Polymer gel lets solar cells cool by sweating

A polymer-based cooling system developed at the King Abdullah University of Science & Technology (KAUST) in Saudi Arabia has improved the efficiency of a prototype solar panel by up to 20% and requires no external energy source to operate.

Commercial silicon photovoltaic panels are only able to transform a small portion of absorbed sunlight into electricity, while the remainder of the radiation becomes heat. Because solar panels are less efficient for every degree rise in temperature, the problem of heat dissipation becomes more acute in hot environments, such as the Arabian desert.

Unfortunately, efforts to cool solar panels with conventional techniques, including refrigeration or air conditioning, tend to consume more energy than can be gained back through efficiency boosts. Now, a team led by Peng Wang from KAUST's Water Desalination and Reuse Center has produced a proof-of-concept cooling system that aims to solve this conundrum by tapping into the natural properties of the Earth's climate. Wang and his team report this cooling system in a paper in Nature Sustainability.

In earlier work, the KAUST researchers had developed a polymer that contains calcium chloride, a powerful desiccant. When exposed to humid air, this novel material gradually expands as the calcium salts pull water into the polymer gel, eventually doubling its initial weight. By also incorporating heat-absorbing carbon nanotubes into the polymer framework, the team have now found they can reverse this process and trigger the release of water with solar energy.

Renyuan Li, a former PhD student and now postdoctoral researcher in Wang's group, notes that one of the intriguing properties of the gel was its ability to self-adhere to numerous surfaces – including the underside of solar panels. After controlled experiments with artificial sunlight revealed that a fully filled gel could free enough water to reduce panel temperatures by 10°C, the team decided to build a prototype for outdoor tests at KAUST.

During both summer and winter seasons, the researchers watched as the gel absorbed moisture from the muggy air at night and then released this water as the daytime temperatures ramped up. Surprisingly, the solar panels showed an increase in efficiency even greater than that measured during the indoor experiments, a jump the researchers theorize may be due to improved heat and mass transfer outdoors.

"This work shows the benefits of using atmospheric water generation to help fight climate change," says Li. "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."

This story is adapted from material from KAUST, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.