The thing is, if the demand of the grid raises, you have to raise power production. Period. Of course, if e.g. it is dark, you cannot raise the power production of solar cells. That is bad. But if your nuclear plant is running at 100% already, you cannot rise the power production either. So it doesn't help you. "Base load" is only the statistical number of load you can expect 24/7 for your planning.

So you always have to have some means of power generation available for demand raises at any point and you have to be able to throttle down power generation in case of a demand drop, because otherwise the grid goes down equally as if you had not enough power capacity.

The good news is: renewables can be throttled down quickly, better than most other sources, the bad news is, you can only know about 3 days in advance what the maximum output of your renewables will be and there are days with very low total production. A future grid concept would have to come up with a solution for that. Gas would have been the easy way and probably will be the future when based on gas created via power2gas.