ᐅ Backup power system for two single-family homes

Created on: 6 Feb 2026 16:41
P
Pianist
Good day!

Due to the power outage in southern Berlin, my father considers it necessary to examine to what extent it is possible to prepare for such an event, and he has asked me to gather relevant information. Before I speak with an electrical contractor, I would like to understand the technical and legal conditions under which this could be done.

It is important to distinguish between a "temporary solution" (where only the heating system is powered) and a proper installation (where the entire house is supplied). Additionally, one should clarify whether major appliances such as the stove and oven are included or not.

In theory, a diesel generator (with HVO 100 fuel in the tank to prevent degradation) could suffice if a supply connection point has been created at both houses, for example under a stair landing or similar. The supply lines to the heating systems would then be disconnected (each originating from the emergency switch) and connected to the supply point, while the generator runs outside.

A proper installation as part of the overall system would, however, need to ensure that when the generator is in use, the connection to the public grid is simultaneously disconnected. This is necessary firstly to prevent backfeeding, and secondly because the grid power would eventually be restored.

I don’t believe that a well-insulated house would cool down enough over a week for the heating pipes to freeze, but he wants me to clarify this.

Thank you, Matthias!
Tolentino10 Feb 2026 10:23
Why gas? Isn't a diesel generator generally easier to run on vegetable oil? I mean, if you're already fully into prepping theory...
familie_s10 Feb 2026 11:00
We asked ourselves the same question....
Musketier10 Feb 2026 16:34
The question is, when do you really need the generator the most?

From spring to autumn, you will likely manage mainly with a photovoltaic system with a battery storage, assuming it can operate off-grid and, for example, you can do without a heat pump. The problem arises during the late autumn to early spring heating season.

If you consider a power outage caused by an extreme cold spell, for example due to iced-over and then broken power lines or fallen power poles, a gasoline generator is probably much more reliable than a diesel one that may gel. You might also have one or more gasoline generators rather than a diesel in your garage.

You should also think about where to get large amounts of vegetable oil if all the stores are closed due to power outages.
P
Pianist
10 Feb 2026 18:17
Of course, I wouldn’t use regular diesel but HVO 100. I also use it in my boat.

Regarding gasoline: years ago, I bought a small generator and deliberately filled it with Aspen because I thought it wouldn’t gum up when needed. But when I tried to start it for a test, it still wouldn’t run…

Equipment that you probably rarely or only every few years use is always problematic. Who thinks about running them for a moment every few months?

And honestly, if we ever have a widespread, long-lasting power outage, we’ll have much bigger problems…
Tolentino10 Feb 2026 22:31
I argue that in such a situation you are more likely to find vegetable oil than gasoline (in an emergency, you could loot a snack bar). Above all, you can first use vegetable oil for cooking, then filter it and still burn it as fuel. But anyway, this really starts to lead into prepping territory...
P
Pianist
11 Feb 2026 07:51
Yes, I agree. It’s not my world either. I still have a relatively strong trust in our institutions and assume that something like what happened recently in Berlin will not become the norm. However, I do need to present my father with a result, and he will want to know exactly why there isn’t a satisfactory solution for him.