This is one of the big problems with renewables. We need to over supply, to cope with variability. We also don't yet have the storage capacity to buffer it.
When the price goes negative, it's bad. It means that more power is entering the grid that is being used. This will destabilise the grid and cause a shutdown. Negative prices are basically a desperate attempt to get anyone to burn off the excess.
The solution is more storage either short term (batteries etc) or long term (hydrogen, or desalination).
Every system operator where renewable saturation is even remotely possible requires it for all large plants. It's a technically trivial problem that has no impact on grid stability.