An off grid home battery really works without the grid when its inverter forms its own grid and separates your house from the street automatically. It also keeps your solar panels producing. A normal battery for self-consumption cannot do that: it stops with the grid. A Victron MultiPlus-II or Quattro can, single-phase or three-phase.
The street goes dark. Your app shows a full battery, the panels are in the sun, and still your house has no power. We read that story again and again on Belgian and Dutch forums.
Adding it later costs extra work: the circuits that must keep running are rewired in the meter box and inspected again. A home in Zele chose a three-phase battery of 15.4 kWh with an off-grid mode from the start. When the street fails, panels and battery keep working.
What is an off grid home battery?
An off grid home battery powers your house without the grid. It forms its own grid, keeps your solar panels producing and, with enough storage and a generator, runs for days or weeks without the grid. A home battery with an off-grid mode is more than a battery for self-consumption.
Why does a normal home battery switch off when the grid fails?
Because the rules require it. Under Synergrid C10/11 a battery is a generating unit: it must disconnect as soon as the grid fails. For sources up to 30 kVA the AREI allows an automatic separation within 5 seconds.
The reason is safety: a technician working on a dead cable must not get voltage back from your house. Battery and inverter stop together, even with a full battery and full sun. Switching that protection off is not allowed, and the inspection tests it.
A grid-tied battery when the street goes dark
What does an off grid home battery do during a power cut?
First a relay separates your house from the street. C10/11 calls that break-before-make. Then the inverter-charger forms your own grid in island mode, and your solar panels keep producing. With a Victron MultiPlus-II that takes less than 20 milliseconds, fast enough for computers. Some backup boxes need up to 3 seconds.
An off-grid capable battery when the street goes dark
Six home batteries we installed show how that works in practice. In every one the power stays on when the street goes dark. In off-grid mode the panels and battery keep working, with full back-up (no-break) the whole house has power. Tap a project for the details.
Single-phase or 3 x 400 V: both can get an off-grid mode. Mostly want to know how much of your house stays on in a power cut? Read our article on home batteries with backup power.
How do you choose the best off grid home battery?
The best off grid home battery answers these six questions well. Ask them before you sign.
Can the inverter form its own grid?
Look for an island or off-grid mode. An emergency socket powers a fridge or a router, not your house.
How fast does it switch over?
Under 20 milliseconds, computers keep running. A few seconds means a short blackout.
Which circuits and phases are covered?
One socket, a few circuits or everything. For three-phase home battery backup, check that all three phases are covered. One backup box on the market covers only one phase, at most 3,300 VA.
Do your solar panels keep producing?
With Victron an existing inverter keeps working through AC coupling, if its power stays below that of the inverter-charger (the factor 1.0 rule). Panels on a solar charger (MPPT) charge the battery directly.
How much power does it deliver?
Look at kW, not only kWh. A MultiPlus-II 48/5000 delivers 4,000 W continuous at 25 °C and 9,000 W peak.
Can a generator be added?
A Quattro has two AC inputs. A GX device starts and stops the generator on the battery level.
Not sure what your battery can do?
Send us the brand and type of battery and inverter. We tell you honestly whether an off-grid mode is possible.
Can a home battery take your house fully off the grid in Belgium?
Not with a battery alone. Winter decides.
In Hamme, 1 kWp of south-facing solar panels gives on average 32.8 kWh in December and 127.5 kWh in June (PVGIS, 35° tilt). In the weakest five measured winter days, 1 kWp gave 0.63 kWh in total. No home battery bridges that.
Why winter decides whether a home can go off-grid
A fully off-grid home therefore needs more panels, more storage and usually a generator. Our Maaseik project shows the simple version: an off-grid mode with a generator connection. If you want to leave the grid for good, size for December.
Read on about choosing an off-grid battery, sizing off-grid solar panels with a battery and what off-grid means in Flanders. For a complete system see our off-grid systems. Often a semi off-grid system is the better middle way, with the grid as a backup charger.
Can you make your existing home battery work off-grid?
Sometimes. It depends on your inverter and your wiring. A Victron system works with many existing installations.
A home in Bornem combines its battery with an SMA inverter. A home in Roosdaal added panels on a solar charger (MPPT), without grid study costs.
The work is usually in the meter box. The circuits that must keep running move behind the inverter-charger. That is a major change, so an inspection follows.
Which rules apply to an off-grid capable home battery in Belgium?
- Register with Fluvius, with an AREI inspection report and a single-line diagram. After a move a new inspection follows, after an extra battery module it does not.
- Safe separation. Switching devices act on all live conductors and never connect sources in parallel at the wrong moment.
- Protection on the island. The MultiPlus-II links neutral and earth with an earthing relay when the grid is gone, so your RCD keeps working.
- Fully off-grid. An island installation with an inverter from 800 VA is reported to the Vlaamse Nutsregulator. Your permit decides whether a home without a connection is allowed.
Wondering if your battery can work off-grid? Call us or send a message.
When is an off-grid capable home battery not worth it?
Our verdict
Power cuts are rare where you live and you mostly want a lower bill? Then a normal battery for self-consumption and peak shaving does the job. Off-grid mode pays off when an outage really hurts. Think of working from home, animals, medication that must stay cool, or a street where the power often fails.
Frequently asked questions
Can a home battery work off-grid?
Only a home battery with an off-grid mode. A normal battery for self-consumption stops during a power cut, even when it is full.
Can a washing machine run on a home battery?
Usually, if the inverter delivers enough power. A MultiPlus-II 48/5000 delivers 4,000 W continuous: washing machine, oven and kettle at once can be too much.
How long does a 15 kWh home battery last in a power cut?
It depends on what you keep running. In our worked example the critical circuits use 5.22 kWh a day. Then 15 kWh usable storage lasts almost three days, before any solar.
Want to know if your home battery can work off-grid?
This is how we work:
- Measure: your use, your connection (single-phase or 3 x 400 V) and your solar installation.
- Choose: you decide what must keep running. We size kVA and kWh on that.
- Install and inspect: AREI inspection and registration with Fluvius.
- Follow up: production, storage and use in the VRM app, with an alert on a low battery.
We are a Victron Energy Certified Partner, with three certified battery experts. We also service and repair existing systems.
Sources
- synergrid.be/images/downloads/Technical_prescription_C10-11_ed2-4_20251015_tekst_NL.pdf
- economie.fgov.be/sites/default/files/Files/Publications/files/AREI-Bijlage-Boek-1-installa
- fluvius.be/nl/groene-energie/thuisbatterij
- victronenergy.com/upload/documents/Datasheet-MultiPlus-II-inverter-charger-EN-.pdf
- victronenergy.com/media/pg/MultiPlus-II_230V/en/installation.html
- victronenergy.com/inverters-chargers/quattro
- victronenergy.com/live/ac_coupling:start
- victronenergy.com/media/pg/Cerbo_GX/en/gx---generator-auto-start-stop.html
- re.jrc.ec.europa.eu/pvg_tools/en/
- vlaamsenutsregulator.be/elektriciteit-en-aardgas/netbeheer/directe-lijnen-en-leidingen-ges
- solar.huawei.com/download