Construction costs are currently skyrocketing

if I invest, for example, €15,000 – then earn a return of €1,050 = 7% annually for 15 years – and after 15 years disposal costs of €750 occur (because the cheap Chinese photovoltaic system is unfortunately then broken) – then the return is exactly ZERO

RETURN is what I can skim off in terms of margins/earnings WITHOUT the capital stock losing value

As I said, my photovoltaic system has a return of just under 10%. 6kwp (and that through kfw40+)
Our old one on the hall has a return of 7%, back then still subsidized with 42 cents per kwh.
Sorry that I expressed myself incorrectly. :D

RETURN is what I can skim off as cream/profits WITHOUT the capital stock losing value

Then let's put it differently: A photovoltaic system with a decent self-consumption pays off after about +/- 9 years. From then on, you earn money so that with a 20-year lifespan (= feed-in tariff) you have an average return of about +/- 5%. Increased self-consumption and/or rising electricity prices can significantly increase the return.

And the 10-15 years that it will continue to run beyond the 20 years with feed-in tariffs, as well.

So, to get back to the topic. As I see it, a lot of panic and nonsense is being spread regarding construction costs. Yes, they have increased and yes, probably more expensive than ever before, but the horror stories about 20-50% higher prices are simply not true. On the one hand, I spoke with my general contractor who told me that prices have increased by about 5-10% since August last year. However, not for everything! In addition, I had the prefabricated garage offer from 03.21 updated because we will be starting soon. After all the statements here, I was expecting the worst but, behold, a “manageable” 8% more. Of course, that is also a lot of money but far from these horror scenarios. Maybe this helps some of you :)

Congratulations on the small increase. Unfortunately, this is not the norm. I know two companies that are currently building in BW and their prices are just flying through the roof. I also know some contractors. They no longer provide any fixed prices. Anyone building now should definitely insist on fixed prices and then not make any changes.

But how does that happen? As I observe it, the prices for building materials are rather stagnating (at a high level since the drastic dynamics last summer). So how does a [BU] justify such a large increase that prices seem to "explode"? Isn't it often the case in such situations to push things to the limit one last time and jump on the bandwagon to make big money?