Battery guide · Updated 3 November 2026
Will My Battery Work in a Blackout? Essential Circuits vs Whole-Home Backup
Why solar switches off when the grid fails, how essential-circuit and whole-home backup differ, and how long a battery can realistically run your home.
By the SimpliSolar team · Published 3 November 2026
Key takeaways
- Solar alone switches off in a blackout by law (AS/NZS 4777 anti-islanding).
- A battery only provides backup if the product, isolation device and wiring support it.
- Essential-circuit backup suits most homes and lasts longest.
- Whole-home backup is limited by inverter output, typically 5–10kW.
- Ask whether the panels can recharge the battery during a long outage.
Many people buy a home battery expecting the lights to stay on when the grid goes down, then find out during the first storm that they don’t. Whether a battery keeps your home running depends on how it is installed, not just on the battery itself. This guide explains why, the two main ways to set up backup, and how long a battery can realistically run your home.
Why solar on its own switches off in a blackout
A grid-connected solar inverter must stop exporting when the grid fails. This is a safety requirement under the Australian inverter standard (AS/NZS 4777), so line workers repairing the network are not exposed to power coming back from homes. That means a normal solar system goes dark in a blackout, even on a sunny day.
A battery system can keep power flowing only if it can disconnect your home from the grid and run it as a small, isolated “island”. That needs three things: a battery and inverter with a backup function, a way to isolate the home from the grid (built into the inverter or a separate backup gateway), and wiring that decides which circuits get backup.
Option 1: essential-circuit backup
The most common set-up. A small dedicated section of your switchboard, often called an essential or backup sub-board, carries only the circuits you choose. Typical choices are:
- The fridge and freezer
- Lights in the main living areas
- The Wi-Fi modem and router
- A few power points for phones, laptops and the TV
- Medical or security equipment, if you have it
Large loads such as ovens, ducted air-conditioning, electric hot water and pool pumps are left off. This keeps the battery’s limited power output and stored energy for the things that matter, so it lasts much longer.
Good for: most households, lower cost, longest runtime.
Option 2: whole-home backup
The whole switchboard is backed up. Everything stays on, at least in principle. In practice the inverter can only supply so much power at once, commonly 5 to 10kW depending on the model. If the oven, kettle and air-conditioner run together, the system can overload and shut down. Whole-home systems often need load management or simple household habits during an outage to stay within limits.
Three-phase homes need extra care: many home battery systems only back up one phase, so three-phase appliances such as some ducted air-conditioners and pool heaters will not run in a blackout.
Good for: homes that want everything to work, with a larger inverter and battery, and owners comfortable managing big loads during an outage.
How fast does it switch over?
Switchover time varies by product. Some systems change over in a fraction of a second, so most appliances do not notice. Others take a few seconds, which can make computers, modems and clocks restart. If seamless switching matters, for home offices or medical equipment for example, tell us and we will recommend products that support it.
Can solar recharge the battery during a blackout?
With most hybrid inverters, yes: once the home is islanded, the panels keep running and recharge the battery during the day, so a long outage can be ridden through. Some AC-coupled set-ups cannot recharge from the panels while off-grid. This is an important question to ask before choosing a product.
How long will a battery last?
Runtime depends on how charged the battery is when the power goes out and what you leave on. Here is a simple example for essential circuits only, using typical figures:
- Fridge-freezer: about 1 to 1.5kWh per day
- Wi-Fi modem and router: about 0.2kWh per day
- LED lights for an evening: about 0.5kWh
- TV, phones and a laptop: about 0.5 to 1kWh
That totals roughly 2.5 to 3kWh a day. A 16kWh battery holding half its charge (8kWh) could cover those essentials for two days or more, before counting any solar recharging. Add air-conditioning or cooking and the runtime drops sharply.
Set a backup reserve
Most batteries let you keep a reserve, such as 20 or 30%, that is held back for outages and not used for everyday savings. A higher reserve gives more blackout protection but slightly smaller bill savings. If you join a virtual power plant, check the provider’s rules, because some draw the battery down during peak events.
What to ask before you buy
- Does this battery and inverter support backup, and is it included in the price?
- Essential circuits or whole-home, and which circuits exactly?
- How many kW can it supply during a blackout?
- How fast does it switch over?
- Can the panels recharge the battery while the grid is down?
- Is my home three-phase, and which phase is backed up?
Essential-Circuit vs Whole-Home Backup
| Essential circuits | Whole-home | |
|---|---|---|
| What stays on | Chosen circuits: fridge, lights, Wi-Fi, some power points | Everything on the switchboard, within inverter limits |
| Cost | Lower: small backup sub-board | Higher: larger inverter, often a backup gateway |
| Runtime | Longest, because big loads are excluded | Shorter if large appliances run |
| Overload risk | Low | Higher with ovens, air-con and hot water |
| Three-phase homes | Single-phase essentials only | Often one phase only, so check |
| Best for | Most Sydney households | Homes that need near-normal living during outages |
How We Set Up Backup
- We ask which appliances matter most before choosing the product
- Backup circuits listed by name on the quote
- Backup reserve set up in the app at handover
- Three-phase homes checked so you know what will and won’t run
- Switchover tested on installation day
Questions We Get Asked
Does every home battery provide backup power?
No. Backup depends on the battery and inverter supporting it and on how it is wired. Some batteries offer no backup at all unless extra hardware is added. We state clearly on every quote whether backup is included and which circuits are covered.
Can I run air-conditioning from my battery during a blackout?
Sometimes, with whole-home backup and an inverter large enough for the load. It uses stored energy quickly, so runtime is much shorter. Many owners keep air-con off the backup circuits to protect the fridge and lights.
Will my solar panels work in a blackout with a battery?
With most hybrid systems, yes. Once the home is isolated from the grid, the panels keep running and recharge the battery during the day. Some AC-coupled systems cannot, so check before you buy.
How long does the switchover take?
It depends on the product. Some switch in a fraction of a second, so most devices don't notice; others take a few seconds, which can restart computers and modems.
Can I add backup to a battery I already have?
Often, yes, if the inverter supports it. It usually means adding a backup gateway or a dedicated sub-board and rewiring the circuits you want covered.
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