Backup is not automatic
When the grid fails, grid-connected solar must stop exporting for the safety of line workers. A battery can keep part of the home running only if the system is designed and wired to island safely from the grid. That usually needs a specific gateway, backup interface or a hybrid inverter with a backup output.
If your quote does not mention backup, assume it is not included and ask.
Whole-home or essential circuits
Some designs back up the whole switchboard. Many back up selected circuits, often lights, the fridge, internet and some power points. Large loads such as ducted air conditioning, ovens, cooktops and EV chargers are often left off because they can exceed the battery's output.
Which approach suits you depends on the battery's power rating, your switchboard and what you actually need during an outage.
How long it lasts
Run-time depends on how full the battery is when the outage starts and what is running. Some systems let you keep a reserve level for backup, which trades a little daily saving for more resilience. During the day, some systems can also recharge from solar while off-grid, but this depends on the equipment and setup.
Switch-over
Some systems switch over fast enough that most devices do not notice. Others have a short interruption. Manufacturers publish their own specifications; for example, Tesla describes Powerwall's backup features on its Australian site. Confirm the behaviour of the specific system you are quoted rather than relying on general claims.
Put it in writing
Before you sign, ask the installer to confirm:
- Whether backup is included, and what extra equipment it needs
- Exactly which circuits are backed up
- The continuous power available in backup mode
- Whether solar can recharge the battery during an outage
- How the reserve level is set and changed
Medical and critical needs
If anyone in your home relies on powered medical equipment, do not treat a home battery as your only plan. Speak to your retailer and network about life support registration and keep a separate plan.
Sources
Sources are linked for background reading. They do not endorse Green Home. This is general information, not advice for your home; a site assessment is needed for a recommendation.
