Solar for 220 volt well pump

Shadow83 Registered Users Posts: 2
I am trying to build a PV/battery backup to power my 220volt 30amp well pump for up to eighteen hours during grid failure for irrigation but do not know how to calculate the number of batteries or the amount of PV needed to keep them charged. I have considerable money invested in the variable output pump so do not want to change to a DC pump. I know how to set up the circuitry.


  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Welcome to the forum.

    6600 watts for 18 hours is 118.8 kwh.  With inverter losses, add maybe 15%.  Since you don't want to drain your battery more than 50%, you are looking far a battery that stores about 275 kwh.  With a 48 volt battery, that would be a 5700 ah battery. 

    I think they make batteries that big for submarines.   You haven't mentioned the power factor or locked rotor amps of the pump, but if those are a consideration you will need multiple stacked inverters.

    The size of the array needed to recharge the battery depends upon your location and the time of year.  Hopefully the irrigation season coincides with the sunny season. 

    I think that when you spec out the size and cost of such a system, you will buy a generator.

    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Shadow83
    Shadow83 Registered Users Posts: 2
    Thanks for the insightful comments, that is exactly the information I was seeking. A complete generator and electric transfer setup is about a thousand dollars, not counting fuel costs.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    How often do you think you need to resort to backup power?  A couple hours a month, go with the generator,   Couple hours a day, and you still can buy a lot of fuel for the cost of the solar & batteries.
    When sizing the generator, be sure to note the PF of the motor and size the generator to serve that.
    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: ,