Kirigami-inspired solar cells can track the sun
12 September 2015
Solar cells capture up to 40 percent more energy when they can track the sun across the sky, but conventional, motorised tracking systems can be heavy and bulky.
Residential rooftops, for example, need significant reinforcing to support the weight of conventional sun-tracking systems.
Now, by borrowing from kirigami, the ancient Japanese art of paper cutting, researchers at the University of Michigan (UM) have developed solar cells that can have it both ways.
"The design takes what a large tracking solar panel does and condenses it into something that is essentially flat," says Aaron Lamoureux, a doctoral student at UM and first author of a paper desacribing the work in the journal, Nature Communications.
A team of engineers and an artist developed an array of small solar cells that can tilt within a larger panel, keeping their surfaces more perpendicular to the sun's rays.
To explore suitable patterns, the team of engineers worked with paper artist Matthew Shlian, a lecturer in the UM School of Art and Design. Shlian showed Lamoureux and Shtein how to create them in paper using a plotter cutter. Lamoureux then made more precise patterns in Kapton, an aerospace-grade plastic, using a carbon-dioxide laser.
Although the team tried more complex designs, the simplest pattern worked best. With cuts like rows of dashes, the plastic pulled apart into a basic mesh. The interconnected strips of Kapton tilt in proportion to how much the mesh is stretched, to an accuracy of about one degree.
To make the solar array, Lamoureux and colleagues built custom solar cells and attached them to an uncut piece of Kapton, leaving spaces for the cuts. They then patterned the Kapton with the laser cutter.
The design with the very best solar-tracking promise was impossible to make at UM because the solar cells would be very long and narrow. Scaling up to a feasible width, the cells became too long to fit into the chambers used to make the prototypes on campus, so the team is looking into other options.
The optimised design is effective because it stretches easily, allowing a lot of tilt without losing much width. According to the team's simulations of solar power generation during the summer solstice in Arizona, it is almost as good as a conventional single-axis tracker, offering a 36 percent improvement over a stationary panel.