Experimental Study on Fluorine Release from Photovoltaic Backsheet Materials Containing PVF and PVDF during Pyrolysis and Incineration in a Technical Lab-Scale Reactor at Various Temperatures

Abstract

With a sharp increase in photovoltaic (PV) installations across the world, PV waste is now a relatively new addition to the e-waste category. From 45,000 tonnes in 2016, the PV waste stream is rapidly increasing and is projected to reach 60 million tonnes by 2050. Backsheets are composite structures made from several material layers of polymer, adhesive, and primer. Widely used PV backsheets can be classified into three core types: (a) KPK (Kynar®/polyethylene terephthalate (PET)/Kynar®), (b) TPT (Tedlar®/PET/Tedlar®), and (c) PPE (PET/PET/ethylvinylacetate). Kynar® and Tedlar® are based on polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), respectively. PPE backsheets are fluorine-free composites made primarily from PET. With increasing focus on the end-of-life (EoL) handling of PV waste, the handling of fluoropolymers, which is largely unexplored, requires closer examination to avoid environmental damage. The aim of this study was to obtain information on the fluorine released from PV backsheet materials into the gas phase during combustion and pyrolysis as EoL pathways. Therefore, several experimental trials were conducted to measure fluorine transfer into the gas phase at 300 °C, 400 °C, 500 °C, and 900 °C (for pyrolysis) and at 750 °C, 850 °C, and 950 °C (for incineration).

Experimental Study of the Fire Dynamics in a Semi-enclosure Formed by Photovoltaic (PV) Installations on Flat Roof Constructions

“…Those conclusions align well with the back sheet only representing 2.8 to 3.5% of the module weight, whereas the encapsulate represents 6.3 to 8% [55]. The two highly thermally stable fluoropolymers Tedlar and Kynar are among the most used products for back sheets [55,56] and with a heat of combustion between 4.1 kJ/g and 5.4 kJ/g [57], a very limited additional heat flux was expected. In contrast, the heat of combustion of the commonly used encapsulate ethyl vinyl acetate (EVA) [55] is 41.6 kJ/g [58] and despite previous research indicating that the contribution is limited, it does, theoretically, increase the fire load on the roof.…”

Recycling of Discarded Photovoltaic Solar Modules for Metal Recovery: A Review and Outlook for the Future

“…A c-Si absorber layer (6 wt %) is connected by Pb-coated Cu wires and Ag grid wires on the front, while Al is on the back for current transfer. , The front layer is usually made of glass, and the back sheet (0.8 wt %) comprises polymers, fluorinated polymers such as polyvinyl fluoride (Tedlar), polyvinylidene fluoride, or ethylene chlorotrifluoroethylene . The back sheet is widely of three types, (a) KPK (PET/Kyner), (b) TPT (PET/Tedler), and (c) PPE (PET/EVA), and comprises C (54.9%–63.8%), H (4.3%–6.6%), O (24.5%–30.5%), N (0.2%), and F (0–9%) . The average composition of c-Si entails 75%–80% glass (front layer), 10% polymer (encapsulant and back sheet, SiN x ), 10% Al (mostly frame), 3%–5% Si (solar cells), and 1% Cu (connectors) .…”

Thermal delamination of end-of-life crystalline silicon photovoltaic modules

“…While no flue gas characterization has been performed in this work, this topic is of high importance and is therefore discussed briefly. Danz et al (2019) have shown that F-containing backsheets (containing PVF or PVDF) release notable amounts of fluorine (mostly in the form of hydrofluoric acid) when subjected to a thermal process. Detrimental effects on the environment and human health are expected if these emissions are handled incorrectly.…”