Short answerLet the solar well pump fill a cistern by day, and put a small pressure (booster) pump with a pressure switch and a small pressure tank between the cistern and the house, running from the house battery. Set the tank's air pre-charge about 2 psi below the switch's cut-in pressure.
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Key takeaways
- Solar fills the cistern by day; a battery-powered booster gives pressure on demand.
- Set the pressure tank pre-charge 2 psi below cut-in.
- The booster only works on water used, so its energy is small.
How the parts fit
- Solar well pump to cistern, direct drive, stopped by a float switch when full. It works at low head, with no pressure to supply.
- Cistern holding several days of household use, ideally below the frost line or indoors.
- Booster pump drawing from the cistern, wired to the house battery and switched by a pressure switch.
- Pressure tank after the booster, so the pump does not start for every glass of water.
- Filter after the pressure tank; treatment as your water test requires.
Sizing the booster
Size flow for the fixtures that run at once: a shower and a kitchen tap together might need 3 to 5 gpm. Small 12V or 24V diaphragm pumps of the kind sold for RVs and boats serve a small cabin; a larger house needs a bigger booster on an inverter. Pressure is set by the switch, typically a cut-in and cut-out pair such as 30/50 or 40/60 psi.
Energy is modest because the booster only works on water actually used. Raising 150 gallons a day to 50 psi (115 ft of head) is about 54 Wh of water work; at a small pump's roughly 30% efficiency, about 180 Wh a day from the battery.
With no house battery, or as a backup when the grid goes down, a 120V booster can run from a portable power station plugged in beside it. At 180 Wh a day, a 2 kWh unit such as the BLUETTI Elite 200 V2 (2,073.6 Wh, 2,600 W at 120V, merchant figures) covers more than a week of that use. Check the booster's starting current against the unit's rating first; the listing gives no motor-surge figure. This works because the cistern already holds the water: a power station sized for a booster will not start a 240V deep-well pump.
Pressure tank pre-charge
With the tank empty of water and the pump off, set the air pre-charge about 2 psi below the switch's cut-in pressure, for example 28 psi for a 30/50 switch. Too high and the tank does nothing; too low and the bladder overworks. Check it once a year.
Eco-Worthy 12V 100Ah LiFePO4 battery
1.28 kWh of storage for night or cloudy-day pumping. Low-temperature charge protection.
- Chemistry
- LiFePO4
- Capacity
- 12.8V 100Ah (about 1.28 kWh)
- Extras
- Bluetooth, low-temperature protection
on eco-worthy.com, 18 October 2026
Eco-Worthy Cubix100 48V 100Ah LiFePO4 rack battery
About 5.1 kWh at 48V: the battery side of an inverter-driven AC well pump.
- Chemistry
- LiFePO4
- Capacity
- 51.2V 100Ah (about 5.12 kWh)
- BMS
- 100 A
- Expands
- Up to 32 units in parallel (merchant figure)
on eco-worthy.com, 18 October 2026
LiTime 12V 100Ah self-heating LiFePO4 (Canadian store)
For a battery that has to charge in a cold pump house. Sold from LiTime's Canadian store, priced in CAD.
- Chemistry
- LiFePO4, Group 24
- Capacity
- 12.8V 100Ah
- Extras
- Self-heating, Bluetooth
on ca.litime.com, 18 October 2026
We have not tested these products; specifications are the merchant's own. Affiliate disclosure.
Why not pump straight into the pressure tank
A battery-powered well pump feeding a pressure tank works, but the well pump then has to make the house pressure too, adding 92 to 139 ft of head at 40 to 60 psi, and it needs a battery and inverter large enough to start it. See off-grid cabin water for the three designs and running an AC well pump on solar.
Questions
- What should the pressure tank be set to?
- About 2 psi below the pressure switch's cut-in pressure, measured with no water pressure in the system: 28 psi for a 30/50 switch, 38 psi for a 40/60 switch.
The calculator opens with a cabin setup; set people, lift and pipe.