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Thread: Pump for a 300 foot well?

  1. #1

    Default Pump for a 300 foot well?

    I'm looking to install a solar pump for a well to serve a small off-grid residence. The well is 330 feet deep, with water struck at 260 feet and a final water level of 110 feet. The plan is to have a 1000 to 2000 gallon cistern, and the pump keeping it topped off.

    The cistern is only 10 or 15 feet above the level of the home, so some sort of pressure system will also be needed, I expect. Can anyone recommend a pump for this application? And what are the best solutions for adding pressure to the home water supply?

    Thanks!

  2. #2
    Join Date
    Mar 2006
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    SF Bay Area (California)
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    19,653

    Default Re: Pump for a 300 foot well?

    I don't have a well--so my experience is limited... Check our host's well pump website.

    The Grundfos line has some very nice pumps... They can run on AC or DC power--Basically, you can run several panels in series (for high enough voltage) directly to the pump, or run with batteries and a charger, or even switch over to an AC backup genset--all with the same exact pump.

    One way to do the well pump is use a DC capable pump with its own dedicated solar panels. When the sun is up the pump starts up and pumps a little water--and at high noon (+/-)--the pump will pump at rated power.

    If you can avoid batteries and just use solar panels--you save a whole bunch of costs (solar charge controller, large battery bank, battery maintenance, and bank replacement every 5-10 years or so). Also, batteries and charge controllers cost you ~25% in loss power.

    However--if your pump is next to your off-grid cabin--you probably would like battery/AC power there too...

    So, you may end up choosing to install an off-grid solar power system there (panels, charge controller, batteries, AC inverter) and use that system to power your deep well pump. This makes sense because you can share the panels/power system between the needs of the cabin and the pumping (probably with backup genset).

    If the well pump has its own panels--when water is not needed (no irrigation, rain collection, etc.)--those panels are just sitting there not generating any power for your cabin.

    For pressurizing your cabin's water system--a simple Shurflo (or equivalent) DC water pump is probably good for a start. Only takes power when the water is needed (and/or to fill a local pressure tank).

    The DC pump will need maintenance (brushes, seals, etc.)--but it is easy to get at (above ground) and is not an expensive unit.

    You can certainly make a large Solar PV Electric system with 3-6kW inverter to power just about any type of standard AC well pump--but it depends on how much you want to spend--and what is really practical for your residence (full-time home, vacation cabin, etc.).

    You probably will need to cost out several options (solar panels + pumps) vs a "large" solar PV system for the residence that can power the in ground/above ground pump. There is no one perfect answer--but after you work through a couple of the options--you should see one that meets your requirements.

    If you are in the Arizona region--you might want to call Northern Arizona Wind & Sun directly.

    The folks here (like me) are just "volunteers" and have some solar experience with personal systems--and a few are designers and support people too.

    But none of us are associated with NAWS (other than our Admin--"Windsun"). And they prefer that customers contact them directly for Solar RE designs/components that go beyond what we can help you with here.

    -Bill

  3. #3

    Default Re: Pump for a 300 foot well?

    If the well does not have inherently low flow (requiring slow pumping over a long time to extract usable water volume) you might be better off just putting in an efficient pump (Grundfos SQFlex) and a pressure tank. Using a large pressure tank (or several large pressure tanks in parallel) will give you some storage under pressure, at less cost and space use than a cistern.

    I have a very similar (depth & static) well, and that was my plan up until things reconfigured so I might be getting a grid connection after all. The SQFlex control box will accept power in a variety of forms and run the pump, and powering it from the general system avoids the condition where you have a full cistern but the batteries (on the off-grid electric system we assume you'll also want) need charging. It soft-starts, so there is not a big starting load as you get with a typical pump.

    Low well recharge rates, small well diameters, and any potential for the well to run dry all lean in favor of the cistern option. If the well may run dry part of the year, a considerably larger cistern might be called for.
    Offgrid non-system consisting of Kohler and Northern Lights generators plus years of fiddling with what panels - inverters - batteries to buy when I finally pry my wallet open and get going on that. Likewise a radiant floor which has air in the tubes, waiting for me to sort out the solar and connection to the cooling systems of the Kohler and Nothern Lights (which might as well provide heat while they are burning fuel to make electricity). In progress, very slowly in progress - but not in debt.

  4. #4

    Default Re: Pump for a 300 foot well?

    Before you choose the pump it's a good idea to check how quickly your well re-charges. I made the mistake of assuming that my well would recharge very quickly when in fact it takes about 5 days to get back to its normal level.
    The recharge rate and your water requirements will determine how much you pump out of the well every day and therefore the level of the water in the well. You should know what this level is in order to choose the most efficient pump.

    My well is 110m deep with water level at 30m.
    The recharge rate looks something like this:
    - From empty to 700 litres in the well takes 1 day
    - From 700 litres to 1000 litres takes another day
    - From 1000 to 1300 takes another day

    So the first 700 litres fills up twice as fast as the next. It makes sense to keep the well almost empty and pump 700 litres every day from the very bottom. This means that I should choose a pump with the highest efficiency for those depths (110m to 70m).

    Note that this is only the case if you want to extract the maximum amount of water from the well. If not, then the design criteria should be how much you use everyday so that you can extract water from the highest levels to reduce power consumption - and then choose the most efficient pump for those levels.

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