The amount of energy required to evaporate water means you need a lot of sunlight (area) to evaporate a relatively small amount of salt water.
You can save a lot of energy by getting some water out of sea water, leaving extra-salty brine, rather than trying to get all the water out, leaving dry salt.
The brine can be evaporated into salt as well, right?
It seems to mean that problems like this have to be solved via an entire system and not via individual components.