Concept and structure of solar photovoltaic backplane
Solar cell backplane is also called solar cell backplane film, photovoltaic backplane, photovoltaic backplane film, and solar backplane. It is widely used in solar cell (PV) modules, located at the back of the solar panel, to protect the solar cell modules from moisture erosion in outdoor environment, and to prevent oxygen from internal oxidation of the modules. It has reliable insulation, water resistance, aging resistance, high and low temperature resistance, and corrosion resistance. It can reflect sunlight and improve the conversion efficiency of components; It has high infrared reflectivity, which can reduce the temperature of the module.
Classification of photovoltaic backplane
According to the membrane classification of the backplane, it can be divided into three types:
1. Glued composite back plate film
Composite fluorine film or EVA adhesive film on both sides of PET polyester film with three-layer structure.
2. Coating back plate film
Fluorine resin is coated on both sides of PET polyester film, and the film is formed after drying and curing.
3. There are also a few manufacturers that use the crosslinking reaction method to produce composite film or EVA film on both sides of PET through the reaction of crosslinking agent.
According to the different classification of materials, the backplane can be divided into FPF (represented by TPT), KPK, FPE (represented by TPE), KPE and multi-layer PET backplane, TAPE (aluminum layer is added between T layer and P layer), TFB (PVF/PET/fluorine-containing adhesive layer), KFB (PVDF/PET/fluorine-containing adhesive layer), BBF (THV/PET/EVA), FFC (modified PTFE coated on both sides of PET), KPC (PVDF/special treatment PET), KPF (invented by Suzhou Saiwu, fluorine-coated film technology, the structure is PVDF/PET/fluorine-coated film) PPC (special treatment PET/weather resistant PET), etc.
PV backplane structure
The structure of the photovoltaic backplane is shown in Figure 1. It is generally divided into five layers, and the core has three layers:
(1) The outer protective layer is the weathering layer:
In order to have good weather resistance, the outer material is generally required to contain fluorine. PVF and PVDF are two well-known weather resistant polymer materials. Because the C-F bond energy existing in them is 485KJ/mol, which is the largest bond energy among the covalent bonds of organic compounds.
Only photons with wavelength less than 220 nm can dissociate the C-F bond, while these photons in the sun account for less than 5%, and are easily absorbed by the ozone layer, and very few can reach the ground. THV, ETFE and ECTFE are also used by manufacturers. PTFE with coated structure is also common.
(2) Middle layer:
As a support, it is required to be able to withstand high and low temperatures, stable mechanical properties, excellent electrical insulation, good creep resistance, fatigue resistance, friction resistance and dimensional stability, and low gas and steam permeability. Modified PET materials are generally used.
(3) Laminated adhesive layer:
The unmodified fluorine-containing film and PET have poor adhesion with EVA, so it is necessary to use modified fluorine-containing materials or EVA, PE and PA films with strong adhesion.