Photovoltaic system 120 sqm living area - cover the entire roof?

This is the calculation from two independent solar experts. One would personally only do south.
Let someone else calculate and you get something different.
It’s not about the absolute numbers, but about their ratio.
The result remains the same. If I fully cover my roof, the payback period is only slightly longer.

PS: In my calculation, I come to a longer period. But the bottom line remains the same.

PPS: I include the ongoing costs, of course.

ok. with my rough calculations I always end up with a loss for me, with or without subsidies, and that’s why I always try to find out why it makes sense for others.

I always end up with a loss for me in my rough calculations

That is so unusual that I am interested in your calculation method. How do you calculate? What assumptions do you make?

For me, with a conservative calculation, it’s also a close call. There are better investments. But it’s enough for me that I don’t lose money in 20 years. Everything after that is a bonus. But just with future electricity prices and self-sufficiency, the calculation can be influenced in the desired direction. In the end, it’s just a rough estimate for everyone. Besides, I hope to achieve a decent self-sufficiency rate through heat pump optimization and electric car. You can also set the period to 25 or 30 years. Or assume that [Direktvermarktung] will soon be more profitable than [Einspeisevergütung]. If you want ;) PS: have you tried the calculator from [test]? PPS: The biggest lever for profitability lies in the acquisition costs!

This is the calculation from two independent solar installers. One would even personally do only south-facing.
Let someone else calculate and something different will come out.

exactly,
I get something different:

Premises:
Roof pitch RP 35°, panels mounted flat. (Ecliptic 23°)

then for example in FFM (latitude approx. 50°N) the south panels would see a max 52° incidence angle in winter (at noon):
(90° - latitude) + RP - Ecliptic.
For the north panels it would be
(90° - latitude) - RP - Ecliptic. = -18° max incidence angle
meaning the north panels see the sun from about Nov to Feb (when most electricity is needed)
not at all.
They only get some diffuse radiation, typically < 5% nominal output.

That’s why north-facing panels with 35° RP don’t make sense in Germany.

Or with a mounting frame?

ps.: nominal output is defined at 90° incidence angle,
at about 70° solar elevation and
1 kW irradiance/m²
(IIRC)

I don’t know if you mean me. But since you quoted me, I’ll reply.

That’s why north panels at 35° tilt angle make no sense in Germany.

Never claimed otherwise.

Premises:
Roof pitch DN 35°, panels mounted flat. (Ecliptic 23°)

then for example at FFM (latitude approx. 50°N) the south panels in winter (at noon) would see a maximum incidence angle of 52°:
(90° - latitude) + DN - ecliptic.
For the north panels it would be
(90° - latitude) - DN - ecliptic = -18° max incidence angle
meaning the north panels see the sun roughly from Nov to Feb (when the most electricity is needed)
not at all.
They only get some diffuse radiation, typically < 5% nominal power.

Nice calculation, if it has to be complicated. Or simply PVGIS for a first estimate. Anyone can do that in 10 minutes.

Nice calculation, if it has to be complicated. Or just PVGIS for a first estimate.

Well, it's actually quite a simple equation, but:

PVGIS doesn't help. I tried it but found that the inclination of the north side (relative to the radiation direction!!!) would have to be entered as negative. Unfortunately, PVGIS cannot handle that.

If you don't take this into account, it inevitably leads to incorrect results.