Femtosecond Lasers Solve Solar Panels’ Recycling Issue

Solar panels are built to last 25 years or more in all kinds of weather. Key to this longevity is a tight seal of the photovoltaic materials. Manufacturers achieve the seal by laminating a panel’s silicon cells with polymer sheets between glass panes. But the sticky polymer is hard to separate from the silicon cells at the end of a solar panel’s life, making recycling the materials more difficult.

Researchers at the U.S. National Renewable Energy Lab (NREL) in Golden, Colo., say they’ve found a better way to seal solar modules. Using a femtosecond laser, the researchers welded together solar panel glass without the use of polymers such as ethylene vinyl acetate. These glass-to-glass precision welds are strong enough for outdoor solar panels, and are better at keeping out corrosive moisture, the researchers say.

A femtosecond laser welds a small piece of test glass.NREL

“Solar panels are not easily recycled,” says David Young, a senior scientist at NREL. “There are companies that are doing it now, but it’s a tricky play between cost and benefit, and most of the problem is with the polymers.” With no adhesive polymers involved, recycling facilities can more easily separate and reuse the valuable materials in solar panels such as silicon, silver, copper, and glass.

Because of the polymer problem, many recycling facilities just trash the polymer-covered silicon cells and recover only the aluminum frames and glass encasements, says Silvana Ovaitt, a photovoltaic (PV) analyst at NREL. This partial recycling wastes the most valuable materials in the modules.

“At some point there’s going to be a huge amount of spent panels out there, and we want to get it right, and make it easy to recycle.” —David Young, NREL

Finding cost-effective ways to recycle all the materials in solar panels will become increasingly important. Manufacturers globally are deploying enough solar panels to produce an additional 240 gigawatts each year. That rate is projected to increase to 3 terawatts by 2030, Ovaitt says. By 2050, anywhere from 54 to 160 million tonnes of PV panels will have reached the end of their life-spans, she says.

“At some point there’s going to be a huge amount of spent panels out there, and we want to get it right, and make it easy to recycle,” says Young. “There’s no reason not to.” A change in manufacturing could help alleviate the problem—although not for at least another 25 years, when panels constructed with the new technique would be due to be retired.

In NREL’s technique, the glass that encases the solar cells in a PV panel is welded together by precision melting. The precision melting is accomplished with femtosecond lasers, which pack a tremendous number of photons into a very short time scale–about 1 millionth of 1 billionth of a second. The number of photons emitted per second from the laser is so intense that it changes the optical absorption process in the glass, says Young. The process changes from linear…