An encapsulant material suitable for use in photovoltaic modules

Abstract

The invention belongs to the technical field of material engineering and relates to an encapsulant material for photovoltaic cells, providing high light transmittance, electrical insulation, and protection against environmental factors.

Description

[0001] AN ENCAPSULANT MATERIAL SUITABLE FOR USE IN PHOTOVOLTAIC MODULES

[0002] TECHNICAL FIELD

[0003] The invention belongs to the technical field of material engineering and relates to an encapsulant material for cells in photovoltaic modules, providing high light transmittance, electrical insulation, and protection against environmental factors.

[0004] PRIOR ART

[0005] Photovoltaic ceils are semiconductor devices that convert sunlight directly into electrical energy. This conversion process is based on the principle that photons interact with the semiconductor material of the cell to mobilize electrons and generate an electric current.

[0006] Photovoltaic technology has an important place among renewable energy sources and is used in various applications such as solar panels, calculators, satellite systems.

[0007] Photovoltaic cells must not be affected by environmental factors in particular in order to maintain their performance as intended. Examples of these environmental factors include humidity, temperature, UV rays, and wind. Further, dirt and dust may also create a negative situation for photovoltaic cells.

[0008] It is important to increase the efficiency and endurance of the photovoltaic system, to ensure that light reaches the cells effectively, and to maintain electrical insulation.

[0009] For such reasons, encapsulant materials are used as auxiliary components in photovoltaic modules.

[0010] Encapsulant materials are special materials used to protect sensitive electronic components, such as photovoltaic cells. These materials protect cells from environmental damage, such as moisture, mechanical damage, extreme temperatures, and UV radiation. Another technical solution provided by the use of encapsulant materials is maximizing the efficiency and lifespan of solar panels, providing electrical isolation, and improving overall performance.

[0011] In the relevant technical field, encapsulant materials are expected to be flexible materials with high resistance to environmental factors, high optical transmission and homogeneous adhesion performance, dielectric character, and high thermal resistance.

[0012] Ethylene Vinyl Acetate (abbreviated as EVA), Polyvinyl Butylene (abbreviated as PVB), thermoplastic polyurethanes (abbreviated as TPU) or silicone-based materials are generally used as encapsulant materials in photovoltaic modules. These materials protect photovoltaic cells against mechanical impacts, while at the same time providing good light transmission and allowing the ceils to effectively generate energy from sunlight.

[0013] EVA material is often preferred as encapsulant material in the relevant technical field. However, in the materials preferred as other encapsulant materials in EVA, there is also the formation of by-products that trigger the aging of photovoltaic cells. For example, the acetic acid by-product formed as a result of mechanical, thermal, and crosslinking reactions in EVA causes aging for photovoltaic cells. Furthermore, other factors penetrating into the EVA accelerate ion mobility within the module by changing the voltage potential of the module and creating leakage current paths.

[0014] Encapsulant materials suitable for use in photovoltaic cells are also expected to show higher mechanical and thermal properties than those in the present art.

[0015] As a result, it has been determined that new encapsulant materials must be researched and developed in order to maximize efficiency and lifespan, provide electrical isolation, and minimize exposure to environmental factors in photovoltaic modules.

[0016] SUMMARY OF THE INVENTION

[0017] As is known in the art, encapsulant materials are used in photovoltaic modules particularly for protection against environmental factors. EVA, PVB, TPU, or silicone- based materials are preferred as encapsulant materials. However, these materials have technical disadvantages for photovoltaic cells, such as causing aging reactions, exhibiting insufficient mechanical and thermal properties, and causing potential induced degradation effects. The inventors of the present invention aim to introduce a new encapsulant material that offers technical solutions and advantages for photovoltaic modules.

[0018] The object of the present invention is to introduce an encapsulant material for photovoltaic cells resistant to aging and chemical environment.

[0019] Another object of the present invention is to introduce an encapsulant material for photovoltaic cells with high optical transmittance.

[0020] Another object of the present invention is to introduce an encapsulant material for photovoltaic cells in which potential induced degradation effects are reduced.

[0021] Another object of the present invention is to introduce an encapsulant material for photovoltaic cells with a refractive index close to that of glass.

[0022] Another object of the present invention is to introduce an encapsulant material that does not contain liquids that may cause hydrolysis or bubble formation, and that does not harm lamination equipment and photovoltaic cells.

[0023] BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 shows the FTIR test results of the encapsulant material subjected to curing processes and the encapsulant materials not subjected to curing processes.

[0025] Figure 2 shows the first heating curves of the encapsulant material subjected to curing processes and the encapsulant materials not subjected to curing processes.

[0026] Figure 3 shows the second heating curves of the encapsulant material subjected to curing processes and the encapsulant materials not subjected to curing processes.

[0027] DETAILED DESCRIPTION OF THE INVENTION In this detailed description, the subject of the invention relates to an encapsulant material for photovoltaic modules, and is described only with the examples that will not create any limiting effect for a better understanding of the subject.

[0028] Encapsulant materials are used to protect the cells in photovoltaic modules. These materials surround the photovoltaic cells, protecting them from external influences in particular. Also, they play a role in increasing the operating efficiency and lifespan of photovoltaic modules.

[0029] Photovoltaic modules contain multiple components to provide the expected performance. From the bottom layer to the top layer, there is usually a backsheet, back encapsulant material, photovoltaic cells, front encapsulant material, and a protective glass layer.

[0030] Accordingly, photovoltaic modules contain encapsulant materials allowing the photovoltaic cells, which are the main component, to be enclosed in sandwich form. If there are two, the encapsulant materials can be referred to as front encapsulant material for those positioned on top of the cells and back encapsulant material for those positioned under the cells.

[0031] The encapsulant material is usually melted under heat and pressure during the lamination process and is tightly bonded with the glass surface. This bonding process ensures that the photovoltaic cell between the protective glass on the front surface of the photovoltaic cell and the coating layer on the back surface is covered. In this way, it increases the mechanical strength of the photovoltaic cell, prevents moisture and oxygen from reaching it, and generally increases its resistance to environmental factors.

[0032] The inventors of the present invention introduce a new encapsulant material for the relevant technical field in order to eliminate the problems encountered in the art and to provide a technical solution. The encapsulant material of the invention contains polyolefin elastomer as the main component.

[0033] As is known in the art, polyolefin elastomer materials are thermoplastic materials with high elasticity and flexibility belonging to the polyolefin group. These materials are obtained by copolymerization of ethylene and at least one alpha olefin. In this invention, at least one of the group of propylene, butene, hexene, and octene is preferred as alpha olefin.

[0034] As is known in the art, polyolefin elastomer is a copolymer consisting of ethylene and alpha olefins with a molecular chain of saturated carbon-carbon bonds. In this way, owing to its saturated molecular chain, there is no reaction between the polyolefin elastomer copolymer and photovoltaic cells that would cause aging. Likewise, owing to this structure, polyolefin elastomer materials are corrosion resistant materials.

[0035] The polyolefin elastomer-based encapsulant material provides corrosion resistance for the photovoltaic cells it coats and also hinders the formation of aging reactions.

[0036] The WVTR (Water Vapor Transmission Ratio) values of the encapsulant materials in the relevant technical field are expected to be below 4 g / m2. This parameter value measures how much water vapor permeates through a specific material per unit area and unit time. According to the results of the test conducted with an electrolytic sensor at 38 °C*90% RH (Relative Humidity), 500 pm conditions, this parameter value was measured as 3.7 g / m2. If the WVTR parameter value is above 4 g / m2, the water vapor can permeate through the photovoltaic cells of the encapsulant material of the invention. As a result, photovoltaic cells may be adversely affected.

[0037] Polyolefin elastomer copolymer contains at least one alpha olefin component, as mentioned before. The copolymer obtained as a result of the interaction of ethylene and alpha olefin is very difficult to crystallize due to its nature owing to the alpha olefin it contains. With this feature, polyolefin elastomer copolymers have high optical transmittance. A material with high optical transmittance can also be obtained for the photovoltaic cells they are coated on.

[0038] The optical transmittance values of the encapsulant materials of the invention are expected to be >90% in the wavelength range of 380-1100 nm according to the GB / T 29848-2013 standard. It has been determined that the optical transmittance value of the encapsulant materials of the invention is >92% in these standards. With such an increase in optical transmittance, it is observed that the optical efficiency of photovoltaic cells also increases. Polyolefin elastomer copolymer based encapsulant material has been found to provide increased power generation, module life, and mechanical strength values for photovoltaic modules in the studies conducted.

[0039] The refractive index value of polyolefin elastomer copolymer based encapsulant material is very close to the refractive index value of glass. With this feature, light refraction losses at the glass-encapsulant material interface are reduced and light transmission to the active photovoltaic cell is maximized.

[0040] The encapsulant material of the invention is a product obtained mainly as a result of extrusion processes. In order to improve the properties of the polyolefin elastomer based copolymer, which will be used as the main component for obtaining encapsulant material in the invention, more than one additional component is added during extrusion.

[0041] According to what is mentioned herein, polyolefin elastomer copolymers, which are the main components of the encapsulant material, contain ethylene and at least one alpha olefin. At least one of the group of propylene, butene, hexene, and octene is preferred as alpha olefin.

[0042] Accordingly, in this invention, the encapsulant material contains at least one of the group of ethylene-1 -octene copolymer, metallocene polyethylene elastomer, ethylene butene copolymer, ethylene-1 -butene as the main component polyolefin elastomer copolymer.

[0043] The encapsulant material of the invention contains a polyolefin elastomer copolymer material obtained as a result of the polymerization of ethylene and at least one alpha olefin at a value in the range of 95% to 99% by weight.

[0044] The encapsulant material of the invention preferably contains at least one crosslinking agent. By crosslinking the chains within the copolymer, the crosslinking agent increases the mechanical strength values for the encapsulant material, improves its thermal properties and makes it more resistant to environmental conditions. In this invention, at least one of the compounds comprising the peroxide, silane, phenolic resin functional groups or compounds comprising one of the zinc, magnesium ions is included as a crosslinking agent.

[0045] In a preferred embodiment, the compound comprising at least one peroxide functional group is used as a crosslinking agent. At least one of the group of O-(2-ethylhexyl)O,O- tert-pentyl peroxide, t-amyl(2-ethylhexyl)monoperoxycarbonate, 1 ,3,5-Triallyl-1 ,3,5- triazine-2,4,6(1 H,3H,5H)-trione, triallyl ester of isocyanuric acid, triallyl isocyanurate, 2,2,4,6,6-pentamethylheptane, tert-amyl hydroperoxide, 2-ethyl hexane-1-ol, 0,0-tert- butyl 0-(2-ethylhexyl)peroxycarbonate, tert-butyl-hydroperoxide, 2- ethylhexylchloroformate, 2-ethylhexanol, tert-butylperoxy 2-ethylhexyl carbonate, tertamylperoxy 2-ethylhexylcarbonate is preferred as compounds comprising the crosslinking peroxide functional group.

[0046] The encapsulant material of the invention contains at least one crosslinker at a value in the range of 0.5% to 2.5% by weight. In order for the encapsulant material of the invention to have the targeted adhesion strength, moisture resistance, penetration resistance and formability properties, it is critical to react crosslinker and other components in certain weight ratios and obtain crosslinking ratios. In cases where it is used more than the specified ratios by weight, the crosslinker may be rapidly removed from the environment together with other components by side reactions for polymerization and may not have the desired effect. In cases where it is used less than the specified ratios, it may cause physical deterioration for the encapsulant material or prolong the curing time.

[0047] The encapsulant material of the invention contains at least one UV absorbing agent. The UV absorbing agent is contained in the encapsulant material to absorb ultraviolet rays and thereby protect the material and the underlying photovoltaic cell from damage caused by UV rays. In this way, it is possible to maintain the mechanical properties and transparency of the encapsulant material during the exposure period to UV rays. The final product shows positive effects on the efficiency and lifespan of the photovoltaic modules.

[0048] At least one of the group of Bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, sebacic acid, decanedioic acid, bis(2,2,6,6-tetramethylpiperidine-4-yl) decandioate, octabenzone, Bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, 2-hydroxy-4-(octyloxy) benzophenone is preferred as a UV absorbing agent within the encapsulant material.

[0049] The encapsulant material of the invention contains at least one UV absorbing agent at a value in the range of 0.05% to 0.15% by weight. The use of UV absorbing agent(s) in the ratios by weight specified in the invention is to improve the stability of the final product and to reduce the negative effects that may arise from UV radiation.

[0050] The encapsulant material of the invention contains at least one silane based coupler. Said silane based coupler is used to establish the coupling between the main component polyolefin elastomer copolymer and the added components, to increase the mechanical and physical properties of the encapsulant material, and to improve moisture resistance. It increases the integrity and endurance of the encapsulant material.

[0051] The encapsulant material contains at least one of the group of 3- methryloxypropyltrimethoxysilane, vinylsilane oligomer, trimethoxylyethylene, ethyleneyltrimethoxysilane, trimethoxy(vinyl)silane, vinyltrimethoxysilane, 3- (trimethoxyl)propyl methacrylate, y-methacryloxypropyltrimetoxysilane, methacryloxysilane as a silane based coupler.

[0052] The encapsulant material of the invention contains at least one silane based coupler at a value in the range of 0.25% to 0.75% by weight. In cases where it is used below the specified weight ratios, the silane based coupler causes insufficient strength for the target product encapsulant material. If silane based binders are used above the specified value, the target product encapsulant material will have high strength values, which will cause it to be not formable and reduce the activity of other properties.

[0053] The encapsulant material of the invention does not contain liquids that may cause hydrolysis or bubble formation. In this way, there is no formation of acetic acid that can damage lamination equipment and photovoltaic modules.

[0054] In the invention, the encapsulant material is subjected to characterization tests. Encapsulant samples containing at least one polyolefin elastomer, at least one silane based coupler, at least one UV absorbing agent, and at least one crosslinking agent in the described weight ratios are obtained. The encapsulant samples obtained in the following lines are subjected to various tests.

[0055] First, FTIR spectrophotometry test is applied to evaluate the chemical structures of the encapsulant materials obtained. The tests were carried out on cured (referred to as CSAT) or uncured encapsulant materials (referred to as CSBT) using the Perkin Elmer 400 instrument. The curing temperature in these tests are at a value between 140-170 °C. FTIR spectra were recorded in the range of 500 to 4000cm1, with a resolution of 4cm1and 16 scans. FTIR experiment results are shared in Figure 1. According to the FTIR results shared in Figure 1 , it was observed that there was a change in the chemical structures of the samples in the wavelength range of 1600-1800 cm1due to lamination. Since this range is called the carbonyl range, the reason for the change here can be stated as the stretching of the carbonyl band. This can be cited as evidence that the cured encapsulant material undergoes a crosslinking reaction and is cured compared to the uncured encapsulant material. The endurance of the encapsulant material is evaluated by monitoring the formation of new oxygencontaining types with absorption bands at the carbonyl site in the polyolefin elastomer copolymer, which is the main component. The lamination process results in the production of encapsulant materials that are more resistant to oxygen.

[0056] Subsequently, Differential Scanning Calorimetry experiments were carried out for the encapsulant material obtained. These experiments were carried out with the TA Instruments DSC250 instrument and conditions of nitrogen medium, temperature range of 10 °C to 200 °C, heating rate of 10 °C / min.

[0057] The samples subjected to the test were named CSAT (Polyolefin elastomer copolymer encapsulant film after Capssun lamination) and CSBT (Polyolefin elastomer copolymer encapsulant film before Capssun lamination). Both samples were taken from the same encapsulant roll and prepared in 7*25 cm dimensions. The first heating curves of cured and uncured samples are shared in Figure 2. According to the graphs shared in the figures, the samples were observed to be in the cross-linking zone at -160 °C. When the before and after lamination data of the samples are compared, it can be seen that curing and therefore crosslinking reaction take place during lamination. The second heating curves samples are shared in Figure 3. In the DSC second heating curves shared in the figure, the melting and glass transition temperatures of polyolefin elastomer copolymer based encapsulant samples were determined. The values obtained according to the results of the conducted DSC test can be observed from Table 1 below.

[0058] Table 1. DSC test results for cured and uncured polyolefin elastomer copolymer based encapsulant samples.

[0059] The increase in Tg after the material is laminated can be cited as evidence that a crosslinking reaction has taken place.

[0060] As the next test process, shrinkage parameter control was carried out. For shrinkage parameter control, samples prepared from rolls in 10 cm * 20 cm dimensions are kept on Teflon (PTFE) for 3 minutes in a furnace at 120 °C. According to the standards, there is a shrinkage or expansion tolerance of ±2% for the short side and ±3% for the long side of the sample as well as the rolls. In the results obtained by the tests carried out, it was observed that the shrinkage and expansion rates of the encapsulant material of the invention were within the desired value ranges. If it is not within the range of ±2% for the short side and ±3% for the long side; performance and functional defects occur for the final product photovoltaic module.

[0061] As the next test process, the separation force control operations were carried out. For separation force control, tensile test is applied to 2 samples prepared in 12.5*12.5 cm dimensions. An arrangement is prepared such that the samples are stacked on top of each other on the glass and a backsheet is placed on top, and is laminated. After the samples are adhered to the glass and backsheet surface, the test is applied with a hand operated tensile testing device. According to the standards, the magnitude of the tensile force should be greater than 60 Newton for glass and 40 Newton for backsheet. According to the results obtained in the tests, it was determined that the encapsulant materials of the invention reached the desired values. If the tensile force is below the desired values, the encapsulant material will not be able to perform the function of holding the glass and solar cells together.

[0062] Tests were performed to determine the crosslinking ratio for the POE-based encapsulant samples obtained. For the crosslinking ratio test, 2 samples of 12.5*12.5 cm are prepared from the rolls, and the samples are laminated by placing them between two Teflons on top of each other. After the lamination process, sample pieces between 35 and 50 g and 2 mm in size are cut from the middle parts of the samples and filled into an empty container that will not react with chemicals. In the crosslinking chamber, Xylene + Butylene mixture at the ratios of 1.25-12.5 is tested for 5 hours, then the samples are baked for 3 hours under 150 °C and 1 atm pressure and the test is completed after a total of 8 hours. The percentage of polyolefin elastomer copolymer remaining in the container is calculated. The percentage of crosslinking ratio must be greater than 70% according to the standards. This test is called the Soxhlet Extraction method in the literature. Extraction of compounds from solid samples is carried out by this method. With this test, it is observed whether the Cross Link Ratios reach the desired values. The Crosslink Ratio should not be below a certain ratio (Standard > 70%) as it improves chemical, optical, etc. properties. In the tests performed on the samples, it was determined that the result obtained was 78%.

[0063] In a preferred embodiment, polyolefin elastomer copolymer based encapsulant material is used as the front encapsulant material positioned on top of the cells in photovoltaic modules.

[0064] In a preferred embodiment, a polyolefin elastomer copolymer based encapsulant material is used as the back encapsulating material positioned under the cells in the photovoltaic modules.

[0065] The polyolefin elastomer copolymer based encapsulant material of the invention is obtained by applying the extrusion method process steps to include the components described. In order to obtain polyolefin elastomer copolymer, the production method known in the art is applied using Ziegler Natta or metallocene catalysts.

[0066] The raw material of the polyolefin elastomer copolymer obtained and various additives are melted in the extruder including a heater and pressure screw and subjected to a continuous flow that allows it to be shaped by passing through the shaped mold located at the extruder outlet by means of the screw. The material takes its final shape with the cooling process in the next stage. For the cooling process, the extruded polymer is passed through shaped calibrators with a cooling system and advanced along the line. In the next stage, the polymer is subjected to cutting / sizing process and takes the form of the final product. The components in the extrusion line are screw extruder, melting pump, die, calender, thickness scanner, cooling bracket cutting blade, and film coil winder, respectively. It is possible to optimize the tension and temperature values of the rollers used in the production method of the invention; this improvement eliminates the slipperiness of the final product polyolefin elastomer copolymer based encapsulant material.

[0067] The scope of protection of the invention is specified in the appended claims and cannot be limited to what is described for illustrative purposes in this detailed description. It is clear that a person skilled in the art can produce similar embodiments in the light of what is explained above, without deviating from the main theme of the invention.

Claims

CLAIMS1. An encapsulant material to be positioned under and / or on top of at least one photovoltaic cell in photovoltaic modules, characterized in that it contains a polyolefin elastomer copolymer as the main component.

2. An encapsulant material according to claim 1 , characterized in that said polyolefin elastomer copolymer contains at least one of the group of propylene, butene, hexene, and octene as olefin.

3. An encapsulant material according to one of the preceding claims, characterized in that the polyolefin elastomer copolymer is one of the group of ethylene-1 -octene, metallocene polyethylene elastomer, ethylene butene copolymer, ethylene-1 -butene copolymer.

4. An encapsulant material according to one of the preceding claims, characterized in that it contains polyolefin elastomer copolymer in a ratio of at least 95% by weight as the main component.

5. An encapsulant material according to one of the preceding claims, characterized in that it contains at least one crosslinking agent.

6. An encapsulant material according to claim 5, characterized in that it comprises at least one of the compounds comprising the peroxide, silane, phenolic resin functional groups or at least one of the compound groups comprising one of the zinc, magnesium ions as a crosslinking agent.

7. An encapsulant material according to claim 6, characterized in that it comprises at least one of the group of O-(2-ethylhexyl)O,O-tert-pentyl peroxide, t-amyl(2- ethylhexyl)monoperoxycarbonate, 2,2,4,6,6-pentamethylheptane, tert-amyl hydroperoxide, 2-ethyl hexane-1 -ol, O,O-tert-butyl O-(2- ethylhexyl)peroxycarbonate, tert-butyl-hydroperoxide, 2- ethylhexylchloroformate, 2-ethylhexanol, tert-butylperoxy 2-ethylhexyl carbonate, tert-amylperoxy 2-ethylhexylcarbonate as a crosslinking agent.

8. An encapsulant material according to one of claims 5-7, characterized in that it contains at least one crosslinking agent at a value of 0.5 to 2.5 by weight.

9. An encapsulant material according one of the preceding claims, characterized in that it contains at least one UV absorbing coupling agent.

10. An encapsulant material according to claim 9, characterized in that it comprises at least one of the group of Bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, sebacic acid, decanedioic acid, bis(2,2,6,6-tetramethylpiperidine-4-yl) decandioate, octabenzone, Bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, 2- hydroxy-4-(octyloxy) benzophenone as a UV absorbing agent.

11. An encapsulant material according to one of claim 9 or 10, characterized in that it contains at least one UV absorbing agent at a value of 0.05 to 0.15 by weight.

12. An encapsulant material according one of the preceding claims, characterized in that it contains at least one silane based coupler.

13. An encapsulant material according to claim 12, characterized in that it comprises at least one of the group of 3-methryloxypropyltrimethoxysilane, vinylsilane oligomer, trimethoxylyethylene, ethyleneyltrimethoxysilane, trimethoxy(vinyl)silane, vinyltrimethoxysilane, 3-(trimethoxyl)propyl methacrylate, y-methacryloxypropyltrimetoxysilane, methacryloxysilane as a silane based coupler.

14. An encapsulant material according to one of claim 12 or 13, characterized in that it contains at least one silane based coupler at a value of 0.25 to 0.75 by weight.

15. The use of an encapsulant material according to one of the preceding claims as a back encapsulant material positioned under photovoltaic cells.

16. The use of an encapsulant material according to one of claims 1 -15 as a front encapsulant material positioned on top of the photovoltaic cells.