Photovoltaic system that pays for itself monthly and amortizes

Yep, and you first have to have the days, just counted, I could have drawn more than 4 kWh from a battery on 18 days... For me, a 3 kWh battery would probably be enough, but the costs are hardly any lower, so it's even less worthwhile.
A DIY solution would be something, there are instructions for a 2 kWh battery for 2000€, but that’s also not really worth it.

18 days ops:, only? If I understand my meter correctly then I fed in 2300 kWh alone in the last 4 months. And the months weren’t really great either.

It's not about it coming in, but you also have to use it. In summer, the photovoltaic system turns off around 8...9 PM and turns back on around 5...6 AM. In the 10 hours in between, I consume 1-2 kWh. Now, when the heating is running, of course, it's more, but not as much comes in that you could store then.

It's not about the electricity coming in, but you also have to consume it. In the summer, the photovoltaic system shuts off around 8...9 PM and turns back on around 5...6 AM. In the 10 hours in between, I consume 1-2 kWh. Now, when the heating is running, it's of course more, but not that much electricity comes in then that could be stored.

I assume that I empty the storage every day with the electric car. So there is no lack of consumers. The BM will be interesting, when, how, and what happens. Ideally, there would be a control system like: the photovoltaic system is used as long as the power to charge the car is sufficient. After that, the storage is accessed.

By the way, my photovoltaic system is currently delivering 248 watts, which is not even enough for the refrigerator.

If the e-car stood in the garage during the day, you would have a (drivable) storage...

If the e-car stood in the garage during the day, you would have a (drivable) storage...

That's right! That's why I also believe that, in theory, the degree of self-sufficiency without storage in my case is over 30% (i.e., the commonly promoted self-consumption).

That's right! That is why I also believe that theoretically the degree of self-sufficiency without storage is over 30% for me (that is, the commonly promoted self-consumption rates).

And therefore, a stationary storage system would be even less worthwhile for you.