Is a photovoltaic system also sensible in the west or east?

Come on. The Dax yields an average of 14% p.a. over such a period. You might as well pack up your records at the cabin, which will be hazardous waste later anyway.

Completely different risk class, therefore nonsense.

Apologies if I don’t fully grasp all the financial models, but do I understand correctly that depending on the size, it can even be worthwhile if it is fully financed?

A photovoltaic system is practically always worthwhile, unless you let them sell you the kWp for 2000+€. We are now at 9.6kWp completely fixed and finished at just under 12,500€ gross. Yield forecast of over 10,000kWh p.a. with perfect southwest orientation. The whole thing discreetly financed for <1%.

I recently entered our data into an online calculator. I got just under 17 years until it is supposed to pay off. Maybe I am doing something wrong - or here in Hamburg there is simply too little sun.

From when does it pay off for you and with how much?

In general, it can be said that it easily pays off over the total financing period. Have some offers made for you; the kWp should be around €1100-1200 net for a system size of about 9-10 kWp. Slightly more if it is smaller and slightly less if you plan the system larger.

nms_hs, on the one hand, you save on your own consumption and on the other hand, you receive the feed-in tariff. Assuming:

Annual yield of the system: 10,000 kWh:
Total annual electricity consumption (air-to-water heat pump, controlled residential ventilation, household electricity): 7,500 kWh
Own consumption 30% of 7,500 kWh = 2250 kWh * current electricity cost 25.04 cents = €563 savings per year

Feed-in tariff 7750 kWh * 0.9875 cents = €765 remuneration

Yield €563 + €765 = €1,328 per year

System costs €12,500

That means the system pays off with interest and insurance in about 11-12 years. The higher the electricity price rises, the more savings the system brings you, and the payback period is shortened accordingly.

Please forgive me if I don't fully understand the financial models, but do I understand correctly that depending on the size, it can even be worthwhile if you fully finance it?

Yes, that's exactly how it is. I fully financed my 24.5 kWp system. I calculated the financing so that from the beginning I have a positive cash flow, meaning I never have to pay upfront (except for the VAT until I get it back from the tax office). Unfortunately, 1700,- euros do not stay with me but go to the bank; however, I did not have to invest any equity and could use it for the special repayment of my mortgage. I pay 1.03% interest via KFW.

I don't see any risk there. Over the period considered, it is negligible, and if you want, you can diversify even more with a global ETF. But the average German prefers to put money in a savings account, I know.

The fact that you can sell the securities also argues against photovoltaics as a concentration risk.

The advantage of photovoltaics is the financing option.

If you can ignore risks, the world is naturally always rosy.

Concentration risk? Ridiculous. Photovoltaics cost up to €10,000 in usual size. Plus, they are almost financed for free; you can even fully deduct the costs. €0.0 equity if you want.

And in the same breath recommend the DAX, which consists of only 30 stocks, represents a small region, and only a few sectors.

By the way, the DAX has a risk class of 6 (out of 7) according to SRRI. And the 14% (unchecked) obviously fluctuate and are a look back. With photovoltaics, you have a 20-year state-secured guarantee. Apples and oranges.