By Andrea Hargraves 
Microwave technology invented at Australia’s Macquarie University promises to provide “significant energy savings” in the manufacture of photovoltaic solar cells, while also making it easier to recycle them at the other end of their life cycle.
A new solution for solar PV panel recycling
In an article published in the US Journal Applied Physics Letters, a team at Macquarie Uni led by Dr. Bench Putin Vettel showed that microwave radiation works equally well for “hardening” solar cells – a high-temperature process usually done by cooking them in an oven.
Not only does the study show that it heats cells using microwave radiation “almost as efficiently” as conventional processes, it also saves significant time and energy and offers other benefits – Including for the sustainability of solar cells.
“Because microwave radiation selectively heats silicon, it leads to almost immediate effects with significant energy savings.”said the team from the College of Engineering.
This is partly because the rest of the glass, plastic and aluminum laminated panels are largely unaffected. And it is this property that has led to the unexpected recycling feature, for which the group has a patent pending.”
Advantages of the new solar cell recycling method
An unexpected, patent-worthy benefit, the researchers explain, is that, under microwave treatment, the plastic coating protecting the silicone softens so much that it can be mechanically peeled off.
This means that silicon wafers can be easily removed and their components reused without the need for harsh chemicals – and a much stronger economic case can be made against simply throwing old solar PV panels into landfills.
“Now, as solar panels that began to be installed in large numbers around 20-30 years ago are nearing the end of their useful lives and being decommissioned, governments are calling for them to be recycled.”says d. Viettel.
Using current technology, Vettel says this is shredding the panels, heating them to about 1,400 degrees Celsius, and washing them with chemicals to remove the plastic—”a high-energy process,” he says.
In addition to recycling, microwave annealing has several other advantages, including an improvement in the type of highly tunable selective annealing needed for more recent solar heterogeneous technology, in which crystalline and amorphous silicon are interleaved.
In these cells, faster and better-directed microwave annealing may be very beneficial, say the researchers.
The more precise focus also means that the annealing can be directed at specific parts of solar panels, making it ideal for annealing solar panels with more complex internal structures made for special purposes.
Veettil also notes that microwave annealing is a cleaner process with less contamination and can be done at room temperature.
Meanwhile, the co-author of the annealing work, Associate Professor Shujuan Huang, is also investigating the possibility of microwave annealing in perovskite solar cells.
Investigation d. Veettil in association with the PV School University of New South Wales It was supported by funding from the Australian Center for Advanced Photovoltaics and the Australian Renewable Energy Agency.
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