AC or DC pump for off grid well supplying water to a 2 bedroom cabin?

slippery.fish

New Member
Joined
Apr 5, 2022
Messages
1
Hello solar experts, I need some advice. Solar systems are new to me but I've been doing a lot of research and watching videos tying to figure out my path forward.

Currently I have a 120v 1/2hp above ground pump rated at 10gpm with an connected 18gal air/reservoir tank ( I inherited the system and I don't know much about it). I don't know how deep the well is but the pump is rated at a maximum of 70ft so I assume it's less than 70ft. I want to setup solar for this well and I'm debating between continuing to use my current pump and buying all the stuff I need (inverter, panels, batteries, etc.) or switching to a DC pump. I don't know much about DC pumps but I see pros and cons with both forms of power but the reason I learn towards DC is, if any of the electronics fail or we have an extended time of very cloudy days, I can just plug the pump into grid power or a generator.

If you're doing it new, or starting over how would you set it up? Understanding you're dealing with sinks, showers, water heater, and some minor irrigation.

If you recommend a DC pump, let me know the brand/model I should look at.

Thanks,
James
 

DThames

Photon Sorcerer
Joined
Nov 22, 2019
Messages
2,338
Why do you want to power this by solar? (grid down standby?)

A battery and inverter setup will cost about $2000 and up, to run a 1/2hp AC pump. There are a few solar type pump specific inverters, but I don't recall if they have battery backup type options.

A good quality DC powered pump will cost as well. I helped a friend test a low end DC pump that will run off of a batter and also has a built in solar controller. We didn't test it with a pressure tank. But just pumping water out of a shallow well, I was impressed. He got the pump for watering cattle, so not house critical. At this price, if I were depending on it, I could keep a spare on hand. You often get what you pay for.
 

TorC

Solar Enthusiast
Joined
Jan 13, 2022
Messages
229

AIUI, it will take circuitry to run most DC pumps from an AC source. Just a question of which circuitry.

Regarding that link, looks decent, but I take issue with their calculation of dynamic head. The numbers they use won't leave you without water, but they are still wrong. First, the h1/h2 line should be the well drawdown depth, if known. Second, the depth of the pump below water is irrelevant to head, except as relates to friction loss in the pipe.

In their example, you'd be much better served with the formula h1+(h1+h2+d)/10 or, for their numbers, 50+(50+30+20)/10=60m. Add a little for each elbow, so 61m should do, call it 62-64m if you want a little margin of safety and still get your calculated flow rate. If you care to get that detailed, Franklin (and I'm sure others) have charts for actual dynamic head for various pipe diameters and fitting at given flow rates.
 
Top