December 23, 2015

Solar energy from discarded car batteries

MIT researchers have developed a simple procedure for making a promising type of solar cell using lead recovered from discarded lead-acid car batteries — a practice that could benefit both the environment and human health. As new lead-free car batteries come into use, old batteries would be sent to the solar industry rather than to landfills. And if production of this new, high-efficiency, low-cost solar cell takes off — as many experts think it will — manufacturers’ increased demand for lead could be met without additional lead mining and smelting. Laboratory experiments confirm that solar cells made with recycled lead work just as well as those made with high-purity, commercially available starting materials. Battery recycling could thus support production of these novel solar cells while researchers work to replace the lead with a more benign but equally effective material.

Much attention in the solar community is now focused on an emerging class of crystalline photovoltaic materials called perovskites. The reasons are clear: The starting ingredients are abundant and easily processed at low temperatures, and the fabricated solar cells can be thin, lightweight, and flexible — ideal for applying to windows, building facades, and more. And they promise to be highly efficient.

Recovering and processing materials

According to Belcher, recovering lead from a lead-acid battery and turning it into a perovskite solar cell involves “a very, very simple procedure” — so simple that she and her colleagues posted a video of exactly how to do it. (The sequence of steps is illustrated in the slideshow above.) The first step — getting the lead out of the car battery — might seem a simple proposition. Just remove the battery from the car, cut it open with a saw, and scrape the lead off the two electrodes. But opening a battery is extremely dangerous due to the sulfuric acid and toxic lead inside it.

A simple economic analysis shows that the proposed battery-to-solar-cell procedure could have a substantial impact. Assuming that the perovskite thin film is just half a micrometer thick, the researchers calculate that a single lead-acid car battery could supply enough lead for the fabrication of more than 700 square meters of perovskite solar cells. If the cells achieve 15 percent efficiency (a conservative assumption today), those solar cells would together provide enough electricity to power about 14 households in Cambridge, Massachusetts, or about 30 households in sunny Las Vegas, Nevada. Powering the whole United States would take about 12.2 million recycled car batteries, fabricated into 8,634 square kilometers of perovskite solar panels operating under conditions similar to those in Nevada.

Energy and Environmental Science - Environmentally responsible fabrication of efficient perovskite solar cells from recycled car batteries

“When perovskite-based solar cells first came out, they were a few percent efficient,” says Angela Belcher, the James Mason Crafts Professor in biological engineering and materials science and engineering at MIT. “Then they were 6 percent efficient, then 15 percent, and then 20 percent. It was really fun to watch the efficiencies skyrocket over the course of a couple years.” Perovskite solar cells demonstrated in research labs may soon be as efficient as today’s commercial silicon-based solar cells, which have achieved current efficiencies only after many decades of intensive research and development.

Research groups are now working to scale up their laboratory prototypes and to make them less susceptible to degradation when exposed to moisture. But one concern persists: The most efficient perovskite solar cells all contain lead.

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