“Large, all day supply hot water heaters could be made to store water heated up to 180 degrees.”
We do this. Have a rooftop copper piped collector that in summer will bring water temps in 80 gallon tank to 160 F.
Be careful thou, we have a plumbed in mixing valve to limit the hot distributed to the house to 125F. It will mix in the cold with the extremely hot water to a safer temp. Have well water here too.
On the electric heaters that are no plumbed to roof collector, we heat the water when the pv production has filled the batteries. aka 11 or noon ish and beyond.
I had solar water heaters in Tampa when I lived down there.
At Christmas I flew back to Indy to visit family. When I came back to Tampa that there had been a hard freeze while I was gone and water had been rolling off the roof the entire time.
Had one hell of a water bill, not to mention the solar panels I had to replace required insurance help.