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Promising Solar Technology Would Expand Drinking Water Access

Several advancements in solar technology may provide the answer to drinking water production in distressed regions of the world.

A new material developed by researchers speeds up the process in solar stills, the tank-like devices used to evaporate impure water and condense the vapor into potable form. Current products on the market are big, pricey and can barely produce enough water for a small family. However, shrinking the size and cost of solar stills would open access for many people lacking water resources.

The traditional solar still is simple: a black-bottomed vessel filled with dirty or salty water and topped with clear glass or plastic. The bottom absorbs sunlight, heating the water so that it evaporates and leaves the contaminants behind. The vapor then condenses on the covering and trickles into a collector. Until now, the output has been low because the sun’s rays must heat the entire volume of water before evaporation begins.

A materials scientist at the University of Texas in Austin and his colleagues report having found a way around this limit using hydrogels, polymer mixtures that form a porous, water-absorbent network.

The most recent version of the hydrogel in testing allowed a solar still to produce water at the highest rate ever reported, about 12 times the amount produced by today’s commercially available versions, according to a report in Science Advances.

Waste heat shed by solar cells may offer another path to drinking water production. A new design by researchers at King Abdullah University of Science and Technology in Saudi Arabia folds the components for distillation under a typical silicon photovoltaic cell in a way that doesn’t impact its energy output.

Combining solar and water decontamination isn’t a novel idea, but this newer technology would bypass some of the issues preventing the practice from being more widespread.

Slightly more than 10 percent of the sunlight collected on a clear day using the new cell design goes towards generating electricity, a rate that isn’t far behind conventional solar technology. Then, some of the remaining solar radiation —which normally goes to waste — becomes thermal energy. That energy is absorbed by a pancake-like stack of membranes shuffled between materials selected to assist evaporation and condensation.

The heat turns the water into vapor, but the energy is passed to lower membranes so the process can repeat. This makes for a higher distillation rate. Stacking the membranes could potentially produce as much as five times the clean water produced by conventional solar stills, according to the researchers.

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