When the grid goes down.

01Why solar switches off

It surprises nearly everyone. The power goes out on a sunny afternoon, the panels are in full sun, and the house is dark anyway.

It's deliberate. When the grid fails, people are sent to repair it, and they need the lines to be dead. A solar system that kept pushing power out to the street would make those lines live. So every grid-connected inverter is required to shut down the moment it loses the grid, and to stay off until the grid returns.

02A battery alone doesn't change it

Adding a battery doesn't, by itself, change any of that. A battery on a standard installation shuts down with the rest of the system.

What changes it is a system designed for backup. That means equipment that disconnects your home from the street when the grid fails, so your system can keep running the house without sending anything out to the lines. With that in place, the battery and the panels carry on.

Backup isn't something a battery has. It's something a system is designed to do.

03What it can run

Backup comes in two forms. Some systems back up a few chosen circuits: the fridge, some lights, the internet, a couple of power points. Others back up the whole home.

Either way the limit is the battery's power rating, which is how much it can run at once. Lights, fridge and the television are easy. An electric oven, ducted air conditioning and a car charger together are not. Deciding what matters in an outage is part of the design.

04How long it lasts

That depends on how full the battery was when the grid went down and on what you run. A home being careful can stretch a modest battery through a night.

In a system designed for it, the panels keep charging the battery during the outage, so a long daytime blackout may hardly be noticed. A long one on a dark winter evening is a different matter.

05Decide at the start

Backup is far simpler to include when a system is designed than to add afterwards, because it affects the wiring at your switchboard. If it matters to you, say so in your first conversation with us. If it doesn't, there's no reason to pay for it.

06If you rely on medical equipment

A home battery is not a substitute for a proper plan. If someone in your home depends on powered medical equipment, register for life support with your electricity retailer and distributor, and keep the plan your doctor recommends, whatever is on your wall.