Run a well pump on solar and battery: sizing guide

On a rural property, no power means no water. The good news: a well pump uses little energy. The catch is the surge it needs to start.

Short answer: yes. A typical 1 hp submersible pump uses less than a kilowatt-hour a day for a family. What decides your system is the starting current, often five times the running current for a split second. Size the battery or inverter to start the pump, and the energy takes care of itself.

Step 1: Read the pump’s nameplate

You need horsepower, voltage, and whether it’s a 2-wire or 3-wire motor. It’s on the control box in the basement, or on the paperwork from the well driller. Here’s what Franklin Electric lists for its common 4-inch, 230 V single-phase motors:

Motor	Running watts (full load)	Max watts (service factor)	Starting amps (LRA)
½ hp, 2-wire	670	960	32.2
¾ hp, 2-wire	940	1,310	40.7
1 hp, 2-wire	1,210	1,600	48.7
1 hp, 3-wire	1,210	1,600	41.8
1½ hp, 3-wire	1,660	2,100	52
2 hp, 3-wire	2,060	2,610	51

Your pump may differ. Use your own nameplate when you can.

Step 2: Estimate the energy (it’s small)

The EPA puts average use at about 88 gallons per person per day at home. A family of four uses about 350 gallons. Say your pump delivers 10 gallons a minute, a common rate (check yours). That’s 35 minutes of pumping a day. At 1,210 W, it comes to about 0.7 kWh a day, about 5% of a typical 13.5 kWh battery.

Irrigation, livestock and filling a pool change that math fast. Add those separately.

Step 3: Check the starting surge

Locked rotor amps (LRA) is the current a motor draws for the instant it starts. Your battery’s inverter has to supply it or the pump won’t start, and in off-grid mode the whole house may drop out.

Tesla Powerwall 3 supports 185 A of motor-start current per unit. Every pump in the table above starts easily on one unit. Tesla’s design rule: the motor’s LRA must be under 185 A times the number of units.
Enphase IQ Battery 5P provides 3.84 kVA continuous per battery and 7.68 kVA for 3 seconds. A 1 hp pump starting near 49 A at 240 V needs about 11.7 kVA in that instant. That points to two or more batteries, depending on the motor, so confirm with Enphase’s backup load guidance.
Off-grid inverters list a surge rating in watts or amps for a few seconds. Compare it with LRA × voltage.

Step 4: Make the start easier

A soft starter or a constant-pressure variable-speed drive ramps the motor up instead of slamming it on, cutting the surge sharply. On off-grid systems this is often the cheapest fix. Have the change done by a well contractor and confirm it’s compatible with your motor.

Also check the pressure tank. A waterlogged tank makes the pump cycle on and off constantly, and every start is a surge.

Step 5: If a generator is the backup

Franklin’s minimum generator sizes for a 1 hp 3-wire motor are 2.5 kW for an internally regulated generator (most inverter generators) or 4 kW for an externally regulated one. For 2-wire motors, add 50%. Undersized generators sag on voltage during the start, and the motor can overheat trying.

Run water when the sun is outFill tubs and run the washer at midday during an outage. The panels handle the pump while the battery stays charged for the night.

Putting it together

For a typical Hudson Valley household with a 1 hp pump, one Powerwall 3, or two to three IQ Battery 5P units with a soft starter, will run water through an outage. Pick “Farm or rural” in the design app and it adds well-pump advice to your plan. Run your numbers in the free design preview.

Quick answers

How much electricity does a well pump use per day?

A 1 hp submersible pump draws about 1,200 W. For a family using around 350 gallons a day at 10 gallons per minute, that’s roughly 35 minutes of run time, or about 0.7 kWh per day.

Can a Powerwall 3 start a well pump?

Each Powerwall 3 supports 185 A of locked rotor current. Common ½ to 2 hp residential submersible motors start at roughly 32 to 52 A, well within one unit.

What size generator do I need for a 1 hp well pump?

Franklin Electric lists a minimum of 2.5 kW for an internally regulated generator or 4 kW for an externally regulated one, for a 3-wire motor. Add 50% for 2-wire motors.

Does a soft starter help a well pump run on batteries?

Yes. A soft starter or variable-speed drive ramps the motor up gradually, sharply reducing the starting surge the inverter has to supply.

Can solar and a battery run your well pump? How to size it