Germany's Fraunhofer Institute for Solar Energy Systems (ISE) has achieved a power conversion efficiency of 19.7% for PERC solar cells made out of purified silicon and wafers that came from 100% recycled silicon, on an industrial scale from discarded modules.
"This is below the efficiency of today's premium PERC solar cells, which have an efficiency of around 22.2%, but it is certainly above that of the solar cells in the old, discarded modules," explained Prof. Dr. Peter Dold, Project Manager at Fraunhofer CS .
The silicon was recycled on an industrial scale from discarded modules to produce the new PERC cells.
The team deployed a process, developed by Fraunhofer Center for Silicon Photovoltaics (CSP) and German PV module recycling company Reiling GmbH & Co. KG, to recover silicon by separating and collecting solar cell fragments from by-products of the mechanical recycling process.
Fraunhofer CSP said it first freed cell fragments with sizes from 0.1 to 1.0 millimeter from glass and plastic, followed by step-by-step removal of the backside contact, the silver contacts, the anti-reflective layer and then the emitter by wet chemical etching.
Silicon thus cleaned this way is processed into monocrystalline or quasi-monocrystalline ingots in standard processes and then into wafers.
Currently, the German technology research firm explained, aluminum, glass, and copper of the discarded modules are reprocessed but not silicon solar cells. This makes this process quite remarkable since it would mean there is life for silicon after operating life of a module finishes, it emphasized.
Fraunhofer counts Germany to have several hundred thousand tons of discarded solar modules annually by 2029 after the feed-in-tariff (FIT) expires for the first big chunk of installed PV modules that were installed as of 2009. Prof. Dr. Andreas Bett, Director of Fraunhofer ISE, explained, "Therefore, it is necessary to establish adequate processes and procedures for recovering the silicon material from the discarded modules at an early stage."
Silicon is not only the main component of PERC solar cells, but it is also one of the most expensive parts of the solar module. The world is still reeling from the impacts of its tight supply in 2021 that pushed up module costs and overall project costs, forcing some developers to push back their project completion deadlines.
With a recycling process to fish out silicon available at an industrial scale, this could really be helpful to make PV all the more competitive, according to the institutes.
The process developed by the trio can be deployed to recycle all crystalline silicon PV modules 'regardless of manufacturer and origin'. "It was important for us to develop a scalable process that makes economic sense. A lot is possible in the lab, but our new process should prove itself in the practice for the recycling industry," added Dold.