Researchers develop solar cells that follow the sun

A team of engineers and an artist drew inspiration from kirigami, the Japanese art of paper folding, to make solar panels that follow the sun.

The paper on this work titled “Dynamic kirigami structures for integrated solar tracking” was published in the journal Nature Communications.

Solar panels can absorb 40% more light if they can track the movements of the sun throughout the day. However, conventional motorized trackers are too heavy to be used on the roofs of cars and houses.

“The design takes what a large tracking solar panel does and condenses it into something that is essentially flat,” said lead researcher Aaron Lamoureux, a doctoral student in materials science and engineering in the University of Michigan.

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.

“The beauty of our design is, from the standpoint of the person who’s putting this panel up, nothing would really change,” said Max Shtein, associate professor of materials science and engineering. “But inside, it would be doing something remarkable on a tiny scale: the solar cell would split into tiny segments that would follow the position of the sun in unison.”

Solar cell researchers think of tracking in terms of how much of a solar panel the sun can “see.” When the panel is at an angle, it looks smaller. By designing an array that tilts and spreads apart when the sun’s rays are coming in at lower angles, they raise the effective area that is soaking up sunlight.

To explore patterns, the team of engineers worked with paper artist Matthew Shlian, a lecturer in the U-M 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, 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 in proportion to how much the mesh is stretched, to an accuracy of about one degree.

To make the solar array, Kyusang Lee, a doctoral student in electrical engineering, built custom solar cells in the lab of Stephen Forrest, the Peter A. Franken Distinguished University Professor of Engineering and Paul G. Goebel Professor of Engineering. He and Lamoureux attached them to an uncut piece of Kapton, leaving spaces for the cuts. Then, Lamoureux patterned the Kapton with the laser cutter.

The optimized 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% improvement over a stationary panel. Conventional trackers produce about 40% more energy than stationary panels under the same conditions, but they are bulky, prone to catching the wind and ten or more times heavier, Shtein said.

“We think it has significant potential, and we’re actively pursuing realistic applications,” he said. “It could ultimately reduce the cost of solar electricity.”