Let’s start honest, because this is where 90% of people fall flat on their face.
You’ve got solar panels on your roof and you think “then I’m sorted if the power goes out”? Wrong. When the grid goes down, your solar panels shut off too. Along with everything else.
That’s not a fault. That’s the inverter doing exactly what it’s supposed to do.
In this article I’ll explain which inverter you actually need for backup power, why a normal inverter leaves you out in the cold, and how to pick the right one in a few clear steps. No sales talk. Just straight facts.
Short answer: which inverter do I need for backup power?
For backup power during a blackout you need a grid-forming inverter, meaning an island-capable or hybrid inverter with a backup function, combined with an automatic transfer switch (a backup box or ATS).
A normal inverter (grid-following, so an ordinary grid-tied inverter) shuts down precisely when the grid fails. It can only work as long as the grid is there; it can’t build its own “grid” on its own.
Without a battery you also only have power while the sun is shining. If you want power in the evening or at night during an outage, a home battery has to be part of it.
That’s the core of it. Now the explanation, because the devil really is in the detail here.
Why does a normal inverter shut down during a blackout?
This is the part almost every blog skips, and it’s exactly the most important bit.
A normal solar inverter is called “grid-following”. Loosely translated: it follows the grid. It measures the voltage and frequency of the grid and synchronises with it. If the grid disappears, it has nothing left to synchronise to and shuts off within a fraction of a second.
That’s called anti-islanding. And it’s mandatory.
Why? Safety. Picture the grid going down and an engineer from the network operator working on the cables in the street, assuming everything is dead.
If your inverter just kept pumping away, you’d be feeding power back into a “dead” grid. That is lethal for that engineer.
That’s why every certified grid-tied inverter shuts off hard the moment the grid drops. So it’s not a bug, it’s a life-saving feature.
The trick with backup power is: how do you supply your own house with power without dangerously feeding back into the grid? Answer: your house has to be physically disconnected from the grid. And that’s exactly what a transfer switch does.
Grid-following vs. grid-forming: the real difference
Two terms you need to get. I’ll keep it simple.
Grid-following
This is your standard inverter. It only delivers power when there’s already a grid to run alongside. No grid, no power. Full stop.
Grid-forming
This one can build a grid itself. It sets the voltage and frequency on its own and forms a small “island” within which your house runs. We call that island mode.
A grid-forming inverter knows: the grid is gone, I’ll take over for the part of the house connected to me. As long as the house is properly disconnected from the public grid for that, it’s safe.
Almost all backup-capable systems are hybrid inverters: they can run grid-following on a normal grid and switch to grid-forming island mode during an outage.
Black start: do your solar panels keep producing during the outage?
Important question, because there’s a catch here.
Some backup power systems can get the solar panels running again during an outage, so you have free power during the day and recharge your battery. That’s called black start: the system “boots the island” without a grid.
Other, simpler systems can’t do that. During the outage they lean purely on the battery. Sun blazing but your battery flat? Tough luck, no power.
For a short outage (an hour or so) it barely matters. For a longer disruption of half a day or more the difference is enormous. With black start you can bridge indefinitely in theory; with battery only you’re stuck at your battery capacity.
So ask your installer this explicitly: “Do my panels keep producing during an outage, yes or no?” Don’t let yourself be fobbed off with a half answer.
Seamless or with an interruption? The transfer time
When the grid drops, your system has to switch to island mode. How fast that happens decides whether you notice it.
Seamless (UPS level, less than roughly 10 to 20 milliseconds)
You don’t notice a thing. Your computer keeps running, your PC doesn’t reboot, your NAS or medical equipment doesn’t so much as flinch. This is genuine online-UPS behaviour.
Fast transfer (roughly 10 milliseconds to a few seconds)
Your lights flicker for a moment, appliances with a clock blink, your PC may reboot. For a fridge or heating, no problem at all. For sensitive electronics, sometimes it is.
Slow transfer (several seconds)
Some cheaper backup boxes have a noticeable pause. Fine for “the freezer stays cold”, not for “my home office can’t go down”.
Do you really want seamless? Then look for systems that advertise a UPS function or a switchover under 20 milliseconds. Be critical here, because “fast” is a stretchy term in brochures.
Inrush current: the trap of pumps, fridges and air conditioners
Now a mistake that genuinely costs people money. They count on the normal consumption, and then when the fridge kicks in it blows the whole thing.
Motors, so fridges, freezers, pumps, heat pumps, air conditioners, submersible pumps, briefly draw a multiple of their normal power when they start up. That’s called inrush current or startup current.
A fridge compressor rated at 150 watts can briefly draw 600 to 900 watts of peak when it kicks in. A submersible or pond pump of 500 watts can easily demand 1500 to 3000 watts of peak. A heat pump with an old-fashioned compressor is a real beast on top of that.
That’s why with backup power you look at two numbers:
- Continuous power: what the system can deliver on an ongoing basis (for example 3 kW).
- Peak power: what it can deliver briefly to absorb that inrush current (for example 6 kW for a few seconds).
Systems with a decent peak margin (often 1.5 to 2 times the continuous power) swallow those inrush currents without complaint. Systems without a margin trip out. And then you’re standing in the dark, cursing.
My rule of thumb: add up your continuous consumption and add a fat margin on top for the heaviest motor appliance. Better too generous than just too tight.
Whole house or only critical circuits?
Two flavours. Choose deliberately, because this decides your entire budget.
Critical circuits (recommended for most people)
You set up a separate “backup circuit” or emergency circuit with only what really has to keep working: fridge, freezer, boiler (that pump and ignition!), wifi/modem, some lighting, charging your phone.
This is cheaper, because you need a smaller system, and more reliable, because you’re not overloading anything. A family often gets by with 1 to 3 kW on the critical circuits.
Whole house
Everything keeps running, including the induction hob, dishwasher, washing machine and heat pump. Sounds great, but you need a hefty system (think 5 to 10 kW plus plenty of battery capacity) and therefore a hefty budget. And you have to be careful not to switch everything on at once during an outage.
My down-to-earth advice: start with critical circuits. Ask yourself what genuinely can’t go down during a disruption. That list is shorter than you think.
Separate hybrid inverter or all-in-one home battery?
Roughly two routes to backup power.
Separate (hybrid) inverter plus a separate battery
Think Victron MultiPlus or Quattro with separate batteries, or a hybrid string inverter with battery modules. Flexible, expandable, strong on peak power. Popular with people who take it seriously or want a lot of power. It does require more engineering.
All-in-one home battery with built-in inverter and backup
One cabinet holding the inverter, battery and sometimes the transfer switch. Tidier, quicker to install, less loose kit on the wall. Handy, but you’re more tied to what the manufacturer offers in terms of power and expansion.
There’s no right or wrong. If you want maximum control and peak load (for example for a workshop or pump), the separate-inverter route is often stronger. If you just want a tidy solution for the family, an all-in-one with backup is perfectly fine.
Comparison table: which inverters can do backup power?
Note: these are broad indications. Exact specs differ by model, generation and configuration. Always check the datasheet of the specific type.
| System / brand | Island mode (grid-forming)? | Transfer time | Solar during outage (black start)? | 1- or 3-phase | Suitable for |
|---|---|---|---|---|---|
| Normal grid-tied inverter | No | Shuts down | No | Both | Nothing, shuts down during an outage |
| SolarEdge Home Hub + Backup Interface | Yes | Fast, tending towards seamless | Yes, with backup config | 1- and 3-phase | Whole house or critical circuits |
| Enphase IQ8 microinverters + backup | Yes, “sunlight backup” | Can run on sunlight without a battery | Yes | 1- and 3-phase | Critical circuits, flexibly scalable |
| Victron MultiPlus / Quattro | Yes, strong | Seamless (UPS, ms level) | Yes, with MPPT/inverter added | 1- and 3-phase (parallel) | Heavy, peak load, off-grid, workshop |
| Growatt SPH + backup box | Yes | Fast transfer (seconds) | Yes | Mostly 1-phase, also 3-phase models | Family, critical circuits |
| GoodWe ES / EM (hybrid) | Yes | Fast transfer | Yes | 1- and 3-phase | Family, critical circuits |
| Huawei hybrid + backup box | Yes | Fast transfer | Yes | 1- and 3-phase | Family, whole house |
| Sungrow hybrid + backup | Yes | Fast transfer | Yes | 1- and 3-phase | Family, whole house |
The common thread: a normal inverter can’t do it, all the other systems in this list can, provided you have the matching backup box or transfer switch with it. Without that switching, nothing safe happens.
1-phase or 3-phase: what should you watch out for?
If you have a 3-phase connection (more and more houses, certainly with a car charger or heat pump), there’s an extra thing to watch.
Some backup power systems only back up a single phase. If your fridge happens to sit on a different phase, it’s no use to you during an outage.
So with 3-phase you want either a 3-phase backup solution, or your installer deliberately puts your critical appliances on the phase that gets backed up. That’s a design choice, not chance. Discuss it explicitly.
Heavier 3-phase appliances (induction, some heat pumps) need a 3-phase backup system anyway just to run. Count on serious power for that.
Safety: this is not a DIY job on the consumer unit
Now I’ll put on my strict hat for a moment, because this is where it goes wrong and where people die.
Never just connect backup power directly to your consumer unit. Never. Without correct, certified switching you run two big risks:
-
You feed back into a dead grid. If during a disruption your system is simply sitting on the consumer unit and the house isn’t properly disconnected from the grid, you can put voltage on the street cable. The engineer working there thinks it’s dead. That is lethal.
-
The grid comes back onto your system. If the grid returns while your inverter is still forming its own “grid”, and the two aren’t in phase, you get a jolt that wrecks appliances and the inverter.
The solution is an automatic transfer switch, an ATS (Automatic Transfer Switch) or a manufacturer’s backup box. It makes sure your house is physically disconnected from the public grid before your own system takes over, and only reconnects when the grid is stably back.
So: have backup power installed by a certified installer (think of a Part P certified electrician or a comparably certified firm). Not because I underestimate you, but because a mistake here doesn’t mean “the little light won’t come on”, it means “someone gets a fatal shock” or “fire”.
The work in the meter cabinet and the switching are not a hobby job. The rest, like thinking along and preparing, you’re welcome to do yourself. This switching, no.
Step-by-step choice guide: how to choose your backup power inverter
A no-nonsense step-by-step plan. Work through this before you sign a quote.
Step 1. What has to keep working?
Write down the appliances that genuinely have to keep going during an outage. Usually: fridge, freezer, boiler, modem/wifi, some light, phone. That’s your critical list.
Step 2. Work out the simultaneous power (in watts).
Add up what’s running at the same time. Not your annual consumption, but the simultaneous peak power at that moment. Add a fat margin for inrush current on the heaviest motor appliance.
Step 3. How long do you want to bridge?
An hour or so? Then battery capacity matters less. Half a day or longer? Then you want plenty of battery and black start, so your panels recharge it.
Step 4. Do you need seamless or not?
Do you have a home office, NAS, or sensitive equipment? Choose UPS level (under roughly 20 ms). Is it purely about keeping the freezer cold? Then a few seconds of transfer is perfectly fine and saves you money.
Step 5. 1-phase or 3-phase?
Check your connection. With 3-phase: choose a 3-phase solution or have your critical appliances deliberately placed on the backup phase.
Step 6. Critical circuits or whole house?
For most people: critical circuits. Cheaper, more reliable. Whole house only if you’ve got the budget and the power to spare for it.
Step 7. Separate inverter or all-in-one?
Lots of peak load or maximum flexibility? Separate hybrid inverter plus battery (for example Victron). Tidy family solution? All-in-one home battery with backup.
Step 8. Have it installed by a certified installer.
With a correct automatic transfer switch. Ask for the transfer time in writing and whether black start is included. No half measures.
Work through this list and you’ll ask the right questions, and no one will sell you a system that still fails at the first disruption.
Frequently asked questions about choosing a backup power inverter
Do my solar panels work during a blackout?
No, not with a normal inverter. It’s required to shut down during a grid outage because of anti-islanding, a safety measure. Only with a grid-forming/hybrid inverter with a backup function and the right switching can your panels keep producing during a disruption (in sunlight).
Do I need a home battery for backup power?
For power in the evening and at night, yes. Without a battery you only have power during an outage as long as the sun is shining and your system supports black start. For reliable backup power, including in the dark, a battery has to be part of it.
What’s the difference between seamless and normal transfer?
Seamless (UPS, under roughly 10 to 20 milliseconds) you don’t notice: appliances keep running. Normal transfer takes from a few hundred milliseconds to a couple of seconds, during which lights flicker and sensitive equipment may reboot. For a fridge and heating it makes no difference, for computers it does.
Can I connect a backup power system to my consumer unit myself?
No. That is lethal without correct automatic switching. You can feed back into a dead grid (danger to engineers) or get damage when the grid returns. Always have this done by a certified installer.
How much power do I need for backup power?
For critical circuits (fridge, freezer, boiler, wifi, light) a family often gets by with 1 to 3 kW continuous, plus plenty of peak power for the inrush current of motors. For the whole house including induction and a heat pump you’re quickly at 5 to 10 kW.
What is black start and why does it matter?
Black start means the system can independently boot the “island” during an outage and let your solar panels produce again, without a grid. That lets you bridge indefinitely during the day in theory. Without black start you lean purely on your battery capacity.
In closing: do it right once
Backup power isn’t a gadget, it’s an insurance policy. And just like with an insurance policy, you don’t want to discover at the first disruption that the small print disappoints.
Choose a grid-forming/hybrid inverter with backup, with enough peak power for your inrush currents, with the transfer time that matches what you’re backing up, and have it installed safely. Then you’re sorted when the lights go out in the street and you just carry on.
Do you want to be smart not just during an outage, but also to bring your energy bill down properly with sustainability that genuinely pays off? Then take a look at https://energie-verpulveraar.fredsbouwtekeningen.nl/. There I show you plainly where you save the most, without sales talk and without needlessly expensive purchases. Being smart with your energy starts with understanding what you need, and that’s exactly what we do there.
Regards from Fred Schouten
PS: Test your backup power deliberately at least once a year, by flicking the main switch off for a moment. A system you never test is a system you only hope works. And hoping is not a plan.