Sure. So if for example your city has an average of 3400 hours of sun per year like Jerusalem does, and you know how much water you need to produce in the 8760 hours of the year, you can calculate how much to desalinate during sunny hours. Excesses can be used for excess water or sold back to the grid.
desalination plants don't serve one city. they serve country. also, in general, it's not economical to build plants that do not work 24/7 unless you are country that can spend x3 to overbuild and keep equipment idle
Israel btw supplies desalinated water to Jordan and PA.
I think we’re talking past one another. Solar is definitely economical in certain circumstances, and every country overbuilds to some extent. Whether building excess solar makes sense is a question of cost of a marginal unit of energy, since the water doesn’t care what powered its desalination. The energy isn’t wasted since it will eventually need to come from somewhere.
Another consideration is political sovereignty, since solar can’t easily be turned off by a foreign adversary.
