Water evaporated and leaves brine behind, at any temperature above 0C (even below through sublimation). Theoretically I guess you can imagine the sun evaporatin

Water evaporated and leaves brine behind, at any temperature above 0C (even below through sublimation). Theoretically I guess you can imagine the sun evaporating the water that you capture, so you could have close to 0 energy input. So there is no physical limit I suppose. But you don't want to wait for the sun, you want to speed up that process, I don't know what the limit is there, when the speed matters (how much does it matter?).