Remember Carbon Nanotubes? They’re Back, & They’re Sucking Moisture

Clean Power[1] Carbon nanotubes could juice the energy-water nexus with new solar cell efficiency twist (image via National Renewable Energy Laboratory,

Published on June 13th, 2020 | by Tina Casey

June 13th, 2020 by Tina Casey[2] 

Before perovskites and graphene captured the imagination of the clean tech world, carbon nanotubes were all the rage. What happened? Where did they go? Well, they never went away, but they did fall off the CleanTechnica radar for a while there, so we have some catching up to do particularly in the area of solar cell efficiency, where an interesting twist on the energy-water nexus is afoot.

carbon nanotubes solar cell efficiency energy-water nexus

Carbon nanotubes could juice the energy-water nexus with new solar cell efficiency twist. Image courtesy National Renewable Energy Laboratory[3].

Thanks, Physics World, For Reminding Us About Carbon Nanotubes & Solar Cell Efficiency

The latest big development in the carbon nanotube / solar cell efficiency space hit the Intertubes last month, but what with the COVID-19 outbreak and everything else going on nobody paid much attention until last Friday, when Physics World[4] contributing editor Isabelle Dumé took notice and now everybody is talking about it.

The basic idea is to boost solar cell efficiency by keeping the solar panels cool. That sounds simple enough. Everybody knows that solar cells lose efficiency when they are too hot. The problem is that when you start engineering cooling systems into a solar panel then you’re adding expense and if that system takes energy to run then you are right back where you started.

The solution, as developed by a team of researchers at KAUST (the King Abdullah University of Science and Technology[5]), is, well, a solution. The team added carbon nanotubes to a self-adhering polymer gel that absorbs water when the air is humid, like at night.

With the addition of the carbon nanotubes, the gel can reverse direction and release water when a solar cell needs to be cooled down, like during the day.

Interesting! CNTs have been a hot topic[6] as applied directly to the inner workings of solar cells as well as energy storage[7], and the new gel provides them with another opportunity for relevance in the sparkling green economy of the future.

How Much More Efficient Is A Solar Cell With Carbon Nanotube Gel?

Potentially, lots! The team initially demonstrated their gel in the lab and found it could hold and release enough water to cool a solar panel down by 10 degrees Celsius. They got even better results when they repeated the experiments outdoors.

Aside from the implications for solar cell efficiency, the new gel could also have an impact on water resources globally. Here’s the take from Renyuan Li, a member of the research group (break added for reading):

“This work shows the benefits of using atmospheric water generation to help fight climate change. We believe this cooling technology can fulfill the requirements of many applications because water vapor is everywhere and this cooling technology is easy to adapt to different scales.

“The technology could be made as small as several millimeters for electronic devices, hundreds of square meters for a building, or even larger for passive cooling of power plants.”

The cumulative impact on global solar generating capacity could be pretty impressive. Dumé cites the figure of 3000 gigawatts globally by 2030. With the current crop of silicon solar cells clocking in at 6% to 25% solar conversion efficiency, there is plenty of room for improvement.

Aside from improving efficiency, the new carbon nanotube gel could also help prevent heat damage, leading to a longer lifespan and lower maintenance costs for solar panels.

So, What Is A Hydrogel Anyways?

To be more precise, the new carbon nanotube gel from KAUST is a hydrogel, which is a material that can absorb and release copious amounts of water in response to a stimulus, such as a change in temperature or an electrical current, all without breaking apart.

Okay, so sponges absorb water too, but hydrogels are more special[8]. As our friends over at the National Institutes of Health explain it, the properties of sponges are determined by their morphology, which is fancyspeak for things like the size of their pores and their interconnectivity.

Hydrogels, on the other hand, are “hydrophilic, swollen polymer matrices with a cross-linked structure and which retains a large amount of water.” That’s a fine way of saying that hydrogels are defined by hydrophobicity.

Solar Cell Efficiency & The Energy-Water Nexus

As for KAUST’s even more special carbon nanotube hydrogel, that didn’t just pop up out of thin air.

Back in 2018, Li and other members of the research team published the results of a pre-nanotube hydrogel study[9] that cited the potential for use in atmospheric water harvesting, as a solution for the problem of global water scarcity[10].

“The harvested water could be easily released under regular sunlight via the photothermal effect, and it can be directly reused without noticeable capacity fading,” the team enthused.

“This type of atmospheric water generator is cheap and affordable, works perfectly with a broad range of humidity, does not need any electricity, and thus is especially suitable for clean water production in remote areas,” they enthused more.

Their initial small-scale DIY model showed some promise, delivering 20 grams of fresh water within 2-1/2 hours under natural sunlight. They estimated that a scaled-up device would cost about $3.20 and deliver about 3 kilograms daily, which is pretty close to the recommended water intake[11] for the average adult.

Add the solar cell efficiency angle and there you have an interesting twist on the energy-water[12] nexus.

Follow me on Twitter[13].

Image: Vials of single-walled carbon nanotubes separated by electronic structure[14]; diameter-dependent optical absorption produces tunable colors, via National Renewable Energy Laboratory.

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Tags: access to water, carbon nanotubes, Electricity, Energy, KAUST, Solar Cell Efficiency

About the Author

Tina Casey[21] specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey[22] and Google+[23].


  1. ^ Clean Power (
  2. ^ Tina Casey (
  3. ^ National Renewable Energy Laboratory (
  4. ^ Physics World (
  5. ^ Science and Technology (
  6. ^ CNTs have been a hot topic (
  7. ^ energy storage (
  8. ^ hydrogels are more special (
  9. ^ hydrogel study (
  10. ^ lobal water scarcity (
  11. ^ recommended water intake (
  12. ^ energy-water (
  13. ^ Twitter (
  14. ^ electronic structure (
  15. ^ access to water (
  16. ^ carbon nanotubes (
  17. ^ Electricity (
  18. ^ Energy (
  19. ^ KAUST (
  20. ^ Solar Cell Efficiency (
  21. ^ Posts by Tina Casey (
  22. ^ @TinaMCasey (
  23. ^ Google+ (

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