Engineers attempting to make solar energy more affordable for the average user have long faced a conundrum. Solar panels capture much more energy when they can shift to follow the movement of the sun across the sky. But the apparatuses needed to move the panels are expensive, and they are generally too heavy to use on slanted roofs.
Now, researchers at the University of Michigan have borrowed from kirigami, the Japanese art of paper cutting, to make a new kind of tracking panel. Flat plastic sheets of solar cells are scored with small cuts using a laser. When pulled, the sheets twist open into three dimensions, offering raised surfaces to face the direction of the sun.
“Here we have a substrate, which is really thin. It’s lightweight, it doesn’t have to be tilted with big supports or machines,” says Max Shtein, an associate professor of materials science and engineering at the university. “All you have to do is kind of stretch it.”
The kirigami solar cells are the result of a collaboration between Shtein’s team and paper artist Matthew Shlian. Shlian, who is known for his futuristic-looking sculptures made of geometrically folded, pleated and sliced paper, had come by Shtein’s lab several years ago, looking for scientists to work with. He and Shtein hit it off immediately. They would meet regularly, trying to figure out how Shlian’s expertise with manipulating flat surfaces could be used in one of Shtein’s projects. Then one day, Shlian showed Shtein a form he’d been working with, where a paper is sliced with small slits. When Shtein pulled on the ends, it expanded into a three dimensional mesh.
“I thought ‘ah ha, bingo!’” Shtein recalls. This would be perfect for a solar panel.
The team ran a simulation using the kirigami panels, based on conditions during the summer solstice in Arizona. The simulation suggested the kirigami panel worked almost as well as a conventional mechanically-powered tracking solar panel, and it was 36 percent more efficient than a stationary panel. The results were reported in the journal Nature Communications.
The kirigami panels are years away from consumer use—Shtein hopes to obtain more funding to further the project. But they could potentially be cheaper than conventional panels. While the cost of solar modules has gone down dramatically over the years (about 75 percent since 2009, according to an International Renewable Energy Agency report), the price of installation has remained stubbornly high. The kirigami panels would likely be easier to install and require less heavy equipment.
The project is still in the conceptual stage; the team has not yet created a working prototype of the panel. Further testing will be needed to see if the thin, flexible solar sheets are durable enough to be tugged into new positions daily over a period of years. If the team hopes to build a panel capable of lasting for 25 years, the sheets, by Shtein's estimate, will need to withstand some 25,000 movements.
“Can it do that?” Shtein asks. “We haven’t tested it that much.”
It’s also not yet clear what kind of mechanism would be used to stretch the panels, though it would likely be much lighter than traditional trackers.
The same kirigami pattern used on the solar panels may have applications far beyond solar energy, Shtein says. It's possible the pattern could be useful in cameras and the aerospace and automotive industries, though Shtein says he’s not at liberty to give much detail.
Origami, kirigami’s better-known cousin, has been used for many scientific and technical applications, from heart stents to aerospace mirrors to car airbags. Kirigami itself was recently used by Cornell researchers to make tiny, bendable transistors. Cut from graphene (sheets of carbon one atom thick), the transistors could be used to create nanomachines for any number of purposes.