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Solar Panel Backsheet: [All To Know About]

Solar panels are an excellent way to generate renewable energy, but they need the right type of backing.

This is where solar panel backsheet materials come in. They are essential for protecting fragile solar cells from harsh weather conditions and other potential damage that may occur on the back exterior side of the PV module.

What is a backsheet?

The backsheet is the outermost layer of the PV module and is designed to protect the inner components of the photovoltaic cells, electrical system, and to serve as an electrical insulator.

Its functions as a weather barrier and seal off the components from rain, moisture, or other environmental conditions.

Backsheets are generally made from polymer materials like polyvinylidene fluoride (PVDF), polyesters (PET), polyamides (PA), ethylene chlorotrifluoroethylene (ECTFE), ethylene-vinyl acetate copolymer (EVA), and tetrafluoroethylene hexafluoropropylene vinylidene fluoride (THV).

A backsheet can also be made from a blend of different polymers to achieve the desired properties.

There are single fluoropolymers, double fluoropolymers, and non-fluoro polymers are all common backsheets that contain a different combination of polymers.

What is the importance of backsheet in PV systems?

The backsheet is important because it protects the photovoltaic cells from damage caused by water, dust, debris, insects, and other environmental conditions that could potentially disrupt the system’s function.

Here are how a backsheet serves its purpose:

Protects from mechanical stress

Backsheet provides durability and strength to the module. If there is no backsheet, the photovoltaic cells and electrical system will be subjected to potential mechanical stress, which could damage them.

Mechanical stress can be in form of pressure, impacts, vibrations, and shock from a variety of sources such as human activity, wind load, snow and ice weight, falling objects such as rocks or branches from nearby trees or buildings, and even earthquakes.

All of these factors can cause damage to the PV cells and/or electrical system if the proper backsheet is not in place.

Protects from water & dust intrusion

The backsheet layer serves as an effective barrier against water and dust intrusion. Water and dust particles can cause a variety of issues for photovoltaic cells, such as corrosion and pitting.

Backsheet helps to prevent the damage caused by moisture, such as corrosion of electrical connections or components in addition to insulation degradation and potential short-circuiting.

Dust particles can also be a nuisance, causing the system to lose efficiency and even stop functioning if they accumulate on the cell surfaces. Backsheet helps to prevent this from happening by protecting against those particles so they do not build up or accumulate on the cell surfaces.

Protects against UV exposure

The solar panel backsheet also helps to prevent damage caused by ultraviolet (UV) exposure by protecting the system from solar radiation. UV radiation can cause the cell’s semiconductor materials to break down, which will affect their performance and efficiency.

The backsheet assists in keeping UV radiation at bay and protecting the cells from its harmful effects. However, regardless of the material used, all backsheets will change color over time due to UV exposure.

That said, a color change doesn’t always indicate a defective backsheet. However, if a color change is severe and the backsheet shows signs of deterioration, this may indicate an issue.

Reduces thermal stress

Backsheets also help to reduce thermal stress in the PV module. Photovoltaic cells can become stressed when there is too much heat or cold, which will affect their performance and efficiency. A backsheet helps by insulating the system from both high and low temperatures to avoid thermal stress.

The backsheet also helps to reduce solar heat gain by preventing high-energy photons from reaching the PV cells, which will help prevent overheating that can cause damage or poor performance.

As we already know, solar cells’ performance drops as temperature increases over a certain threshold, so minimizing heat gain is important. Backsheet plays an important role in this aspect by reducing solar heat gain and protecting the cells from overheating.

Dielectric strength

A solar panel is a self-contained energy system that should not be affected electrically by anything on the outside of it. The backsheet acts as a protective barrier, preventing electrical conductivity between the cells and the surrounding environment.

Dielectric strength is the maximum electric potential that can be applied across a material without causing an electrical breakdown or loss of insulating properties. This is because materials with high dielectric strength can be subjected to the high voltage without undergoing dielectric breakdown.

The backsheet should have electrical integrity, preventing any disturbance from outside to the solar cells so that the system can function properly and efficiently as it is supposed to. Without the right type of backsheet insulating the solar cells, there is always the potential for short circuits and other electrical failures to occur.

As you can see, the backsheet is critical in dealing with different types of environmental conditions like mechanical stress, corrosion, and degradation caused by UV radiation, extreme temperature fluctuations, humidity.

What properties does a high-quality backsheet layer should have?

Low cost

Cost is the most important factor in choosing any material and backsheets are no different. As a result, manufacturers have been known to lower costs by cutting back on quality and using cheaper materials for the backsheet layers in their solar panels.

The backsheet should have high quality without being too costly because it plays a very important role in the energy system, protecting expensive cells and keeping them safe and efficient.

A typical solar panel has a life expectancy of 25 to 30 years. However, cheaper PV modules are proven to be a costly long-term investment due to the ongoing need for replacing backsheets and other components that may not last as long.

Manufacturers continue to reduce the outside protective layer’s thickness while also maintaining the PET core’s vulnerability to moisture under continual cost pressure.

Recently, backsheets with a fluoropolymer outer film with a thickness of less than 20 microns have flooded the market, whereas previously this layer was more than 40 microns. The outer “protective” layer may be as thin as 10 microns in some situations, exposing the backsheet to more serious harm.

There are many manufacturers employing shady tactics in order to exploit loopholes in regulations and cut costs to maximize profits.

Many companies continue to use low-cost materials such as low-stabilized PET for core layers, which is one of the primary causes of backsheet failure. Despite its ability to provide good electrical insulation, PET polymer is extremely sensitive to moisture and sunlight, limiting its use in outdoor applications.

As a solution to low-stabilized PET for core layers, some manufacturers add thin layers of fluoropolymers such as PVF (Tedlar), PVDF, or highly stabilized PET in backsheet content.

Although this is considered a more cost-effective alternative to stabilizing the entire PET core layer, it limits the shelf-life to the quality of the outer layers only, which has been shown to be a short-sighted strategy in real-world applications.

This is why it’s crucial to choose a solar panel manufacturer that has its backsheets tested by independent third-party laboratories.

That said, basic regulatory tests are usually not enough, many manufacturers’ products can barely pass tests that are minimum standards in the industry. This is why it’s important to look for an advanced and more thorough backsheet testing procedure.

The right backsheet material should be tested and proven to pass all industry standards such as IEC, NEMA, UL, and demonstrate superior performance over the entire module lifetime in real-world applications.

A lot of manufacturers claim that their products have high-quality backsheets, but in reality, they’re just trying to market their products in a way that makes them seem better than they actually are.

Therefore, independent testing is the only way to validate a backsheet’s quality, as it offers unbiased data on its durability and performance.

Backsheet materials that are tested by certified third-party laboratories for a certain number of days, months, and years for various environmental conditions and standards will create less confusion for customers.

Manufacturers that have their backsheets tested by independent third-party laboratories are more trustworthy. Because they’re willing to put out all the information about their products and prove that they’re not just trying to sell a sub-par product for high-profit margins but are actually doing their best to provide high-quality products.

In addition, certified manufacturers’ backsheets tend to use high-performance materials and construction techniques, ensuring a long product lifetime.

Solid

The backsheet has to be solid enough to keep its form and withstand the pressure applied by the environmental factors. Although backsheets are made of polymer material that is flexible to some degree, they should be solid enough to withstand the outside pressure.

Chemical inertness

The backsheet has to be chemically inert, which means it should not react with its surroundings or other components in the photovoltaic system that can damage them over time. The goal is to have a material that is stable and will not change its composition over time.

Durability

The backsheet has to be highly durable so that it can last for a significant period of time without breaking or tearing. The materials used in the backsheet should be durable and resistant to weathering, heat, dirt, grease, and other environmental elements.

Resistance to UV radiation

The backsheet should be resistant to UV radiation and doesn’t allow UV radiation to permeate through it. High-quality backsheets can sustain long exposures to UV radiation without losing their structural integrity or letting the cells behind them break down.

Resistance to moisture

The backsheet has to be resistant to water, which means it should not absorb or allow water to permeate through it.

Because of this, high-quality backsheets are usually made with materials that have hydrophobic properties that repel water. The backsheet has to be durable enough so that it can last for a significant period of time while exposed to moisture.

Resistance to high temperatures

The backsheet should be able to withstand extreme high and low temperatures without becoming flimsy, softening, or allowing other heat-related damage to the solar cells.

When exposed to high temperatures, backsheets should maintain their structure and not affect the cells behind them. Also, the backsheet should be able to withstand thermal shrinkage without losing its form and structure.

Lightweight

The weight of the backsheet should be as low as possible so that it does not add to the weight of the entire system and affect its function.

Because extra weight creates problems for handling and transport and can make the entire system more difficult to install. The lower the weight of backsheet as any other component of the solar panel, the better.

Good Adhesion Strength

The backsheet should have a high level of adhesion strength so that it will stay attached to the PV cells even when exposed to strong winds and other weather conditions, or in cases where there is thermal cycling. In this way, the backsheet can protect the cells from damage caused by outside forces.

Environmentally Friendly

The backsheet should be environmentally friendly to ensure that it doesn’t cause damage over time. The materials used in the manufacturing process of the backsheet should not affect human health or impact wildlife and other natural resources.

Polyethelene (PET) backsheets have more disposal options than fluorinated backsheets. Because there is not much to do with fluorinated backsheets other than sending them to landfill which is not a good option for the planet.

What layers does a Backsheet have?

Backsheets are generally made up of three different layers. These are the protective layer, inner side layer, and cell side layer.

Protective Layer (Air/Outside Layer)

The protective layer is also known as the outside layer or outermost layer. It protects the inner core PET film from any environmental interference, such as rain or debris, while also preventing it from being scratched or damaged easily.

This layer is resistant to tear and puncture and is made up of a high-quality polymer that will not easily crack or break under pressure.

The protective layer has also electrical insulation properties that prevent solar panels from electrically shorting and will not interfere with any electrical current.

Inner Side Layer

The inner side layer is in between the protective layer and the cell side layer of the backsheet.

It is thicker than other layers and gives backsheet the mechanical stability it needs so that it can protect solar cells from damage, while also providing adhesion for the adhesive layers. The inner side layer also has good electrical insulation properties.

Cell Side Layer

The cell side layer is closest to the solar cells on the other side. It protects them from various factors that can cause degradation of their performance. It is usually made up of a thinner polymer material that has good ductility and flexibility.

This layer has typically high reflectance to reduce the amount of heat that gets trapped inside to prevent overheating. It dissipates heat quickly and effectively so that the solar cells can function properly.

How are backsheets manufactured?

There are several methods used today to manufacture backsheets.

Extrusion Method

The extrusion method is a very common backsheet manufacturing process since it is cost-effective and efficient.

The molten polyethylene terephthalate resin (PET) is forced through a die to create a film that will then be used as a backsheet. There are different thicknesses of backsheets that can be made with this method depending on the need.

Lamination Method

Another popular manufacturing method is the lamination process which uses a strong adhesive material, typically EVA (ethylene vinyl acetate) to stick two layers together. This process is typically used to make thicker backsheets.

The process involves several steps, including pressing the PET film between two metal rollers to create a smooth surface while heating it up under high pressure. The film is then rolled onto another metal roller to increase its thickness and cooled down under low pressure until it becomes durable enough for use.

Co-extrusion Method

Co-extrusion method is replacing the traditional lamination method since it requires no adhesives and produces highly coherent multi-material products. The process uses a multilayer co-extrusion die that has different layers of materials and can produce many types of backsheets at once.

In addition to co-extrusion, the reinforcement of the core has a great deal of promise. Because reinforcing the core of the backsheet improves its stiffness and tear resistance, and can help reduce production costs as well.

What types of backsheet materials are available on the market?

There are many different types of backsheets available on the market today, but the most common types are as below.

Polyethylene Terephthalate (PET) Backsheet

Polyethylene terephthalate (PET) is a very common material used in manufacturing backsheets. It has good mechanical properties but cannot resist solar radiation for a long time.

PET backsheets tend to degrade when exposed to ultraviolet (UV) light and turn to yellow over time. Degradation can be characterized by the yellowness index (YI), which represents the color change of polymer and is associated with chemical change due to irradiance, high temperature, and other process.

To overcome this problem, one of the most common applications utilized in back-sheet fabricating is to include thin layers of fluoropolymers like PVF, PVDF, or highly stabilized PET to secure the main material.

Fluoropolymer Backsheets

Fluoropolymer Backsheets dominate the backsheet market because of their excellent chemical resistance to many harsh factors that can cause degradation of the solar cells.

Fluoropolymers are chemically inert, hydrophobic materials that are superior to PET as backsheets because they are resistant to chemical substances and UV light. They feature good thermal stability and mechanical properties and can be made very thin yet highly durable.

However, fluoropolymers are expensive to produce because of their complex manufacturing process that requires the use of a combination of different polymers, catalysts, and additives.

The most common types of fluoropolymers used as backsheets are perfluoroalkoxy copolymer (PFA), polyvinylidene fluoride (PVDF), and ethylene-tetrafluoroethylene copolymer (ETFE).

What are the most common backsheet problems likely to occur?

Peel Off Issue with EVA

When backsheets are exposed to the sun’s UV rays, they will gradually break down over time. This can cause them to lose their adhesive properties and peel off leaving them exposed to other problems.

However, UV rays are not the only factor that can contribute to backsheet degradation. High humidity levels, high temperatures, and chemical contaminants from the environment are also factors that will contribute towards backsheet peeling.

Air Side Layer Coating Issue

One of the most common backsheet problems that are likely to occur is the air side layer coating issue.

This happens when there is poor adhesion between polymer materials on either side of back sheets, usually caused by humidity or high temperatures during module manufacture or installation process.

Since the backsheet is made up of two polymer layers, it requires a good adhesive force to bind and protect solar cells from moisture and any other environmental factors. When the adhesive strength of these polymer materials is compromised, it can cause delamination of backsheet layers.

Layers Crack Issue

The backsheet layers are more likely to crack when exposed to high temperatures and moisture over a long period of time. This can cause them not only to peel off but also allow moisture into the cell side layer which will damage solar cells from exposure.

Unless the cracks are so big they can go unnoticed for long time. However, if there is too much cracking in one area of the backsheet or on both sides of it near to each other, this can cause problems with moisture penetration.

Yellowing Issue

Backsheet yellowing can be caused by both UV rays and moisture. When backsheets are exposed to the sun’s ultraviolet light, they will gradually begin to yellow over time.

Yellowing is usually the first sign of backsheet degradation. The same also applies to moisture. When backsheets are exposed to high humidity levels or liquids, they can begin to yellow since the material is made up of organic compounds that will react to changing environmental chemistry.

Delamination Issue

Delamination is a problem that occurs when the backsheet layers are not properly bonded together. When this happens, it can cause damage to any solar cells under the surface which may lead to cell degradation or failure.

This usually occurs because of poor adhesion between polymer materials on either side of backsheets due to humidity levels during the assembly process and high temperatures.

Conclusion

Backsheets are a critical component in photovoltaic solar panels because they protect the cell side layers from moisture and other environmental factors. There are many different types of backsheet materials and newer materials are being developed every year.

All backsheets will eventually begin to experience some level of degradation due to environmental factors or materials compatibility issues. Different types of degradation can lead to different problems that may or may not be easily noticeable.

Therefore, it’s important to know the different types of backsheet materials and what concerns each one has since they are all suited for specific purposes. The more you know about your materials, the more you can do to prevent backsheet problems from occurring.