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Home Battery Backup: The Ultimate Guide to Powering Your Home
Quick answer: A home battery backup supplies a designated panel of essential loads when the grid fails. It requires three things: a battery, an inverter with a backup output, and an automatic transfer switch that isolates the critical-loads panel from the grid. Sizing comes from the backup loads and the hours of autonomy required — 10kWh to 15kWh covers an ordinary household overnight — and a grid-tied solar system cannot provide backup on its own, because it must shut down during an outage.
What a home battery backup is
A home battery stores energy — from solar, from off-peak grid power, or both — and discharges it when the grid is unavailable. It serves two purposes that are often conflated: reducing cost by shifting consumption away from expensive periods, and providing backup during an outage. The hardware is the same; the sizing and the system design differ.
The backup function is the more demanding of the two, because it has to work without the grid. That constraint reaches beyond the battery into the inverter, which must have a backup output, and into the house wiring, which must have a critical-loads panel that can be isolated.
Why backup needs more than a battery
During a grid outage a grid-tied inverter must stop producing, so that it does not energise the network while line crews are working. This is a safety requirement, not a limitation of the equipment. The consequence is that a solar array with no battery contributes nothing during an outage — which is exactly when the homeowner expects it to help.
Backup therefore requires three components working together: the battery to store energy, an inverter with a designated backup or EPS output, and an automatic transfer switch that disconnects the critical-loads panel from the grid and connects it to that output. If backup is a requirement, the inverter choice has to anticipate it — a unit without a backup output cannot be made to provide backup afterwards.
Sizing the battery
| Backup scope | Typical load | Suggested capacity | Duration |
|---|---|---|---|
| Essential only | Lighting, fridge, router, phone charging | 5–10kWh | One night |
| Essential plus comfort | Above plus TV, fans, computers | 10–15kWh | One night with margin |
| Whole home, no heavy loads | Above plus laundry, microwave | 15–20kWh | About a day |
| Whole home with air-conditioning | Multiple AC units, pumps | 20kWh+ | Several hours to a day |
Sizing runs from the backup panel, not from the house. Summing the wattage of the appliances that will actually be backed up, multiplying by the hours of autonomy required, and dividing by the usable depth of discharge gives a starting figure; headroom for inverter surge and gradual aging is then added. The second check is the current: the battery’s continuous discharge rating has to cover the sum of the backed-up loads running at once.
Chemistry and cycle life
| Property | LiFePO4 | Lead-acid |
|---|---|---|
| Usable capacity | 90–95% | About 50% |
| Cycle life | Thousands | Hundreds at shallow DoD |
| Maintenance | None | Water topping and ventilation |
| Weight and footprint | Much lower | Higher |
| Up-front cost | Higher | Lower |
For a stationary household battery, LiFePO4 has become the default because the properties that matter in an installation — cycle life, usable depth of discharge, absence of maintenance and thermal stability — are the ones it does best, while the energy density it gives up in exchange is irrelevant where weight and volume are not binding.
Battery or generator
| Consideration | Battery | Generator |
|---|---|---|
| Response time | Instant | Seconds, plus start delay |
| Duration | Finite — set by capacity | Indefinite while fuel lasts |
| Fuel | None | Fuel supply and storage required |
| Maintenance | Minimal | Exercise runs, servicing, fuel management |
| Noise and emissions | None | Significant |
| Cost | Higher up front per kW | Lower up front per kW |
The two are complements rather than alternatives. A battery carries the loads through short outages and the first minutes of a long one; a generator takes over for extended outages. Where both are installed, the battery also runs the generator’s start-up loads and smooths the transition, which removes the interruption that an unprotected generator start would otherwise cause.
Installation and permitting
A home battery installation is electrical work with a permit and an inspection in most markets, and the siting rules are usually specific: indoors or weather-protected, clear of heat sources and flammable materials, with the ventilating clearances the datasheet specifies and a mounting surface that carries the unit’s weight. The critical-loads panel also has to be identified and wired, which is the step that turns a storage installation into a backup installation. The documentation set supplied with the unit is what an inspector will ask for.
Home battery backup FAQ
What does a home battery backup actually power?
Whatever is wired to the backup panel. The usual set is lighting, refrigeration, communications, security and medical equipment. Air-conditioning, electric heating and EV charging are normally left off the backup circuit because carrying them would require a far larger battery.
How does it switch over during an outage?
An automatic transfer switch isolates the critical-loads panel from the grid and connects it to the inverter’s backup output. The switchover is fast enough that most equipment does not notice, though sensitive electronics are better served by a small UPS in addition.
Why can’t a grid-tied solar system provide backup on its own?
Because it must shut down during an outage. A grid-tied inverter is required to stop exporting so it does not energise the network while line crews are working. Without a battery and a backup output, the array produces nothing while the grid is down.
How much capacity do I need?
From the backup loads and the hours required: sum the wattage of the appliances on the backup panel, multiply by the hours of autonomy, divide by the usable depth of discharge, and add headroom. Ten to fifteen kilowatt-hours covers an ordinary household overnight; whole-home backup with air-conditioning needs considerably more.
How long will a battery carry the house?
At an average draw of 400W a 10kWh battery lasts roughly 20 hours; at 1kW, about 8 hours; at 3kW, under three. The meaningful figure is the average draw of the backed-up loads, not the total house load.
Is a battery or a generator the better backup?
They answer different questions. A generator runs indefinitely as long as fuel is supplied but needs fuel, exercise runs and maintenance, and takes time to start. A battery responds instantly, needs no fuel and no maintenance, but has a finite duration. Many sites use both: the battery rides through short outages and carries the critical loads while the generator starts.
What maintenance does a home battery need?
Very little beyond keeping the firmware current and the ventilation clear. Monitoring state of charge and delivered runtime will show a degrading pack before it becomes a failure.
What should I check before buying?
Whether the inverter has a backup output, what the total backup load will be, whether the unit’s continuous discharge rating covers the simultaneous load, and what documentation the local authority requires for the installation.
Explore related pages
- Solar battery backup for home
- 48V 200Ah Powerwall guide
- Powerwall installation and maintenance
- Home battery storage: 5kWh vs 10kWh
- Whole home battery backup
- Contact us
Plan a home backup system
Send the loads you want backed up, the hours of autonomy required, your inverter details and the installation market — we will recommend a capacity and a configuration.