While a PV backsheet is intended to protect solar PV modules, some solar plants are not able to operate for as long as they were intended to. Asset managers and O&Ms are increasingly finding systemic solar PV module backsheet failures, with 12GW already known to be at risk. Owners of assets are dealing with systemic failures of early modules that are occurring gradually and eventually cause losses in value. Any time during the life of a solar plant, systemic degenerative problems can develop in a variety of ways. The cost and impact of systemic degenerative issues like backsheet failure can be significantly decreased by fully digitizing the asset down to the module record.
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How Crucial Is The Backsheet Of A Solar Panel?
The backsheet is crucial because it guards the photovoltaic cells against damage from water, dust, debris, insects, and other environmental factors that might impair the system’s functionality.
Here are how a backsheet serves its purpose:
Protects From Mechanical Stress
The backsheet gives the module strength and durability. In the absence of a backsheet, the electrical system and photovoltaic cells may be subjected to potential mechanical stress, which could harm them.
Mechanical stress can take the form of pressure, impacts, vibrations, and shock from many different sources, including earthquakes, wind load, snow and ice weight, falling objects like rocks or branches from nearby trees or buildings, human activity, and wind load.
If the correct backsheet is not in place, each of these factors may result in damage to the PV cells and/or electrical system.
Protects From Water & Dust Intrusion
A strong defense against dust and water infiltration is provided by the backsheet layer. Photovoltaic cells may experience corrosion and pitting as a result of water and dust particles, among other problems.
A backsheet aids in preventing moisture-related damage such as corrosion of electrical connections or parts, deterioration of the insulation, and potential short circuits.
Additionally bothersome, dust particles can reduce the effectiveness of the system or even stop it from working altogether if they build up on the cell surfaces. This can be avoided with the aid of a backsheet, which shields against the particles, preventing accumulation on the cell surfaces.
Protects Against Uv Exposure
By shielding the system from solar radiation, the solar panel backsheet also helps to prevent damage brought on by ultraviolet (UV) exposure. The semiconductor components of the cell may degrade due to UV radiation, which will impair their effectiveness.
The backsheet helps to block UV radiation and shield the cells from its damaging effects. All backsheets, however, will eventually lose their color due to UV exposure, regardless of the material used.
However, a color shift isn’t always a sign of a broken backsheet. However, a problem might be present if a color change is significant and the backsheet exhibits signs of deterioration.
Reduces Thermal Stress
In the PV module, backsheets also lessen thermal stress. When temperatures are too high or low, photovoltaic cells may become stressed, which will reduce their effectiveness. In order to prevent thermal stress, a backsheet protects the system from both high and low temperatures.
By keeping high-energy photons from reaching the PV cells, the backsheet also helps to reduce solar heat gain and avert overheating, which could harm the cells or result in poor performance.
Minimizing heat gain is crucial because, as we already know, solar cells’ performance declines as temperature rises above a certain point. By lowering solar heat gain and shielding the cells from overheating, the backsheet contributes significantly to this aspect.
Dielectric Strength
A solar panel is a self-contained energy system, so nothing outside shouldn’t interfere with it electrically. A protective barrier, the backsheet prevents electrical conductivity between the cells and the environment.
The maximum electric potential that can be applied to a material without causing an electrical breakdown or losing its insulating properties is known as the dielectric strength. Because high voltage can be applied to materials with high dielectric strength without causing dielectric breakdown, this is true.
In order for the system to operate as it should—properly and efficiently—the backsheet must have electrical integrity, shielding the solar cells from any outside interference. Short circuits and other electrical failures are always a possibility when the solar cells aren’t protected by the proper kind of backsheet.
As you can see, the backsheet plays a crucial role in protecting materials from a variety of environmental factors, including mechanical stress, corrosion, and degradation brought on by UV radiation, extreme temperature changes, and humidity.
What Characteristics Should A Backsheet Layer Of Superior Quality Possess?
Low Cost
Backsheets are no different from other materials in that cost is the main consideration when selecting one. In order to reduce costs, manufacturers have been known to compromise on quality and use less expensive materials for the backsheet layers of their solar panels.
Because it plays a crucial role in the energy system, protecting expensive cells and maintaining their efficiency, the backsheet should be of a high quality without being overly expensive.
A typical solar panel can last for 25 to 30 years. However, because backsheets and other components may not last as long, cheaper PV modules have been shown to be an expensive long-term investment.
Under constant cost pressure, manufacturers keep thinning the outer protective layer while also maintaining the PET core’s susceptibility to moisture.
Backsheets with an outer fluoropolymer film that is less than 20 microns thick have recently flooded the market, whereas this layer used to be more than 40 microns thick. The outer “protective” layer may be as thin as 10 microns in some situations, exposing the backsheet to more serious harm.
Many manufacturers use shady strategies to take advantage of regulatory gaps and reduce expenses in order to increase profits.
One of the main reasons why backsheet failure occurs is that many businesses still use inexpensive materials for the core layers, like low-stabilized PET. The use of PET polymer in outdoor applications is constrained despite the fact that it can offer good electrical insulation because it is so sensitive to moisture and sunlight.
Some manufacturers substitute thin layers of fluoropolymers like PVF (Tedlar), PVDF, or highly stabilized PET for low-stabilized PET for the core layers.
Despite the fact that stabilizing the entire PET core layer is still preferred, this method only preserves the quality of the outer layers, which has been shown to be a shortsighted approach in practical applications.
For this reason, it’s essential to pick a solar panel manufacturer that has its backsheets tested by unbiased third-party laboratories.
Despite this, many manufacturers’ products can hardly pass tests that are the industry’s bare minimum requirements, meaning that basic regulatory tests are frequently insufficient. It is crucial to search for a more sophisticated and thorough backsheet testing method because of this.
The appropriate backsheet material should have undergone testing and been shown to pass all applicable industry standards, including IEC, NEMA, and UL, and exhibit superior performance over the course of the module lifetime in practical applications.
Many manufacturers tout the superior backsheets on their products, but in reality, they’re just trying to market them in a way that makes them appear better than they are.
Since independent testing provides unbiased information on a back sheet’s durability and performance, it is the only way to verify its quality.
Customers will be less confused if backsheet materials are tested by accredited third-party laboratories for a specific number of days, months, and years for various environmental conditions and standards.
Manufacturers who have their backsheets examined by unbiased, outside laboratories are more reliable. Because they’re willing to disclose all the details about their products and demonstrate that they’re actually trying their best to provide high-quality products, rather than just trying to sell a subpar product for high profit margins.
Backsheets from certified manufacturers also typically make use of high-performance components and construction methods, resulting in a long product lifespan.
Solid
The backsheet must be strong enough to maintain its shape and withstand pressure from the outside elements. Although backsheets are made of polymer material, which is somewhat flexible, they should be sturdy enough to withstand pressure from the outside.
Chemical Inertness
The backsheet needs to be chemically inert, which means it can’t interact with its surroundings or other photovoltaic system parts in a way that could eventually harm them. The objective is to create a material that is stable and whose composition won’t change over time.
Durability
To last for a long time without breaking or tearing, the backsheet must be extremely strong. The backsheet should be made of sturdy materials that can withstand weathering, heat, dirt, grease, and other environmental factors.
Resistance To Uv Radiation
UV rays shouldn’t be able to pass through the backsheet because it should be UV resistant. Backsheets of superior quality can withstand prolonged UV radiation exposures without losing structural integrity or allowing the cells behind them to degrade.
Resistance To Moisture
Water must not absorb into or pass through the backsheet, which means it must be water resistant.
As a result, high-quality backsheets are typically made from materials that repel water and have hydrophobic properties. The backsheet needs to be tough enough to withstand moisture exposure for a prolonged period of time.
Resistance To High Temperatures
Extreme high and low temperatures should not cause the backsheet to weaken, soften, or allow other heat-related harm to the solar cells.
Backsheets should be able to withstand high temperatures without losing their structural integrity or affecting the cells behind them. Additionally, thermal shrinkage should be tolerated by the backsheet without causing it to lose its shape or structure.
Lightweight
The backsheet should be as light as possible to avoid adding to the overall system’s weight and impairing its performance.
The system may be more challenging to install as a result of additional weight, which also causes handling and transport issues. The backsheet of a solar panel should weigh no more than any other component, ideally less.
Good Adhesion Strength
In order to remain attached to the PV cells even when exposed to strong winds, other weather conditions, or in situations where there is thermal cycling, the backsheet needs to have a high level of adhesion strength. The backsheet is able to shield the cells from harm as a result of outside forces in this way.
Environmentally Friendly
In order to prevent long-term damage, the backsheet should be environmentally friendly. The backsheet’s manufacturing process’s materials shouldn’t be harmful to people’s health or have an adverse effect on wildlife or other natural resources.
There are more disposal options for polyethelene (PET) backsheets than for fluorinated backsheets. Because the only thing you can really do with fluorinated backsheets is throw them in the trash, which is bad for the environment.
What Are The Impacts And Failures In The Field?
Backsheet field failures have been rising alarmingly in recent years. These consist of inner or outer layer cracking, delamination, and yellowing. According to a recent 2019 study, the backsheet is to blame for 14.3% of all field-occurring module defects. when compared to 2018, there will be a 48% increase in 2019. According to field observations, all types of backsheet materials exhibit accelerating rates of backsheet deterioration over time. According to reports, after only six years of operation, the PA type of backsheet experiences up to 95% of field failures.
A flaw or failure in the backsheet typically has a negative effect on the performance of the PV module because the backsheet is intended to act as an insulator. The most frequent outcome of backsheet failure is ground faults brought on by decreased insulation resistance. which frequently causes the inverter to trip, cutting off a lot of power. In addition to affecting performance, ground faults can also cause safety problems like arcing, which could put the entire system at risk of fire. Particularly risky for large PV systems because the sensitivity range of fault detection components allows the leakage current to go undetected for an extended period of time.
Corrosion of ribbon connections and busbars inside the internal circuit can also result from the backsheet’s cracking and delamination. Corrosion will result in hot spots, which means that energy is lost as heat and results in further power loss.
Testing, Inspection, And Detection Of Backsheet Degradation
The safety standard IEC 61730 and the certification standard IEC 61215 for photovoltaic modules are made to test for early failures of the modules rather than to simulate the environmental stresses that the modules might encounter in the field. Backsheets can now be put through combined and sequential accelerated stress tests to reveal failures that are similar to those seen in the field thanks to advancements in PV module and material reliability testing.
PV module backsheet degradation and field failures are typically found through visual inspection. You can perform a rubbing test using an insulating material to observe chalking, depending on the severity of the degradation. The string needs to be disconnected from the electrical circuit before doing this. Additionally, hot spots brought on by corrosion or delamination as a result of a backsheet flaw can be located using thermal imaging. This can be used in conjunction with high-resolution imaging taken by drones to document any possible delamination that is visible on the PV module’s front side.
Fourier Transform Infrared (FTIR) spectroscopy, a method for identifying the polymeric materials, is a technique that can be used to determine the type of backsheet used in a PV module and the degradation (if any). It scans the samples and determines the chemical characteristics of the substance using infrared light. By comparing results with an unaged material, any alteration in the chemical composition brought on by degradation can be found.
What Layers Does A Backsheet Contain?
Typically, there are three layers in a backsheet. These are the protective layer, inner side layer, and cell side layer.
Protective Layer (air/outside Layer)
The outside layer or outermost layer are other terms for the protective layer. It guards against environmental interference, such as rain or debris, and shields the inner core PET film from being easily scratched or damaged.
This layer is made of a top-notch polymer that resists breaking or easily cracking under pressure and is tear- and puncture-resistant.
Additionally, the protective layer has electrical insulation properties that ensure that no electrical current will be interfered with and that solar panels won’t electrically short out.
Inner Side Layer
The backsheet’s inner side layer is sandwiched between the protective layer and the cell side layer.
Because it is thicker than other layers, it gives the backsheet the mechanical stability it needs to shield solar cells from harm while also promoting the adhesion of the adhesive layers. Good electrical insulation qualities are also present in the inner side layer.
Cell Side Layer
Nearest to the solar cells on the opposite side are the cell side layers. They are shielded from a number of things that could harm their performance. A thinner polymer material with good ductility and flexibility is typically used to make it.
This layer typically has a high reflectance to lessen the heat that is trapped inside and prevent overheating. It quickly and efficiently dissipates heat to allow the solar cells to operate as intended.
Backsheet Production: How Are They Made?
Backsheets are currently made using a variety of techniques.
Extrusion Method
Due to its affordability and efficiency, the extrusion method is a widely used backsheet manufacturing process.
To create a film that will be used as a backsheet, molten polyethylene terephthalate resin (PET) is pushed through a die. Depending on the requirements, different backsheet thicknesses can be produced using this method.
Lamination Method
Another well-liked manufacturing technique is lamination, which involves joining two layers together with a powerful adhesive, most frequently EVA (ethylene vinyl acetate). Usually, this procedure is used to produce backsheets that are thicker.
The procedure entails a number of steps, including heating the PET film under high pressure while pressing it between two metal rollers to create a smooth surface. In order to increase the film’s thickness and make it more durable, it is then rolled onto another metal roller.
Co-extrusion Method
The co-extrusion method has replaced the conventional lamination method because it generates highly coherent multi-material products without the use of adhesives. A multilayer co-extrusion die is used in the procedure, and it can simultaneously produce a variety of backsheet types because it has multiple layers of different materials.
The reinforcement of the core holds great promise in addition to co-extrusion. Since the backsheet’s core can be reinforced, its stiffness and tear resistance are improved, and production costs may be decreased as well.
Which Materials For Backsheets Are Offered On The Market?
Today’s market offers a wide variety of backsheet types, but the following are the most popular ones.
Polyethylene Terephthalate (pet) Backsheet
Backsheets are frequently made from the polyethylene terephthalate (PET) material. Although it has good mechanical qualities, it can’t withstand solar radiation for very long.
When exposed to UV light, PET backsheets typically deteriorate and eventually turn yellow. The yellowness index (YI), which represents the color change of polymer and is connected to chemical change brought on by irradiance, high temperature, and other processes, can be used to identify degradation.
One of the most popular solutions used in back-sheet fabrication is the addition of thin layers of fluoropolymers like PVF, PVDF, or highly stabilized PET to secure the primary material.
Fluoropolymer Backsheets
Fluoropolymer Backsheets are the industry standard for backsheets due to their outstanding chemical resistance to a variety of harsh elements that can degrade solar cells.
In terms of backsheets, fluoropolymers—materials that are hydrophobic and chemically inert—outperform PET because they are UV and chemically resistant. They can be made very thin but are incredibly strong, and they have good mechanical and thermal stability.
However, due to their intricate manufacturing process, which calls for the use of a variety of different polymers, catalysts, and additives, fluoropolymers are expensive to produce.
Perfluoroalkoxy copolymer (PFA), polyvinylidene fluoride (PVDF), and ethylene-tetrafluoroethylene copolymer (ETFE) are the three fluoropolymers most frequently used as backsheets.
How To Address The Problem Of Backsheet Failure
The intelligent software and inspection solutions mentioned above can help you build strong PV module warranty claims, understand the seriousness of the problem, and provide a digital solar plant for the stringent monitoring of your modules. Get in touch with us to learn how our solutions can assist you in maintaining the health of your solar plant’s modules.
What Are The Most Typical Backsheet Issues That Could Happen?
Peel Off Issue With Eva
Backsheets will gradually deteriorate over time if they are exposed to the sun’s UV rays. When they peel off as a result of this, other issues may become visible and they may lose their adhesive qualities.
The degradation of backsheets can occur for a variety of reasons in addition to UV rays. Backsheet peeling can also be caused by high humidity, high temperatures, and environmental chemical contaminants.
Air Side Layer Coating Issue
The issue with the air side layer coating is one of the most frequent backsheet issues that is likely to arise.
This occurs when the polymer materials on either side of the back sheets have poor adhesion, which is typically brought on by humidity or high temperatures during the manufacturing or installation process of the module.
Due to the two polymer layers that make up the backsheet, a strong adhesive force is needed to bind and shield solar cells from moisture and other environmental factors. Backsheet layer delamination can occur when these polymer materials’ adhesive strength is compromised.
Layers Crack Issue
When exposed to high temperatures and moisture for an extended period of time, the backsheet layers are more susceptible to cracking. In addition to making them peel off, this may also allow moisture to penetrate the cell side layer, damaging solar cells through exposure.
If the cracks aren’t too large, they can go unnoticed for a very long time. However, excessive cracking in a single area of the backsheet or on both sides of it close to one another may hinder moisture infiltration.
Yellowing Issue
Moisture and UV rays both have the potential to cause backsheet yellowing. Backsheets gradually start to turn yellow over time when they are exposed to the sun’s ultraviolet rays.
The first indication of backsheet deterioration is typically yellowing. Water has the same properties. Backsheets may start to turn yellow when they are exposed to high humidity levels or liquids because the material is made of organic compounds that respond to shifting environmental chemistry.
Delamination Issue
When the backsheet layers are improperly bonded together, a problem called delamination arises. When this occurs, any solar cells below the surface may sustain damage, which could result in cell deterioration or failure.
This typically happens as a result of poor adhesion between the polymer materials on either side of the backsheets during the assembly process and high temperatures.
Conclusion
The fact that backsheets shield the cell side layers from moisture and other environmental factors makes them a crucial part of photovoltaic solar panels. Backsheets can be made of a variety of materials, and new ones are constantly being created.
Due to climatic conditions or problems with the materials, all backsheets will eventually start to degrade to some extent. Different degradations can cause various issues that might or might not be immediately apparent.
Since they are all suited for particular purposes, it is crucial to understand the various types of backsheet materials and the issues that each one raises. The more you understand about your materials, the more you can do to avoid backsheet issues.
