I think the point is that the existing grid has the ability to do that on-demand scaling, so adding variable solar or wind capacity to the grid means the proble

I think the point is that the existing grid has the ability to do that on-demand scaling, so adding variable solar or wind capacity to the grid means the problem is already dealt with. Of course as we transition to higher percentages of solar and wind capacity the demand scaling will become a bigger issue and storing the solar and wind output will be needed. I'm not sure how far away that is now - perhaps the existing hydro and nuclear capacity is enough to deal with all of that variability, but I expect at some point we'll need to figure out the storage issue.