The honest answer right up front: most home batteries deliver NO power during an outage. Even when they’re full. That’s not a fault and not a sales trick, it’s a safety rule. The moment the grid drops out, the inverter shuts itself down. If you want to keep the lights on and the fridge running during an outage, you need a battery with a real backup function, plus extra hardware: island mode, a backup box or gateway, and an automatic grid disconnect.
So if you’re thinking “I’ve got a home battery, so I’m fine during an outage,” I have to disappoint you. As standard, that isn’t how it works.
The reason is called anti-islanding. And once you understand how it works, you’ll also understand exactly what you need to add to make your battery work as backup power, what that costs, and how long it will last you.
Below I’ll walk you through it step by step. With the difference between an emergency socket and true island mode, a calculation of how long you’ll last, which systems support backup in 2026, and what to watch out for when it comes to safety. So that by the end you know exactly whether your battery can do it, and if not, what you need.
Does a home battery work during a power outage?
No, an ordinary grid-tied home battery does not work during a power outage. And that surprises almost everyone.
Your battery is full to the brim, the sun is shining on your panels, and yet you’re sitting in the dark. How is that possible?
Here’s how it works. A standard home battery is a grid-tied system. The inverter needs the grid voltage as a reference: it “listens” to the 230 volts and 50 hertz of the grid and synchronises with it. If that grid voltage disappears, the inverter has nothing left to align itself with. And then it does exactly what the law requires: it shuts down.
We call that anti-islanding. And as annoying as it seems in the moment you’re sitting without power, there’s a good reason for it.
Just to be clear: this applies to the vast majority of home batteries sold in recent years. Your solar panels also stop doing anything during an outage, incidentally, for exactly the same reason. More on that further down.
What is anti-islanding and why does your battery shut down?
Anti-islanding is the protection that stops your installation from feeding voltage onto the public grid during an outage. It’s mandatory, and it saves lives.
Imagine what would happen without that protection. There’s a fault in the street. An engineer from the grid operator goes to work on the cables and assumes they’re dead, because the grid is down. But meanwhile your battery or your solar panels are cheerfully pumping 230 volts back onto the grid. Then that cable is live after all. Potentially lethal.
To prevent that, every grid-tied inverter has to shut down automatically the moment the grid voltage disappears. It’s laid down in the connection conditions and in the standard that inverters have to meet. No certified installer is allowed to deviate from it.
The term “island” refers to the situation where a piece of grid (your house) would keep carrying voltage like a little island while the rest of the grid is dead. Anti-islanding prevents that. Hence the name.
And this is exactly the misunderstanding almost everyone falls for. People think their expensive battery is broken or that they’ve been ripped off. No. Your battery is simply doing what it’s supposed to do. It just isn’t built to run safely detached from the grid.
And that’s where the solution sits. If you want backup power, you need a system that can actively disconnect itself from the grid and then keep running as a safe, sealed-off island. That’s called, you guessed it, island mode.
What do you need to use your home battery as backup power?
To get real backup power out of your home battery, you need three things. Miss one, and you’re still sitting in the dark.
1. An inverter or battery that supports island mode. This is the heart of it. The inverter has to be able to generate 230 volts / 50 hertz on its own, without the grid feeding it. Not every inverter can do that. A hybrid inverter or an all-in-one system with a backup function can.
2. An automatic grid disconnect (ATS or gateway). This device physically disconnects your house from the public grid the moment the outage begins. That lets your installation run safely as an island without a single volt leaking towards the grid. ATS stands for Automatic Transfer Switch. Some brands call it a gateway or backup interface.
3. A backup box or backup circuit in the fuse cabinet. This is where you decide which circuits stay running on backup power. Often that isn’t your whole house, but a selection of critical circuits: fridge, lighting, internet, boiler. We call that a backup group.
These three together make sure that during an outage the following happens: the grid disconnect cuts your house off, the inverter takes over the voltage within milliseconds, and your backup group simply keeps running. Often you barely notice anything, apart from the rest of the street being dark.
Important: this is not a weekend job. A grid disconnect and a backup box have to be connected by a certified installer. It’s about safely separating the grid and the installation. Do it wrong, and you’ll still put voltage onto the grid. That’s exactly what anti-islanding is meant to prevent. So always have this done by a professional.
Emergency socket, EPS or full island mode: what’s the difference?
Not every “backup function” is the same. There are roughly three levels, and the difference in comfort (and price) is enormous. This is what most articles steamroll straight over, even though it’s the core of your choice.
Level 1: the emergency socket. The simplest form. The battery or inverter has a single socket that provides voltage during an outage. You have to plug something in yourself. No automatic switchover, no connection to your fuse cabinet. Handy for your modem, a lamp and your phone charger, but no use to the fridge in your kitchen. The power is limited, often around 1.5 kW.
Level 2: EPS (Emergency Power Supply). A backup supply for a fixed, pre-selected circuit. The switchover is automatic, but not always seamless: there can be a brief interruption between the grid dropping out and the backup power starting up. Your computer briefly switches off, your fridge doesn’t notice. EPS feeds a selection of circuits, not your whole house.
Level 3: full island mode (whole-home backup). The inverter runs continuously as a voltage source and takes over within milliseconds during an outage. The transition is imperceptible for most devices. Depending on the configuration, this feeds a large backup group or even your whole house. This is as close as you’ll get to a true home UPS.
Here are the switchover times side by side, because this determines whether sensitive equipment drops out or not:
| Type | Switchover time | Comfort | Feeds |
|---|---|---|---|
| Emergency socket | Manual (you plug it in) | Low | 1 device |
| EPS | A few seconds, noticeable | Medium | Fixed circuit |
| Island mode (Enphase) | Less than 2 ms, imperceptible | High | Backup group or whole house |
| Island mode (SolarEdge, Victron) | Around 20 ms, usually imperceptible | High | Backup group or whole house |
See the difference? With a true home UPS (level 3) your light doesn’t even flicker. With an emergency socket you’re the one dragging an extension lead around. So choose deliberately what fits your situation.
Whole house or just a backup group on backup power?
Almost nobody actually needs their whole house on backup power. And the difference in cost is substantial. This is the most important dial you turn.
Option A: a backup group (critical circuits). You pick a few circuits that absolutely have to keep running: fridge and freezer, lighting, internet router, boiler (for your heating), and a few sockets for laptop and phone. For most households this is the sensible choice. Your battery lasts longer, because you use less, and the installation is a good deal cheaper.
Option B: the whole house. Everything keeps running, including your oven, washing machine and air conditioning. Sounds luxurious, but it costs more to install and your battery empties much faster. And watch out: many batteries can’t deliver enough power to switch everything on at once. A backup inverter often delivers 3.68 to 7.68 kW. Switch on your induction hob, oven and kettle at the same time, and the whole thing still trips out from overload.
My advice: pick a backup group with the things that really mustn’t go off. Frozen food that thaws is a waste, a cold shower is annoying, and without internet you’re blind in 2026. Your oven survives a few hours without power just fine.
One more technical point that’s often forgotten: if you have a three-phase connection, a single-phase backup system can’t feed your whole house. Heavier appliances that run on three-phase (for example a heat pump or a powerful EV charger) drop out anyway. Discuss this with your installer.
Will my solar panels keep working during a power outage?
Only if you have a suitable hybrid inverter with island mode. Otherwise your panels drop out during an outage just as hard as your battery.
This surprises a lot of people with solar panels. You’d think: the sun is shining, so I have power. But your ordinary solar inverter is also grid-tied and shuts down during an outage because of that same anti-islanding. Your panels then literally sit on your roof gleaming for nothing.
If you want your panels to keep charging during an outage, they have to fall within the island grid your inverter generates. With a hybrid setup that’s possible: the PV inverter runs along inside the island and keeps topping up the battery.
And that’s when it gets really interesting. During the day your panels top up the battery, at night you draw from the battery. During a longer outage on a sunny day you can, in theory, keep running indefinitely on your backup group, as long as the sun delivers more than you use. That’s the difference between bridging a few hours and being self-sufficient for days.
Without that hybrid setup? Then you’re drawing purely on what’s in the battery, and your panels are worthless during the outage.
How long will I last on my home battery? A worked example
How long you’ll last depends on two things: how much is in your battery, and how hard you’re using power. I’ll work it out with you, using real numbers.
The situation: a home battery of 10 kWh, of which you have about 90 percent usable during an outage, so 9 kWh. You’re feeding a backup group with the essential appliances.
Step 1: work out your backup group’s consumption.
Count what’s on continuously:
| Appliance | Power | Runs |
|---|---|---|
| Fridge + freezer | 100 to 150 W on average | Continuously (in cycles) |
| Lighting (LED) | 50 to 100 W | In the evening |
| Internet router + modem | 20 W | Continuously |
| Boiler (pump + electronics) | 100 to 150 W | During the heating season |
| Charging laptop / phone | 50 W | Now and then |
Together you’re at roughly 300 to 500 watts continuously for a lean backup group. Say 400 watts.
Step 2: work out the runtime.
9,000 watt-hours divided by 400 watts = 22.5 hours.
So with a 10 kWh battery and an economical backup group you’ll get nearly a full day. Switch on more (that crucial word: on average) and it drops accordingly. At 800 watts on average you’ll still last around 11 hours.
Step 3: add the sun (if you have a hybrid setup).
If the sun shines and your panels deliver a net 6 kWh into the battery that day, the calculation shifts dramatically. You use, say, 8 kWh a day, your panels top up 6 kWh, so your net draw from the battery is only 2 kWh per day. Then with 9 kWh you’ll get several days. On a genuinely sunny day you might even break even.
The pitfall almost every article leaves out: inrush current.
Motors and compressors (fridge, freezer, boiler pump, sump pump) briefly draw far more current at the moment they start up than during normal operation. A fridge that normally draws 100 watts can briefly demand 600 to 800 watts when it kicks in. We call that peak the inrush or startup current.
Why does that matter? Because your backup inverter has to be able to deliver that peak, even if your average consumption is low. An inverter that delivers 1.5 kW on paper can still trip if three motors start up at the same time. So don’t just look at the capacity in kWh, but also at the peak power in kW that your system can handle. Reckon with plenty of margin above your average consumption.
Which home batteries and inverters support backup power in 2026?
Not every brand can do it, and the differences are large. This is an overview of systems that support backup in 2026. Prices are indicative for a complete system including installation, and vary widely by situation.
| System | Backup type | Power | Switchover time | Indicative system price |
|---|---|---|---|---|
| Enphase IQ | Whole-home / backup group | up to 7.68 kW | less than 2 ms | 8,000 to 10,500 euros |
| SolarEdge Energy Hub | Whole-home / backup group | up to 5 kW (3.68 kW backup) | around 20 ms | 7,500 to 9,000 euros |
| Victron MultiPlus-II | Whole-home / off-grid | up to 15 kVA (modular) | around 20 ms | 5,800 to 8,000 euros |
| Huawei LUNA2000 | Whole-home / backup group | 3 to 6 kW | around 20 ms | 6,000 to 8,500 euros |
| SMA (Secure Power Supply) | Emergency socket | around 1.5 kW | n/a (manual) | often at no extra cost |
| Sessy (with backup module) | Backup group via external inverter | depends on the inverter | automatic or manual | plus cost of inverter |
A few things to know about this overview.
Victron is the flexible all-rounder. The MultiPlus-II and Quattro let you connect the solar inverter on the backup side (AC-out), so your panels keep charging during an outage. Popular with people heading towards off-grid.
Enphase switches the fastest, in less than 2 milliseconds. So fast that even sensitive electronics notice nothing. Pricey, but the comfort is top-notch.
SolarEdge with the Energy Hub inverter is a commonly chosen all-in-one route. Note that the backup power (3.68 kW) is lower than the charging power, so size your backup group to that.
SMA offers a basic backup supply with Secure Power Supply: a single socket that provides voltage when there’s sun and a grid outage. Limited, but often at no extra cost.
Already have a battery? Then check with your installer whether the brand supports island mode and whether a backup box exists for it. With some systems you can add backup power afterwards, with others you can’t. That makes a difference.
What does backup power from your home battery cost?
The extra cost depends on which level you choose. Roughly speaking there are three price tags on top of the battery itself.
| Level | What you get | Extra cost (indicative 2026) |
|---|---|---|
| Emergency socket | One socket, manual | around 300 euros |
| Backup group (partial backup) | Automatic switchover, critical circuits | around 1,000 euros |
| Whole house (whole-home) | Automatic switchover, everything | around 3,000 euros |
That extra cost sits in the separate components:
- Automatic transfer switch (ATS): 150 to 300 euros
- Backup box / gateway: 1,000 to 1,500 euros
- Extra wiring and modifications to the fuse cabinet: a few hundred euros
- Installer’s labour: depends on the job
A complete system with battery and full backup quickly reaches 5,000 to 13,000 euros. That’s a serious chunk of money for something you rarely need.
And that brings me to an honest caveat. The grid in Western Europe is among the most reliable in the world. The average household sits without power for only around 20 minutes a year. Hanging thousands of euros of backup up for those 20 minutes rarely pays off in pure money terms.
Where it can still be worth it: if you live somewhere with more frequent or longer outages, if you depend on medical equipment, if you work from home and can’t do without internet, or simply for peace of mind. That’s a perfectly good reason. But then call it comfort and security, not an investment that pays for itself. Because backup power doesn’t do that.
If you just want something simple for short bridging, an emergency socket or a portable power station is often enough. If you’re after real self-sufficiency during longer outages, a battery with island mode and solar panels on the backup side is king. Choose according to your needs, not according to the most expensive brochure.
Frequently asked questions
Does every home battery work during a power outage?
No. The vast majority of home batteries shut down during an outage because of anti-islanding, a mandatory safety protection. Only batteries with a backup function (island mode) and the accompanying hardware, an automatic grid disconnect and a backup box, keep delivering power during an outage.
What’s the difference between an emergency socket and island mode?
An emergency socket is a single socket on your battery that you plug something into yourself, with limited power. Island mode means your entire installation (or a backup group) switches over to the battery automatically and seamlessly, without you having to do anything. Island mode is more comfortable and more expensive.
Will my solar panels keep working if the power goes out?
Only with a suitable hybrid inverter that supports island mode. An ordinary grid-tied solar inverter shuts down during an outage just as much as your battery. If your panels do run within the island grid, they can top up the battery during the outage, which extends your runtime considerably.
How long can I last on my home battery without the grid?
With a 10 kWh battery and an economical backup group (fridge, light, internet, boiler) of 400 watts on average, you’ll get around 20 to 22 hours. Use more, and that drops proportionally. If you have solar panels on the backup side, on a sunny day you can keep running for several days or even indefinitely.
Can I install a backup box myself?
No. A grid disconnect and a backup box have to be connected by a certified installer. It’s about safely separating your installation and the public grid, so that you don’t send voltage towards the grid during an outage. Wired wrong, this is potentially lethal for engineers working on the grid. This is not a DIY job.
Does backup power from a home battery pay for itself?
No, not in money terms. The grid is very reliable (around 20 minutes of outage a year on average), and the extra cost for backup runs into several thousand euros. See backup power as comfort and security, not as a profitable investment. For people with medical equipment, frequent outages nearby or a home office, it can still be worth that security.
Backup power is one small piece of a much bigger energy story. The real gain on your energy bill usually sits somewhere else: in smartly charging and discharging your battery, in making the most of your solar power, and in waste you don’t even see.
I’ve lined up everything I know about bringing your energy bill down in the guide on the Energy Smasher. Concrete steps and honest numbers, no sales talk. Have a look around: energie-verpulveraar.fredsbouwtekeningen.nl