Twenty Five Years of Gasoline Powered Water Pumping
I was eleven years old when my family dug the well on our property, in 1997. Since then, every drop of water consumed on this property has been pumped out of the ground... with a gasoline generator powering the pump.
Why didn't we run it on solar? Well, it's just one of those things that never got to the top of the list, and it’s not a trivial job.
So when I got back from Europe in September 2022 and made the family land my home base, my parents asked me to solarize the well for them. What a perfect job for a solarpunk polymath, amiright?
The Standard Solarization Approach
Here's the thing. The default solution for well pump solarization is to pull the AC pump, replace it with a DC pump, drop that in the well, and install solar panels and a DC controller. When the sun shines, the pump pumps. No batteries, no inverter. That's the standard approach.
Well, there were a few things about the standard approach that bothered me. For one, it was expensive. Solar pumps are a few grand, paying for a driller to come pull the old pump, which is on 300' of galvanized steel pipe, is expensive, and a roll of 300' of polyethylene pipe is expensive.
Also, a lot of neighbors around here have had to replace their DC pumps after a few years, while they almost never replace AC pumps. The AC pumps seem to be more reliable than DC pumps.
The last thing I didn't like about replacing the AC pump was that.... that AC pump isn't broken. We send power down that hole, and it sends water back up, and it's been doing that for 25 years. When things aren't actually broken, I really prefer to just leave them alone.
My Idea: A Full 240v System with a Modified Sine Wave Inverter
So, I had a hunch that I could come up with an alternative design that didn't involve pulling and throwing away a perfectly good, reliable pump, and didn't involve spending so much money. This is what I came up with.
The system is
six 120w used solar panels we got from a neighbor,
a 150v charge controller,
three 12v 100Ah AGM batteries, and
an AIMS modified sine wave, 5kw continuous 10kw surge 240v inverter.
This inverter is key to the system, and key to the low cost. It does one thing only: it takes 12v DC and makes 240v AC, single phase, NOT split phase, meaning, there's no neutral center tap, just two hots and a ground.
It's modified sine wave, which a lot of fancy household electronics don't like, so most inverters used for homes are pure sine wave. But pumps.... pumps aren't purists. They don't complain. Modified sine wave is fine with them. So this inverter is perfect for this application, and it's cheaper because it doesn't need to do anything other than generate that 240v AC. This inverter was about six hundred dollars.
Originally this shed was oriented 90 degrees so the roof faced West. Well, actually, the roof was on the ground fifty yards that way because a couple years ago a dust devil came up and ripped the roof off and threw it over there.
Anyway, I wanted the panels on the roof, so I wanted the roof to face south, obviously. Also I wanted the roof on the shed, not the ground.
So I jacked the whole thing up and just turned it around, then set it back on the bolts. Then I put the roof back on, and used screws and a35's this time. I also had to put siding on this wall and build the door.
The roof rack is just unistrut on top of S5 corrubrackets bolted to the 1x battens.
Controlling the Pump
The pump flowrate is much higher than the natural recharge rate of the well. One hour is the maximum amount we can run the pump before the water level get close to the pump, and you don't want to run pumps dry. Then you have to let the well recharge for several hours before you can pump again.
However, pumping one hour a day is more water than we use, so that works out well.
I installed a programmable timer to run the pump. I have it set to run two, half hour sessions, one in the late morning and one in the early afternoon. This is for two reasons.
1) It ensures that we never risk running the pump dry.
2) It decreases the maximum depth of discharge on the batteries. A half hour pump session discharges the batteries to about 70%. A full hour will discharge them by about 50%. The batteries will last longer if we only discharge them to 70%. Letting the solar panels recharge the batteries in the middle of the day allows us to get an hour of pumping in a day, with only a 75% discharge.
So the two half hour sessions are good for the pump, and they're good for the batteries.
