Low-loss encapsulant sheet for photovoltaic module and photovoltaic module including same

Abstract

The present invention relates to a low-loss encapsulant sheet for a photovoltaic module and a photovoltaic module including same. The present invention may provide an encapsulant sheet for a solar cell module, the encapsulant sheet comprising ethylene vinyl acetate (EVA), wherein the thickness of the sheet is 300-700 µm, the melt index (MI) of the EVA is 10-30, and the degree of pre-cure is 1-99%.

Description

Low-breakage encapsulant sheet for solar modules and solar modules including the same

[0001] The present invention relates to a low-breakage encapsulation sheet for a photovoltaic module and a photovoltaic module including the same.

[0002] In the solar industry, the most important characteristics of solar cell modules sold to customers are module output and module efficiency. While module output is a critical factor for utility solar modules, residential solar modules require high efficiency to achieve high output even within limited installation space.

[0003] One of the methods to increase the efficiency of solar cell modules is to use gapless technology, which minimizes the gap between solar cells. This technology eliminates the gap between cells by overlapping solar cells, thereby increasing the effective area of ​​the module and achieving an efficiency improvement of at least 0.4%.

[0004] However, when applying this gapless technology, serious problems arise in the overlapping portions of the solar cells. In the overlapping portions, there are two solar cells and a wire connecting them, which increases the overall thickness. Consequently, cracks in the solar cells are inevitable during the module manufacturing process (laminator process).

[0005] As an attempt to solve this problem, flattening technology was applied to reduce the thickness of the wires, but this alone was insufficient to completely resolve the cell cracking issue. As another solution, solar cell manufacturers tried using thicker encapsulants. Generally, the thickness of the encapsulant is about 400 to 500 µm, but a thick encapsulant of 600 µm or more was required to prevent cracking in the overlapping areas.

[0006] However, the use of thicker packaging materials leads to increased costs, making practical application in the industry difficult. In particular, for packaging materials such as EVA (ethylene vinyl acetate), the industry has been unable to adopt them because increasing thickness results in a direct rise in material costs.

[0007] Furthermore, existing studies have primarily focused on the thickness or physical properties of encapsulants, and there has been insufficient research on the impact of their chemical properties or process conditions on the occurrence of cracks in solar cells. In particular, there has been almost no systematic research on the effects of encapsulant properties, such as melt index (MI) or degree of curing, on cell crack prevention.

[0008] Therefore, there is a need for a new technical solution that can effectively prevent cell cracking while improving the efficiency of solar cell modules. In particular, an innovative approach is required to prevent cell cracking without significantly increasing the thickness of existing encapsulation materials.

[0009] [Prior Art Literature]

[0010] [Patent Literature]

[0011] Patent Document 1. Korean Registered Patent Publication No. 10-1130508 (Date of publication: March 28, 2012)

[0012] The present invention aims to provide an encapsulation sheet for a solar cell module.

[0013] The present invention also aims to provide a solar cell module.

[0014] The problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by a person skilled in the art from the description below.

[0015] The present invention can provide an encapsulating sheet for a solar cell module comprising EVA (ethylene vinyl acetate), wherein the thickness of the sheet is 300 to 700 μm, the melt index (MI) of the EVA is 10 to 30, and the degree of pre-curing is 1 to 99%.

[0016] The present invention also provides a solar cell module characterized by comprising: a glass layer; a front encapsulant sheet layer comprising EVA (ethylene vinyl acetate) below the glass layer; a plurality of solar cells disposed below the front encapsulant sheet layer and overlapping each other to form a gapless structure; a rear encapsulant sheet layer comprising EVA (ethylene vinyl acetate) below the solar cells; and a back sheet layer below the rear encapsulant sheet layer.

[0017] The thickness of the above-mentioned front encapsulation sheet layer is 300 to 700 μm, and the melt index (MI) of the EVA may be 10 to 30.

[0018] The thickness of the above rear encapsulant sheet layer is 300 to 700 μm, the melt index (MI) of the EVA is 10 to 30, and the degree of pre-curing may be 1 to 99%.

[0019] The thickness of the glass layer is 2 to 8 mm, the thickness of the solar cell is 130 to 200 μm, and the overlap length of the solar cells may be 0.2 to 1.0 mm.

[0020] The EVA of the above rear encapsulant sheet layer may be 10% pre-cured.

[0021] The present invention can provide an encapsulation sheet for a solar cell module.

[0022] The present invention can also provide a solar cell module.

[0023] The present invention can also effectively prevent cracks from occurring in the cell overlap portion, reduce costs by using thinner encapsulation material compared to existing ones, and improve module efficiency by more than 0.4%.

[0024] Fig. 1: Shows a cross-sectional view of the cell overlap portion of a gapless solar cell module.

[0025] Fig. 2: Shows the cell cracking phenomenon that occurs when using general bagging materials.

[0026] FIG. 3: Shows a solar cell module structure diagram according to one embodiment of the present invention.

[0027] Fig. 4: Shows the dynamic shear viscosity characteristic graph of the bag material.

[0028] Fig. 5: Shows an EL (electrical luminescence) image when the encapsulation material of the present invention is applied.

[0029] The foregoing and additional aspects are embodied through embodiments described with reference to the attached drawings. It is understood that the components of each embodiment may be combined in various ways within the embodiment or with components of other embodiments, unless otherwise stated or contradicted. Based on the principle that the inventor may appropriately define the concepts of terms to best describe his invention, the terms used in this specification and claims shall be interpreted in a meaning and concept consistent with the description or proposed technical idea.

[0030] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

[0031] The encapsulating sheet of the present invention is composed mainly of EVA (ethylene vinyl acetate).

[0032] EVA (Ethylene Vinyl Acetate) is the most widely used polymer material as an encapsulant for solar modules. EVA is a copolymer of ethylene and vinyl acetate that provides excellent light transmittance, weather resistance, adhesion, and buffering properties as a solar cell encapsulant.

[0033] The main characteristics of the EVA used in the present invention are the melting index (MI) and the degree of pre-curing. The melting index is an indicator representing the flowability of a polymer material in a molten state, with a unit of g / 10 min, and in the present invention, a range of 10 to 30 is used. If the melting index falls outside this range, problems may occur during the lamination process. If the melting index is less than 10, the flowability is insufficient, and the gaps between solar cells may not be sufficiently filled; if it exceeds 30, it may be difficult to achieve a uniform distribution of the encapsulant due to excessive flow.

[0034] The degree of pre-curing, another important characteristic of EVA, indicates the degree to which the EVA sheet is partially cross-linked. In the present invention, the EVA used as a back encapsulant is imparted a degree of pre-curing of 1 to 99%, which serves to effectively relieve stress caused by heat and pressure generated during the lamination process. The most preferred embodiment is to use EVA having a degree of pre-curing of 10%.

[0035] The thickness of the EVA is also an important factor, and the present invention uses a thickness in the range of 300 to 700 μm. This is slightly thicker than the 400 to 500 μm generally used in existing solar modules, but it is thinner than conventional technology, which required a thickness of 600 μm or more to prevent cell cracking. This thickness range satisfies both goals of protecting the solar cell and reducing costs.

[0036] EVA encapsulates solar cell modules through the following steps in the lamination process:

[0037] Melting phase: EVA begins to melt at 80~90℃.

[0038] Gelation step: EVA forms cross-links and gels at 130~150℃.

[0039] Curing stage: Complete curing is achieved at 150~170℃.

[0040] In this invention, EVA with different characteristics is used on the front and back surfaces. Unpre-cured high melt index EVA is used as the front encapsulant to ensure excellent light transmittance and adhesion, while pre-cured high melt index EVA is used as the back encapsulant to provide stress relief. The use of these differentiated EVAs is a key factor in effectively resolving the cell cracking problem that occurs in gapless structures.

[0041] The solar cell module of the present invention has a structure in which a glass layer, a front encapsulant sheet layer, a solar cell cell layer, a rear encapsulant sheet layer, and a back sheet layer are sequentially stacked from the top.

[0042] The glass layer is located at the top of the solar cell module and serves to protect the module from the external environment and transmit sunlight to the maximum extent. The glass used in this invention is tempered glass with an anti-reflective coating applied, with a thickness of 2 to 8 mm. The glass for solar cell modules applies an anti-reflective coating, such as SiNx, to the glass surface to minimize reflection of sunlight and improve transmittance. In addition, the tempering process through heat treatment increases mechanical strength, thereby improving resistance to external impacts or hail, and lowers the iron content compared to ordinary glass to increase solar transmittance. In particular, the thickness of the glass directly affects the mechanical strength, weight, and manufacturing cost of the module. Thin glass of 2 mm is advantageous for lightweighting but has relatively low mechanical strength, while thick glass of 8 mm provides excellent mechanical strength but has the disadvantage of increasing weight and cost.

[0043] The front encapsulant sheet layer completely fills the voids around the solar cell and enables the formation of a uniform adhesive layer. In the present invention, the front encapsulant sheet is used without pre-curing treatment to ensure optimal flowability and adhesion during the lamination process. This allows for the formation of excellent optical and mechanical bonding between the glass and the solar cell.

[0044] The solar cell layer is a core component of a photovoltaic module and consists of multiple solar cells with a thickness of 130 to 200 μm. The present invention is characterized by the solar cells overlapping each other with an overlap length of 0.2 to 1.0 mm to form a gapless structure. This gapless structure maximizes the effective area of ​​the module to improve overall efficiency, and generally, an efficiency increase of 0.4% or more can be achieved. The solar cells are electrically connected in series via wires, and the wires have a bending region of approximately 4 to 5 mm at the overlap portion. In this overlap structure, the total thickness increases at the point where two cells and wires overlap, which can cause stress concentration during the lamination process. In particular, solar cells are fabricated based on silicon wafers and possess highly brittle characteristics, making them highly vulnerable to mechanical stress. Therefore, stress management at the overlap portion is critical, and this can be resolved by optimizing the characteristics of the encapsulation material.

[0045] The back encapsulant sheet layer is located between the solar cell layer and the back sheet layer, and is the layer to which the most characteristic technology of the present invention is applied. As the back encapsulant, pre-cured high melt index EVA with a thickness of 300 to 700 μm is used; the melt index of the EVA is 10 to 30, and the degree of pre-curing ranges from 1 to 99%. In particular, the best performance is exhibited when using EVA with a degree of pre-curing of 10%. The pre-cured EVA serves to effectively disperse stress caused by heat and pressure generated during the lamination process. Unlike general EVA, a partially cross-linked structure is formed through pre-curing treatment, allowing for more effective buffering when stress is applied. Additionally, the pre-cured EVA has reduced flowability during the lamination process compared to general EVA, thereby alleviating excessive pressure that may occur at the overlap portion. The back encapsulant sheet layer also provides electrical insulation to protect the back electrode of the solar cell and performs the function of preventing moisture penetration. In particular, the physical properties of the rear encapsulant presented in the present invention enable effective prevention of cell cracking without using a thick encapsulant of 600㎛ or more, which was required in existing technologies.

[0046] The backsheet layer is a protective layer located at the bottom of a photovoltaic module and consists of a multilayer structure of PE (Polyethylene) / PET (Polyethylene Terephthalate) / PE. The backsheet plays a critical role in protecting the rear surface of the solar cell module, primarily providing moisture barrier, electrical insulation, UV blocking, and mechanical protection functions. The outermost PE layer of the backsheet provides excellent weather resistance and durability, while the middle PET layer is responsible for high mechanical strength and dimensional stability. The inner PE layer provides excellent adhesion to the EVA encapsulant, preventing delamination between layers. In particular, the moisture barrier performance of the backsheet is a critical factor for the long-term reliability of the solar cell module, as moisture penetration into the module can cause corrosion of the solar cells or degradation of electrical characteristics. The backsheet used in this invention maintains stable characteristics even at high temperatures above 105°C and possesses excellent cold resistance, preventing cracking even at low temperatures of -40°C. Furthermore, it ensures the electrical safety of the solar cell module by providing an insulation breakdown voltage of over 1000V. The thickness of the backsheet is generally in the range of 300 to 500 µm, which is an optimized range that provides sufficient protection without excessively increasing the overall thickness and weight of the module. The color of the backsheet is generally white, which reflects sunlight to enable additional power generation from the rear of the module, and at the same time lowers the operating temperature of the module, thereby improving power generation efficiency.

[0047] The front encapsulant utilizes high melt index EVA as is to provide excellent light transmittance and adhesion, whereas the back encapsulant uses pre-cured high melt index EVA to provide stress relief. The use of these differentiated encapsulants is a key factor in improving the overall performance and reliability of solar cell modules.

[0048] The present invention will be explained in detail below through examples.

[0049] First, tempered glass with a 3.2 mm thick anti-reflective coating was used as the substrate. As the front encapsulant, a high melt index EVA sheet with a melt index of 14–18 was applied to a thickness of 450 µm. Monocrystalline silicon solar cells were used, with a thickness of 180 µm and dimensions of 156 mm × 156 mm. The solar cells were arranged with an overlap length of 0.4 mm to form a gapless structure. As the rear encapsulant, EVA with a melt index in the range of 10–30 was pre-cured by 10% and applied to a thickness of 450 µm. A multilayer film with a PE / PET / PE structure was used as the backsheet, with a total thickness of 380 µm. After sequentially stacking these components, a lamination process was performed. Lamination was carried out under vacuum at a temperature of 148°C for 15 minutes.

[0050] To compare the experimental results, modules under four different conditions were fabricated. Case 1 used high melt index EVA (MI: 14-18) on the front and low melt index EVA (MI: 2-3) on the back, while Case 2 used high melt index EVA (MI: 14-18) on both the front and back. Case 3 is an embodiment of the present invention, using high melt index EVA (MI: 14-18) on the front and pre-cured high melt index EVA (MI: 10-30) on the back. Case 4 used TPO on both the front and back for comparison.

[0051] As a result of analyzing the cell crack occurrence rate of the modules fabricated for each case through EL (Electroluminescence) inspection, Case 1 showed crack occurrence rates of 20.5% and 21.8%, while Case 2 showed cracks of 3.9% and 12.2%. The module using TPO in Case 4 showed high crack occurrence rates of 32.1% and 34.6%. On the other hand, in Case 3, which is an embodiment of the present invention, no cracks occurred at all (0% crack occurrence rate).

[0052] These experimental results demonstrate that using the pre-cured high melt index EVA presented in the present invention as a back encapsulator is highly effective in preventing cracks in solar cells. In particular, the module in Case 3, which had no cell cracks, showed the best performance in the module output measurement results and maintained stable characteristics in long-term reliability tests.

Claims

1. In a sealing sheet for a solar cell module, Contains EVA (ethylene vinyl acetate), The thickness of the above sheet is 300 to 700 μm, and A sealing sheet for a solar cell module characterized by the melt index (MI) of the EVA being 10 to 30 and the degree of pre-curing being 1 to 99%.

2. In a solar cell module, Glass layer; A front encapsulating sheet layer comprising EVA (ethylene vinyl acetate) below the glass layer; A plurality of solar cells disposed below the above-mentioned front encapsulation sheet layer and overlapping each other to form a gapless structure; A rear encapsulating sheet layer comprising EVA (ethylene vinyl acetate) at the bottom of the solar cell; and A solar cell module characterized by including a back sheet layer below the rear encapsulation sheet layer.

3. In Paragraph 2, The thickness of the above-mentioned front encapsulation sheet layer is 300 to 700 μm, and A solar cell module characterized by the melt index (MI) of the above EVA being 10 to 30, 4. In Paragraph 2, The thickness of the above rear encapsulation sheet layer is 300 to 700 μm, and A solar cell module characterized by the melt index (MI) of the above EVA being 10 to 30 and the degree of pre-curing being 1 to 99%, 5. In Paragraph 2, The thickness of the above glass layer is 2 to 8 mm, and The thickness of the above solar cell is 130 to 200 μm, and A solar cell module characterized by the overlapping length of the above solar cells being 0.2 to 1.0 mm.

6. In Paragraph 4, A solar cell module characterized by the EVA of the rear encapsulant sheet layer being 10% pre-cured.

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