Water Vapor Could Be Surprise Source of Renewable Energy

Renewable energy resources aren't just an opportunity, they are now part of a necessity for new methods that scientists worldwide are working hard to meet.

One potentially new method, that can draw from an abundant source, is outlined in a Tel Aviv University study that found that water vapor in the atmosphere might serve as a potential renewable energy source in the near future.

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Capitalizing on naturally occurring phenomena 

Published on May 6, 2020 in Scientific Reports, the research is based on the discovery that electricity materializes in the interaction between water molecules and metal surfaces.

Led by Prof. Colin Price in collaboration with Prof. Hadas Saaroni and doctoral student Judi Lax, all of TAU's Porter School of the Environment and Earth Sciences, a team set out to produce a tiny low-voltage battery that utilized only humidity in the air.

"We sought to capitalize on a naturally occurring phenomenon: electricity from water," Prof. Price explained in a press release.

"Electricity in thunderstorms is generated only by water in its different phases — water vapor, water droplets, and ice," he continued. "Twenty minutes of cloud development is how we get from water droplets to huge electric discharges — lightning — some half a mile in length."

The goal of the researchers was not to create a huge electrical discharge but, rather, to see if their small battery could be charged by water vapor in the air — they succeeded.

Building on old observations

The research builds on the findings of earlier observations and discoveries: in the nineteenth century, English physicist Michael Faraday observed that water droplets could charge metal surfaces due to friction between the two; a more recent study, meanwhile, showed that certain metals spontaneously build up an electrical charge if they are exposed to humidity. 

In order to test their battery, the researchers conducted an experiment to determine the voltage between two different metals exposed to high amounts of humidity — one of these metals was grounded.

"We found that there was no voltage between them when the air was dry," Prof. Price explains.

"But once the relative humidity rose above 60%, a voltage began to develop between the two isolated metal surfaces. When we lowered the humidity level to below 60%, the voltage disappeared. When we carried out the experiment outside in natural conditions, we saw the same results."

"Water is a very special molecule. During molecular collisions, it can transfer an electrical charge from one molecule to the other. Through friction, it can build up a kind of static electricity," Prof. Price continued. "We tried to reproduce electricity in the lab and found that different isolated metal surfaces will build up different amounts of charge from water vapor in the atmosphere, but only if the air relative humidity is above 60%."

Renewable energy for developing countries

Importantly, the conditions outlined in the study are seen almost on a daily basis in many countries: "this occurs nearly every day in the summer in Israel and every day in most tropical countries," Prof. Price explained.

The study challenges established ideas about the potential for using humidity as an energy source. The team of researchers showed that humid air can be used to charge surfaces to voltages of approximately one volt. What's more, the method could be used as a valuable means to bring electricity to remote as well as poor areas that are off the grid.

"If a AA battery is 1.5V, there may be a practical application in the future: to develop batteries that can be charged from water vapor in the air," Prof. Price adds.

"The results may be particularly important as a renewable source of energy in developing countries, where many communities still do not have access to electricity, but the humidity is constantly about 60%," Prof. Price concludes.