Seminar on Energy-passive approaches to maximize water generation from air

The content in non-condensed water of the atmosphere is considerable (13000 km³) and has only been recently considered as a new source of fresh water. Although active cooling devices can extract such water at the cost of considerable energy, water appears to be routinely and passively condensed by Nature as dew. However, although the available maximum cooling energy in dew is on the order of 100 W/m², the corresponding maximum available yield (~3.5 L/m²/day) is far from being reached by natural dew. In order to approach that limit, one here reviews the main parameters that can improve the process of (i) water condensation and (ii) water collection by gravity. Condensation (i) is limited by the cooling power and the heat transfer from the condensing surface with the surrounding air. The cooling power can be enhanced by taking benefit of the angle dependence of the atmosphere emissivity and the use of substrates with high emissivity in the sky window (8-13 µm), together with high solar reflectivity. The heat losses with the surrounding air can be reduced by considering special forms that reduces the negative effect of wind. Collection of water (ii) can be enhanced thanks to dedicated micro-patterned substrates, some of them (micro-grooves) exhibiting interesting properties of anti-aging effects when used in harsh outdoor conditions.