Quick answer: start with 800 W of solar
A shallow-well pump is a moderate load with a hard start. At about 900 W for 2 hours it uses 1,800 Wh a day, roughly 800 W of solar, but each start can briefly pull around three times its running watts, so the inverter must handle a 3,000 W surge.
Planning result
At 200 W per module, the array target is 4 panels. That count assumes four peak-sun-hours, 75% end-to-end solar yield, 90% conversion efficiency, and a 20% planning margin. Summer garden watering can double or triple the runtime.
How a shallow well pump actually uses power
Planning case: a 1/2 HP shallow-well jet pump that draws water by suction from a well or cistern no deeper than about 25 feet and pressurizes a tank, drawing about 900 W for 2 hours a day in total. Goulds rates its 1/2 HP jet-pump motor at 880 W (10.8 A at 115 V) at its maximum service-factor load, which this case rounds up.
A jet pump runs whenever its pressure switch calls: it starts when tank pressure falls to cut-in and stops at cut-out. A larger pressure tank means fewer, longer runs, while a waterlogged tank makes it start for every glass of water. Jet pumps use more energy per gallon than submersible pumps because they recirculate part of the water to create suction.
Load calculation from running watts and duty cycle
The appliance-class estimate is 900 W running for 2 h/day at a 100% duty cycle, an average of about 900 W across those hours:
Then losses and reserve raise the energy the system must collect to about 2,400 Wh/day.
Typical manufacturer nameplate/manual range for the shallow well pump class, triangulated with Goulds Water Technology (Xylem): Water products technical manual: jet pump motor data and Goulds Water Technology (Xylem): JS+ shallow well jet pumps technical brochure, then reduced to a conservative planning midpoint; this is not a product specification. Verify the exact unit's nameplate and manual before sizing.
Use a plug-in energy meter on a 120 V pump or a circuit monitor on a 240 V one over a normal day, and count starts as well as watt-hours.
Solar and battery sizing table
| Design item | Planning value | Basis |
|---|---|---|
| Appliance energy | 1,800 Wh/day | Running W × hours × duty cycle |
| Solar collection target | 800 W | 4 peak-sun-hours, 75% yield, 20% margin |
| 200 W panel count | 4 | Rounded up; real modules must satisfy controller voltage/current limits |
| One-day battery allowance | 3,000 Wh | 90% conversion efficiency, 80% LiFePO4 usable fraction, 20% margin |
| 12.8 V LiFePO4 equivalent | 235 Ah | Nominal planning conversion |
| 25.6 V LiFePO4 equivalent | 120 Ah | Nominal planning conversion |
The battery carries every night-time start; a large pressure tank or a raised storage tank filled during the day reduces how often that happens.
Build the closest passing wiring-diagram preset
The Shallow Well Pump Planning System preset is an engine-passing starting point whose array, battery bank, continuous inverter rating, and surge rating each meet or exceed this page's stated planning allowances. Adjust it only from measured load data and verified equipment limits.
Inverter and startup current
Use at least 1,200 W continuous with 3,000 W surge for this planning case. Every start is a full motor start of several times the running current, and a short-cycling pump starts dozens of times a day. That repeated surge, not the energy, is what usually trips an undersized inverter.
The 2,700 W startup estimate is not a substitute for the manual's locked-rotor, compressor-start, or motor-start requirements, and an inverter's surge rating usually lasts seconds, not minutes. A battery-to-inverter cable that is too long or too small can pull the DC input below the inverter's low-voltage threshold during that start even when the battery has plenty of energy, so use the diagram machine's real run length.
The common mistake
Ways to cut the load
- Check and set the pressure tank's air charge to the pump maker's instruction.
- Fill a storage tank during sunny hours and pressurize from it.
- Fix dripping fixtures that make the pump cycle overnight.
- When the jet pump is due for replacement, compare a submersible or DC pump; they move water with less energy.
What to verify before buying equipment
- The exact running watts, startup current, voltage, frequency, and required circuit from the appliance label and manual.
- Actual watt-hours over a representative day; seasonal heating or cooling loads need a design-day measurement.
- Local peak-sun-hours for the worst operating season, plus shade and array orientation.
- Controller maximum input voltage at the coldest expected temperature and maximum output current.
- Battery discharge current, series/parallel permission, terminal torque, low-temperature controls, and overcurrent protection.
- Conductor ampacity, voltage drop, terminal temperature ratings, disconnecting means, grounding, local amendments, and inspection requirements.
For a whole-system load list, use the load and appliance calculator. For the system context around this appliance, continue to the Solar water and well-pump guide.
Frequently asked questions
How much solar do I need for a shallow well pump?
For the planning case on this page (a 1/2 HP jet pump running two hours a day), allow about 800 watts of solar at four peak-sun-hours per day. That covers an estimated 1,800 Wh daily load plus conversion, temperature, and recharge margin. Daytime watering and a storage tank can move most of the load into sun-hours.
What size inverter should I use for a shallow well pump?
Plan on at least 1,200 W continuous and 3,000 W surge. Motor start is the peak; size the surge rating from the starting current in the pump manual, or use a soft-start pump.
What battery size keeps a shallow well pump running for one day?
The one-day planning allowance is about 3,000 Wh nominal usable design capacity, roughly 235 Ah at 12.8 V or 120 Ah at 25.6 V for LiFePO4. A larger pressure tank cuts night-time starts and the battery's share of the load.