Polyolefin PV Backsheet Structure for Thermal Cycling Crack Resistance
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Solution Overview
Problem
Photovoltaic module backsheets experience cracking issues due to temperature cycling, particularly above metal tabbing and adjacent to slits, leading to reduced electrical insulation and increased risk of electrical failure, which is exacerbated by the use of fluorinated polymers that are difficult to recycle and can decompose, releasing harmful compounds.
Innovation Solution
A coextruded photovoltaic module backsheet comprising a functional layer with a blend of polyethylene and polyethylene copolymer, and a weather-resistant layer with multiple sub-layers of polypropylene, where one sub-layer has a glass transition temperature below −40° C, reducing stress and allowing movement to prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fluorinated polymers (PVF, PVDF) are used in backsheets, then barrier properties and protection against environmental conditions are improved, but recyclability deteriorates and harmful fluorinated compounds may be released during decomposition
Solution Approach 1:
The patent removes fluorinated polymers from the backsheet composition entirely, extracting the harmful substance while maintaining protective functions through alternative materials. The backsheet uses polypropylene and polyethylene layers that provide barrier properties without fluorinated compounds, eliminating the source of harmful emissions during decomposition or recycling.
Solution Approach 2:
The patent changes the material composition parameters by substituting fluorinated polymers with polyolefin-based materials. This parameter change maintains the barrier function against moisture and UV radiation while fundamentally altering the chemical composition to eliminate harmful fluorinated compound release, achieving both protection and environmental safety.
2Reliability
If fluorinated polymers are used in backsheets, then protection against environmental conditions is improved, but ease of manufacture deteriorates due to difficulty in recycling
Solution Approach 1:
The patent extracts fluorinated polymers from the backsheet structure, eliminating the recycling difficulty associated with these materials. The remaining polypropylene and polyethylene layers are readily recyclable, significantly improving the ease of manufacture and end-of-life processing while preserving the environmental protection function.
Solution Approach 2:
The patent changes the material composition from fluorinated polymers to polyolefin-based materials, fundamentally altering the recyclability parameter. Polypropylene and polyethylene are well-established recyclable materials, making the manufacturing process and end-of-life processing significantly easier compared to fluorinated polymer alternatives.
3Power
If temperature cycling occurs in desert climates, then electrical energy generation is improved due to high insolation, but cracking of the backsheet increases leading to reduced electrical insulation
Solution Approach 1:
The patent uses a composite multi-layer structure combining polypropylene and polyethylene materials with different thermal properties. This composite construction allows the backsheet to accommodate thermal expansion and contraction during temperature cycling without cracking, maintaining electrical insulation integrity while operating in high-insolation desert environments where power generation is maximized.
Solution Approach 2:
The patent changes the thermal and mechanical parameters of the backsheet by selecting materials with appropriate glass transition temperatures and flexibility characteristics. The polyolefin-based composite maintains flexibility across wide temperature ranges, preventing crack formation during thermal cycling and preserving electrical insulation properties while enabling sustained high-power operation in desert climates.
4Strength
If coextrusion is used to produce multi-layer backsheet, then interlaminar strength is improved reducing delamination, but device complexity increases due to processing requirements
Solution Approach 1:
The patent employs homogeneous polyolefin-based materials (polypropylene and polyethylene) that are chemically compatible and can be coextruded without complex compatibility management. This homogeneity in material type simplifies the coextrusion process while achieving strong interlaminar bonding, reducing delamination risk without requiring overly complex processing equipment or procedures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces cracking in the backsheet under thermal cycling, maintaining electrical insulation and water resistance, and avoids the environmental concerns associated with fluorinated polymers by using recyclable polyolefin-based materials.
Implementation Method 1
the second sub-layer has a glass transition temperature (Tg) below −40° C.
Data Source
AI summary
The present invention relates to a photovoltaic module backsheet comprising, in order: photovoltaic module backsheet comprising a functional layer and a weather-resistant layer, wherein the backsheet is free of fluorinated polymers, characterized in that: i) the functional layer comprises a blend of polyethylene and a polyethylene copolymer, wherein at least 50 wt. % of the functional layer is polyethylene; and ii) the weather-resistant layer comprises, a first sub-layer facing the functional layer and a second sub-layer, wherein a) each of the first sub-layer and the second sub-layer comprise at least 50 wt. % polypropylene; and b) the second sub-layer has a lowest glass transition temperature (Tg) below −40° C. The present invention also relates to a process for producing the backsheet and a photovoltaic module comprising the backsheet according to the present invention.