According to the International Renewable Energy Agency, global solar panel waste could exceed 70 million tons by 2050. These panels contain valuable materials such as silicon (Si), silver (Ag), and aluminum (Al), yet current disposal practices often consign them to landfills. Unlike glass and metal recycling, which are well-established, solar cell recycling remains in its infancy. Without effective recovery methods, the promise of solar power as a sustainable energy solution risks being undermined by its own waste stream.
Most existing recycling approaches emphasize mechanical separation or bulk material recovery. Panels are typically disassembled to recycle glass and aluminum, which account for most of the panel’s mass but only a fraction of its potential recoverable economic value. The most critical components, the high-purity silicon wafers and silver conductors, are frequently lost in mixed waste streams. Additionally, encapsulating polymers complicate leaching and thermal treatments, making it difficult to achieve the purity levels required for reuse in solar applications.
Thermal methods, such as high-temperature incineration, consume large amounts of energy, generate greenhouse gases, and often degrade the quality of the recovered silicon. Mechanical routes face limitations due to polymer entanglement with fine silicon particles, leading to contamination and low recovery efficiency. Even chemical leaching processes, while more selective, often rely on strong acids such as hydrofluoric acid and oxidizers that pose environmental and safety hazards, yet still fail to deliver the six nines (99.9999%) purity demanded by high-value electronic and energy applications. Collectively, these drawbacks render solar panel recycling uneconomical, energy-intensive, and environmentally suboptimal, with recovery rates for silicon remaining far below industrial needs.
To address these challenges, researchers at Worcester Polytechnic Institute (WPI), through the National Science Foundation (NSF)-funded Industry-University Cooperative Research Center (IUCRC) for Resource Recovery and Recycling (CR3), are pioneering a hydrometallurgical process that simultaneously recovers solar-grade silicon while extracting high-purity silver from waste panels. The innovation goes beyond material recovery and allows for a more circular economy where recycled silicon can feed directly into high-value applications.
The CR3 process begins with a detailed characterization of solar panel waste that maps elemental distribution. Pretreatment with sulfuric acid selectively removes aluminum impurities, followed by alkaline leaching that achieves silicon extraction efficiencies above 93%. The recovered silicon — which is in the form of silica (SiO2) — undergoes advanced purification, reaching six nines purity. Through a magnesiothermic reduction reaction in which magnesium is used as a reducing agent, silica is then converted into battery-grade silicon powder. In parallel, silver is separated from leaching residues and precipitated as AgCl, attaining 99.86% purity with nearly 99% recovery efficiency.
This process combines selective hydrometallurgy with pretreatment and reduction strategies to produce ultra-pure materials from polymer-rich, highly contaminated waste streams. Unlike conventional thermal processes, WPI’s method avoids excessive energy use and preserves material value. The dual recovery of solar-grade silicon and silver at electronic-grade purity represents a significant breakthrough, enabling their direct reuse in manufacturing. Furthermore, by transforming recovered silicon into battery-grade anode powder, the process connects the solar and battery industries in a closed-loop cycle that amplifies both economic and environmental benefits.
Lab demonstrations have validated the process, yielding six nines-purity SiO2 and battery-grade Si with purities exceeding 99.995%. Real-world waste trials, however, highlighted polymer contamination as a critical bottleneck. Therefore, the next phase of research will focus on scaling pretreatment and separation strategies to address this challenge. Industrial partners, who have supplied authentic panel waste, ensure the project remains grounded in commercial reality. A technoeconomic analysis is underway, and pilot-scale validation is planned for the near term, paving the way for industry adoption.
“By demonstrating economic feasibility, WPI aims to position solar panel recycling as a cost-competitive alternative to landfilling, echoing its earlier success in catalyzing battery recycling commercialization,” says Fred Rucker, Chair of the Industrial Focus Group and CEO of Global Mineral Recovery. “While a handful of industry participants have entered this market with a variety of recycling technology approaches, the WPI CR3’s innovation and bench-scale development has recovered 99.9999% purity SiO2, the highest and most valuable quality SiO2 known to date recovered from solar panel recycling undertakings. This and the recovery of high-purity silver represent two strategically critical minerals for the U.S. supply chain.”
This research was supported by the Industry-University Cooperative Research Centers (IUCRC) program of the NSF.
This article was prepared by the U.S. National Science Foundation in partnership with CEP.
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