TEXTURED GLASS FOR PHOTOVOLTAIC INSTALLATION

Abstract

A translucent glass pane-type substrate, adapted to serve as a cover element for a photovoltaic cell, the substrate including at least one textured surface intended to be oriented towards the outside of a building and wherein for any texture orientation, the fraction of local surfaces having said texture orientation is less than or equal to 2×10.sup.−4 of a given sampling surface

Claims

1. A translucent glass pane-type substrate adapted to serve as a cover element for a photovoltaic cell, said substrate comprising at least one textured surface intended to be oriented towards an outside of a building and wherein for any texture orientation, a fraction of local surfaces having said texture orientation is less than or equal to 2×10.sup.−4 of a sampling surface greater than or equal to 5×5 cm.sup.2.

2. The substrate according to claim 1, wherein a maximum height of said textured surface is less than 1.1 mm.

3. The substrate according to claim 1, wherein a thickness of said substrate is less than or equal to 4.0 mm.

4. The substrate according to claim 1, wherein at all points of said sampling surface, a radius of curvature is greater than 300 micrometers for a curvature oriented towards an outside of the substrate, and greater than 200 micrometers for a curvature oriented towards an inside of the substrate.

5. The substrate according to claim 1, wherein the texture orientation represented at a maximum has an angle θ equal to 0°.

6. The substrate according to claim 1, wherein the texture orientation represented at the maximum has an angle θ equal to 45°.

7. The substrate according to claim 1, wherein at least 50% of a sampling surface has a texture orientation an angle θ of which is greater than 30°.

8. The substrate according to claim 1, wherein for any angle φ, a distribution of the texture orientations according to the angle θ is identical.

9. The substrate according to claim 1, wherein the textured surface is at least partially coated with an anti-reflective coating.

10. The substrate according to claim 1, wherein said textured surface covers the entirety of at least one main face of the glass pane-type substrate.

11. The substrate according to claim 1, wherein a surface intended to be oriented towards an photovoltaic cell, and opposite to said textured surface, is smooth or textured.

12. The substrate according to claim 1, wherein a material comprising said textured surface is a mineral glass.

13. A manufacturing method of a substrate according to claim 1 comprising rolling a substrate using a textured print cylinder that bears designs having a local slope greater than the local slope of said textured surface.

14. A photovoltaic installation adapted to be integrated in a building, comprising a photovoltaic cell at least partially covered by a translucent substrate according to claim 1.

15. A method comprising at least one step for building, facade and/or roof mounting, of at least one photovoltaic installation according to claim 14.

16. A method comprising providing a photovoltaic installation according to claim 14 for the production of electric energy.

17. The method according to claim 13, wherein the local slope is at least 0.5°.

Description

[0057] Other features and advantages of the invention will become apparent upon reading the following description of particular embodiments, provided by way of simple illustrative and non-limiting examples, and from the attached figures, whereby:

[0058] FIG. 1 is a schematic depiction of the vector (n) normal to a local textured surface,

[0059] FIG. 2 is a sectional schematic view of FIG. 1 according to the plane containing the axis (z) normal to the general plane (π) of the substrate and the local normal vector (n),

[0060] FIG. 3 is a schematic transverse section of a photovoltaic installation (1) adapted to be building-integrated,

[0061] FIGS. 4 and 5 are respectively the map of the local heights and the angular histogram of the local texture orientations obtained after the implementation of a first test, according to a particular embodiment of the invention,

[0062] FIGS. 6 and 7 are respectively the map of the local heights and the angular histogram of the local texture orientations obtained after the implementation of a second test, according to a particular embodiment of the invention,

[0063] FIGS. 8 and 9 are respectively the map of the local heights and the angular histogram of the local texture orientations obtained after the implementation of a third test, according to a particular embodiment of the invention,

[0064] FIGS. 10 and 11 are respectively the map of the local heights and the angular histogram of the local texture orientations obtained after the implementation of a fourth test, according to an embodiment not covered by the invention.

[0065] The different features illustrated by the figures are not necessarily depicted at full scale, the focus being more on the depiction of the general operation of the invention. In the various figures, unless otherwise stated, the reference numbers that are the same represent similar or identical elements.

[0066] Several particular embodiments of the invention are presented below. It is understood that the present invention is not limited in any way by these particular embodiments and other embodiments can be implemented perfectly.

[0067] FIG. 3 illustrates, according to a sectional schematic view, a photovoltaic installation (1) adapted to be building-integrated. Such an installation (1) comprises a photovoltaic cell (2) covered by a transparent or translucent substrate (3) according to the invention. This photovoltaic cell benefits from the technical effects linked to the implementation of a textured substrate. Thus, the light rays impacting on the outer surface of the substrate (3) are only partially reflected and/or absorbed, particularly due to the advantageous surface texturing of the substrate, and due to the composition thereof with glass of the extra clear type.

[0068] Due to the diffuse reflection, a portion of the incident solar rays is thus reflected in a diffuse manner to the surface of the substrate, which enables limiting glare and the generation of hot points.

[0069] Due to the specular transmission, another portion of the incident rays is specularly refracted and transmitted through the substrate, which enables the energy losses to be limited, and thus maximize the exposure of the photovoltaic cell (2).

[0070] The implementation of such a substrate (3) thus enables satisfactory performance of light transmission to be obtained while limiting the risks of reflection glare.

[0071] Added to this is a light trapping effect at the level of the inner face of the substrate (3). Specifically, after passing through this substrate (3) a first time, a first portion of incident rays is absorbed by the photovoltaic cell (2), while a second portion is reflected towards the same substrate (3). A sub-portion of this reflected light is thus retro-reflected by the substrate (3) towards the photovoltaic cell (2), which enables the energy efficiency to be further improved, or in other words, to optimize the electrical energy production thereof.

[0072] FIG. 3 represents the angular components 6 (theta) of a plurality of local normal vectors (n1, n2, n3, n.sub.x) relating to different local surfaces of the textured surface (3A).

[0073] In order to assess the role played by the texture orientation (θ; φ) distribution on the reduction of the reflection luminance, a series of 3 (three) tests are computer simulated for a substrate (3) according to the invention. A final test is computer simulated for a substrate that does not conform to the distribution criteria set by the invention, by way of counterexample. These four tests are simulated under perfectly identical conditions, and only differ from one another in their texture orientation distribution.

[0074] For each test, a map of the local heights, as well as an angular histogram of the slopes of the surface are extracted and discussed. The map of the heights presents a graduated gray scale related to computer simulated heights on the sampling surface. The angular histogram of local texture orientations presents a gray scale related to the concentration of local surfaces presenting the orientation (θ; φ) given in the histogram, the concentric circles relate to the value of the angle θ (theta), increasing from the inside towards the outside of the histogram, while the values of the quadrant relate to the value of the angle φ (phi).

[0075] It must be noted that in practice, and in a non-limiting manner, the texture orientation (θ; φ) measurement of a local surface is carried out based on a measurement of the local height of the surface, according to a 20 micrometer (μm) dot grid at the most, in two orthogonal directions of the space hereinafter referred to as x and y. The high-pitch waves (in general greater than 10 mm, or even greater than 15 mm) are hereinafter eliminated by computer processing. Based on this two-dimensional height matrix, the local texture orientation according to two directions x and y is obtained by differentiating two consecutive points of the grid in the direction of interest, and dividing by the pitch of the grid. A two-dimensional vector is thus obtained at each point of the grid surface, in the x y space. It is then more practical to convert it in space (theta, phi) by using formulae known in the state of the art. By denoting n as the vector, and n.sub.x and n.sub.y as the previously calculated components, theta and phi can be obtained as theta=acos(1/sqrt(1+nx.sup.2+ny.sup.2)) and phi=atan 2(−ny/sqrt(nx.sup.2+ny.sup.2),−nx/sqrt(nx.sup.2+ny.sup.2)). A theta angle and a phi angle is thus obtained for each point of the meshed surface.

[0076] FIGS. 4 and 5 are respectively the map of the local heights and the angular histogram of the local texture orientations (θ; φ) obtained after the implementation of the first test. According to this first test, the orientation (θ; φ) having the highest distribution or, in other words, the texture orientation (θ; φ) represented at the maximum, has an angle θ (theta) equal to 0°, although a sufficient amount of the surface has been deviated from this direction to provide the low luminance of the reflection of the sun in any direction. The most represented texture orientation (θ=0°; φ) only occupies 1×10.sup.−4 of the textured surface (3A), which experimentally leads to a luminance value of 4500 cd/m.sup.2, experimentally observed for the sun entering at angles less than 30°. In practice, such a value is measure by means of a Minolta™ luminance meter on a day with full sunshine in June.

[0077] An orientation of the texture at θ=0° particularly favors the transmission of incident rays oriented according to a direction substantially orthogonal to the general plane of the substrate or in other words, the component θ (theta) of which is equal to or close to 0°. In practice, such a configuration is found in roof mountings of photovoltaic installation, which are preferred herein.

[0078] In addition, the angular histogram of the local texture orientations (θ; φ) (FIG. 5) shows a central symmetry as well as according to all the directions of φ (phi), which demonstrates the fact that for all angles φ (phi), the distribution of texture orientations according to the angle θ (theta) is identical. A textured surface according to this first test thus has an isotropic behavior.

[0079] FIGS. 6 and 7 are respectively the map of the local heights and the angular histogram of the local texture orientations (θ; φ) obtained after the implementation of the second test. According to this second test, a large portion of the surface (more than 50%) is maintained at high angular component texture orientations θ (about 50°). However, the distribution of these orientations is spread out according to the angles θ and φ, so that the most represented texture orientation only occupies 4×10.sup.−5 of the textured surface (3A). A luminance of 1500 cd/m.sup.2 is obtained. This configuration is best adapted to being facade mounted for which the trapping effects of the light due to the presence of slopes with high angles θ are favored.

[0080] In addition, the angular histogram of the local texture orientations (θ; φ) (FIG. 7) shows a central symmetry as well as very small variations of the angle θ depending on the angle φ, not visible to the human eye. A textured surface according to this second test thus has a substantially isotropic behavior.

[0081] FIGS. 8 and 9 are respectively the map of the local heights and the angular histogram of the local texture orientations (θ; φ) obtained after the implementation of the third test. According to this third test, the implemented designs are pyramid-shaped with a square base and the orientation (θ; φ) having the highest distribution has an angle θ (theta) equal to 45°. The angular spread according to θ is less effective than according to the second test, with a fraction of 8.2×10.sup.−5 of the textured surface (3A) thus oriented, which experimentally leads to a maximum of 3500 cd/m2 experimentally observed for the sun entering at angles lower than 30. Therefore, this is far from the glare values that can cause discomfort to the human eye. It must be noted that such a texture, although it is less efficient in terms of reducing the risks of glare that a structure according to the second test, has the benefit of being easier to produce due to the regularity of the designs thereof (see FIG. 9).

[0082] FIGS. 10 and 11 are respectively the map of the local heights and the angular histogram of the local texture orientations (θ; φ) obtained after the implementation of the fourth test, not covered by the present invention.

[0083] According to this fourth test, by way of counterexample, the most represented texture orientation (θ=0°; φ) occupies 3×10.sup.−3 of the textured surface (3A) which, although appearing to be an insignificant fraction, leads to a luminance of 1.5×10.sup.5 cd/m.sup.2, and thus a glare to be avoided.

[0084] The texturing of a translucent substrate according to the invention can be obtained by any known texturing method, for example by embossing the surface of the substrate previously heated to a temperature at which it is possible to deform it, in particular by rolling by means of a roller having on the surface thereof a complementary texturing of the texturing to be formed on the substrate, by engraving, or even by 3D printing, preferentially from a computer-generated texture.

[0085] According to a particular embodiment described for illustrative purposes, the texturing of a translucent substrate according to the invention is obtained by passing over an engraved roller, referred to as lower rolling roller, which is thus positioned facing the lower face of the glass on the production line. Typically, the lower (rolling) roller and the upper roller both have an outer diameter in the order of 200 mm. The upper roller may additionally have at the center thereof a concavity in the order of a millimeter.

[0086] In a manner known and controlled by a person skilled in the art, this lower roller is made of a steel (for example XC45F) the nature of which varies based on the method selected for the engraving of the surface. Thus, the engraving of the surface of the lower roller can be performed according to at least two alternative methods: engraving by laser ablation or the knurling of the surface. In the latter case, the knurl is made of a harder steel is itself engraved with the negative design of that of the rolling roller. In this case, the engraving is performed by the knurl compressing the material of the rolling roller. According to these methods, the engraving of the rolling roller is performed very accurately.

[0087] At first glance, the design engraved in the rolling roller corresponds to the negative of the texture desired for the surface of the rolled substrate. However, a person skilled in the art knows empirically how to anticipate the effects of the manufacturing method (relaxation of the textures during the cooling of the glass, stretching of the pattern substantially according to the axis of the production line, that is, the drawing axis) in order to determine the geometry of the design to be engraved in order to obtain, in fine, the target texture on the substrate.

[0088] Thus, preferentially, the height of the engraved design in the roller is increased, with respect to the target depth in the glass, by a factor depending on the lateral dimension of the design. The lateral dimension of the engraved design is, on the other hand, reduced according to the axis of the drawing, in order to obtain the lateral dimension desired for the texture of the substrate. Alternatively, or in a combined manner, the designs of the engraved roller have a local slope greater than the local slope of said textured surface, preferentially of at least 0.5°.

[0089] In a known and common manner for a person skilled in the art, other parameters of the production line are selected and adjusted to obtain a target texture, such as the temperature of the glass at the feeder (in the order of 1170° C.), the temperature of the cooling water of the rollers (37-38° C.), the temperature of the rolling temperature (comprised between 1100 and 1200° C.), the running speed of the substrate line. Thus, by way of example, a person skilled in the art knows how to adjust the rolling temperature depending on the thickness; a thinner glass needing to be hotter since it cools relatively quicker, while a thicker glass, on the contrary, must not be too hot so that it does not stick to the roller.

[0090] Generally, a person skilled in the art has the general knowledge to, based on a given objective of a texturing to be achieved, accurately obtain a dedicated engraving from the rolling roller, and adjust the parameters of the rolling method by rollers in order to obtain, by means of simple iterative tests, a substrate having the desired texturing.