Microwave Technology Solar Panel Recycling

Researchers at Macquarie University in Sydney have made a groundbreaking discovery that promises to revolutionize the production and recycling of solar cells. Currently, during solar panel fabrication, silicon undergoes several high-temperature procedures known as annealing, traditionally conducted in an oven. This process, however, is laborious and energy-intensive.

Enter microwave annealing, a technique spearheaded by senior lecturer Binesh P Veettil and his team, and demonstrated in a research paper published in Applied Physics Letters. This process utilizes microwave radiation to heat silicon, leading to almost instantaneous effects, and thereby conserving substantial amounts of energy.

According to the research team, in their findings published in Applied Physics Letters, "Microwave annealing of semiconductor devices has not been extensively researched and is rarely utilized in the industry, yet it has the potential to significantly reduce the time and cost associated with large-volume semiconductor processing."

Benefits for solar panel recycling

One of the intriguing benefits of microwave annealing lies in its potential for solar panel recycling. The process leaves the laminated panel of glass, plastic, and aluminium largely unaffected, softening the plastic coating that protects the silicon plate and allowing it to be mechanically peeled off. This contrasts starkly with the current recycling methods, which involve crushing the panels and washing them with chemicals, a process Veettil describes as "highly energy-demanding."

“Until now it made economic sense to just dump the panels in the landfill,” says Dr Veettil. “In the rare instances when they are recycled, you crush the panels, heat them to about 1400°C and wash them with chemicals to remove the plastic — a highly energy-demanding process. But now, as the solar panels which began to be installed in vast numbers about 20-30 years ago are reaching the end of their life and being decommissioned, governments are demanding they be recycled.”

Selective annealing

Microwave annealing offers additional advantages, including the ability to focus the radiation, allowing selective and highly tuned heating. This precision is particularly beneficial in reprocessing the increasingly popular PV panels that feature heterojunction technology, where crystalline and amorphous silicon are interleaved.

In addition to recycling benefits, microwave annealing offers selective heating. This precision means annealing can be directed to specific parts of the solar panel, which is particularly advantageous for newer panels employing heterojunction technology - an arrangement of interleaved crystalline and amorphous silicon.

Another major advantage is the cleanliness of the process. Unlike an oven where chemicals can be shed from the walls, microwave annealing occurs in a clean environment, reducing contamination. "And the whole process can be undertaken at room temperature," Veettil explains.

The future for microwave annealing

Aside from the silicon solar cells project, other studies at Macquarie University are also exploring the applications of microwave annealing. Co-author Shujuan Huang leads a group examining its use in perovskite solar cells, where microwave radiation has led to more efficient solar cells.

Microwave annealing technology presents significant progress for the solar power industry, improving solar cell production and recycling with energy savings, faster processing times, and cleaner manufacturing, and with the potential for even greater impact in the future.