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diy solar

Planning solar power well

NakeDiesel

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Jul 22, 2022
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My first solar project here on the farm is to provide a solar solution to my water well. When I get my generator installed for the house, the well won't be on it. Eventually the house will have a sol-ark 15 or 2 on it with panels supplying it as well as a lifepo4 battery bank, but that's way further down the road.

I replaced the metal siding on the well and added trim and a new roof and removed the old batt insulation, 2 weekends ago. Installed a new 86 gallon pressure tank and new lines inside the well house this past weekend. I'm waiting on my closed cell foam kit to get here so I can insulate it.

Finally got my hobo data logger and current switch yesterday and put it on the well. It's been on there for 22 hours so far and has logged 9 minutes, 44 seconds of run time since install. Not much use in the next 2 hours, so that gives me a start baseline. I'll continue logging run times for the next 2 weeks to get a good summer average. Part of that usage is I irrigate my fruit and nut trees for 2 hours every evening, my wife's night bath in the garden tub, 2 load of dishes, etc... The irrigation won't be going on in winter so winter use will be dramatically reduced. Run time with the new 86 gallon pressure tank is 2 minutes 20 seconds from 30psi to 50psi.

So breaking down the math:

Surge amps were 45.5amps * 240 volts = 10,920 watts surge
10.5 amps (running pump amps measured) * 240 volts = 2520 watts
2520 watts * .25 hours a day (rounded up to 15 minutes) = 630 watt/hours
630 watt/hours a day * 3 days backup = 1890 watt/hours
1890 watt/hours /48 vdc = 39.3 amp hours of storage needed
1890 watt/hours /24 vdc = 78.75 amp hours of storage needed.

2520 watts a day / 4 hours sun (think average is between 4.5 and 5 hours in my location) = 630 watts of panels needed minimum.
MPPT Charger size = 800 watts / 24 vdc =

I think my calculations are pretty spot on. Will collect run time data over the next 2 weeks to get an average.

But as of this info, plan is as follows:

1 - 4kw Aims 120/240 split phase inverter charger 24vdc
2 - 12v 100Ah lifepo4 batteries
1 - Aims 40 amp charge controller
800 or so watts of panels

plus wiring and disconnects, etc.

Any thoughts?

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I would question if a 4kw inverter will sustain a 11k starting load. I know this is a LF inverter and should sustain a good surge but not sure about nearly 300%. Any voltage drop from the battery (at all) will further degrade your surge energy. 11k watts will pull over 400amp from the battery, so the chances of a voltage drop are high.
 
Fun project!

You should add the tare losses of your inverter to the daily energy needs. IE: 30(?) watts x 24 hours = 720 more watt hours you need to produce.

Then inverters aren't 100% efficient. Charging and discharging batteries isn't 100% efficient either. So there's some more energy that you need to produce.

You may need to add more batteries to deal with the surge of your well. The BMS of most batteries is limited to 100 amps. Paralleling two 24V batteries is likely better than putting two 12v in series. But I'm not totally sure on that as I'm still running FLA batteries.

Our 1HP well pump averages .84 kWh per day but climbs to a little over 3 depending when we are adding water to the pool and watering the garden so what you've found so far on your energy usages lines up with what I would expect.



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I started looking at batteries yesterday and may end up going with a bank of AGM's due to the surge watts needed as I started looking at specs. I plan on keeping the poco line out there with a manual disconnect and an outlet that I can switch too if needed, but would like to be able to not have to switch to it if possible. I drain and refill our hot tub every 3 months, that will be the hardest/longest use of the well we have.
 
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