Microwave technology invented at Australia’s Macquarie University promises to deliver “huge energy savings” in the manufacture of photovoltaic solar cells, while also making them easier to recycle at the other end of their life cycle.
New solution for recycling photovoltaic solar panels
In an article published in the US Journal Applied Physics Letters, a team at Macquarie Uni led by dr. Binesh Puthen Veettil showed that microwave radiation works equally well to “anneal” solar cells – a high-temperature process normally carried out by cooking them in an oven.
The study showed that not only does it heat cells using microwave radiation “almost as efficiently” as traditional 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 results in near-instantaneous effects with massive energy savings”said the team from the School of Engineering.
“This is partly because the rest of the laminated glass, plastic and aluminum panel is largely untouched. And that property led to an unexpected recycling benefit, for which the group has a patent pending.”
Advantages of the new solar cell recycling method
The researchers explain that the unexpected advantage worth patenting is that, under microwave treatment, the plastic coating protecting the silicon becomes so soft that it can be peeled off mechanically.
This means that silicon wafers can be easily delaminated and their components reused without the need for harsh chemicals – and a much stronger economic case can be made for simply dumping old photovoltaic solar panels in landfills.
“Now, as solar panels that were installed in large numbers some 20-30 years ago are reaching the end of their useful life and being decommissioned, governments are demanding that they be recycled.”, this oh Dr. Veettil.
Using current technology, Veettil says it shreds the panels, heats them to around 1400°C and washes them with chemicals to remove the plastic – “a highly energy-intensive process”, he says.
Besides recycling, microwave annealing has a number of other advantages, including being better at the kind of selective, highly tuned annealing needed for more modern solar heterojunction technology, where crystalline and amorphous silicon are intertwined.
In these cells, the use of faster and better targeted microwave-based annealing could be very beneficial, say the researchers.
A more precise focus also means that the annealing can be directed to specific parts of the solar panel, making it ideal for annealing solar panels with more complicated internal structures made for special purposes.
Veettil also notes that microwave annealing is a much cleaner process with less contamination and can be performed at room temperature.
Meanwhile, a co-author of the annealing paper, Associate Professor Shujuan Huang, is also looking at the potential of microwave annealing in perovskite solar cells.
The investigation of Dr. Veettil in collaboration with the photovoltaic school of UNSW was supported with funding from the Australian Center for Advanced Photovoltaics and the Australian Renewable Energy Agency.
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