# How many Batteries do I need for my Solar system to run my Pond Pump?

My Pond waterfall, the pump failed and I decided to get a DC Pump to save electricity on the longrun.

I got a 1000Watt Power Inverter.

I got the nessecary Cables, and 8 of 100 Watt Solar Panels, Polycrystalline.

I have 3 of 100 Ah Deep Cycle Acid Sealed Batteries.

I have 100A MPPT Charge Controller.

The Pump uses 115 Watt

How many Batteries do I need to keep this pump running 10 Hours without daylight charging the system?

We have 14 Hours of Daylight at the solar point.

I'll be adding an extra battery incase, too.

Relevance
• The 1000W power inverter converts DC to AC. If you got a DC motor why did you buy a power inverter?

What is the operating power consumption of the PUMP.

Measure the operating voltage and current of the Pump. P= Voltage * Current.  Add ~ 2%. This is the required power in Watts.

Multiply by 10. This is The Power in Watt-Hours. for 10 hours.

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• Is the pump rated at 115 watts, or does it actually consume 115 watts? The rating is maximum load. Actual usage generally is less.

Assuming it consumes 115W, that means it will take about 10 amps at 12V. 10A x 10 hours means you need a 100 A-h battery if you fully discharge the battery (not a good thing) and the inverter is 100% efficient. Using an efficiency of 80% for the inverter, that means you need 125 A-h. You'll need at least two batteries, safer to have three.

During winter, you'll need longer battery powered times than you specified unless you're on the equator.

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• 115 Watt is 115 J/s

10 hr x 60 min/hr x 60 s/min = 36000 s

energy needed is 115 J/s x 36000 s = 4.14 MJ

missing the voltage on the batteries. If they are 12 volts...

100 amp-hour x 12 v = 1200 watt-hour

1200 watt-hour x 3600 s/hr = 4.32 M watt-s = 4.32 MJ

looks like just over one battery will do, two to allow for battery degradation and losses in the system.

note that this just answers the question, how many batteries to run the load for 10 hours, nothing about what is needed to charge those batteries. That depends on location, angle of the solar panels, other factors.

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