Recycling Car Batteries into Solar Cells

Thursday, August 21, 2014 @ 05:08 PM gHale

Discarded car batteries could end up going green by recycling into new, long-lasting solar panels that provide emissions-free power.

This new system makes use of a compound called perovskite — specifically, organolead halide perovskite — a technology rapidly progressing from initial experiments to a point where its efficiency is nearly competitive with that of other types of solar cells.

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“It went from initial demonstrations to good efficiency in less than two years,” said Angela M. Belcher, the W.M. Keck Professor of Energy at MIT. Already, perovskite-based photovoltaic cells have achieved power-conversion efficiency of more than 19 percent, which is close to that of many commercial silicon-based solar cells.

Initial descriptions of the perovskite technology identified its use of lead, whose production from raw ores can produce toxic residues, as a drawback. But by using recycled lead from old car batteries, the manufacturing process can instead divert toxic material from landfills and reuse it in photovoltaic panels that could go on producing power for decades.

Because the perovskite photovoltaic material takes the form of a thin film just half a micrometer thick, the team’s analysis shows the lead from a single car battery could produce enough solar panels to provide power for 30 households.

As an added advantage, the production of perovskite solar cells is a relatively simple and benign process. “It has the advantage of being a low-temperature process, and the number of steps is reduced” compared with the manufacture of conventional solar cells, Belcher said.

Those factors will help to make it “easy to get to large scale cheaply,” said MIT graduate student Po-Yen Chen.

One motivation for using the lead in old car batteries is battery technology is undergoing rapid change, with new, more efficient types, such as lithium-ion batteries, taking over the market.

“Once the battery technology evolves, over 200 million lead-acid batteries will potentially be retired in the United States, and that could cause a lot of environmental issues,” Belcher said.

Today, 90 percent of the lead recovered from the recycling of old batteries ends up used to produce new batteries, but over time the market for new lead-acid batteries is likely to decline, potentially leaving a large stockpile of lead with no obvious application, Belcher said.

In a finished solar panel, the lead-containing layer would be fully encapsulated by other materials, as many solar panels are today, limiting the risk of lead contamination of the environment. When the panels end up retired, the lead can recycle into new solar panels.

“The process to encapsulate them will be the same as for polymer cells today,” Chen said. “That technology can be easily translated.”

“It is important that we consider the life cycles of the materials in large-scale energy systems,” said Paula T. Hammond, a MIT professor and co-author of a paper on the subject. “And here we believe the sheer simplicity of the approach bodes well for its commercial implementation.”

Belcher said the recycled perovskite solar cells will end up embraced by other photovoltaics researchers, who can now fine-tune the technology for maximum efficiency. The team’s work demonstrates that lead recovered from old batteries is just as good for the production of perovskite solar cells as freshly produced metal.

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