Around 10 000 tonnes of silicon from used solar panels is scrapped in Germany every year. There is no commercial recycling solution for the material but researchers at the Fraunhofer Institute are working on one.
While the aluminium, glass and copper from discarded panels are reprocessed, silicon from solar cells remains something of a recycling challenge. The industry expects this growing waste stream to reach several hundred thousand tonnes per year by 2030. In Germany alone, over five million tonnes of PV modules have been installed with a silicon content of 150 000 tonnes.
Fraunhofer specialists have formed a working group with Germany’s largest PV module recycler Reiling to find a solution. They have developed what is described as a ‘promising’ process to recover and recycle all crystalline silicon PV modules regardless of manufacturer and origin. Better still, the government funded project supports the production of new solar cells.
For the process, cell fragments are separated and collected during an established mechanical recycling process. At Fraunhofer, fragments from 0.1 to 1 millimetre are freed from the glass and plastic by various sorting processes. This is followed by the step-by-step removal by wet chemical etching of the rear contact, the silver contact, the anti-reflective layer and finally the emitter.
Silicon cleaned in this way is processed into monocrystalline or quasi-monocrystalline ingots in standard processes and then into wafers. The crystallisation is carried out with 100% recycled silicon without adding commercial ultrapure silicon. Wafers of recycled silicon were fabricated into passivated emitter and rear contact (perc) cells. In the first trial, the conversion efficiency was 19.7%.
‘This is below the efficiency of today’s premium perc cells, which have an efficiency of around 22.2% but it is certainly above that of the cells in old, discarded modules,’ says Professor Peter Dold, project manager at Fraunhofer. ‘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.’
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