Why a smaller angle for solar panels on a flat roof

If you want to install solar panels on a flat roof with an alignment to the sun, then the optimal angle in the Netherlands is 35 degrees. However, there are reasons to choose for a lower angle: The material (standards, assembly material and necessary ballast) at an angle of 15 degrees is a lot less (lower angle captures less wind) and the additional costs for an inclination of 35 degrees are the higher result not worth (2% more output). So, the payback period can be longer at an inclination of 35 degrees.

It should be avoided throughout the year that the rows of panels are not placed in each other's shadow (a shadow behind the row of solar panels in an angel of 15 degrees is less than an angle of 35 degrees). The optimal angle and shadow can be calculated with the App Solar Consult (iPhone/iPad only). The shadow of solar panels of 6.6 feet X 3.3 feet at an angle of 35 degrees is in the Netherlands 3.8 feet. The shadow is in case of an angle of 15 degrees not more then 1.7 feet during the winter. That's a big difference.

Furthermore, in case of an angle of 35 degrees, the solar panels need to be installed at a distance of 3.8 feet from the edges of the roof (depends per country). These three reasons should be balanced with knowledge of 2% loss of output.

My father (see one of my previous blogs) was aware of the differences, so he had deliberately chosen an angle of 15 degrees. The decisive argument for him was to see much less from the solar panels standing from the ground level. He has decided with good arguments and accepted the lost of 2% output.