Economics of Photovoltaics - My Findings - Is Something Missing?

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Do you have a number for how much you lose annually due to 70% shading, e.g. as a percentage of total output or as a value in kWh?

Do you have exactly east-west? What roof pitch?

10° and a pure system exactly facing southwest (so rotated 45° from south to west, I think it is also called 225°)

So no east/west system.

The difference between hard and soft is the self-consumption at times when more than 70% is fed in. Since I don’t even know how often or how much that was, I also don’t have a number for what I get from it. In any case, it concerns the base load of 300W in my case and well-timed household appliances on sunny summer days.

I reach the 70% limit relatively quickly, but it is difficult to go much beyond that and to do so consistently.

Here is a day where 70% paid off softly, but I did not consciously decide for or against it, rather because there was virtually no additional effort and the technology allowed it anyway.

Photo: The peak would have been clipped for me here, but let's say it's 1 kWh, and then optimistically 30 days a year... (5.4 kWp system).

Cap from 12 to 4 pm in the peak 500W over cap... so no 2kWh... and I had that, quickly calculated, 35 days in 2017.

So maybe 40-50kWh is realistic.

There will probably be more losses with systems that a) are larger and b) are optimally aligned. But for that, you would need someone who has it fully facing south and mounted at 20°. Then such a peak naturally hits fully on the days when it is possible.

Your estimated 50 kWh would be 120 € of lost remuneration over 20 years. The Sunny Home Manager was offered to us for 590 €. So the 590 € would not be worthwhile for you either.

But yes, if you only have one half of the roof occupied, the 70% is reached relatively often, especially if the system is perfectly oriented to the south. With an east/west system, the 70% is never or at least almost never reached.

The entire calculation fails with the decreasing performance of the modules, which is not taken into account by you.

What if the yield is only 50% after 20 years?
Is the decline in performance linear or exponential?

In the end, you have to want it, even if it maybe just barely pays off or maybe not at all.