New Solar Vapor Generator to Deal with Global Drinking Water Shortages

Many developing regions in the world are affected with a shortage in drinking water, and many areas can be affected by natural disasters which limit access to clean water.

A new, low cost and more efficient solar still has been developed that can potentially make a huge impact on global water shortages.

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Many people have seen survival videos of using a plastic bag or bottle to distill water through evaporation and collect it for drinking. Improving on this basic survival mechanism is of great benefit to address the global drinking water shortages, with 1/10th of the world's population already lacking clean water.

There have already been solar stills for thousands of years that use a black bottomed vessel to evaporate cleaner water. But a lot of the sun's energy is wasted through the process of heating such a large volume of water. These kinds of stills need to be 6 m² in order to provide water for one person each day.

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The mechanism to evaporate water has been improved in recent years, by restricting the heat and evaporation to the very top layer which reduces energy loss, and also using nano materials to absorb more of the sun's rays. The problem with nano materials, is they cost hundreds of dollars per gram. This is not a viable solution to deal with global water shortages.

A paper published on January 30 in Global Challenges shows how Qiaoqiang Gan and his colleagues made a cheaper light absorbing solar still through the use of carbon-dipped paper. It costs less than $2 per square meter, and purifies dirty water up to four times faster than current commercial solar stills.

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The normal method traps solar energy in the plastic container causing the water to evaporate under the heat and condense at the top of the container. This new method maximizes the use of solar energy and also minimizes the heat loss. Downward thermal radiation suppressed which acts like a thermal radiation shield.

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The researchers have dubbed this the "solar vapor generator" to clean and desalinate water. The sun evaporates the water, leaving behind salt, bacteria and other elements. The water vapor condensates as it cools and returns to liquid where can be collected and trapped without any of the contaminants.

It's made from expanded polystyrene foam and porous paper coated in black carbon. The paper absorbs the water, and the black carbon absorbs sunlight.

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The energy conservation and efficiency is conveniently done without any optical concentrators like mirrors or lenses that concentrate the light and are costly to purchase. Only 12% of the available energy is lost during the evaporation process which is unheard of in other solar stills. This is made possible due to the evaporation of surface water alone that covers the black carbon absorption medium. The water evaporates at 44°C which doesn't take as long as requiring a very deep amount of water to heat up and eventually evaporate.

Estimations are that the still can produce 3 to 10 L of water per day which is a big improvement over most solar stills of similar size that can do 1 to 5 L per day.

The cost is a dollar $1.60 per square meter compared to optical concentrators at $200 per square meter. The world economic forum estimates world water infrastructure upgrades between 2010 and 2030 to cost $26 trillion. Commercializing this solar vapor generator would greatly reduce the funding gap to meet their desired goals of improving global drinking water access.

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References:

• Sunlight-powered purifier could clean water for the impoverished
• Academics build ultimate solar-powered water purifier
• Extremely Cost-Effective and Efficient Solar Vapor Generation under Nonconcentrated Illumination Using Thermally Isolated Black Paper

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2017-02-03, 12:05pm@krnel