Expanding solar-power production is key to reducing emissions worldwide. Globally, solar panels produced 720 terawatt-hours of energy in 2019, accounting for around 3% of the world’s electricity generation. And it took about 46 million metric tons of solar panels to do it.
About 8 million metric tons of decommissioned solar panels could accumulate globally by 2030. By 2050, that number could reach 80 million. Recycling these panels could provide a new source for materials that would otherwise need to be mined (potentially under unsafe or exploitative working conditions), making solar a more sustainable piece of the clean-energy puzzle.
What’s in a solar panel?
Solar panels are laid out like a sandwich with cells in the center. About 90% of commercial solar panels use silicon as the semiconductor, which converts light into electricity. Thin strips of metal, usually silver, crisscross the surface of silicon crystals in each cell and move electricity into the panel’s copper wiring.
The solar cells are encased in a protective barrier, usually a transparent plastic called EVA. Another layer of glass goes on top, and a different kind of plastic, like PET, covers the back. The whole thing is surrounded by an aluminum frame.
This layered construction protects cells from the elements while allowing sunlight through, but it can be difficult to deconstruct when the panels have reached the end of their life.
A second life
Some companies try to refurbish and reuse panels that have lost efficiency, or at least rescue some of their components. Reuse is the simplest and cheapest way to “recycle” panels—it requires the least processing and commands the highest price.
A panel might cost around $55, while a used panel might be resold for around $22. Or the used panel’s components might be sold for a total of up to $18, according to Meng Tao, an engineering professor at Arizona State University and founder of a solar-panel recycling startup called TG Companies.
Although some resellers offer used panels for sale to residential customers, they don’t offer much price savings. Panels only make up, at most, about half the cost of a residential solar array, with the other equipment and permits accounting for the rest. Given that used panels don’t generate as much electricity, the money saved by buying them might not be worth it.
Used panels that can’t be resold are destined for either the landfill or some type of recycling. In the absence of federal mandates, Washington recently passed recycling requirements for manufacturers, and other states are now considering doing the same. The EU, meanwhile, requires manufacturers to collect and recycle used solar panels and fund research on end-of-life solutions for the technology they produce.
Some waste facilities can recycle solar panels using mechanical methods. Most pop off the aluminum frame and grind all the glass, silicon, and other metals into a mixture called glass cullet, which can be sold for building materials or other industrial applications.
But cullet isn’t worth much—around $3 for a panel’s worth of the mixture. And it’s not clear if there will be buyers for all the cullet that would result from recycling many more solar panels, Tao says. Being able to extract pure, valuable materials might help make recycling more profitable.
In 2018 the waste management company Veolia, based near Paris, opened what it says is the first recycling line developed specifically for recycling solar panels. Located in Rousset, France, the plant also uses a mechanical recycling process, although since it’s designed for solar panels, more components are recycled separately than at facilities using general e-waste recycling equipment. But some companies are betting that other methods, like thermal and chemical processes, will be even more efficient.
Mining old panels
ROSI Solar, a French startup founded in 2017, recently announced plans to build a new recycling plant in Grenoble, France. Yun Luo, ROSI’s CEO, says the company has developed a process to extract the silver, silicon, and other high-value materials from used panels. The plant should open before the end of 2022 with a contract from Soren, a French trade association.
Soren is also working with a French logistics company called Envie 2E Aquitaine, which will try to find other uses for decommissioned solar panels. If the panels aren’t operational, the company will remove the aluminum frame and glass before passing them along to ROSI to recycle, Luo says.
ROSI focuses on recovering silver and solar-grade silicon, since these two materials make up over 60% of a panel’s cost. The company uses a proprietary chemical process on the remaining layers, focusing on removing the tiny silver threads that transmit electricity through a working solar panel.
Luo declined to go into specifics but says the company can recover nearly all the silver in a solid form, so it’s easier to separate from the other metals, like lead and tin. Luo says that the company also recovers the silicon in a pure enough form to reuse in new panels or EV batteries.
To be profitable, ROSI will need to recycle at least 2,000 to 3,000 tons of panels per year, Luo says. Soren expects to collect about 7,000 tons of panels in 2021, and that number will probably more than double by 2025.
The Download: Introducing our TR35 list, and the death of the smart city
Spoiler alert: our annual Innovators Under 35 list isn’t actually about what a small group of smart young people have been up to (although that’s certainly part of it.) It’s really about where the world of technology is headed next.
As you read about the problems this year’s winners have set out to solve, you’ll also glimpse the near future of AI, biotech, materials, computing, and the fight against climate change.
To connect the dots, we asked five experts—all judges or former winners—to write short essays about where they see the most promise, and the biggest potential roadblocks, in their respective fields. We hope the list inspires you and gives you a sense of what to expect in the years ahead.
Read the full list here.
The Urbanism issue
The modern city is a surveillance device. It can track your movements via your license plate, your cell phone, and your face. But go to any city or suburb in the United States and there’s a different type of monitoring happening, one powered by networks of privately owned doorbell cameras, wildlife cameras, and even garden-variety security cameras.
The latest print issue of MIT Technology Review examines why, independently of local governments, we have built our neighborhoods into panopticons: everyone watching everything, all the time. Here is a selection of some of the new stories in the edition, guaranteed to make you wonder whether smart cities really are so smart after all:
– How groups of online neighborhood watchmen are taking the law into their own hands.
– Why Toronto wants you to forget everything you know about smart cities.
– Bike theft is a huge problem. Specialized parking pods could be the answer.
– Public transport wants to kill off cash—but it won’t be as disruptive as you think.
Toronto wants to kill the smart city forever
Most Quayside watchers have a hard time believing that covid was the real reason for ending the project. Sidewalk Labs never really painted a compelling picture of the place it hoped to build.
The new Waterfront Toronto project has clearly learned from the past. Renderings of the new plans for Quayside—call it Quayside 2.0—released earlier this year show trees and greenery sprouting from every possible balcony and outcropping, with nary an autonomous vehicle or drone in site. The project’s highly accomplished design team—led by Alison Brooks, a Canadian architect based in London; the renowned Ghanaian-British architect David Adjaye; Matthew Hickey, a Mohawk architect from the Six Nations First Nation; and the Danish firm Henning Larsen—all speak of this new corner of Canada’s largest city not as a techno-utopia but as a bucolic retreat.
In every way, Quayside 2.0 promotes the notion that an urban neighborhood can be a hybrid of the natural and the manmade. The project boldly suggests that we now want our cities to be green, both metaphorically and literally—the renderings are so loaded with trees that they suggest foliage is a new form of architectural ornament. In the promotional video for the project, Adjaye, known for his design of the Smithsonian Museum of African American History, cites the “importance of human life, plant life, and the natural world.” The pendulum has swung back toward Howard’s garden city: Quayside 2022 is a conspicuous disavowal not only of the 2017 proposal but of the smart city concept itself.
To some extent, this retreat to nature reflects the changing times, as society has gone from a place of techno-optimism (think: Steve Jobs introducing the iPhone) to a place of skepticism, scarred by data collection scandals, misinformation, online harassment, and outright techno-fraud. Sure, the tech industry has made life more productive over the past two decades, but has it made it better? Sidewalk never had an answer to this.
“To me it’s a wonderful ending because we didn’t end up with a big mistake,” says Jennifer Keesmaat, former chief planner for Toronto, who advised the Ministry of Infrastructure on how to set this next iteration up for success. She’s enthusiastic about the rethought plan for the area: “If you look at what we’re doing now on that site, it’s classic city building with a 21st-century twist, which means it’s a carbon-neutral community. It’s a totally electrified community. It’s a community that prioritizes affordable housing, because we have an affordable-housing crisis in our city. It’s a community that has a strong emphasis on green space and urban agriculture and urban farming. Are those things that are derived from Sidewalk’s proposal? Not really.”
Rewriting what we thought was possible in biotech
What ML and AI in biotech broadly need to engage with are the holes that are unique to the study of health. Success stories like neural nets that learned to identify dogs in images were built with the help of high-quality image labeling that people were in a good position to provide. Even attempts to generate or translate human language are easily verified and audited by experts who speak a particular language.
Instead, much of biology, health, and medicine is very much in the stage of fundamental discovery. How do neurodegenerative diseases work? What environmental factors really matter? What role does nutrition play in overall human health? We don’t know yet. In health and biotech, machine learning is taking on a different, more challenging, task—one that will require less engineering and more science.
Marzyeh Ghassemi is an assistant professor at MIT and a faculty member at the Vector Institute (and a 35 Innovators honoree in 2018).