The other grid operators have to lower their production during the day. That itself can be expensive, but more importantly they run their same equipment to power fewer hours of the day; when solar is not available, which is expensive since they have significant fixed costs. Batteries are not a grid scale solution any time soon, but maybe one day.
You can also adjust energy prices to shape demand. It's not like baseload power plants have ever had constant demands there's always a curve.
The solution is of course a mix. Solar/wind/hydrogen/gas/etc., big grid/home systems. It will require grid upgrades.
Batteries are already happening [0]. And electric cars + home solar systems with batteries have a further ability to allow additions to this at scale if the grid supports it
In 2010, someone sticked some battery shortcoming knowledge (e.g., not grid scale) into their head, but it takes double the amount of energy to update it today.
What we see at grid scale are batteries being used for quick response power while other generators are being spun up. The thing is the grid very much doesn't like it when demand exceeds supply. Systems shut down to protect themselves and you either dump loads very quickly or suffer a cascade failure (see the 1965 blackout--and note that that only stopped growing when the operators were able to dump enough load.)
Since this is in disaster territory the utilities obviously try to avoid it and ensure there's always enough to cope with any surges--which means they must have more stuff spinning than they actually need. Enter facilities like the big batteries: keeping them hot costs almost nothing and they have a very fast response when called upon. This buys the utilities time in which to spin up other generators and thus allows them to operate with less waste.
... you started your comment with "batteries are not a grid scale solution" and then you described one of the primary reasons batteries are useful at grid scale.
I don't get it, did you put an extra "not" in your opening sentence?
