Solar Backsheets Unveiled: Understanding Types, Functions,and Challenges

· About Solar Panels,PV Technology News,PV Industry News

Introduction:

The dependability of solar modules is influenced by the caliber of the solar glass, backsheets, and encapsulating materials, which are essential parts of solar cell lamination. Any subpar part quickens the solar module's aging process. Poor quality backsheets for solar panels can result in lower performance, higher maintenance expenses, and additional costs for testing, repair, and inspection. Therefore, the long-term viability of your photovoltaic modules depends on making sure your solar panels have high-quality backsheets.

Content: 

  1. What are Solar panel Backsheets?
  2. What Certifications Are Required for Solar Panel Backsheets?
  3. What’s The Structure Of the Solar Panel Backsheet?
  4. What Are the Different Types of Solar Panel Backsheets?
  5. What Functions Of Solar Panel Backsheets?
  6. Which Backsheet is Best for your solar panels?
  7. Why does the Solar panel Backsheet have problems?
  8. What Are The Market Trends For Backsheets?

What are Solar panel Backsheets?

The backsheet of a solar panel is the outermost layer of a PV (photovoltaic) module and plays several vital functions. Its main purpose is to protect the PV cells and internal electrical parts while also offering electrical insulation.

Moreover, the backsheet provides a strong barrier against the elements, defending the module from environmental factors such as precipitation, humidity, and other unfavorable conditions.

Typically, backsheets come in various colors: entirely white, entirely black, white exterior with a black interior, and transparent (clear backsheets). The white color enhances light reflection between the cells to the front, with some light reflecting back onto the solar cell, optimizing light energy use and benefiting the photovoltaic conversion efficiency. Meanwhile, black backsheets are favored by European customers due to their aesthetic appeal on rooftops.

Solar panel Backsheets

What Certifications Are Required for Solar Panel Backsheets?

Solar panel backsheets typically need to undergo TUV certification, an internationally recognized testing and certification body. The TUV certification primarily involves partial discharge testing to ensure the quality and performance of the backsheet meets specific standards and requirements.Solar panel backsheets typically need to undergo TUV certification, an internationally recognized testing and certification body. The TUV certification primarily involves partial discharge testing to ensure the quality and performance of the backsheet meets specific standards and requirements. As the photovoltaic industry continually seeks higher power generation efficiency, some high-performance solar backsheets also have a higher light reflectance to enhance the photovoltaic conversion efficiency of solar modules.

What’s The Structure Of the Solar Panel Backsheet?

Initially, solar backsheets had a three-layer structure (PVDF/PET/PVDF). The outer PVDF layer offers excellent environmental corrosion resistance, the middle PET layer provides insulation, and the inner PVDF layer, combined with EVA, ensures good adhesion. To reduce costs and consider environmental factors, fluorine-free backsheet structures, such as the APE structure, were introduced.

A typical backsheet is composed of three core layers:

Outer Protective Layer (Weathering Layer): For optimal weather resistance, the outer layer material usually contains fluorine. PVF and PVDF are well-known polymers with high weather resistance. Some manufacturers also use THV, ETFE, ECTFE, and coated PTFE.

Middle Layer: This layer provides support and must withstand temperature fluctuations. It should have stable mechanical properties, excellent electrical insulation, and low gas and vapor permeability. Modified PET material is commonly used.

Lamination Adhesive Layer:

Unmodified fluorine films and PET have poor adhesion to EVA, so modified fluorine materials or adhesives like EVA, PE, or PA films are used.

What Are the Different Types of Solar Panel Backsheets?

Backsheets fall into three primary categories: bifluoropolymers, monofluoropolymers, and non-fluoropolymers, with multiple structural variations within each category.

1. Double-sided fluorine film composite backsheet

A. TPT Backsheet (PVF/PET/PVF)

The TPT backsheet, using a composite process, is the most common type of double-sided fluoropolymer backsheet available in the market. It combines DuPont’s Tedlar brand PVF fluorine film from the United States with an intermediate layer of PET base film, bonded together with adhesive. The inner fluorine material shields the PET from UV corrosion, and with special treatment and encapsulation of the adhesive film, it enhances bonding. The outer fluorine material provides protection for the back of the solar module against moisture, heat, and UV erosion.

B. KPK Backsheet (PVDF/PET/PVDF)

Compared to TPT, the KPK backsheet differs in that it uses PVDF film for both the inner and outer fluorine layers. This type of backsheet is known for its high mechanical strength, excellent irradiation resistance, good chemical stability, and resistance to corrosion by acids, alkalis, strong oxidizing agents, and halogens at room temperature. Originally, this backsheet was referred to as the KPK backsheet, made from Arkema France’s Kynar brand PVDF fluorine film.

C. KPF Backsheet (PVDF/PET/Fluorine Skin Film)

The KPF backsheet employs a composite process, laminating PVDF fluorine film to one side of the PET base film using adhesive. On the other side, a fluorine resin mixed with titanium dioxide is evenly coated onto the PET base film through a cast filming process. After a high-temperature maturation process, this coating forms a self-adhesive fluorine skin film, which is different from traditional fluorine coatings that tend to peel off easily. The fluorine skin film meets the high-performance requirements of foreign fluorine film products, including UV resistance and water resistance, while significantly reducing costs.esistance, while the price is significantly reduced.

2. Single-side fluorine film composite backsheet

A. TPE Type Backsheet (PVF/PET/PE)

The TPE type backsheet (PVF/PET/PE) primarily employs PE (polyolefin film) in place of the inner fluorine film. Due to the single-sided fluorine protection, it does not offer the same level of protection as the TPT structure, making it less capable of withstanding long-term UV aging tests. However, it presents a cost-effective alternative with lower expenses compared to the TPT structure.

B. KPE Type Backsheet (PVDF/PET/PE)

The KPE type backsheet (PVDF/PET/PE) largely relies on PE (polyolefin film) as a substitute for the inner fluorine film. With fluorine protection on one side, its protective performance is not as robust as that of the KPK-type backsheet, and it may struggle to endure prolonged UV aging tests. Nevertheless, it provides a more budget-friendly solution when compared to the FPF structure.

3. Non-fluoropolymers

This category involves two layers of PT and a primer or EVA layer, making it the most cost-effective choi