My brother, who lives in germany, has told me about this before and i love the idea so much. Its so simple to implement and has no downsides whatsoever. The person renting the appartment buys the solar panel and if they leave they can easily take it with them.
And yet, i can not for the life of me get my land lord convinced to allow me to do this too despite it needing no permanent changes to the apartment... Solar panels rules are too strict here too, and i love that germany just embraced them like its nothing