Adding Batteries

I live with a radically small off grid system, 200 watts of panels backed by three 300 aH batteries. My question is this; I've recently come into ownership of six new deep cell batteries and was hoping to switch the older and smaller battery bank for the newer six for added storage through gloomy days and nights. I am planning on upgrading the entire system to around 750 watts this summer, but am only able to do it piece by piece.

Sorry for the vagueness of my post, this is my first post here and greatly appreciate any guidance given. I have lived in a remote off grid cabin since 2012 and have the desire for just a bit more power as all I can support is an 8 cubic foot Sundanzer refrigerator and several LED lights.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,485 admin
    In general, you should probably add solar panels to your installation. Having a lot of battery bank and few watts of solar panels is usually a prescription for short battery life.

    Exactly, what is the voltage/AH of the new batteries and are they flooded cell or AGM/some other type?

    And, roughly, where is the system installed (hours of sun per day) and have you measured your loads (Amp*Hours @ xx Volts/Watt*Hours per day, etc.)?

    Lead acid batteries do not like to sit at (roughly) less than 75% state of charge, or they will begin to sulfate and die. If they are cycling (above 50% state of charge) they can go longer between full charge (charging back over ~90% state of charge). But even then, the batteries really need a minimum rate of charge (5% minimum, 10-13% or so nominal) too.

    You don't want your new bank to be treated badly early in their life--They will not last nearly as long.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CALLDCALLD Solar Expert Posts: 230 ✭✭
    BB. wrote: »

    Lead acid batteries do not like to sit at (roughly) less than 75% state of charge, or they will begin to sulfate and die. If they are cycling (above 50% state of charge) they can go longer between full charge (charging back over ~90% state of charge). But even then, the batteries really need a minimum rate of charge (5% minimum, 10-13% or so nominal) too.

    -Bill

    Bill - is there a rough formula one can apply to determine when a battery absolutely needs to be brought back up to 100% SOC before permanent sulfation sets in?

    > time elapsed since last full charge
    > average depth of discharge
    > average temperature of the battery
    > rate of discharge
    > rate of charge
    > battery type
    There maybe more factors...

    I've seen some battery manufactures saying 24hours max between 100% soc's, other simply say "recharge after use". Independent advisors say up to 1 week in cold environments and up to 24hours in hot environments. Others have claimed that certain charge regimes can restore batteries that have sat discharged for over a month to perfect health.

    I bring mine to 100% almost daily for fear of damaging them - I use my chargers if I must...
  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    I live with a radically small off grid system, 200 watts of panels backed by three 300 aH batteries. My question is this; I've recently come into ownership of six new deep cell batteries and was hoping to switch the older and smaller battery bank for the newer six for added storage through gloomy days and nights. I am planning on upgrading the entire system to around 750 watts this summer, but am only able to do it piece by piece.

    Sorry for the vagueness of my post, this is my first post here and greatly appreciate any guidance given. I have lived in a remote off grid cabin since 2012 and have the desire for just a bit more power as all I can support is an 8 cubic foot Sundanzer refrigerator and several LED lights.




    Check out my set up in my signature...

    Your set up is kind of like minez... small. Im on ~800watts of panels and 6 autozone batteries hooked up in parrallel (some people get jelly of my battery situation). I run a fridge 24/7 too. No generator. You dont need the expensive sundanzer fridge, kenmoore makes a 40watt refridgerator... we been using it for about a year or 2. Its prolly about $100

    Where you live is improtant, as Im in the desert where theres sun every day... you may need to double or triple your system if you live not in the desert.

    --cake


    PS here is the youtube link for that fridge I was mentioning:

    www.youtube.com/watch?v=YrHN6iTMtvM
    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


  • softdownsoftdown Solar Expert Posts: 2,360 ✭✭✭✭
    I tried a similar system awhile ago. December disaster for me... Currently batteries are expensive while panels are cheap. Seems a bit logical to be panel intensive and battery light these days.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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