How many Batteries do I need?

BB. said:

You need to first tell us about how much energy per day your pond pump will take... Is this a 24x7 operation, or just a few hours per day? Using a Kill-a-Watt type meter will be much more accurate:

https://www.amazon.com/s?k=kill+a+watt+meter

Is this to "go green" or because there is no 120 VAC power close to the pond?

Where is the pond located (nearest major city)? The "hours of sun" per day--In reasonably sunny South West US location, you are looking at >3 hours per day of "good sun" in the winter... Is the pond seasonal (less/no pumping in winter)?

http://www.solarelectricityhandbook.com/solar-irradiance.html

Based on what you have said so far, this is what a system would look like for 24 hour per day pumping all year long:

• 24 hours per day * 250 Watt AC load = 6,000 WH per day

This is as much power as an off grid home would use... A lot of power for a "low cost" solar project. To run the system 1 day on 12 volt lithium battery bank:

• 6,000 WH per day * 1/0.85 AC inverter eff * 1/0.70 lithium "usage factor" * 1/12 volts = 840 AH @ 12 volt lithium bank for 1 day "no sun"

If you are in a sunny region with at least 3 hours of sun per day:

• 6,000 WH per day * 1/0.61 Li Ion battery bank solar efficiency * 1/3 hours per day Winter sun = 3,279 Watt array "winter sun" break even array

That is a large system, and no "safety factor" (stormy weather, etc.)--So if you have a couple days of bad weather/overcast, the system would shutdown until the sun returned (to protect the battery bank from over discharging).

In general, solar power will cost you more money that simply burying 100-200 Feet of direct burial 14 or 12 AWG copper cable from your home to the bond (typical 18" deep at least, below the frost line in cold climates).

Also, looking for the most efficient loads (for a small pond, a 12 volt or 24 volt DC air or water pump, as small as would work for yoru place.

If you only need pumping air/water when the sun is up--You can also save on battery bank--Just power the pump directly from solar panels (not always easy either to match solar array output to DC pump input requirements.

-Bill

Great ideas people! How about this, Is there a device that I can plug into a wall outlet and the Solar system? Where as it automatically switches back and forth when solar or solar batteries are low to Wall outlet, then switches back when the Solar system is receiving sun and ready to use? I can have an electrician run a buried cable from the meter pole to the pond. There is a well on the property connected to the grid. But the Pond is very far away. What happen is in Summer when the water is very warm, Oxygen levels in the pond depletes. I need this pump 24-7 to produce oxygen. It's going to be around 900 feet of cable, but like you guys mentioned, the big solar offgrid system will cost me too much. I am just trying to Save money on my monthly bill, as I live in California. Electricity runs about $0.40 per Kwh. Bills can reach as high as $300 a month!!!! I am in zone 9B, where temps can get in the low 25F in winter.  I will stick with 200AH Lithium batteries. Get two, to make 400AH. Hoping the times it run, I can save a few dollars a month. Also, when We are out at the pond, I can charge my phones, or add lights to a porch at night and utilize the solar system.  If you know what I mean.