Recycling photovoltaic modules

Updated on 18/07/2024: We have revised this interview to improve readability.

"Don't lose it, reuse it!" is not just the exclamation of a puppy from a well-known animated children's series when he creates new objects from supposed garbage. Rather, it shows how important the topic of ‘recycling’ and ‘sustainability’ has become in general. Renewable energy hardware, such as the photovoltaic modules that can now often be found on house roofs and balconies, are now being taken into account. According to the Bundesnetzagentur (in English: Federal Network Agency), 260,000 of these so-called ‘balcony systems’ alone were installed in 2023 - and many more will follow. In an interview with K-Mag, Dr. Sylke Meyer, Group Leader "Materials Analysis", Fraunhofer Center for Silicon Photovoltaics CSP, explains how materials, such as plastics, are laboriously extracted for recycling.

Dr. Meyer, can you give us an overview of how the recycling of components from end-of-life solar modules is carried out, particularly with regard to plastics?

Dr. Sylke Meyer: Theoretically, up to 95% of end-of-life modules can be recycled if various processes are combined. In practice, however, mechanical shredding is currently mainly used. This involves first removing the frame and the junction box/cable and then shredding the laminate of glass, plastic, and solar cells. The resulting material mixture must then be separated and cleaned using complex mechanical, physical, and chemical processes. As aluminum frames and glass account for more than 80% of the weight of a PV module, the established recycling technologies focus on these materials.

What types of plastics are contained in solar modules and what challenges do they pose when it comes to recycling?

Meyer: Plastics make up less than 10% of the total weight of a PV module but are essential for durability and operational safety. The spectrum ranges from ethylene vinyl acetate (EVA), polyolefin elastomers (POE) or thermoplastic olefins (TPO) for encapsulating the cells to fluoropolymers (PVF), polyamide (PA) and polyester (PET) as backing surfaces and other plastics that are used as adhesives for parts of the housing or for transparent covers instead of glass. It is precisely this complexity that poses the greatest technical challenge in recycling. Specifically, this concerns, for example, the high degree of cross-linking in EVA or the multilayer nature of the underside sheets.

Could you please explain how carbon capture works in the recycling process of solar module components?

Meyer: Ethylene vinyl acetate (EVA) can be effectively recycled by catalytic thermopyrolysis, for example. This process lowers the required temperature at which plastic is broken down into valuable petrochemical products. However, CO2 is released at several points in the process. Various processes can be used to capture and utilize it, e.g. by means of membranes or chemical absorption.

You also investigate material-specific pyrolytic polymer degradation mechanisms at the institute. Can you briefly explain the process?

Meyer: This refers to the thermal decomposition of polymers in the absence of oxygen, which can produce gases such as methane, ethylene or benzene, as well as valuable liquid products and solids. To control the process as efficiently and purposefully as possible, it is important to have a precise understanding of the influencing factors. These include the polymer structure itself and the reaction conditions. In the RETRIEVE project, we are supporting our project partners with our expertise in material analysis to improve the application potential of this process for recycling and beyond. For example, we are using pyrolysis gas chromatography-mass spectrometry (py-GC-MS). This allows the polymer composition of samples to be determined and additives and/or impurities to be detected.

How does the cost-effectiveness of the recycling process for solar modules compare with the production of new materials?

Meyer: Economic efficiency is a challenge. Separating and processing the plastic content, for example, is not yet economically viable. However, in addition to additional political requirements for recycling quotas, I also see opportunities through scaling effects. The large volume of old modules can make the development of suitable processes worthwhile, which in turn can lead to a greater supply and therefore lower prices for recyclates.

How do you see the future development of the recycling of solar module components, particularly regarding the optimization of plastic recovery?

Meyer: The aim must be a genuine circular economy in which as many of the materials used in the module as possible are returned to the product cycle with the highest possible added value. An important issue here is the development of standards for functional testing so that we can assess when a module has reached the end of its life. More consideration should be given to approaches for "design for recycling" – this can be an important approach, especially when using plastics. In addition, further efforts should be made to improve the reliability and service life of the modules: The longer the modules are intact in operation, the lower the need for recycling.