Have you considered looking at building an air lift pump. The cost would be tiny. You would need to pump into a storage tank. It works on the basis that you pump a constant supply of water in small volume into a header tank. A small solar panel and a 12v aquarium air pump are the basic parts. You can lift water from very deep wells. The air is pumped just below the surface of the water and the air bubbles trap water as the bubbles rise up a small diameter pipe. If you pump 2-4 gallons of water per hour for 8 hours per day, that's more than enough water for a family and livestock. If you require more water you can scale up the size of the 12v aquarium air pump, or add a second one. Once you tank is full a switch turns off the pump. You don't even need a battery. I know an on demand water pump is nice but the whole system gets expensive. A raised header tank will give you plenty of water pressure. Loads of info online about air lift pumps. The bonus is there are no mechanical parts to break or wear out. Just a 12v aquarium air pump and they run for years if you put a basic filter on the air intake. No expensive large diameter pipe to buy. You always have the option to pump from the water tank up the the house but that requires less power and a smaller pump, than lifting ground water hundreds of foot to the surface.
Andy, thanks. I did look into this, it's not a widely known approach to lifting water, I'm surprised you came across it.
As I understand things (and I may >very< well be wrong), it's not the action of the rising bubbles that does the work. Instead, by adding bubbles to a column of water we are decreasing the density of that column (the air bubbles are a lot less dense than the water they displace, so the column as a whole is considerably less dense than an equivalent column of pure water. The bubbly column is buoyed up surrounding column of "pure" water ).
A simple example: If we imagine my 5" diameter steel well bore that goes down 150' below grade. The static water level is at, say, 40' below grade. I put a 1" diameter PVC pipe down 120' below grade (so the top 40' is filled with air, the bottom 80' is filled with water). Now, I bubble in air at the bottom of that PVC pipe, and as the bubbles rise they eventually reach to the top. For simplicity, let's say the resulting column of water in the PVC pipe has 1/2 the density of the "unbubbled" water in my well. So, it has buoyancy (just as if it were made of styrofoam, etc of similar density) and this less dense bouyant column is lifted up by the more dense "pure" water surrounding it in my well casing. It gets lifted, and the top of the column is now above the static water level in my well. A few observations:
1) The air from my pump must enter way down in the PVC column so it can fill it with air bubbles. The air bubbles won't come out of my bubbler unless the air pressure exceeds the water pressure at that depth. In our example above, our 80 ft of water above the air bubbler exerts a hydrostatic pressure of 35psi (238 kPa), so my air compressor needs to pump air against that pressure to get the first bubble out.
2) Since the bubbles do rise through the column and exit at the top, I need to continually add air to the column just to keep its density at the same low amount so that the column remains buoyant. I don't recall the formula for this air volume, but it isn't trivial. Working from memory, I
think I figured out I'd need about a 1/2 hp compressor to produce the needed air volume (in CFM) against that 35PSI backpressure and get a fairly small flow of water at the top. That's about the same power requirement as my existing conventional well pump.
3) My well is deep enough, but some aren't. Again, working from memory, I believe the general rule is something like: "you need 2 feet of bubbly column below the static water line for every foot of lift you want."
Anyway, you jogged my memory and I'll look for my notes again sometime. The approach is pretty popular among folks doing hydroponics because their lifts are small (so, little back pressure at the compressor) and very filthy water can be pumped this way. If you need to aerate the water anyway to keep the pond/crops health, then this amounts to a "free" way to lift water. For my use it might not be perfect. It does have the (significant) advantage that all the mechanical stuff is outside the well and easily serviced.
I've also considered:
- Replacing my "everyday" 115VAC 1/2 hp electric pump (they cost about $250, last about 15 years) with a Grundfos 1/2 HP DC pump (about $900 to replace). Advantage--no-fuss transition to "solar" pumping of residential water if the AC power becomes unavailable.
- Hand pumps (not fun, but apparently pretty bulletproof as long as the water level in my well doesn't go down too far during a dry period). As you suggested, I'd pump the water into a tank and move it wherever I want (even pressurize the house plumbing) with a simple 12VDC diaphragm pump as used by RVs (caravans), etc
- When the AC goes out, snake a small diameter (approx 1.8") 12VDC deep well pump into my well in addition to the existing pipe and wires from the existing pump. A pump like this one (approx $200):
https://www.ierents.com/product-p/prop-10300.htm
165 watts, it provides about 1.2 GPM at a lift of 40 feet (above the static height of the water, not the depth of the pump). At that wattage, in good sun I could run it continually during the daylight hours on two 100W panels (so, about 360 gallons over 5 hours, MUCH more than I need). Pros: This approach works even if my well pump AND inverter crump out: the pump can be powered directly from my battery (or panels-->SCC in the daytime). Cons: Apparently the pump isn't supposed to sit in water continuously and the motor can only be expected to last 400 hours.
Anyway, I need some sort of inverter anyway for other loads, so going with a "beefy" LF inverter lets me use my existing 115VAC well pump with no new piping, etc. Overall, it's the low-cost option (about $250 more than the 1500w HF inverter I'd otherwise buy). I'll surely also build a hand-pump and get a small12VDC membrane pump (a very handy thing).
Sorry to get off-track from the inverter issue.
