offgrid solar for AC water pump

albertcuy

New Member
Joined
Feb 27, 2022
Messages
5
Hi All,

i apologize in advance if i'm posting in the wrong place, and please do point me to the correct one :)

Total noob here. A recent typhoon got me thinking about making an offgrid backup for my home. Nothing too big, just enough to run the lights and a few appliances.
That said, it seems like a waste to have an offgrid system just sitting there, waiting for disaster to strike(thankfully quite rare in our case), so i had the bright(?) idea of hooking up the water pump to it. So basically what should happen is

Normal days: offgrid kit powers AC water pump
Power gets cut off: lay down extension cords to power some lights, gadgets, fans, small appliances

So here's what i have in mind:

Bill of materials:

100-watt mono solar panel, output = ~17.6V max, 5.71A max
100Ah LiFePo4 battery
MPPT charge controller, max 20A
Inverter, 2000W max
Water pump, 220V AC, P1 = 1100W, P2 750W(amps estimated at 5-6A)


solar water pump setup.png


The pump is hooked up to a water tank, and only engages when near empty. My rough guess is that the pump engages only around 2-3 hours daily as the tank water level drops.

You think this will work? tia
 

time2roll

Photon Sorcerer
Joined
Mar 20, 2021
Messages
3,871
If the pump run 3 hours per day 3.3 kWh
If the panel is lucky and gets six hours of good sun 0.6 kWh per day.

I am thinking 5 kWh battery and 1000 watts of solar.
 

OffGridInTheCity

Photon Sorcerer
Joined
May 23, 2021
Messages
920
Location
Southern Oregon
I typically get 500kwh/month on a 13kw PV array in a cloudy/rainy winter month. This is an average of 16kwh/day. I have a whole house water pump - its does maybe 2kwh/day. Taking 2/16 I get 12.5%.

You can use PVWatts - https://pvwatts.nrel.gov/pvwatts.php - to see what panels you need for 2kwh/day in your location. But if we extrapolate on my stats - 13kw PV * 12.5% = 1.6kw of PV

I'd guestimate that on the order of 1600w of panels would be needed. And I agree with @time2roll that a 5kwh battery would be well matched. A 100ah LifePo4 @ 16s (48v nominal) is aprox 5kwh.

Note1: In an abnormally harsh month (as in this last December) I hit an all time low of 250kwh for the month instead of the usual 500kwh low. and I had 14days in a row of <6khw/day. This would double the numbers above and/or one should have a backup plan to cover 'bad solar PV'. :)

Note2: If you plan for winter, then in summer you'll a great deal of extra power (3x or 4x) that isn't used!
 
Last edited:

Don B. Cilly

Energetic energy padawan
Joined
Aug 24, 2021
Messages
1,118
Location
Mallorca ES
I estimate my water (pressure) pump runs five minutes or less per day. Not counting showers or washing machine.
Counting those - the washing machine runs every two weeks or so - say 10-15 minutes.
-
 

albertcuy

New Member
Joined
Feb 27, 2022
Messages
5
Wow...i am way off the mark.

Let me read up more and get back to you guys. Really appreciate the response (y)
 
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