Construction costs are currently skyrocketing

It's clearly a simple calculation If I make a rough estimate: 5kwh charging per day x 365 = 1825 kwh savings per year in the best case. Subtract the feed-in tariff of about 6 cents (electricity costs 30 C/kwh), that is 400 euros savings per year. Battery lifespan 15-17 years? Possibly subtract financing costs as well. Not worth it in 98 percent of cases. Just as useless as with solar thermal.

Fill the roof completely now (unless you have a steep north side), no matter what the solar installer says, and possibly upgrade the storage if the money is not enough.

In 98 percent of cases, it is not worth it.

On the one hand, the VAT can be deducted. On the other hand, there are sometimes quite high subsidies in the countries. And if you have a lenient tax office, you can even apply depreciation (AfA).

We are, however, in Germany. Therefore, this has hardly any relevance. Especially not for construction interest rates.

I agree with you, not for now. But if the USA reports good figures, the market will initially infer the same for Europe, until actually poor figures are reported in Europe. Whether the gas is really turned off and the unemployment rate really rises remains to be seen.

If I do a rough calculation: 5kwh charging per day x 365 = 1825 kwh savings per year in the best case. Deducting the feed-in tariff of about 6 cents (electricity costs 30 C/kwh) results in 400 euros savings per year.

Electricity costs currently(!), when I compare new contracts, are between 45 and 50 cents.

It's a clear calculation
If I do a simple calculation: 5 kWh charge per day x 365 = 1825 kWh savings per year in the best case. Deduct the feed-in tariff of about 6 cents (electricity costs 30 C/kWh), that is 400 euros savings per year. Battery lifetime 15-17 years? Possibly subtract financing costs.
Not worth it in 98 percent of cases.

Just as useless as with solar thermal.

Counter-calculation: Last year I stored 2,600 kWh with my battery. With your 6 cent feed-in tariff and 30 cent electricity costs, that's 624€ per year. Taking your 15 years as lifetime as well, the battery (in my case 10 kWh) must cost less than 9,360€ net, i.e. 11,138.40€ gross. Taxes and rising electricity costs left aside.
And as already mentioned, the 30 cents will soon be very unrealistic. Some are already paying over 40 cents per kWh.