I understand Germany is dense, but you definitely have some open land. The threshold to make rooftop solar the most efficient approach is incredibly dense, pretty much constant dense urban sprawl for an entire nation. Solar installations can replace a field, but a single field can replace entire neighborhoods worth of rooftop solar.

The point I am making is that the distributed infrastructure required, awkward installation geometry and therefore overall inefficiency means that rooftop solar is about 50% less “useful” compared to the equivalent panels in a grid scale facility.