Investigating the potential of air-based freshwater and hydrogen production technologies in the Witzenberg Valley of South Africa

Self-sufficient fresh water and renewable energy are two pillars of sustainable development. In regions with limited fresh water sources, air capture of water vapor is an alternative solution. The captured water can be made potable and serve uses in agriculture and industrial activity. Hydrogen gas is an emerging energy vector. At remote locations with limited water sources it may be produced by electrolytically splitting the water molecules found in the air. In this work the potential of atmospheric water harvesting technologies to produce water and hydrogen gas at a specific location in South Africa, is analyzed. The research departs from a microclimate study in the Witzenberg valley. Temperature profiles, relative humidity and wind speed and direction were monitored with a weather station over a 3-year period. Three different water capturing technologies were considered, namely, the use of desiccants, the use of deliquescent salts in combination with reverse osmosis (DESARO), and thermoresponsive polymers. A computer model was developed to predict water yields and energy needs of the rival technologies using the microclimate data. The model predictions were verified with water capturing experiments using a device that was designed, built and mounted next to the weather station. The model also enabled an estimation of the possible impact of extracting water from the air on the local air-borne water content. The modelling results showed a potential to produce 16 of fresh water using thermoresponsive polymer during the year 2021 at the Witzenberg valley site, 30  using desiccant, and 7.7  using a DESARO-system. The model furthermore predicts that thermoresponsive polymers will remove 2.6% of the available moisture in the air, when replacement rates based on wind speeds are taken into account. The extraction rate for a DESARO-system was estimated to be 0.6%, while it was estimated to be 8.5% for a desiccant-based system. Energy autonomy based on locally produced hydrogen was the second aspect of the research. Solar hydrogen generators produce hydrogen using sunlight and do not need electricity supply from the grid. Hydrogen panels producing hydrogen gas from water captured from the air is a pioneering example. Hydrogen produced with solar hydrogen generators is intrinsically additional, and contrasting with hydrogen gas produced by electrolysers powered by electricity from a grid. The new category of Golden hydrogen is introduced to emphasize the distinction from other types of hydrogen contributing differently to reaching global sustainability. The outcome of this study at one specific location was used to define a protocol for estimating the potential of water-from-air technologies at different locations. The potential value in the broader context of water and energy supply in SouthAfrica is also discussed.