Backup power with a home battery: how it works

It sounds logical: there is a full battery on the wall, so during an outage the lights simply stay on. That is not how it works. A grid-connected home battery is designed to stop as soon as the grid drops out, partly so engineers can work on the fault safely. Without a dedicated backup provision you sit in the dark, battery and all.

Backup power is therefore not a property of the battery itself, but of the installation around it: a backup provision that safely disconnects your home (or part of it) from the grid during an outage and keeps feeding it from the battery. Whether you want that option is one of the choices when buying; the other considerations are in our guide which home battery suits you.

The Netherlands has one of the most reliable grids in Europe. According to the annual reliability figures from Netbeheer Nederland (Dutch), the average outage time has been well under half an hour per connection per year for years, and an unplanned outage lasts a good hour on average. The chance of experiencing one is small, and it is usually over quickly.

For most households backup power is therefore comfort, not necessity. It becomes a different story if your home office cannot go down, there is medical equipment in the house, or a freezer full of supplies. So weigh up what an hour without power really costs you; that decides whether the extra cost of a backup provision pays off for you.

The most chosen variant in our installations is hybrid backup. The system automatically detects that the grid has dropped out and switches over to backup power; on the HYXi Power systems we install, that switchover takes 0.01 seconds, so short that most appliances never notice. Typically a maximum of two B16 circuits can be connected to the backup.

You choose those two circuits deliberately. In practice they are the fridge and freezer, lighting, internet and router, some sockets and often the central heating boiler, which needs power for its pump and controls even on gas. Heavy consumers such as an induction hob, heat pump or EV charger are usually not connected under hybrid backup: they drain the battery in a few hours.

If you want the whole house to keep functioning, that is possible with an All-in-One system: the entire fuse box is placed on backup power, so all circuits can stay active. The induction hob, the heat pump and the EV charger then keep working during an outage too. In return, such a system needs more space and budget. What the variants look like and how the switchover works is on the HYXi Power home battery page.

That depends on two things: how much is in the battery and what you connect to it. A worked example with round numbers: fridge, router and some lighting together draw in the order of 150 to 200 watts. A 10 kWh battery that is half full keeps that going for roughly a day; a full battery twice as long. For outages averaging a good hour, that is more than enough.

If you also connect heavy consumers through an All-in-One system, it goes fast: a heat pump or EV charger easily draws several kilowatt-hours per hour. The whole fuse box on backup mainly means everything can keep working; how long is up to you, by being frugal during an outage. What a battery with the matching capacity costs is covered under what a home battery costs.

A plug-in battery that feeds back through a wall socket goes just as quiet during an outage as a fixed battery without backup: it too must not put voltage on the grid during a fault. Some models have their own outlet to power one appliance directly, but that is something else than putting your fuse box on backup power. The differences between the two types are in our comparison plug-in battery or fixed home battery.

If you only want an emergency battery for a single device, for example to keep your router or a medical device running for a few hours, a portable power station can be enough. We do not sell those, but it is only fair to say you do not need a fixed home battery for that single purpose. A fixed battery with backup becomes interesting once you also want it to work the rest of the year: storing your own solar power and charging and discharging smartly.

During the site survey we first look at which circuits are genuinely critical for you and whether your fuse box allows a backup provision. Then we advise a configuration: no backup if saving money is the goal, hybrid backup for the essential circuits, or All-in-One if the whole house must keep running. We size the battery capacity on your normal consumption, because the battery spends 99 percent of its time simply storing your own power.

You get a no-obligation quote within 24 hours and after approval we usually install within three weeks. Not sure which variant fits? Put your situation to us or browse the options on our home battery page first.