The reason was that in case of an angle of 36 degrees, I was supposed to install each row of panels at a distance of 14.4 feet of each other. Otherwise, they would stand in each other's shadow (in the winter). I didn’t want more then 8.2 feet space for shadow and I wanted the rows of panels with no more than that distance from each other installed (otherwise I could not install18 solar panels on my roof).
In my case, we came up with an angle of approximately 20 degrees: According to the following image shows an inclination angle of 20 degrees to a loss of 4%. Since my panels were aligned to the South-East, there was already a small loss taken into account. The combination of South-East and 20 degrees still fits within the first circle of the diagram and gives only a loss of less than 5% output.
For the iPhone and iPad is the free App Solar Consult developed, which - depending on the size of the roof - the most optimal setup for solar panels on your roof will be calculated using most types of solar panels. In addition to the location of the rows and orientation of the solar panels (landscape or portrait), the angle of the solar panels will be calculated, so that the rows of solar panels will not be installed in each other's shadow in the winter.
The App Solar Consult gives the setup with the highest output as advice.