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Researchers from the University of Los Angeles and Arizona State University have developed tiny artificial sunflowers that can automatically lean in the direction of sunlight.
In a study published this month in Nature Nanotechnology, the team reported the innovative new system, called SunBOT (Sunflower-like Biomimetic Omnidirectional Tracker), which has a stem made of a special material that reacts to light, and a ‘flower’ which has integrated solar cells.
Efficiency (and Looks)
The world is waking up to climate change, and initiatives are being set in place to reduce emissions around the globe, cut back on relying on our almost depleted non-renewable energy sources, and assist green technology in being adopted on a large scale.
Climate change is motivating researchers to find new ways to optimize renewable energy harvesting techniques so that they can work more efficiently, converting as much useable power as possible from their renewable source. There is also a focus now on the aesthetics of renewable energy systems. Renewable energy has made great strides in the past decade, allowing researchers to dedicate time to solving how renewable energy methods can blend into the environment better. Developing aesthetics in this way will increase their rate of adoption and give them greater longevity.
These two challenges are what led the LA and Arizona team to design SunBOT.
Inspiration from Nature
The team of US scientists looked to nature for inspiration for their innovative design. Increasingly, biometric devices are being used to solve a variety of challenges across a range of industries. These devices emulate nature in their designs and mimic the natural intuitiveness of biological mechanisms and structures.
In nature, there are many organisms that can adjust their movement to pursue a light source. This is known as phototropism, and it is a highly common behavior in plants, which adapt to the direction of the sunlight.
For plants to achieve this feat, they have stems which bend in response to a light source: as sunlight hits part of a plant, it triggers the release of the hormone auxin, which diffuses across to the shaded side of the plant, and causes the cells to grow longer. This adjustment in cell length causes the stem to bend in the direction of the light, resulting in the plant benefiting from accessing optimal light energy.
The researchers wanted to mimic this intuitive behavior and aimed to develop the first artificial smart material that could copy the nastic movements of plants. They noted that the establishment of such an artificial material, that can intrinsically detect and track a moving stimulus, had not yet been accomplished. They set about to create a material with this tropistic capability.
400% More Energy Captured
Using the model of phototropism in plants, the team was able to create an artificial phototropic system that relies on nanostructured stimuli-responsive polymers that have the ability to track and align to the direction of sunlight.
To achieve this they created a built-in feedback loop within the photothermal and mechanical properties of the polymers. When the stem is in the direction of sunlight, the feedback loop causes the stem to heat up and shrink, bending the stem towards the light source. As the stem bends, it becomes shadowed as the artificial flower aligns with the light, and this shading cools the stem and stops further shrinkage. Each SunBOT measures just 1 mm wide, making them easier to blend into surroundings in comparison with traditional large solar panels.
The results of their study demonstrated that their system was able to achieve a 400% increase in solar energy harvesting in comparison with conventional systems.
A Shift in the Solar Energy Sector
Such a significant increase in energy harvesting could help with the widespread adoption of solar power, and help to reduce emissions and switch to renewable energy sources.
The scientists involved in the project believe that the principle has the potential to be developed for a broad range of stimuli, opening up its possible use in other applications.
References and Further Reading
Qian, X., Zhao, Y., Alsaid, Y., Wang, X., Hua, M., Galy, T., Gopalakrishna, H., Yang, Y., Cui, J., Liu, N., Marszewski, M., Pilon, L., Jiang, H. and He, X. (2019). Artificial phototropism for omnidirectional tracking and harvesting of light. Nature Nanotechnology, 14(11), pp.1048-1055. https://www.nature.com/articles/s41565-019-0562-3
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