Fraunhofer Institute for Surface Engineering and Thin Films IST
Silicon layers produced by hot wire CVD for a heterostructure solar cell.
Sustainable recycling of silicon photovoltaic modules
Pyrolysis as a key technology
Photovoltaic modules have an average service life of 25-30 years. In addition to natural ageing, other issues that can lead to modules having to be replaced prematurely include economic factors or damage caused by environmental influences. With the rapid expansion of solar energy, the quantity of disused solar cells will therefore increase considerably in the coming years. This development presents a major challenge, as the raw materials incorporated into the modules, such as silver, glass, silicon, metals and polymers, are valuable resources that must be recovered efficiently. In this respect, pyrolysis offers promising approaches for sustainable and economical recycling.
Efficient recycling through microwave-excited pyrolysis
Conventional recycling processes have their limitations, particularly in the case of damaged or broken PV modules. The approach investigated at the Fraunhofer IST therefore relies on the thermal decomposition of the organic components by means of microwave-excited pyrolysis. This innovative method enables the efficient heating of the modules, which is necessary for the separation of the different materials. Simultaneously, the polymers contained in the modules can be recycled both materially and energetically in the form of pyrolysis oils and gases. This not only contributes towards the recovery of valuable raw materials, but also offers a sustainable solution for a resource-conserving circular economy.
Microwave pyrolysis system developed within the “PV-Kreis” project.
Results
In a first step, the structure and material composition of various silicon PV modules were examined in detail. By means of thermogravimetric analysis (TGA), the temperature required for thermal decomposition as well as the composition of the gaseous pyrolysis products of granular PV modules were determined in particular. Based on these findings, a system concept was developed in collaboration with the project partners, which has since been implemented in a prototype plant.
This prototype plant represents an important step forwards in the practical application of microwave-excited pyrolysis and offers the possibility of further optimizing the efficiency and economic viability of the recycling process.
Outlook
In the further course of the project, the prototype plant will be put into operation and intensively tested in order to continuously optimize the process control. The primary focus will thereby be on the neutralization of toxic process gases – such as hydrofluoric acid – and the determination and minimization of the required energy input. Furthermore, plans are in place to integrate other composite materials into the recycling process in the future; these include glass-fiber- or carbon-fiber-reinforced polymers as well as electrical elements or electronic components.
System concept for the microwave pyrolysis of PV modules.
Determined material composition of an Si PV module.
Microscope image of the cross-section of an Si PV module.
The project
The work was funded within the framework of the BMBF joint project “Circular Economy menschengerecht gestalten” (Circular economy with human-oriented design, “PV-Kreis”) under the funding reference 02L22C114.
This article is part of the Annual Report 2024.