Blanketing swaths of open land. Covering the roofs of homes. Floating on canals and reservoirs. Solar panels are popping up everywhere, playing a key part in helping the world move toward renewable energy.
But the rapid rise of solar power might not be all sunshine. Although the life span of panels is increasing, many that have been installed could only last for up to a few decades and could become a waste problem if they wind up in landfills. There are also questions about whether the small amounts of toxic metals within them, such as lead, could be harmful to the environment. But so far, recycling them has been difficult and expensive.
Researchers in Australia say they have come up with a way that could help solve that problem using a common household technology: the microwave.
The same microwave technology that warms food could be used to heat up parts of a solar panel, making it easier to take it apart and recover materials, said Binesh Puthen Veettil, a senior lecturer in the School of Engineering at Macquarie University, who led the research.
“We started our work with a modified kitchen microwave,” Veettil said. “The principle is the same and the frequency we’re using is 2.45 gigahertz, which is the same as what a kitchen microwave uses.”
The peer-reviewed research comes amid growing interest in figuring out the fate of old panels. The solar power community “is working on doing the right thing because it’s a very manageable problem,” said Teresa Barnes, a photovoltaics expert with the Energy Department’s National Renewable Energy Laboratory.
“It’s a technologically solvable problem,” she said. “It’s an economically solvable problem.”
Solar panels are generally constructed out of layers of different materials, including aluminum, glass, silicon, plastic, and valuable metals such as copper and silver. These layers are sealed together – and to recycle the components, the panels have to be disassembled.
Silver is the most valuable material in solar panels, said Meng Tao, an engineering professor at Arizona State University and founder of a Tuscon-based solar panel recycling company called TG Companies. One panel typically has about a quarter of an ounce of silver, which could be worth $5, Tao said.
The aluminum frame and glass, which typically make up about 85 percent of the total weight of a solar panel, also have value and can be recovered, he said.
But panels can also contain other metals, such as lead, which can be toxic at certain concentrations.
The challenge with silicon solar modules is “people don’t quite know how to handle them,” Barnes said. “There’s a real mix of regulations. There’s a mix of materials that can be in there.”
Currently, about 10 to 15 percent of a solar panel’s materials by weight are being recovered at end of life, Tao said. The goal, he said, should be to reach 90 to 95 percent.
One major challenge is cost. Recycling one panel costs about $20 to $30, he said, but the recovered materials are typically worth about $3.
“Solar panels are improperly recycled,” he said. All the recoverable materials could probably be worth $11 or $12 per panel, he noted.
But the panels, which are designed to withstand the elements, are also difficult to take apart, he and other experts say. Removing the polymer layers that protect a panel from the weather often requires high temperatures – a process known as delamination.
“Besides aluminum, if you want to recover anything else, you must do delamination first,” Tao said. “Delamination is really the next biggest bottleneck.”
That’s the challenge tackled by the Australian researchers. They found that when exposed to the microwave treatment, a solar panel’s protective plastic coating softened to the point where it could be peeled off, meaning the panel could be easily delaminated and its parts retrieved without using harsh chemicals.
This approach could allow recyclers to recover the high-quality glass from panels whole instead of having to crush it and sell the pieces as raw material, Veettil said.
“Just by extracting that glass intact, you are readily making solar panel recycling economically more viable,” he said.
The Australian researchers aren’t the only group attempting to tackle the delamination issue. One company, for example, is experimenting with using a heated blade to remove the coating while another is trying an infrared lamp, Tao said.
Other experts, however, say there are questions about whether recovering the glass as one piece is easily doable – or worth it.
“There’s a lot of processes that propose to take those glass sheets off full, and there’s a big challenge with that,” Barnes said. “If you’ve ever imagined trying to pull your windows apart in your house, even if you got really good and you had a lot of practice at it, you had a good process, it would still be difficult.”
And there’s likely a limited market for older-size glass, because the module sizes are constantly changing, and the glass industry also uses old broken glass, she said.
“The benefits of a decarbonized electricity system greatly outweigh the risks of having some solid waste at the end of life, especially when we’re already putting the infrastructure in place to start to manage that,” she said.