I completely agree with Zaba12. It is really the only thing on the house that doesn't cost money, but rather brings in money.
I planned my system like this:
Roof as full as possible (where it makes sense)
No storage
100% financed
Financing structured so that a positive cash flow after taxes arises from the first year.
After about 14/15 years, the system is actually paid off
Total profit after taxes over 20 years: 12,000,- (repairs, maintenance, insurance, etc. already factored in)
That’s not a huge amount of money. You don’t get rich with it. But the system generates a few euros and you do something good for the environment.
For €0 investment and relatively little effort (especially in acquisition and later a bit of tax), the profit is already okay