When the power goes out, your storage system can step in. How much of it reaches your home depends on how it is connected. The terms are not used consistently in the industry, so here is what we mean by them.
Why the storage system doesn't simply keep running
In everyday operation, your storage system is connected to the public grid. If the grid goes down, it must not keep feeding into it, otherwise lines could be live while someone may be working on them. The inverter detects the outage and disconnects from the grid. Which circuits in your home keep running is something you decide in advance: only selected ones or all of them.
Backup circuit: selected circuits, automatically
For a backup circuit, the electrician sets up a dedicated circuit that is connected to the inverter's backup output. Typical loads are the fridge, the heating controls, the router and a few lights. If the grid fails, the system switches over automatically within 10 ms. That is so fast that most devices usually don't notice anything. Depending on the model, the backup output delivers up to 10 kW (HM10-H), 15 kW (HM15) or 20 kW (HM20) across three phases. For a short time it can handle more, namely 120 % for 30 seconds, for example when a device briefly draws more power when switching on.
Whole-home backup: the entire house, with a changeover switch
With whole-home backup, the storage system supplies every circuit in the house. A changeover switch is installed in the meter cabinet for this. If the grid fails, you flip it by hand. The house is then disconnected from the grid and runs on the storage system. All circuits keep running as long as together they draw no more than the backup output delivers, so 10, 15 or 20 kW depending on the model. Large loads such as an instantaneous water heater, a sauna or a wallbox are best not run at the same time during this period. When the grid comes back, you switch back.
At a glance
| Backup circuit | Whole-home backup | |
|---|---|---|
| What keeps running | selected circuits | the whole house |
| Switching | automatic, within 10 ms | by hand at the changeover switch |
| Power | 10, 15 or 20 kW depending on the model | 10, 15 or 20 kW for all circuits together |
| Also needed | backup circuit in the meter cabinet | changeover switch |
Which option suits you?
If the fridge, heating and internet matter most to you, a backup circuit is enough: it kicks in immediately and you don't have to do anything. If you want to power the whole house during a longer outage, add the changeover switch. How long the power lasts depends on the storage size and your consumption. All three series grow in steps of 10 kWh up to 90 kWh. Work out which size suits your home in the storage configurator.
How to use the changeover switch and how long the power lasts is explained in the article Changeover switch: power for the whole house when the grid fails
More about the systems: HM10-H · HM15 · HM20
Answers to further questions about power outages and backup power can be found in our FAQ (in German).