An experiment from researchers at Tel Aviv University uses metal surfaces to recreate the kind of charge generation seen in a lightning storm.

By generating the electric interactions between water molecules, the team is exploring an intriguing idea: water vapor as an energy source.

"Who knows? Maybe one day we will have roofs covered with humidity panels together with solar panels," TAU professor Colin Price told Tech Briefs.

Price and his colleagues set out to produce a tiny, low-voltage battery  that utilizes only the air's humidity.

The Tel Aviv team determined that certain metals, when exposed to a high relative humidity (RH) and isolated from the ground, can build-up charge spontaneously.

While some metals were unaffected by high relative humidity, others did acquire charge. When RH was greater than 60%, metals like zinc and stainless steel energized a capacitor to a voltage of 1 V.

In a thunderstorm, with heavy precipitation, the cloud charge builds into cracks of lightning. As water splits intro hydrogen and oxygen ions, the separation of charge causes a large electric field to build up — like a battery, says Price — between the top and bottom of the cloud.

Lightning ultimately forms to discharge those large fields, and Price's lab demonstrates the same kind of effect, using metal surfaces instead of ice surfaces in the clouds.

The Tel Aviv researchers also performed outdoor experiments, showing that the phenomenon works under similar natural ambient humid conditions.

In a Q&A with Tech Briefs below, Price explains what is possible when the results of their experiments are scaled up.

Tech Briefs: How much energy can be generated via humidity, with your low-voltage battery?

Colin Price: At the moment we have only focused on the voltage generated. The currents are tiny (although we have not measured them) and hence we do not have numbers for energy yet. But for the lab experiments we assume they are also small.

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Tech Briefs: Can you take us through the test? What were you able to demonstrate?

Prof. Colin Price: Our experiment is trying to copy in some ways the charging within the clouds, although instead of ice we are using metals of different types. What we found was that when the droplets start condensing on the metal surfaces in the lab (and outside), the interaction between the liquid droplets and the metal surfaces results in charge transfer and charge separation. That results in a voltage buildup between two metals, but only when the air between the metals is above 60% relative humidity. When the relative humidity is below 60%, nothing happens.

Tech Briefs: What kinds of applications do you envision with this type of electricity production?

Prof. Colin Price: Well, many locations in the world in summer have hot humid air, with relative humidities (RH) above 60% in the day, and even 80% at night. RH depends on temperature, and so at night the RH goes up as the temperature goes down while the daytime warming reduces the RH, even if the absolute humidity remains the same during the 24 hour period.

In tropical developing countries, the RH is about 60% all year long. Some countries in Africa have no electricity at all, especially in rural areas. We envision developing small batteries, like AA or AAA, that will work on humidity alone: Always charged if the RH is high. And especially at night, when solar panels do not work, the humidity batteries may be able to provide an alternative source of energy for small appliances.

Who knows? Maybe one day we will have roofs covered with humidity panels together with solar panels. Furthermore, these panels do not need to be on the roof or even outside. If the windows are open, the humidity could also be felt inside, in places like houses and schools.

Tech Briefs: And what’s next?

Prof. Colin Price: We want to try to improve the efficiency of the charge transfer, try additional materials, even synthetic nano-materials, and try to improve the voltage levels and storage of the charge for later use.

What do you think? Will we see roofs with humidity panels? Share your questions and comments below.