Off-Grid Solar Calculators

Appliance-specific

Off-Grid Well Pump Solar Sizer

A ½ HP 240 V pump might run near 1,000 W (about 4 A FLA) but locked-rotor amps are often 5–7× that. Energy is running watts × hours; the inverter must still cover the surge.

Inputs

W

≈ watts = FLA × voltage. A ½ HP 240 V motor is often near 1,000 W running.

h
h

Usable fraction of rated capacity.

System voltage of the battery or series string.

Results

Daily energy
1,000Wh
Inverter surge to meet
5,000W
Battery capacity
44Ah
Array size
267W

Recommended gear

Engineering methodology

Daily watt-hours = running watts × pump hours. Surge watts = running watts × LRA factor (often 5–7× for induction motors). Battery amp-hours = daily Wh ÷ (V × DoD). Array watts = daily Wh ÷ (peak sun hours × derate). When you can, compute running watts from nameplate FLA × voltage (P = V × I).

Frequently asked questions

What LRA surge factor should I use for a well pump inverter?

Read locked-rotor amps from the motor nameplate. LRA / FLA is often about 5–7× without a soft starter. Soft-start kits can cut that toward 2–3×. Surge is for the inverter, not extra daily watt-hours.

How many watts is a ½ horsepower well pump?

Mechanical ½ hp is about 373 W, but electrical input is higher. A 240 V ½ hp motor might run near 4 A FLA, about 1,000 W. Always use FLA × voltage from the nameplate.

Does a pressure tank reduce solar and battery size?

It reduces how often the pump starts and can shorten total run hours, which lowers daily Wh. It does not remove the surge the inverter must still supply at each start.

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