Why your solar stops working in a blackout

Every summer we get the same call after a storm. The power is out, the sun is shining, the panels are on the roof — and nothing is working. People assume the system has failed.

It has not. It is doing exactly what it is designed to do.

Anti-islanding

Grid-connected inverters are required to disconnect within moments of losing the grid. The requirement is called anti-islanding, and it exists to protect people.

When the network goes down, line workers have to be able to treat those wires as dead. If thousands of rooftop systems kept pushing power into the network during an outage, sections of it would stay live unpredictably. That is a serious hazard for anyone working on the lines, and it can damage equipment when supply is restored out of sync.

So the inverter monitors the grid constantly, and the instant it sees the grid is gone, it stops. Your panels are still generating; there is simply nowhere safe to send it.

A battery on its own does not fix this

This is the part that surprises people. Adding storage does not automatically give you blackout power. Many batteries are installed in a configuration that also shuts down with the grid, for exactly the same safety reason.

Keeping power during an outage requires the system to deliberately disconnect your house from the network first, then run as its own isolated island. That needs specific hardware and specific design.

What backup actually requires

Three things:

A battery and inverter that support it. Not all do. This has to be specified when you buy, not discovered afterwards.

A changeover mechanism. Something that physically isolates your house from the grid before the battery starts supplying, so you cannot backfeed the network.

A dedicated essential-services circuit. This is the part people underestimate. Backup usually does not power the whole house. Your switchboard is rewired so a subset of circuits — typically lights, fridge, internet, a few power points — sits on the backup supply.

That last point is where expectations need managing. A domestic battery will comfortably run lights, a fridge and a modem for a long time. It will not run ducted air conditioning through a 40-degree afternoon, and designing for that is rarely worth the cost.

Is backup worth it?

It depends almost entirely on where you live.

On a well-served part of the network in an established suburb, genuine outages might happen once every year or two and last an hour. The cost of backup is hard to justify on inconvenience alone.

On the semi-rural fringe — Warrandyte, parts of Eltham, the outer north — storm outages are a regular event and can last most of a day. There the value proposition is completely different, particularly if you are on tank water with an electric pump, or someone in the house relies on powered medical equipment.

Decide it on your actual outage history, not on the sales pitch.

One thing worth checking

If you already have a battery and have never confirmed whether it provides backup, find out now rather than during the next storm. Check your commissioning paperwork for an essential-services or backup circuit, and look for a separate sub-board.

Plenty of people have discovered, mid-outage, that the expensive box on the garage wall was never wired to help.