Solarpunk

It's not "just" a solar panel, to be legally compliant in Germany. The part you plug in is basically a control unit. They aren't super big and complex, but they need to be able to do 2 things:

1. Detect if there's a live circuit, and not transmit any power if not. This is because sometimes electricity is turned off for maintenance. You don't want an electrician dying because a line they turned off is actually live due to someone having this plugged in.

2. Power limiter, similar in function to a circuit breaker. This prevents overcurrents happening in your walls and starting a fire. Because all of this is happening after a house's breaker box, they won't flip if the combined grid + solar current is too high, so the solar unit's control unit has to be able to deal with it.

Disclaimer: I'm a layman, not an electrician. Just read into the tech because it's interesting to me.