Sunlight-Tracking Polymer, Inspired by Sunflowers, Could Maximize Solar Power

The SunBOTS bend toward light source and could help solar cells capture more direct sunlight all day long

Laslovarga via Wikimedia Commons under CC Attribution-Share Alike 3.0 Unported license

In recent decades, solar cells have gotten better and cheaper, leading to a boom in the solar energy industry. But most solar panels have one major drawback—they don’t move. That means the sunlight reaching them often comes in at an angle, which hinders maximum power production. But a new light-loving, sunflower-inspired polymer may help boost the productivity of solar panels in the near future.

The new polymer, described in a paper in the journal Nature Nanotechnology, is capable of phototropism, or the ability to follow the sun in its daily journey across the sky. Inventor Xiaoshi Qian of the University of California, Los Angeles and the team call the new polymer SunBOT, which stands for sunflower-like biomimetic omnidirectional tracker. Each stem is roughly one millimeter in diameter and infused with a nanomaterial that turns light into heat with a little “flower” coated with solar energy-collecting material at the top. When light hits one side of the stem, the material heats up and shrinks, bending the stem points directly at the light source while it moves around and strikes from various angles.

To test the SunBOTs, the team submerged a bot-covered panel in water with just the solar-gathering tips sticking out. To measure how much light had been converted into heat, they tracked how much water vapor the panel generated. They found that the SunBOTS produced 400 percent more vapor than materials that didn’t track the light source.

Seung-Wuk Lee, a bioengineer at the University of California, Berkeley, not involved in the study, tells Sofie Bates at Science News that the most promising use of the SunBOTs would be integrating the material with solar cells, which could give solar technology a huge boost. Currently, solar cells capture about 24 percent of the sunlight available. By allowing the cells to operate at a near-maximum absorption rate almost all day long, the SunBOTS could boost that 90 percent, reports Bates.

“That is a major thing that they achieved,” Lee says.

SunBOTs video 1

The team originally created a batch of SunBOTS using gold nanoparticles and a hydrogel. Additional experiments showed that other materials, including carbon black nanoparticles and liquid crystalline polymers, also worked. This suite of ready-to-use materials shows the bots’ promising versatility, Lee tells Bates.

While the most obvious use is to improve solar cells, the team writes in their paper that the light-sensitive stems may have other applications as well.

According to the paper:

This work may be useful for enhanced solar harvesters, adaptive signal receivers, smart windows, self-contained robotics, solar sails for spaceships, guided surgery, self-regulating optical devices, and intelligent energy generation (for example, solar cells and biofuels), as well as energetic emission detection and tracking with telescopes, radars and hydrophones.

The bots aren’t the only new tech the could improve the efficiency of solar cells—and advancements in solar energy are progressing rapidly. Earlier this year, MIT researchers found a way to use organic photovoltaic cells that allow photons of sunlight to “kick” loose two electrons instead of just one, which can boost solar cell output. Researchers are also making progress on solar cells made of perovskite, or materials with a unique crystal structure that allows them to be much more efficient than the current generation silicon solar cells. Add to that an array of coatings that improve solar cell efficiency and the advent of thinner, more flexible solar panels and the future of energy is looking decidedly sunny.

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