Solar backup in Florida hurricanes and outages: why your panels shut off and what a battery keeps running

A grid-tied solar system shuts off when the power goes out, even at noon in full sun. It is a safety rule to protect the crews repairing the lines. To have electricity during an outage you need a battery and an inverter that isolates your home from the grid. With that, one 13.5 kWh unit keeps a fridge running for days, but a central A/C drains it in an afternoon.

Why do panels shut off in an outage?

Because they are designed to. The U.S. Department of Energy says it plainly: solar systems depend on the grid to produce and, for safety, they switch off if grid power cuts out. If your panels kept pushing electricity into downed lines, an FPL or Duke lineworker could be electrocuted believing the line was dead.

To produce without the grid you need two things, per the same source: an inverter configured to run isolated and a storage system that steadies the supply. This is what the industry calls “islanding”: the equipment physically disconnects your home from the grid, and inside that island the battery sets the rhythm while the panels recharge it.

Watch for a detail nobody mentions: many solar systems in Florida were sold without that isolation equipment. They have panels, they have an inverter, and during Milton they went dark just like the neighbor’s house. If your system is like that, adding a battery later also means adding (and permitting) the isolation equipment. More on how panels handle wind in solar and hurricanes in Florida.

How often does the power go out in Florida?

Often enough for the question to be serious. Per Utility Dive, Hurricane Milton left 3.4 million customers without electricity in Florida on October 10, 2024: 1.2 million of FPL’s 5.4 million, about 923,000 of Duke Energy Florida’s 2 million, and about 594,000 at TECO, 71% of its customers. Two years earlier, Ian peaked at 2.7 million customers without service per the Department of Energy, cited by the American Public Power Association.

That is the big event. The everyday risk is summer storms, a blown transformer or a tree-lined feeder. Your personal outage history (your utility has it) weighs more in the decision than the statewide statistic.

What can a battery keep running?

It depends on two numbers: how much energy fits (kWh) and how much power it delivers at once (kW). Using EnergySage data for appliance draw and the Tesla and Enphase datasheets for the batteries:

The “no sun” column is arithmetic on those figures, for a single load. In real life the fridge shares the battery with lights, wifi, chargers and the well pump if you have one. And the next day, if there is sun, the panels recharge; if the sky stays closed after the storm, they do not.

The other number is power. A Tesla Powerwall 3 delivers 11.5 kW continuous per its datasheet; an Enphase IQ Battery 5P, 3.84 kVA continuous and 7.68 kVA peak. Central A/C demands more at compressor start-up than while running; that peak is checked against the unit’s nameplate, not guessed. We compare both brands in Enphase vs Tesla Powerwall.

Heads up: “whole-home backup” with a single battery is the most repeated and least true phrase in the proposals we review. With a central A/C on, one 13.5 kWh unit does not make it to dawn. Whole-home with A/C requires two or more units, and the price multiplies accordingly.

Partial vs whole-home backup

Partial: the electrician installs a critical-loads subpanel and moves your chosen circuits there: fridge, freezer, wifi, some lights, one room with a mini-split, the well pump if applicable. One battery feeds only that subpanel. It is the configuration that fits most budgets and lasts the most hours, because there is no way for the oven or dryer to drain it by accident.

Whole-home: the isolation equipment goes at the service entrance and the whole house is inside the island. Convenient, but it demands more kWh (several units) and more kW (so the central A/C can start), and during the outage you depend on your own discipline not to turn on what you shouldn’t.

There is a middle path: whole-home with load control, where the system automatically sheds the A/C or water heater when the battery drops below a set level. It costs more than partial and less than doubling batteries.

When it is NOT worth it

• When your history is one short outage every few years and nothing critical is in the house: the battery is expensive insurance for a low risk.
• When the installer promises “the whole house” from one unit and does not show you the load list or the hours.
• When the solar system was sold without isolation equipment and the budget does not cover adding it; without that, the battery turns nothing on either.
• When what you need is to run central A/C for days: there, a gas generator may come out cheaper, as we compare in battery vs generator.

What to check before you decide

• Whether your current (or proposed) system includes grid isolation equipment. Without it there is no backup, battery or not.
• The written list of circuits that will be backed up and the estimated hours without sun for that list.
• The battery’s continuous and peak power against the start-up of the largest piece of equipment you want to keep.
• What kind of inverter you have: it affects how the battery couples. We explain it in string inverters vs microinverters.
• Where the battery will physically sit: a closed garage in August can exceed the optimal temperature manufacturers specify.