By Denny Honen, Founder — Jousto
24+ years in solar & battery design · Published June 2026
The solar industry has a favourite story. "When the grid goes down, your battery kicks in. Lights stay on. Family stays protected." It's dramatic, emotional, and it sells. But almost nobody asks the more important question: what happens when your hybrid inverter itself fails? Over the life of a 10-year battery system, you're statistically more likely to experience an inverter fault than a major extended blackout — even outside a capital city. Here's the honest answer.
Watch the explainer
Prefer to read? The full guide is below.
The Fridge Test
The question nobody asks at the kitchen table
You'd naturally expect the fridge, freezer, internet, lights and phone charging to keep running when the grid goes down. But here's the question: would those same things still work if your inverter failed — not the grid, the inverter?
In many hybrid systems, the inverter sits between your battery and your backup loads. If the inverter faults — hardware failure, firmware issue, component fatigue — the backup goes with it.
Even with all of this present:
A full battery — still offline if the inverter fails
The grid running perfectly — doesn't help if loads are wired behind the inverter
Bright sun outside — no solar, no charging — the inverter is the bottleneck
The fridge goes off. The freezer goes off. The router drops out. That's the conversation worth having before you buy — not after.
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How Battery Backup Actually Works
There are essentially four ways hybrid inverters handle backup power in Australia. Each works differently — and each has a very different answer to the fridge question.
Dedicated Backup Port
The inverter has two separate AC outputs — one for your normal house circuits, one specifically for backup loads. The backup port is live whenever the inverter is running. When the grid drops, it switches to battery in under 10 milliseconds.
The catch: "Whenever the inverter is running" is doing a lot of work in that sentence. If the inverter itself fails, the backup port goes dark. Every manufacturer manual quietly recommends a bypass switch for this scenario — it's in the installation guide, rarely in the quote.
EPS Sub-Board (In-Series)
A separate sub-board is wired to nominated essential circuits — fridge, lights, whatever you specified. In a grid outage, those circuits switch to battery power via the inverter's EPS output.
The catch: This is disabled by default and must be switched on during commissioning — a step that gets missed more often than it should. Backup circuits still run through the inverter. Inverter fails, backup fails.
Internal Bypass Relay (UPS-Class)
best for grid outagesA built-in relay inside the inverter allows the full grid supply to pass through to your entire home during normal operation. When the grid fails, it switches to battery in under 4 milliseconds. Whole home covered. No external gateway needed.
The catch: The relay is powered by the inverter. If the inverter hardware fails completely, the relay opens and the passthrough is gone. Best for blackouts — same vulnerability on a complete inverter failure.
External Changeover Switch
only type that survives a complete inverter failureA physical switch — manual or automatic — installed outside the inverter entirely. In a fault scenario, it routes grid power directly to your essential circuits, completely bypassing the inverter.
The catch: Typically $200–$800 in hardware plus electrician labour. Rarely included in a standard quote. The solution exists — it just doesn't sell systems.
Do You Actually Need Whole Home Backup?
The answer the industry rarely gives
Most Australian homes don't need whole home backup. For the majority of households in metro and suburban areas, major extended outages are genuinely infrequent. Paying $1,200–$1,500 for a full sub-board upgrade for an event that may statistically never happen in your area is a significant spend for peace of mind you might never need to cash in.
The real question isn't "can my whole house run on backup?" It's: what do I actually need to keep on?
For most households, the honest list is:
The Simplest Solution Nobody Mentions
Instead of a $1,500 switchboard upgrade and sub-board rewire — you could install one or two backup GPOs (power points) wired directly to the inverter's backup port.
A double power point in the kitchen. Maybe one near the living room. That's it.
It won't run your air conditioner or oven. But it keeps everything that actually matters running — and works with almost any hybrid system. For the overwhelming majority of homeowners in reliable-grid areas, a backup GPO is genuinely all they need.
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What Inverter Failure Actually Looks Like
We've talked about grid outages. Let's talk about the scenario that's statistically more likely: the inverter itself breaking down.
Monitoring app shows a fault
The system has gone offline. No solar. Battery not charging.
You call your installer
They remote-diagnose. Confirmed: inverter failure. Warranty claim lodged.
Manufacturer assessment
Replacement stock checked. If the unit comes from overseas — and many do — you're waiting 2–6 weeks depending on brand and availability.
Parts sourced
Installer schedules the job. If you're more than 40km away, they may batch your visit with others in the area.
Finally installed
The whole time: no solar generation, battery offline, and your backup connection broken — not because of a blackout, but because the inverter that was supposed to protect you is the thing that failed.
The warranty covers the part. It doesn't cover the groceries.
Know what to ask your installer
Whether you're buying new or reviewing an existing system — these are the questions that actually matter.
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What to Ask Before You Sign
Whether you're buying a new system or reviewing what you already have, these are the questions that actually matter:
"If the inverter fails completely, does my backup port still work?"
Get a specific answer, not a vague yes.
"Is an external bypass switch included in this quote? If not, why not?"
This is $200–$800 of hardware that routinely gets left out of quotes.
"For my situation, do I actually need whole home backup — or would a backup GPO do the job?"
An honest installer will give you an honest answer.
"What's your actual process when a replacement is needed? What's a realistic timeframe?"
You want to hear "2–4 weeks" explained honestly, not glossed over.
"How far are you from my property, and what does a service call actually cost?"
Distance matters more than most buyers realise — especially for rural and outer-suburban homes.
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