Self-cleaning anti-reflective film for permanent anti-reflective coating and performance enhancement of new and already installed solar modules.

Abstract

Self-cleaning anti-reflective film for permanent anti-reflective coating and performance enhancement of new and already installed solar modules, consisting of a single- or multi-layered transparent thermoplastic film with an outer statistically microstructured superhydrophobic first surface (110) and an opposing second surface (120) designed to allow a permanent bond with the front glass of a solar module.

Description

[0001] In conventional solar modules without an anti-reflective coating, strong reflections (reflection at the air-front glass interface) occur, especially at shallow angles of incidence (relative to the module surface), which reduce the electrical performance of the modules and can lead to unwanted glare or even glare that is relevant under building or traffic law.

[0002] Commercially available single-layer anti-reflective coatings on the front glass or plastic front panel of modules – as described, for example, in EP-A-2598561 or US-B-11,969,753 – lack the necessary long-term weather and UV resistance, as well as abrasion resistance to external mechanical influences such as dusty air currents (e.g., "Saharan winds") and hail. Furthermore, these coatings cannot be retrofitted to modules that have already been installed and reduce or prevent the required recyclability of the modules.

[0003] While targeted or statistical microstructuring (matting) of the front glass using embossing rollers or acid etching during production reduces reflections, it simultaneously increases the module surface's susceptibility to soiling and thus significantly increases the ongoing cleaning effort required to maintain performance. In principle, this approach cannot achieve a performance increase. Furthermore, this method is limited to the production of new modules.

[0004] EP-B-1479734 describes the production and use of nanostructured surface coatings which, according to the patent claims, can optionally be antireflective, self-cleaning / superhydrophobic, or highly transparent – ​​a targeted combination of these properties is not disclosed in the document. Furthermore, the production and application of these coatings requires cleanroom conditions and is therefore very costly and unsuitable for modules that are already installed.

[0005] EP-B-2903031 claims an antireflective coating for solar modules based on small glass particles dispersed in an inorganic binder and modules coated in this way. The application does not suggest, nor is it to be expected by a person skilled in the art, that modules with a coating according to the invention possess a self-cleaning ability and / or an increase in performance. On the contrary, such a person must assume a higher susceptibility to soiling compared to an uncoated module. Furthermore, the coating method according to the invention can only be used in the production of new modules, not for retrofitting modules that are already installed.

[0006] US Patent 2008 / 0135091 describes the use of a multilayer film consisting of at least one very thin fluoropolymer-containing top layer and an ethylene copolymer carrier layer for anti-reflective coating and wavelength-selective transparency enhancement of solar cells and modules. Since the aforementioned properties of the invention are highly dependent on the integrity of the top layer and its outer surface for physical reasons, and since no measures for increasing abrasion and weather resistance are disclosed, nor are they obvious to a person skilled in the art, continuous use under outdoor application conditions is not recommended.

[0007] WO-A-2025 / 056128 claims an acrylate-based, optionally SiO2 nanoparticle-containing, statistically microstructured, glare-reducing coating for solar cells and solar modules, as well as correspondingly coated solar cells and modules. Performance-enhancing, abrasion-resistant, or self-cleaning properties of this coating are not disclosed in the application and are not to be expected by a person skilled in the art. Direct coating of solar modules and cells is only possible when they are new.

[0008] The present invention was therefore based on the objective of providing an anti-reflective coating that increases the average electrical performance compared to the prior art, both for brand new and already installed solar modules, which meets the service life requirements of a modern solar system of typically 30 years and has a self-cleaning function.

[0009] Surprisingly, the solution specified in claim 1 was found for the problem described above.

[0010] This consists of a single- or multi-layered transparent thermoplastic film with an outer statistically microstructured and thus glare-reducing superhydrophobic surface and an opposing second surface designed to either be permanently laminated onto the front glass during the manufacturing process of a conventional solar module, or to be provided with a durable and weather-resistant transparent adhesive layer that allows subsequent permanent bonding to the front glass of an already installed solar module.

[0011] An embodiment of a single-layer self-cleaning anti-reflective film according to the invention is shown in Fig. 1 shown. Fig. Figure 2 shows an embodiment of a multi-layered, here exemplarily four-layered, self-cleaning anti-reflective film according to the invention. Fig. Figure 3 shows a greatly enlarged side view of the outer first surface of the particularly advantageous embodiment of the self-cleaning anti-reflective film according to claims 6-10. These drawings are explicitly referenced below.

[0012] In the case of a multi-layered film structure (e.g., in the case of...) Fig. 2 of a four-layer film structure) the outer film layer (101), facing away from the front glass of the solar module, has an optical refractive index that lies between that of the front glass and that of air, and the remaining film layers (in the case of Fig. 2 (102)-(104)) exhibit optical refractive indices that lie between that of the front glass. These additional film layers allow the mechanical (such as tear resistance or elasticity) and additional optical properties (such as the energy distribution of incident sunlight) of the self-cleaning antireflective film according to the invention to be selectively adjusted or modified.

[0013] In the case of a single-layer film structure ( Fig. 1) The entire film (100) has a uniform optical refractive index which lies between that of the front glass and that of air.

[0014] In all cases, this adjustment of the refractive index serves to reduce the coupling losses of the incoming sunlight into the solar module and thus to increase its average electrical power.

[0015] The glare-reducing statistical microstructuring of the outer first surface (110) is advantageously applied directly during film production via mechanical microtexturing using a roughened / matted embossing roller or by adding suitable surface matting agents. The former mechanical microtexturing using an embossing roller is particularly preferred, the result of which is Fig. Figure 3 is shown schematically. A corresponding microstructuring of the second opposite surface (120) of the antireflective film according to the invention can be carried out to increase adhesion to the front glass of the solar module, but is irrelevant for the actual glare-reducing optical function of the film.

[0016] The superhydrophobic and thus self-cleaning function of the first outer surface (110) can be generated by a hierarchical microstructuring of this surface (as described, for example, in US-B-8,785,556 or Onda et al., Langmuir 12(9):2125-2127) or advantageously by a simple microstructuring of the previously hydrophobized surface or particularly advantageously by a simple microstructuring of the first outer surface of an antireflective film according to the invention made of an intrinsically hydrophobic base material, such as a fluorine- or silicone-containing thermoplastic polymer. Reference symbol list 100 single film layer in single-layer design 101 outer first film layer in multi-layer design 102 second film layer in multi-layer design 103, 104 additional optional film layers in multi-layer versions 110 outer first surface facing away from the front glass of the solar module 120 second surface facing the front glass of the solar module QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP-A-2598561

[0002] US-B-11,969,753

[0002] US-A-2008 / 0135091

[0006] WO-A-2025 / 056128

[0007] US-B-8,785,556

[0016] Cited non-patent literature

[0000] Onda et. Al, Langmuir 12(9):2125-2127

[0016]

Claims

[1] Self-cleaning anti-reflective film for permanent anti-reflective coating and performance enhancement of new and already installed solar modules, consisting of a single or multi-layer transparent thermoplastic film with an outer statistically microstructured superhydrophobic first surface (110) and an opposing second surface (120) designed to allow permanent bonding with the front glass of a solar module. [2] Single-layer self-cleaning anti-reflective film according to claim 1, characterized by , that the entire film (100) exhibits an optical refractive index that lies between that of the front glass of the solar module and that of air. [3] Multi-layer self-cleaning anti-reflective film according to claim 1, characterized by, that the outer film layer (101) facing away from the front glass of the solar module has an optical refractive index that lies between that of the front glass and that of air, and the remaining film layers have optical refractive indices that lie between this and that of the front glass. [4] Self-cleaning anti-reflective film according to any of the preceding claims, characterized by , that it has an opposing second surface (120) which is such that it can be permanently laminated onto the front glass during the manufacturing process of a conventional solar module. [5] Self-cleaning anti-reflective film according to one of claims 1-3, characterized by , that the opposite second surface (120) is provided with a durable and weather-resistant transparent adhesive layer, which allows subsequent permanent bonding to the front glass of an already installed solar module. [6] Self-cleaning anti-reflective film according to any of the preceding claims, characterized by , that the glare-reducing microstructuring on the first outer surface (110) is applied via mechanical microtexturing using a roughened / matt embossing roller. [7] Self-cleaning anti-reflective film according to any of the preceding claims, characterized by , that the self-cleaning function of the first outer surface (110) is generated by a simple microstructuring of the previously hydrophobized surface. [8] Self-cleaning anti-reflective film according to one of claims 1-6, characterized by , that the self-cleaning function of the first outer surface (110) is generated by a simple microstructuring of the first outer surface of an anti-reflective film according to the invention, in which at least the outer film layer ((100) facing away from the front glass of the solar module is made of Fig. 1) or (101) from Fig.2) consists of an intrinsically hydrophobic base material. [9] Self-cleaning anti-reflective film according to claim 8, characterized by , that a fluorine-containing polymer is used as an intrinsically hydrophobic base material. [10] Self-cleaning anti-reflective film according to claim 8, characterized by that a silicone-containing polymer is used as an intrinsically hydrophobic base material.

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