I am not an electrician but I try to tell you what I understand.
The grid has a frequency and this is 50hz at normal level.
When there is to little the frequency drops and when there is to much it rises.
Until a point this is normal, under 49,9HZ they start some plants to stabalize it and when it is to high the grid needs to shut down some generators or find someone who takes the overproduces energy.
In both ways it can cause a blackout.
I couldnt find a article in english and this problem is much easier to handle as to little energy but it could take the grid to its limit.
I hope this was the answer you hoped for and I would be happy to learn more about this.
RE: Tesla’s massive battery in Australia was paid up to $1000/MWh to absorb excess electricity