Solar panels

Abstract

We provide solar panels that generate electricity while relatively evenly bringing light into the vehicle. [Solution] The solar panels 401 to 801 are solar panels comprising two translucent plate materials 302 and 304 (arranged spaced apart in the thickness direction of the plates) and a plurality of solar cells (101, 201) arranged between the two plate materials 302 and 304, wherein at least a portion of the plurality of solar cells (101, 201) are provided with a mirror surface (mirror metal film 107, back electrode 205) on the back surface opposite to the light-receiving surface that receives incident light (passed through the plate material 302), which reflects light reflected from the light-receiving surface of the other solar cells (101, 201) to the side opposite to the incident light side (light-receiving surface side).

Description

Technical Field

[0001] The present invention relates to a solar panel (hereinafter also referred to as a solar panel) that generates electricity while taking in light relatively evenly inside a vehicle.

Background Art

[0002] Conventionally, a power generation window system in which solar cells are provided on a window has been known (see, for example, Patent Document 1). Patent Document 1 describes, as a problem, "to provide a power generation window system that can obtain daylighting as a window and is easy to construct." As a solution, it is described that "the power generation window system 1 receives the power generated by the solar power generation module 4 attached to the window frame 31 attached to the building 2 by the power receiving means 5 disposed in the window frame 31, and supplies it to the storage battery 6 for storage. On the outdoor side of the translucent glass plate 41, a translucent solar cell 42 and a power transmission means 43 for wirelessly transmitting the power generated by the solar cell 42 are laminated and formed, and further, the driving of the dimming panel 44 is laminated on the solar cell 42 to constitute the solar power generation module 4. The power of the storage battery 6 is supplied to the dimming panel 44 together with a control signal via the control means 8 and the transmission means 7 disposed in the window frame 31, and the light transmission is controlled according to the external light intensity detected by the sensor 81. The dimming panel 44 can be operated without losing the daylighting function as a window." In this conventional technology, the use of a translucent solar cell suppresses the reduction in daylighting performance as a window.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Traditionally, in-vehicle solar panels have used transparent panels such as laminated glass for the roof, sides, and rear, with solar cells installed between them. This allows for both light penetration and power generation due to the transparency of the panels. In this case, crystalline silicon solar cells are generally used because they offer a good balance of performance and cost. However, when these solar cells are placed inside laminated glass, they absorb almost all visible light or reflect it outwards, resulting in a dark interior and a lack of openness despite the use of transparent laminated glass. Furthermore, if gaps are left between the solar cells to allow more light in, the light becomes lattice-like, which is unsightly.

[0005] As described in Patent Document 1, by combining a translucent solar cell with a light-adjusting sheet, uniform light intake and dimming become possible. On the other hand, translucent solar cells have lower power generation efficiency compared to general solar cells, which can lead to a significant decrease in power generation efficiency.

[0006] In other words, if there are gaps between the solar cells, the light will be arranged in a grid pattern, resulting in shadows in some areas and preventing even lighting. On the other hand, if the solar cells themselves are transparent, the power generation efficiency will decrease. Therefore, a solar panel is needed that can generate power while guiding light relatively evenly into the vehicle.

[0007] This invention has been made in view of the above problems, and aims to provide a solar panel that generates electricity while relatively evenly bringing light into the interior of a vehicle. [Means for solving the problem]

[0008] To solve the above problems, the solar panel according to the present invention comprises two light-transmitting plates and a plurality of solar cells arranged between the two plates, characterized in that at least a portion of the plurality of solar cells is provided with a mirror surface on the back surface opposite to the light-receiving surface that receives incident light, which reflects the light reflected from the light-receiving surface of the other solar cells of the plurality of solar cells toward the side opposite to the incident light side. [Effects of the Invention]

[0009] According to the present invention, by making the back surface of a solar cell a mirror surface, light reflected from the surface (light-receiving surface) of another solar cell can be re-reflected by the mirror surface on the back and guided into the vehicle. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view showing an example of a solar cell used in a solar panel according to an embodiment of the present invention. [Figure 2] This is a cross-sectional view showing another example of a solar cell used in a solar panel according to an embodiment of the present invention. [Figure 3] This is a cross-sectional view showing a conventional solar panel. [Figure 4] This is a cross-sectional view showing an example (diagonal arrangement) of a solar panel according to an embodiment of the present invention. [Figure 5] This is a cross-sectional view showing another example (alternating arrangement) of a solar panel according to an embodiment of the present invention. [Figure 6] This is a cross-sectional view showing another example of a solar panel according to an embodiment of the present invention (alternating + diagonal arrangement). [Figure 7] This is a cross-sectional view showing another example (diagonal arrangement) of a solar panel according to an embodiment of the present invention. [Figure 8] This is a cross-sectional view showing another example of a solar panel according to an embodiment of the present invention (alternating + diagonal arrangement). [Modes for carrying out the invention]

[0011] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. In the following description, elements that are the same or have the same function will be denoted by the same reference numeral, and redundant descriptions will be omitted. Also, the dimensional ratios in the drawings may differ from those of the actual components.

[0012] The solar panel of this embodiment can be used in various locations such as vehicles like automobiles and buildings. In the following embodiment, we will describe an example in which the solar panel is mounted on a vehicle and generates electricity while bringing sunlight or other light into the vehicle. In the following description, two examples of solar cells that guide light into the vehicle using the mirrored surface on the back side are shown below. After that, we will describe an example of a solar panel using these solar cells, that is, how these solar cells are arranged in the solar panel.

[0013] [Solar cell configuration] First, Figure 1 shows an example using a typical crystalline silicon solar cell. Figure 1 is a cross-sectional view of a solar cell 101 with a mirrored surface on its back side.

[0014] Solar cell 101 has an insulating film 106 and a mirrored metal film 107 provided on the back side of a normal crystalline silicon solar cell (equivalent to a solar cell) 102. The crystalline silicon solar cell 102 consists of a metal electrode 103 on the front side (light-receiving side), a crystalline silicon 104 which is a power generation layer, and a back side electrode 105 on the opposite side from the light-receiving side. If the mirrored metal film 107 is provided directly on the back side electrode 105 and the crystalline silicon 104, the back side electrode 105 will short-circuit and power generation will become impossible. Therefore, an insulating film 106 is provided between the mirrored metal film 107 and the back side electrode 105 and the crystalline silicon 104. There are various types of crystalline silicon solar cells 102, such as TOPcon, PERC, HIT, and back-contact type, but this is not limited to them.

[0015] As the material of the insulator film 106, a resin with high heat resistance is desirable. For example, polyimide with a maximum heat resistance temperature of 400°C or the like can be mentioned. As the thickness of the insulator film 106, a thickness that can sufficiently absorb the unevenness of the crystalline silicon solar cell 102 is desirable. Generally, considering that the thickness of the crystalline silicon solar cell 102 is around 0.2 mm, a thickness of about 0.4 mm, which is twice that, is desirable.

[0016] As the material of the mirror metal film 107, aluminum or silver with high reflectivity in the entire visible light wavelength range is desirable. As the thickness of the mirror metal film 107, a film thickness of about 50 to 100 nm, at which the transmittance is almost zero, is sufficient. Considering the absorption of process variations, a thickness of about 80 to 100 nm is better. If it is laminated more than that, there is a risk of increased cost and loss of flexibility due to improved rigidity (cracking).

[0017] Next, an example of realizing a mirror by a solar cell with an integrated structure is shown in FIG. 2. As solar cells with an integrated structure, perovskite solar cells, organic thin-film solar cells, amorphous silicon solar cells, etc. can be mentioned as candidates. Here, as an example, it is assumed to be a figure assuming a perovskite solar cell. FIG. 2 shows a cross-sectional view of the solar cell 201 with an integrated structure. Four solar cell portions are drawn in FIG. 2, and since these solar cells are integrated, it is called an integrated structure.

[0018] The solar cell (equivalent to a solar cell module) 201 is composed of a transparent substrate 202, a transparent electrode 203, a power generation layer 204, and a back electrode (counter electrode) 205 from the surface side (light-receiving surface side). For the transparent electrode 203, ITO (indium tin oxide) or FTO (fluorine-doped tin oxide) with a thickness of about 300 nm is mainly used. For the power generation layer 204, a metal halide perovskite crystal such as CsFAMAPbI3 (cesium-formamidinium-methylammonium lead iodide) with a thickness of about 300 to 500 nm, and a laminated film in which thin films of oxides or organic substances for transporting electrons and holes, called carrier transport layers, are laminated to a thickness of several nm to about 100 nm are used. For the back electrode 205, gold, silver, or copper with a thickness of usually about 100 nm is mainly used. Industrially, copper is often used considering the cost and the balance with the energy level of the carrier transport layer. When the back electrode 205 contacts the transparent electrode 203 on the left side in Fig. 2, the solar cells 206 (four in Fig. 2) are directly connected to each other. The portion from the transparent electrode 203 to the back electrode 205 is formed into strips by a cutting process called scribing after film formation on the transparent substrate 202.

[0019] In this integrated structure, the back surface side of the solar cell 201 is already almost entirely covered with the back electrode 205, which is a metal film. Specifically, it is covered except for the spaces between the solar cells 206. Therefore, by making the surface of the back electrode 205 a metal film with a high reflectance, a mirror surface portion on the back surface side is realized. Thus, as the configuration of the back electrode 205, it is desirable to provide about 80 to 100 nm of aluminum or silver with a high reflectance in the entire visible light wavelength range on top of an existing material (mainly copper). Note that the timing for providing aluminum or silver needs to be before the scribing process is carried out after the back electrode 205 is coated over the entire surface. If it is not before the scribing process, the back electrode 205 will all be short-circuited, and power generation as a solar cell will become impossible.

[0020] [Configuration of a solar panel] Next, we will explain the arrangement of the above-mentioned solar cells (solar cells or solar modules) on an in-vehicle solar panel. Here, as an example, we will show a diagram of a configuration (solar module) in which multiple solar cells 101, each having a mirror-like metal film 107 (which is a mirror surface) on the back side (via an insulating film 106) of a typical crystalline silicon solar cell 102, are arranged.

[0021] First, Figure 3 shows the structure of a typical automotive solar panel. Figure 3 shows the cross-sectional structure of an automotive solar panel 301, which consists of a transparent plate material 302 on the incident light side, a sealing material 303, a transparent plate material 304 on the vehicle side (opposite the incident light side), and multiple conventional crystalline silicon solar cells 102. For automotive use, the plate materials 302 and 304 should be made of materials that are rigid and highly transparent (light-transmitting), such as a combination of glass, polycarbonate, or acrylic. Considering rigidity, the thickness of the plate materials 302 and 304 is generally about 4 mm. When using glass, it can be thinned to about 2 mm by thermal or chemical strengthening. Since these plate materials 302 and 304 are automotive panels, they basically take on a curved shape with three-dimensional curvature, regardless of whether they are on the roof, side, rear, etc. The encapsulant 303 is responsible for protecting and securing the solar cell from impact, and is generally made of resins such as polyolefin, PVB (polyvinyl acetate polymer), or EVA (ethylene vinyl acetate polymer).

[0022] In a typical automotive solar panel 301, when the crystalline silicon solar cell 102 is positioned between curved plate materials 302 and 304 (spaced apart in the thickness direction), it is positioned such that the normal to plate material 302 (or plate material 304) and the normal to the crystalline silicon solar cell 102 are parallel, as shown in Figure 3. In other words, the crystalline silicon solar cell 102 is positioned along the direction of extension of plate material 302 (or plate material 304) perpendicular to the direction of the normal to plate material 302 (or plate material 304). This is intended to minimize the thickness of the sealing material 303 through which light such as sunlight incident on the solar cell passes. In this arrangement, incident light (solid arrows in the figure) is irradiated by the crystalline silicon solar cell 102 (or its light-receiving surface) and partially reflected, but the reflected light is not guided into the vehicle but is emitted to the outside.

[0023] Next, Figure 4 shows the structure of a light-capable in-vehicle solar panel. Figure 4 shows the cross-sectional structure of a light-capable in-vehicle solar panel 401. Similar to solar panel 301, solar panel 401 is composed of a transparent plate material 302 on the incident light side, a sealing material 303, a transparent plate material 304 on the vehicle side (opposite the incident light side), and a solar cell. The difference from solar panel 301 is that the solar cell portion has a mirror-finish metal film 107 on the back side, and the angle (tilt) of the arrangement of the solar cells is different.

[0024] In the arrangement of the solar cells 101, by shifting their normal direction from parallel to the normal of the plate material 302 (or plate material 304), the positions of the edges of adjacent solar cells 101 are shifted, and the surface (light-receiving surface) of one solar cell 101 faces the back surface of another adjacent solar cell 101. This allows some of the light, such as sunlight, reflected from the surface (light-receiving surface) of one solar cell 101 to be guided (irradiated) to the back surface of another adjacent solar cell 101. Furthermore, the light reflected by the mirror-finish metal film 107 on the back surface of the solar cell 101 on the opposite side from the incident light can be guided into the vehicle (through the plate material 304). In other words, the solar cells 101 in this embodiment are arranged at an angle with respect to the extending direction of the plate material 302 (or plate material 304), which is perpendicular to the normal direction of the plate material 302 (or plate material 304). With this light guidance, the entire surface of the solar cell 101 is used, so a grid-like distribution of light, such as that caused by simply leaving gaps between cells, is less likely to occur inside the vehicle. Regarding the angle of deviation from the normal (i.e., the tilt angle), if it is too small, light guidance cannot be achieved, and if it is too large, the thickness of the encapsulant 303 increases, and it becomes difficult to receive light such as sunlight, reducing the power generation efficiency. Taking the above into consideration, the deviation angle (tilt angle) of the solar cell 101 is preferably no more than about 30 degrees from the normal of the plate material 302 (or plate material 304). 30 degrees is the tilt angle of panels that are adopted nationwide for installed solar cells in Japan, and it poses few problems in terms of power generation efficiency.

[0025] Figure 5 shows another example of the cross-sectional structure of a light-capable vehicle-mounted solar panel 501. This solar panel 501 differs from the solar panel 301 in that the solar cell portion consists of a solar cell 101 with a mirror-finish metal film 107 on the back side and a normal crystalline silicon solar cell 102, and the position of the solar cells is different.

[0026] In arranging the solar cell 101 and crystalline silicon solar cell 102, by alternately arranging the solar cell 101 and crystalline silicon solar cell 102 along the extension direction of the plate materials 302 and 304, and offsetting their normal positions from near the center of the plate materials 302 and 304 (placing the solar cell 101 on the upper side and the crystalline silicon solar cell 102 on the lower side in different positions in the normal direction perpendicular to the extension direction of the plate material 302 or plate material 304), the positions of the ends of adjacent solar cells 101 and crystalline silicon solar cells 102 are offset, and the surface (light-receiving surface) of the crystalline silicon solar cell 102 and the back surface of the adjacent solar cell 101 are staggered, so that the same effect as the solar panel 401 described above can be obtained, as shown by the solid line in Figure 5.

[0027] Figure 6 shows yet another example of the cross-sectional structure of a light-capable vehicle-mounted solar panel 601. This solar panel 601 differs from the solar panel 301 in that the solar cell portion consists of a solar cell 101 with a mirror-finish metal film 107 on the back side and a normal crystalline silicon solar cell 102, and the position and angle (tilt) of the solar cells are different.

[0028] In this solar panel 601, compared to the solar panel 501, the arrangement of the crystalline silicon solar cells 102 is such that the normal direction of the solar cells is shifted from being parallel to the normal direction of the plate material 302 (or plate material 304) (they are arranged at an angle to the extending direction of the plate material 302 (or plate material 304)). As a result, the positions of the edges of adjacent solar cells 101 and crystalline silicon solar cells 102 are shifted, the surface (light-receiving surface) of the crystalline silicon solar cell 102 and the back surface of the adjacent solar cell 101 are staggered, and the surface (light-receiving surface) of the crystalline silicon solar cell 102 faces the back surface of the adjacent solar cell 101. Therefore, as shown by the solid line in Figure 6, the same effect as the solar panel 401 and solar panel 501 is obtained.

[0029] Although Figure 6 shows an example where only the crystalline silicon solar cell 102 is tilted, the solar cell 101 may also be tilted, or both the solar cell 101 and the crystalline silicon solar cell 102 may be tilted.

[0030] Furthermore, while Figure 4 shows an example where the tilt angles of multiple solar cells 101 are basically uniform, the tilt angle of the solar cells 101 may be changed at predetermined locations, as in the solar panel 701 shown in Figure 7 and the solar panel 801 shown in Figure 8. In other words, the solar cells placed between the plate materials 302 and 304 may include solar cells with different tilt angles relative to the extending direction of the plate materials 302 and 304. By arranging the solar cells in this way, it becomes possible to respond to light from various directions, as shown by the solid arrows in Figures 7 and 8.

[0031] Furthermore, in the embodiment described above, an example was shown in which light reflected from the surface (light-receiving surface) of one solar cell is irradiated onto the mirrored surface on the back side of another adjacent solar cell and reflected. However, it is not necessary for the light reflected from the surface (light-receiving surface) of one solar cell to be irradiated onto the mirrored surface on the back side of another adjacent solar cell, nor is it necessary to provide a mirrored surface on the back side of all solar cells. For example, a mirrored surface may be provided on the back side of every other solar cell or every few cells, so that the light reflected from the surface (light-receiving surface) of one solar cell or every few cells is irradiated onto the mirrored surface on the back side of the solar cells arranged every other cell or every few cells and reflected.

[0032] Furthermore, although the above-described embodiment shows an example in which the solar cell (solar cell or solar module) placed between the plate materials 302 and 304 has a flat shape, it is of course possible to place solar cells with curved shapes such as convex downwards, convex upwards, or wavy.

[0033] Furthermore, although the above-described embodiment shows light being irradiated (incident) towards the solar panel from one direction, sunlight and other light include direct light (incident in a linear fashion connecting the sun and the ground) and scattered light (incident to the ground from all directions). Therefore, by providing a mirrored surface on the back side as described above, it is possible to utilize both direct light and scattered light to bring light into the vehicle relatively evenly.

[0034] In summary, the solar panels 401 to 801 of this embodiment provide solar panels that generate electricity while relatively evenly bringing light into the vehicle, for example, by having the following configuration. The solar cell is placed between two transparent, light-transmitting plates 302 and 304. Examples of transparent plates 302 and 403 include glass, polycarbonate, and acrylic, and the solar cell is placed between them or a combination thereof. The back surface of the solar cell (solar cell 101) or solar cell module (solar cell 201) that constitutes the solar cell is made into a mirror surface. When creating a mirrored surface on the back, insulation is necessary between the solar cell and the mirrored surface. Without insulation, a short circuit will occur between the back electrodes on the back of the solar cell and the material of the mirrored surface, preventing power generation. To achieve both a mirrored surface and insulation between the electrodes and the mirrored surface, it is desirable to, for example, attach an insulating film 106 with a metal film to the back surface of the solar cell. Another method for achieving a mirrored surface is to use integrated solar cells (such as perovskite solar cells, organic thin-film solar cells, and amorphous silicon solar cells) where the back surface is almost entirely composed of metal film electrodes from the outset. In these solar cells, metal electrodes are deposited on almost the entire surface as the back surface electrode, and by using copper or aluminum laminated films as the electrode material, a mirrored surface can be achieved on the back surface without the need to attach additional insulating films or mirrored metal films. When arranging the solar cell (solar cell 101) or module (solar cell 201) with a mirrored surface on its back surface between light-transmitting transparent plates 302 and 304, for example, it is tilted even more diagonally than the general shape of plates 302 and 304 (Figure 4). This allows light reflected from the surface (light-receiving surface) of the solar cell to be guided (irradiated) to, for example, the mirrored surface on the back side of the adjacent solar cell, and the light reflected from the mirrored surface on the opposite side from the incident light can be guided into the car. Here, since this light guidance uses the entire surface of the solar cell, it does not result in an unsightly grid-like appearance as if gaps were simply left. Also, since the material of the solar cell is not changed, it does not lead to a decrease in power generation efficiency that would be necessary to make the solar cell transparent.

[0035] As described above, the solar panels 401 to 801 of this embodiment are solar panels comprising two translucent plate materials 302 and 304 (arranged spaced apart in the thickness direction) and a plurality of solar cells (101, 201) arranged between the two plate materials 302 and 304, wherein at least a portion of the plurality of solar cells (101, 201) is provided with a mirror surface (mirror metal film 107, back electrode 205) on the back surface opposite to the light-receiving surface that receives incident light (passed through the plate material 302), which reflects light reflected from the light-receiving surface of the other solar cells (101, 201) to the side opposite to the incident light side (light-receiving surface side) (Figures 4 to 8).

[0036] At least some of the plurality of solar cells (101, 201) are arranged at an angle to the extending direction of the two plate materials 302 and 304 (or the normal direction perpendicular to that extending direction), or are arranged in a different position (alternating) from the other solar cells of the plurality of solar cells (101, 201) in the normal direction perpendicular to the extending direction of the two plate materials 302 and 304, so that light reflected from the light-receiving surface of the other solar cells of the plurality of solar cells (101, 201) is irradiated onto the mirror surface (mirror metal film 107, back electrode 205) and reflected to the opposite side from the incident light side (light-receiving surface side) (Figures 4, 5, and 6). Furthermore, at least some of the plurality of solar cells (101, 201) include solar cells with different inclination angles to the extending direction of the two plate materials 302 and 304 (Figures 7 and 8).

[0037] The solar cell is composed of a solar cell module having an integrated structure in which a plurality of solar cells are integrated, and the mirror surface portion is composed of the electrode portion (including a metal film) (back electrode 205) of the solar cell of the solar cell module (Figure 2), or the solar cell is composed of solar cells, and the mirror surface portion is composed of a mirror metal film 107 provided on the back surface of the solar cell (Figure 1).

[0038] According to this embodiment, the mirrored surface (mirror-like metal film 107, back electrode 205) provided on the back surface of the solar cells (101, 201) re-reflects light such as sunlight that has been reflected off the surface (light-receiving surface) of other solar cells, thereby guiding light into the inside of the solar panel (inside the vehicle). Furthermore, when the solar cells are composed of a solar cell module having an integrated structure, the electrode portion (back electrode 205) of the solar cell (201) also serves as the mirrored surface, thus simplifying the configuration.

[0039] Furthermore, the present invention is not limited to the embodiments described above, and can be appropriately modified and altered without departing from the objectives of the present invention. [Explanation of symbols]

[0040] 101 Solar cell, 102 Crystalline silicon solar cell, 103 Metal electrode, 104 Crystalline silicon, 105 Back electrode, 106 Insulating film, 107 Mirror-finish metal film (mirror surface), 201 Solar cell, 202 Transparent substrate, 203 Transparent electrode, 204 Power generation layer, 205 Back electrode (mirror surface), 301, 401, 501, 601, 701, 801 Solar panel, 302 Sheet material, 303 Encapsulating material, 304 Sheet material

Claims

1. Two translucent boards, A solar panel comprising a plurality of solar cells arranged between the two aforementioned plate materials, A solar panel in which at least some of the plurality of solar cells are provided with a mirror surface on the back surface opposite to the light-receiving surface that receives incident light, which reflects light reflected from the light-receiving surface of the other solar cells of the plurality of solar cells toward the side opposite to the incident light side.

2. A solar panel according to claim 1, A solar panel in which at least some of the plurality of solar cells are arranged at an angle with respect to the extending direction of the two plate materials, so that light reflected from the light-receiving surface of the other solar cells is irradiated onto the mirror surface and reflected on the side opposite to the incident light side.

3. A solar panel according to claim 1, A solar panel in which at least some of the plurality of solar cells are arranged in a normal direction perpendicular to the extending direction of the two plate materials, at a different position from the other solar cells of the plurality of solar cells, so that light reflected from the light-receiving surface of the other solar cells of the plurality of solar cells is irradiated onto the mirror surface and reflected on the side opposite to the incident light side.

4. A solar panel according to claim 2, A solar panel in which at least some of the plurality of solar cells include solar cells with different inclination angles with respect to the extending direction of the two plate materials.

5. A solar panel according to claim 1, The solar cell is composed of a solar cell module having an integrated structure in which multiple solar cells are integrated, and the mirror surface is composed of the electrode portion of the solar cell of the solar cell module. or, The solar panel comprises a solar cell and the mirrored portion is made of a mirrored metal film provided on the solar cell.

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