From Air to Aid: Solar SAWE for Water-Scarce Regions

Introduction

It is a known fact that the demand for basic necessities such as water,energy and food is increasing continuously. However, due to the combination of excess demand and less supply, the  basic economic problem (scarcity) arises. All these necessities are interconnected as water is an essential resource for the growth of crops from which food comes.

Additionally, irrigation and electrical energy are the main processes that require freshwater in immense amounts. This method uses atmospheric water (moisture present in the air) as well as sunlight (in the form of solar energy) to produce freshwater. In specific, this method uses a renewable resource of energy, solar power, which is in infinite supply.

 In the case of freshwater generation, atmospheric water is prevalent in massive amounts - it is predicted to increase in the future due to global warming. This system solves the problems of the co-dependencies between energy,water and food supply, especially in arid regions. 

Skeletal Structure of SAWE 

The method Solar-driven atmospheric extraction (SAWE) can constantly manufacture freshwater as long as sunlight is present. 

The system is filled with hygroscopic sorbents(substances that absorb water molecules) to capture the moisture from the air.The Mass Transport Bridges(MTBs) structure is the core operating system - it is divided into two temperature-oriented regions.The high temperature zone is used for generating vapors and the room temperature zone is used for collecting atmospheric water. Glass fiber membrane(GFM) is used to create MTBs allowing productive water transport to occur. 

Lithium chloride solution can help in the capturing of water molecules in different relative humidities. The structure consists of the solar absorber and the GFM papers within a PMMA frame. Consequently, the saturated LiCl solution spreads into the MTBs structure. 

Overall, this method allows optimum generation of freshwater production from a combination of atmospheric water and sun rays. 

Beneath the Surface of SAWE

 During the operation, the room-temperature region grasps the moisture-filled air. The sun’s radiation is absorbed by the solar absorber using thermal absorption,where the light energy is transformed into heat energy. Therefore, vaporisation(the conversion of water to air) occurs in the high-temperature area due to the heat energy being a catalyst in overcoming intermolecular forces between molecules. 

The released vapour is stored on the chamber wall which is condensed, generating freshwater. Due to capillary action(the wicking of liquid) , it is transferred back into the high temperature area. This ensures consistency and efficiency in the production of the vapour. The transportation does not end: through both diffusion(down the concentration gradient and convection(where molecules expand due to higher temperature and travel to the top because of low density)  into the room-temperature area. 

The Unseen Struggles

Initially, many challenges were faced by the prior SAWE systems.

 Firstly, due to the low activities of the sorbents, the efficiency was affected as only one absorption cycle could occur per day . In depth, the generation of freshwater occurred during the day whilst the extraction of moisture from atmospheric air occurred during the night. This was unproductive and led to a restriction to the capacity of absorption by the sorbents. This difficulty was solved by creating a system where multiple cycles could be executed by using an enormous number of sorbents.

Secondly, the development of this system is very expensive especially as a consequence of costly nanomaterials. The upgrading of the model by adding different features also leads to a pricey result.

Thirdly, the sunlight is not constant- it varies between day and night which is very unreliable. Furthermore, changing the cycles requires a live system or a labor intensive system which will lead to the waste of heaps of energy. 

Hence, to maximize the capability of the SAWE, a passive system which can be scalable is required to produce the freshwater without any manual work.

Outcome of the investigation

The performance of the upgraded version(simple and affordable model) was tested in Saudi Arabia. The system was working constantly whilst experiencing a diverse set of weather conditions. The atmospheric water was successfully being converted to freshwater which was useful in the irrigation of the crops (in specific, Chinese cabbage). This underlines the impact of SAWE in areas especially, arid regions where acquiring water seems impossible.

The importance of SAWE

SAWE is a very prominent tool in helping to solve the problems related to the surplus of water,food resources and energy in a sustainable way.This is vital for regions suffering from water scarcity, such as deserts. Implementation of SAWE can support agriculture by providing freshwater and essential minerals for crops, potentially aiding millions by supplying both drinking water and nutrition.

Summary:

SAWE(Solar-drive atmospheric extraction) harnesses solar energy and atmospheric water to produce freshwater continuously with no maintenance needed. Mass Transport Bridges (MTBs) with Glass Fiber Membrane (GFM) and LiCl solution enable dual zones: room-temp for capture, high-temp for vapor generation via solar absorber. It overcomes prior limits through multicycle operation and low-cost materials. Real-world tests in Saudi Arabia show 0.65 L/m²/h at 90% RH, with scaled systems yielding 2-3 L/m²/day for off-grid irrigation like Chinese cabbage.This suggests that SAWE is ideal for arid regions tackling the water-energy-food bond.​

Bibliography

Yang, K., Pan, T., Farhat, N., Felix, A. I., Waller, R. E., Hong, P., Vrouwenvelder, J. S., Gan, Q., & Han, Y. (2024c). A solar-driven atmospheric water extractor for off-grid freshwater generation and irrigation. Nature Communications, 15(1), 6260. https://doi.org/10.1038/s41467-024-50715-0

Aishwarya V. Pillai | Writer, The STEM Review