I'm trying to design a solar system to convert an existing 240v well pump with pressure tank to solar.

[mikeytmh]

Hi folks, I'm trying to design an off grid solar system with battery bank, for my well pump with pressure tank. It's 240v, draws 10A running (haven't actually put my amp meter on it yet), that's 2400w. It cycles on & off depending on the pressure in the tank (30 - 50 pressure switch). I plan on running a 48v system & 5kw split phase inverter (will that be sufficient) , so how many batteries & panels? although I taught electronics, solar is a new field for me so I need some of your expertise. I have no idea what hp the pump is as it was already there & works fine, standard household use (showers, dishes, cooking periodically throughout the day).

 

[Mattb4]

Bit hard to say what you might need to start it without an inrush current measurement. For total loading it really is going to depend on running current over time. If the inverter you are considering is LF style at 5kw split phase I would expect it to be sufficient tehy generally have 3 times surge and a longer surge period than a HF style. This also means that your 48vDC battery and associated cabling could handle the current demands.

Just for instance using the 2400w figure you give. 2400w/50vDC=48 amps. Allowing for some conversion efficiency you could place this at 55a draw. A 48vDC LiFePO4 100ah battery could supply the pump for ~2hours. To charge the battery after being depleted you would need 5000Wh from a supply such as PV. PV collects sun based on an average rate in hours dependent on Season and weather for a location. Most typically you see 5 hours average over the year (2-7hours Winter to Summer). Using 5 hours, 5000wh/5h=1000w worth of panels. If you run longer or less the math is basically the same.

 

[mikeytmh]

UPDATE. The pump draws 15a at startup & 10a running. So I believe a 1200W solar array, 2 48V 100ah batteries (in parallel), & a 5kw, 48v split phase inverter/charger combination should work. Please let me know if I'm missing something. I think the above system is larger than required, but I'd rather have too much, than not enough.
Thanks in advance for your input.