There probably is at some times and at other times too little. Getting the highs and lows to match or storage may or may not have problems

I very much doubt that there is REGULARLY any significant surplus of renewably generated electricity, for two reasons.

Firstly, observation of the gridwatch site shows that we still burning gas even overnight in windy weather. Also during bright weather when solar input is significant.

Secondly, if potentially available electricity was REGULARLY going unused, then what is done with it ? I am not aware of any utility sized load banks whereby hundreds of MW could be dumped. Neither am I aware of significant numbers of wind turbines being shut down for want of demand. There will always be some shut down for maintenance or repairs, but not aware of any significant shutdowns.

This just goes to show the manifest ignorance of journalists. Yes, I have heard of batteries. I think that what they mean is that generating capacity may sometimes exceed demand, but wasn't that always the case.