Expecting it to operate most of the time is a safer bet than expecting it to have a peak output that’s substantially higher than the average. It’s be smart to try to align it with power usage, but in truth it’ll lag behind peak water usage by however long it takes to top off the tanks. I don’t know when that is but I would suspect before morning rush hour.
Probably this thing peaks at 120-150KW which isn’t going to fix the grid.
You might use this as a big battery where you store the desalination brine during the day when you have excess solar power and run the recombination in the evening and overnight when solar drops.