Pumping water without batteries in emergency situations

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  • 123easy
    Junior Member
    • Nov 2020
    • 22

    Pumping water without batteries in emergency situations

    Im sure i will be lambasted for this question but has anybody tried to run their pump with panels straight into the inverter for emergency situations? I was thinking the panels would have to be configured to the inverter and pump need sminus losses for both voltage and amps and a DC to dc regulator might be required. It of course would only work for a constant period of sun on the panels say ten minutes. Around here everyone is using the grundfos sq pumps and their soft start demands are pretty light. If the power could be configured so the inverter didnt choke I dont see why it couldnt be done... Thoughts?
  • SunEagle
    Super Moderator
    • Oct 2012
    • 15126

    #2
    First off pv panels are current sources and inverters are looking for voltage source like a battery. So connecting the panels directly to an inverter will not work.

    Now you can run a DC pump directly from the panels provided the pump is rated for the output current and voltage the panels system produces.

    I have a DC fan in my shed that is connected directly to a small panel and it runs at different speeds depending on the amount of sun hitting it.

    If you are trying to use solar to run a water pump during an emergency you will need to build a solar/battery system which includes batteries and charger along with the panels and inverter. Depending on what the pump requires to run it will probably be cheaper to just get a small generator to run it to some type of tank and then send the water to the use point by gravity.

    Comment

    • 123easy
      Junior Member
      • Nov 2020
      • 22

      #3
      Thank you for the reply! While I understand that the panels are a current devices like a semi conductor but they also have voltage. For instance a 48v MPPT charge controller will not function unless enough panels are placed in series to exceed its output voltage by a margin. If I put a DMM on the panels output it shows a increase of voltage as i add each panel. This voltage is still present with current flowing. Would this not meet the input requirements of the inverter if configured to them? I know your answer is no but i dont understand why... Is it Because the current is determined by the panels not the load of the inverter even if they are matched?

      Comment

      • Mike90250
        Moderator
        • May 2009
        • 16020

        #4
        PV panels cannot produce consistent power. The sun is always fading in and out - our eyes cant see it. And Panels cannot produce surges of current needed to start an AC pump.

        Sadly, a generator is a better option for short term emergencies.
        Powerfab top of pole PV mount (2) | 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

        solar: http://tinyurl.com/LMR-Solar
        gen: http://tinyurl.com/LMR-Lister

        Comment

        • SunEagle
          Super Moderator
          • Oct 2012
          • 15126

          #5
          Originally posted by 123easy
          Thank you for the reply! While I understand that the panels are a current devices like a semi conductor but they also have voltage. For instance a 48v MPPT charge controller will not function unless enough panels are placed in series to exceed its output voltage by a margin. If I put a DMM on the panels output it shows a increase of voltage as i add each panel. This voltage is still present with current flowing. Would this not meet the input requirements of the inverter if configured to them? I know your answer is no but i dont understand why... Is it Because the current is determined by the panels not the load of the inverter even if they are matched?
          Basically the panels rarely provide a constant current output to a load which why that load need to be variable speed. Fans and DC pumps work with panels but an AC load connected to an inverter will not be able to run if the panel current & voltage changes. You need a constant voltage source like a battery to feed the inverter.

          Comment

          • 123easy
            Junior Member
            • Nov 2020
            • 22

            #6
            Thank you for the reply suneagle!

            Comment

            • 123easy
              Junior Member
              • Nov 2020
              • 22

              #7
              Ok I found this. "DC-DC Boost Converter with Constant Output Voltage for Grid Connected Photovoltaic Application System " https://core.ac.uk/download/pdf/12342408.pdf

              And this ... https://www.ebay.com/itm/1500W-DC-DC...oAAOSwRWdfROTu

              Assuming i can get max power out of it 20 amps at 60v, Its very marginal with inverter losses. However I was running my pump and household needs off a 1500 watt inverter for a while till I upgraded with no problem. Lighting desktop and on demand propane water heater all on at same time as pump and inverter didnt choke so... Maybe that grundfos SQ is pulling under 10a 120... Have to get a clamp on amp meter on it. The "soft start" claims start amps same as run amps.

              Hey what can I say it how i get my kicks. It a relatively inexpensive way to have fun.

              Comment

              • SunEagle
                Super Moderator
                • Oct 2012
                • 15126

                #8
                Originally posted by 123easy
                Ok I found this. "DC-DC Boost Converter with Constant Output Voltage for Grid Connected Photovoltaic Application System " https://core.ac.uk/download/pdf/12342408.pdf

                And this ... https://www.ebay.com/itm/1500W-DC-DC...oAAOSwRWdfROTu

                Assuming i can get max power out of it 20 amps at 60v, Its very marginal with inverter losses. However I was running my pump and household needs off a 1500 watt inverter for a while till I upgraded with no problem. Lighting desktop and on demand propane water heater all on at same time as pump and inverter didnt choke so... Maybe that grundfos SQ is pulling under 10a 120... Have to get a clamp on amp meter on it. The "soft start" claims start amps same as run amps.

                Hey what can I say it how i get my kicks. It a relatively inexpensive way to have fun.
                That item may work. But it is your money and time to spend on experiments.

                Let us know how it works out for you.

                Comment

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