Major challenges and opportunities in silicon solar module recycling

This article examines some of the basic questions about silicon module recycling: (1) What can be recovered from silicon modules? (2) What recycling technologies are needed? (3) What are the potential revenues for different recycling scenarios? And (4) what are the major challenges for different recycling scenarios? Three recycling scenarios are considered: module reuse, component extraction, and material extraction. Recycling process sequences for different scenarios are outlined. The discussions conclude that module reuse generates the highest revenue with the fewest processing steps, while material extraction leads to the lowest revenue with the most processing steps. It is suggested that gentle and clean separation of silicon solar cells from the glass pane is a critical technology for silicon module recycling. It is also argued that two low-concentration metals must be recovered from silicon modules: silver as a scarce material and lead as a toxic material. Their recovery requires chemical methods, while bulky materials including glass cullet, aluminum frame, and copper wiring can be recovered with physical methods. The silicon in the cells can be extracted with different qualities: ferro-silicon, metallurgical-grade silicon, or solar-grade silicon, with a higher revenue and more complicated recycling process for purer silicon. Markets outside the solar industry for the recovered silicon should be explored. The biggest challenge for module reuse is to find a large and sustained market for hundreds of gigawatts peak of decommissioned modules a year, and the biggest challenge for component extraction is the many different module and cell structures on the market and cell efficiency variability. For all the three scenarios, the cost of collecting and processing waste modules is a common challenge.