Economics of Photovoltaics - My Findings - Is Something Missing?

Just buy the system and tick it off "for the environment." If it’s still profitable, all the better.

In the end, it doesn’t matter whether 200 euros are saved per year or the decision "for nature" cost an additional 100 euros.
That's basically the range it will be in.

Two posts above was a botched improvement of the calculation, the self-consumption was counted twice. Here now again the updated calculation:

Value-added tax on self-consumption in the first five years, as long as you are not yet a small business, calculated per year:
5/20 * (22% * 8300 kWh * 5 cents/kWh)
= €23

Electricity generation costs:
(Depreciation + Insurance + Maintenance + VAT) / Yield
(€665 + €50 + €100 + €23) / 8300 kWh = 10.1 cents/kWh

Yield of the system per year (monetary benefit through extraction or self-consumption may be calculated with
electricity generation costs):
78% * 8300 kWh * 12.2 cents/kWh + 22% * 8300 kWh * 10.1 cents/kWh
= €969

Income tax after income-expenditure calculation per year:
Marginal tax rate * (Yield of the system - Depreciation - VAT self-consumption - Insurance - Maintenance):
42% * (€969 - €665 - €23 - €50 - €100)
=
€55

Personal profit per year (feed-in tariff + saved electricity costs through self-consumption - VAT self-consumption - Insurance - Maintenance - Income tax)
78% * 8300 kWh * 12.2 cents/kWh + 22% * 8300 kWh * 32.2 cents/kWh - €23 - €50 - €100 - €55
=
€1151

Return:
€1151 / €13300
=
8.7%

You do know, however, that when you get an offer for a photovoltaic system, you also receive a qualified yield and return calculation?

[*]Own consumption share set unrealistically high at 43%.
[*]Electricity price increase set very high at 5% (1998-2018 average 2.7%)
[*]No or only minimal maintenance and repair costs included
[*]Value added tax for own use not included
[*]Income tax not included
[*]Values for payable value added tax as well as maintenance and repair costs indicated but not considered in the return calculation.