Idk what's going on in NL, but here in Estonia it's necessary because there's so much excess production in the summer sometimes that it could destabilize the grid if it was all allowed to the grid.

This makes the fossil fuel plants shut down completely during excess periods and people get smart inverters and batteries to prevent selling to the grid when there's too much production.

It's a variable rate though. For example tonight the lowest price will be 1.45 cents per kWh, but if there's a ton of sunlight being predicted for a weekend in the summer, it can go negative.