Path to easier recycling of solar modules

The welds would eliminate the necessity for plastic polymer sheets which can be now laminated into solar modules but make recycling tougher. At the top of their useful lifespan, the modules made with the laser welds could be shattered. The glass and metal wires running through the solar cells could be easily recycled and the silicon could be reused.

“Most recyclers will confirm that the polymers are the predominant issue by way of inhibiting the means of recycling,” said David Young, senior scientist and group manager for the High-Efficiency Crystalline Photovoltaics group within the Chemistry and Nanoscience department at NREL. Young is lead creator of a brand new paper outlining using laser welds for solar modules. The paper, “Towards Polymer-Free, Femto-Second Laser-Welded Glass/Glass Solar Modules,” appears within the IEEE Journal of Photovoltaics.

Written with NREL colleagues Tim Silverman, Nicholas Irvin, and Nick Bosco, the paper also counts as its coauthors two employees of Trumpf Inc., the California company that made the femtosecond laser involved. A femtosecond laser uses a brief pulse of infrared light that melts the glass together to form a robust, hermetic seal.

The glass weld could be used on any form of solar technology — silicon, perovskites, cadmium telluride — since the heat of the weld is confined to a number of millimeters from the laser focus.

Solar modules are made from semiconductors designed to capture a particular portion of the solar spectrum, harnessing sunlight to create electricity. Typically, the semiconductors are sandwiched between two sheets of glass laminated along with polymer sheets.

NREL’s research showed that femtosecond laser, glass/glass welds are essentially as strong because the glass itself.

“So long as the glass doesn’t break, the weld is just not going to interrupt,” he said. “Nonetheless, not having the polymers between the sheets of glass requires welded modules to be much stiffer. Our paper showed that with proper mounting and a modification to the embossed features of the rolled glass, a welded module could be made stiff enough to pass static load testing.”

NREL’s research is the primary to make use of a femtosecond laser to form glass/glass welds to be used in a module. A unique form of edge sealing using nanosecond lasers and a glass frit filler was tried up to now, however the welds proved too brittle to be used in outdoor module designs. The femtosecond laser welds offer superior strength with hermetic sealing at a compelling cost.

Young said the research is “definitely high risk, high reward,” but points to a direction for further research to increase the lifetime of solar modules to beyond 50 years and to permit easier recycling.