For the first time, researchers at the Fraunhofer Center for Silicon Photovoltaics CSP in Halle (Saale) have successfully developed a process for recovering silicon for solar use from end-of-life PV modules. The project plays a key role in the energy transition and the circular economy.
At the site of the Fraunhofer Center for Silicon Photovoltaics CSP in Halle (Saale) in Saxony-Anhalt, a small solar module in a fenced area is generating electricity. You might think that there is nothing unusual in this, but it is in fact a special module being used for research purposes. The ReModul is the world’s first solar module made from 100 percent recycled silicon. The researchers at the institute have succeeded for the first time in developing a process for recovering silicon from end-of-life modules and retaining it in the material cycle.
From solar waste to a secondary raw materia
The recovery of materials from photovoltaic modules at the end of their useful life is an important consideration for the energy transition and resource planning. “The majority of photovoltaic systems in Germany were installed during the first wave of expansion from 2009 to 2011. At the latest when the 20-year feed-in tariff scheme comes to an end in 2029, there is likely to be a first wave of disposal. This year, we are expecting 10,000 metric tons of end-of-life modules, which will have to be recycled under the provisions of the Circular Economy Act. Next year, the figure will be 50,000. By the end of the decade there will be several hundred thousand tons per year,” explains Professor Peter Dold, director of the Fraunhofer CSP. At the moment, only the aluminium, glass and copper from the PV modules are recycled. It has unfortunately not been possible to recycle the main component – the silicon solar cells – until now. The cells are currently shredded and then incinerated, together with the silver that is also used in the solar modules. The solar modules currently in use in Germany contain around 3000 metric tons of silver, according to Professor Dold.
Recovering silver and silicon
For around ten years, the researchers at the Fraunhofer CSP have been trialling new procedures for cleaning wafer and cell waste, separating materials and, in particular, returning the solar silicon to the material cycle. The center has special melting machines with induction heating systems that can heat and cool the materials rapidly. The researchers at the Fraunhofer CSP and the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, together with the largest German recycling company for PV modules, Reiling GmbH & Co. KG, have now succeeded in their ReModul project in recycling the silicon from end-of-life solar modules. The process takes the by-products of established mechanical recycling processes and separates out and collects the fragments of silicon solar cells. A variety of sorting processes are used to separate the plastic and the silver from the end-of-life cells. The silver that is removed and melted has a purity of 99.6 percent. Finally, the glass and silicon are separated from one another using an electrostatic method. After a number of mechanical, physical, thermal and chemical steps, the silicon that is recovered can be melted, processed and subsequently made into wafers for new modules at the Fraunhofer CSP.
The process must be financially viable
“Of course, this is just a pilot project. We need to analyse what the whole process costs because financial viability is the decisive factor. It’s possible to do almost anything in the laboratory, but ensuring that the complex process is ultimately cost-effective is the really big challenge,” says Professor Dold. “Our task and our vision is to develop this process so that it can be industrialized. We need to ensure that it is easy to scale up and manageable.” An important consideration for him is that Germany, with its limited natural resources, currently has to import nearly all its raw materials, in particular silicon and silver. “We must make sure that we retain these materials in the material cycle and that they don’t go into an incinerator.” In 2022, the global PV industry used 700,000 metric tons of silicon. By 2024 at the latest, this figure will have risen to one million tons. “I’m optimistic that we in Germany are prepared for the future volume of end-of-life PV modules. Using the methods that we have developed, we can be certain that we won't be overwhelmed by a mountain of PV waste.”
Author: Michael Falgowski