Introduction to Photovoltaics (New Construction)

... that’s not quite it either, but that’s no longer the topic now. But you can quickly research that.

True, we got off topic. Just calculate it yourself or think about what an investment including tax for a photovoltaic system with storage costs. You easily break the €17,500 revenue limit with that, meaning the small business regulation is not applicable in the founding year, at the latest it would be void in the following year.
By the way, I don’t need to research that anymore, since I am married to a small business owner who constantly has to deal with the revenue limits, has exceeded them once and thus lost the regulation, later could opt in again. Accompanied by a tax advisor. By the way, we did not fall into the trap from #23 because we were properly informed.
In this respect, I feel quite well prepared, especially since I myself have already been self-employed as a main occupation.

+ whoever exceeds the €17,500 has to consider whether it makes sense to register a photovoltaic system under their name.

Yes, registering it under the partner’s name can be a good solution.

I could follow the argument if you were an expert in the field. But that’s not the case.

True, I’m not an expert. Why a comprehensible argument would be invalidated by that is not clear to me yet. Too bad you apparently have a different opinion and do not want to argue it. But I of course accept that, I can hardly force you :) We are engaged laypeople here exchanging our insights, expert advice is always worth more. Just be careful not to confuse a seller with an expert.

Based on your “simple facts,” you come to this result.

Calculations of returns for photovoltaics down to the last detail seem quite difficult to me, because several tax issues are involved. Therefore, simplification is necessary. But if these already show very clear tendencies (and that is the case here in my opinion), there is no need to haggle over the last decimal place.

Admittedly, I’m playing it a bit easy now if I don’t present another economic consideration or address your “simple facts” in detail, but it’s not worth the effort to me.

As stated above—too bad. I am certainly willing to learn.
Maybe another time.

I recommend you enter “photovoltaic” and “forum” in Google and just read there. You’ll even find some oddballs who apply the small business regulation (motivation in my observation: no desire for taxes/accounting, returns don’t matter).

Interesting here!

I suspect that laien.haft does not mean tax issues, but rather refers to technical boundary conditions, that is the integration of electromobility and/or participation in smart grids or smart markets.

I see it similarly, that Alex85's calculation may be correct by itself, but the system boundaries are set incorrectly, so that certain effects cannot arise at all.

It's a pity that this is not elaborated further.