to handle that, then figure out what is needed in PV to recharge the batteries.

    But to go with existing array ...
    600 Watts is likely to be 480 "usable". A nice size for a small 12V system. It could easily recharge about 340 Amp hours of battery (about 34 Amps max). There's no simple division of this to fit the least expensive "golf cart" type deep cycle batteries, which are around 225 Amp hours. L16 'A' would fit this scenario, but they are expensive. So the most you could do would be two sets of the T105 type (golf cart) @ 450 Amp hours being recharge at around 7% capacity. That should work. It would give you approximately 225 Amp hours maximum to work with, or roughly 2.7 kW hours. But since the panels will only 'harvest' about 1900 Watt hours per day, you should keep the usage below this. Use 25% DOD: 1350 Watt hours per day. That should keep everything 'happy'.

    Usual disclaimer: all calculations approximate and do not include specific system efficiency factors, et cetera.
  • With54With54 Registered Users Posts: 21
    Re: Battery Bank

    Xantrex Mppt 60 charge controller and will go either 12 volt or 24. Approx. 2000 watt hours per day.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Bank
    With54 wrote: »
    Xantrex Mppt 60 charge controller and will go either 12 volt or 24. Approx. 2000 watt hours per day.

    Amazingly close to my predicted 1900 Watt hours per day, eh? :p
    Not much advantage going up to 24V on a system this size. Not much reason to use a 60 Amp MPPT controller either, unless it's what you've already got and/or you're planning on expanding the array.

    To use a metaphor: You've got to figure out your destination before you continue your journey.
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Battery Bank

    And to anyone/everyone reading these type of threads... I have some parts and want to build a system out of them for not much money.

    When "we" provide some advise--It is almost always because "we" have made the same mistakes ourselves first--And don't want to see the posters make the $ame mi$take$ that we have made ourselves.

    Sometimes that is done with humor--Sometimes that intended humor does not read right on the Internet. :blush:

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Battery Bank

    And sometimes we're just a gouchy old bear with a sore tooth. (Points at self.) :D
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery Bank
    dwh wrote: »
    And sometimes we're just a gouchy old bear with a sore tooth. (Points at self.) :D

    well it could be worse as you could be grouchy, but that'll teach you to make your tooth angry.:p niel ducks from flying internet tomatoes.:-)
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