Using microwaves improves production, recyclability of solar cells

Using microwaves improves production, recyclability of solar cells
Researchers have developed a more energy-efficient technique for producing solar cells that also makes them recyclable
Researchers have developed a more energy-efficient technique for producing solar cells that also makes them recyclable
View 1 Image
Researchers have developed a more energy-efficient technique for producing solar cells that also makes them recyclable
Researchers have developed a more energy-efficient technique for producing solar cells that also makes them recyclable

Solar cells are good for the environment, but they have downsides. They’re expensive to make, and there are limited ways to recycle them. But researchers have developed a new manufacturing technique that may address both of these issues.

It’s well known that solar power is good for the environment. There are no direct greenhouse gas emissions, and sunlight is a renewable resource that is unlikely to run out any time soon.

Solar panels are comprised of solar cells, which convert light energy from the sun or artificial light directly into electricity through the photovoltaic effect. But the disadvantages to making solar panels are that the production of solar cells is very energy-heavy and there are limited ways of recycling them once they’ve reached the end of their lifespan.

Now, researchers might have a solution. A team from Australia's Macquarie University has developed an improved, time-saving solar cell fabrication process with the added benefit of making them easier to recycle.

Silicon is the most common semiconductor material used in solar cells. To make solar panels, silicon undergoes a heat treatment process called annealing, which alters its physical properties and performance. Annealing is currently done in a furnace, requiring temperatures between 1,652 and 2,012 °F (900 to 1,100 °C).

The researchers found that using microwave radiation to heat the silicon was almost as efficient as using a furnace. Microwave heating is already used in rubber, ceramic and wood industries because of its energy efficiency, speed and uniformity of heating, and economic viability.

Microwave radiation selectively heats silicon, making the annealing process faster and extremely energy efficient. In addition, microwaves can be focused and used to selectively heat sections of the solar panel, making them good for annealing newer solar panels, which employ heterojunction technology, where crystalline and amorphous silicon are interwoven.

And, unlike a furnace that accumulates chemical substances during the heating process, microwave annealing is clean.

“So, there is less contamination,” said Binesh Veettil, lead author of the study. “And the whole process can all be undertaken at room temperature.”

Through their experiments with microwave annealing, the researchers discovered an added benefit: microwaving caused the plastic coating that protects the silicon plate from moisture and contamination to soften. This means the coating can be peeled off and the plate’s components reused.

“Until now, it made economic sense to just dump the panels in the landfill,” said Veettil. “In the rare instances when they are recycled, you crush the panels, heat them to about 1,400 °C [2,552 °F] and wash them with chemicals to remove the plastic – a highly energy-demanding process.”

The researchers intend to undertake further research to optimize the production process.

The study was published in the journal Applied Physics Letters.

Source: Macquarie University

Could re-annealing restore efficiency to an old panel? If we're going to have megatonnes of solar panels whose efficiency has dropped too much, it might be economical to restore them. The exterior coatings would have to be stripped, and the metal layer too, so it would be expensive for small runs, but for gigawatts of cells, maybe it would be economical.
Thomas McGuire
I wonder about the energy efficiency of this process, most solar panels will never generate the power equivalency of the energy used in their creation.
Expanded Viewpoint
You are right, Thomas! It's just like wind turbines, the amount of energy that is used to make them has been said to exceed the amount of power that they will generate over their life span. Now I haven't seen the actual numbers on the energy audit sheet to know for sure, but it might be true!
Back in about 1996 or so, a fellow took on the task of doing an energy audit of a typical nuke plant, adding up all of the Carbon based fuels needed to mine, transport and refine the Uranium ore, mine and process the Iron ore and other materials needed for the plant, and he showed that we would have been better off by just burning the Carbon based fuels directly in a regular steam plant to make the electricity! So the only conclusion that could be reached as to why we went to nuke plants, was as a cover story to get Uranium for making nuclear bombs!!
@Thomas McGuire The payback period for home solar panel arrays in the US is around 8 years. This is the point when the panels have generated more power than the cost of purchase. Since the cost of purchase includes the cost of manufacture + company profit, the panels have absolutely generated more power than the power needed to manufacture them.
@Expanded Viewpoint A recent Life Cycle Assessment study of a wind turbine installation in Brazil yielded an energy payback of 0.5 to 1 year. This includes the amount of energy used to manufacture and install them. The study cites other examples of off-shore and on-shore wind farms with paybacks of around 1 year.
What are problems with recycling solar panels? Perhaps main problem is no need to recycle them since they still have 80% of starting efficiency after 20-30 years. Who would throw away panels still making 80% power instead of installing some more new ones elsewhere. Even if they need recycling they are mostly glass, aluminium frame, some silicon (think sand) and little bit of copper. All recyclable without problem
@A-A-Ron thanks very much for the great reference.
@Thomas McGuire and @Expanded Viewpoint it's important to have verifiable references before making statements about things like this. It makes discussion so much easier and keeps us talking about facts rather than Facebook assertions.
Baker Steve
I don't much like the sound of making the plastic coating 'peelable' – what's to stop it peeling off in service, particularly in harsh environments?