9

I have a well drilled and set up soon on my property where I plan to use completely off-grid (not tied to city power) solar array. Obviously I plan to optimize the power usage for everything that is going to be there. The well pump is one of those things.

So the well people recommend to install medium (40 gal) pressure tank with cycle stop valve (CSV) while I think I might be better off with a larger tank (80 gal) and a pressure switch (PS).

I understand that the CSV is good for the pump longevity with a continuous water usage (like showers), but I think a larger tank with PS is good for both - pump life & energy conservation (with considerable water usage). 4 people are going to live in 2 cabins on and off with each cabin having 1 kitchen sink, bathroom sink, toilet & shower. What do you, experts out there, think about it?

I am completely new to this whole thing, so I need guidance. Thank you!

EDIT: I guess I should have phrased the question simpler, like "what will use more energy CSV or PS in a well with the pressure tank setup?". That is the answer I am looking for the most. But nice to hear about alternatives as well.

8
  • 5
    How hilly is your property? Can you put a water tank (desired PSI x 2) feet above your points of use? Things get amazingly simpler if you can. Aug 22, 2022 at 22:40
  • 1
    The cabins are below the well (one is probably 8" below & 100" away, the other about 20" below and 200" away) I need to research this. I am not sure about the gravity pressure if that would be sufficient enough or are there ways to improve this?
    – i--
    Aug 22, 2022 at 22:49
  • 2
    Each 28" of height gives you 1 extra PSI.
    – Jeffrey
    Aug 23, 2022 at 0:32
  • 10
    Below-freezing temperatures do complicate that and/or raise the cost, but otherwise, yes, a gravity tank is good, a huge gravity tank is better (because you can pump whenever the sun shines and NOT have to store electricity for the pump. Which de-complicates your off-grid water immensely. You'll want the tank located above the level of the well in order to have useful pressure at the cabins
    – Ecnerwal
    Aug 23, 2022 at 1:13
  • 1
    if there adequate wind available? you could put a windmill pump on the well and pump the water into a higher cistern from which you need less electricity to pump up to pressure. Aug 23, 2022 at 9:42

1 Answer 1

22

If the terrain allows siting a tank above the level of the cabins by at least 50 vertical feet or so, put a 1000 gallon (or even larger) tank there, and run pipes up to it from the well, and down from it to the cabins. A tank on a tower can be done if the terrain does not allow, but is typically going to be cost-prohibitive .vs. one on the ground, even with longer pipe runs associated with the ground-mount tank.

That will give you ~ 25 PSI at the cabin where I assume you meant 8 feet (since you used the " which normally means inches for the horizontal distance as well, and I doubt the cabins are 200 inches apart...) below the well head (so 58 feet below the tank) and 30 at the one 20 (so 70) feet below. Which is quite decent backwoods pressure, but we see city folks cranking 60 up to 80 because there "isn't enough pressure" so you may need a higher hill if you are one of those folks, or you may need to adjust your expectations.

That way, the stored power associated with "the sun shines sometimes, but you want water other times" is stored directly as water available at pressure, and you can use a dedicated solar-powered pump that pumps any time there is sunshine and the tank isn't full, with no battery storage needed for that part of your power system. That is a HUGE win in off-grid. Battery storage is expensive and inefficient. Storing water up high is relatively cheap and very efficient. Unlike batteries, gravity does not wear out or become less efficient.

It sounds like you are building a typical on-grid pump system either way you describe it, and that is likely a mistake that will prove expensive, as there are a number of water pumping options that are fine-tuned for solar power off grid use, and a normal on-grid "well guy" may not even be aware of them, much less sell them. A normal on-grid pump setup is a huge load for a normal off-grid solar system to support - it can be done, but it's vastly expensive.

You should spend some time looking through the water pumping sections of serious off-grid suppliers (and the terms here prevent me from directing you to any, so go look for yourself.)

8
  • Agree. There would be a challenge in SC having that tank exposed in the summer sun & would cost probably way more to install a tower like that then to buy a 13kW output with 28kW battery that I am targeting. There are probably ways to overcome those challenges though. And I do agree that your setup will outlast the solar by a few folds. Thanks for your answer. Upvoted, but not going to accept it just yet.
    – i--
    Aug 23, 2022 at 2:52
  • 3
    No worries, you might get another answer you like better. If your terrain is lacking, you still might get some benefit from a large tank (in ground, but in high ground) as high as you can get it given your terrain to hold water pumped up from the well, and a lower-power pump to provide more pressure at each cabin, without having to provide that pressure from well water level below ground.
    – Ecnerwal
    Aug 23, 2022 at 2:59
  • Good post :) just one remark: battery storage is just expensive, not inefficient. You'll typically get 80-90% of the electricity back that you put into most types batteries (which is pretty good as far as energy storage in general is concerned). It's just that you'll need a lot of those for practical use, especially in an off grid situation. So as you mention it's better to store this energy in a different (cheaper) way, in this case literally by pumped hydro storage (which is exactly the same concept that some hydroelectric dams in Norway use) :)
    – MiG
    Aug 23, 2022 at 8:03
  • 1
    Very expensive Li-Ion batteries can be as good as 90+ % recovery (what you get out for what you put in.) Lead-Acid (which is still quite commonly used) is a lot worse, (as little as 30% depending on discharge rate - ~70% Watt-hour {energy} efficiency at best, ~85% is the Amp-hour number that makes them look better than they are by ignoring voltage drop, and "at best" is rarely the case) but lower up front cost. Both need regular replacement.
    – Ecnerwal
    Aug 23, 2022 at 12:53
  • I guess it depends on usage patterns, but lead acid doesn't have to be that bad :)
    – MiG
    Aug 23, 2022 at 13:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.