New welding technology makes solar panels easy to recycle

A proof-of-concept study conducted by researchers at the US Department of Energy’s National Renewable Energy Laboratory (NREL) and Trumpf Inc., found that the use of femtosecond lasers to form glass-to-glass welds for solar modules would make the panels easier to recycle.

In a paper published in the IEEE Journal of Photovoltaics, the researchers behind the development explain that 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 lifespan, the modules made with the laser welds can be shattered. The glass and metal wires running through the solar cells can be easily recycled and the silicon can be reused.

“Most recyclers will confirm that the polymers are the main issue in terms of inhibiting the process of recycling,” David Young, lead author of the article, said in a media statement.

Femtosecond laser

To carry out their experiment, the scientists employed a femtosecond laser which uses a short pulse of infrared light that melts glass together to form a strong, hermetic seal.

The glass weld can be used on any solar technology—silicon, perovskites, cadmium telluride—because the weld heat is confined to a few millimetres from the laser focus.

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

NREL’s research showed that 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 said. “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.”

This research is the first to employ a femtosecond 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.

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