NREL researchers find path to easier solar panel recycling

According to a proof-of-concept study conducted by researchers at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL), the use of femtosecond lasers to form glass-to-glass welds for solar panels would make them easier to recycle.

The study claims the welds would eliminate the need for plastic polymer sheets that are now laminated into solar modules but make recycling more difficult. At the end of their useful lifespan, the study says modules made with the laser welds can be shattered, and the glass and metal wires running through the solar cells can be easily recycled and the silicon can be reused.

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“Most recyclers will confirm that the polymers are the main issue in terms of inhibiting the process of recycling,” says David Young, senior scientist and group manager for the High-Efficiency Crystalline Photovoltaics group in the Chemistry and Nanoscience department at NREL.

Young is the lead author of a new paper outlining the use of laser welds for solar modules titled, “Towards Polymer-Free, Femto-Second Laser-Welded Glass/Glass Solar Modules,”, which appears in the IEEE (Institute of Electrical and Electronics Engineers) Journal of Photovoltaics.

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

The research shows the glass weld can be used on any type of solar technology, including silicon, perovskites and cadmium telluride, because the heat of the weld is confined to a few millimeters from the laser focus. NREL adds that solar modules are made of semiconductors designed to capture a specific portion of the solar spectrum, harnessing sunlight to create electricity, and the semiconductors are sandwiched between two sheets of glass laminated together with polymer sheets.

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

“As long as the glass doesn’t break, the weld is not going to break,” Young says. “However, 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 can be made stiff enough to pass static load testing.”

NREL says its research is the first to use such a laser to form glass/glass welds for use in a module. A different type of edge sealing using nanosecond lasers and a glass frit filler was tried in the past, but the welds proved too brittle for use in outdoor module designs. The femtosecond laser welds offer superior strength with hermetic sealing at a compelling cost, NREL says.

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Young says the research is “definitely high risk, high reward,” but points to a direction for further research to extend the life of solar modules to beyond 50 years and to allow easier recycling.

The research was done through the Durable Module Materials Consortium, which is led by NREL and funded through the U.S. Department of Energy’s Solar Energy Technologies Office in the Office of Energy Efficiency and Renewable Energy.