Sunflower heliotropic ability inspires passive solar tracking

As we reported in our article about a similar technology, sunflowers are able to slowly rotate from east to west during the course of a sunny day in order to maximize the amount of received sunlight in a process called heliotropism. Researchers from University of Wisconsin-Madison found a way to create their version of a passive system which mimics heliotropism in order to maximize the output of solar power generation systems.

Led by Hongrui Jiang, UW-Madison electrical and computer engineering professor, the team decided to rely on the properties of unique materials to create a passive method of re-orienting solar panels in the direction of the most direct sunlight, instead using active solar tracking systems which require usage of GPS and motors to reposition the panels.

The technology employs a combination of liquid crystalline elastomer (LCE) with carbon nanotubes. The properties of these two materials enable passive tracking by relying on the phase change and contraction of the LCE in the presence of heat, as well as the ability of carbon nanotubes to effectively absorb a wide range of light wavelengths.

A mirror beneath the solar panel focuses the sunlight onto one of multiple actuators composed of LCE laced with carbon nanotubes. The carbon nanotubes heat up as they absorb light, and the heat causes the LCE to contract and bow the mounted solar panel into the direction of the strongest sunlight. As the sun moves across the sky, the actuators will cool and re-expand, while other sections contract and reposition the panel into the direction of strongest sunlight.

In tests performed by UW-Madison researchers, the system improved the efficiency of solar panels by 10 percent. While it may not seem as much, keep in mind that progress in the efficiency of solar panels is usually around a few percents.

Development of passive heliotropic systems is important due to their independence from no motors and circuits which require some of the generated energy. Jiang’s and his team are now researching ways to refine the materials in order to enable their usage along larger solar panels, where the net energy gain from his system will be the greatest.

For more information, read the article published in the Advanced Functional Materials: “Direct Sun-Driven Artificial Heliotropism for Solar Energy Harvesting Based on a Photo-Thermomechanical Liquid-Crystal Elastomer Nanocomposite”.