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Thread: Can I Use Solar for 220 volt AC Well Pump?

  1. #1

    Default Can I Use Solar for 220 volt AC Well Pump?

    Lets say I wanted to use solar power to operate a 3/4 hp well pump that runs off of 220 AC, how many solar panels, how big of an inverter, and how many batteries would I have to have for this to work?

    If I used 12 volt batteries wouldn't I need about 19 batteries to get 220 volts?

  2. #2
    Join Date
    Mar 2006
    SF Bay Area (California)

    Default Re: Can I Use Solar for 220 volt AC Well Pump?

    In general, the first place is to start with understanding the load.

    A typical AC induction motor well pump will need around 3-5 times is rated wattage for an inverter to start it. Say your pump needs 1,000 watts to run, you will probably need a 2,000 watt or larger inverter to run it (it also depends on the inverters--some are much better at supporting surge loads than others).

    All About Inverters
    Choosing an inverter for water pumping

    Since well pumps are a major load (both surge and running)--Working to reduce those loads can be a big help in reducing the costs providing the power.

    For example, there are VFD controller (variable frequency drives). These drive three phase (or well pumps with an external capacitor at the well head) can can "soft start" or even limit pump RPM/Power (if pump is larger than you need, the VFD can "throttle back" on its output frequency and reduce peak power usage).

    Another option is to get well pumps with soft start (Grundfos SQ series are an example). An in well pump that will use much less power (more efficient, VFD built in pump).

    Or, you can get pumps that will work directly with AC or DC power (inverters, generators, battery banks) or even directly with Solar Panels (Grundfos SQF series--not cheap at ~$1,700 or so--not in business, just a guess). If you use solar panels direct--You pump into a cistern/storage tank while the sun is shining and use gravity or a small DC (or AC) pump for home pressure (with bladder tank).

    A version of the above is "slow pumping"--Just a few GPM filling the cistern (low peak power, very efficient pump), and the cistern supplies the "peak" water flows.

    The money you put "in the well" can save you the money that you would have to put in an off-grid solar+battery+inverter system.

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

  3. #3

    Default Re: Can I Use Solar for 220 volt AC Well Pump?

    Yes you can use solar to run a 220 VAC water pump. It isn't very efficient, as it would cost a lot of money to build a system capable of it.

    The number of batteries isn't dependent on the pump Voltage but rather on the over-all power capacity needed.

    Like this:
    The pump has a demand of X Amps @ 220 VAC. You need an inverter capable of 220 (actually 240 VAC these days) output with enough Watt capacity to handle both the running power and the start-up surge demand, which can be very heavy (like 5 times the running Watts).
    The inverter is power by a battery bank capable of the system Voltage required (12, 24, or 48) and with sufficient Amp hours to run the inverter and pump as demand requires. Determining that can be a bit tricky, as you can't plug a 240 VAC appliance into a Kill-A-Watt; they are limited to 120 VAC (except perhaps in Europe?). Knowing how long the pump will run each day requires some investigation. If you can control the run time (by using large pressure tank(s) to store water) you're ahead.
    The size of the battery bank determines what is needed for solar panels and charge controller to replenish it.
    Last edited by BB.; August 24th, 2012 at 8:44 PDT.
    Four 175 Watt panels, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

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

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