Lightweight solar cells track the sun, providing 40 percent more energy than fixed cells

Inspired by Japanese paper-cutting art, they replace heavy conventional Sun-tracking systems
September 14, 2015

By borrowing from kirigami, the ancient Japanese art of paper cutting, researchers at the University of Michigan have developed solar cells that can track the sun. A flat plastic sheet backing the solar cells splits into wavy, connected ribbons when stretched. The tilt of each of the cells depends on the stretching, a simple mechanism for tracking the sun across the sky. (credit: Aaron Lamoureux)

University of Michigan engineers have developed an innovative array of solar cells that can capture up to 40 percent more energy than conventional fixed solar cells. The trick: borrowing from kirigami (the ancient Japanese art of paper cutting), the solar cells are aimed at different angles, allowing for part of the array to be always perpendicular to the Sun’s rays.

“The design takes what a large tracking solar panel does and condenses it into something that is essentially flat,” said Aaron Lamoureux, a doctoral student in materials science and engineering and first author on the open-access paper in Nature Communications. Residential rooftops would need significant reinforcing to support the weight of conventional costly sun-tracking systems, he said.

Tilting toward the Sun

Cuts in plastic substrate allow for an array of solar cells titled at different angles (credit: University of Michigan)

To explore patterns for the array, the engineers worked with paper artist Matthew Shlian, a lecturer in the U-M School of Art and Design, who showed them how to create the solar array in paper using a plotter cutter. Lamoureux then made more precise patterns in Kapton, a space-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 at different angles in proportion to how much the mesh is stretched, to an accuracy of about one degree.

The design with the very best solar-tracking promise was impossible to make at U-M 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.

“We think it has significant potential, and we’re actively pursuing realistic applications,” said Max Shtein, associate professor of materials science and engineering. “It could ultimately reduce the cost of solar electricity.”

The study was funded by National Science Foundation and NanoFlex Power Corporation. The university is pursuing patent protection for the intellectual property, and is seeking commercialization partners to help bring the technology to market.

Michigan Engineering | Kirigami for sun-tracking solar cells

Abstract of Dynamic kirigami structures for integrated solar tracking

Optical tracking is often combined with conventional flat panel solar cells to maximize electrical power generation over the course of a day. However, conventional trackers are complex and often require costly and cumbersome structural components to support system weight. Here we use kirigami (the art of paper cutting) to realize novel solar cells where tracking is integral to the structure at the substrate level. Specifically, an elegant cut pattern is made in thin-film gallium arsenide solar cells, which are then stretched to produce an array of tilted surface elements which can be controlled to within ±1°. We analyze the combined optical and mechanical properties of the tracking system, and demonstrate a mechanically robust system with optical tracking efficiencies matching conventional trackers. This design suggests a pathway towards enabling new applications for solar tracking, as well as inspiring a broader range of optoelectronic and mechanical devices.