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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
    Location
    SF Bay Area (California)
    Posts
    21,543

    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.

    -Bill
    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 9:44 PDT.
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

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

  4. #4

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

    We have a challenge in sizing and setting up a proper solar PV array. Our farm has a 7.5HP 3phase AC water pump that is used to lift water from 300ft deep borwell. We have been recommended a 10HP VFD controller and have been asked to layout 30 Nos of 250w/24v solar panels as a array. 15 each in series / parallel of 2 arrays so that the required VFD voltage of say 600v can be achieved. I want someone to help me find the right answer for the following doubts...

    a. How does one calculate the required PV overall wattage wrt. to this 7.5HP 3 phase pump already in use? Is 7.5KW PV needed?
    b. How important is the Amps then and how can we achieve max amps based on knowing the AC pump ampere needs?
    c. Is there other proven methods of alternatives apart from these VFD for pumping water during the day by directly from solar?

    Appreciate a few expert thoughts and make me learn!

    Cheers

  5. #5

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

    Quote Originally Posted by prookie View Post
    We have a challenge in sizing and setting up a proper solar PV array. Our farm has a 7.5HP 3phase AC water pump that is used to lift water from 300ft deep borwell. We have been recommended a 10HP VFD controller and have been asked to layout 30 Nos of 250w/24v solar panels as a array. 15 each in series / parallel of 2 arrays so that the required VFD voltage of say 600v can be achieved. I want someone to help me find the right answer for the following doubts...

    a. How does one calculate the required PV overall wattage wrt. to this 7.5HP 3 phase pump already in use? Is 7.5KW PV needed?
    b. How important is the Amps then and how can we achieve max amps based on knowing the AC pump ampere needs?
    c. Is there other proven methods of alternatives apart from these VFD for pumping water during the day by directly from solar?

    Appreciate a few expert thoughts and make me learn!

    Cheers
    Welcome to the forum.

    Let's ask the simple question: Why on Earth do you want to do this?
    Unless you have no grid power at all and the pump has to run off a generator solar is not going to be a cheap solution to supply that much power.
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

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

  6. #6
    Join Date
    Mar 2006
    Location
    SF Bay Area (California)
    Posts
    21,543

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

    How is the system going to be setup? Is this grid tied (solar panel to Grid Tied AC Inverter to AC mains), off grid (solar+battery bank+AC inverter), or panels to VFD (fairly recent "invention")?

    VFDs allow the pump (motor) to operate at different RPMs other than fixed frequency (50 or 60 Hz input). Gives you the option to slow the pump down to operate at lower power/more efficient volume pumping. Also supports "soft start" (starts at near zero Hz and brings pump up to speed/frequency slowly).

    And pump power consumption is highly dependent on pump type, lift, water flow. Have you measured the Pump's current draw (AC Clamp Meter) or Power (Clamp Meter+Voltage Phase measurements using a power meter)?

    The amount of array really depends on your pump's power needs and AC power system type (GT, off grid, VFD connected array).

    A grid tied system (no battery) is fairly standard and usually the most cost effective. The Solar Array and GT inverter are sized to "turn the utility power meter backwards" and credit the amount of power the pump uses. This also depends on your billing agreement with the utility. In some regions (such as California, where it can literately take a Power/Electrical Engineer to design the system and calculate all the ins and outs of peak power usage, kVA usage, time of day, seasonal, 15 minute peak power usage/and even power fed back to grid, etc.).

    Off Grid power is the most expensive (battery bank is very costly, and somewhat inefficient). Used if there is no Utility power and/or utility power is unreliable. Can be 3 to 10x the co$t per kWH vs utility power.

    Using a solar array to VFD is relatively new technology (and not very common yet) to use the solar array to power the pump directly. Can be cost effective and has been used in regions of the world where utility power is expensive or not available. The solar panel provides power to the input of the VFD, and the VFD outputs the power needed to the pump and based on available sunlight (i.e., the pump turns relatively slowly during morning/late afternoon sun, and at "full speed" during the middle of the day). Great for pumping to a storage tank/ponds or flood type irrigation. For sprinkler irrigation, probably not so great--Changing sun gives you changing flow rates/pressure--Sprinkler emitters and drip irrigation may not work well under changing water conditions.

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

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