It's like saying that the fact that the word "balcony power plant" exists is a sign of how popular it is in the English speaking world. Except that German compound words are seen as more legitimate because they lack the spaces and sound German.

Thanks! You wrote it much better than I did!

Quite the opposite. Balkonkraftwerk sounds immediately clear and convincing.

German Wikipedia has an article about it: https://de.wikipedia.org/wiki/Balkonkraftwerk

Nah, any German word with Kraft in it, is a strong sign of it's popularity ;-)

Balkonkraftwerk sounds powerful. Not like Aufhängesolarpaneel, or Steckersolargerät.

Kraftwerk even!

https://en.wikipedia.org/wiki/Kraftwerk