Rooftop solar in a blackout: why it switches off and where a power station fits

Ordinary grid-connected rooftop solar turns itself off when the power goes out, sunshine or not, so it won't run anything in a blackout. That's a safety rule, not a fault. A portable power station is the simple fix: charge it from a power point while the grid's up (on a sunny day your roof is doing a lot of that work), then run the fridge, modem and lights from its own outlets once the power drops.

The rules here come from Energex, Queensland's Electrical Safety Office, AusNet, the federal energy.gov.au guide and the Queensland Government's battery buyers guide. The station figures come from EcoFlow's Australian site, and the runtimes are our sums, not measurements.

Why the solar stops

A grid-connected inverter needs the grid to work against. When the network drops out, the inverter has to stop exporting so it doesn't keep the street lines live while crews are repairing them. AusNet's factsheet says solar systems must shut down automatically in an outage for this reason, and to protect your appliances from the unstable voltage solar would produce on its own.

The Australian standard for these inverters is AS/NZS 4777.2. Jemena's summary of the required settings lists active anti-islanding protection with a maximum disconnection time of 2 seconds, and a 60 second reconnection delay once the grid comes back. So the inverter goes quiet within a couple of seconds of the outage and waits at least a minute after the power returns before it starts again. If your app shows no solar during a blackout, that's the system doing its job.

The energy.gov.au guide notes that a few solar-only inverters can island and run some loads, but only while the sun's shining. Unless your installer set yours up that way, assume it can't.

The panels are still live

Here's the part people miss. The inverter switches off, but the panels don't. Energex says your panels keep producing electricity when the mains is disconnected, and to treat the modules and their cables as live at all times. Queensland's Electrical Safety Office says to shut the system down using its safe isolation procedure when a storm's coming, and to stay off the roof and away from the panels and cables afterwards unless you have to go up.

Most systems have the shutdown steps on a label at the inverter or the switchboard. Energex says they usually involve turning off the inverter's AC isolator in the meter box, then the PV array isolator next to the inverter. Follow your installer's version, not a generic one.

If the system has been damaged or got wet, keep away. Energex says not to touch it or switch it on or off even if it looks dry, and to have it recommissioned by an accredited installer, or tested by a licensed electrical contractor if no installer is available. A submerged inverter gets replaced. The Electrical Safety Office wants that check done before other clean-up starts around the system.

What does keep the lights on

There are three common setups, and they behave very differently when the grid fails.

A home battery only helps if it was set up for backup. The Queensland Government's battery buyers guide says grid-connected solar typically switches off in an outage with or without a battery, and that backup comes either as whole-of-home or essential-load circuits. energy.gov.au adds that not all battery systems can do it. Solar Victoria says the same and points out that a battery joined to a virtual power plant isn't necessarily set up for outages. If you're not sure what you've got, ask your installer in writing which circuits stay on.

A power station needs none of that. You plug the fridge into the station, not into the wall, which is why our renters' guide uses one, and why it's the plan in our cyclone season sizing guide.

Use the roof before the storm

Your rooftop solar can still help, just earlier. When a storm warning goes out, charge the power station from a power point in the middle of the day while the grid's on. If the panels are producing more than the house is using at the time, most of that charge is coming off your own roof.

EcoFlow lists the DELTA 3 Plus at 1,024Wh with a 1,500W AC input and a full charge in 56 minutes from the wall, so an hour at lunchtime fills it. Then turn off the solar using the isolation procedure if the ESO's storm advice applies to you.

The blackout sums

Say you go into the outage with the DELTA 3 Plus full. Allowing 15% for conversion losses, which is our assumption, that's 1,024 x 0.85 = 870Wh. A fridge with a 400kWh a year Energy Rating label uses about 400,000 / 365 = 1,096Wh a day. Add a 15W modem for 24 hours (360Wh) and four 9W LED lamps for 5 hours (180Wh), and a full day needs 1,636Wh. The full battery covers about 870 / 1,636 x 24 = 13 hours.

To go longer you need the station's own portable panels, not the roof. The DELTA 3 Plus takes two solar inputs at 11 to 60V and up to 500W each. With 400W of portable panels and a grey post-storm day giving the equivalent of 2 hours of full sun (our assumption for a cloudy day, not a forecast), you'd put back about 400 x 2 x 0.75 = 600Wh, allowing 25% for heat, angle and charging losses. That doesn't cover a full day, so run the fridge in blocks as our fridge guide explains. On a clear day the same panels do much better, and our solar recharge guide has Bureau of Meteorology sun hours by city. Our solar pairing guide shows how to match panels to the input limits.

Keep the station itself in the shade and charge it on a hard, non-combustible surface with some airflow. The Queensland Fire Department says not to charge a lithium-ion battery that's hot or damaged, and not to leave it charging unattended.

If you want the house wired for backup

Some people would rather have circuits wired to a backup source. That's either a backup-capable battery system from a solar installer, or a changeover switch and inlet put in by a licensed electrician. Our changeover switch guide covers what that involves. Tell the installer or electrician about your rooftop solar up front, because how the inverter and switchboard fit together is their call.

Where to buy in Australia

Buying from the brand's Australian store means 230V AU outlets, the local warranty and local support. Prices move around a lot, so check on the day.

• EcoFlow DELTA 3 PlusEcoFlow AustraliaSee it at EcoFlow Australia

Quick questions

Will a home battery keep my solar going in a blackout?

Only if the battery and inverter were designed and set up for backup. The federal energy.gov.au guide says not all battery systems can do it, so ask your installer what yours does and which circuits it covers.