The US National Renewable Energy Laboratory (NREL) has conducted a proof-of-concept study according to which using femtosecond (fs) lasers to form glass-to-glass welds for solar modules would make the panels easier to recycle.
Made by California-based Trumpf Inc., the fs laser uses a short pulse of infrared light that melts the glass together to form a strong, hermetic seal, says the lab.
The production process majorly in use currently involves the semiconductors being sandwiched between 2 sheets of glass laminated together with polymer sheets. Using welds would do away with the need to use plastic polymer sheets that are right now laminated into solar modules, since it is the polymers that make recycling more difficult, according to the research.
NREL argues that the solar PV modules made with laser welds can be shattered at the end of their working life and the glass and metal wires can be easily recycled, and silicon can be reused.
Their research claims that fs laser, glass/glass welds are 'essentially as strong as the glass itself.' This glass weld can be used on any type of solar technology, namely silicon perovskites and cadmium telluride (CdTe) because the heat of the weld is confined to a few millimeters from the laser focus.
According to the results of the study conducted by the Durable Module Materials Consortium, the fs laser welds are strong enough for a suitably framed module to pass the IEC 61215 static load test with a load of 5400 Pa.
"As long as the glass doesn't break, the weld is not going to break," said Senior Scientist and Group Manager for the High-Efficiency Crystalline Photovoltaics group in the Chemistry and Nanoscience department at NREL David Young. "However, not having the polymers between the sheets of glass requires welded modules to be much stiffer."
Researchers share that the fs laser weld method offers superior strength with hermetic sealing at a compelling cost, compared to a different type of edge sealing using nanosecond lasers and a glass frit filler tried in the past. The latter method was too brittle for use in outdoor module designs, they add.
Calling it 'definitely high risk, high reward,' the researchers believe this method points to a direction for further research to extend the life of solar modules to over 50 years and to allow easier recycling.
The research work led by Young is now published in a paper in the IEEE Journal of Photovoltaics under the title Towards Polymer-Free, Femto-Second Laser-Welded Glass/Glass Solar Modules. It was funded by the US Department of Energy's Solar Energy Technologies Office.