TPU (Thermoplastic Polyurethane) film: composition and application
TPU is the abbreviation of Thermoplastic Polyurethane film which is a resin that is used as a back sheet material in solar modules.
The solar module backsheets contain multiple layers of barrier films and adhesives. The backsheet construction is critical in protecting the solar cells from different environmental conditions like moisture, UV exposure and other performance threats while also improving solar module efficiency by aiding the reduction of partial discharge. To accomplish this, the solar panel material should be of a robust construction, usually a three-layer laminate, and it should possess high dielectric properties. Most backsheets consist of combinations of films chosen for their different properties. Examples of standard films include: PET or EVA, Tedlar and Kynar. Combinations can be TPT (Tedlar/PET/Tedlar), KPK (Kynar/PET/Kynar) or PPE (PET/PET/EVA) among other combinations.
What is TPU?
TPU (Thermoplastic polyurethane) is a copolymer block which consist of different arrangements of soft and hard segments which are formed by the reaction of diisocyanates with short chain diols and diisocyanates with long-chain diols. TPU is produced by changing the ratio or structure of the reaction compounds, different types of TPU can be produced.
TPU is mainly used in different applications like automotive panels, caster wheels, medical devices, cases of mobile devices and most importantly solar panel backsheets.
TPU use in solar panels
TPU is becoming more popular in manufacturing of backsheet of solar PV modules. The different Properties of commercially available TPU makes it a prime candidate for backsheet material as it has high abrasion resistance, good high elasticity, high transparency, oil resistance, shear strength and low temperature performance.
TPU backsheets show much less yellowing induced by UV than EVA . Yet, delamination of TPU glass can cause some problems as adhesion of TPU to glass can be seriously degraded by exposure to damp heat.
Alternatives to TPU
TPU has many alternatives available on the market. EVA is still the most popular encapsulant material for PV modules. TPT, TPAT (Tedlar/Polyester/Eva Film) backsheets among other combinations. Other famous alternatives are Tedlar and Kynar based backsheets.