How do TPT, PVF and PET compare to each other?
TPT, PVF and PET backsheets
TPT(Tedlar Polyester Tedlar), Polyvinyl fluoride (PVF) and PET (Polyethylene terephthalate) are all different materials used in solar panel backsheets.
The purpose of photovoltaic (PV) backsheet is to protect the backside of the solar module from the effects of weather conditions and to mitigate any electric shock hazards. They are typically based on polymer materials and have multi-layer construction, with a weather resistant outer layer, a core layer which is electrically insulating, and an adhesive inner layer. The outer layer is most commonly based on a fluoropolymer, such as PVF (polyvinyl fluoride). Yet, the growing need to reduce cost while maintaining or extending backsheet service lifetime has led to the development of new PV backsheets, like those based on non-fluoropolymer outer layers.
Some of these newer backsheet materials are based on polyamides (PA) or polyesters (for example PET (polyethylene terephthalate) or PEN (polyethylene naphthalate) among others). These materials are more susceptible to environmental degradation than fluoropolymers, and must be appropriately modified so as to make them suitable for use as a backsheet. Nonetheless, they are typically less expensive, and have a more complete material life cycle (as they allow for easier module recycling for example), which better aligns with the ultimate goal of sustainability in all PV technologies.
How performance of TPT, PVF and PET compare to each other
TPT and PVF are fluoropolymer-based backsheets while PET is a non-fluoropolymer-based backsheet. Fluoropolymer-based backsheets have high performance and properties, yet the cost of TPT and PVF is high and has a more complex manufacturing process. Tedlar based backsheets are the most expensive, while PVF is cheaper and non-fluoropolymer-based backsheets are the least expensive.
TPT, PVF and PET have many common qualities as they have good mechanical strength, high transparency, good thermal and chemical resistance and low water absorption rate. Yet, for field performance the ageing for PET is the worst. Research has shown PET backsheets to show clear evidence of yellowing and cracking. The overall comparison has shown that the performance of the backsheets vary differently.
The newer types of non-fluoropolymer-based backsheets provide a more economic option (mainly PET), but the fluoropolymer-based backsheets (PVF, TPT) are more expensive but their performance is field tested. Degradation of the PET is the worst as it has shown crack formation yellowing, gloss-loss, and chemical changes in recent tests. Best performance was achieved by TPT backsheet.