Single-phase or three-phase home battery: what do you need?

Open your fuse box and look at the main switch. If it is one position wide, you have a single-phase connection: all power comes in over one phase wire. If the main switch is three positions wide, you have three-phase (usually 3x25 amps) and the fuse box spreads the circuits across three phase wires. Many existing homes are single-phase; in new builds and homes with a heat pump or EV charger, 3x25 has become the standard.

That connection sets the limits. A three-phase home battery needs all three phase wires, so it does not fit a single-phase connection. The other way round is fine: a single-phase battery works well on a three-phase connection, and in practice that happens regularly. Upgrading from single-phase to 3x25 is possible through the grid operator, but costs a one-off fee and only makes sense if you will use it for more than the battery alone.

The power difference is arithmetic. A single-phase 1x25 amp connection can deliver about 5.7 kilowatts in total (230 volts times 25 amps), a 1x35 connection roughly 8 kilowatts. Everything in the house shares that ceiling: if your battery charges at 3 kilowatts while the oven and washing machine run, you get close fast. A 3x25 connection handles over 17 kilowatts in total, spread across three phases, so battery and household get in each other's way far less.

Faster charging and discharging is more than comfort. If you use the cheap hours of a dynamic energy contract, more power means storing more per hour. For an average household with a 5 to 10 kWh battery, the power of a single-phase system is simply sufficient; it only pinches with large systems or lots of simultaneous consumption. What capacity costs is covered in what a home battery costs.

A persistent misunderstanding: if the battery discharges on phase 1 while the dishwasher runs on phase 2, you would "lose" power to the grid. That is not how it works. The smart meter determines the balance of all three phases together at every moment and only updates that total. If the battery discharges 800 watts on one phase and the house uses 800 watts on another, the meter registers nothing on balance. That behaviour is fixed in the meter standard (DSMR) that Dutch smart meters follow; there is no separate government page explaining it, but you can see it on the meter itself.

Look at the display: it shows four registers, consumption and export in two tariffs each, and no separate counters per phase. The manual of widely installed smart meters at grid operator Liander (Dutch) shows that same setup. For the choice between single-phase and three-phase it simply means: your energy bill is not an argument. The difference sits in power and backup.

For the bill the phase is irrelevant, for backup power it is not. When the grid drops out, the battery only feeds what is physically wired to the backup provision. With hybrid backup that is one or two circuits, such as the fridge and the router; a single-phase system handles that fine. If you want the whole fuse box to keep running, induction hob, heat pump and EV charger included, the system must be able to feed all three phases and you end up with a three-phase All-in-One.

A three-phase home battery with backup power for the full fuse box is the most complete variant: everything keeps working and the system has the power to feed heavy circuits too. How the switchover works, what keeps running and how long the battery lasts is covered in backup power with a home battery.

During the site survey we look at three things: your main fuse, the free space and circuits in the fuse box, and your consumption profile. The right version follows from that. Up to about 8 kWh of storage we usually advise a single-phase system, unless there is a reason to go heavier: stacked modules, lots of simultaneous consumption or the wish to put the whole fuse box on backup power. We only include a connection upgrade in the advice when it genuinely pays off, because above 3x25 amps your fixed grid fees rise too.

Not sure what your fuse box can handle? Put your situation to us and we will take a look. Or read on first on our home battery page.