Battery Recommendations?



  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Battery Recommendations?

    Okay you're looking at two different things for off-grid power needs: one is the maximum power demand at any given time which tells you how big an inverter you need, the other is total daily Watt hours required which tells you how much battery capacity you need.

    Technically a 1/2 HP pump is "373 Watts" but in reality it can draw a lot more. For accuracy's sake it is a good idea to measure the running current of the pump and if possible the start demand; getting a motor spinning against a head of water takes quite a bit more effort than keeping it spinning. If there is a locked rotor Amps for the motor use that for the maximum.

    So let's say you need 1200 Watts for the pump and another few hundred for everything else. Then the total maximum Watts is <2000 and you don't need a 6kW inverter.

    But you still need to know how long things run for. I know my water pump runs for 6 minutes because I turn it on manually midday to fill up the pressure tank while the sun is shining and the power from the panels would otherwise go unrealized. For most things you can plug them in to a Kill-A-Watt while using them under 'normal' circumstances and see how many Watt hours are used. From this info you can size a battery bank.

    Now there is another issue; converting your 8.4 kW grid-tie array to recharge batteries. There are several ways of doing this, and one of them is to use the GTI's AC coupled to a Sunny Island or XW. Another is to install some switching on the array to power a high Voltage charge controller (up to 600V) or with some more re-wiring a standard Voltage charge controller (up to 250V). Which you choose depends on what sort of GTI system you have now, how fond you are of rewiring, and how much money you want to spend.
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Battery Recommendations?
    .....Water is my main concern, I have a 1/2 hp submersible pump that pumps to a storage tank and a 1/2 hp centrifugal booster pump that pressurizes the pressure tank....

    My "1/2" hp pump (see my .sig, deep well, 160' lift, 7GPM), logs 1.0Kw according to my XW 6048. It has been accurate for every other measurable load I've had on it (750w toaster, 1200w blow dryer) and it may be reflecting the Power Factor of the motor too, still the inverter needs to supply it, so maybe the batteries don't. You will, if you don't have a huge battery bank, need to have an interlock, to only allow 1 pump at a time to run, and increase your pressure tank size to reduce "starts" so you don't bleed the batteries down at night just to pump flush water for toilets.
    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: ,

  • BB.BB. Super Moderators, Administrators Posts: 33,082 admin
    Re: Battery Recommendations?

    Or go with pumps designed for low surge/off grid use...

    Grundfos SQ-Flex (ac/dc/solar panel $$$$) or FLEX (AC $$) will only draw 800-900 Watts max and very little surge. The SQ-Flex pumps are really nice--The FLEX are also nice for AC systems and a bit less costly (as I understand, I am not in the solar biz).

    There are other offgrid pumps that will only draw 300 watts or so. (other poster here recommended)

    Pump to a cistern with in well pump, then use a relatively inexpensive pump to pressurize the home (efficient, surface pump easy to access/repair).

    You can even use a big/cheap genset to pump to a cistern for a few hours per week, then use the DC (or small AC) surface pump.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ChrisChris Solar Expert Posts: 135 ✭✭
    Re: Battery Recommendations?

    So I ended up with T-105+'s......when I came down to placing my order, I got them for $75 less then the US2200's
    They were stamped as being filled with in the last 2 weeks, so I figured this was a no brainer.

    Not sure what the difference between the regular T-105's and the plus's are...any idea?
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