Disposal and recycling of photovoltaic modules raises environmental challenges and opportunities with respect to the energy transition
Unused solar panels stored by NGO PV Cycle, from Belgium
PV CYCLE
A 2000-square-meter hangar in Valinhos, inland São Paulo State, is receiving and storing hundreds of solar panels every month. In May alone, the material received — essentially modules disabled for solar energy production — reached 80 tons. This is not a new renewable energy plant, but a company that opened a little over three years ago and has decided to break into an incipient but expanding market, set to skyrocket in the coming years: the recycling of discarded solar panels.
“Last year we grew more than 700% in terms of received material volumes, and we are projecting even more for this year,” says 27-year-old entrepreneur Leonardo Duarte, founder of SunR, one of the few companies in Brazil fully dedicated to recycling of solar modules that have lost their efficiency. “Since we began, we have received more than 25,000 panels, equivalent to 730 tons of material,” he adds.
The question about what to do with discarded solar panels has been increasingly posed around the globe, primarily in European countries such as Germany, which began its use of solar energy in the 1990s. The estimated operational lifespan of these panels is between 25 and 30 years, and large quantities of modules in Europe and other locations have already become scrap.
A 2016 report published by the International Renewable Energy Agency (IRENA) on the management of solar panels at the end of their lifespan warns that the annual amount of waste at the beginning of the 2030s will reach somewhere between 1.7 and 8 million tons. In 2050, this waste type could total 78 million tons around the globe.
On the other hand, in 2016 the agency estimated that the value of recoverable materials in these items could reach US$450 million in 2030, enough to produce 60 million solar panels. Twenty years later, the recycling value would exceed US$15 billion, enough to produce 2 billion panels, according to IRENA projections.
The modules are 90% glass and aluminum, but also contain small amounts of valuable metals such as silver and copper, along with more polluting substances such as lead and polymers (see infographic). In Brazil, where photovoltaic technology was more widely adopted from the 2010s, the volume should increase in a few years, but is already starting to cause concern.
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“The biggest misconception is to think that these residues will only arise after 30 years. On the contrary,” says Duarte, who works directly with plants, assemblers, and importers of solar modules throughout Brazil. “We estimate that more than 7% of these panels are discarded before reaching 15 years of their lifespan.”
Accidents in transportation, loading, and unloading, installation and maintenance errors, external events such as windstorms and fires, and scrap in the production of panel assemblers are some of the reasons he points out for the retirement or early loss of crystalline silicon modules. This material is the semiconductor element used in most solar panels sold in Brazil and around the world.
The adhesive polymer layers, which protect the product from weathering, make it difficult to dismount and recycle them. The easiest part to recover during the process is the aluminum structure and external copper wires. In second place comes the glass, which makes up a significant part of the panel (70–95%), and there is already a well-established glass recycling industry in place. Other materials contained in solar cells present a bigger challenge. Silver, tin, copper, and the silicon itself are valuable elements, although their quantities in the modules are minute compared to the glass. However, specialists calculate that they account for more than 40% of the panel value.
“Separating noble materials is not simple. There is still much research and development to be done to progress in this regard,” says physicist Carlos Frederico de Oliveira Graeff, of the São Paulo State University (UNESP) School of Sciences, Bauru, where solar cell development work is ongoing. One of its most recent projects, supported by FAPESP, focuses on investigating the stability of solar cells made from perovskite, a semiconductor element superior in efficiency to silicon but still not very durable (see Pesquisa FAPESP issue nº 260).
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In addition to reducing residues and waste-related carbon emissions, the recycling of solar modules also has the potential to cut the amount of energy required for exploration and production of the original material, such as silver and silicon, and lessen the environmental impacts associated to their extraction. “It may be possible to reuse more than 95% of panel materials,” he says. “This market is starting to open up now,” adds Graeff.
Physicist Francisco das Chagas Marques, a solar energy researcher at the Gleb Wataghin Institute of Physics of the University of Campinas (UNICAMP), states that the key challenge is to obtain cost-effective recycling technology, since current processes are wasteful and, for now, do not restore operating costs. “Most commonly only the copper from wiring, aluminum from the frames, and the glass have been recovered,” he says.
According to the researcher, the area is under development, particularly in the United States and Europe. There are no solar cell manufacturers in Brazil. Modules are imported or only assembled in the country, using silicon cells, which also come from overseas, as do the glass, the silver paste, encapsulants, and other items, highlights Marques. China is the biggest global producer of solar panels.
Léo Ramos Chaves/Revista Pesquisa FAPESPModule stored in a hangar of recycling company SunR, in Valinhos, inland São Paulo StateLéo Ramos Chaves/Revista Pesquisa FAPESP
At SunR in Valinhos, following removal of the aluminum structure and the electronic and connector components, the panels are mechanically crushed. The material undergoes density and particle-size separations, in which glass and metals are detached from each other. “The material outputs of our company are aluminum, cabling, junction boxes, plastic, glass, and a mix of metals comprising silicon, silver, copper, tin, and others,” says Duarte.
He goes on to say that the mix of metals is sold to industries interested in performing chemical extraction. “As the volume of metal is very low within the panel, it’s not worth us becoming a chemical industry; our process is 100% mechanical,” he adds. “We have viable solutions, but these do not guarantee repurposing of all the materials. We are developing new partners and studies to harness each one of them as much as possible.” According to Duarte, the recycling percentage of the metallic mix depends on the buyer, and whether they intend to make use of all the materials, or just the silver or silicon.
Outside Brazil, some companies promise to recycle more than 90% of solar panel materials, including silver and copper. In June of this year, French operation Rosi, based in Grenoble, inaugurated its first industrial plant and says it uses physical, thermal, and chemical mechanisms in the process of adequately separating the materials. In the United States, SolarCycle was founded in 2022 as a California start-up, and built a recycling center in Texas where it reports extraction of 95% of the value of solar panel materials and their reintroduction into the supply chain.
SolarCycle has developed special machines to remove all of the glass from the panel, and this is done after the frame, the cables, and the junction box are removed. The remaining mixture is separated: plastic on one side, metals on the other (primarily metallic silicon, copper, silver, lead, and tin). The metals are currently sold to third parties, but the company is about to inaugurate a new plant to chemically recover the metals, mainly silver and silicon.
Alexandre Affonso / Revista Pesquisa FAPESP
In Germany, researchers from the Fraunhofer Institute for Solar Energy Systems, and the Fraunhofer Center for Silicon Photovoltaics, announced, in 2022, the development of a solution in partnership with the biggest local recycling company, Reiling GmBH & Co. KG; the Fraunhofer Institute is a German research association of 76 units across the country, with different focuses on applied science. The process involves silicon recovery from discarded modules, and their reuse in the production of new solar cells, using PERC (Passivated Emitter Rear Cell) technology, used in new generations of panels, with finer photovoltaic cells.
After undergoing mechanical recycling and separation of other materials, solar cell fragments sized between 0.1 and 1 millimeter undergo chemical attack. They are then processed into monocrystalline silicon ingots from which the wafers originate to make up the panels.
One of the SolarCycle cofounders is Brazilian engineer Pablo Ribeiro Dias, currently the company’s Director of Technology. He obtained his degree, master’s, and PhD in engineering at the Federal University of Rio Grande do Sul (UFRGS). Working with Hugo Marcelo Veit, his master’s thesis tutor, Dias invented a specific method for removal and recovery of silver from photovoltaic modules, with an efficiency rate between 92% and 94%, using mechanical operations such as mills and hydrometallurgical units, with acid and salt solutions to promote leaching and decanting of the metal.
The patent for this technology was granted by the Brazilian National Institute of Industrial Property (INPI) last year. “The process on an industrial scale is yet to be adopted by any company,” says Veit, not part of the SolarCycle team and devoted exclusively to UFRGS. “If any corporation wanted to do that in Brazil, they would have to obtain a permit.” The patent is protected only in Brazil.
The two researchers have two other patent applications ongoing, one of which is for a method developed in Australia — Dias did part of his doctorate at Macquarie University, and Veit obtained his postdoctorate from the University of New South Wales, both in Sydney. “The second method is a more chemical process than mechanical, but uses an organic solvent, while the first uses acids to recover not only the silver, but other components. It is a slightly more comprehensive method,” says the UFRGS professor.
The third application was lodged in Australia in 2021 and covers other technology with a mechanical and chemical process to recycle all solar panel components. Neither of the three methods patented by the Brazilian researchers is used at SolarCycle, which employs a different recycling route.
Carl de Souza / AFP via Getty ImagesSolar energy plant in Pirapora, Minas Gerais: one of Latin America’s biggestCarl de Souza / AFP via Getty Images
According to Veit, several research groups around the globe are looking to develop more efficient module recycling methods. “We can’t forget that there is a cost involved in making the panel, as it consumes a lot of raw material. Interest in this area is up because the volume and quantity of panels discarded is starting to draw attention,” comments Veit.
The results of their studies on solar panel recycling were published in the journals Resources, Conservation and Recycling in 2021, and Renewable and Sustainable Energy Reviews in 2022. The process described in one of these articles provided guidelines for SolarCycle, but was modified, says Dias. The company does not currently adopt the technologies detailed in the Brazilian or Australian patent applications.
“We had to develop that process in layers. It’s more advanced now. We can use our technology to remove all the glass from the panel before separating the metals and plastics. This is a different and much more effective, efficient way to recycle panels,” says Dias.
Specialists state that, in addition to technology, political mechanisms and regulatory structures are needed to develop and stimulate appropriate treatment of industrial panel waste. The current Brazilian Law 12.305/2010, which provides on the National Solid Waste Policy, does not explicitly or specifically cover solar modules.
“Who has, and how will you confer, responsibility for residues from photovoltaic systems?” asks electrical engineer Clóvis Bôsco Mendonça Oliveira, a professor at the Federal University of Maranhão (UFMA), who this year published a revision article on the theme in the journal Social Sciences & Humanities Open, with his master’s tutor Nelson Monteiro de Sousa and Darliane Cunha, professor of the vocational master’s in Energy & Environment at UFMA.
“More efficient technological solutions and process development will be needed to deal adequately with issues arising at the end of photovoltaic system lifespans,” point out the authors in the article. “However, even more is needed. Political mechanisms and regulatory structures will also need to be developed and implemented at the end stage of the life cycle to prepare, encourage, and develop appropriate industrial waste treatment applications.”
For Oliveira, discussing regulatory aspects is a pressing matter. “If only 20 years from now we have a specific law on this matter, we will only have an effective return in 40 years, as you cannot backdate a norm like that; it involves financial cost. We have to act now.” European Union countries, Japan, and Canada, who are more advanced in this area, have already updated their legislation.
Project Optimization of perovskite solar cell stability (nº 20/12356-8); Modality Thematic Project; Principal Investigator Carlos Frederico de Oliveira Graeff (UNESP); Investment R$1,914,365.90.
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