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Why Backup Power Matters
Grid outages are becoming more common across Australia as extreme weather events intensify. Heatwaves, storms, and bushfires can knock out power for hours or even days.
What many homeowners do not realise is that standard grid-tied solar systems shut down during blackouts. This is a safety requirement called anti-islanding: your inverter must stop exporting power so line workers can safely repair the grid. Without backup hardware, your solar panels and battery sit idle while the grid is down.
To keep the lights on during a blackout, you need a system that can disconnect from the grid and run independently. This guide walks you through planning that setup, from choosing which circuits to back up, to sizing your battery, to understanding the hardware involved.
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Essential vs Nice-to-Have Circuits
Not every appliance needs to run during a blackout. Installers typically split your loads into three tiers to help you prioritise what matters most.
| Appliance | Typical Wattage | Daily Usage | Priority Tier |
|---|---|---|---|
| Fridge/freezer | 150W | 3.6 kWh | Essential |
| LED lights (whole home) | 50W | 0.4 kWh | Essential |
| Internet router | 15W | 0.36 kWh | Essential |
| Phone charger | 10W | 0.05 kWh | Essential |
| Medical equipment | Varies | Varies | Essential |
| TV | 100W | 0.5 kWh | Nice-to-Have |
| Microwave | 1,200W | 0.2 kWh | Nice-to-Have |
| Air conditioner | 2,000–3,500W | 8–14 kWh | Heavy Draw |
| Pool pump | 1,500W | 6–12 kWh | Heavy Draw |
| EV charger | 7,000W | 14–35 kWh | Heavy Draw |
For essential-circuits backup, most installers wire up the fridge, lights, internet router, phone chargers, and one or two power points. This keeps your core needs running while stretching battery life as long as possible.
How Long Will Your Battery Last?
Battery duration depends on two things: how much usable capacity you have, and how much power you are drawing. Here is a rough guide based on three common load scenarios.
| Battery Size | Essentials Only (~500W) | Essentials + Comfort (~1,500W) | Whole Home (~3,000W) |
|---|---|---|---|
| 5 kWh | 10 hours | 3.3 hours | 1.7 hours |
| 10 kWh | 20 hours | 6.7 hours | 3.3 hours |
| 13.5 kWh | 27 hours | 9 hours | 4.5 hours |
| 20 kWh | 40 hours | 13.3 hours | 6.7 hours |
These estimates assume continuous draw. In practice, appliances cycle on and off (your fridge does not run constantly), so real-world backup times are often longer. However, batteries also have continuous power output limits, typically 3.3 kW to 5 kW. If your total load exceeds that limit, the system may shut down to protect itself.
Whole-Home vs Essential-Circuits Backup
The biggest decision in backup planning is whether to back up just your essential circuits or your entire home. Here is how they compare.
| Feature | Essential Circuits | Whole Home |
|---|---|---|
| Circuits covered | Fridge, lights, router, chargers | Every circuit in the home |
| Additional hardware cost | $0–$500 | $500–$2,000 |
| Backup gateway required | Sometimes | Yes |
| Battery drain rate | Slow (longer backup) | Fast (shorter backup) |
| Best for | Most homes, occasional short outages | Medical needs, work-from-home, frequent long outages |
For most Australian homes with occasional short outages, essential-circuits backup provides the best balance of cost and coverage. Whole-home backup makes sense if you have medical equipment that requires power, you work from home and cannot afford downtime, or your area experiences frequent extended outages.
Transfer Switches and Backup Gateways
A backup gateway is the hardware that sits between your battery system and the grid. When it detects a grid outage, it disconnects your home from the grid and switches to battery power. This process is called islanding: your home becomes an electrical island, running independently.
The switchover time varies by product. The Tesla Backup Gateway switches in under 20 milliseconds, fast enough that most appliances do not even notice. Other systems may take a few seconds, which can cause sensitive electronics to restart.
Standard grid-tied systems without a gateway cannot island. The inverter detects the grid outage and shuts down, leaving you without power even though your battery is fully charged.
Tesla Backup Gateway
Switchover: <20ms
Seamless transition. Pairs with Powerwall. Supports whole-home backup with multiple Powerwalls.
Enphase IQ System Controller
Switchover: <1 second
Works with Enphase IQ batteries. Supports essential-circuits or whole-home configurations.
SolarEdge Backup Interface
Switchover: seconds
Pairs with SolarEdge inverters and batteries. Typically used for essential-circuits backup.
Does Your Inverter Support Backup?
Not all inverters can run in backup mode. The type of inverter you have determines what is possible.
Hybrid Inverters
Hybrid inverters manage both solar panels and batteries in a single unit. Most modern hybrids support backup mode natively, though some require an additional backup box. This is the simplest path to backup capability.
Standard Solar Inverters (AC-Coupled Retrofit)
If you already have a standard solar inverter, you can add a battery with its own inverter (AC-coupled). Backup is possible but typically requires a backup gateway and may have limitations on which circuits are covered. This is the most common retrofit approach.
DC-Coupled Systems
DC-coupled systems connect the battery directly to the solar panels before the inverter. This is more efficient for charging but typically means replacing your existing inverter with a hybrid. Best suited for new installations or full system upgrades.
For a detailed breakdown of inverter compatibility when adding a battery, see our battery buying guide.
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Backup Generators and Remote Homes
For suburban homes on the grid, a battery with solar covers most blackout scenarios. But if you live remotely, are off-grid, or experience multi-day outages, a battery alone may not be enough. Extended cloudy weather can prevent solar from recharging the battery, and you could be left without power at the worst possible time.
A backup generator bridges this gap. It acts as a last-resort power source when both the grid (if you have one) and solar are unavailable.
When a Generator Makes Sense
Off-grid properties with no mains connection. Remote homes where the nearest town or fuel supply is an hour or more away. Areas prone to extended outages from bushfires, floods, or severe storms. Properties with high seasonal loads (heating in winter, irrigation pumps) that can exceed what solar and battery provide.
Generator Types and Costs
A small portable petrol generator (2 to 3 kW) costs $1,000 to $2,000 and can keep essentials running. Larger diesel generators (5 to 10 kW) cost $3,000 to $8,000 and can power more of the home. Auto-start models connect to your battery system and kick in automatically when the battery drops below a set level, so you do not need to be home to start it manually.
Fuel and Logistics
Factor in fuel storage and resupply. A 3 kW generator running essentials uses roughly 10 to 15 litres of petrol per day. If you are hours from the nearest service station, you need enough stored fuel to cover extended outages. Keep fuel in approved containers, store it safely away from the house, and rotate stock every 6 to 12 months so it does not degrade.
Solar panels as the primary source, a battery for overnight and cloudy-day coverage, and a generator as the emergency fallback. This layered approach means the generator only runs when absolutely needed, minimising fuel costs and maintenance. Ask your installer about systems that integrate all three automatically.
Planning Checklist
Questions to Ask Your Installer
Frequently Asked Questions
Can solar charge my battery during a blackout?
Yes, if your system supports islanding. When the grid goes down, an islanding-capable system disconnects from the grid and forms a self-contained circuit. Your solar panels continue generating power and can recharge the battery during daylight hours, potentially extending your backup indefinitely in good weather.
How much does backup add to battery cost?
Essential-circuits backup adds $0 to $500 to most installations. Whole-home backup typically adds $500 to $2,000, mainly for the backup gateway and additional wiring. Some battery systems like the Tesla Powerwall include backup capability as standard.
Do I need backup if I rarely lose power?
It depends on your risk tolerance. If outages are rare and short in your area, essential-circuits backup may be all you need. However, extreme weather events are becoming more frequent across Australia, and backup adds peace of mind. If you have medical equipment that requires power, backup is strongly recommended regardless of outage history.
Can I add backup capability later?
In most cases, yes, but it is cheaper to include it from the start. Retrofitting backup often requires adding a backup gateway, rewiring your switchboard, and potentially upgrading your inverter. This can cost $1,000 to $3,000 as a standalone job versus $500 to $2,000 when included in the initial installation.
Do I need a backup generator as well as a battery?
For most suburban homes, a well-sized battery with solar is enough. But if you are remote or off-grid, a backup generator adds a critical safety net. Extended cloudy periods, high seasonal loads, or being hours from the nearest fuel supply all increase the risk of running your battery flat with no way to recharge. A small petrol or diesel generator ($1,000 to $3,000) can keep essentials running while solar recharges the battery. Talk to your installer about auto-start generators that kick in when battery levels drop below a set threshold.
The next step
If you have any questions about the information in this guide, feel free to get in touch:
Email: hello@whysolar.com.au
Tel: +61 455 221 921
If you're considering a home battery system, Kim and the team can help you get quotes from trusted, pre-vetted local installers:
Written by
Kim TranBattery Storage Expert
Specialist in home battery systems and energy independence solutions. Kim analyses the rapidly evolving battery market to help homeowners decide if, when, and which battery to add to their solar setup.
Learn more about Kim Tran