Going beyond efficiency for solar evaporation

Interfacial solar evaporation, which captures solar energy and localizes the generated heat for evaporating water molecules, is regarded as an important emerging strategy for solar energy conversion. In the past decade, global collective efforts have propelled fast and exciting advancements, with solar-to-vapour efficiencies approaching the thermodynamic limit. This has also spurred significant interest in many applications. However, improving the energy efficiency alone cannot move the field towards the practical development of these applications. A matrix of different factors and fundamental challenges should therefore be taken into consideration in addition to the solar-to-vapour efficiency or evaporation flux. In this Perspective we first discuss several promising applications of solar evaporation, and the corresponding figures of merit, for clean water production, wastewater and brine management, resource recovery, sterilization and power generation. We then discuss the fundamental aspects of solar evaporation that need to be determined, such as microscopic thermal transfer and water molecule bonding, which are closely related to evaporative performance. Finally, energy sources beyond solar energy will be discussed to further boost the evaporative performance. Efficiency is only one of the parameters involved in solar evaporation that should be improved to make it practical. Depending on the application, various factors of merit should be taken into consideration, as discussed in this Perspective.