Battery backup for a well pump in Florida

Your well pump runs on electricity. When the grid goes down, the pump stops, the pressure tank empties after a few uses, and there's no running water, no flushing and no showers until power comes back.

About 12% of Floridians, roughly 2.5 million people, rely on a private well, according to UF/IFAS. Palm Beach County's health department says new homes in the county's fast-growing western areas "necessarily" use private wells and septic tanks, and many Southwest Ranches homes are on wells too. See also Jupiter Farms, The Acreage and Loxahatchee Groves.

Usually, if it's rated for the pump's starting surge. Starting power matters more than storage.

• Tesla Powerwall 3: 11.5 kW continuous, and it can start loads drawing up to 185 amps for one second.
• FranklinWH aPower 2: 10 kW continuous and 15 kW for 10 seconds.
• Enphase IQ Battery 5P: 3.84 kVA continuous per battery and 7.68 kVA for three seconds; Enphase lists its Power Start at up to 48 amps and says it may vary.

Franklin says two-wire motors need about 50% more. A battery isn't a generator, but the table shows why a 1 HP pump needs a system that can deliver several kilowatts at once. Check the pump's nameplate for its horsepower and voltage.

• A soft starter ramps the motor up gradually. The maker of the SoftStart well pump kit says it cuts starting current by as much as 40%. Enphase sells soft starters for its batteries; ask whether your pump type is compatible.
• A constant-pressure pump with a variable-speed drive starts gently by design. Grundfos says its SQ pumps have a built-in soft start that brings the motor up to speed in about 2 seconds.
• Load management keeps the pump from starting at the same moment as the AC or another big motor.

For essentials plus the well pump, one large battery is often enough, especially with a soft starter. Adding central air, which most Florida homes want in a summer outage, usually takes two or more. Solar recharges the batteries each sunny day, which is what carries you through a multi-day outage. See solar battery backup for hurricanes, the best home batteries for Florida and what a home battery costs.

On acreage, a ground-mounted array can be sized and aimed freely, away from trees.

Backup power keeps the pump running, but it doesn't make the water safe. If floodwater reached your well, Palm Beach County's health department says the water may carry disease-causing organisms. Use bottled water, or boil water at a rolling boil for one minute, or disinfect it with 8 drops of unscented household bleach per gallon, for drinking, cooking and brushing teeth, until the well has been disinfected and a lab test comes back clean.

Boil-water notices from local utilities don't cover private wells, so well owners have to act on their own, the Taylor County health department reminded residents after Hurricane Idalia. Mount the battery and inverter above flood level too; see solar and batteries in a flood zone.

It depends on the type. A conventional gravity septic system works without electricity. Systems with pumps, such as mound systems and aerobic treatment units, need power, so put the septic pump on your list of backed-up circuits.

1. 1

   Will the battery start my well pump?

   Give them the pump's horsepower and voltage, and ask for the starting check in writing.

2. 2

   Do I need a soft starter?

   Ask whether one is included, what it costs and whether it suits your pump type.

3. 3

   What else is on the backup panel?

   Make sure the well pump, any septic pump, the refrigerator and at least one AC zone are covered.

4. 4

   How long will water last in an outage?

   Ask for an estimate with and without solar recharging.

Weighing a generator instead? See generator vs. solar battery. To see what solar and a battery would cost for your home, try the solar savings calculator.