Salt production through solar evaporation has been used for centuries and it remains an essential industrial process worldwide. It is the most important method of salt exploitation for table salt (NaCl), but it also finds applications in several other fields, such as desalination3,4,5,6,7, water supply8,9, wastewater treatment14,15, medical sterilization16,17, and concentration of dilute salt solutions to avoid excessive salt discharge into waste water treatment plants18.

The solar evaporation in salt production has not changed much over the centuries: sea water or natural brine is evaporated up to saturation in dedicated open basins. These ponds are called concentrating ponds or salterns and they are usually separated by levees. The concentrated brine then flows through crystallizing ponds where the pure salt is made. The whole process is very labor intensive and the equipment can vary from sophisticated in developed countries to quite primitive in developing ones.

Harvesting the Sun: Exploring Solar Evaporation in Salt Production”

A key bottleneck for highly efficient solar evaporation is the ability to simultaneously achieve thermal localization and salt rejection. The current approach to this problem uses a capillary wick structure. However, this solution introduces significant transport resistance and can lead to clogging or crystallization on the evaporating surface under intense solar flux or after long-term operation. To overcome this obstacle it is necessary to engineer passive convective flow. We present a novel concept to achieve this, based on a neutrally buoyant and self-floating thermal insulation that moves synchronously with the evaporating surface through vertical macrochannels (Fig. 1c). This allows for a continuous separation of the water layer and the bulk water while still providing high thermal localization comparable to that of the traditional wick structure.