A team of engineers at the University of Colorado Boulder has developed a novel metamaterial with extraordinary properties not found in nature. The material is scalable, and has commercial applications as a kind of air conditioning system for structures. It also has the ability to cool objects, even when in direct contact with sunlight, with no consumption of energy or water.

The invention is a product of a $3 million grant by the Energy Department's Advanced Research Projects Agency-Energy (ARPA-E), which was awarded back in 2015. The technology is currently under patent review and the researchers are working with UC Boulder’s Technology Office to explore potential markets for commercialisation. A plan has been set in place to create a 200 sqm ‘cooling farm’ in Boulder in 2017.

The research has been published in the journal Science, and is stipulated to be an eco-friendly way to supplement cooling for thermoelectric power plants. Current methods require a large amount of water and electricity to maintain the machinery operating temperatures and are not very cost-effective. This has presented new challenges, which paves the way for novel methods to reduce the energy cost, of which this material may be a serious contender.

The technology has a major advantage over other materials and processes, in that it can work 24/7 without any electrical or water input. As such, this novel metamaterial could find itself across a range of industries including aerospace, agricultural and power industries. The researchers themselves have stated that they are excited to see what commercial applications could come from this research.

It may also find itself in residential applications, as the researchers have stated that just 10-20 sqm of the material could cool down a family house in the summer. It also has the potential to enhance the lifetime and efficiency (by 1-2%) of solar panels, as direct sunlight can damage solar panels and prevent them from efficiently converting solar rays into electricity.

What is the material?

When the metamaterial is applied to a surface, the film cools the object underneath by reflecting solar radiation back into space, whilst simultaneously allowing the surface to expel its own heat as transparent infrared radiation.

The material is a glass-polymer hybrid consisting of randomly embedded resonant polar dielectric (insulating) microspheres within a polymer matrix. The material is coated with a thin silver film to enhance the spectral reflectance of the material.

Both the metamaterial and the silver coating are manufactured economically using roll-to-roll processes, which presents a high throughput process open to scalability and commercial viability.

The material exhibits a passive radiative cooling process, where objects naturally shed heat to their surroundings in the form of infra-red radiation, without consuming energy. The material is just 50 micrometers thick and can demonstrate a radioactive cooling power greater than 110 Wm-2 for 72 hours continuously; and up to 93 Wm-2 in direct, midday sunlight. The cooling power is similar to that produced by solar cells, but with the advantage of continuous running throughout the day and night.

These properties allow for effective cooling, even in challenging daytime conditions and under exposed sunlight. They bring to the market an effective cooling system that doesn’t just rely on overnight thermal radiation cooling. As such, it is expected that we will see this product on the market in the near future throughout a multitude of industries, covering various applications.

Meet the Research Team

The engineering team who authored this paper consists of eight people:

Xiaobo Yin, who is the co-director of the research and an assistant professor of CU Boulder's Department of Mechanical Engineering and Materials Science and Engineering; Gang Tan, who is a co-author and an Associate Professor in the University of Wyoming's Department of Civil and Architectural Engineering; Ronggui Yang, a Professor of Mechanical Engineering; Yao Zhai, an Assistant Professor; Runnan Lou, a research assistant; Yaoguang Ma, a Postdoctoral researcher; Dongliang Zhao, a Postdoctoral researcher; and Sabrina David, who is a PhD student.

References

Newly Engineered Material Can Cool Roofs and Structures with Zero Energy Consumption - University of Colorado at Boulder, Press Release

Zhai Y., Ma Y., David S., Zhao D., Lou R., Tan G., Yang R., Yin X., Scalable-manufactured randomized glass-polymer hybrid metamaterial for daytime radiative cooling, Science, 2017, DOI:10.1126/science.aai7899

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