When following Carnot`s link above we can find more information as to why the solar utilities have switched off sometimes during the day. It has not much to do with reaching the lowest min load the coal guys can do (running at 60% instead of 40%), but more to do with playing the market and hurting your competitor (it is alleged).
Is this a deliberate strategy to restrict the amount of solar production? If so, how much is it costing the state-owned generators. (It is not so easy to find out because the nature of most contracts is not revealed, and they are likely to be heavily hedged).So if true, not a technical problem but a commercial strategy.
Sth Aust played the "we don't need coal" game and look at the damage it caused and SA was able to fall back on the east coast coal generators to keep the lights on. Still 3 years after Nth's closure, SA still does not have a solution for shutting down its gas supply. It can be argued both ways how much SA really needed Nth, however power prices speak for themselves.
In comparison to the parasitic load called SA which is a minor fraction of the total output on the east coast for which if the coal power stations were to closed now or even with 5 years notice, there is or would be no practical solution to replace their 24/7/365 availability.
Liddle is expected to be the next to close due to age, however with 4 years notice, look at the work being done to replace its output to ensure NSW doesn't face power shortages. ie modernising Bayswater, installation of gas turbines, RE and maybe, SA-NSW link, just maybe someone may make a start on Snowy 2.0, although I'm sure it will miss the time line. All this effort to replace one aging coal power station that rarely runs above 75% output (1500MW).
NSW is also heavily reliant on Qld coal power to keep the lights on as is Vic and SA with an average of 1GW crossing the border any time of the day. A far cry from 20 years ago when the inter-tie was built to enable Qld to source NSW power.
Meanwhile in Qld, despite roll out of PV domestic, solar farms and wind farms, there has yet not been any expansion of storage such as chemical or pumped hydro. With govt money the Kindston pumped hydro may get of the ground but is a mere 250MW, less than one large coal turbine, but will help with the peaks and throughs.
So should the govt and/or regulators be protecting the coal power stations viability until a proven viable alternative is ready and operating? Hell Yes! Unless of course you are ready to return to the 19th century.
....and we still have the EV boom expected to create a much bigger strain on the over night grid supply.