Researchers from the Fraunhofer Center for Silicon Photovoltaics (CSP) and the Fraunhofer Institute for Solar Energy Systems (ISE), in partnership with Reiling GmbH – a Germany-based recycling company of solar modules, have developed a solution to recycle discarded modules on an industrial scale and reuse them to produce passivated emitter and rear contact (PERC) solar cell.

The researchers said approximately 10,000 tons of silicon in discarded solar modules end up on the recycling market annually in Germany. The figure is expected to increase several hundred thousand tons annually by 2029. The aluminum, glass, and copper of the discarded modules are reprocessed, whereas silicon solar cells are not.

By-products of the treatment process at Reiling GmbH, from which the solar cell fragments are separated and collected (left). Purified silicon and wafers made from 100% recycled silicon (middle). PERC solar cells made of 100 % recycled silicon with an efficiency of 19.7 percent (right). Image credit: © Fraunhofer ISE

Andreas Bett, institute director of Fraunhofer ISE, said, “Most solar systems in Germany were installed between 2009 and 2011 during the first wave of photovoltaic (PV) expansion. This expansion will foreseeably be followed by a first wave of disposal 20 years later, around 2029 when the feed-in tariff for the installed PV modules expires. Therefore, it is necessary to establish adequate processes and procedures for recovering the silicon material from the discarded modules at any stage.”

The researchers developed a process for recovering silicon material that recycles all crystalline silicon solar modules, regardless of manufacture and origin. They separated solar cell fragments and collected them from by-products of the mechanical recycling process. The cell fragments with sizes from 0.1 to 1 millimeter were freed from the glass and plastic by various sorting processes. The process was followed by removing the backside contact, the silver contacts, the anti-reflective layer, and the emitter by wet chemical etching. Later, the researchers processed the cleaned silicon into monocrystalline or quasi-monocrystalline ingots in the standard process and then into wafers.

The researchers carried out crystallization with 100% recycled silicon without adding commercial ultrapure silicon. They fabricated the wafers made of recycled silicon into PERC solar cells. The solar cell conversion efficiency was 19.7%, below the efficiency of existing premier PERC solar cells, with 22.2%. However, the efficiency is higher than solar cells in the old and discarded modules.

In July 2021, at the 48^th IEEE Photovoltaic Specialists Conference, Fraunhofer Institute for Solar Energy Systems demonstrated how they obtained a record conversion efficiency of 68.9% with a photovoltaic cell under monochromatic light.

Mercom had earlier reported that Fraunhofer Institute for Solar Energy Systems obtained a record conversion efficiency of 26% for both-sides-contacted silicon solar cells.