I'm currently working on two PV projects: one for our well pump, and one for a neighbor in need of an upgrade. These will be my third and fourth PV builds (first was the system in Serenity, second was for Barry’s van in the South of France). I’m excited to level up to the 5Kw club.
We get our water from a well, which is on the other side of a hill from the house. A five thousand gallon tank is on top of the hill. Since 1998, we've pumped water up from the well to the tank with a gasoline generator. The main house already has its PV power system, but it's too far from the well site to just run a line over.
It costs something like $75 a month in gasoline to pump the well. Every few years, the generator breaks and we need a new one. We're reliant on having a vehicle capable of driving to town to fill up gas cans, and reliant on their being gas at the gas station, and reliant on being able to afford whatever price gasoline currently is at.
It's not ideal.
So, before I'd even shook off the jet lag from Scotland, I'd begun thinking about the best way to go solar for our well.
What's in the hole is a 3/4hp, 240v single phase AC pump, that runs at about 8 amps and inrushes at 12 amps. That pump is on the end of 14 sticks of 21' long galvanized steel pipe.
The standard approach is to pull the pump and all that steel pipe, put a DC pump on the end of a spool of polyethylene piping, and get a no-battery, DC only PV system that runs the pump when the sun shines and doesn't when it isn't.
That's a fine solution of course, but a couple aspects of it nagged at me.
For one thing, the pump down there is running fine. Those AC pumps are a very mature technology. Ours has been down there since 1998. Is it near the end of its life? God knows, but a neighbor has had a similar pump at the bottom of his well since 1975 and it still works fine. In other words, it ain't broke. So why pull it now?
Conversely, another neighbor has a DC pump, which is a newer technology. He's had four different pumps in 14 years. Also, they're more expensive than the AC pumps. They seem to be less reliable.
All right, so what would it take to keep the AC pump? Well, technically speaking, it'd take 240v single phase at about 8 amps, with an inrush of 12 amps, for an hour a day. That's a hefty ask of an offgrid PV system - 2kW running, almost 3kW startup. On the DC side, at 12 volts, that's 160 amps running, 240 amps startup. Oof. Most 5kW inverters are a handful of thousands of dollars.
My google fu came to the rescue. I found a 5kW inverter that puts out 240 volts for $530. I didn't trust that it wasn't some shady scam until I looked closer at the specs. This unit seems designed specifically for this kind of application - it has no bells or whistles whatsoever. You can't even change the low voltage shutoff setting. And it puts out a modified sine wave, not a pure sine wave, meaning it's only appropriate for powering dumb brute appliances like pumps and motors - delicate household electronics might find the modified sine wave distasteful. So the unit is basically a stripped down drag racer built for just one thing: running motors. Well, that's all I need it to do. Sold.
With that inverter as the crucial element, the rest of the system design is straightforward. 300Ah of 12v AGM batteries will store enough juice to get an hour of runtime a day, and six twenty-year-old hand me down 120watt panels from a neighbor ought to collect enough sunlight to keep the batteries charged.
I've finished system design and am on to installing the thing. First order of business is to address the shed.
We've had this shed for the generator since 1998. I remember building it with dad and my brother. A few years back a good gust of wind came up and ripped the roof off. A few days ago I turned it around - literally. I undid the anchor bolts, pried it up onto stickers, and shoved it inch by inch, then drilled new holes in the plates and dropped it onto the bolts. I need the roof to face south!
There we go.
The next step is to reinforce everything, rebuild the roof, figure out how to mount six solar panels on it (the reason for rotating it south), put a door on it, and then get the rest of the electronics installed.
Messing around in Blender to figure out panel mounting…
Total system cost is going to be something like $2-3k, including stuff like new rafters and concrete anchors for the shed. That’s a simple return on money invested of less than three years. A no brainer. I’ll follow up when it’s up and running.