A new microwave technology can ease solar cell recycling

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As a renewable source of energy, solar power has become a trend. Unlike fossil fuels like coal, solar power is clean and emissions-free. While it is good for the environment, it has some drawbacks. It is not entirely cost-efficient, and we need better ways of recycling it.

But now we’re learning that researchers in Sydney may have found a way to tackle this issue.

A solar panel consists of a layer of silicon cells. Silicon, acting as a conductor and an insulator for solar panels, is the second most abundant material found on the planet after oxygen. The silicon found in solar panels is highly processed and goes through annealing. This heat treatment process is used to increase the flexibility of a material and reduce its hardness.

Currently, annealing is done in a furnace with a high temperature ranging between 1652 and 2012 °F (900 and 1100 °C). In a paper published this week, a team has shown that heating silicon solar cells using microwave radiation is nearly as efficient as using a furnace. However, the former is time-saving and energy efficient, over many other advantages.

In a statement released by Macquarie University, the researchers explain that microwave radiation selectively heats silicon and leaves the laminated panel of glass, aluminum, and plastic largely unaffected. This has a significant recycling benefit.

Under treatment, the plastic coating, which protects the silicon plate from contamination and moisture, gets softened and hence can be peeled off mechanically. The scale can be then easily delaminated, and its components can be reused without harsh chemicals.

Macquarie University

“Until now, it made economic sense just to dump the panels in the landfill,” says Dr. Binesh Puthen Veettil, study lead and senior lecturer of the School of Engineering at Macquarie University. “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.”

Microwave heating is an economically viable, fast, and energy-saving option used extensively in the rubber, wood, and ceramic industries.

The research, done in collaboration with the School of photovoltaics at UNSW Sydney, was funded by the Australian Centre for Advanced Photovoltaics and is supported by the Australian Government.

Study abstract:

The microwave annealing of semiconductor devices has not been extensively researched. It is rarely utilized in industry, yet it has the potential to significantly reduce the time and cost associated with large-volume semiconductor processing, such as the various heating and annealing processes required in the manufacture of photovoltaic modules. In this paper, we describe microwave annealing of silicon solar cells, the effective passivation of light-induced defects, and a reduction in light-induced degradation. We find that silicon solar cells are heated rapidly in a microwave field and that effective B–O defect passivation can be achieved by microwave processing in less than 2 s. Microwave annealing yields similar results as compared to rapid thermal annealing.

The authors acknowledge ACAP funding for enabling this work. This program has been supported by the Australian Government through the Australian Renewable Energy Agency (ARENA). Responsibility for the views, information, or advice expressed herein is not accepted by the Australian Government.