Sunflower heliotropism could inspire design of solar panels

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A University of Wisconsin-Madison electrical and computer engineer has found a way to mimic the passive heliotropism seen in sunflowers 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, electrical and computer engineering Prof Hongrui Jiang’s concept employs a combination of liquid crystalline elastomer (LCE), which goes through a phase change and contracts in the presence of heat, and carbon nanotubes that absorb a wide range of light wavelengths.

‘Carbon nanotubes have a very wide range of absorption: visible light all the way to infrared,’ said Jiang in a statement. ‘That is something we can take advantage of, since it is possible to use sunlight to drive it directly.’

Direct sunlight is said to hit a mirror beneath the solar panel, focused onto one of multiple actuators composed of LCE laced with carbon nanotubes. The carbon nanotubes heat up as they absorb light, and the heat differential between the environment and inside the actuator causes the LCE to shrink.

This causes 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 and new ones will shrink, re-positioning the panel over the 180° of sky that the sun covers in the course of the day.

‘The idea is that, wherever the sun goes, it will follow,’ said Jiang.

In Jiang’s tests, the system reportedly improved the efficiency of solar panels by 10 per cent and a passive system means there are no motors and circuits to affect the system’s electricity output.

The materials driving Jiang’s design have only been available in the past few years, so for now he and his team are researching ways to refine them for use driving larger solar panels, where the net energy gain from the system will be the greatest.

Eventually, Jiang hopes to see huge industrial solar farms where fields of photovoltaic solar panels shift effortlessly along with the sunflowers that inspired him.

‘This is exactly what nature does,’ said Jiang, whose work was published on 1 August in Advanced Functional Materials and recently highlighted in Nature.