Solar Power Can Do More than Provide Clean Energy – It Can Generate Clean Water in Arid Regions

In nations like Canada and Brazil, access to fresh water is rarely a concern.  However, the reality is that there are scores of populated and arid regions worldwide where freshwater is a luxury.  Thankfully, there are solutions already in place and being developed to address this issue – such as atmospheric water harvesters (AWH)

In a recent breakthrough, researchers have developed a potentially revolutionary atmospheric water harvester leveraging solar-powered passive adsorption-based technology.  The core of this innovation lies in its use of newly developed ‘super hygroscopic porous gels'.  These are composed of titanium nitride, hydroxypropyl methylcellulose, and LiCl (THL), and have demonstrated exceptional water adsorption capacities across a wide range of humidities (15%–90% RH).  The unique combination of materials is said to enable rapid adsorption and desorption kinetics (the rate at which a previously adsorbed substance is released), significantly enhancing efficiency when used in atmospheric water harvesters.

The study released, detailing the aforementioned breakthrough, underscores the device's ability to achieve high water yields, even in arid environments, with its practical application already having been validated through outdoor testing in different seasons.

This AWH technology, showcasing a sustainable and effective approach to mitigating water scarcity in arid regions, compares favorably against other solar-driven water harvesting systems and, importantly, meets WHO standards for drinking water.

Atmospheric Water Harvesters

So, a new hygroscopic porous gel has been developed that should ramp up the efficiency and effectiveness of AWHs in use around the world.  This is great, but how do these devices actually work?

As its name would imply, an Atmospheric Water Harvester (AWH) is a device designed to extract water from the air. These devices are particularly valuable in arid regions where conventional water sources are scarce or contaminated. The technology behind existing AWHs varies, but it generally revolves around capturing water vapor from the air and condensing it into liquid water.

The most common design of AWH systems is based on the principle of condensation, akin to how dew forms. This design typically involves:

1. Air Intake: Air is drawn into the system using a fan.
2. Cooling and Condensation: The moist air is then cooled down below its dew point, often using a refrigerated or Peltier-cooled condenser, causing the water vapor to condense into droplets.
3. Water Collection: The condensed water is collected in a reservoir, filtered, and sometimes mineralized for taste.
4. Distribution: Finally, the water is either stored for later use or directly piped for immediate consumption.

AWH systems can vary in size from small, portable units suitable for individual or household use to large, industrial-scale installations. The efficiency of these systems largely depends on the ambient humidity and temperature; higher humidity levels typically result in higher water yield – which is why any boost in efficiency provided in arid environments is welcomed, such as that on offer through the use of new super hygroscopic porous gels.

With their ability to scale in size, AWHs are commonly used in various settings:

Arid and Drought-prone Areas: They provide a critical source of clean drinking water in regions where water is scarce.

Military Applications: Portable AWH units are useful for providing water to troops in remote locations.

Remote Communities and Emergency Relief: They offer an immediate source of drinking water in remote communities or during natural disasters when traditional water sources are unavailable or contaminated.

Agriculture: Some AWH systems are used for irrigation in arid regions.

The advancements in AWH technology involving super hygroscopic porous gels and MOFs (Metal-Organic Frameworks) stand poised to improve on traditional refrigeration-based systems, offering the ability to absorb water vapor at a much lower energy cost. These innovations should make AWHs more efficient and feasible in a wider range of climatic conditions.

Fresh Water Supplies

Most of the world's freshwater is found in glaciers and ice caps, accounting for approximately 69% of the global freshwater resources. These are primarily located in polar regions and high-mountain areas, such as Antarctica, Greenland, and various mountain ranges worldwide. The next largest reservoirs of freshwater are groundwater sources, which constitute about 30% of the total. Only a small fraction (less than 1%) of the world's freshwater is accessible in rivers, lakes, and the atmosphere.

In regions where atmospheric water harvesters (AWHs) are required, clean water is often hard to find due to several reasons:

Arid Climates: Many regions with a need for AWHs are arid or semi-arid with low rainfall. This includes vast stretches of Africa, the Middle East, parts of South America, Central Asia, and Australia.

Groundwater Depletion and Contamination: Overuse of groundwater for agriculture and drinking, coupled with inadequate replenishment, leads to depletion. In addition, groundwater can be contaminated by natural and human-made pollutants, making it unsafe for consumption.

Lack of Infrastructure: Many remote or underdeveloped areas lack the infrastructure to collect, treat, and distribute water. This is often compounded by economic constraints.

Climate Change: Changes in climate patterns are affecting traditional water sources. Some regions experience prolonged droughts, while others face the melting of glaciers, which impacts long-term water availability.

Overpopulation and Urbanization: In densely populated or rapidly urbanizing areas, existing water supplies may be insufficient to meet the demand. Moreover, urbanization often leads to pollution of available water sources.

Political and Economic Challenges: In some cases, the management and distribution of water resources are affected by political and economic issues, leading to unequal access to water.

AWHs provide an alternative by extracting water from the air, which can be a viable solution in areas where other sources are non-existent, insufficient, or unsafe. This technology is particularly valuable in regions where the air is humid, but rainfall is low, making conventional water sources unreliable.

Current Solutions

As it stands, there are several technologies that compete with or complement Atmospheric Water Harvesters (AWHs) for generating freshwater, particularly in areas where water scarcity is a significant issue.  However, each comes with its own set of advantages and challenges.  Some of the more notable alternative solutions include,

Desalination: This is one of the most prominent methods for producing fresh water from seawater or brackish water. Desalination predominantly uses two technologies: reverse osmosis, which filters water through a semi-permeable membrane, and thermal desalination, which involves heating and evaporating water and then condensing the steam.  Desalination plants are particularly common in arid regions like the Middle East.  While effective, desalination efforts are typically expensive, requiring a large amount of energy.

Water Recycling and Reuse: Advanced water treatment technologies enable the recycling of wastewater into potable water. This includes the treatment of sewage, industrial, and agricultural wastewater.  Recycled water can be used for various purposes, including irrigation, industrial processes, and replenishment of freshwater supplies.  This approach typically requires large facilities and elevated associated run-costs.

Rainwater Harvesting: This is a simpler and more traditional method of collecting and storing rainwater for later use.  Rainwater harvesting systems capture water from rooftops or other surfaces and store it in tanks.  While less technologically advanced than AWHs, it's a sustainable way to supplement water supplies, especially in regions with seasonal rainfall.  As this method is dependent on rainfall, it is not as reliable as some other approaches.  There is also no guarantee that the collect water will not need to be further treated to ensure it is safe for consumption.

Fog Harvesting: Similar to AWHs, fog harvesters collect water from the atmosphere.  They use large mesh nets to trap water droplets present in fog, which then accumulate and drip into collection tanks.  This method is suitable in coastal or mountainous areas where fog is frequent.

Groundwater Recharging: This involves directing rainwater or reclaimed water into the ground to replenish aquifers.  Techniques include the construction of recharge basins, infiltration ponds, and the use of permeable pavements.  It's a method of ensuring sustainable groundwater supplies, which is a major source of fresh water in many regions.

Solar Water Still: A simple technology where solar energy is used to evaporate contaminated or salt water, and the condensate is collected as distilled water.  This method is more suitable for small-scale applications and is particularly useful in remote areas with abundant sunlight.

Each of these technologies has its application niches based on geographical, climatic, and economic considerations.  In many cases, a combination of these technologies is employed to ensure a reliable and sustainable water supply.