In January, Inhabitat reported that scientists at MIT and RWTH Aachen University were revolutionizing the effectiveness of concentrated solar plants by emulating the pattern found on a sunflower known in science as Fermat’s spiral. Now a team from the University of Wisconsin-Madison have taken the sunflower as their inspiration by replicating the flower’s ability to slowly rotate from east to west during the course of a sunny day.
This process, which is called heliotropism, is a wonderful piece of natural engineering that has inspired the UW-Madison team to mimic it for use in the next crop of solar power systems. Unlike other “active” solar systems that track the sun’s position with GPS and reposition panels with motors, the university team’s method leverages the properties of unique materials in concert to create a passive method of re-orienting solar panels in the direction of the most direct sunlight.
Electrical and computer engineering professor Hongrui Jiang’s came up with the concept and recently published the design in the August 1 issue of Advanced Functional Materials. It utilises a combination of liquid crystalline elastomer (LCE), which goes through a phase change and contracts in the presence of heat, with carbon nanotubes, which can absorb a wide range of light wavelengths.
“Carbon nanotubes have a very wide range of absorption, visible light all the way to infrared,” says Jiang. “That is something we can take advantage of, since it is possible to use sunlight to drive it directly.”
When direct sunlight hits a mirror beneath the solar panel, it focuses upon one of multiple actuators composed of LCE laced with carbon nanotubes. These nanotubes then heat up as they absorb light, and the heat differential between the environment and inside the actuator causes the LCE to shrink. What this does is cause the entire assembly to bow in the direction of the strongest sunlight. As the sun moves across the sky, the actuators cool and re-expand essentially re-positioning the panel over the 180 degrees of sky during the course of the day.
“The idea is that wherever the sun goes, it will follow,” says Jiang. “The whole point of solar tracking is to increase the electricity output of the system.”
Images via Wikimedia Commons