Well Pump Solar Calculator

Well pumps have high starting surge and matter most during outages. Enter horsepower and runtime to size solar and battery support.

⏱ ~15 sec💧 Off-grid & backup🔒 No signup

Result

4500 W surge needed
Inverter/generator must handle
Daily energy use373 Wh
Panels to offset (400W)1

1 HP ≈ 746W running, but well pumps commonly surge 3× or more at startup — this is usually the number that determines inverter or generator sizing, not daily energy use.

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Why well pumps punch above their average energy use

Running watts ≈ HP × 746  |  Surge ≈ Running watts × 3

A well pump's daily energy use is often modest since it only runs a few minutes at a time — the real sizing challenge is surge current at startup, which can be 3-5× the running wattage for a fraction of a second. Undersizing an inverter or generator's surge capacity is the most common reason a well pump fails to start on backup power; check this against the surge watts calculator for other motor loads on the same system.

Frequently asked questions

Is well pump surge really that much higher than running watts?

Yes — submersible well pump motors are notorious for high starting surge, commonly 3-5× running watts for a brief moment, which is why they're a frequent cause of undersized backup systems failing.

Can solar alone run a well pump during an outage?

Yes if the array and inverter are sized for the surge, but most off-grid setups pair solar with a battery bank so the surge can be pulled from the battery instantly rather than waiting on panel output.

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